0001564590-22-009681 | 10-K | XBRL Viewer

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CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 206,325	$ 83,966
Short-term investments		225,186
Prepaid expenses and other current assets	7,548	4,844
Total current assets	213,873	313,996
Property and equipment, net	22,050	23,336
Operating lease right-of-use assets	26,177	24,986
Intangible assets, net	1,320	1,320
Goodwill	4,228	4,228
Other long-term assets	1,661	3,618
Total assets	269,309	371,484
Current liabilities:
Accounts payable	8,961	763
Accrued expenses and other liabilities	23,540	24,454
Operating lease liabilities, current	6,337	4,808
Deferred revenue, current	4,497
Total current liabilities	43,335	30,025
Term debt	29,357	29,133
Deferred CIRM grant liability	3,992	23,755
Deferred revenue, non-current	9,265
Deferred tax liability	55	55
Operating lease liabilities, non-current	25,504	25,374
Other long-term liabilities	1,590	1,174
Total liabilities	113,098	109,516
Commitments and Contingencies (Note 11)
Stockholders’ equity:
Common stock, $0.0001 par value: 250,000,000 shares authorized at December 31, 2021, and 2020; 62,523,596 and 61,860,897 shares issued and outstanding as of December 31, 2021 and 2020, respectively	6	6
Additional paid-in capital	563,064	543,842
Accumulated other comprehensive income		5
Accumulated deficit	(406,859)	(281,885)
Total stockholders’ equity	156,211	261,968
Total liabilities and stockholders’ equity	$ 269,309	$ 371,484

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	62,523,596	61,860,897
Common stock, shares outstanding	62,523,596	61,860,897

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Revenues:
Total revenue	$ 31,238
Operating expenses:
Research and development	136,734	$ 103,520
General and administrative	35,915	23,029
Total operating expenses	172,649	126,549
Loss from operations	(141,411)	(126,549)
Other income (expense):
Interest expense	(3,358)	(3,506)
Other income, net	19,795	280
Net loss before income tax	(124,974)	(129,775)
Income tax expense	0	0
Net loss	(124,974)	(129,775)
Other comprehensive income (expense):
Unrealized loss on short-term investments	(5)	(14)
Comprehensive loss	$ (124,979)	$ (129,789)
Net loss per share attributable to common stockholders, basic and diluted	$ (2.01)	$ (3.61)
Weighted-average number of shares outstanding, basic and diluted	62,235,940	35,996,901
Collaboration Revenue
Revenues:
Total revenue	$ 31,238

CONSOLIDATED STATEMENTS OF CHANGES IN CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Revision of Prior Period, Accounting Standards Update, Adjustment	Series A One And Series B Warrants	IPO	Common Stock	Common Stock IPO	Additional Paid-in Capital	Additional Paid-in Capital Series A One And Series B Warrants	Additional Paid-in Capital IPO	Accumulated Other Comprehensive Income	Accumulated Deficit	Accumulated Deficit Revision of Prior Period, Accounting Standards Update, Adjustment
Balance at Dec. 31, 2019	$ (149,511)		$ 111			$ 2		$ 2,689			$ 19	$ (152,221)	$ 111
Beginning balance, Shares at Dec. 31, 2019		32,934,785
Beginning balance at Dec. 31, 2019		$ 222,173
Beginning balance, Shares at Dec. 31, 2019						13,196,419
Accounting Standards Update [Extensible Enumeration]	us-gaap:AccountingStandardsUpdate201602Member
Issuance of common stock under employee stock compensation plans	$ 224							224
Issuance of common stock under employee stock compensation plans, Shares						219,370
Issuance of preferred stock for cash net of issuance costs, Shares	10,018,300
Issuance of preferred stock for cash net of issuance costs		$ 104,140
Issuance of common stock for conversion of preferred stock in closing of IPO					$ 326,312		$ 3			$ 326,309
Conversion of preferred stock shares for common stock					(42,953,085)
Conversion of preferred stock value for common stock					$ (326,313)
Issuance of common stock for conversion of preferred stock in closing of IPO, Shares							34,445,108
Issuance of common stock from initial public offering	$ 205,743					$ 1		205,742
Issuance of common stock from initial public offering, Shares						14,000,000
Stock-based compensation expense	7,220							7,220
Reclassification of warrants				$ 1,658					$ 1,658
Unrealized loss on short-term investments	(14)										(14)
Net loss	(129,775)											(129,775)
Balance at Dec. 31, 2020	261,968					$ 6		543,842			5	(281,885)
Ending balance, Shares at Dec. 31, 2020						61,860,897
Issuance of common stock under employee stock compensation plans	2,518							2,518
Issuance of common stock under employee stock compensation plans, Shares						662,699
Stock-based compensation expense	16,704							16,704
Unrealized loss on short-term investments	(5)										$ (5)
Net loss	(124,974)											(124,974)
Balance at Dec. 31, 2021	$ 156,211					$ 6		$ 563,064				$ (406,859)
Ending balance, Shares at Dec. 31, 2021						62,523,596

CONSOLIDATED STATEMENTS OF CHANGES IN CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Initial public offering, net of issuance costs	$ 18,018
Series D Preferred Stock
Payments of stock issuance costs	$ 5,359

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating Activities:
Net loss	$ (124,974)	$ (129,775)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	4,552	2,586
Stock-based compensation	16,704	7,220
Write off of deferred CIRM grant liability	(19,763)
Change in fair value of warrant liability		387
Accretion of discount on issued term debt	639	805
Amortization of premium and accretion of discounts on investments, net	133	(174)
Gain on disposal of property and equipment	(2)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,656)	(3,296)
Operating lease right-of-use assets	3,580	3,108
Other long-term assets	1,957	(207)
Accounts payable	7,842	(4,171)
Accrued liabilities	(1,204)	10,320
Operating lease liabilities	(3,113)	(131)
Deferred revenue	13,762
Net cash used in operating activities	(102,543)	(113,328)
Investing Activities:
Purchases of property and equipment	(2,634)	(16,908)
Proceeds from disposal of property and equipment	18
Purchases of short-term investments		(295,023)
Proceeds from maturities of short-term investments	225,000	107,500
Net cash provided by (used in) investing activities	222,384	(204,431)
Financing Activities:
Net proceeds from issuance of common stock under employee stock compensation plans	2,518	223
Issuance of Series D financing, net of issuance costs		104,141
Proceeds from initial public offering, net of issuance costs		205,743
Net proceeds from CIRM grant awards		4,163
Payment of debt issuance costs		(329)
Net cash provided by financing activities	2,518	313,941
Net increase (decrease) in cash and cash equivalents	122,359	(3,818)
Cash and cash equivalents at beginning of period	83,966	87,784
Cash and cash equivalents at end of period	206,325	83,966
Non-cash operating, investing and financing activities:
Purchases of property and equipment included in accounts payable and accrued liabilities	647	211
Tenant improvement receivable from landlord		137
Right-of-use assets obtained in exchange for operating lease liabilities	4,771	5,346
Conversion of redeemable convertible preferred stock to common stock upon closing of initial public offering		326,313
Supplemental disclosure of cash flow information:
Interest paid	$ 2,719	$ 3,027

Nature of Business and Basis of Presentation

12 Months Ended

Dec. 31, 2021

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Business and Basis of Presentation

Note 1. Nature of Business and Basis of Presentation

Nature of Operations

Poseida Therapeutics, Inc. (the “Company” or “Poseida”) is a clinical-stage biopharmaceutical company dedicated to utilizing its proprietary gene engineering platform technologies to create next generation cell and gene therapeutics with the capacity to cure. The Company has discovered and is developing a broad portfolio of product candidates in a variety of indications based on its core proprietary platforms, including its non-viral piggyBac DNA Delivery System, Cas-CLOVER Site-specific Gene Editing System and nanoparticle- and AAV-based gene delivery technologies.

The Company is subject to risks and uncertainties common to development-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s therapeutic development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

Liquidity and Capital Resources

The Company has experienced net losses and negative cash flows from operations since its inception and has relied on its ability to fund its operations primarily through equity financings. For the years ended December 31, 2021 and 2020, the Company has incurred net losses of $125.0 million and $129.8 million respectively, and negative cash flows from operations for these same periods of $102.5 million and $113.3 million, respectively. The Company expects it will continue to incur net losses and negative cash flows from operations for at least the next several years. As of December 31, 2021 the Company had an accumulated deficit of $406.9 million.

The Company expects that its cash and cash equivalents as of December 31, 2021 of $206.3 million will be sufficient to fund its operations for at least the next twelve months from the date of issuance of these consolidated financial statements. In the long term the Company will need additional financing to support its continuing operations and pursue its business strategy. Until such time as the Company can generate significant revenue from product sales, if ever, it expects to finance its operations through a combination of equity offerings, debt financings, collaborations, strategic alliances, and licensing arrangements. The Company may be unable to raise additional funds or enter into such other agreements when needed on favorable terms or at all. The inability to raise capital as and when needed would have a negative impact on the Company’s financial condition and its ability to pursue its business strategy. The Company will need to generate significant revenue to achieve profitability, and it may never do so.

Basis of Preparation and Consolidation

The consolidated financial statements reflect the Company’s financial position, results of operations and cash flows, in conformity with generally accepted accounting principles in the United States (“GAAP”) and include the accounts of Poseida Therapeutics, Inc. and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated.

These consolidated financial statements reflect a 1-for-1.247 reverse stock split of the Company’s common stock, which became effective on July 2, 2020. All share and per share data for all periods presented in the accompanying consolidated financial statements and notes thereto have been adjusted retrospectively, where applicable, to reflect the reverse stock split.

Risk and Uncertainties

In March 2020, the World Health Organization made the assessment that a novel strain of coronavirus, SARS-CoV-2, a novel strain of coronavirus, commonly referred to as COVID-19 had become a global pandemic. The impact of this pandemic has been and may continue to be extensive in many aspects of society, which has resulted in and may continue to result in significant disruptions to the global economy, as well as businesses and capital markets around the world.

the diversion of healthcare resources away from the conduct of clinical trials to focus on pandemic concerns, interruptions or delays in the operations of the U.S. Food and Drug Administration (“FDA”) or other regulatory authorities, and the Company’s ability to raise capital and conduct business development activities.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Note 2. Summary of Significant Accounting Policies

Use of Estimates

The preparation of consolidated financial statements in conformity with GAAP requires the Company to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company evaluates its estimates, which include, but are not limited to, estimates related to revenue, accrued expenses, stock-based compensation expense, deferred tax valuation allowances and, prior to the Company’s initial public offering (“IPO”) completed in July 2020, the fair value of common stock and warrant liability. The Company bases its estimates on historical experience and other market-specific or relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions.

Prior to the IPO, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company has utilized various valuation methodologies in accordance with the framework of the 2004 American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common stock. Each valuation methodology includes estimates and assumptions that require the Company’s judgment. These estimates and assumptions include a number of objective and subjective factors, including the prices at which the Company sold shares of preferred stock and the superior rights, preferences and privileges of the preferred stock relative to the common stock; the Company’s stage of development and material risks related to its business; the progress of the Company’s research and development programs, including the status and results of preclinical studies for its product candidates and progress of its development of manufacturing processes; external market conditions affecting the biopharmaceutical industry and trends within the biopharmaceutical industry; the Company’s results of operations and financial position, including its levels of available capital resources, outstanding debt and its historical and forecasted performance and operating results; the lack of an active public market for the Company’s common stock and preferred stock; the likelihood of achieving a liquidity event, such as an IPO or sale of the Company in light of prevailing market conditions; the hiring of key personnel; and the analysis of IPOs and the market performance of publicly traded companies in the biopharmaceutical industry, as well as recently completed mergers and acquisitions of peer companies. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date.

Segment Information

The Company’s sole operations consist of developing therapeutics for patients with high unmet medical need. Accordingly, the Company has determined that it operates in one operating and reportable business segment. Operating segments are defined as components of an enterprise about which separate financial information is evaluated regularly by the Company’s chief operating decision maker, who is its Chief Executive Officer, in deciding how to allocate resources and assess performance. The Company’s chief operating decision maker allocates resources and assesses performance based upon discrete financial information at the consolidated level. All of the Company’s tangible assets are held in the United States.

Fair Value Measurements

Certain financial instruments are required to be recorded at fair value. Other financial instruments, like cash are recorded at cost, which approximates fair value. Cash equivalents and short-term investments are comprised of available-for-sale securities, which are carried at fair value. Additionally, carrying amounts of accounts payable and accrued liabilities approximate fair value because of the short maturity of those instruments. The carrying value of the Company’s term debt approximates its fair value due to its variable interest rate, which approximates a market interest rate.

Concentration of Business Risk

The Company relies, and expects to continue to rely, on a small number of vendors to manufacture supplies and materials for its development programs. These programs could be adversely affected by a significant interruption in these manufacturing services. The Company’s revenue has been derived from a collaboration and license agreement with a single customer.

Leases

The Company accounts for leases in accordance with Accounting Standards Codification Topic 842, Leases, (“ASC 842”). The Company determines if an arrangement is a lease at contract inception. A lease exists when a contract conveys the right to control the

use of identified property, plant, or equipment for a period of time in exchange for consideration. The definition of a lease embodies two conditions: (1) there is an identified asset in the contract that is land or a depreciable asset (i.e., property, plant, and equipment), and (2) the Company has the right to control the use of the identified asset.

Operating leases where the Company is the lessee are included in lease receivables, operating lease right-of-use (“ROU”) assets, operating lease liabilities, current and operating lease liabilities, non-current on its consolidated balance sheets. The lease liabilities are initially and subsequently measured at the present value of the unpaid lease payments at the lease commencement date.

ASC 842 requires a lessee to discount its unpaid lease payments using the interest rate implicit in the lease or, if that rate cannot be readily determined, its incremental borrowing rate. The rates implicit in the Company’s leases are not known, therefore, the incremental borrowing rate is used based on the information available at commencement date in determining the present value of lease payments. The Company’s incremental borrowing rate for a lease is the rate of interest it would have to pay on a collateralized basis to borrow an amount equal to the lease payments under similar terms.

The lease term for all of the Company’s leases includes the noncancelable period of the lease. Where the Company’s lease term is impacted by options to extend or terminate the lease, when it is reasonably certain that it will exercise such option, then the lease payments are included in the measurement of the lease asset or liability.

The Company has elected not to recognize ROU assets and lease liabilities for all short-term leases that have a lease term of 12 months or less. The Company recognizes the lease payments associated with its short-term leases as an expense on a straight-line basis over the lease term. There are no variable lease payments associated with these leases. Additionally, the Company has elected to account for the lease and non-lease components together as a single lease component for its real estate asset class.

Deferred Offering Costs

The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of an equity financing, these costs are recorded as a reduction of additional paid-in capital generated as a result of the offering. Should the in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations and comprehensive loss. Deferred offering costs of $18.3 million, incurred in connection with the Company’s July 2020 IPO, were net against the gross proceeds on the statement of stockholders’ equity (deficit) for the year ended December 31, 2020.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents and short-term investments. The Company maintains its cash and cash equivalent balances with high-quality financial institutions and, consequently, the Company believes that such funds are subject to minimal credit risk. Deposits held at these institutions may exceed the amount of insurance provided on such deposits.

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with original final maturities of 90 days or less from the date of purchase to be cash equivalents. Cash and cash equivalents consist of deposits with financial institutions and marketable securities. Cash equivalents are reported at fair value. The Company utilizes a credit card that requires a cash collateral account to secure its outstanding balance. While cash in this account is not legally restricted, the availability of future credit is dependent upon maintenance of a compensating balance sufficient to cover outstanding balances. The balance held in this account as of both December 31, 2021 and 2020 was $0.2 million. Amounts outstanding on the credit card and recorded as accounts payable were $0.1 million as of both December 31, 2021 and 2020.

Short-Term Investments

Investments with a remaining maturity when purchased of greater than three months are classified as short-term investments in the consolidated balance sheet and consist primarily of U.S. Treasury and other government agency obligations. As the Company’s entire investment portfolio is considered available for use in current operations, the Company classifies all investment as available-for-sale and as current assets. Debt securities are carried at fair value with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the instrument. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented.

Goodwill and Other Intangible Assets

Intangible assets were acquired as part of a business combination and have been capitalized at their acquisition date fair value. Indefinite-lived in process research and development (“IPR&D”) is not subject to amortization but is tested annually for impairment or more frequently if there are indicators of impairment. The Company tests its indefinite-lived IPR&D annually for impairment during the fourth quarter. In testing indefinite-lived IPR&D for impairment, the Company has the option to first assess qualitative factors to determine whether the existence of events or circumstances would indicate that it is more likely than not that its fair value is less than its carrying amount, or the Company can perform a quantitative impairment analysis to determine the fair value of the indefinite-lived IPR&D without performing a qualitative assessment. Qualitative factors that the Company considers include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If the Company chooses to first assess qualitative factors and it determines that it is more likely than not that the fair value of the indefinite-lived IPR&D is less than its carrying amount, the Company would then determine the fair value of the indefinite-lived IPR&D. Under either approach, if the fair value of the indefinite-lived IPR&D is less than its carrying amount, an impairment charge would be recognized for the difference between the fair value and the carrying amount. There was no impairment of IPR&D for the years ended December 31, 2021 and 2020.

The Company additionally tests its goodwill for impairment annually during the fourth quarter, or whenever events or changes in circumstances indicate an impairment may have occurred. Should an impairment exist, the impairment loss would be measured based on the excess of the carrying amount of the asset or asset group over the estimated asset’s fair value. Impairment may result from, among other things, deterioration in the performance of the acquired business, adverse results from developmental work, adverse changes in applicable laws or regulations and a variety of other circumstances. In evaluating the recoverability of the carrying value of goodwill, the Company must make assumptions regarding estimated future cash flows and other factors to determine the fair value of the acquired assets. Changes in strategy or market conditions could significantly impact those judgments in the future and require an adjustment to the recorded balances. There were no impairments of goodwill for the years ended December 31, 2021 and 2020.

Property and Equipment

Property and equipment are stated at cost and depreciated or amortized using the straight-line method, based on their estimated useful lives as follows:

Asset Classification	Estimated Useful Life (years)
Laboratory equipment		5
Leasehold improvements	Lesser of useful life or lease-term
Computer equipment and software		3
Furniture and fixtures		7

Maintenance and repair costs are charged to expense as incurred. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the Company’s consolidated balance sheet and any resulting gain or loss is reflected in the Company’s consolidated statement of operations and comprehensive loss.

Property and equipment are reviewed annually for impairment or whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amount to the future net undiscounted cash flows which the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset. There has been no impairment of long-lived assets during the years ended December 31, 2021 and 2020.

Revenue Recognition

The Company’s revenues to date have been generated primarily through collaboration and license agreements. The Company’s collaboration and license agreements may contain multiple elements including intellectual property licenses and research, and development services. Consideration the Company receives under these arrangements may include upfront payments, research and development funding, cost reimbursements, research, development, regulatory and commercial milestone payments, and royalty payments.

The Company applies Accounting Standard Codification Topic 606, Revenue from Contracts with Customers (“ASC 606”), issued by the Financial Accounting Standards Board (“FASB”) to account for its contracts with customers. Under ASC 606, revenue is recognized when a customer obtains control of promised goods or services. The amount of revenue recognized reflects the consideration that the Company expects to be entitled to receive in exchange for these services and excludes sales incentives and

amounts collected on behalf of third parties. The Company analyzes the nature of these performance obligations in the context of individual collaboration and license agreements in order to assess the distinct performance obligations. The Company evaluates its contracts with customers for proper classification in the consolidated statements of operations based on the nature of the underlying activity. Transactions with customers recorded in the Company’s consolidated statements of operations are recorded on either a gross or net basis, depending on the characteristics of the collaborative relationship.

To determine revenue recognition for arrangements within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price, including variable consideration, if any; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that it will collect the consideration to which it is entitled in exchange for the goods or services it transfers to the customer.

The Company uses judgment in determining the customer's ability and intent to pay, which is based upon factors including the customer's historical payment experience or, for new customers, credit and financial information pertaining to the customers. Determining whether a promised goods or service is a separate performance obligation requires the use of significant judgment. A change in such judgment could result in a significant change in the period in which revenue is recognized. The Company determines standalone selling price based on its overall pricing and discounting objectives, taking into consideration the type of services, estimates of hourly market rates, and stage of the research, development or clinical trials. The process for determining the transaction price involves significant judgment and includes consideration of multiple factors such as estimated revenues, market size, and development risk, among other factors contemplated in negotiating the arrangement with the customer. The Company determines the transaction price based on the consideration to which it expects to be entitled in exchange for transferring goods and services to the customer. In determining the transaction price, any variable consideration would be considered, to the extent applicable, if, in the Company’s judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. In accordance with the royalty exception under ASC 606 for licenses of intellectual property, the transaction price excludes future royalty payments to be received from our customers. The Company’s collaboration and license agreement contains no consideration payable to our customer or a significant financing component.

Performance Obligations

The following is a description of principal goods and services from which the Company generates revenue.

Intellectual property licenses

The Company generates revenue from licensing its intellectual property including know-how and development and commercialization rights. These licenses provide customers with a term-based license to further research, develop and commercialize the Company’s internally-discovered platform technologies for specified therapeutic indications. The consideration the Company receives in the form of nonrefundable upfront consideration allocated to the functional intellectual property licenses is recognized at a point in time for licenses determined to be distinct from other performance obligations in the contract when the Company transfers such license to the customer. If the license is combined with other goods or services into one performance obligation, the revenue is recognized over a period of time based on the Company’s method of measuring progress in which it satisfies the combined performance obligation. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The Company’s licensing agreements are generally cancelable. Customers have the right to terminate their contracts upon notice. The Company has the right to terminate the contracts generally only if the customer is in breach of the contract and fails to remedy the breach in accordance with the contractual terms.

Material Rights

Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right (i.e., an optional good or service offered for free or at a discount) to the customer and if so, whether they are considered performance obligations. The identification of material rights requires judgments related to the determination of the value of the underlying license relative to the option exercise price, including assumptions about the amount of the discount and likelihood that the option will be exercised. The exercise of a material right is accounted for as a contract modification for accounting purposes. Amounts allocated to any material right are recognized as revenue when or as the related future goods or services are transferred or when the option expires.

Research and development services

The Company generates revenue from research and development services it provides to its customers in connection with the licensed intellectual property. The services the Company provides to its customers primarily include scientific research activities.

Revenue associated with these services is recognized over time using the cost-to-cost input method, based on the total estimated costs to fulfill the obligations.

Contracts with Multiple Performance Obligations

The Company’s collaboration and license agreements with customers may contain multiple promised goods or services. Based on the characteristics of the promised goods and services the Company analyzes whether they are separate or combined performance obligations. The transaction price is allocated to the separate performance obligations on a relative standalone selling price basis. The Company determines standalone selling price based on its overall pricing and discounting objectives, taking into consideration the type of services, estimates of hourly market rates, and stage of the development and clinical trials.

ASC 606 requires the Company to allocate the arrangement consideration on a relative standalone selling price basis for each performance obligation after determining the transaction price of the contract and identifying the performance obligations to which that amount should be allocated. The relative standalone selling price is defined in ASC 606 as the price at which an entity would sell a promised good or service separately to a customer. If other observable transactions in which the Company has sold the same performance obligation separately are not available, the Company estimates the standalone selling price of each performance obligation. When standalone selling prices for the Company’s products or services are not directly observable, the Company determines the standalone selling prices using relevant information available and apply suitable estimation methods considering market conditions and entity-specific factors including, but not limited to, features and functionality of the underlying intellectual property licenses and the economic potential associated with ongoing research activities. Key assumptions to determine the standalone selling price may also include development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success.

Variable Consideration

The Company’s contracts with customers generally include two types of variable consideration: (i) research, development and regulatory milestone payments, which the Company is entitled to upon achievement of such specific milestones and (ii) one-time sales-based payments and sales-based royalties associated with licensed intellectual property.

If an arrangement includes research, development or regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal will not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control are generally not considered probable of being achieved until those approvals are received.

Product sales-based royalties under licensed intellectual property and one-time payments are accounted for under the royalty exception. The Company recognizes revenue for sales-based royalties under licensed intellectual property and one-time payments at the later of when the sales occur or the performance obligation is satisfied or partially satisfied.

Under the royalty exception in ASC 606 for licensed intellectual property the Company does not recognize any revenue for the variable amounts related to sales-based royalties and milestones until the later of when the sales occur, or the performance obligation is satisfied or partially satisfied. Accordingly, the revenue related to future sales-based royalties and milestones are excluded from the estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied.

Disaggregation of Revenue

The Company operates in one reportable business segment and has one customer.

Contract Assets and Contract Liabilities

The Company receives payments from customers based on contractual terms. Accounts receivable are recorded when the right to consideration becomes unconditional. For research and development services, the Company generally bills its customers monthly or quarterly as the services are performed. Payment terms on invoiced amounts are typically 30 - 60 days. Contract assets include amounts related to the Company’s contractual right to consideration for both completed and partially completed performance obligations that have not been invoiced and for which the Company does not yet have the right to payment. The current portion of contract asset is included in prepaid expenses and other current assets in the consolidated balance sheet. The non-current portion of contract assets is included in other non-current assets in the consolidated balance sheet. Contract liabilities consist of deferred revenue and include payments received in advance of performance under the contract.

Cost to Obtain and Fulfill a Contract

The Company generally does not incur costs to obtain new contracts. Costs to fulfill contracts are expensed as incurred.

Research and Development

Research and development expense consists of labor, material, equipment, and allocated facilities costs of the Company’s scientific staff who are working on research and development projects. Research and development costs are charged to operations as incurred.

Upfront payments and milestone payments made for the licensing of technology are expensed as research and development in the period in which they are incurred. Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses or other long-term assets. The advanced payments are expensed as the related goods are delivered or the services are performed.

Research and Manufacturing Contract Costs and Accruals

The Company has entered into various research and development and manufacturing agreements. These agreements are generally cancelable, and related payments are recorded as the corresponding expenses are incurred. The Company records accruals for estimated costs incurred to date. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the research studies or clinical trials and manufacturing activities, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Patent Costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.

Stock-Based Compensation

Stock-based compensation related to stock options granted to the Company’s employees and consultants and the 2020 Employee Stock Purchase Plan (“ESPP”) awards is measured at the grant date based on the fair value of the award. The fair value is recognized as stock-based compensation expense in the consolidated financial statements over the requisite service period, which is generally the vesting period of the respective awards. Compensation related to service-based awards is recognized starting on the grant date on a straight-line basis over the vesting period, which is typically two to four years. The Company recognizes the fair value of stock options granted to non-employees as stock-based compensation expense over the period in which the related services are received. Stock-based compensation expense related to stock options granted to non-employees is recognized based on the grant date fair value of awards as the stock options are earned. The Company believes that the estimated fair value of stock options is more readily measurable than the fair value of the services rendered. All option grants require continued service to continue vesting. For the ESPP, the requisite service period is generally the period of time from the offering date to the purchase date. The Company accounts for the forfeitures in the period in which they occur.

The Company uses the Black-Scholes valuation model to estimate the grant date fair value of the stock option awards and shares purchasable under the ESPP. The determination of the fair value of each stock award using the option-pricing model is affected by the Company’s assumptions regarding a number of variables including the fair value of the common stock at the date of grant, the expected term of the awards, the expected stock price volatility over the term of the awards, risk-free interest rate, and dividend rate. The Company’s assumptions with respect to these variables are as follows:

•

Fair Value of Common Stock—Prior to the IPO, the Company’s common stock was not publicly traded, therefore the Company estimated the fair value of its common stock. Following the IPO, the fair value of the Company’s common stock for awards with service-based vesting is the closing selling price per share of its common stock as reported on the Nasdaq Global Select Market on the date of grant or other relevant determination date.

•

Expected Term—The expected term represents the period that the stock-based awards are expected to be outstanding. The Company determines the expected term using the simplified method. The simplified method deems the term to be the average of the time-to-vesting and the contractual life of the options. For stock options granted to non-employees, the expected term equals the remaining contractual term of the option from the vesting date. For the ESPP, the expected term is the period of time from the offering date to the purchase date.

•

Expected Volatility—Given the limited period of time the Company’s stock has been traded in an active market, the expected volatility is estimated by taking the average historical price volatility for industry peers, consisting of several public companies in the Company’s industry that are similar in size, stage, or financial leverage, over a period of time commensurate with to the expected term of the awards.

•

Risk-Free Interest Rate—The risk-free interest rate is calculated using the average of the published interest rates of U.S. Treasury zero-coupon issues with maturities that are commensurate with the expected term.

•

Dividend Rate—The dividend yield assumption is zero, as the Company has no plans to make dividend payments in the foreseeable future.

Comprehensive Loss

Comprehensive loss includes net loss as well as other comprehensive income (loss). Other comprehensive income (loss) consists of unrealized gains and losses on available-for-sale securities.

Net Income (Loss) Per Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per common share, since the effects of potentially dilutive securities are anti-dilutive due to the net loss position of all periods presented.

Income Taxes

Deferred tax assets and liabilities are determined based on the difference between the financial statement carrying amounts of assets and liabilities and their respective tax bases, as well as net operating losses and credit carry forwards applied by the enacted tax rates expected to be in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Emerging Growth Company Status

The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the “JOBS Act”). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it (i) is no longer an emerging growth company or (ii) affirmatively and irrevocably opts out of the extended transition period provided in the JOBS Act. As a result, these consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates.

Recently Adopted Accounting Pronouncements

In January 2017, the FASB issued ASU 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. The new standard simplified the measurement of goodwill by eliminating step two of the two-step impairment test. Step two measures a goodwill impairment loss by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. The new guidance requires an entity to compare the fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value. Additionally, an entity is required to consider income tax effects from any tax-deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. The Company adopted this standard on January 1, 2021. The adoption of this standard had no impact on the Company’s consolidated financial statements and disclosures.

In December 2019, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify the

accounting for income taxes. ASU 2019-12 removed certain exceptions to the general principles in Topic 740 and also clarified and amended existing guidance to improve consistent application. The Company adopted this standard on January 1, 2021. The adoption of this standard had no impact on the Company’s consolidated financial statements and disclosures.

Recently Issued Accounting Pronouncements

In June 2016, the FASB issued ASU 2016-13, Financial Instruments — Credit Losses, to improve financial reporting by requiring timely recording of credit losses on loans and other financial instruments held by financial institutions and other organizations. The ASU requires the measurement of all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions and reasonable and supportable forecasts. This guidance will become effective for the Company beginning January 1, 2023, with early adoption permitted. The Company is currently evaluating the potential impact the adoption of ASU 2016-13 may have on its financial position and results of operations.

In May 2021, the FASB issued ASU 2021-04, Earnings Per Share (Topic 260), Debt-Modifications and Extinguishments (Subtopic 470-50), Compensation- Stock Compensation (Topic 718), and Derivatives and Hedging-Contracts in Entity’s Own Equity (Subtopic 815- 40) which provides guidance on modifications or exchanges of a freestanding equity-classified written call option that is not within the scope of another Topic. An entity should treat a modification of the terms or conditions or an exchange of a freestanding equity-classified written call option that remains equity classified after modification or exchange as an exchange of the original instrument for a new instrument ASU 2021-04 also provides further guidance on measuring the effect of a modification or an exchange of a freestanding equity-classified written call option that remains equity classified after modification or exchange. ASU 2021-04 also provides guidance on the recognition of the effect of a modification or an exchange of a freestanding equity-classified written call option that remains equity classified after modification or exchange on the basis of the substance of the transaction, in the same manner as if cash had been paid as consideration. This guidance will become effective for the Company beginning January 1, 2022. The Company is currently evaluating the potential impact the adoption of ASU 2021-04 may have on its financial position and results of operations.

Composition of Certain Balance Sheet Components

12 Months Ended

Dec. 31, 2021

Balance Sheet Related Disclosures [Abstract]

Composition of Certain Balance Sheet Components

Note 3. Composition of Certain Balance Sheet Components

Prepaid expenses and other current assets

Prepaid expenses and other current assets consist of the following as of (in thousands):

	December 31,
	2021		2020
Contract research services	$	2,739	$	651
Prepaid insurance		2,355		2,226
Prepaid rent		354		217
Landlord reimbursement		—		137
Other		2,100		1,613
Total prepaid expenses and other current assets	$	7,548	$	4,844

Property and equipment, net

Property and equipment, net consist of the following as of (in thousands):

	December 31,
	2021			2020
Laboratory equipment	$	14,192		$	11,420
Leasehold improvements		13,910			13,826
Computer equipment and software		2,137			1,381
Furniture and fixtures		928			928
Construction in progress		20			376
Total property and equipment		31,187			27,931
Less: Accumulated depreciation and amortization		(9,137	)		(4,595	)
Total property and equipment, net	$	22,050		$	23,336

Depreciation expense associated with property and equipment was $4.6 million and $2.6 million for the years ended December 31, 2021 and 2020, respectively.

Goodwill and other intangible assets, net

Goodwill and other intangible assets, net consist of the following as of (in thousands):

	December 31,
	2021		2020
Goodwill	$	4,228	$	4,228
Indefinite lived intangible assets:
IPR&D	$	1,320	$	1,320
Total intangible assets, net	$	1,320	$	1,320

There were no impairments of goodwill and other intangible assets for the years ended December 31, 2021 and 2020.

Accrued and other liabilities

Accrued and other liabilities consisted of the following as of (in thousands):

	December 31,
	2021		2020
Contract research services	$	12,292	$	15,822
Payroll and related expense		8,760		6,793
Other		2,488		1,839
Total accrued expenses and other liabilities	$	23,540	$	24,454

Financial Instruments

12 Months Ended

Dec. 31, 2021

Investments Debt And Equity Securities [Abstract]

Financial Instruments

Note 4. Financial Instruments

The following table summarizes the amortized cost and fair value of available-for-sale securities at December 31, 2021 and 2020 (in thousands):

	Amortized Cost/Cost		Unrealized Gains		Unrealized Losses		Fair Value
At December 31, 2021:
Money market fund	$	176,102	$	—	$	—	$	176,102
Total	$	176,102	$		$		$	176,102

At December 31, 2020:
Money market fund	$	70,713	$	—	$	—	$	70,713
U.S. government agency securities and treasuries		225,181		5		—		225,186
Total	$	295,894	$	5	$		$	295,899

No available-for-sale debt securities held as of December 31, 2021 and 2020 had remaining maturities greater than one year. Unrealized gains and losses on available-for-sale securities are included as a component of comprehensive loss. At December 31, 2021, the Company did not have any securities in material unrealized loss positions.

The Company reviews its investments to identify and evaluate investments that have an indication of possible other-than-temporary impairment. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the investee, and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value. The Company does not generally sell any investments prior to recovery of their amortized cost basis for any investments in an unrealized loss position.

Fair Value Measurement

12 Months Ended

Dec. 31, 2021

Fair Value Disclosures [Abstract]

Fair Value Measurement

Note 5. Fair Value Measurement

Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants as of the measurement date. Applicable accounting guidance provides an established hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs that market participants would use in valuing the asset or liability and are developed based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s

assumptions about the factors that market participants would use in valuing the asset or liability. There are three levels of inputs that may be used to measure fair value:

•

Level 1 — Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities

•

Level 2 — Significant other observable inputs other than Level 1 prices such as quoted prices in markets that are not active, or inputs that are observable, either directly or indirectly, for substantially the full term of the asset or liability

•

Level 3 — Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity)

The Company classifies its money market funds and U.S. treasury securities, which are valued based on quoted market prices in active markets with no valuation adjustment, as Level 1 assets within the fair value hierarchy.

The following table summarizes the Company’s valuation hierarchy for its financial assets and liabilities measured at fair value on a recurring basis as follows (in thousands):

	Level 1		Level 2		Level 3
At December 31, 2021:
Assets
Money market funds(1)	$	176,102	$	—	$	—
Short-term investments		—		—		—
Total	$	176,102	$		$

At December 31, 2020:
Assets:
Money market funds(1)	$	70,713	$	—	$	—
Short-term investments		225,186		—		—
Total	$	295,899	$	—	$	—

(1)

Included in cash and cash equivalents in the accompanying consolidated balance sheet.

Warrant liability

Prior to the IPO, the Company had 42,953,085 shares of outstanding convertible preferred stock and outstanding warrants to purchase an aggregate of 151,042 shares of convertible preferred stock. The fair value of these warrants was based on significant inputs not observable in the market, which represented a Level 3 measurement within the fair value hierarchy. The Company’s valuation of the preferred stock warrants utilized the Black-Scholes option-pricing model, which incorporated assumptions and estimates to value the preferred stock warrants. For the year ended December 31, 2020, the change in fair value of warrant liability was recorded as a loss of $0.4 million included in other income, net in the Company’s consolidated statement of operations and comprehensive loss.

At the closing of the IPO in July 2020, 42,953,085 shares of outstanding convertible preferred stock were automatically converted into 34,445,108 shares of common stock, and outstanding warrants to purchase an aggregate of 151,042 shares of convertible preferred stock became exercisable for 121,122 shares of common stock and were reclassified into permanent equity. Upon conversion, the Company reclassified the balance of warrant liability of $1.7 million to additional paid in capital.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Collaborations and License Agreement with Takeda	12 Months Ended
Collaborations and License Agreement with Takeda	Dec. 31, 2021
Collaborations and License Agreement with Takeda	Note 7. California Institute of Regenerative Medicine Awards The Company has been awarded funding from California Institute of Regenerative Medicine (“CIRM”) to develop internal programs. Under the terms of the funding, both CIRM and the Company have co-funded specified programs, under which funding is provided in developmental milestones determined as a part of the award. The Company is obligated to share potential future revenues for the related programs with CIRM. The percentage of revenues due to CIRM in the future is dependent on the amount of the award received and whether revenue is from product sales or through license fees. The maximum revenue sharing amount the Company may be required to pay to CIRM is equal to nine times the total amount awarded and paid to the Company. The Company has the option to decline any and all amounts awarded by CIRM. As an alternative to revenue sharing, the Company has the option to convert the award to a loan, which such option the Company must exercise on or before ten business days after the FDA notifies the Company that it has accepted the Company’s application for marketing authorization. In the event the Company exercises its right to convert any award to a loan, it would be obligated to repay the loan within ten business days of making such election. Repayment amounts due to CIRM vary dependent on when the award is converted to a loan, ranging from 60% of the award granted to the full amount received plus interest at the rate of the three-month LIBOR rate plus 10% per annum. Since the Company may be required to repay some or all of the amounts awarded by CIRM, the Company accounts for these awards as a liability rather than revenue if the Company’s intention is to convert the awards into a loan. Given the uncertainty in amounts due upon repayment, the Company has recorded amounts received without any discount or interest recorded, upon determination of amounts that would become due, the Company will adjust accordingly. In December 2017, the Company was granted an award in the amount of $19.8 million from CIRM to support the Company’s P-BCMA-101 Phase 1 clinical trial. The award is paid based on developmental milestones, of which $19.7 million had been received as of December 31, 2021 with up to an aggregate of $0.1 million in future milestone payments. In the fourth quarter of 2021, the Company made the decision to wind down clinical development of the P-BCMA-101 program, which resulted in write off of the amount previously included in the deferred CIRM grant liability as the Company no longer intends to repay the award and is included in other income in the accompanying consolidated statement of operations. In September 2018, the Company was granted an award in the amount of $4.0 million from CIRM to support the Company’s preclinical studies for its P-PSMA-101 program. The award is paid based on developmental milestones, of which the full $4.0 million had been received as of December 31, 2021.
Takeda Pharmaceuticals USA, Inc.
Collaborations and License Agreement with Takeda	Note 6. Collaborations and License Agreement with Takeda In October 2021, the Company entered into a collaboration and license agreement (the “Takeda Collaboration Agreement”) with Takeda Pharmaceuticals USA, Inc. (“Takeda”), pursuant to which the Company granted to Takeda a worldwide exclusive license under the Company’s certain platform technologies including piggyBac, Cas-CLOVER, biodegradable DNA and RNA nanoparticle delivery technology and other proprietary genetic engineering platforms to research, develop, manufacture and commercialize gene therapy products for certain indications, including Hemophilia A. The parties are collaborating to initially develop up to six in vivo gene therapy programs and Takeda also has an option to add two additional programs to the collaboration. The Company is obligated to perform research activities to the extent requested by Takeda up to the candidate selection stage, after which Takeda is obligated to assume responsibility for further development, manufacturing and commercialization of each program. Under the Takeda Collaboration Agreement, the Company received an upfront payment of $45.0 million, of which $5.0 million represents prepaid research funding. Takeda is obligated to provide funding for all collaboration program development costs; provided that the Company is obligated to perform certain platform development activities at its own cost. Under the Takeda Collaboration Agreement, the Company is eligible to receive preclinical milestone payments that could potentially exceed $82.5 million in the aggregate if preclinical milestones for all six programs are achieved. The Company is also eligible to receive future clinical development, regulatory and commercial milestone payments of $435.0 million in the aggregate per target, with a total potential deal value over the course of the collaboration of up to $2.7 billion, if milestones for all six programs are achieved and up to $3.6 billion if the milestones related to the two optional programs are also achieved. The Company is entitled to receive tiered royalty payments on net sales in the mid-single to low double digits, subject to certain standard reductions and offsets. Royalties will be payable, on a product-by-product and country-by-country basis, until the latest of the expiration of the licensed patents covering such product in such country, ten years from first commercial sale of such product in such country, or expiration of regulatory exclusivity for such product in such country. The promised goods and services under the Takeda Collaboration Agreement were accounted for as following separate performance obligations: (i) development and commercialization licenses for initial two indications, (ii) separate material rights associated with four additional licenses Takeda has an option to acquire individually, (iii) platform technology enhancement services, and (iv) research and development services. In order to determine the transaction price, the Company evaluated all the payments to be received during the duration of the Takeda Collaboration Agreement. Certain milestones and additional fees were considered variable consideration, which were not included in the initial transaction price based on the most likely amount method. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. The Company determined that the transaction price at the inception of the Takeda Collaboration Agreement consists of the upfront payment of $40.0 million and $5.0 million in prepaid research funding. The Company allocated the transaction price to individual performance obligations on their relative standalone selling price basis. Standalone selling prices are based on observable prices at which the Company separately sells the products or services. If a standalone selling price is not directly observable, then the Company estimates the standalone selling price considering market conditions and entity-specific factors including, but not limited to, features and functionality of the products and services. The performance obligation associated with the development and commercialization licenses for initial two indications was satisfied at the inception of the Takeda Collaboration Agreement. The separate material rights associated with additional licenses Takeda has an option to acquire individually are satisfied at a point in time in the future upon the earliest of Takeda exercising the option to acquire additional licenses or the expiration of the option. The platform technology enhancement services and the research and development services are satisfied over time as the Company performs the services for Takeda. The Company determined that the cost-based input method most faithfully depicts the pattern in which these performance obligations are satisfied. The Company recognizes revenue based on actual costs incurred as a percentage of total estimated costs as the Company completes its performance obligation under the Takeda Collaboration Agreement. Costs consist primarily of internal full-time employee (FTE) and certain reimbursable costs. The Company recognized revenue for the combined performance obligation consisting of a development and commercialization license and platform technology enhancement services based on the amount of incurred development expenses reimbursed by the customer as a percentage of total expected reimbursable expenses associated with the contract. As of December 31, 2021, all future potential milestone payments were excluded from the estimated total transaction price as they were considered constrained. For the year ended December 31, 2021, the Company recognized revenue of $31.2 million from the Takeda Collaboration Agreement, consisting of $30.2 million recognized at a point in time related to the development and commercialization licenses for the initial two indications, and $1.0 million recognized for the platform technology enhancement services and the research and development services, which are delivered over time. As of December 31, 2021, the balance of estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied, or partially unsatisfied, pursuant to the Company’s existing collaboration and license agreement consisted of $4.5 million presented as a deferred revenue, current and $9.3 million presented as a deferred revenue, non-current, in the accompanying consolidated balance sheet.

California Institute of Regenerative Medicine Awards

12 Months Ended

Dec. 31, 2021

Collaborative Arrangement [Abstract]

Collaborations and License Agreement with Takeda

Note 7. California Institute of Regenerative Medicine Awards

The Company has been awarded funding from California Institute of Regenerative Medicine (“CIRM”) to develop internal programs. Under the terms of the funding, both CIRM and the Company have co-funded specified programs, under which funding is provided in developmental milestones determined as a part of the award. The Company is obligated to share potential future revenues for the related programs with CIRM. The percentage of revenues due to CIRM in the future is dependent on the amount of the award received and whether revenue is from product sales or through license fees. The maximum revenue sharing amount the Company may be required to pay to CIRM is equal to nine times the total amount awarded and paid to the Company. The Company has the option to decline any and all amounts awarded by CIRM. As an alternative to revenue sharing, the Company has the option to convert the award

to a loan, which such option the Company must exercise on or before ten business days after the FDA notifies the Company that it has accepted the Company’s application for marketing authorization. In the event the Company exercises its right to convert any award to a loan, it would be obligated to repay the loan within ten business days of making such election. Repayment amounts due to CIRM vary dependent on when the award is converted to a loan, ranging from 60% of the award granted to the full amount received plus interest at the rate of the three-month LIBOR rate plus 10% per annum. Since the Company may be required to repay some or all of the amounts awarded by CIRM, the Company accounts for these awards as a liability rather than revenue if the Company’s intention is to convert the awards into a loan. Given the uncertainty in amounts due upon repayment, the Company has recorded amounts received without any discount or interest recorded, upon determination of amounts that would become due, the Company will adjust accordingly.

In December 2017, the Company was granted an award in the amount of $19.8 million from CIRM to support the Company’s P-BCMA-101 Phase 1 clinical trial. The award is paid based on developmental milestones, of which $19.7 million had been received as of December 31, 2021 with up to an aggregate of $0.1 million in future milestone payments. In the fourth quarter of 2021, the Company made the decision to wind down clinical development of the P-BCMA-101 program, which resulted in write off of the amount previously included in the deferred CIRM grant liability as the Company no longer intends to repay the award and is included in other income in the accompanying consolidated statement of operations.

In September 2018, the Company was granted an award in the amount of $4.0 million from CIRM to support the Company’s preclinical studies for its P-PSMA-101 program. The award is paid based on developmental milestones, of which the full $4.0 million had been received as of December 31, 2021.

Term Debt

12 Months Ended

Dec. 31, 2021

Debt Instruments [Abstract]

Term Debt

Note 8. Term Debt

In 2017, the Company entered into a loan and security agreement with Oxford Finance LLC (“Oxford”), as amended, pursuant to which the Company borrowed $20.0 million under a Term A loan and $10.0 million under a Term B loan (collectively with the Term A Loan, the “Term Loans”) for a total outstanding balance of $30.0 million as of December 31, 2021 and 2020.

In June 2021, the Company entered into an amendment to the Amended Loan Agreement (“2021 Amended Loan Agreement”) with Oxford. Pursuant to the terms of the 2021 Amended Loan Agreement, the interest-only period on the Term Loans and the final maturity date were extended by 18 months. As a result, all amounts outstanding under the Term Loans will mature on December 1, 2025 (the “Maturity Date”) and have interest-only payments through June 30, 2023, followed by 30 equal monthly payments of principal and unpaid accrued interest. The 2021 Amended Loan Agreement also included a facility fee of $1.1 million due on the earlier of (i) the Maturity Date, (ii) acceleration of any Term Loan, or (iii) the prepayment of the Term Loans. All other terms under the Amended Loan Agreement remained unchanged. The Company accounted for this amendment as debt modifications in accordance with ASC Topic 470, Debt because the modification was not considered substantial.

The Term Loans bear interest at a floating per annum rate equal to (i) 6.94% plus (ii) the greater of (a) the 30-day U.S. Dollar LIBOR rate and (b) 2.0%. The interest rate for the Term Loans as of December 31, 2021 was 8.94% per annum. The Company is required to make a final payment of 7.5% of the principal balance outstanding, payable on the earlier of (i) the Maturity Date, (ii) acceleration of any Term Loan, or (iii) the prepayment of the Term Loans. In connection with the Term A Loan and the Term B Loan, the Company incurred debt issuance costs of $1.0 million and $0.3 million, respectively, which have been recorded as a debt discount and are being accreted to interest expense over the term of the Term A Loan and the Term B Loan, respectively. Interest on the Term A Loan and the Term B Loan, consisting of the stated interest rate, final payment fee and amortization of the discount, is being recognized under the effective interest method using a rate of 10.86% and 10.72%, respectively. As of December 31, 2021, the balance of the unamortized debt discount was $0.6 million. The balance of the accrued final payment fee was $1.6 million as of December 31, 2021 and is presented as other long-term liability in the accompanying consolidated balance sheet.

The Company has an option to prepay all, but not less than all, the Term Loans borrowed, provided that the Company will be obligated to pay a prepayment fee equal to 1.0% of the Term Loans prepaid. As disclosed in Note 15, subsequent to December 31, 2021, the Company repaid all balances outstanding under the Term Loans and entered into a new loan agreement with Oxford.

The Company may use the proceeds from the Term Loans solely for its working capital requirements and to fund its general business operations. The Company’s obligations under the 2021 Amended Loan Agreement are secured by a first priority security interest in substantially all of its current and future assets, other than its intellectual property. In addition, the Company has also agreed not to encumber its intellectual property assets, except as permitted by the 2021 Amended Loan Agreement. While any amounts are outstanding under the 2021 Amended Loan Agreement, the Company is subject to a number of affirmative and restrictive covenants, including covenants regarding dispositions of property, business combinations or acquisitions, among other customary covenants. The Company is also restricted from declaring dividends or making other distributions or payments on its capital stock in excess of $0.3 million per calendar year, subject to limited exceptions. As of December 31, 2021, the Company was in compliance with all covenants under the 2021 Amended Loan Agreement.

Pursuant to the loan and security agreement with Oxford, in 2017, the Company issued to Oxford warrants to purchase an aggregate of up to 116,618 shares of the Company’s Series A-1 Preferred Stock (“Series A-1 Warrants”) at an exercise price of $3.43 per share. The Company determined the fair value of the Series A-1 Warrants on the date of issuance was $0.3 million. Upon the closing of the IPO, the Series A-1 Warrants became exercisable for 93,518 shares of common stock at an exercise price of $4.28 per share. The fair value of the warrant liability at the date of the IPO was reclassified to additional paid-in-capital.

Also pursuant to the loan and security agreement with Oxford, in 2018, the Company issued to Oxford warrants to purchase an aggregate of up to 17,212 shares of the Company’s Series B Preferred Stock with an exercise price of $5.81 per share (“2018 Series B Warrants”) and in 2019, in conjunction with drawing the additional $10.0 million in principal, the Company issued to Oxford warrants to purchase an aggregate of up to an additional 17,212 shares of the Company’s Series B Preferred Stock, with an exercise price of $5.81 per share (“2019 Series B Warrants”). The Company determined the fair value of the 2018 Series B Warrants and the 2019 Series B Warrants on the date of issuance was $0.1 million and $0.2 million, respectively. Upon the closing of the IPO, the Series B Warrants became exercisable for 27,604 shares of common stock at an exercise price of $7.25 per share.

The fair value of the warrant liability at the date of the IPO was reclassified to additional paid-in-capital. The warrants will expire ten years from the date of the grant unless earlier exercised. The fair value of the warrants was originally treated as a debt discount and recorded as a preferred stock warrant liability. The debt discount is amortized over the term of the Term Loans to interest expense.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

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+ Details

Stockholders Equity

12 Months Ended

Dec. 31, 2021

Equity [Abstract]

Stockholders Equity

Note 9. Stockholders’ Equity

Authorized Shares

In connection with the completion of the Company’s IPO in July 2020, the Company amended its certificate of incorporation to authorize 250,000,000 shares of common stock, par value $0.0001 per share, and 10,000,000 shares of undesignated preferred stock, par value $0.0001 per share, that may be issued from time to time by the Company’s board of directors in one or more series. Each share of common stock is entitled to one vote. The holders of common stock are also entitled to receive dividends whenever funds are legally available and when declared by the Company’s board of directors. Since the Company’s inception, there have been no dividends declared.

Public Offering and Related Transaction

In July 2020, the Company completed its IPO selling 14,000,000 shares of its common stock at a public offering price of $16.00 per share. Proceeds from the Company’s IPO, net of underwriting discounts and other offering costs, were $205.7 million. In connection with the IPO, all 42,953,085 shares of outstanding convertible preferred stock were automatically converted into 34,445,108 shares of the Company’s common stock. Additionally, the outstanding warrants to purchase an aggregate of 151,042 shares of convertible preferred stock became exercisable for 121,122 shares of common stock and were reclassified into permanent equity.

Convertible Preferred Stock

Prior to its conversion to common stock, the Company’s convertible preferred stock was classified as temporary equity on the Company’s balance sheets in accordance with authoritative guidance for the classification and measurement of potentially redeemable securities whose redemption is based upon certain change in control events outside of the Company’s control, including liquidation, sale or transfer of control of the Company. The Company had determined not to adjust the carrying values of the convertible preferred stock to the liquidation preferences of such shares because of the uncertainty of whether or when such events would occur.

In June 2020, the Company issued and sold 10,018,300 shares of Series D Preferred Stock, at a price of $10.93 per share, for aggregate gross proceeds of $109.5 million.

Convertible preferred stock immediately prior to the closing of the IPO consisted of the following (in thousands, except share amounts):

	July 14, 2020
	Preferred Stock Authorized		Preferred Stock Issued and Outstanding		Carrying Value		Liquidation Preference		Common Stock Issuable Upon Conversion
Series A Preferred Stock		9,696,798		9,696,798	$	31,063	$	31,063		7,776,095
Series A-1 Preferred Stock		3,370,263		3,253,645		11,083		11,083		2,609,176
Series B Preferred Stock		5,283,992		5,249,568		30,314		30,314		4,209,754
Series C Preferred Stock		14,734,774		14,734,774		149,713		149,713		11,816,169
Series D Preferred Stock		13,723,696		10,018,300		104,140		104,140		8,033,914
Total		46,809,523		42,953,085	$	326,313	$	326,313		34,445,108

Common Stock

Each share of common stock is entitled to one vote. The holders of common stock are also entitled to receive dividends whenever funds are legally available and when declared by the Company’s board of directors. Since the Company’s inception, there have been no dividends declared.

Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consists of the following at December 31, 2021:

Stock options issued and outstanding			9,899,707
Authorized for future options and award grants			3,752,093
Authorized for future issuance under Employee Stock Purchase Plan			1,154,241
Total			14,806,041

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

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+ Details

Stock-Based Compensation

12 Months Ended

Dec. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

Note 10. Stock-Based Compensation

In July 2020, the Company’s board of directors and stockholders approved and adopted the 2020 Equity Incentive Plan (the “2020 Plan”). The 2020 Plan became effective as of the completion of the IPO. Under the 2020 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units and other stock or cash-based awards to individuals who are employees, officers, directors or consultants of the Company. A total of 11,183,476 shares of common stock were approved to be initially reserved for issuance under the 2020 Plan. The number of shares that remained available for issuance under the Company’s previous equity incentive plan as of the effective date of the 2020 Plan and shares subject to outstanding awards under the Company’s previous equity incentive plan as of the effective date of the 2020 Plan that are subsequently canceled, forfeited or repurchased by the Company are added to the shares reserved under the 2020 Plan. The number of shares of common stock available for issuance under the 2020 Plan is automatically increased on the first day of each calendar year during the ten-year term of the 2020 Plan, beginning with January 1, 2021 and ending with January 1, 2030, by an amount equal to 5% of the outstanding number of shares of the Company’s common stock on December 31 of the preceding calendar year or such lesser amount as determined by the Company’s board of directors. The number of stock options and exercise prices were adjusted retrospectively for the Company’s reverse stock split, which became effective in July 2020.

As of December 31, 2021, there were 3,752,093 shares available for future option grants or direct issuance under the 2020 Plan. Through December 31, 2021, the Company has exclusively granted stock options under the 2020 Plan. Shares issued under the 2020 Plan are newly issued shares and the Company has no intention to repurchase previously issued shares. The exercise price of stock options granted under the 2020 Plan cannot be less than 100% of the fair value of the common stock on the grant date. The term and vesting period of each option shall be stated in the underlying agreements. However, the term shall be no more than ten years from the date of grant. The stock options generally vest over a four-year period. If stock options are granted to an optionee who, at the grant date, owns the Company common stock representing more than ten percent of the voting power of all classes of stock of the Company, then the term of the stock option shall be five years from the date of grant and the stock option exercise price is equal to 110% of the fair value at the date of grant.

Following is a summary of the Company’s stock option plan activity and related information for the year ended December 31, 2021:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Intrinsic Value (thousands)
Balance at January 1, 2021		4,738,607		$	10.34		8.34
Granted		7,228,445			8.81
Exercised		(583,332	)		3.39
Forfeited/Cancelled		(1,484,013	)		10.83
Balance at December 31, 2021		9,899,707		$	9.57		8.57	$	2,938
Options vested and expected to vest as of December 31, 2021		9,899,707		$	9.57		8.57	$	2,938
Options vested and exercisable as of December 31, 2021		3,033,767		$	9.81		7.43	$	2,792

The aggregate intrinsic value of options exercised during the years ended December 31, 2021 and 2020 was $3.4 million and $2.4 million, respectively, determined as of the date of exercise. The Company received $2.0 million and $0.2 million in cash from options exercised during the years ended December 31, 2021 and 2020, respectively.

As of December 31, 2021, total unrecognized compensation cost related to stock options was $42.8 million, and the weighted-average period over which this cost is expected to be recognized is approximately 2.9 years.

The weighted-average fair value of options granted during the years ended December 31, 2021 and 2020 was $6.12 and $8.65 per share, respectively. Total fair value of shares vested during the years ended December 31, 2021 and 2020 was $16.7 million and $6.9 million, respectively.

The assumptions that the Company used to determine the fair value of options granted to employees, non-employees and directors were as follows:

	Year Ended December 31,
	2021		2020
Risk-free interest rate	0.5%–1.3%		0.4%–1.4%
Expected volatility	82.2–84.3%		79–86%
Expected term (years)	5.5–6.0		5.5–6.0
Dividend yield		—		—

Risk-free interest rate—The risk-free interest rate is based on the U.S. Treasury zero coupon issues in effect at the time of grant for periods corresponding with the expected term of option.

Expected volatility—The expected volatility is estimated based on the average volatility for comparable publicly traded biotechnology companies over a period equal to the expected term of the stock option grants. The comparable companies were chosen based on their similar size, stage in the life cycle or area of specialty.

Expected term—The expected term represents the period that stock-based awards are expected to be outstanding. The expected term for option grants is determined using the simplified method which is used when there is insufficient historical data about exercise patterns and post-vesting employment termination behavior. The simplified method deems the expected term to be the midpoint between the vesting date and the contractual life of the stock-based awards.

Expected dividend—The Company has never paid dividends on its common stock, and has no plans to pay any dividends on its common stock. Therefore, the Company used an expected dividend yield of zero.

In July 2020, the Company’s board of directors and stockholders approved and adopted the 2020 Employee Stock Purchase Plan (the “ESPP”), which became effective as of the pricing of the IPO. A total of 615,000 shares of common stock were approved to be initially reserved for issuance under the ESPP. The number of shares of common stock available for issuance under the ESPP is automatically increased on the first day of each calendar year during the first ten-years of the term of the ESPP, beginning with January 1, 2021 and ending with January 1, 2030, by an amount equal to the lessor of (i) 1% of the outstanding number of shares of the Company’s common stock on December 31 of the preceding calendar year, (ii) 1,230,000 shares of common stock or (iii) such

lesser amount as determined by the Company’s board of directors. Under the 2020 ESPP, substantially all employees can elect to have up to 15% of their annual compensation withheld to purchase up to 3,000 shares of common stock per purchase period, subject to certain limitations. The shares of common stock can be purchased over an offering period of six months and at a price of 85% of the fair market value per share of common stock on the first trading day of the applicable offering period or on the exercise date of the applicable offering period, whichever is less. Under applicable accounting guidance, the 2020 ESPP is classified as a compensatory plan. The initial purchase period commenced in March 2021. For the year ended December 31, 2021, the assumptions used to estimate the fair value of shares purchasable under the ESPP using the Black-Scholes valuation model included risk-free interest rate of 0.05%, expected volatility ranging from 74.8% to 87.9%, expected term of 0.5 years and zero dividend yield. During the year ended December 31, 2021, a total of 79,367 shares were purchased by the Company’s employees under the 2020 ESPP resulting in net proceeds of $0.5 million.

The Company recorded total stock-based compensation expense in the following expense categories of the accompanying consolidated statements of operations and comprehensive loss (in thousands):

	Year Ended December 31,
	2021		2020
Research and development	$	8,090	$	3,872
General and administrative		8,614		3,348
Total stock-based compensation expense	$	16,704	$	7,220

Commitments and Contingencies

12 Months Ended

Dec. 31, 2021

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note 11. Commitments and Contingencies

Operating Leases

As of December 31, 2021, the Company had operating leases for manufacturing, laboratory and office space in San Diego, California consisting of approximately 87,000 square feet with remaining lease terms of 8.0 years. The manufacturing and laboratory and office space lease agreements include two options to extend the term for a period of 5 years each. Additionally, the Company had operating leases for dedicated manufacturing suites at its contract manufacturers with remaining lease terms of up to 2 years.

In October 2018, the Company entered into a lease agreement for a facility in San Diego, California to be used for research and development and administrative activities. The lease term commenced on April 1, 2019 and will expire on December 31, 2029.

In October 2019, the Company entered into a lease amendment to expand the existing premises. The lease term for the additional premises commenced on July 29, 2020 and will expire on December 31, 2029. The lease amendment provided for additional tenant reimbursements of $1.5 million and as costs were incurred, the Company performed additional analysis to determine treatment based on the type of leasehold improvement. Both the original lease and amendment provides for rent abatements and scheduled increases in base rent. In connection with the lease and its amendment, the Company made cash security deposits in the amount of $0.3 million, included in other long-term assets in the Company’s consolidated balance sheets as of December 31, 2021 and 2020.

In July 2019, the Company entered into a lease agreement for a facility in San Diego, California that was retrofitted to Good Manufacturing Practice standards and is used for manufacturing in its early-stage clinical trials. The lease term commenced on June 26, 2020 and will expire on December 31, 2029. The lease provided for tenant improvements of $2.9 million and as costs were incurred, the Company performed analysis to determine treatment based on the type of leasehold improvement. As of December 31, 2020, all costs were incurred, and construction was completed. The lease provides for rent abatements and scheduled increases in base rent. In connection with the lease, the Company made a one-time cash security deposit in the amount of $0.1 million, included in other long-term assets in the Company’s consolidated balance sheets as of December 31, 2021 and 2020.

Upon adoption of ASC 842 on January 1, 2020, the Company determined its leases meet the criteria of operating leases. Further, upon adoption of ASC 842, the Company determined it was the owner of certain tenant improvements but did not control the construction project and therefore the fair value of the building was derecognized and costs incurred by the Company related to the tenant improvements of $13.3 million were recorded as leasehold improvements in property and equipment, net on the consolidated balance sheet as of December 31, 2020 and will be depreciated over the remaining lease term.

In connection with the adoption of ASC 842, the Company recognized initial lease receivables of $2.7 million, right-of-use (“ROU”) lease assets of $22.3 million, which was adjusted for the deferred rent balance of $2.3 million and an initial lease liability of $27.3 million, with respect to the existing leases. The leases in San Diego include an option to extend, which was not recognized as part of the lease liability and ROU lease assets as it was not reasonably certain the Company would exercise the extension right. Additionally, under lease accounting guidance, the Company had been the deemed owner under construction of the manufacturing facility. Upon the adoption of ASC 842 the Company derecognized the amounts previously presented on its balance sheet related to its manufacturing facility including construction in progress of $2.1 million within property and equipment, and the construction financing obligation of $2.5 million recorded within other long-term liabilities and $0.3 million of other receivables within prepaid and other current assets as of December 31, 2019. The Company also recorded a cumulative adjustment to the opening balance of accumulated deficit of $0.1 million as of January 1, 2020.

During the years ended December 31, 2021 and 2020, the Company recognized $6.3 million and $6.0 million, respectively, of operating lease expense. The Company recognized an immaterial amount of variable operating lease expense for the twelve months ended December 31, 2021. During the year ended December 31, 2021, the Company paid $6.1 million in cash payments for its operating leases. As of December 31, 2021, the weighted average remaining lease term for operating leases was 7.4 years and the weighted-average discount rate for operating leases was 8.92%.

As of December 31, 2021, maturities of lease liabilities were as follows (in thousands):

Year ending December 31,
2022	$	6,577
2023		5,723
2024		4,814
2025		4,958
2026		5,107
Thereafter		16,259
Total future lease payments		43,438
Imputed interest		(11,597	)
Total lease liability balance		31,841
Less current portion of lease liability		6,337
Lease liability, net of current portion	$	25,504

Lease Agreement not Commenced as of December 31, 2021

In October 2021, the Company entered into a sublease agreement for a facility in San Diego, California consisting of approximately 24,000 square feet to be used for administrative activities. The lease term commenced in March 2022 and will expire on December 31, 2025. Future payments under the lease agreement are approximately $5.2 million.

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, contract research organizations, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and certain of its executive officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. The Company has not incurred any material costs as a result of such indemnifications and is not currently aware of any indemnification claims.

License Agreement with Janssen Biotech Inc.

In August 2015, the Company entered into a license agreement (“Janssen Agreement”) with Janssen pursuant to which the Company obtained exclusive worldwide rights to research, develop, manufacture and commercialize pharmaceutical products comprising autologous CAR-modified T-cells or any CAR-modified natural killer or CAR-modified natural-killer-like cells expressing certain Centyrin molecules or Centyrin CAR molecules for the treatment or prevention of any disease in humans. Pursuant to the Janssen Agreement, the Company paid Janssen an upfront fee of $0.2 million. Based on milestone developments, the Company has paid an additional $4.0 million through December 31, 2021. The Company is required to pay Janssen up to an aggregate of $75.8 million upon the achievement of certain clinical, regulatory and sales milestones for the first licensed product and up to an aggregate of $46.8 million upon the achievement of certain clinical, regulatory and sales milestones for each licensed product thereafter. The Company is also obligated to pay, on a product-by-product and country-by-country basis, royalties in the low single-digit percentage range on annual net sales.

April 2017 Commercial License Agreement with TeneoBio, Inc.

In April 2017, the Company entered into a commercial license agreement (the “2017 TeneoBio Agreement”) with TeneoBio, Inc. (“TeneoBio”) pursuant to which the Company obtained exclusive worldwide rights to use and develop pharmaceutical products comprising allogeneic T-cells expressing a CAR molecule containing certain heavy chain sequences provided by TeneoBio.

Pursuant to the 2017 TeneoBio Agreement, the Company has paid TeneoBio $0.5 million through the Company’s selection of the antibodies licensed under the 2017 TeneoBio Agreement. The Company is required to pay TeneoBio up to an aggregate of $20.5 million upon the first achievement of certain clinical and regulatory milestones for any allogeneic product and up to an aggregate of $20.5 million upon the first achievement of certain clinical and regulatory milestones for any autologous product. The Company is also obligated to pay, on a product-by-product and country-by-country basis, a royalty in the low single-digit percentage on net sales of any licensed products.

August 2018 Commercial License Agreement with TeneoBio, Inc.

In August 2018, the Company entered into a commercial license agreement (the “2018 TeneoBio Agreement”) with TeneoBio pursuant to which the Company obtained exclusive rights to research, develop and commercialize up to a certain number of targets from TeneoBio. Pursuant to the 2018 TeneoBio Agreement, the Company has paid TeneoBio an upfront fee of $4.0 million. The Company is required to pay TeneoBio up to an aggregate of $31.0 million upon the first achievement of certain clinical and regulatory milestones for each product, none of which have been met. The Company is also obligated to pay, on a product-by-product and country-by-country basis, a royalty in the low single-digit percentage on net sales of any licensed products.

October 2019 License Agreement with Genus Oncology, LLC

In October 2019, the Company entered into a license agreement (the “Genus Agreement”) with Genus Oncology, LLC (“Genus”), pursuant to which the Company paid Genus an upfront fee of $1.5 million and Genus granted the Company the option, which is exercisable for an additional $1.5 million fee, to obtain an exclusive worldwide license to research, develop and commercialize pharmaceutical products incorporating CAR cells expressing antibodies and derivatives thereof targeting MUC1.

Pursuant to the Genus Agreement, the Company is also required to pay Genus up to an aggregate of $71.0 million upon first achievement of certain clinical, regulatory and sales milestones for any Genus licensed product and companion diagnostics. The Company is also obligated to pay, on a product-by-product and country-by-country basis, tiered royalties in the low to mid-single-digit percentage on net sales of any Genus licensed products and related companion diagnostics.

Legal Contingencies

In the ordinary course of business, the Company may face claims brought by third parties against the Company. The Company does not believe that there is any litigation, asserted or unasserted claim pending that could, individually or in the aggregate, have a material adverse effect on the Company’s results of operations or financial condition.

Income Taxes

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Income Taxes

Note 12. Income Taxes

The components of the pretax loss from operations were all attributed to the United States. There was no income tax expense or benefit for the years ended December 31, 2021 and 2020.

The (benefit from) provision for income taxes differs from the amount of income tax determined by applying the applicable U.S. statutory federal income tax rate to pretax income as a result of the following differences as of (in thousands):

	Year Ended December 31,
	2021			2020
Federal statutory rate	$	(26,245	)	$	(27,253	)
Adjustments for tax effects of:
Tax credits		(22,448	)		(10,735	)
State taxes, net		(7,575	)		(8,581	)
Unrecognized tax benefits		3,431			2,445
Stock-based compensation		2,308			956
Permanent adjustments		53			134
Other, net		(192	)		(27	)
Change in valuation allowance		50,668			43,061
Total	$	—		$	—

Significant components of the Company’s deferred tax assets and liabilities consist of the following as of (in thousands):

	December 31,
	2021			2020
Deferred tax assets:
Net operating losses	$	98,815		$	65,058
Income tax credit carryforwards		33,524			15,727
Lease liabilities		8,885			8,388
Deferred revenue		2,280			—
Accrued expenses		2,233			1,855
Amortization		1,406			1,558
Grant income		1,114			6,648
Other, net		2,430			982
Total deferred tax assets		150,687			100,216
Deferred tax liabilities:
Right of use assets		(7,305	)		(6,934	)
Depreciation		(1,308	)		(1,877	)
Acquired indefinite lived intangibles		(368	)		(369	)
Total deferred tax liabilities		(8,981	)		(9,180	)
Valuation allowance		(141,761	)		(91,091	)
Net deferred tax liability	$	(55	)	$	(55	)

The realization of deferred tax assets may be dependent on the Company’s ability to generate sufficient income in future years in the associated jurisdiction to which the deferred tax assets relate. The Company considers all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax planning strategies, and recent financial performance. A valuation allowance of $141.8 million has been recorded as of December 31, 2021, as compared to $91.1 million as of December 31, 2020. The valuation allowance is based on management’s assessment that it is more likely than not that the Company will not have taxable income in the foreseeable future.

Deferred tax liabilities associated with indefinite-life intangibles cannot be considered a source of income to support the realization of deferred tax assets because the reversal of these deferred tax liabilities is considered indefinite. However, as the Company has an indefinite-life asset with an unlimited loss carryforward period within the same jurisdiction, and of appropriate character, the deferred tax liability associated with the indefinite-life intangible constitutes a source of taxable income to support the realization of the deferred tax asset, since both have indefinite reversal or expiration periods.

As of December 31, 2021, the Company had federal and state net operating loss carryforwards of $23.3 million and $350.8 million, respectively, which begin to expire in 2032 and the Company had federal net operating loss carryforwards that do not expire but utilization is limited to 80% of taxable income for any given tax year in the amount of $329.9 million.

As of December 31, 2021, the Company had federal orphan drug credits and research and development credits and state research and development tax credits of $33.2 million and $11.8 million, respectively. The federal research and development tax credits will begin to expire in 2032, while the state credits do not expire.

Additionally, the utilization of the net operating loss and research and development tax credit carryforwards is subject to an annual limitation under Section 382 of the Internal Revenue Code. Future ownership changes as determined under Section 382 could further limit the utilization of net operating loss carryforwards. Due to the existence of the valuation allowance, future changes in the deferred tax assets related to these tax attributes will not impact the Company’s effective tax rate.

The Company is subject to taxation in the U.S. and state jurisdictions. As of December 31, 2021, the Company’s tax years beginning 2012 to date are subject to examination by federal and other state taxing authorities due to the carry forward of unutilized net operating losses and research and development tax credits. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service or state tax authorities to the extent utilized in a future period. The Company is not currently under examination by the IRS or state and local tax authorities.

As of December 31, 2021, the Company had unrecognized tax benefits of $9.5 million, determined as follows:

	December 31,
	2021			2020
Balance at beginning of year	$	5,457		$	2,470
Increase for current year positions		4,105			3,211
Decrease for prior year positions		(68	)		(224	)
Balance at the end of year	$	9,494		$	5,457

These unrecognized tax benefits are not expected to change within the next twelve months. Of the $9.5 million of unrecognized tax benefits, zero would impact the effective tax rate due to the valuation allowance, if reversed. The Company recognizes interest and penalties related to uncertain tax positions as a component of income tax expense. As of December 31, 2021, there are no accrued interest or penalties.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 21
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32857-109319

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330215-122817

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 17
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32809-109319

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 270
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6424409&loc=d3e44925-109338

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-URI http://asc.fasb.org/topic&trid=2144680

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Employee Benefit Plan

12 Months Ended

Dec. 31, 2021

Compensation And Retirement Disclosure [Abstract]

Employee Benefit Plan

Note 13. Employee Benefit Plan

The Company has a defined contribution retirement savings plan under Section 401(k) of the Internal Revenue Code. This plan covers all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. Company contributions to the plan may be made at the discretion of the Board of Directors. Total contributions by the Company during the years ended December 31, 2021 and 2020 were $0.9 million and $0.6 million, respectively.

Net Loss Per Share

12 Months Ended

Dec. 31, 2021

Earnings Per Share [Abstract]

Net Loss Per Share

Note 14. Net Loss Per Share

Net loss per share is computed by dividing net loss attributable to common stockholders for the period by the weighted average number of common shares outstanding during the period. Diluted loss per share reflects the additional dilution from potential issuances of common stock, such as stock issuable pursuant to the exercise of stock options and from purchases under the ESPP, as well as from the possible conversion of the Company’s preferred stock and exercise of the outstanding warrants.

The Company’s potentially dilutive securities, which include warrants to purchase common stock, common stock options and common stock from the ESPP, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of shares of common stock outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same.

The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect:

	Year Ended December 31,
	2021		2020
Stock options to purchase common stock		9,899,707		4,738,607
Warrants to purchase convertible preferred stock (as converted to common stock)		121,122		121,122
ESPP shares		5,310		—
		10,026,139		4,859,729

Subsequent Events

12 Months Ended

Dec. 31, 2021

Subsequent Events [Abstract]

Subsequent Events

Note 15. Subsequent Events

In February 2022, the Company entered into a new Loan and Security Agreement (“2022 Loan Agreement”) with Oxford. Pursuant to the terms of the 2022 Loan Agreement, the Company borrowed $60.0 million in term loans, a portion of which was used to repay the balance outstanding under the 2021 Amended Loan Agreement. Under the 2022 Loan Agreement the interest-only period is through April 1, 2025, with interest-only payments through March 1, 2025, followed by 23 equal monthly payments of principal and applicable interest. Upon the satisfaction of certain conditions set forth in the 2022 Loan Agreement, the interest-only period may be extended through April 1, 2026, followed by 11 equal monthly payments of principal and applicable interest. As a result, all amounts outstanding under the 2022 Loan Agreement will mature on February 1, 2027. Upon occurrence of a qualifying equity event, the interest-only period is subject to an extension to 48 months followed by 11 equal monthly payments of principal and applicable interest. In connection with the repayment of the balance outstanding under the 2021 Amended Loan Agreement, the Company incurred amendment and final payment fees of $1.6 million previously due on the earlier of (i) the maturity date, (ii) acceleration of any Term Loan, or (iii) the prepayment of the Term Loans. The Company has an option to repay the outstanding debt under the 2022 Loan Agreement at any time in increments of $5.0 million, subject to a prepayment fee of 1.0% if the term loans are prepaid on or prior to February 22, 2024, after which no prepayment penalty would be applied. Consistent with the 2021 Amended Loan Agreement, there is a 7.5% final payment fee payable on the earlier of (i) the new maturity date, (ii) acceleration of the new loan, or (iii) the prepayment of the new loan.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Nature Of Operations

Nature of Operations

Basis of Preparation and Consolidation

Risk And Uncertainties

Risk and Uncertainties

Impacts to the Company’s business, some of which the Company has already experienced, include, but are not limited to, temporary closures of its facilities or those of its vendors, disruptions or restrictions on its employees’ ability to travel, disruptions to or delays in ongoing laboratory experiments, preclinical studies, clinical trials, third-party manufacturing supply and other operations, the diversion of healthcare resources away from the conduct of clinical trials to focus on pandemic concerns, interruptions or delays in the operations of the U.S. Food and Drug Administration (“FDA”) or other regulatory authorities, and the Company’s ability to raise capital and conduct business development activities

Use of Estimates

Segment Information

Fair Value Measurements

Concentration Of Business Risk

Concentration of Business Risk

Leases

Deferred Offering Costs

Concentration of Credit Risk

Cash and Cash Equivalents

Short Term Investments

Short-Term Investments

Goodwill and Other Intangible Assets

Property and Equipment

Property and equipment are stated at cost and depreciated or amortized using the straight-line method, based on their estimated useful lives as follows:

Asset Classification	Estimated Useful Life (years)
Laboratory equipment		5
Leasehold improvements	Lesser of useful life or lease-term
Computer equipment and software		3
Furniture and fixtures		7

Revenue Recognition

Performance Obligations

The following is a description of principal goods and services from which the Company generates revenue.

Intellectual property licenses

Material Rights

Research and development services

Revenue associated with these services is recognized over time using the cost-to-cost input method, based on the total estimated costs to fulfill the obligations.

Contracts with Multiple Performance Obligations

Variable Consideration

Disaggregation of Revenue

The Company operates in one reportable business segment and has one customer.

Contract Assets and Contract Liabilities

Cost to Obtain and Fulfill a Contract

The Company generally does not incur costs to obtain new contracts. Costs to fulfill contracts are expensed as incurred.

Research and Development

Research and Manufacturing Contract Costs and Accruals

Patent Costs

Stock-Based Compensation

•

Dividend Rate—The dividend yield assumption is zero, as the Company has no plans to make dividend payments in the foreseeable future.

Comprehensive Loss

Comprehensive loss includes net loss as well as other comprehensive income (loss). Other comprehensive income (loss) consists of unrealized gains and losses on available-for-sale securities.

Net Income (Loss) Per Share

Income Taxes

Emerging Growth Company Status

Recently Adopted Accounting Pronouncements

Recently Issued Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Schedule of Estimated Useful Lives of Property and Equipment

Property and equipment are stated at cost and depreciated or amortized using the straight-line method, based on their estimated useful lives as follows:

Asset Classification	Estimated Useful Life (years)
Laboratory equipment		5
Leasehold improvements	Lesser of useful life or lease-term
Computer equipment and software		3
Furniture and fixtures		7

Composition of Certain Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2021

Balance Sheet Related Disclosures [Abstract]

Summary of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consist of the following as of (in thousands):

	December 31,
	2021		2020
Contract research services	$	2,739	$	651
Prepaid insurance		2,355		2,226
Prepaid rent		354		217
Landlord reimbursement		—		137
Other		2,100		1,613
Total prepaid expenses and other current assets	$	7,548	$	4,844

Summary of Property and Equipment Net

Property and equipment, net consist of the following as of (in thousands):

	December 31,
	2021			2020
Laboratory equipment	$	14,192		$	11,420
Leasehold improvements		13,910			13,826
Computer equipment and software		2,137			1,381
Furniture and fixtures		928			928
Construction in progress		20			376
Total property and equipment		31,187			27,931
Less: Accumulated depreciation and amortization		(9,137	)		(4,595	)
Total property and equipment, net	$	22,050		$	23,336

Summary of Goodwill and Other Intangible Assets, Net

Goodwill and other intangible assets, net consist of the following as of (in thousands):

	December 31,
	2021		2020
Goodwill	$	4,228	$	4,228
Indefinite lived intangible assets:
IPR&D	$	1,320	$	1,320
Total intangible assets, net	$	1,320	$	1,320

Schedule of Accrued and Other Liabilities

Accrued and other liabilities consisted of the following as of (in thousands):

	December 31,
	2021		2020
Contract research services	$	12,292	$	15,822
Payroll and related expense		8,760		6,793
Other		2,488		1,839
Total accrued expenses and other liabilities	$	23,540	$	24,454

Financial Instruments - (Tables)

12 Months Ended

Dec. 31, 2021

Investments Debt And Equity Securities [Abstract]

Summary of Amortized Cost and Fair Value of Available-for-Sale Securities

The following table summarizes the amortized cost and fair value of available-for-sale securities at December 31, 2021 and 2020 (in thousands):

	Amortized Cost/Cost		Unrealized Gains		Unrealized Losses		Fair Value
At December 31, 2021:
Money market fund	$	176,102	$	—	$	—	$	176,102
Total	$	176,102	$		$		$	176,102

At December 31, 2020:
Money market fund	$	70,713	$	—	$	—	$	70,713
U.S. government agency securities and treasuries		225,181		5		—		225,186
Total	$	295,894	$	5	$		$	295,899

Fair Value Measurement (Tables)

12 Months Ended

Dec. 31, 2021

Fair Value Disclosures [Abstract]

Schedule of Company's Valuation Hierarchy of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis

The following table summarizes the Company’s valuation hierarchy for its financial assets and liabilities measured at fair value on a recurring basis as follows (in thousands):

	Level 1		Level 2		Level 3
At December 31, 2021:
Assets
Money market funds(1)	$	176,102	$	—	$	—
Short-term investments		—		—		—
Total	$	176,102	$		$

At December 31, 2020:
Assets:
Money market funds(1)	$	70,713	$	—	$	—
Short-term investments		225,186		—		—
Total	$	295,899	$	—	$	—

(1)

Included in cash and cash equivalents in the accompanying consolidated balance sheet.

Stockholders Equity (Tables)

12 Months Ended

Dec. 31, 2021

Equity [Abstract]

Summary of Preferred Stock

Convertible preferred stock immediately prior to the closing of the IPO consisted of the following (in thousands, except share amounts):

	July 14, 2020
	Preferred Stock Authorized		Preferred Stock Issued and Outstanding		Carrying Value		Liquidation Preference		Common Stock Issuable Upon Conversion
Series A Preferred Stock		9,696,798		9,696,798	$	31,063	$	31,063		7,776,095
Series A-1 Preferred Stock		3,370,263		3,253,645		11,083		11,083		2,609,176
Series B Preferred Stock		5,283,992		5,249,568		30,314		30,314		4,209,754
Series C Preferred Stock		14,734,774		14,734,774		149,713		149,713		11,816,169
Series D Preferred Stock		13,723,696		10,018,300		104,140		104,140		8,033,914
Total		46,809,523		42,953,085	$	326,313	$	326,313		34,445,108

Schedule of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consists of the following at December 31, 2021:

Stock options issued and outstanding			9,899,707
Authorized for future options and award grants			3,752,093
Authorized for future issuance under Employee Stock Purchase Plan			1,154,241
Total			14,806,041

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of the Company's Stock Option Plan Activity

Following is a summary of the Company’s stock option plan activity and related information for the year ended December 31, 2021:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Intrinsic Value (thousands)
Balance at January 1, 2021		4,738,607		$	10.34		8.34
Granted		7,228,445			8.81
Exercised		(583,332	)		3.39
Forfeited/Cancelled		(1,484,013	)		10.83
Balance at December 31, 2021		9,899,707		$	9.57		8.57	$	2,938
Options vested and expected to vest as of December 31, 2021		9,899,707		$	9.57		8.57	$	2,938
Options vested and exercisable as of December 31, 2021		3,033,767		$	9.81		7.43	$	2,792

Schedule of Assumptions Used to Determine the Fair Value of Options Granted

The assumptions that the Company used to determine the fair value of options granted to employees, non-employees and directors were as follows:

	Year Ended December 31,
	2021		2020
Risk-free interest rate	0.5%–1.3%		0.4%–1.4%
Expected volatility	82.2–84.3%		79–86%
Expected term (years)	5.5–6.0		5.5–6.0
Dividend yield		—		—

Schedule of Stock-Based Compensation Expense

The Company recorded total stock-based compensation expense in the following expense categories of the accompanying consolidated statements of operations and comprehensive loss (in thousands):

	Year Ended December 31,
	2021		2020
Research and development	$	8,090	$	3,872
General and administrative		8,614		3,348
Total stock-based compensation expense	$	16,704	$	7,220

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2021

Commitments And Contingencies Disclosure [Abstract]

Summary of Maturities of Lease Liabilities

As of December 31, 2021, maturities of lease liabilities were as follows (in thousands):

Year ending December 31,
2022	$	6,577
2023		5,723
2024		4,814
2025		4,958
2026		5,107
Thereafter		16,259
Total future lease payments		43,438
Imputed interest		(11,597	)
Total lease liability balance		31,841
Less current portion of lease liability		6,337
Lease liability, net of current portion	$	25,504

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Schedule of (Benefit from) Provision for Income Taxes Differs from Income Tax Determined by Applicable U.S. Statutory Federal Income Tax Rate to Pretax Income

	Year Ended December 31,
	2021			2020
Federal statutory rate	$	(26,245	)	$	(27,253	)
Adjustments for tax effects of:
Tax credits		(22,448	)		(10,735	)
State taxes, net		(7,575	)		(8,581	)
Unrecognized tax benefits		3,431			2,445
Stock-based compensation		2,308			956
Permanent adjustments		53			134
Other, net		(192	)		(27	)
Change in valuation allowance		50,668			43,061
Total	$	—		$	—

Significant Components of Deferred Tax Assets and Liabilities

Significant components of the Company’s deferred tax assets and liabilities consist of the following as of (in thousands):

	December 31,
	2021			2020
Deferred tax assets:
Net operating losses	$	98,815		$	65,058
Income tax credit carryforwards		33,524			15,727
Lease liabilities		8,885			8,388
Deferred revenue		2,280			—
Accrued expenses		2,233			1,855
Amortization		1,406			1,558
Grant income		1,114			6,648
Other, net		2,430			982
Total deferred tax assets		150,687			100,216
Deferred tax liabilities:
Right of use assets		(7,305	)		(6,934	)
Depreciation		(1,308	)		(1,877	)
Acquired indefinite lived intangibles		(368	)		(369	)
Total deferred tax liabilities		(8,981	)		(9,180	)
Valuation allowance		(141,761	)		(91,091	)
Net deferred tax liability	$	(55	)	$	(55	)

Schedule of Unrecognized Tax Benefits

As of December 31, 2021, the Company had unrecognized tax benefits of $9.5 million, determined as follows:

	December 31,
	2021			2020
Balance at beginning of year	$	5,457		$	2,470
Increase for current year positions		4,105			3,211
Decrease for prior year positions		(68	)		(224	)
Balance at the end of year	$	9,494		$	5,457

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2021

Earnings Per Share [Abstract]

Schedule of Anti-Dilutive Securities Excluded From Computation of Diluted Net Loss per Share Attributable to Common Stockholders

	Year Ended December 31,
	2021		2020
Stock options to purchase common stock		9,899,707		4,738,607
Warrants to purchase convertible preferred stock (as converted to common stock)		121,122		121,122
ESPP shares		5,310		—
		10,026,139		4,859,729

Nature of Business and Basis of Presentation - Additional Information (Details) $ in Thousands		12 Months Ended
	Jul. 02, 2020	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Nature Of Business And Basis Of Presentation [Line Items]
Net loss		$ 124,974	$ 129,775
Net cash used in operating activities		102,543	113,328
Accumulated deficit		406,859	$ 281,885
Cash, cash equivalents and marketable securities		$ 206,300
Common Stock
Nature Of Business And Basis Of Presentation [Line Items]
Reverse stock split	1-for-1.247
Reverse stock split, conversion ratio	0.801924

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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+ Details

- Definition

The cumulative amount of the reporting entity's undistributed earnings or deficit.

+ References + Details

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) Segment PerformanceObligation Customer Contract	Dec. 31, 2020 USD ($)	Jul. 31, 2020 USD ($)
Recent Accounting Guidance [Line Items]
Number of operating segment \| Segment	1
Variable lease, payments	$ 0
Balance held in account	200,000	$ 200,000
Accounts payable	100,000	100,000
Impairment of goodwill	0	0
Impairment of long-lived assets	0	0
Consideration payable to customer	$ 0
Number of revenue performance obligation \| PerformanceObligation	1
Number of reportable segment \| Segment	1
Number of customer \| Customer	1
Description of payment terms	Payment terms on invoiced amounts are typically 30 - 60 days.
Costs incurred to obtain contracts \| Contract	0
Dividend yield assumption rate	0.00%
Dividend payments	$ 0
Minimum
Recent Accounting Guidance [Line Items]
Stock based compensation, vesting period	2 years
Maximum
Recent Accounting Guidance [Line Items]
Stock based compensation, vesting period	4 years
IPR&D
Recent Accounting Guidance [Line Items]
Impairment of intangible assets, indefinite-lived	$ 0	$ 0
IPO
Recent Accounting Guidance [Line Items]
Deferred offering costs			$ 18,300,000

Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2021
Laboratory Equipment
Property Plant And Equipment [Line Items]
Estimated useful life of property and equipment	5 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Estimated useful life of property and equipment	Lesser of useful life or lease-term
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Estimated useful life of property and equipment	3 years
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Estimated useful life of property and equipment	7 years

Composition of Certain Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Contract research services	$ 2,739	$ 651
Prepaid insurance	2,355	2,226
Prepaid rent	354	217
Landlord reimbursement		137
Other	2,100	1,613
Total prepaid expenses and other current assets	$ 7,548	$ 4,844

Composition of Certain Balance Sheet Components - Summary of Property and Equipment Net (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Total property and equipment	$ 31,187	$ 27,931
Less: Accumulated depreciation and amortization	(9,137)	(4,595)
Total property and equipment, net	22,050	23,336
Laboratory Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	14,192	11,420
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	13,910	13,826
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Total property and equipment	2,137	1,381
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	928	928
Construction in Progress
Property Plant And Equipment [Line Items]
Total property and equipment	$ 20	$ 376

Composition of Certain Balance Sheet Components - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Depreciation and amortization expense	$ 4,552,000	$ 2,586,000
Impairment of goodwill	0	0
Impairment of other intangible assets	$ 0	$ 0

Composition of Certain Balance Sheet Components - Summary of Goodwill and Other Intangible Assets, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Goodwill	$ 4,228	$ 4,228
Indefinite lived intangible assets:
IPR&D	1,320	1,320
Total intangible assets, net	$ 1,320	$ 1,320

Composition of Certain Balance Sheet Components - Summary of Accrued and Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Contract research services	$ 12,292	$ 15,822
Payroll and related expense	8,760	6,793
Other	2,488	1,839
Total accrued expenses and other liabilities	$ 23,540	$ 24,454

Financial Instruments - Summary of Amortized Cost and Fair Value of Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost/Cost	$ 176,102	$ 295,894
Available-for-Sale Securities, Unrealized Gains		5
Available-for-Sale Securities, Fair Value	176,102	295,899
Money Market Fund
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost/Cost	176,102	70,713
Available-for-Sale Securities, Fair Value	$ 176,102	70,713
U.S. Government Agency Securities and Treasuries
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost/Cost		225,181
Available-for-Sale Securities, Unrealized Gains		5
Available-for-Sale Securities, Fair Value		$ 225,186

Financial Instruments - Additional Information (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Debt securities, available-for-sale, noncurrent	$ 0	$ 0
Debt securities, available-for-sale, unrealized loss position	$ 0

Fair Value Measurement - Schedule of Company's Valuation Hierarchy of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($)
$ in Thousands

Dec. 31, 2021

Dec. 31, 2020

Assets

Cash and cash equivalents

$ 206,325

$ 83,966

Recurring Basis | Level 1

Assets

Short-term investments

225,186

Total

176,102

295,899

Recurring Basis | Level 1 | Money Market Fund

Assets

Cash and cash equivalents

^[1]

$ 176,102

$ 70,713

[1]	Included in cash and cash equivalents in the accompanying consolidated balance sheet.

Fair Value Measurement - Additional Information (Details) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
	Jul. 14, 2020	Jul. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Temporary equity, shares outstanding	42,953,085
Change in fair value of warrant liability			$ 387
Reclassification of warrant liability to additional paid in capital		$ 1,700
Convertible Preferred Stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Temporary equity, shares outstanding	42,953,085	42,953,085		32,934,785
Warrants to purchase stock	151,042
Number of outstanding securities converted		34,445,108
Convertible Preferred Stock \| Common Stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Warrants to purchase stock		151,042
Number of outstanding securities converted	34,445,108
Convertible Preferred Stock \| Warrant
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of outstanding securities converted	121,122	121,122

Collaborations and License Agreement with Takeda - Additional Information (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2021 USD ($) Program	Dec. 31, 2021 USD ($)
Collaborations And License Agreement [Line Items]
Revenues recognized		$ 31,238
Deferred revenue, current		4,497
Deferred revenue, non-current		9,265
Collaboration Agreement \| Takeda Pharmaceuticals USA, Inc.
Collaborations And License Agreement [Line Items]
Number of initially developing gene therapy programs \| Program	6
Number of option to add additional gene therapy programs \| Program	2
Upfront payment from collaboration agreement	$ 45,000
Prepaid research funding	5,000	5,000
Minimum upfront and preclinical milestone payments receivable	82,500
Maximum clinical development, regulatory and commercial milestone payments receivable	$ 435,000
Collaboration revenue receivable terms	10 years
Upfront payment		40,000
Revenues recognized		31,200
Deferred revenue, current		4,500
Deferred revenue, non-current		9,300
Collaboration Agreement \| Takeda Pharmaceuticals USA, Inc. \| Development and Commercialization Licenses [Member]
Collaborations And License Agreement [Line Items]
Revenues recognized		30,200
Collaboration Agreement \| Takeda Pharmaceuticals USA, Inc. \| Technology Enhancement Services And Research And Development Services[ Member]
Collaborations And License Agreement [Line Items]
Revenues recognized		$ 1,000
Collaboration Agreement \| Takeda Pharmaceuticals USA, Inc. \| Minimum
Collaborations And License Agreement [Line Items]
Collaboration agreement revenue receivable	$ 2,700,000
Collaboration Agreement \| Takeda Pharmaceuticals USA, Inc. \| Maximum
Collaborations And License Agreement [Line Items]
Collaboration agreement revenue receivable	$ 3,600,000

California Institute of Regenerative Medicine Awards - Additional Information (Details) $ in Millions	1 Months Ended			12 Months Ended
	Dec. 31, 2021 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2021 USD ($) Time
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue sharing multiple \| Time				9
Period to exercise loan option upon food and drug administration authorization				10 days
Repayment period				10 days
Repayment of awards percentage				60.00%
P B C M A101 Phase1 Clinical Trial
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Award received			$ 19.8
Proceeds form award received upon achievement of development milestones	$ 19.7
Milestone payments receivable	0.1			$ 0.1
P-PSMA-101 program
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Award received		$ 4.0
Proceeds form award received upon achievement of development milestones	$ 4.0
LIBOR
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Debt instrument basis spread on variable rate				10.00%

Term Debt - Additional Information (Details) $ / shares in Units, $ in Millions		1 Months Ended	12 Months Ended
	Jul. 25, 2017 USD ($)	Jun. 30, 2021 USD ($) mo	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jul. 14, 2020 $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Debt Instrument [Line Items]
Long-term debt			$ 30.0	$ 30.0
Debt issuance costs			0.6
Debt instrument final payment fee accrued			$ 1.6
Capital stock in excess	$ 0.3
Series A-1 Warrants
Debt Instrument [Line Items]
Warrants to purchase stock \| $ / shares								$ 3.43
Fair value of warrants								$ 0.3
Series A-1 Warrants \| Maximum
Debt Instrument [Line Items]
Warrants to purchase stock \| shares								116,618
2018 Series B Warrants
Debt Instrument [Line Items]
Warrants to purchase stock \| $ / shares							$ 5.81
Fair value of warrants							$ 0.1
2018 Series B Warrants \| Maximum
Debt Instrument [Line Items]
Warrants to purchase stock \| shares							17,212
2019 Series B Warrants
Debt Instrument [Line Items]
Warrants to purchase stock \| $ / shares						$ 5.81
Fair value of warrants						$ 0.2
Debt Instrument, Face Amount						$ 10.0
2019 Series B Warrants \| Maximum
Debt Instrument [Line Items]
Warrants to purchase stock \| shares						17,212
Common Stock \| Series A-1 Warrants \| IPO
Debt Instrument [Line Items]
Warrants to purchase stock \| shares					93,518
Warrants to purchase stock \| $ / shares					$ 4.28
Common Stock \| 2018 and 2019 Series B Warrants \| IPO
Debt Instrument [Line Items]
Warrants to purchase stock \| shares					27,604
Warrants to purchase stock \| $ / shares					$ 7.25
2021 Amended Loan Agreement
Debt Instrument [Line Items]
Long-term debt			In June 2021, the Company entered into an amendment to the Amended Loan Agreement (“2021 Amended Loan Agreement”) with Oxford. Pursuant to the terms of the 2021 Amended Loan Agreement, the interest-only period on the Term Loans and the final maturity date were extended by 18 months. As a result, all amounts outstanding under the Term Loans will mature on December 1, 2025 (the “Maturity Date”) and have interest-only payments through June 30, 2023, followed by 30 equal monthly payments of principal and unpaid accrued interest. The 2021 Amended Loan Agreement also included a facility fee of $1.1 million due on the earlier of (i) the Maturity Date, (ii) acceleration of any Term Loan, or (iii) the prepayment of the Term Loans.
Debt instrument, fee amount		$ 1.1
Term A Loan
Debt Instrument [Line Items]
Long-term debt								$ 20.0
Debt issuance costs			$ 1.0
Interest rate recognized under effective interest method			10.86%
Term B Loan
Debt Instrument [Line Items]
Long-term debt								$ 10.0
Debt issuance costs			$ 0.3
Interest rate recognized under effective interest method			10.72%
Term Loans
Debt Instrument [Line Items]
Debt instrument basis spread on variable rate		6.94%	8.94%
Debt instrument floating per annum rate			30-day U.S. Dollar LIBOR
Debt instrument interest rate during period			2.00%
Debt instrument, final payment fee percentage			7.50%
Term Loans \| Loan Prepayment
Debt Instrument [Line Items]
Debt instrument, final payment fee percentage	1.00%
Term Loans \| 2021 Amended Loan Agreement
Debt Instrument [Line Items]
Original maturity date		Dec. 01, 2025
Debt instrument frequency of periodic payment		monthly
Debt instrument repayment number of month \| mo		30

Stockholders Equity - Additional Information (Details) - USD ($)		1 Months Ended		12 Months Ended
	Jul. 14, 2020	Jul. 31, 2020	Jun. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Common stock, shares authorized				250,000,000	250,000,000
Common stock, par value				$ 0.0001	$ 0.0001
Common stock, voting rights				Each share of common stock is entitled to one vote.
Dividends declared				$ 0
Net proceeds from offering after deducting underwriting discounts and offering expenses					$ 205,743,000
Temporary equity, shares outstanding	42,953,085
Preferred stock issued and sold	42,953,085
Common Stock
Class Of Stock [Line Items]
Number of shares issued and sold					14,000,000
Convertible Preferred Stock
Class Of Stock [Line Items]
Temporary equity, shares outstanding	42,953,085	42,953,085				32,934,785
Number of outstanding securities converted		34,445,108
Warrants to purchase stock	151,042
Convertible Preferred Stock \| Common Stock
Class Of Stock [Line Items]
Number of outstanding securities converted	34,445,108
Warrants to purchase stock		151,042
Convertible Preferred Stock \| Warrant
Class Of Stock [Line Items]
Number of outstanding securities converted	121,122	121,122
Series D Preferred Stock
Class Of Stock [Line Items]
Temporary equity, shares outstanding	10,018,300
Preferred stock issued and sold	10,018,300		10,018,300
Preferred stock, issued and sold price per share			$ 10.93
Gross proceeds from issuance of convertible preferred stock			$ 109,500,000
IPO
Class Of Stock [Line Items]
Common stock, shares authorized		250,000,000
Common stock, par value		$ 0.0001
Undesignated preferred stock, shares authorized		10,000,000
Undesignated preferred stock, par value		$ 0.0001
Number of shares issued and sold	14,000,000
Public offering price per share	$ 16.00
Net proceeds from offering after deducting underwriting discounts and offering expenses	$ 205,700,000
IPO \| Common Stock
Class Of Stock [Line Items]
Number of outstanding securities converted					34,445,108

Stockholders Equity - Summary of Preferred Stock (Details) - USD ($) $ in Thousands	Jul. 14, 2020	Jun. 30, 2020
Class Of Stock [Line Items]
Preferred Stock Authorized	46,809,523
Preferred Stock Issued	42,953,085
Preferred Stock Outstanding	42,953,085
Carrying Value	$ 326,313
Liquidation Preference	$ 326,313
Common Stock Issuable Upon Conversion	34,445,108
Series A Preferred Stock
Class Of Stock [Line Items]
Preferred Stock Authorized	9,696,798
Preferred Stock Issued	9,696,798
Preferred Stock Outstanding	9,696,798
Carrying Value	$ 31,063
Liquidation Preference	$ 31,063
Common Stock Issuable Upon Conversion	7,776,095
Series A-1 Preferred Stock
Class Of Stock [Line Items]
Preferred Stock Authorized	3,370,263
Preferred Stock Issued	3,253,645
Preferred Stock Outstanding	3,253,645
Carrying Value	$ 11,083
Liquidation Preference	$ 11,083
Common Stock Issuable Upon Conversion	2,609,176
Series B Preferred Stock
Class Of Stock [Line Items]
Preferred Stock Authorized	5,283,992
Preferred Stock Issued	5,249,568
Preferred Stock Outstanding	5,249,568
Carrying Value	$ 30,314
Liquidation Preference	$ 30,314
Common Stock Issuable Upon Conversion	4,209,754
Series C Preferred Stock
Class Of Stock [Line Items]
Preferred Stock Authorized	14,734,774
Preferred Stock Issued	14,734,774
Preferred Stock Outstanding	14,734,774
Carrying Value	$ 149,713
Liquidation Preference	$ 149,713
Common Stock Issuable Upon Conversion	11,816,169
Series D Preferred Stock
Class Of Stock [Line Items]
Preferred Stock Authorized	13,723,696
Preferred Stock Issued	10,018,300	10,018,300
Preferred Stock Outstanding	10,018,300
Carrying Value	$ 104,140
Liquidation Preference	$ 104,140
Common Stock Issuable Upon Conversion	8,033,914

Stockholders Equity - Schedule of Common Stock Reserved for Future Issuance (Details)	Dec. 31, 2021 shares
Equity [Abstract]
Stock options issued and outstanding	9,899,707
Authorized for future options and award grants	3,752,093
Authorized for future issuance under Employee Stock Purchase Plan	1,154,241
Total	14,806,041

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2020	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock reserved for issuance		14,806,041
Aggregate intrinsic value of options exercised		$ 3.4	$ 2.4
Cash received from options exercised		2.0	$ 0.2
Unrecognized compensation cost		$ 42.8
Weighted-average fair value of options granted		$ 6.12	$ 8.65
Fair value of shares vested		$ 16.7	$ 6.9
Expected dividend yield		0.00%
Expected volatility, minimum		82.20%	79.00%
Expected volatility, maximum		84.30%	86.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock based compensation, vesting period		2 years
Expected term (years)		5 years 6 months	5 years 6 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock based compensation, vesting period		4 years
Expected term (years)		6 years	6 years
Share-based Payment Arrangement, Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average period over which cost expected to be recognized		2 years 10 months 24 days
2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock reserved for issuance	11,183,476
Share-based compensation award term	10 years
Percentage increase of outstanding number of shares of common stock	5.00%
Number of shares available for future options grants		3,752,093
2020 Equity Incentive Plan \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted as percentage of fair value of common stock		100.00%
Stock based compensation, vesting period		4 years
2020 Equity Incentive Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Term of award		ten years
2020 Equity Incentive Plan \| Incentive Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted as percentage of fair value of common stock		110.00%
Term of award		five years
Maximum percent of voting power		10.00%
2020 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock reserved for issuance	615,000
Share-based compensation award term	10 years
Percentage increase of outstanding number of shares of common stock	1.00%
Options granted as percentage of fair value of common stock	85.00%
Expected dividend yield		0.00%
Share-based compensation shares issued in period	1,230,000
Offering period of common stock	six months
Initial purchase period, commenced	2021-03
Risk-free interest rate		0.05%
Expected volatility, minimum		74.80%
Expected volatility, maximum		87.90%
Expected term (years)		6 months
Total shares purchased by employees		79,367
Net proceeds from share purchase by employees		$ 0.5
2020 Employee Stock Purchase Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of annual compensation	15.00%
Number of shares purchased	3,000

Stock-Based Compensation - Summary of the Company's Stock Option Plan Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Balance, Shares	4,738,607
Granted, Shares	7,228,445
Exercised, Shares	(583,332)
Cancelled, Shares	(1,484,013)
Balance, Shares	9,899,707	4,738,607
Options Vested & Expected to Vest as of December 31, 2021, Shares	9,899,707
Options Exercisable as of December 31, 2021, Shares	3,033,767
Balance, Weighted Average Exercise Price	$ 10.34
Options Granted, Weighted Average Exercise Price	8.81
Exercised, Weighted Average Exercise Price	3.39
Cancelled, Weighted Average Exercise Price	10.83
Balance, Weighted Average Exercise Price	9.57	$ 10.34
Options Vested & Expected to Vest as of December 31, 2021, Weighted Average Exercise Price	9.57
Options Exercisable as of December 31, 2021, Weighted Average Exercise Price	$ 9.81
Balance, Weighted Average Remaining Contractual Term (Years)	8 years 6 months 25 days	8 years 4 months 2 days
Options Vested & Expected to Vest as of December 31, 2021, Weighted Average Remaining Contractual Term (Years)	8 years 6 months 25 days
Options Exercisable as of December 31, 2021, Weighted Average Remaining Contractual Term (Years)	7 years 5 months 4 days
Balance, Intrinsic Value	$ 2,938
Options Vested & Expected to Vest as of December 31, 2021, Intrinsic Value	2,938
Options Exercisable as of December 31, 2021, Intrinsic Value	$ 2,792

Stock-Based Compensation - Schedule of Assumptions Used to Determine the Fair Value of Options Granted (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	0.50%	0.40%
Risk-free interest rate, maximum	1.30%	1.40%
Expected volatility, minimum	82.20%	79.00%
Expected volatility, maximum	84.30%	86.00%
Dividend yield	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 6 months	5 years 6 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years	6 years

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 16,704	$ 7,220
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	8,090	3,872
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 8,614	$ 3,348

Commitments and Contingencies - Additional Information (Details) $ in Thousands	1 Months Ended						12 Months Ended
	Oct. 31, 2021 USD ($) ft²	Oct. 31, 2019 USD ($)	Oct. 31, 2018	Aug. 31, 2018 USD ($)	Apr. 30, 2017 USD ($)	Aug. 31, 2015 USD ($)	Dec. 31, 2021 USD ($) ft² Option	Dec. 31, 2020 USD ($)	Jan. 01, 2021 USD ($)	Jan. 01, 2020 USD ($)
Commitments And Contingencies [Line Items]
Operating leases, number of square feet \| ft²	24,000						87,000
Operating leases remaining lease terms							8 years
Operating lease, number of options to extend term \| Option							2
Operating lease, extended term							5 years
Operating lease, option to extend							true
Operating lease, option to extend, description							The manufacturing and laboratory and office space lease agreements include two options to extend the term for a period of 5 years each.
Operating lease, commencement date	Mar. 31, 2022	Jul. 29, 2020	Apr. 01, 2019				Jun. 26, 2020
Operating lease, expiration date		Dec. 31, 2029	Dec. 31, 2029				Dec. 31, 2029
Additional tenant reimbursements		$ 1,500
Security deposit		300					$ 100
Tenant improvements							2,900
Operating lease right-of-use assets							26,177	$ 24,986
Initial lease liability							31,841
Accumulated deficit							406,859	281,885
Operating lease expense							6,300	$ 6,000
Operating lease, payments							$ 6,100
Operating lease, weighted-average remaining lease term							7 years 4 months 24 days
Operating lease, weighted-average discount rate							8.92%
Lease expiry date	Dec. 31, 2025
Future payments under lease agreement	$ 5,200						$ 43,438
License Agreement \| Janssen Biotech Inc.
Commitments And Contingencies [Line Items]
Upfront fee						$ 200
Milestone payments							4,000
Initial milestone payments payable							75,800
Additional milestone payments payable							$ 46,800
License Agreement \| Genus Oncology, LLC
Commitments And Contingencies [Line Items]
Upfront fee		1,500
Initial milestone payments payable		71,000
Additional milestone payments payable		$ 1,500
Commercial License Agreement \| TeneoBio, Inc.
Commitments And Contingencies [Line Items]
Upfront fee				$ 4,000	$ 500
Milestone payments				$ 31,000
Initial milestone payments payable					20,500
Additional milestone payments payable					$ 20,500
ASC 842
Commitments And Contingencies [Line Items]
Operating lease, option to extend							true
Operating lease, option to extend, description							The leases in San Diego include an option to extend, which was not recognized as part of the lease liability and ROU lease assets as it was not reasonably certain the Company would exercise the extension right.
Initial lease receivables										$ 2,700
Operating lease right-of-use assets										22,300
Deferred rent balance										2,300
Initial lease liability										$ 27,300
Derecognition of construction in progress related to manufacturing facility									$ 2,100
Derecognition of construction financing obligation related to manufacturing facility									2,500
Derecognition of other receivables related to manufacturing facility									300
Accumulated deficit									$ 100
Property and Equipment
Commitments And Contingencies [Line Items]
Tenant improvements							$ 13,300
Maximum
Commitments And Contingencies [Line Items]
Operating lease remaining lease term dedicated to manufacturing suites							2 years

Commitments and Contingencies - Summary of Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Oct. 31, 2021	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
2022	$ 6,577
2023	5,723
2024	4,814
2025	4,958
2026	5,107
Thereafter	16,259
Total future lease payments	43,438	$ 5,200
Imputed interest	(11,597)
Total lease liability balance	31,841
Operating lease liabilities, current	6,337		$ 4,808
Operating lease liabilities, non-current	$ 25,504		$ 25,374

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Income tax expense	$ 0	$ 0
Valuation allowance	141,761,000	91,091,000
Unrecognized tax benefits	9,494,000	$ 5,457,000	$ 2,470,000
Accrued interest or penalties	0
Federal
Income Taxes [Line Items]
Operating loss carryforwards	$ 23,300,000
Operating loss carryforwards, limitations on use	the Company had federal net operating loss carryforwards that do not expire but utilization is limited to 80% of taxable income for any given tax year in the amount of $329.9 million.
Operating loss carryforwards limitations on use percentage of taxable income	80.00%
Operating loss carryforwards limitations on use taxable income	$ 329,900,000
Research and development credits	$ 33,200,000
Research and development tax credit carryforward expiration year	2032
State
Income Taxes [Line Items]
Operating loss carryforwards	$ 350,800,000
Research and development credits	$ 11,800,000

Income Taxes - Schedule of (Benefit from) Provision for Income Taxes Differs from Income Tax Determined by Applicable U.S. Statutory Federal Income Tax Rate to Pretax Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Federal statutory rate	$ (26,245)	$ (27,253)
Adjustments for tax effects of:
Tax credits	(22,448)	(10,735)
State taxes, net	(7,575)	(8,581)
Unrecognized tax benefits	3,431	2,445
Stock-based compensation	2,308	956
Permanent adjustments	53	134
Other, net	(192)	(27)
Change in valuation allowance	50,668	43,061
Total	$ 0	$ 0

Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Net operating losses	$ 98,815	$ 65,058
Income tax credit carryforwards	33,524	15,727
Lease liabilities	8,885	8,388
Deferred revenue	2,280
Accrued expenses	2,233	1,855
Amortization	1,406	1,558
Grant income	1,114	6,648
Other, net	2,430	982
Total deferred tax assets	150,687	100,216
Deferred tax liabilities:
Right of use assets	(7,305)	(6,934)
Depreciation	(1,308)	(1,877)
Acquired indefinite lived intangibles	(368)	(369)
Total deferred tax liabilities	(8,981)	(9,180)
Valuation allowance	(141,761)	(91,091)
Net deferred tax liability	$ (55)	$ (55)

Income Taxes - Schedule of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 5,457	$ 2,470
Increase for current year positions	4,105	3,211
Decrease for prior year positions	(68)	(224)
Balance at the end of year	$ 9,494	$ 5,457

Employee Benefit Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Defined contributions, total	$ 0.9	$ 0.6
Defined Contribution Plan, Tax Status [Extensible List]	Defined Contribution Plan, Tax Status [Extensible List]	Defined Contribution Plan, Tax Status [Extensible List]

Net Loss Per Share - Schedule of Anti-Dilutive Securities Excluded From Computation of Diluted Net Loss per Share Attributable to Common Stockholders (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	10,026,139	4,859,729
Warrants to Purchase Convertible Preferred Stock (As Converted to Common Stock)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	121,122	121,122
Stock Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	9,899,707	4,738,607
ESPP Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	5,310

Subsequent Event - Additional Information (Details) $ in Millions		1 Months Ended	12 Months Ended
	Jul. 25, 2017	Feb. 28, 2022 USD ($) mo	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Subsequent Event [Line Items]
Long-term debt			$ 30.0	$ 30.0
Term Loans
Subsequent Event [Line Items]
Debt instrument, final payment fee percentage			7.50%
Term Loans \| Loan Prepayment
Subsequent Event [Line Items]
Debt instrument, final payment fee percentage	1.00%
2022 Loan Agreement \| Term Loans \| Loan Prepayment
Subsequent Event [Line Items]
Debt instrument term loan prepaid Period description			on or prior to February 22, 2024
2022 Loan Agreement \| Subsequent Event
Subsequent Event [Line Items]
Debt instrument maturity date		Feb. 01, 2027
Repayment of outstanding debt		$ 5.0
Debt instrument, final payment fee percentage		7.50%
2022 Loan Agreement \| Subsequent Event \| Term Loans \| Loan Prepayment
Subsequent Event [Line Items]
Debt instrument, final payment fee percentage		1.00%
2022 Loan Agreement \| Oxford
Subsequent Event [Line Items]
Long-term debt			In February 2022, the Company entered into a new Loan and Security Agreement (“2022 Loan Agreement”) with Oxford. Pursuant to the terms of the 2022 Loan Agreement, the Company borrowed $60.0 million in term loans, a portion of which was used to repay the balance outstanding under the 2021 Amended Loan Agreement. Under the 2022 Loan Agreement the interest-only period is through April 1, 2025, with interest-only payments through March 1, 2025, followed by 23 equal monthly payments of principal and applicable interest. Upon the satisfaction of certain conditions set forth in the 2022 Loan Agreement, the interest-only period may be extended through April 1, 2026, followed by 11 equal monthly payments of principal and applicable interest. As a result, all amounts outstanding under the 2022 Loan Agreement will mature on February 1, 2027.
2022 Loan Agreement \| Oxford \| Subsequent Event
Subsequent Event [Line Items]
Long-term debt		$ 60.0
Debt instrument repayment number of month \| mo		23
2021 Amended Loan Agreement \| Subsequent Event
Subsequent Event [Line Items]
Debt instrument repayment number of month \| mo		11
Debt instrument, fee amount		$ 1.6
Debt instrument repayment of interest only extension period		48 months