0001564590-21-012509 | 10-K | XBRL Viewer

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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2020	Mar. 05, 2021	Jul. 14, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Trading Symbol	PSTX
Entity Registrant Name	Poseida Therapeutics, Inc.
Entity Central Index Key	0001661460
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Security12b Title	Common stock, $0.0001 par value per share
Security Exchange Name	NASDAQ
Entity File Number	001-39376
Entity Incorporation State Country Code	DE
Entity Tax Identification Number	47-2846548
Entity Address, Address Line One	9390 Towne Centre Drive
Entity Address City Or Town	San Diego
Entity Address State Or Province	CA
Entity Address Postal Zip Code	92121
City Area Code	858
Local Phone Number	779-3100
Document Annual Report	true
Document Transition Report	false
ICFR Auditor Attestation Flag	false
Entity Common Stock, Shares Outstanding		62,108,168
Entity Public Float			$ 516.1
Documents Incorporated by Reference	Certain information required to be disclosed in Part III of this report is incorporated by reference from the registrant’s definitive Proxy Statement for the 2021 Annual Meeting of Stockholders, which proxy statement will be filed not later than 120 days after the end of the fiscal year covered by this report.

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 83,966	$ 87,784
Short-term investments	225,186	37,534
Prepaid expenses and other current assets	4,844	1,861
Total current assets	313,996	127,179
Property and equipment, net	23,336	10,858
Operating lease right-of-use assets	24,986
Intangible assets, net	1,320	1,320
Goodwill	4,228	4,228
Other long-term assets	3,618	3,411
Total assets	371,484	146,996
Current liabilities:
Accounts payable	763	4,929
Accrued and other liabilities	24,454	13,926
Operating lease liabilities, current	4,808
Term debt - short-term		3,000
Total current liabilities	30,025	21,855
Term debt - long-term	29,133	26,140
Deferred CIRM grant liability	23,755	19,592
Warrant liability		1,271
Deferred tax liability	55	55
Operating lease liabilities, non-current	25,374
Other long-term liabilities	1,174	5,421
Total liabilities	109,516	74,334
Commitments and contingencies (Note 10)
Convertible preferred stock (Series A, A-1, B, C and D), $0.0001 par value: 0 and 33,085,827 shares authorized at December 31, 2020 and December 31, 2019, respectively; 0 and 32,934,785 shares issued and outstanding at December 31, 2020 and December 31, 2019, respectively		222,173
Stockholders’ equity (deficit):
Common stock, $0.0001 par value: 250,000,000 and 57,013,463 shares authorized at December 31, 2020 and December 31, 2019, respectively; 61,860,897 and 13,196,419 shares issued and outstanding as of December 31, 2020 and December 31, 2019, respectively	6	2
Additional paid-in capital	543,842	2,689
Accumulated other comprehensive income	5	19
Accumulated deficit	(281,885)	(152,221)
Total stockholders’ equity (deficit)	261,968	(149,511)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	$ 371,484	$ 146,996

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Convertible preferred stock (Series A, A-1, B, C and D), par value	$ 0.0001	$ 0.0001
Convertible preferred stock (Series A, A-1, B, C and D), authorized	0	33,085,827
Convertible preferred stock (Series A, A-1, B, C and D), issued	0	32,934,785
Convertible preferred stock (Series A, A-1, B, C and D), outstanding	0	32,934,785
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	250,000,000	57,013,463
Common stock, shares issued	61,860,897	13,196,419
Common stock, shares outstanding	61,860,897	13,196,419

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating expenses:
Research and development	$ 103,520,000	$ 60,393,000
General and administrative	23,029,000	18,457,000
Increase in contingent consideration (inclusive of related party amounts of $0 and $2,739, respectively)		6,683,000
Total operating expenses	126,549,000	85,533,000
Loss from operations	(126,549,000)	(85,533,000)
Other income (expense):
Interest expense	(3,506,000)	(3,553,000)
Other income, net	280,000	2,559,000
Net loss before income tax	(129,775,000)	(86,527,000)
Income tax benefit	0	0
Net loss	(129,775,000)	(86,527,000)
Other comprehensive income (expense):
Other comprehensive income (loss) (net of tax expense of $0 for each of the periods ending December 31, 2020 and 2019)	(14,000)	19,000
Total other comprehensive income (loss)	(14,000)	19,000
Comprehensive loss	$ (129,789,000)	$ (86,508,000)
Net loss per share attributable to common stockholders, basic and diluted	$ (3.61)	$ (6.86)
Weighted-average shares of common stock, basic and diluted	35,996,901	12,618,413

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Increase in contingent consideration, related party amounts	$ 0	$ 2,739
Other comprehensive income, tax expense	$ 0	$ 0

- Definition

Amount of tax expense (benefit) allocated to other comprehensive income (loss).

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+ Details

CONSOLIDATED STATEMENTS OF CHANGES IN CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Series C Preferred Stock	Series D Preferred Stock	Transition Adjustment	Series A-1 and Series B Warrants	IPO	Common Stock	Common Stock IPO	Additional Paid-in Capital	Additional Paid-in Capital Series A-1 and Series B Warrants	Additional Paid-in Capital IPO	Accumulated Other Comprehensive Income	Accumulated Deficit	Accumulated Deficit Transition Adjustment
Balance at Dec. 31, 2018	$ (76,718)							$ 2		$ (11,026)				$ (65,694)
Beginning balance, Shares at Dec. 31, 2018		18,200,011
Beginning balance at Dec. 31, 2018		$ 72,460
Beginning balance, Shares at Dec. 31, 2018								12,275,579
Net loss	(86,527)													(86,527)
Issuance of common stock under employee stock compensation plans	69									69
Issuance of common stock under employee stock compensation plans, Shares								54,715
Issuance of common stock for acquisition of Vindico	10,596									10,596
Issuance of common stock for acquisition of Vindico, Shares								866,125
Issuance of preferred stock for cash net of issuance costs, Shares			14,734,774
Issuance of preferred stock for cash net of issuance costs			$ 149,713
Stock-based compensation expense	3,050									3,050
Unrealized gain on marketable securities	19												$ 19
Balance at Dec. 31, 2019	$ (149,511)				$ 111			$ 2		2,689			19	(152,221)	$ 111
Ending balance, Shares at Dec. 31, 2019	32,934,785	32,934,785	14,734,774
Balance at Dec. 31, 2019	$ 222,173	$ 222,173	$ 149,713
Ending balance, Shares at Dec. 31, 2019								13,196,419
Net loss	$ (129,775)													(129,775)
Accounting Standards Update [Extensible List]	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 gain on marketable securities	(14)												(14)
Balance at Dec. 31, 2020	$ 261,968							$ 6		$ 543,842			$ 5	$ (281,885)
Ending balance, Shares at Dec. 31, 2020	0
Ending balance, Shares at Dec. 31, 2020								61,860,897

CONSOLIDATED STATEMENTS OF CHANGES IN CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Initial public offering, net of issuance costs	$ 18,018
Series C Preferred Stock
Payments of stock issuance costs		$ 287
Series D Preferred Stock
Payments of stock issuance costs	$ 5,359

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
OPERATING ACTIVITIES
Net loss	$ (129,775)	$ (86,527)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	2,586	1,193
Loss on disposal of assets		448
Stock-based compensation	7,220	3,050
Change in fair value of contingent liabilities		6,679
Change in fair value of warrant liability	387	(519)
Accretion of discount on issued term debt	805	853
Accretion of investment discount, net	(174)	(128)
Imputed rent expense		111
Write off of deferred financing costs		855
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(3,296)	726
Operating lease right-of-use assets	3,108
Other long-term assets	(207)	(1,676)
Accounts payable	(4,171)	1,530
Accrued liabilities	10,320	7,132
Operating lease liabilities	(131)
Other long-term liabilities		1,755
Net cash used in operating activities	(113,328)	(64,518)
INVESTING ACTIVITIES
Purchases of property and equipment	(16,908)	(5,156)
Purchases of short-term investments	(295,023)	(71,308)
Proceeds from maturities of short-term investments	107,500	34,000
Net cash used in investing activities	(204,431)	(42,464)
FINANCING ACTIVITIES
Net proceeds from stock option exercises	223	69
Proceeds from initial public offering, net of issuance costs	205,743
Net proceeds from CIRM	4,163	4,642
Proceeds from term debt		10,000
Payment of debt issuance costs	(329)	(53)
Net cash provided by financing activities	313,941	164,371
Net increase (decrease) in cash and cash equivalents	(3,818)	57,389
Cash and cash equivalents at beginning of period	87,784	30,395
Cash and cash equivalents at end of period	83,966	87,784
Non-cash investing and financing activities:
Issuance of common stock for acquisition		10,596
Purchases of property and equipment included in accounts payable and accrued liabilities	211	1,887
Tenant improvement receivable from landlord	137	421
Construction financing liability		2,166
Right-of-use assets and lease liabilities	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	3,027	2,631
Series C Convertible Preferred Stock
FINANCING ACTIVITIES
Issuance of Series financing, net of issuance costs		$ 149,713
Series D Convertible Preferred Stock
FINANCING ACTIVITIES
Issuance of Series financing, net of issuance costs	$ 104,141

Nature of Business and Basis of Presentation

12 Months Ended

Dec. 31, 2020

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 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.

Reverse Stock Split

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.

Initial Public Offering

On July 14, 2020, the Company completed its initial public offering (“IPO”), in which the Company issued and sold 14,000,000 shares of its common stock, at a public offering price of $16.00 per share, for aggregate gross proceeds of $224.0 million. The Company received approximately $205.7 million in net proceeds after deducting underwriting discounts and offering expenses payable by the Company. At the closing of the IPO, 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. Following the IPO there were no shares of preferred stock outstanding. 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 that may be issued from time to time by the Company’s board of directors in one or more series, par value of $0.0001 per share.

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. The Company has incurred net losses for the years ended December 31, 2020 and 2019 of $129.8 million and $86.5 million, respectively, and negative cash flows from operations for these same periods of $113.3 million and $64.5 million, respectively. The Company expects to continue to incur net losses and negative cash flows from operations for at least the next several years. As of December 31, 2020, the Company had an accumulated deficit of $281.9 million.

The Company expects that its cash, cash equivalents and marketable securities as of December 31, 2020 of $309.2 million will be sufficient to fund its operations for at least the next twelve months from the date of issuance of these financial statements. In the long term the Company will need additional financing to support its continuing operations and pursue its growth 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.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2020

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 accrued expenses, contingent consideration, warrant liability, stock-based compensation expense, deferred tax valuation allowances and, prior to the Company’s IPO, the fair value of common stock. 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 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.

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.

Lease receivables, included within prepaid and other currents assets within the consolidated balance sheets, are comprised of the expected tenant improvement reimbursement from the landlord and the rent abatement period to be recognized over the following twelve months.

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.

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 will likely continue to be extensive in many aspects of society, which has resulted in and will likely continue to result in significant disruptions to the global economy, as well as businesses and capital markets around the world.

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 or other regulatory authorities, and the Company’s ability to raise capital and conduct business development activities.

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. During the year ended December 31, 2019, the Company expensed $1.8 million of costs, within general and administrative expenses, previously capitalized and associated with the Company’s abandoned efforts to complete an IPO in early 2019. 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) as of 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, 2020 and 2019 was $0.2 million. Amounts outstanding on the credit card and recorded as accounts payable were $0.1 million and zero as of December 31, 2020 and 2019, respectively.

Short-Term Investments

Investments with a remaining maturity when purchased of greater than three months are classified as short-term investments on the balance sheet and consist primarily of U.S. Treasury and government agency obligations. As our 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.

Other Receivables, Net

Other receivables is recorded at the invoiced amount and is non-interest bearing. Other receivables, net consists of reimbursements from the Company’s landlord for ongoing construction and is included within other current assets.

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, 2020 and 2019.

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, 2020 and 2019.

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)
Lab equipment		5
Leasehold improvements	Lesser of useful life or lease-term
Computer equipment and software		3
Furniture and fixtures		7

Maintenance and repairs 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, 2020 and 2019.

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

Equity awards to employees are measured and recognized in the consolidated financial statements based on the fair value of the award on the grant date. The Company currently uses the Black-Scholes valuation model to estimate the grant date fair value of their share-based payments. The model requires the Company to make a number of assumptions including expected volatility, risk-free interest rate, expected term and expected dividend. Stock-based compensation expense is recognized straight-line over the term of the option grant. All option grants require continued service to continue vesting. Forfeitures are recognized as they occur.

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.

Contingent Consideration

In connection with the Company’s acquisition of Vindico in October 2016, the Company agreed to pay additional consideration based on the achievement of a certain developmental milestone using the acquired technology. The additional purchase consideration was payable in shares of its common stock. The number of shares of common stock issuable and the associated fair value could vary depending on (1) the price paid by investors in a qualified equity financing prior to the achievement of the milestone and (2) when and if the milestone was reached. Prior to the milestone being met, the Company classified this contingent consideration as a liability on its consolidated balance sheet that was remeasured to fair value at each reporting date, and recognized changes in the fair value of the contingent consideration liability as a component of operating expenses in its consolidated statements of operation and comprehensive loss. The Company recognized changes in the fair value of the contingent consideration liability until the milestone was met in July 2019. Upon issuance of the common stock related to the milestone in July 2019, the liability was reclassified to stockholder’s deficit, within additional paid-in capital.

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 marketable 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/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 February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). The FASB subsequently issued ASU 2018-10 Codification Improvements to Topic 842, Leases, ASU 2018-11, Leases (Topic 842): Targeted Improvements, and ASU 2019-01, Leases (Topic 842): Codification Improvements, to further amend ASU 2016-02. ASU 2016-02, as amended, provides revised guidance related to the accounting and reporting of leases, including a requirement for lessees to recognize most leases on the balance sheet. The recognition, measurement and presentation of expenses and cash flows arising from a lease by a lessee depends on its classification as a finance or operating lease. For public entities, the guidance is effective for fiscal years beginning after December 15, 2018, and for non-public entities, the guidance was effective for fiscal years beginning after December 15, 2020, with early adoption permitted. Companies may adopt retrospectively as of the earliest period presented or retrospectively at the beginning of the period of adoption through a cumulative-effect adjustment, in each case with a number of practical expedients that entities may elect to apply. The Company adopted this standard on January 1, 2020, early adopting ASC 842 using a modified retrospective transition approach as of the effective date, as permitted by the amendments in ASU 2018-11, which provides an alternative modified retrospective transition method. As a result, the Company was not required to adjust its comparative period financial information for effects of the standard or make the new required lease disclosures for periods before the date of adoption. The Company has elected to adopt the package of transition practical expedients and, therefore, it has not reassessed (1) whether existing or expired contracts contain a lease, (2) lease classification for existing or expired leases or (3) the accounting for initial direct costs that were previously capitalized. The Company did not elect the practical expedient to use hindsight for leases existing at the adoption date. See Note 10 for the adoption impact.

In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Topic 350): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. This standard requires capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The Company adopted this standard on January 1, 2020 using the prospective method. The adoption of this standard did not have a material impact on our consolidated financial statements and disclosures.

In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement. The new standard removes certain disclosures, modifies certain disclosures and adds additional disclosures related to fair value measurement. The Company adopted this standard on January 1, 2020 using the prospective method. The adoption of this standard did not have a material impact on our 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 ASU 2016-13 may have on its financial position and results of operations upon adoption.

In December 2019, the FASB issued 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 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard will be effective for the Company beginning January 1, 2021. The Company is currently evaluating the potential impact ASU 2019-12 may have on its financial position and results of operations upon adoption.

Reclassification

Certain amounts in the consolidated financial statements have been reclassified from their original presentation to conform to current year presentation.

Composition of Certain Balance Sheet Components

12 Months Ended

Dec. 31, 2020

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,
	2020		2019
Landlord reimbursement	$	137	$	421
Rent		217		259
Insurance		2,226		204
Contract research services		651		543
Other		1,613		434
Total prepaid expenses and other current assets	$	4,844	$	1,861

Property and equipment, net

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

	December 31,
	2020			2019
Lab equipment	$	11,420		$	6,957
Leasehold improvements		13,826			165
Computer equipment and software		1,381			456
Furniture and fixtures		928			560
Construction in progress		376			4,729
Total property and equipment		27,931			12,867
Less: Accumulated depreciation and amortization		(4,595	)		(2,009	)
Total property and equipment, net	$	23,336		$	10,858

Depreciation expense associated with property and equipment was $2.6 million and $1.2 million for the years ended December 31, 2020 and 2019, respectively.

Goodwill and other intangible assets, net

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

	December 31,
	2020		2019
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 for the years ended December 31, 2020 and 2019.

Accrued and other liabilities

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

	December 31,
	2020		2019
Contract research services	$	15,822	$	7,993
Payroll and related expense		6,793		3,283
Lease cancellation fee		—		979
Other		1,839		1,671
Total accrued and other liabilities	$	24,454	$	13,926

Financial Instruments

12 Months Ended

Dec. 31, 2020

Investments Debt And Equity Securities [Abstract]

Financial Instruments

Note 4. Financial Instruments

The following table summarizes the amortized cost and fair value of securities available-for-sale at December 31, 2020 and 2019 (in thousands):

	Amortized Cost/Cost		Unrealized Gains		Unrealized Losses		Fair Value
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
At December 31, 2019:
Money market fund	$	63,744	$	—	$	—	$	63,744
U.S. government agency securities and treasuries		42,503		19		—		42,522
Total	$	106,247	$	19	$	—	$	106,266

No available-for-sale debt securities held as of December 31, 2020 and 2019 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, 2020, 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 intend to 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, 2020

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 Company has classified assets and liabilities measured at fair value on a recurring basis as follows (in thousands):

	Level 1		Level 2		Level 3
At December 31, 2020:
Assets
Cash equivalents	$	70,713	$	—	$	—
Short-term investments		225,186		—		—
Total assets	$	295,899	$	—	$	—
At December 31, 2019:
Assets
Cash equivalents	$	68,732	$	—	$	—
Short-term investments		37,534		—		—
Total assets	$	106,266	$	—	$	—
Liabilities
Warrant liability	$	—	$	—	$	1,271
Total liabilities	$	—	$	—	$	1,271

As of December 31, 2019, the preferred stock warrant liability in the table above consisted of the fair value of warrants to purchase Series A-1 convertible preferred stock (“Series A-1 Preferred Stock”) and Series B convertible preferred stock (“Series B Preferred Stock”) and was based on significant inputs not observable in the market, which represent 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 incorporates assumptions and estimates to value the preferred stock warrants.

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.

As of December 31, 2019, the quantitative elements associated with the Company’s Level 3 inputs impacting the fair value measurement of the preferred stock warrant liability include the fair value per share of the underlying Series A-1 Preferred Stock and Series B Preferred Stock, the remaining contractual term of the warrants, risk-free interest rate, expected dividend yield and expected volatility of the price of the underlying preferred stock. The most significant assumption in the Black-Scholes option-pricing model impacting the fair value of the preferred stock warrants was the fair value of the Company’s convertible preferred stock as of each remeasurement date. The Company determined the fair value per share of the underlying preferred stock by taking into consideration its most recent sales of its convertible preferred stock as well as additional factors that the Company deemed relevant. As of December 31, 2019, the fair value per share of the Series A-1 Preferred Stock was $10.36. As of December 31, 2019, the fair value per share of the Series B Preferred Stock was $10.57. Prior to completing the IPO, the Company was a private company and lacked company-specific historical and implied volatility information of its stock. Therefore, it estimated its expected stock volatility based on the historical volatility of publicly traded peer companies for a term equal to the remaining contractual term of the warrants. The risk-free interest rate was determined by reference to the U.S. Treasury yield curve for time periods approximately equal to the remaining contractual term of the warrants. The Company estimated a 0% dividend yield based on the expected dividend yield and the fact that the Company never paid or declared dividends. The change in fair value of warrant liability was a loss of $0.4 million and a gain of $0.5 million, for the years ended December 31, 2020 and 2019, respectively, included with other income (expense) within the consolidated statement of operations and comprehensive loss.

A reconciliation of the Level 3 liabilities is as follows (in thousands):

Fair value of Level 3 liabilities as of December 31, 2019	$	1,271
Change in fair value of warrant liability		387
Reclassification of warrants to stockholders' equity (deficit)		(1,658	)
Fair value of Level 3 liabilities as of December 31, 2020	$	—

There were no transfers into or out of the Level 3 fair value hierarchy for the years ended December 31, 2020 and 2019.

- 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

California Institute of Regenerative Medicine Awards

12 Months Ended

Dec. 31, 2020

Collaborative Arrangement [Abstract]

California Institute of Regenerative Medicine Awards

Note 6. 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 will co-fund a specified program, under which funding is paid in developmental milestones determined as a part of the award. The Company is obligated to share future revenue for the related program with CIRM. The percentage of revenue is dependent on the amount of the award received and whether revenue is from product sales or 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 (10) 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 the award to a loan, it would be obligated to repay the loan within ten (10) business days of making such election. Repayment amounts vary dependent on when the award is converted to a loan, ranging from 60% of the award granted to amounts 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 accounted for this award as a liability rather than revenue as the Company’s current intent is to convert the award 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, 2020 with up to an aggregate of $0.1 million in future milestone payments.

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, 2020.

Term Debt

12 Months Ended

Dec. 31, 2020

Debt Instruments [Abstract]

Term Debt

Note 7. Term Debt

On July 25, 2017, the Company entered into a loan and security agreement (the “Original Loan Agreement”) with Oxford Finance LLC (“Oxford”), whereby it borrowed $10.0 million (the “Original Term A Loan”). Balances under the Original Loan were due in monthly principal and interest payments, with a final maturity date of August 2021. The Initial Loan included a final payment fee of 8.50% of the original principal amount due upon maturity.

In August 2018, the Company entered into an Amended and Restated Loan and Security Agreement (“Amended Loan Agreement”) with Oxford, pursuant to which Oxford agreed to lend the Company up to $30.0 million, issuable in three separate term loans of the Original Term A Loan, $10.0 million (“New A Term Loan”), and $10.0 million (“Term B Loan”), collectively referred to as the “Term Loans”). The Company received $10.0 million in proceeds from the New Term A Loan, net of debt issuance costs and accrued interest of $0.9 million. Under the terms of the Amended Loan Agreement the Company was permitted, at its sole discretion, to borrow $10.0 million under the Term B Loan following the achievement of a defined milestone event until the earlier of 60 days thereafter or December 20, 2018. In January 2019, the Company entered into an amendment with Oxford to extend the draw period of the Term B Loan through February 15, 2019. The Company drew the remaining $10.0 million in February 2019. In June 2020, the Company entered into an Amended and Restated Loan and Security Agreement (“2020 Amended Loan Agreement”) with Oxford. Under the terms of the 2020 Amended Loan Agreement, the interest only period on both the Term A Loan and Term B Loan was extended by 15 months, originally through September 2020 and extended through December 2021, and the final maturity date was extended by 15 months from March 1, 2023 to June 1, 2024. The 2020 Amended Loan Agreement also included a facility fee of $0.3 million due on the amendment effective date, June 24, 2020. All other terms under the agreement remained unchanged.

The Company evaluated the amendments in accordance with ASC Topic 470 Debt, which requires the assessment of whether the modification was considered a substantial modification, in which case the modification would be accounted for as a debt extinguishment. Based on the Company’s evaluation, the modifications were not considered substantial and as such treated as a debt modification.

All outstanding Term Loans will mature on June 1, 2024 (the “Maturity Date”) and have interest-only payments through December 31, 2021, followed by 30 equal monthly payments of principal and unpaid accrued interest. 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 reported in The Wall Street Journal on the last business day of the month that immediately precedes the month in which the interest accrues and (b) 2.0%. The interest rate for Term Loans as of December 31, 2020 was 8.94%. The Company will be 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.

There is an option to prepay all, but not less than all, of the borrowed amounts, provided that the Company will be obligated to pay a prepayment fee equal to (i) 3.0% of the outstanding principal balance of the applicable Term Loan if prepayment is made after the funding date through and including the first anniversary of the funding date, (ii) 2.0% of the outstanding balance after the first anniversary through and including the second anniversary of the funding date of the Term Loan or (iii) 1.0% of the applicable Term Loan prepaid after the second anniversary of the funding date and prior to the Maturity Date.

The Company may use the proceeds from the Term Loans solely for working capital and to fund its general business requirements. The Company’s obligations under the Loan Agreement are secured by a first priority security interest in substantially all of its current and future assets, other than our intellectual property. In addition, the Company has also agreed not to encumber its intellectual property assets, except as permitted by the Loan Agreement. While any amounts are outstanding under the 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 paying dividends or making other distributions or payments on its capital stock in excess of $0.3 million, on an annual basis, subject to limited exceptions. As of December 31, 2020, the Company was in compliance with all covenants under the Loan Agreement.

Pursuant to the Original Loan Agreement, on July 25, 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 warrants were immediately exercisable and will expire ten years from the date of the grant. Upon the closing of the IPO these became exercisable for 93,518 shares of common stock at an exercise price of $4.28 per share.

Pursuant to the Amended Loan Agreement, on August 13, 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 (“August 2018 Series B Warrants”). On February 19, 2019, in conjunction with drawing the remaining $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 (“February 2019 Series B Warrants”). The August 2018 Series B Warrants and February 2019 Series B Warrants (collectively “Series B Warrants”) were immediately exercisable upon issuance and will expire ten years from the date of the grant. Upon the closing of the IPO these became exercisable for 27,604 shares of common stock at an exercise price of $7.25 per share.

The fair value of the warrants as of the issuance dates was determined to be $0.6 million and was treated as a debt discount and as a preferred stock warrant liability. The debt discount is amortized over the term of the loan to interest expense.

As of December 31, 2020, there was $20.0 million outstanding under the Term A Loan. The Term A Loan was recorded at its initial carrying value of $20.0 million. In connection with the Term A Loan, the debt issuance costs of $1.0 million have been recorded as a debt discount, including the remaining unrecognized discount from the Original Term A Loan, on the Company’s consolidated balance sheets, which are being accreted to interest expense over the life of the Term A Loan. Interest on the term 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 11.28%.

As of December 31, 2020, there was $10.0 million outstanding under the Term B Loan. The Term B Loan was recorded at its initial carrying value of $10.0 million. In connection with the Term B Loan, the debt issuance costs of $0.3 million have been recorded as a debt discount, on the Company’s consolidated balance sheets, which are being accreted to interest expense over the life of the Term B Loan. Interest on the term 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 11.03%.

Equity

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Equity

Note 8. 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 that may be issued from time to time by the Company’s board of directors in one or more series, par value $0.0001 per share.

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 and as of December 31, 2019 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

	December 31, 2019
	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
Total		33,085,827		32,934,785	$	222,173	$	222,173		26,411,194

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, 2020:

Stock options issued and outstanding			4,738,607
Authorized for future options and award grants			6,403,481
Authorized for future issuance under Employee Stock Purchase Plan			615,000
Total			11,757,088

Stock-Based Compensation

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

Note 9. 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 pricing 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 then 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 remain available for issuance under the 2015 Equity Incentive Plan, as amended (the “2015 Plan”), as of the effective date of the 2020 Plan and shares subject to outstanding awards under the 2015 Plan as of the effective date of the 2020 Plan that are subsequently canceled, forfeited or repurchased by the Company will be added to the shares reserved under the 2020 Plan. In addition, the number of shares of common stock available for issuance under the 2020 Plan will be 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 31st of the preceding calendar year or such lesser amount as determined by the Company’s board of directors.

As of December 31, 2020, there were 6,403,481 shares available for future option grants or direct issuance under the 2020 Plan. To date, the Company has issued ISOs and NSOs. Shares issued under the 2020 Plan are newly issued shares and there is no intention to repurchase previously issued shares. The exercise price of options granted under the 2020 Plan cannot be less than 100% of the fair value of the common stock. 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 and the Company’s normal practice is generally a vesting period over four years. In the case of an ISO granted to an optionee who, at the time the option is granted, owns stock representing more than ten percent of the voting power of all classes of stock of the Company, the term of the option shall be five years from the date of grant and issued at 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, 2020:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Intrinsic Value (thousands)
Balance at January 1, 2020		3,611,030		$	8.58		8.65
Options Granted		1,510,762			13.36
Exercised		(219,425	)		1.02
Cancelled		(163,760	)		11.76
Balance at December 31, 2020		4,738,607		$	10.34		8.34	$	10,017
Options Vested & Expected to Vest as of December 31, 2020		4,738,607		$	10.34		8.34	$	10,017
Options Exercisable as of December 31, 2020		1,886,521		$	7.56		6.84	$	8,226

All stock option shares and exercise prices were adjusted retrospectively for the Company’s reverse stock split, which became effective in July 2020.

The aggregate intrinsic value of options exercised during the years ended December 31, 2020 and 2019 was $2.4 million and $0.7 million, respectively, determined as of the date of exercise. The Company received $0.2 million and $0.1 million in cash from options exercised during the years ended December 31, 2020 and 2019, respectively.

The Company recorded stock-based compensation expense in the following expense categories of its consolidated statements of operations (in thousands):

	Year Ended December 31,
	2020		2019
Research and development	$	3,872	$	1,703
General and administrative		3,348		1,347
Total stock-based compensation	$	7,220	$	3,050

As of December 31, 2020, total unrecognized compensation cost related to stock options was $23.0 million, and the weighted-average period over which this cost is expected to be recognized is approximately 3.0 years.

The weighted-average fair value of options granted during the years ended December 31, 2020 and 2019 was $8.65 and $8.47 per share, respectively. Total fair value of shares vested during the years ended December 31, 2020 and 2019 was $6.9 million and $2.8 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,
	2020		2019
Risk-free interest rate	0.4%-1.4%		1.6%-2.6%
Expected volatility	79-86%		80-87%
Expected term (years)	5.5-6		4-6
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”). The ESPP 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. In addition, the number of shares of common stock available for issuance under the ESPP will be 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 31st 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.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note 10. Commitments and Contingencies

Operating Leases

As of December 31, 2020, the Company had operating leases for manufacturing, laboratory and office space in San Diego, California consisting of approximately 83,000 square feet with remaining lease terms of 108 months. 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 12 months.

In March 2016, 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 commenced on June 30, 2016 and had a 10.5-year initial term. The lease provided 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 sheet. As a result of outgrowing the office space and lab space and having executed a lease agreement for a larger facility, the Company terminated this lease agreement effective April 30, 2019. As part of the lease termination agreement, the Company committed to pay a $1.5 million cancellation fee to the landlord in three installments over a 1.5-year period. As of December 31, 2019, the Company recorded the lease cancellation fee, gain from the deferred rent write-off, and abandonment of the fixed assets as part of loss from continuing operations. As of December 31, 2020, there were no further obligations related to this lease.

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. The lease provided for tenant improvements of $4.2 million and as costs were incurred, the Company performed an analysis to determine treatment based on the type of leasehold improvement. Assets determined to be lessee assets were not material and were recorded on the consolidated balance sheet as an asset with a corresponding liability within the lease liability. As of December 31, 2019, all costs were incurred, and construction was completed.

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. As of December 31, 2020, all costs were incurred, and construction was completed. 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 sheet. As of December 31, 2020, the Company held $0.1 million as a receivable within other current assets for amounts to be reimbursed by the landlord.

In July 2019, the Company entered into a lease agreement for a facility in San Diego, California to be retrofitted to Good Manufacturing Practice standards and plans to use the facility 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 sheet.

On January 1, 2020, on the adoption of ASC 842, the Company recognized initial lease receivables of $2.7 million, 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 the Company was not reasonably certain it would exercise the extension right. Under ASC 840, 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.

Upon adoption of ASC 842, the Company determined the lease would be accounted for as an operating lease. Further, upon adoption of ASC 842, the Company determined it was the owner of the 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.

During the twelve months ended December 31, 2020 and 2019, the Company recognized $6.0 million and $2.5 million, respectively, of operating lease expense. The Company recognized an immaterial amount of variable operating lease expense for the twelve months ended December 31, 2020. During the twelve months ended December 31, 2020, the Company paid $4.8 million in cash payments for its operating leases. As of December 31, 2020, the weighted average remaining lease term for operating leases was 8.7 years. As of December 31, 2020 the weighted-average discount rate for operating leases was and 8.9%.

As of December 31, 2020, maturities of lease liabilities were as follows (in thousands):

Year ending December 31,
2021	$	5,225
2022		4,333
2023		4,463
2024		4,597
2025		4,735
Thereafter		20,403
Total lease payments		43,756
Imputed interest		(13,574	)
Total lease liability		30,182
Less current portion of lease liability		4,808
Lease liability, net of current portion	$	25,374

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.

On August 3, 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, 2020. 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.

On April 27, 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.

On August 3, 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

On October 24, 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, 2020

Income Tax Disclosure [Abstract]

Income Taxes

Note 11. 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, 2020 and 2019.

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,
	2020			2019
Federal statutory rate	$	(27,253	)	$	(18,170	)
Adjustments for tax effects of:
State taxes, net		(8,581	)		(5,384	)
Permanent adjustments		134			(43	)
Contingent consideration		—			1,403
Stock-based compensation		956			428
Tax credits		(10,735	)		(5,828	)
Unrecognized tax benefits		2,445			1,643
Other, net		(27	)		55
Change in valuation allowance		43,061			25,896
Total	$	—		$	—

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

	December 31,
	2020			2019
Deferred tax assets:
Amortization	$	1,558		$	1,706
Grant income		6,648			5,483
Accrued expenses		1,855			915
Net operating losses		65,058			33,279
Income tax credit carryforwards		15,727			7,101
Lease liabilities		8,388			—
Other, net		982			1,151
Total deferred tax assets		100,216			49,635
Deferred tax liabilities:
Depreciation		(1,877	)		(1,295	)
Acquired indefinite lived intangibles		(369	)		(369	)
Right of use assets		(6,934	)		—
Other, net		—			—
Total deferred tax liabilities		(9,180	)		(1,664	)
Valuation allowance		(91,091	)		(48,026	)
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 $91.1 million has been recorded as of December 31, 2020, as compared to $48.0 million, as of December 31, 2019. 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, 2020, the Company had federal and state net operating loss carryforwards of $23.3 million and $236.4 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 $205.4 million.

As of December 31, 2020, the Company had federal orphan drug credits and research and development credits and state research and development tax credits of $17.7 million and $4.1 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, 2020, 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, 2020, the Company had unrecognized tax benefits of $5.5 million, determined as follows:

	December 31,
	2020			2019
Balance at beginning of the year	$	2,470		$	755
Increase for current year positions		3,211			1,715
Increase for prior year positions		(224	)		—
Balance at the end of year	$	5,457		$	2,470

These unrecognized tax benefits are not expected to change within the next twelve months. Of the $5.5 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, 2020, 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 + Details

Employee Benefit Plan

12 Months Ended

Dec. 31, 2020

Compensation And Retirement Disclosure [Abstract]

Employee Benefit Plan

Note 12. Employee Benefit Plan

In 2015, the Company adopted 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, 2020 and 2019 were $0.6 million and $0.3 million, respectively.

Net Loss Per Share

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Net Loss Per Share

Note 13. Net Loss Per Share

Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts):

	Year Ended December 31,
	2020			2019
Numerator:
Net loss	$	(129,775	)	$	(86,527	)
Net loss attributable to common stockholders	$	(129,775	)	$	(86,527	)
Denominator:
Weighted-average common stock outstanding, basic and diluted		35,996,901			12,618,413
Net loss per share attributable to common stockholders, basic and diluted	$	(3.61	)	$	(6.86	)

The Company’s potentially dilutive securities, which include warrants to purchase common stock and common stock options, 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,
	2020		2019
Convertible preferred stock (as converted to common stock)		—		26,411,194
Warrants to purchase convertible preferred stock (as converted to common stock)		121,122		121,122
Stock options to purchase common stock		4,738,607		3,610,779
		4,859,729		30,143,095

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Nature of Operations

Basis of Preparation and Consolidation

Use of Estimates

Segment Information

Fair Value Measurements

Concentration of Business Risk

Leases

Risk and Uncertainties

Deferred Offering Costs

Concentration of Credit Risk

Cash and Cash Equivalents

Short-Term Investments

Other Receivables, Net

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)
Lab equipment		5
Leasehold improvements	Lesser of useful life or lease-term
Computer equipment and software		3
Furniture and fixtures		7

Research and Development

Research and Manufacturing Contract Costs and Accruals

Patent Costs

Stock-Based Compensation

Contingent Consideration

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 marketable securities.

Net Income (Loss) Per Share

Income Taxes

Emerging Growth Company Status

Recently Adopted Accounting Pronouncements

Recently Issued Accounting Pronouncements

Reclassification

Certain amounts in the consolidated financial statements have been reclassified from their original presentation to conform to current year presentation.

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

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)
Lab 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, 2020

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,
	2020		2019
Landlord reimbursement	$	137	$	421
Rent		217		259
Insurance		2,226		204
Contract research services		651		543
Other		1,613		434
Total prepaid expenses and other current assets	$	4,844	$	1,861

Summary of Property and Equipment Net

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

	December 31,
	2020			2019
Lab equipment	$	11,420		$	6,957
Leasehold improvements		13,826			165
Computer equipment and software		1,381			456
Furniture and fixtures		928			560
Construction in progress		376			4,729
Total property and equipment		27,931			12,867
Less: Accumulated depreciation and amortization		(4,595	)		(2,009	)
Total property and equipment, net	$	23,336		$	10,858

Summary of Goodwill and Other Intangible Assets, Net

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

	December 31,
	2020		2019
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,
	2020		2019
Contract research services	$	15,822	$	7,993
Payroll and related expense		6,793		3,283
Lease cancellation fee		—		979
Other		1,839		1,671
Total accrued and other liabilities	$	24,454	$	13,926

Financial Instruments - (Tables)

12 Months Ended

Dec. 31, 2020

Investments Debt And Equity Securities [Abstract]

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

The following table summarizes the amortized cost and fair value of securities available-for-sale at December 31, 2020 and 2019 (in thousands):

	Amortized Cost/Cost		Unrealized Gains		Unrealized Losses		Fair Value
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
At December 31, 2019:
Money market fund	$	63,744	$	—	$	—	$	63,744
U.S. government agency securities and treasuries		42,503		19		—		42,522
Total	$	106,247	$	19	$	—	$	106,266

Fair Value Measurement (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis

The Company has classified assets and liabilities measured at fair value on a recurring basis as follows (in thousands):

	Level 1		Level 2		Level 3
At December 31, 2020:
Assets
Cash equivalents	$	70,713	$	—	$	—
Short-term investments		225,186		—		—
Total assets	$	295,899	$	—	$	—
At December 31, 2019:
Assets
Cash equivalents	$	68,732	$	—	$	—
Short-term investments		37,534		—		—
Total assets	$	106,266	$	—	$	—
Liabilities
Warrant liability	$	—	$	—	$	1,271
Total liabilities	$	—	$	—	$	1,271

Schedule of Reconciliation of Fair Value Liabilities

A reconciliation of the Level 3 liabilities is as follows (in thousands):

Fair value of Level 3 liabilities as of December 31, 2019	$	1,271
Change in fair value of warrant liability		387
Reclassification of warrants to stockholders' equity (deficit)		(1,658	)
Fair value of Level 3 liabilities as of December 31, 2020	$	—

Equity (Tables)

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Summary of Preferred Stock

Convertible preferred stock immediately prior to the closing of the IPO and as of December 31, 2019 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

	December 31, 2019
	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
Total		33,085,827		32,934,785	$	222,173	$	222,173		26,411,194

Schedule of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consists of the following at December 31, 2020:

Stock options issued and outstanding			4,738,607
Authorized for future options and award grants			6,403,481
Authorized for future issuance under Employee Stock Purchase Plan			615,000
Total			11,757,088

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

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, 2020:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Intrinsic Value (thousands)
Balance at January 1, 2020		3,611,030		$	8.58		8.65
Options Granted		1,510,762			13.36
Exercised		(219,425	)		1.02
Cancelled		(163,760	)		11.76
Balance at December 31, 2020		4,738,607		$	10.34		8.34	$	10,017
Options Vested & Expected to Vest as of December 31, 2020		4,738,607		$	10.34		8.34	$	10,017
Options Exercisable as of December 31, 2020		1,886,521		$	7.56		6.84	$	8,226

Schedule of Stock-Based Compensation Expense

The Company recorded stock-based compensation expense in the following expense categories of its consolidated statements of operations (in thousands):

	Year Ended December 31,
	2020		2019
Research and development	$	3,872	$	1,703
General and administrative		3,348		1,347
Total stock-based compensation	$	7,220	$	3,050

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,
	2020		2019
Risk-free interest rate	0.4%-1.4%		1.6%-2.6%
Expected volatility	79-86%		80-87%
Expected term (years)	5.5-6		4-6
Dividend Yield		—		—

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Summary of Maturities of Lease Liabilities

As of December 31, 2020, maturities of lease liabilities were as follows (in thousands):

Year ending December 31,
2021	$	5,225
2022		4,333
2023		4,463
2024		4,597
2025		4,735
Thereafter		20,403
Total lease payments		43,756
Imputed interest		(13,574	)
Total lease liability		30,182
Less current portion of lease liability		4,808
Lease liability, net of current portion	$	25,374

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

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,
	2020			2019
Federal statutory rate	$	(27,253	)	$	(18,170	)
Adjustments for tax effects of:
State taxes, net		(8,581	)		(5,384	)
Permanent adjustments		134			(43	)
Contingent consideration		—			1,403
Stock-based compensation		956			428
Tax credits		(10,735	)		(5,828	)
Unrecognized tax benefits		2,445			1,643
Other, net		(27	)		55
Change in valuation allowance		43,061			25,896
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,
	2020			2019
Deferred tax assets:
Amortization	$	1,558		$	1,706
Grant income		6,648			5,483
Accrued expenses		1,855			915
Net operating losses		65,058			33,279
Income tax credit carryforwards		15,727			7,101
Lease liabilities		8,388			—
Other, net		982			1,151
Total deferred tax assets		100,216			49,635
Deferred tax liabilities:
Depreciation		(1,877	)		(1,295	)
Acquired indefinite lived intangibles		(369	)		(369	)
Right of use assets		(6,934	)		—
Other, net		—			—
Total deferred tax liabilities		(9,180	)		(1,664	)
Valuation allowance		(91,091	)		(48,026	)
Net deferred tax liability	$	(55	)	$	(55	)

Schedule of Unrecognized Tax Benefits

As of December 31, 2020, the Company had unrecognized tax benefits of $5.5 million, determined as follows:

	December 31,
	2020			2019
Balance at beginning of the year	$	2,470		$	755
Increase for current year positions		3,211			1,715
Increase for prior year positions		(224	)		—
Balance at the end of year	$	5,457		$	2,470

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Schedule of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders

Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts):

	Year Ended December 31,
	2020			2019
Numerator:
Net loss	$	(129,775	)	$	(86,527	)
Net loss attributable to common stockholders	$	(129,775	)	$	(86,527	)
Denominator:
Weighted-average common stock outstanding, basic and diluted		35,996,901			12,618,413
Net loss per share attributable to common stockholders, basic and diluted	$	(3.61	)	$	(6.86	)

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

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,
	2020		2019
Convertible preferred stock (as converted to common stock)		—		26,411,194
Warrants to purchase convertible preferred stock (as converted to common stock)		121,122		121,122
Stock options to purchase common stock		4,738,607		3,610,779
		4,859,729		30,143,095

Nature of Business and Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	Jul. 14, 2020 USD ($) $ / shares shares	Jul. 02, 2020	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Jul. 31, 2020 $ / shares shares	Dec. 31, 2018 shares
Nature Of Business And Basis Of Presentation [Line Items]
Net proceeds from offering after deducting underwriting discounts and offering expenses \| $			$ 205,743
Temporary equity, shares outstanding	42,953,085		0	32,934,785
Common stock, shares authorized			250,000,000	57,013,463
Common stock, par value \| $ / shares			$ 0.0001	$ 0.0001
Net loss \| $			$ 129,775	$ 86,527
Net cash used in operating activities \| $			113,328	64,518
Accumulated deficit \| $			281,885	$ 152,221
Cash, cash equivalents and marketable securities \| $			$ 309,200
Convertible Preferred Stock (As Converted to Common Stock)
Nature Of Business And Basis Of Presentation [Line Items]
Temporary equity, shares outstanding	42,953,085			32,934,785		18,200,011
Warrants to purchase stock	151,042
IPO
Nature Of Business And Basis Of Presentation [Line Items]
Issuance of common stock from initial public offering, Shares	14,000,000
Public offering price per share \| $ / shares	$ 16.00
Aggregate gross proceeds from offering \| $	$ 224,000
Net proceeds from offering after deducting underwriting discounts and offering expenses \| $	$ 205,700
Preferred stock, shares outstanding	0
Common stock, shares authorized					250,000,000
Preferred stock, shares authorized					10,000,000
Common stock, par value \| $ / shares					$ 0.0001
Preferred stock, par value \| $ / shares					$ 0.0001
Common Stock
Nature Of Business And Basis Of Presentation [Line Items]
Reverse stock split			1-for-1.247
Reverse stock split, conversion ratio		0.8019246
Issuance of common stock from initial public offering, Shares			14,000,000
Common Stock \| Convertible Preferred Stock (As Converted to Common Stock)
Nature Of Business And Basis Of Presentation [Line Items]
Number of outstanding securities converted	34,445,108
Common Stock \| IPO
Nature Of Business And Basis Of Presentation [Line Items]
Number of outstanding securities converted			34,445,108
Warrants to Purchase Convertible Preferred Stock (As Converted to Common Stock) \| Convertible Preferred Stock (As Converted to Common Stock)
Nature Of Business And Basis Of Presentation [Line Items]
Number of outstanding securities converted	121,122

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)	Jul. 31, 2020 USD ($)
Recent Accounting Guidance [Line Items]
Number of operating segment \| Segment	1
Variable lease, payments	$ 0
General and administrative	23,029,000	$ 18,457,000
Balance held in account	200,000	200,000
Accounts payable	100,000	0
Impairment of goodwill	0	0
Impairment of long-lived assets	$ 0	0
ASU 2016-02
Recent Accounting Guidance [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU 2018-15
Recent Accounting Guidance [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU 2018-13
Recent Accounting Guidance [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
IPR&D
Recent Accounting Guidance [Line Items]
Impairment of intangible assets, indefinite-lived	$ 0	0
IPO
Recent Accounting Guidance [Line Items]
General and administrative		$ 1,800,000
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, 2020
Lab 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, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Landlord reimbursement	$ 137	$ 421
Rent	217	259
Insurance	2,226	204
Contract research services	651	543
Other	1,613	434
Total prepaid expenses and other current assets	$ 4,844	$ 1,861

Composition of Certain Balance Sheet Components - Summary of Property and Equipment Net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Total property and equipment	$ 27,931	$ 12,867
Less: Accumulated depreciation and amortization	(4,595)	(2,009)
Total property and equipment, net	23,336	10,858
Lab Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	11,420	6,957
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	13,826	165
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Total property and equipment	1,381	456
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	928	560
Construction in Progress
Property Plant And Equipment [Line Items]
Total property and equipment	$ 376	$ 4,729

Composition of Certain Balance Sheet Components - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Depreciation expense	$ 2,600,000	$ 1,200,000
Impairment of goodwill	$ 0	$ 0

Composition of Certain Balance Sheet Components - Summary of Goodwill and Other Intangible Assets, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
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, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Contract research services	$ 15,822	$ 7,993
Payroll and related expense	6,793	3,283
Lease cancellation fee		979
Other	1,839	1,671
Total accrued and other liabilities	$ 24,454	$ 13,926

Financial Instruments - Summary of Amortized Cost and Fair Value of Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost/Cost	$ 295,894	$ 106,247
Available-for-Sale Securities, Unrealized (Losses) Gains	5	19
Available-for-Sale Securities, Fair Value	295,899	106,266
Money Market Fund
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost/Cost	70,713	63,744
Available-for-Sale Securities, Fair Value	70,713	63,744
U.S. Government Agency Securities and Treasuries
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost/Cost	225,181	42,503
Available-for-Sale Securities, Unrealized (Losses) Gains	5	19
Available-for-Sale Securities, Fair Value	$ 225,186	$ 42,522

Financial Instruments - Additional Information (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
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 Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring Basis - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Level 1
Assets
Cash equivalents	$ 70,713	$ 68,732
Short-term investments	225,186	37,534
Total assets	$ 295,899	106,266
Level 3
Liabilities
Warrant liability		1,271
Total liabilities		$ 1,271

Fair Value Measurement - Additional Information (Details)		12 Months Ended
	Jul. 14, 2020 shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 shares
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Temporary equity, shares outstanding	42,953,085	0	32,934,785
Gain (loss) on fair value of warrant liability \| $		$ 387,000	$ (519,000)
Transfers into or out of Level 3 fair value \| $		$ 0	$ 0
Measurement Input, Expected Dividend Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Dividend yield		0
Convertible Preferred Stock (As Converted to Common Stock)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Temporary equity, shares outstanding	42,953,085		32,934,785	18,200,011
Warrants to purchase stock	151,042
Series A-1 Preferred Stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Temporary equity, shares outstanding	3,253,645		3,253,645
Fair value per share \| $ / shares			$ 10.36
Series B Preferred Stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Temporary equity, shares outstanding	5,249,568		5,249,568
Fair value per share \| $ / shares			$ 10.57
Common Stock \| Convertible Preferred Stock (As Converted to Common Stock)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of outstanding securities converted	34,445,108
Warrants to Purchase Convertible Preferred Stock (As Converted to Common Stock) \| Convertible Preferred Stock (As Converted to Common Stock)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of outstanding securities converted	121,122

Fair Value Measurement - Schedule of Reconciliation of Fair Value Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Fair value of Level 3 liabilities as of December 31, 2019	$ 1,271
Change in fair value of warrant liability	387
Reclassification of warrants to stockholders' equity (deficit)	$ (1,658)

California Institute of Regenerative Medicine Awards - Additional Information (Details) - CIRM $ in Millions	1 Months Ended			12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2020 USD ($) 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-BCMA-101 Phase 1 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)		1 Months Ended	12 Months Ended
Term Debt - Additional Information (Details)	Jul. 25, 2017 USD ($) $ / shares shares	Aug. 31, 2018 USD ($) mo	Dec. 31, 2020 USD ($)	Jul. 14, 2020 $ / shares shares	Jun. 24, 2020 USD ($)	Feb. 19, 2019 USD ($) $ / shares shares	Feb. 15, 2019 USD ($)	Dec. 20, 2018 USD ($)	Aug. 13, 2018 $ / shares shares
Debt Instrument [Line Items]
Capital stock in excess	$ 300,000
Fair value of warrants			$ 600,000
Series A-1 Warrants
Debt Instrument [Line Items]
Warrants exercise price \| $ / shares	$ 3.43
Warrants expiration term	10 years
Series A-1 Warrants \| Maximum
Debt Instrument [Line Items]
Warrants to purchase stock \| shares	116,618
Series A-1 Warrants \| Common Stock \| IPO
Debt Instrument [Line Items]
Warrants to purchase stock \| shares				93,518
Warrants exercise price \| $ / shares				$ 4.28
February 2019 Series B Warrants
Debt Instrument [Line Items]
Debt instrument, face amount						$ 10,000,000
Warrants exercise price \| $ / shares						$ 5.81
Warrants expiration term						10 years
February 2019 Series B Warrants \| Maximum
Debt Instrument [Line Items]
Warrants to purchase stock \| shares						17,212
August 2018 Series B Warrants
Debt Instrument [Line Items]
Warrants exercise price \| $ / shares									$ 5.81
Warrants expiration term									10 years
August 2018 Series B Warrants \| Maximum
Debt Instrument [Line Items]
Warrants to purchase stock \| shares									17,212
February 2019 and August 2018 Series B Warrants \| Common Stock \| IPO
Debt Instrument [Line Items]
Warrants to purchase stock \| shares				27,604
Warrants exercise price \| $ / shares				$ 7.25
Amended Loan Agreement
Debt Instrument [Line Items]
Maturity date		Mar. 01, 2023
Line of credit facility, maximum borrowing capacity		$ 30,000,000
Proceeds from term loan		10,000,000
Proceeds from net of issuance costs and accrued costs		900,000
Debt instrument, description			Under the terms of the Amended Loan Agreement the Company was permitted, at its sole discretion, to borrow $10.0 million under the Term B Loan following the achievement of a defined milestone event until the earlier of 60 days thereafter or December 20, 2018. In January 2019, the Company entered into an amendment with Oxford to extend the draw period of the Term B Loan through February 15, 2019. The Company drew the remaining $10.0 million in February 2019.
2020 Amended Loan Agreement
Debt Instrument [Line Items]
Maturity date			Jun. 01, 2024
Debt instrument, description			In June 2020, the Company entered into an Amended and Restated Loan and Security Agreement (“2020 Amended Loan Agreement”) with Oxford. Under the terms of the 2020 Amended Loan Agreement, the interest only period on both the Term A Loan and Term B Loan was extended by 15 months, originally through September 2020 and extended through December 2021, and the final maturity date was extended by 15 months from March 1, 2023 to June 1, 2024. The 2020 Amended Loan Agreement also included a facility fee of $0.3 million due on the amendment effective date, June 24, 2020.
Debt instrument, fee amount					$ 300,000
Original Term A Loan
Debt Instrument [Line Items]
Long-term debt	$ 10,000,000
Maturity date	Aug. 31, 2021
Debt instrument, final payment fee percentage	8.50%
New A Term Loan \| Amended Loan Agreement
Debt Instrument [Line Items]
Debt instrument, face amount		10,000,000
Term B Loan
Debt Instrument [Line Items]
Long-term debt			$ 10,000,000
Initial carrying value of loan			10,000,000
Debt issuance costs			$ 300,000
Interest rate recognized under effective interest method			11.03%
Term B Loan \| Amended Loan Agreement
Debt Instrument [Line Items]
Debt instrument, face amount		$ 10,000,000					$ 10,000,000	$ 10,000,000
Term Loans
Debt Instrument [Line Items]
Maturity date		Jun. 01, 2024
Debt instrument, final payment fee percentage		7.50%
Debt instrument frequency of periodic payment			monthly
Debt instrument repayment number of month \| mo		30
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%
Term Loans \| Loan Prepayment After First Anniversary
Debt Instrument [Line Items]
Debt instrument, final payment fee percentage	3.00%
Term Loans \| Loan Prepayment Including Second Anniversary
Debt Instrument [Line Items]
Debt instrument, final payment fee percentage	2.00%
Term Loans \| Loan Prepayment After Second Anniversary
Debt Instrument [Line Items]
Debt instrument, final payment fee percentage	1.00%
Term A Loan
Debt Instrument [Line Items]
Long-term debt			$ 20,000,000
Initial carrying value of loan			20,000,000
Debt issuance costs			$ 1,000,000
Interest rate recognized under effective interest method			11.28%

Equity - Additional Information (Details) - USD ($)		1 Months Ended	12 Months Ended
Equity - Additional Information (Details) - USD ($)	Jul. 14, 2020	Jun. 30, 2020	Dec. 31, 2020	Jul. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Common stock, shares authorized			250,000,000		57,013,463
Common stock, par value			$ 0.0001		$ 0.0001
Net proceeds from offering after deducting underwriting discounts and offering expenses			$ 205,743,000
Temporary equity, shares outstanding	42,953,085		0		32,934,785
Preferred stock issued and sold	42,953,085		0		32,934,785
Common stock, voting rights			Each share of common stock is entitled to one vote.
Dividends declared			$ 0
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				32,934,785	18,200,011
Warrants to purchase stock	151,042
Convertible Preferred Stock \| Common Stock
Class Of Stock [Line Items]
Number of outstanding securities converted	34,445,108
Convertible Preferred Stock \| Warrants to Purchase Convertible Preferred Stock (As Converted to Common Stock)
Class Of Stock [Line Items]
Number of outstanding securities converted	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

Equity - Summary of Preferred Stock (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jul. 14, 2020	Jun. 30, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Preferred Stock Authorized	0	46,809,523		33,085,827
Preferred Stock Issued	0	42,953,085		32,934,785
Preferred Stock Outstanding	0	42,953,085		32,934,785
Carrying Value		$ 326,313		$ 222,173
Liquidation Preference		$ 326,313		$ 222,173
Common Stock Issuable Upon Conversion		34,445,108		26,411,194
Series A Preferred Stock
Class Of Stock [Line Items]
Preferred Stock Authorized		9,696,798		9,696,798
Preferred Stock Issued		9,696,798		9,696,798
Preferred Stock Outstanding		9,696,798		9,696,798
Carrying Value		$ 31,063		$ 31,063
Liquidation Preference		$ 31,063		$ 31,063
Common Stock Issuable Upon Conversion		7,776,095		7,776,095
Series A-1 Preferred Stock
Class Of Stock [Line Items]
Preferred Stock Authorized		3,370,263		3,370,263
Preferred Stock Issued		3,253,645		3,253,645
Preferred Stock Outstanding		3,253,645		3,253,645
Carrying Value		$ 11,083		$ 11,083
Liquidation Preference		$ 11,083		$ 11,083
Common Stock Issuable Upon Conversion		2,609,176		2,609,176
Series B Preferred Stock
Class Of Stock [Line Items]
Preferred Stock Authorized		5,283,992		5,283,992
Preferred Stock Issued		5,249,568		5,249,568
Preferred Stock Outstanding		5,249,568		5,249,568
Carrying Value		$ 30,314		$ 30,314
Liquidation Preference		$ 30,314		$ 30,314
Common Stock Issuable Upon Conversion		4,209,754		4,209,754
Series C Preferred Stock
Class Of Stock [Line Items]
Preferred Stock Authorized		14,734,774		14,734,774
Preferred Stock Issued		14,734,774		14,734,774
Preferred Stock Outstanding		14,734,774		14,734,774
Carrying Value		$ 149,713		$ 149,713
Liquidation Preference		$ 149,713		$ 149,713
Common Stock Issuable Upon Conversion		11,816,169		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

Equity - Schedule of Common Stock Reserved for Future Issuance (Details)	Dec. 31, 2020 shares
Equity [Abstract]
Stock options issued and outstanding	4,738,607
Authorized for future options and award grants	6,403,481
Authorized for future issuance under Employee Stock Purchase Plan	615,000
Total	11,757,088

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock reserved for issuance		11,757,088
Aggregate intrinsic value of options exercised		$ 2,400	$ 700
Net proceeds from stock option exercises		223	$ 69
Unrecognized compensation cost		$ 23,000
Weighted-average fair value of options granted		$ 8.65	$ 8.47
Fair value of shares vested		$ 6,900	$ 2,800
Expected dividend yield		0.00%
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average period over which cost expected to be recognized		3 years
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		6,403,481
2020 Equity Incentive Plan \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted as percentage of fair value of common stock		100.00%
Award 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 \| ISOs
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%
Share-based compensation shares issued in period	1,230,000

Stock-Based Compensation - Summary of the Company's Stock Option Plan Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Balance, Shares	3,611,030
Granted, Shares	1,510,762
Exercised, Shares	(219,425)
Cancelled, Shares	(163,760)
Balance, Shares	4,738,607	3,611,030
Options Vested & Expected to Vest as of December 31, 2020, Shares	4,738,607
Options Exercisable as of December 31, 2020, Shares	1,886,521
Balance, Weighted Average Exercise Price	$ 8.58
Options Granted, Weighted Average Exercise Price	13.36
Exercised, Weighted Average Exercise Price	1.02
Cancelled, Weighted Average Exercise Price	11.76
Balance, Weighted Average Exercise Price	10.34	$ 8.58
Options Vested & Expected to Vest as of December 31, 2020, Weighted Average Exercise Price	10.34
Options Exercisable as of December 31, 2020, Weighted Average Exercise Price	$ 7.56
Balance, Weighted Average Remaining Contractual Term (Years)	8 years 4 months 2 days	8 years 7 months 24 days
Options Vested & Expected to Vest as of December 31, 2020, Weighted Average Remaining Contractual Term (Years)	8 years 4 months 2 days
Options Exercisable as of December 31, 2020, Weighted Average Remaining Contractual Term (Years)	6 years 10 months 2 days
Balance, Intrinsic Value	$ 10,017
Options Vested & Expected to Vest as of December 31, 2020, Intrinsic Value	10,017
Options Exercisable as of December 31, 2020, Intrinsic Value	$ 8,226

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 7,220	$ 3,050
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	3,872	1,703
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 3,348	$ 1,347

Stock-Based Compensation - Schedule of Assumptions Used to Determine the Fair Value of Options Granted (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	0.40%	1.60%
Risk-free interest rate, maximum	1.40%	2.60%
Expected volatility, minimum	79.00%	80.00%
Expected volatility, maximum	86.00%	87.00%
Dividend Yield	0.00%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 6 months	4 years
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years	6 years

Commitments and Contingencies - Additional Information (Details) $ in Thousands					1 Months Ended				12 Months Ended
	Oct. 24, 2019 USD ($)	Aug. 03, 2018 USD ($)	Apr. 28, 2017 USD ($)	Aug. 03, 2015 USD ($)	Oct. 31, 2019 USD ($)	Jul. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Mar. 31, 2016 USD ($) Installment	Dec. 31, 2020 USD ($) ft² Option	Dec. 31, 2019 USD ($)	Jan. 01, 2020 USD ($)	Oct. 25, 2019 USD ($)
Commitments And Contingencies [Line Items]
Operating leases, number of square feet \| ft²									83,000
Operating leases remaining lease terms									108 months
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, option to extend									true
Operating lease, extended term									5 years
Operating lease, number of options to extend term \| Option									2
Operating lease, commencement date					Jul. 29, 2020	Jun. 26, 2020	Apr. 01, 2019	Jun. 30, 2016
Operating lease, initial term								10 years 6 months
Security deposit					$ 300	$ 100		$ 100
Operating lease, termination date								Apr. 30, 2019
Operating lease, termination fee								$ 1,500
Operating lease, termination fee, number of installments \| Installment								3
Operating lease, termination fee, term								1 year 6 months
Operating lease, expiration date					Dec. 31, 2029	Dec. 31, 2029	Dec. 31, 2029
Tenant improvements						$ 2,900	$ 4,200
Additional tenant reimbursements					$ 1,500
Operating lease right-of-use assets									$ 24,986
Initial lease liability									30,182
Accumulated deficit									281,885	$ 152,221
Operating lease expense									6,000	$ 2,500
Operating lease, payments									$ 4,800
Operating lease, weighted-average remaining lease term									8 years 8 months 12 days
Operating lease, weighted-average discount rate									8.90%
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 fee payable to exercise option	$ 1,500
Commercial License Agreement \| TeneoBio, Inc.
Commitments And Contingencies [Line Items]
Upfront fee		$ 4,000	$ 500
Initial milestone payments payable			20,500
Additional milestone payments payable			$ 20,500
Milestone payments payable		$ 31,000
ASC 842
Commitments And Contingencies [Line Items]
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 the Company was not reasonably certain it would exercise the extension right.
Operating lease, option to extend									true
Initial lease receivables											$ 2,700
Operating lease right-of-use assets											22,300
Deferred rent balance											2,300
Initial lease liability											27,300
ASC 842 \| Cumulative Adjustment
Commitments And Contingencies [Line Items]
Accumulated deficit											100
Other Current Assets
Commitments And Contingencies [Line Items]
Receivable for amounts to be reimbursed									$ 100
Property and Equipment
Commitments And Contingencies [Line Items]
Tenant improvements									$ 13,300
Property and Equipment \| ASC 842 \| Adoption of ASC 842 Adjustment
Commitments And Contingencies [Line Items]
Derecognition of construction in progress related to manufacturing facility											2,100
Other Long-Term Liabilities \| ASC 842 \| Adoption of ASC 842 Adjustment
Commitments And Contingencies [Line Items]
Derecognition of construction financing obligation related to manufacturing facility											2,500
Prepaid and Other Current Assets \| ASC 842 \| Adoption of ASC 842 Adjustment
Commitments And Contingencies [Line Items]
Derecognition of other receivables related to manufacturing facility											$ 300
Maximum
Commitments And Contingencies [Line Items]
Operating lease remaining lease term dedicated to manufacturing suites									12 months

Commitments and Contingencies - Summary of Maturities of Lease Liabilities (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2021	$ 5,225
2022	4,333
2023	4,463
2024	4,597
2025	4,735
Thereafter	20,403
Total lease payments	43,756
Imputed interest	(13,574)
Total lease liability	30,182
Less current portion of lease liability	4,808
Lease liability, net of current portion	$ 25,374

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Income tax expense or benefit	$ 0	$ 0
Valuation allowance	91,091,000	48,026,000
Unrecognized tax benefits	5,457,000	$ 2,470,000	$ 755,000
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 $205.4 million.
Operating loss carryforwards limitations on use, percentage of taxable income	80.00%
Operating loss carryforwards limitations on use, taxable income	$ 205,400,000
Research and development credits	$ 17,700,000
Research and development tax credit expiration year	2032
State
Income Taxes [Line Items]
Operating loss carryforwards	$ 236,400,000
Research and development credits	$ 4,100,000

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 ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Federal statutory rate	$ (27,253,000)	$ (18,170,000)
Adjustments for tax effects of:
State taxes, net	(8,581,000)	(5,384,000)
Permanent adjustments	134,000	(43,000)
Contingent consideration		1,403,000
Stock-based compensation	956,000	428,000
Tax credits	(10,735,000)	(5,828,000)
Unrecognized tax benefits	2,445,000	1,643,000
Other, net	(27,000)	55,000
Change in valuation allowance	43,061,000	25,896,000
Total	$ 0	$ 0

Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Amortization	$ 1,558	$ 1,706
Grant income	6,648	5,483
Accrued expenses	1,855	915
Net operating losses	65,058	33,279
Income tax credit carryforwards	15,727	7,101
Lease liabilities	8,388
Other, net	982	1,151
Total deferred tax assets	100,216	49,635
Deferred tax liabilities:
Depreciation	(1,877)	(1,295)
Acquired indefinite lived intangibles	(369)	(369)
Right of use assets	(6,934)
Total deferred tax liabilities	(9,180)	(1,664)
Valuation allowance	(91,091)	(48,026)
Net deferred tax liability	$ (55)	$ (55)

Income Taxes - Schedule of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Balance at beginning of the year	$ 2,470	$ 755
Increase for current year positions	3,211	1,715
Increase for prior year positions	(224)
Balance at the end of year	$ 5,457	$ 2,470

Employee Benefit Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Defined contributions, total	$ 0.6	$ 0.3
Defined Contribution Plan, Tax Status [Extensible List]	us-gaap:QualifiedPlanMember	us-gaap:QualifiedPlanMember

Net Loss Per Share - Schedule of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net loss	$ (129,775)	$ (86,527)
Net loss attributable to common stockholders	$ (129,775)	$ (86,527)
Weighted-average common stock outstanding, basic and diluted	35,996,901	12,618,413
Net loss per share attributable to common stockholders, basic and diluted	$ (3.61)	$ (6.86)

- 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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- Definition

Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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+ Details

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, 2020	Dec. 31, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	4,859,729	30,143,095
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount		26,411,194
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
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	4,738,607	3,610,779