CytomX Therapeutics (CTMX) 10-K 1 Mar 22 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Jan. 31, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Trading Symbol	CTMX
Entity Registrant Name	CytomX Therapeutics, Inc.
Entity Central Index Key	0001501989
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity File Number	001-37587
Entity Tax Identification Number	27-3521219
Entity Address, Address Line One	151 Oyster Point Boulevard,
Entity Address, Address Line Two	Suite 400
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	515-3185
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, $0.00001 par value
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Entity Public Float			$ 408.3
Entity Common Stock, Shares Outstanding		65,392,758
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement to be filed for its 2022 Annual Meeting of Stockholders are incorporated by reference into Part III hereof. Such proxy statement will be filed with the Securities and Exchange Commission within 120 days of the end of the fiscal year covered by this Annual Report on Form 10-K.
Auditor Name	Ernst & Young LLP
Auditor Firm Id	42
Auditor Location	Redwood City, California

BALANCE SHEETS

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 205,530	$ 191,859
Short-term investments	99,696	124,260
Accounts receivable	790	798
Prepaid expenses and other current assets	4,285	7,096
Total current assets	310,301	324,013
Property and equipment, net	5,960	6,950
Intangible assets, net	1,021	1,167
Goodwill	949	949
Restricted cash - non-current assets	917	917
Operating lease right-of-use asset	19,362	22,495
Other assets	901	2,172
Total assets	339,411	358,663
Current liabilities:
Accounts payable	2,818	2,996
Accrued liabilities	34,236	23,059
Deferred revenues, current portion	69,262	74,869
Total current liabilities	106,316	100,924
Deferred revenue, net of current portion	125,660	186,261
Operating lease liabilities - long term	18,056	21,675
Total liabilities	250,032	308,860
Commitments and contingencies (Note 11)
Stockholders' equity
Common stock, $0.00001 par value; 150,000,000 and 150,000,000 shares authorized at December 31, 2021 and 2020, respectively; 48,251,819 and 48,251,819 shares issued and outstanding at December 31, 2021 and 2020, respectively	1	1
Additional paid-in capital	623,344	499,964
Accumulated other comprehensive income (loss)	(242)	(47)
Accumulated deficit	(533,724)	(450,115)
Total stockholders' equity	89,379	49,803
Total liabilities and stockholders' equity	339,411	358,663
Convertible Preferred Stock
Stockholders' equity
Convertible preferred stock, $0.00001 par value; 10,000,000 shares authorized and no shares issued and outstanding at December 31, 2021 and 2020	$ 0	$ 0

BALANCE SHEETS (Parenthetical)

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	65,392,758	48,251,819
Common stock, shares outstanding	65,392,758	48,251,819
Convertible Preferred Stock
Convertible Preferred stock, par value	$ 0.00001	$ 0.00001
Convertible Preferred stock, shares authorized	10,000,000	10,000,000
Convertible Preferred stock, shares issued	0	0
Convertible Preferred stock, shares outstanding	0	0

STATEMENTS OF OPERATIONS AND CO

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Comprehensive Income [Abstract]
Revenues	$ 69,573	$ 100,362	$ 57,489
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating expenses:
Research and development	$ 114,194	$ 112,936	$ 131,619
General and administrative	39,160	36,031	36,765
Total operating expenses	153,354	148,967	168,384
Loss from operations	(83,781)	(48,605)	(110,895)
Interest income	255	1,836	8,365
Other expense, net	(83)	(27)	(135)
Loss before income taxes	(83,609)	(46,796)	(102,665)
Benefit from income taxes	0	(13,911)	(427)
Net loss	$ (83,609)	$ (32,885)	$ (102,238)
Net loss per share, basic and diluted	$ (1.30)	$ (0.71)	$ (2.26)
Shares used to compute net loss per share, basic and diluted	64,146,848	46,145,563	45,335,927
Other comprehensive income (loss):
Unrealized gain (loss) on short-term investments, net of tax	$ (195)	$ (104)	$ 139
Impact of adoption of new accounting pronouncement	0	0	11
Total comprehensive loss	$ (83,804)	$ (32,989)	$ (102,088)

Statements of Stockholders' Equ

Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income/(Loss)	Accumulated Other Comprehensive Income/(Loss)Cumulative Effect, Period of Adoption, Adjustment	Accumulated Deficit	Accumulated DeficitCumulative Effect, Period of Adoption, Adjustment
Beginning balance at Dec. 31, 2018	$ 130,883	$ 1	$ 445,956	$ (93)	$ 11	$ (314,981)	$ (11)
Beginning balance, shares at Dec. 31, 2018		45,083,209
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201802Member
Exercise of stock options	$ 633		633
Exercise of stock options, shares		146,930
Issuance of common stock under the Employee Stock Purchase Plan	994		994
Issuance of common stock under the Employee Stock Purchase Plan, shares		142,949
Issuance of common stock in follow-on offering, net of issuance costs	1,602		1,602
Issuance of common stock in follow-on offering, net of issuance costs, shares		150,000
Stock-based compensation	19,100		19,100
Other comprehensive income (loss)	139			139
Net loss	(102,238)					(102,238)
Ending balance at Dec. 31, 2019	51,113	$ 1	468,285	57		(417,230)
Ending balance, shares at Dec. 31, 2019		45,523,088
Exercise of stock options	4,876		4,876
Exercise of stock options, shares		1,064,830
Issuance of common stock under the Employee Stock Purchase Plan	$ 729		729
Issuance of common stock under the Employee Stock Purchase Plan, shares	128,684	128,684
Issuance of common stock in follow-on offering, net of issuance costs	$ 11,288		11,288
Issuance of common stock in follow-on offering, net of issuance costs, shares		1,535,217
Stock-based compensation	14,786		14,786
Other comprehensive income (loss)	(104)			(104)
Net loss	(32,885)					(32,885)
Ending balance at Dec. 31, 2020	49,803	$ 1	499,964	(47)		(450,115)
Ending balance, shares at Dec. 31, 2020		48,251,819
Exercise of stock options	$ 1,428		1,428
Exercise of stock options, shares	528,503	528,503
Issuance of common stock under the Employee Stock Purchase Plan	$ 1,073		1,073
Issuance of common stock under the Employee Stock Purchase Plan, shares	183,865	183,865
Issuance of common stock in follow-on offering, net of issuance costs	$ 107,712		107,712
Issuance of common stock in follow-on offering, net of issuance costs, shares		16,428,571
Stock-based compensation	13,167		13,167
Other comprehensive income (loss)	(195)			(195)
Net loss	(83,609)					(83,609)
Ending balance at Dec. 31, 2021	$ 89,379	$ 1	$ 623,344	$ (242)		$ (533,724)
Ending balance, shares at Dec. 31, 2021		65,392,758

STATEMENTS OF CASH FLOWS

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (83,609)	$ (32,885)	$ (102,238)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Amortization of intangible assets	146	146	146
Depreciation and amortization	2,560	2,427	2,459
Amortization of premium (accretion of discounts) on investments	272	(236)	(2,228)
Stock-based compensation expense	13,167	14,786	19,100
Non-cash lease expense	3,133	2,887	2,672
Issuance of common stock in connection with UCSB sublicense fee	0	0	1,602
Changes in operating assets and liabilities
Accounts receivable	8	(785)	84
Prepaid expenses and other current assets	2,811	81	2,074
Other assets	1,271	(157)	(640)
Accounts payable	(139)	(857)	(374)
Accrued liabilities, income tax payable and other long-term liabilities	7,558	(11,039)	(15,396)
Deferred revenue	(66,209)	30,891	(47,741)
Net cash provided by (used in) operating activities	(119,031)	5,259	(140,480)
Cash flows from investing activities:
Purchases of property and equipment	(1,609)	(2,309)	(3,497)
Purchases of investments	(99,898)	(199,108)	(174,992)
Maturities of investments	123,996	182,699	258,190
Net cash provided by (used in) investing activities	22,489	(18,718)	79,701
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs	107,712	11,288	0
Proceeds from employee stock purchase plan and exercise of stock options	2,501	5,605	1,627
Net cash provided by financing activities	110,213	16,893	1,627
Net increase (decrease) in cash, cash equivalents and restricted cash	13,671	3,434	(59,152)
Cash, cash equivalents and restricted cash, beginning of year	192,776	189,342	248,494
Cash, cash equivalents and restricted cash, end of year	206,447	192,776	189,342
Supplemental disclosures of cash flow information:
Cash paid for income taxes	0	0	13,061
Supplemental disclosures of noncash investing items:
Purchases of property and equipment in accounts payable and accrued liabilities	83	122	428
Right of use assets obtained in exchange for operating lease obligations	$ 0	$ 0	$ 28,054

Description of the Business

Description of the Business	12 Months Ended
	Dec. 31, 2021
Disclosure Text Block [Abstract]
Description of the Business	1. Description of the Business CytomX Therapeutics, Inc. (the “Company”) is a clinical-stage, oncology-focused biopharmaceutical company dedicated to destroying cancer differently. The Company aims to build a commercial enterprise to maximize its impact on the treatment of cancer. The Company is advancing potential first-in-class and best-in-class antibody-based therapeutics created using its Probody® therapeutic technology platform that could meaningfully improve outcomes for cancer patients. Its proprietary and unique Probody technology platform is designed to enable “conditional activation” of antibody-based drugs in the tumor microenvironment while minimizing drug activity in healthy tissues and in circulation. The Company is located in South San Francisco, California and was incorporated in the state of Delaware in September 2010.

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	2. Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Use of Estimates The preparation of the financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates. Concentration of Credit Risk and Other Risks and Uncertainties The Company is subject to a number of risks similar to other biopharmaceutical companies in the early stage, including, but not limited to, the need to obtain adequate additional funding, possible failure of preclinical testing or clinical trials, the need to obtain marketing approval for its product candidates, competitors developing new technological innovations, the need to successfully commercialize and gain market acceptance of the Company’s products, and protection of proprietary technology. If the Company does not successfully obtain regulatory approval, commercialize or partner any of its product candidates, it will be unable to generate revenue from product sales or achieve profitability. Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents, short-term investments and accounts receivable. Substantially all the Company’s cash is held by one financial institution. Such deposits may, at times, exceed federally insured limits. The Company invests its cash equivalents in highly rated money market funds and its short-term investments in U.S. Government Bonds. Customers and collaboration partners who represent 10% or more of the Company’s total revenue during each period presented or accounts receivable balance at each respective balance sheet date are as follows: Revenue Accounts Receivable, net Year Ended December 31, December 31, 2021 2020 2019 2021 2020 (in thousands) (in thousands) AbbVie Ireland Unlimited Company $ 11,845 $ 38,192 $ 5,878 $ — $ — Amgen, Inc. 8,744 * * — — Astellas Pharma Inc. 19,365 13,931 — 790 798 Bristol Myers Squibb Company 29,619 39,630 47,740 — — Total revenue from customers who represent 10% or more $ 69,573 $ 91,753 $ 53,618 $ 790 $ 798 * Less than 10% The Company’s customers are located in the United States of America, Ireland and Japan. Segments Management has determined that it has one business activity and operates as one operating segment as it only reports financial information on an aggregate basis to its chief executive officer and chief financial officer, who are the Company’s chief operating decision makers. All long-lived assets are maintained in the United States of America. Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents. Restricted Cash Restricted cash represents a standby letter of credit issued pursuant to an office lease. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets that sum to the total of the amounts shown in the statement of cash flows: December 31 2021 2020 2019 (in thousands) Cash and cash equivalents $ 205,530 $ 191,859 $ 188,425 Restricted cash - non-current assets 917 917 917 Total $ 206,447 $ 192,776 $ 189,342 Investments All investments have been classified as available-for-sale (“AFS”) and are carried at fair value as determined based upon quoted market prices or pricing models for similar securities at period end. Investments that are required for use in current operations and that mature in less than 12 months are classified as short-term investments in the accompanying balance sheets. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. Dividend and interest income are recognized when earned. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold. The Company assesses impairment of its AFS debt securities investments at each reporting period. Unrealized gains resulting from the excess of the fair value over the amortized cost basis of an investment are reported as a component of accumulated other comprehensive income (loss), net of tax. Unrealized losses or impairments resulting from the fair value of the AFS debt security being below the amortized cost basis are evaluated, using the discounted cash flow model, for identification of credit losses and non-credit related losses. Any credit losses are charged to earnings against the allowance for credit losses of the security, limited to the difference between the fair value and the amortized cost basis of the security. Any difference between the fair value of the security and the amortized cost basis, less the allowance for credit losses, are reported in other comprehensive income (loss). Expected cash inflows due to improvements in credit are recognized through a reversal of the allowance for credit losses subject to the total allowance previously recognized. In the event of impairment of any security, if management (i) has the intent to sell such security or (ii) will more-likely-than-not be required to sell such security before recovery of its amortized cost basis, such AFS debt security’s amortized cost basis will be written down to its fair value through earnings along with any existing allowance for credit losses. Property and Equipment, net Property and equipment are recorded at cost net of accumulated depreciation and amortization. Depreciation is provided using the straight-line method over the estimated useful lives of the respective assets. The useful lives of property and equipment are as follows: Machinery and equipment 5 years Computer equipment and software 3 years Furniture and fixtures 3 years Leasehold improvements Shorter of remaining lease term or estimated life of the assets Maintenance and repairs that do not extend the life or improve the asset are expensed when incurred. Goodwill and Intangible Assets Goodwill represents the excess of the purchase price paid over the fair value of tangible and identifiable intangible assets acquired in business combinations. Goodwill and other intangible assets with indefinite lives are not amortized, but are assigned to reporting units and tested for impairment annually, or whenever there is an impairment indicator. Intangible assets are comprised of in-process research and development. The Company assesses impairment indicators annually as of December 31 or more frequently, if a change in circumstances or the occurrence of events suggests the remaining value may not be recoverable. Intangible assets that are not deemed to have an indefinite life are amortized over their estimated useful lives. There was no impairment of goodwill or intangible assets identified during the years ended December 31, 2021, 2020 and 2019. Impairment of Long-Lived Assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset (or asset group) may not be recoverable and prior to any goodwill impairment test. An impairment loss is recognized when the total of estimated undiscounted future cash flows expected to result from the use of the asset (or asset group) and its eventual disposition is less than its carrying amount. Impairment, if any, would be assessed using discounted cash flows or other appropriate measures of fair value. There was no impairment of long-lived assets during the years ended December 31, 2021, 2020 and 2019. Revenue Recognition The Company’s revenues are primarily derived through its license, research, development and commercialization agreements. The terms of these types of agreements may include (i) licenses for the Company’s technology or programs, (ii) research and development services, and (iii) services or obligations in connection with participation in research or steering committees. Payments to the Company under these arrangements typically include one or more of the following: nonrefundable upfront and license fees, research funding, milestone and other contingent payments to the Company for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of any commercialized products. The Company assesses whether the promises in its arrangements with customers are distinct performance obligations that should be accounted for separately. Judgment is required to determine whether the license to the Company’s intellectual property is distinct from the research and development services or participation on steering committees. The Company’s collaboration and license agreements may include contingent payments related to specified research, development and regulatory milestones. Such milestone payments are typically payable under the collaborations when the collaboration partner claims or selects a target, or initiates or advances a covered product candidate in preclinical or clinical development, upon submission for marketing approval of a covered product with regulatory authorities, or upon receipt of actual marketing approvals of a covered product or for additional indications. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At each reporting date, the Company re-evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price by using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price in such period of determination. The Company’s collaboration and license agreements may also include contingent payments related to sales-based milestones. Sales-based milestones are typically payable when annual sales of a covered product reach specified levels. Sales-based milestones are recognized at the later of when the associated performance obligation has been satisfied or when the sales occur. Unlike other contingency payments, such as regulatory milestones, sales-based milestones are not included in the transaction price based on estimates at the inception of the contract; instead, are included when the sales or usage occur. The transaction price in each arrangement is allocated to the identified performance obligations based on the relative standalone selling price (“SSP”) of each distinct performance obligation, which requires judgment. In instances where SSP is not directly observable, such as when a license or service is not sold separately, SSP is determined using information that may include market conditions and other observable inputs. Due to the early stage of the Company’s licensed technology, the license of such technology is typically combined with research and development services and steering committee participation as one performance obligation. In the event that the Company receives non-cash consideration such as consideration in the form of a research license and research support services from the counterparty, the transaction price of a non-monetary exchange that has commercial substance is estimated based on the fair value of the non-cash consideration received, which may be determined through a valuation analysis. In certain cases, the Company’s performance creates an asset that does not have an alternative use to the customer and the Company has an enforceable right to payment at all times for performance completed to date. In these cases, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. AbbVie Ireland Unlimited Company (“AbbVie”), one of the Company’s collaboration partners, entered into a license agreement with Seagen Inc., formerly Seattle Genetics, Inc. (“SGEN”) to license certain intellectual property rights. As part of the Company’s collaboration agreement with AbbVie, the Company is required to pay SGEN sublicense fees for certain milestone achievements and an annual maintenance fee. These sublicense fees are treated as reductions to the transaction price and combined with the performance obligation to which they relate. Comprehensive Income (Loss) Comprehensive income (loss) represents all changes in stockholders’ equity except those resulting from distributions to stockholders. The Company’s non-credit related unrealized gains and losses on investments and impact of adoption of new accounting pronouncements during the period represent the components of other comprehensive income (loss) that is excluded from the reported net loss. Contract Balances Customer payments are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until the Company satisfies its performance obligations under these arrangements. Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional. Research and Development Expenses The Company records accrued liabilities for estimated costs of research and development activities conducted by third-party service providers, which include the conduct of preclinical and clinical studies, and contract manufacturing activities. The Company records the estimated costs of research and development activities based upon the estimated amount of services provided but not yet invoiced, and includes these costs in accrued liabilities in the balance sheets and within research and development expense in the statements of operations. These costs are a significant component of the Company’s research and development expenses. The Company accrues for these costs based on factors such as estimates of the work completed and in accordance with agreements established with its third-party service providers under the service agreements. The Company makes significant judgments and estimates in determining the accrued liabilities balance in each reporting period. As actual costs become known, the Company adjusts its accrued liabilities. The Company has not experienced any material differences between accrued costs and actual costs incurred. However, the status and timing of actual services performed may vary from the Company’s estimates, resulting in adjustments to expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations. Research and development expenses include costs directly attributable to the conduct of research and development programs, including the cost of salaries, payroll taxes, employee benefits, materials, supplies, depreciation on and maintenance of research equipment, the cost of services provided by outside contractors, and the allocated portions of facility costs, such as rent, utilities, insurance, repairs and maintenance, depreciation, and general support services. All costs associated with research and development are expensed as incurred. In January 2019, the Company acquired certain technology know-how that is complementary to the Company’s proprietary Probody technology from a third party for $ 5.0 million. The Company plans to use this technology in certain of the Company’s discovery stage projects, and has concluded that the technology acquired does not have an alternative future use. Accordingly, the $ 5.0 million has been recorded as research and development expense for 2019. Stock-based Compensation The Company measures compensation expense for all stock-based payment awards, including employee stock options, restricted stock units ("RSUs"), and employee stock purchases related to Employee Stock Purchase Plan ("ESPP") based on estimated fair values of the award at the grant date, and recognizes compensation expense over the requisite service vesting period. Stock options forfeitures are accounted for in the period in which they occur. To determine the fair value of a stock option award on the grant date, the Company uses the Black-Scholes option pricing model which consist of estimating variables such as: expected life, volatility, and risk-free interest rate. Expected life and volatility are estimated primarily from the Company's historical records, and the risk-free rate is based on the U.S. Treasury yield curve in effect at the time of grant commensurate with the expected life assumption. These estimates involve inherent uncertainties and the application of judgment. The Company measures its restricted stock unit awards based on the market price of the Company’s common shares on the date of grant. Share-based compensation expense for performance-based awards is recognized when it becomes probable that the performance condition will be met. The Company reassesses the estimated probability at each reporting period, and if it is determined at a future date that a performance condition is probable of being achieved, the Company will recognize a cumulative catch-up adjustment and record the remaining expense ratably over the remaining requisite service period. Income Taxes The Company accounts for income taxes using an asset and liability approach. Deferred tax assets and liabilities reflect the net tax effects of temporary differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The Company records a valuation allowance to reduce its deferred tax assets to reflect the net amount that it believes as more likely than not to be realized. Realization of the deferred tax assets is dependent on the generation of future taxable income, the amount and timing of which are uncertain. The valuation allowance requires an assessment of both positive and negative evidence when determining whether it is more likely than not that deferred tax assets are recoverable. Based upon the weight of available evidence at December 31, 2021, the Company continues to maintain a full valuation allowance against all of its deferred tax assets after management considered all available evidence, both positive and negative, including but not limited to its historical operating results, income or loss in recent periods, cumulative income in recent years, forecasted earnings, future taxable income, and significant risk and uncertainty related to forecasts. The Company recognizes the tax effects of an uncertain tax position only if it is more likely than not that it will be sustained based solely on its technical merits as of the reporting date and only in an amount more likely than not that it will be sustained upon review by the tax authorities. The Company evaluates uncertain tax positions on a quarterly basis and adjust the liability for changes in facts and circumstances, such as new regulations or interpretations by the taxing authorities, new information obtained during a tax examination, significant amendment to an existing tax law, or resolution of an examination. To the extent that the final tax outcome of these matters is different than the amounts recorded, such differences will impact the income tax provision in the period in which such determination is made. The resolution of its uncertain income tax positions is dependent on uncontrollable factors such as law changes, new case law, and the willingness of the income tax authorities to settle, including the timing thereof and other factors. Although the Company does not anticipate significant changes to its uncertain income tax positions in the next twelve months, items outside of its control could cause its uncertain income tax positions to change in the future, which would be recorded in its statements of operations. Interest and/or penalties related to income tax matters are recognized as a component of income tax expense. Leases The Company determines if an arrangement is or contains a lease at inception. Operating leases are recorded as operating lease right-of-use (“ROU”) assets and operating lease liabilities in the Company’s balance sheet. ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent its obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. The Company uses an implicit rate when readily available, or its incremental borrowing rate based on the information available at lease commencement date in determining the present value of lease payments. The operating lease ROU assets also include any lease prepayments made and reduced by lease incentives. The Company’s lease terms may include options to extend the lease when it is reasonably certain that such option will be exercised. Lease expenses are recognized on a straight-line basis over the lease term. The Company elected the short-term lease recognition exemption. The Company’s operating lease arrangement includes lease and non-lease components which are generally accounted for separately.

Adopted Accounting Pronouncemen

Adopted Accounting Pronouncements	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Adopted Accounting Pronouncements	3. Adopted Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The amendments in this ASU simplify the accounting for income taxes by removing certain exceptions to the general principles of ASC 740 in order to reduce cost and complexity of its application. The ASU removes the exception related to the incremental approach for intra-period tax allocation as well as two exceptions related to accounting for outside basis differences of equity method investments and foreign subsidiaries. The ASU also amends the scope of ASC 740 related to a franchise tax (or similar tax) that is partially based on income; clarifies when a step-up in the tax basis of goodwill should be considered part of the business combination in which the book goodwill was originally recognized and when it should be considered a separate transaction; specifies that an entity is not required to allocate income tax expense to a legal entity that is both not subject to tax and disregarded by the taxing authority; and clarifies that all tax effects, both deferred and current, should be accounted for in the interim period that includes the enactment date. The Company adopted this ASU on January 1, 2021 , and there was no material impact on the financial statements upon adoption of this ASU.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	4. Net 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 for the period. Diluted net loss per share is calculated using the weighted-average number of common shares outstanding, plus potential dilutive common stock during the period. Diluted net loss per share is the same as basic net loss per share since the effect of the potentially dilutive securities is anti-dilutive. The following weighted-average outstanding shares of potentially dilutive securities are excluded from the computation of diluted net loss per share for the periods presented, because including them would have been anti-dilutive: Year Ended December 31, 2021 2020 2019 Options, RSUs and ESPP to purchase common stock 11,987,362 11,388,691 9,687,844

Fair Value Measurements and Inv

Fair Value Measurements and Investments	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements and Investments	5. Fair Value Measurements and Investments In accordance with Accounting Standards Codification (“ASC”) 820-10, Fair Value Measurements and Disclosures, the Company determines the fair value of financial and non-financial assets and liabilities using the fair value hierarchy, which establishes three levels of inputs that may be used to measure fair value, as follows: • Level I: Inputs which include quoted prices in active markets for identical assets and liabilities. • Level II: Inputs other than Level I that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. • Level III: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. The carrying amounts of the Company’s financial instruments, including restricted cash, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities. The Company’s financial instruments consist of Level I assets which consist primarily of highly liquid money market funds, some of which are included in restricted cash; and U.S. government bonds that are included in short-term investments. The following tables set forth the fair value of the Company’s investments subject to fair value measurements on a recurring basis and the level of inputs used in such measurements: December 31, 2021 Valuation Amortized Allowance for Credit Losses Gross Gross Aggregate (in thousands) Assets Money market funds Level I 165,736 $ — $ — $ — $ 165,736 Restricted cash (money market funds) Level I 917 — — — 917 U.S. Government bonds Level I 99,938 — — ( 242 ) 99,696 Total Securities 266,591 $ — $ — $ ( 242 ) $ 266,349 December 31, 2020 Valuation Amortized Allowance Gross Gross Aggregate (in thousands) Assets Money market funds Level I $ 131,121 $ — $ — $ — $ 131,121 Restricted cash (money market funds) Level I 917 — — — 917 U.S. Government bonds Level I 124,254 — 6 — 124,260 Total securities $ 256,292 $ — $ 6 $ — $ 256,298 No securities have contractual maturities of greater than twelve months . As of December 31,2021, the unrealized loss on the Company’s investment in US Government bonds were caused by interest rate changes and were not attributable to credit losses. The remaining contractual terms of those investments are less than a year. The Company does not intend to sell the investments and it is not more likely than not that the Company will be required to sell the investments before recovery of their amortized cost bases.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Property and Equipment	6. Property and Equipment Property and equipment, net consisted of the following: December 31 2021 2020 (in thousands) Machinery and equipment $ 15,086 $ 13,772 Computer equipment and software 1,608 1,600 Furniture and fixtures 1,054 1,024 Leasehold improvements 1,736 1,728 Construction in progress 308 252 19,792 18,376 Less: accumulated depreciation and amortization ( 13,832 ) ( 11,426 ) $ 5,960 $ 6,950 Depreciation and amortization expense was $ 2.6 million, $ 2.4 million and $ 2.5 million for the years ended December 31, 2021, 2020, and 2019, respectively.

Intangible Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	7. Intangible Assets The intangible asset is being amortized over the estimated lives of the patents which average 12 years. The amortization expense for the years ended December 31, 2021, 2020, and 2019 was $ 0.1 million, $ 0.1 million and $ 0.1 million, respectively. December 31, 2021 2020 (in thousands) Probody platform intangible asset $ 1,750 $ 1,750 Less accumulated amortization ( 729 ) ( 583 ) $ 1,021 $ 1,167

Accrued Liabilities

Accrued Liabilities	12 Months Ended
	Dec. 31, 2021
Accrued Liabilities, Current [Abstract]
Accrued Liabilities	8. Accrued Liabilities Accrued liabilities consisted of the following: December 31, 2021 2020 (in thousands) Research and clinical expenses $ 18,861 $ 10,092 Payroll and related expenses 9,576 8,362 Legal and professional expenses 1,468 815 Operating lease liabilities - short term 3,618 3,195 Other accrued expenses 713 595 Total $ 34,236 $ 23,059

Research and Collaboration Agre

Research and Collaboration Agreements	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Research and Collaboration Agreements	9. Research and Collaboration Agreements The following table summarizes the revenue by collaboration partners: Year Ended December 31, 2021 2020 2019 (in thousands) AbbVie $ 11,845 $ 38,192 $ 5,878 Amgen 8,744 8,609 3,871 Astellas 19,365 13,931 — Bristol Myers Squibb 29,619 39,630 47,740 Total revenue $ 69,573 $ 100,362 $ 57,489 AbbVie Ireland Unlimited Company In April 2016, the Company and AbbVie entered into two agreements, a CD71 Co-Development and Licensing Agreement (the “CD71 Agreement”) and a Discovery Collaboration and Licensing Agreement (as amended and restated in June 2019, the “Discovery Agreement” and together with the CD71 Agreement the “AbbVie Agreements”). Under the terms of the CD71 Agreement, the Company and AbbVie will co-develop a conditionally activated antibody-drug conjugate (“ADC”) against CD71, with the Company responsible for preclinical and early clinical development. AbbVie will be responsible for later development and commercialization, with global late-stage development costs shared between the two companies. The Company will assume 35 % of the net profits or net losses related to later development and commercialization unless it opts-out. If the Company opts-out from participation of co-development of the CD71 conditionally activated ADC, which includes CX-2029, AbbVie will have sole right and responsibility for the further development, manufacturing and commercialization of such CD71 conditionally activated ADC. Under the CD71 Agreement, the Company received an upfront payment of $ 20.0 million in April 2016, and was eligible to initially receive up to $ 470.0 million in development, regulatory and commercial milestone payments, a 35 % profit split on U.S. sales, and royalties on ex-U.S. sales at percentages in the high teens to low twenties if the Company participates in the co-development of the CD71 conditionally activated ADC subject to a reversion to a royalty on U.S. sales, and reduction in royalties on ex-U.S. sales, if the Company opts-out from the co-development of the CD71 conditionally activated ADC. The Company’s share of later stage co-development costs for each CD71 conditionally activated ADC is capped, provided that AbbVie may offset the Company’s co-development cost above the capped amounts from future payments such as milestone payments and royalties. In March 2020, the Company earned a $ 40.0 million milestone payment for satisfying the CD71 dose escalation success criteria under the CD71 Agreement. I nclusive of the 2017, 2018 and 2020 milestone payments, as of December 31, 2021, the Company has received in aggregate $ 100.0 million in milestone payments under the agreement. Under the terms of the Discovery Agreement, AbbVie receives exclusive worldwide rights to develop and commercialize conditionally activated ADCs against up to two targets, one of which was selected in March 2017. The Company shall perform research services to discover the Probody therapeutics and create conditionally activated ADCs for the nominated collaboration targets. From that point, AbbVie shall have sole right and responsibility for development and commercialization of products comprising or containing such conditionally activated ADCs (“Discovery Licensed Products”). Under the Discovery Agreement, the Company received an upfront payment of $ 10.0 million in April 2016 and subsequently earned an additional $ 10.0 million milestone payment triggered by selection of the second target by AbbVie in June 2019. The Company is also eligible to receive up to $ 265.0 million for each target, in development, regulatory and commercial milestone payments and royalties at percentages in the high single to low teens from commercial sales of any resulting conditionally activated ADCs. The second target was selected under the Discovery Agreement that allows AbbVie to select a target for developing a conditionally activated ADC or a Probody. The Company has determined that the AbbVie Agreements should be combined and evaluated as a single arrangement in determining revenue recognition, because both agreements were concurrently negotiated and executed. Therefore, the Company concluded that there are two distinct performance obligations: (1) the CD71 Agreement performance obligation consisting of the CD71 Agreement research, development and commercialization license, related research service and participation in the joint research committee, and (2) the Discovery Agreement performance obligation consisting of the Discovery Agreement research, development and commercialization license, related research service and participation in the joint research committee. The total transaction price for the Discovery Agreement and CD71 Agreement, collectively, upon adoption of ASC 606 on January 1, 2018 of $ 39.8 million consists of $ 30.0 million in upfront payments, and a $ 14.0 million milestone payment received under the CD71 Agreement (net of the payment of an associated sublicense fee of $ 1.0 million to SGEN), less $ 4.2 million of estimated sublicense fees. The upfront payments under the AbbVie Agreements were allocated between the two performance obligations based on the estimated relative standalone selling prices. The $30.0 million of upfront payments was allocated $ 20.0 million to the CD71 Agreement, with the remaining $ 10.0 million allocated to the Discovery Agreement. The $ 14.0 million milestone payment received (net of the payment of an associated sublicense fee of $ 1.0 million to SGEN) and the estimated sublicense fees of $ 4.2 million were allocated to the CD71 Agreement performance obligation as they are directly related to the development of the CX-2029. Therefore, of the $ 39.8 million total initial transaction price discussed above, the Company allocated $ 29.8 million to the CD71 Agreement performance obligation and recognized revenue using a cost-based input measure. In applying the cost-based input method, revenue is recognized based on actual FTE hours incurred as a percentage of total estimated FTE hours for completing the combined performance obligation over the estimated service period. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. During 2019, as a result of ongoing dose escalation in the continued development program, there was a change in estimate of the research service period as well as an increase in the projected FTE hours-to-completion. As of December 31, 2021, the research service period for the CD71 Agreement performance obligation was extended during the course of the arrangement from April 2021 to March 2023. The remaining $ 10.0 million of the total initial transaction price of $39.8 million allocated to the Discovery Agreement performance obligation represents an obligation to continuously make the Company’s Probody therapeutic technology platform available to AbbVie. The $ 10.0 million was initially recognized on a straight-line basis over five years , which represented the estimated research service period for the first target, through April 2021 using the time-elapsed input method. During the fourth quarter of 2020, the Company extended the estimated research service period for this first target for an additional twelve months from April 2021 to April 2022. In May 2018, the Company earned a $ 21.0 million milestone payment (net of the payment of an associated sublicense fee of $ 4.0 million to SGEN) under the CD71 Agreement. The $ 21.0 million milestone payment was included as part of the transaction price in May 2018 and a revenue adjustment of $ 9.9 million was recognized in the second quarter of 2018 reflecting the percentage completed to-date on the project related to this milestone. In June 2019, the Company earned a $ 10.0 million milestone payment for the second target selected by AbbVie under the Discovery Agreement. It is recognized also using the time-elapse measure of progress of the related obligation and straight line over the estimated research service period of five years through June 2024. The $ 40.0 million milestone payment earned in March 2020 for satisfying the CD71 dose escalation success criteria under the CD71 Agreement was unconstrained and included as part of the transaction price during the first quarter of 2020 and $ 26.6 million was recognized as revenue related to this milestone reflecting the percentage completed to-date on the project as of March 2020. The remainder is being recognized as revenue over the remaining estimated research service period through March 2023. The Company determined that the remaining potential milestone payments of both agreements, if recognized, are probable of significant revenue reversal as their achievement is highly dependent on factors outside the Company’s control. Therefore, these payments continue to be fully constrained and are not included in the transaction price as of December 31, 2021. As of December 31, 2021 and 2020, deferred revenue related to the CD71 Agreement performance obligation was $ 16.1 million and $ 25.2 million, respectively, and deferred revenue related to the Discovery Agreement performance obligation was $ 5.2 million and $ 8.0 million, respectively. Amgen, Inc. On September 29, 2017, the Company and Amgen, Inc. (“Amgen”) entered into a Collaboration and License Agreement (the “Amgen Agreement”). Pursuant to the Amgen Agreement, the Company received an upfront payment of $ 40.0 million in October 2017. Concurrent with the Amgen Agreement, the Company and Amgen entered into a Share Purchase Agreement pursuant to which Amgen purchased 1,156,069 shares of the Company’s common stock at a price of $ 17.30 per share for total proceeds of $ 20.0 million . In October 2021, CytomX and Amgen executed an amendment to the Amgen Agreement primarily to (1) extend the target selection date for Amgen to select its additional targets for research and development, and (2) reduce the total number of milestone events and increase the total amount of milestone payments for EGFR Products. Under the terms of the Amgen Agreement, as amended, the Company and Amgen will co-develop a conditionally activated T-cell engaging bispecific therapeutic targeting epidermal growth factor receptor (the “EGFR Products”). The Company is responsible for early-stage development of EGFR Products and Amgen will be responsible for late-stage development and commercialization of EGFR Products. Following early-stage development, the Company will have the right to elect to participate financially in the global co-development of EGFR Products with Amgen, during which the Company would bear certain of the worldwide development costs for EGFR Products and Amgen would bear the rest of such costs (the “EGFR Co-Development Option”). If the Company exercises its EGFR Co-Development Option, the Company will share in somewhat less than 50 % of the profit and losses from sales of such EGFR Products in the U.S., subject to certain caps, offsets, and deferrals. If the Company chooses not to exercise its EGFR Co-Development Option, the Company will not bear any costs of later stage development. The Company is also eligible to receive up to $ 460.0 million in development, regulatory, and commercial milestone payments for EGFR Products, and royalties in the low-double-digit to mid-teen percentage of worldwide commercial sales, provided that if the Company exercises its EGFR Co-Development option, it shall receive a profit and loss split of sales in the United States and royalties in the low-double-digit to mid-teen percentage of commercial sales outside of the United States. Amgen also has the right to select a total of up to three targets, including the two additional targets discussed below. The Company and Amgen collaborate in the research and development of conditionally activated T-cell engaging bispecifics products directed against such targets. Amgen has selected one such target (the “Amgen Other Product”). If Amgen exercises its option within a specified period of time, it can select two such additional targets (the “Amgen Option Products” and, together with the Amgen Other Product, the “Amgen Products”). Except with respect to preclinical activities to be conducted by CytomX, Amgen will be responsible, at its expense, for the development, manufacture, and commercialization of all Amgen Products. If Amgen exercises all of its options and advances all three of the Amgen Products, CytomX was initially eligible to receive up to $ 950.0 million in upfront, development, regulatory, and commercial milestones and tiered high single-digit to low-teen percentage royalties. The Company concluded that, at the inception of the agreement, Amgen’s option to select the two additional targets is not a material right and does not represent a performance obligation of the agreement. At the initiation of the collaboration, CytomX had the option to select, from programs specified in the Amgen Agreement, an existing preclinical stage T-cell engaging bispecific product from the Amgen preclinical pipeline. In March 2018, CytomX selected the program. CytomX is responsible, at its expense, for converting this program to a conditionally activated T-cell engaging bispecific product, and thereafter, will be responsible for development, manufacturing, and commercialization of the product (“CytomX Product”). Amgen is eligible to receive up to $ 203.0 million in development, regulatory, and commercial milestone payments for the CytomX Product, and tiered mid-single digit to low double-digit percentage royalties. The Company considered the criteria for combining contracts in ASC 606 and determined that the Amgen Agreement and the Purchase Agreement should be combined into one contract. The Company accounted for the Amgen Agreement based on the fair values of the assets and services exchanged. The Company identified the following promised goods and services at the inception of the Amgen Agreement: (1) the research, development and commercialization license, (2) the research and development services for the EGFR Products and the Amgen Other Product, and (3) the obligation to participate in the joint steering committee (“JSC”) and the joint research committee (“JRC”). For each of the EGFR Products and the Amgen Other Products, the Company determined that the respective promised goods and services identified are not distinct from the related research and development services. Therefore the identified promised goods and services were combined into one single performance obligation for each of the EGFR Product and the Amgen Other Products. Furthermore, the Amgen Other Products are accounted for as a separate performance obligation from the EGFR Products as the nature of the services being performed is not the same and the value that Amgen can derive from one program is not dependent on the success of the other. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Concurrent with the execution of the Amgen Agreement, the Company entered into a sublicense agreement whereby the Company granted Amgen a sublicense of its rights to one patent family that it co-owns with UCSB, that is exclusively licensed to the Company under the UCSB Agreement covering Probody antibodies and other pro-proteins in the fields of therapeutics, in vivo diagnostics and prophylactics. This sublicense was incremental to the patents, patent applications and know-how covering conditionally activated T-cell engaging bispecific molecules that were developed and owned by the Company and licensed to Amgen. Under the UCSB Agreement, as amended, the Company is obligated to make a sublicense payment to UCSB equal to up to 7.5 % of certain upfront and milestone payments owed to or received by the Company. The total transaction price of $ 51.2 million, consisting of the $ 40.0 million upfront payment, an estimated fair value of $ 10.7 million for the CytomX Product and $ 0.5 million of premium on the sale of the Company’s common stock, was allocated between the two performance obligations based on the relative standalone selling price of each performance obligation. To determine the standalone selling price, the Company used the discounted cash flow method by calculating risk-adjusted net present values of estimated cash flows. The Company determined that the remaining potential milestone payments were fully constrained due to the uncertainty in achieving them as of December 31, 2021. Of the $ 51.2 million total transaction price, the Company allocated $ 46.4 million to the EGFR Products performance obligation and $ 4.8 million to the Amgen Other Product performance obligations. The transaction price of the EGFR Product performance obligation was recognized using a cost-based input measure. In applying the cost-based input method of revenue recognition, the Company uses actual FTE hours incurred relative to estimated total FTE hours expected to be incurred for the combined performance obligation over the research service period. At the end of the second quarter of 2019, the Company determined that it will undertake additional testing and assessment of the molecules being evaluated under the EGFR project. As a result, the estimated FTE hours-to-completion and research service period were increased to eight years . In the second quarter of 2020, the Company completed the clinical candidate characterization phase and has moved into the IND-enabling phase earlier than planned. As a result, the estimated FTE hours-to-completion and research service period were decreased from eight to approximately seven years . The $ 4.8 million transaction price allocated to the Amgen Other Product performance obligation represents an obligation to continuously make the Probody therapeutic technology platform available to Amgen, which is recognized over the common measure of progress for the entire performance obligation over the estimated research service period of six years . As of December 31, 2021 and 2020 deferred revenue related to the EGFR Products performance obligation was $ 21.8 million and $ 29.8 million, respectively. As of December 31, 2021 and 2020, deferred revenue related to the Amgen Other Products performance obligation was $ 1.4 million and $ 2.2 million, respectively. Astellas Pharma Inc. The Company and Astellas Pharma, Inc. (“Astellas”) entered into a Collaboration and License Agreement (the “Astellas Agreement”) on March 23, 2020, the effective date, to collaborate on preclinical research activities to discover and develop certain antibody compounds for the treatment of cancer using the Company’s Probody therapeutic technology. Under the terms of the Astellas Agreement, the Company granted Astellas an exclusive, worldwide right to develop and commercialize Probody therapeutics for up to four collaboration targets including one initial target and three additional targets (“Additional Targets”). In addition, Astellas has the right to expand the number of Additional Targets from three up to five (the “Expansion Option”) before the third anniversary of the effective date. Furthermore, for a specified number of targets, at a pre-specified time prior to the initiation of the first pivotal study of a product against such target, the Company may elect to participate in certain development costs and share in the profits generated in the United States with respect to such product (“Cost Share Option”). The Cost Share Option, if exercised, will also provide the option for the Company to co-commercialize such product in the United States. The Company does not consider the Cost Share Option as a performance obligation at the inception of the agreement as the participation is at the Company’s discretion. Pursuant to the Astellas Agreement, the consideration from Astellas is comprised of an upfront fee of $ 80.0 million and contingent payments for development, regulatory and sales milestones of up to an aggregate of approximately $ 1.6 billion. If Astellas exercises its Expansion Option for the two Additional Targets, the Company would be eligible to receive additional upfront and milestone payments aggregating to approximately $ 0.9 billion. The Company is also entitled to tiered royalties from high-single digit to mid-teen percentage royalties from potential future sales. Astellas is responsible for all preclinical research costs incurred by either party as set forth in the preclinical research plan and the Company will receive research and development service fees based on a prescribed FTE rate. The Company determined that the license and expertise related to the development of the product candidates should be combined with the research and development services and participation in the joint research committee as one combined performance obligation. The Company concluded, that at the inception of the agreement, Astellas’ Expansion Option for two Additional Targets were not material rights and therefore not considered performance obligations. As such, each option will be accounted for as a separate arrangement upon exercise. The initial transaction price of $ 90.0 million consists of the upfront fee of $ 80.0 million and research and development service fees of $ 10.0 million. The Company determined that all potential milestone payments are constrained as of December 31, 2021 due to the significant uncertainty of achievement. The upfront fee of $ 80.0 million for the combined obligation to continuously make the Probody therapeutic technology platform available to Astellas is recognized on a straight-line basis for the entire performance obligation over the estimated research service period of five years , which ends in March 2025 . The research and development service fees, estimated to be $ 10.0 million, will be recognized when services are provided based on the prescribed FTE rate. As of December 31, 2021 and 2020, deferred revenue relating to the Astellas Agreement was $ 51.6 million and $ 67.6 million, respectively. The amount due from Astellas under the Astellas Agreement was $ 0.8 million and $ 0.8 million as of December 31, 2021 and 2020, respectively. Bristol Myers Squibb Company On May 23, 2014, the Company and Bristol Myers Squibb Company (“Bristol Myers Squibb”) entered into a Collaboration and License Agreement (the “BMS Agreement”) to discover and develop compounds for use in human therapeutics aimed at multiple immuno-oncology targets using the Company’s Probody therapeutic technology. The effective date of the BMS Agreement was July 7, 2014. Under the terms of the BMS Agreement, the Company granted Bristol Myers Squibb exclusive worldwide rights to develop and commercialize Probody therapeutics for up to four oncology targets. Bristol Myers Squibb had additional rights to substitute up to two collaboration targets within three years of the effective date of the BMS Agreement. These rights expired in May 2017. Each collaboration target had a two-year research term and the two additional targets had to be nominated by Bristol Myers Squibb within five years of the effective date of the BMS Agreement. The research term for each collaboration target could be extended in one year increments up to three times. Pursuant to the BMS Agreement, the financial consideration from Bristol Myers Squibb was comprised of an upfront payment of $ 50.0 million, and the Company was initially entitled to receive contingent payments of up to $ 25.0 million for additional targets and up to an aggregate of $ 1,192.0 million for development, regulatory and sales milestones. In addition, the Company was entitled to royalty payments in the mid-single digits to low double-digit percentages from potential future sales. The Company also received research and development service fees based on a prescribed FTE rate that was capped. The Company identified the following promised goods and services at the inception of the BMS Agreement: (1) the exclusive research, development and commercialization license; (2) the research and development services; and (3) the obligation to participate in the joint research committee. The Company determined that the license, the Company’s research services and expertise related to the development of the product candidates should be combined with the research services and participation in the joint research committee as one combined performance obligation. Additionally, the Company considered whether the services performed for each of the two targets selected under the BMS Agreement should be considered as separate performance obligations and concluded that both targets should be accounted for as one combined stand-ready performance obligation. The Company also concluded that, at the inception of the agreement, Bristol Myers Squibb’s options for the third and fourth targets were not material rights and not performance obligations. As such, each option was accounted for as a separate arrangement upon exercise. The Company received an upfront payment of $50.0 million from Bristol Myers Squibb in July 2014. In January and December 2016, Bristol Myers Squibb exercised the option to select the third and fourth targets, and paid the Company $ 10.0 million and $ 15.0 million, respectively, pursuant to the terms of the BMS Agreement. In December 2016, Bristol Myers Squibb selected a clinical candidate pursuant to the BMS Agreement, which triggered a $ 2.0 million pre-clinical milestone payment to the Company. In November 2017, the Company recognized a $ 10.0 million milestone payment from Bristol Myers Squibb upon approval of the investigational new drug application for the CTLA-4-directed Probody therapeutic. On March 17, 2017, the Company and Bristol Myers Squibb entered into Amendment Number 1 to Extend Collaboration and License Agreement (“Amendment 1”). Amendment 1 granted Bristol Myers Squibb exclusive worldwide rights to develop and commercialize Probody therapeutics for up to eight additional targets. The effective date of Amendment 1 was April 25, 2017 (“Amendment Effective Date”). Under the terms of Amendment 1, the Company continued to have obligations to Bristol Myers Squibb to discover and conduct preclinical development of Probody therapeutics against any targets they chose to select during the research period under the terms of Amendment 1. Pursuant to Amendment 1, the financial consideration from Bristol Myers Squibb was comprised of an upfront payment of $ 200.0 million and the Company was initially eligible to receive contingent payments for development, regulatory and sales milestones of up to an aggregate of $ 3,586.0 million for the eight targets. The Company was also entitled to tiered mid-single to low double-digit percentage royalties from potential future sales. Amendment 1 did not change the term of the Bristol Myers Squibb’s royalty obligation under the BMS Agreement. Bristol Myers Squibb’s royalty obligation continues on a licensed-product by licensed-product basis until the later of (i) the expiration of the last claim of the licensed patents covering the licensed products in the country, (ii) the twelfth anniversary of the first commercial sale of a licensed product in a country, or (iii) the expiration of any applicable regulatory, pediatric, orphan drug or data exclusivity with respect to such product. The initial transaction price for the BMS Agreement and Amendment 1, collectively, was $ 272.8 million consisting of the upfront fees of $ 250.0 million, research and development service fees of $ 10.8 million and milestone payments received to date of $ 12.0 million. The Company determined that the remaining potential milestone payments were probable of significant revenue reversal as their achievement was highly dependent on factors outside the Company’s control. Therefore, these payments were fully constrained and were not included in the transaction price upon the adoption of ASC 606 on January 1, 2018. The BMS Agreement represents an obligation to continuously make the Probody therapeutic technology platform available to Bristol Myers Squibb. Therefore, the initial transaction price is recognized over the estimated research service period, which ends on April 25, 2025 . During the first quarter of 2019, Bristol Myers Squibb terminated pre-clinical activities on three of the first four collaboration targets selected under the original 2014 BMS Agreement. The first and second targets under the BMS Agreement were combined into a single performance obligation. The Company determined that termination of pre-clinical activities on the second target does not impact the Company’s continuing obligation to Bristol Myers Squibb for the first target, CTLA-4, as it is still being actively developed by Bristol Myers Squibb. Therefore, the Company concluded that it will continue to amortize the related deferred revenue over the original performance period. The Company has determined that upon the termination of pre-clinical activities on the third and the fourth collaboration targets selected by Bristol Myers Squibb in January and December of 2016, respectively, under the BMS Agreement, it has no further obligations. As a result of termination of three of the four collaboration targets, the Company is no longer eligible to receive up to an aggregate of $ 894.0 million contingent payments for development, regulatory and sales milestones as well as the related royalty payments for such targets. As a result, the Company recognized $ 18.1 million of revenue for the third and fourth targets in the first quarter of 2019, of which $ 17.4 million represented the accelerated recognition of all of the related deferred revenue upon the effective date of termination. The Company continues to be obligated to perform research work under Amendment 1 executed in March 2017. In February 2020, Bristol Myers Squibb dosed the first patient in the Part 2 cohort expansion portion of its ongoing BMS-986249 clinical study for the CTLA-4 program, which triggered a $ 10.0 million milestone payment to the Company pursuant to the terms of the BMS Agreement. The $ 10.0 million milestone payment was recognized as revenue in the first quarter of 2020. In February 2021, the Company and Bristol Myers Squibb entered into Amendment Number 2 to amend the Collaboration and License Agreement (“Amendment 2”), as amended by Amendment 1. Subsequent to Amendment 2, Bristol Myers Squibb has the exclusive worldwide rights to develop and commercialize Probody therapeutics for up to five oncology targets. Under the terms of Amendment 2, the period for target selection has been extended and the Company will continue to collaborate with Bristol Myers Squibb to discover and conduct preclinical development of Probody therapeutics against targets selected by Bristol Myers Squibb over the estimated research period, which ends in April 2025. Pursuant to Amendment 2, the Company is eligible to receive contingent payments for development, regulatory and sales milestones of up to an aggregate of $ 1,779.0 million. It is also entitled to tiered mid-single to low double-digit percentage of royalties from potential future sales. In addition, the Company will no longer be entitled to receive the research and development service fee as part of the arrangement. The Company reevaluated the remaining potential milestone payments and determined that significant revenue reversal was still probable as the achievement of such milestones was highly dependent on factors outside the Company’s control. As a result, these payments continued to be fully constrained and were not included in the transaction price on December 31, 2021. As of December 31, 2021 and 2020, deferred revenue relating to the BMS Agreement was $ 98.8 million and $ 128.3 million, respectively. ImmunoGen, Inc. In January 2014, the Company and ImmunoGen, Inc. (“ImmunoGen”) entered into the Research Collaboration Agreement (the “ImmunoGen Research Agreement”). The ImmunoGen Research Agreement provided the Company with the right to use ImmunoGen’s Antibody Drug Conjugate (“ADC”) technology in combination with the Company’s Probody therapeutic technology to create a conditionally activated ADC directed at one specified target under a research license, and to subsequently obtain an exclusive, worldwide development and commercialization license to use ImmunoGen’s ADC technology to develop and commercialize such conditionally activated ADCs. The Company made no upfront cash payment in connection with the execution of the agreement. Instead, the Company provided ImmunoGen with the rights to CytomX’s Probody therapeutic

License Agreement

License Agreement	12 Months Ended
	Dec. 31, 2021
Research and Development [Abstract]
License Agreement	10. License Agreement UCSB The Company has an exclusive, worldwide license agreement with UCSB (the “UCSB Agreement”), relating to the use of certain patents and technology relating to its core technology, including its therapeutic antibodies, and to certain patent rights the Company co-owns with UCSB covering Probody antibodies and other pro-proteins. Pursuant to the UCSB Agreement, the Company is obligated to (i) make royalty payments to UCSB on net sales of its products covered under the agreement, subject to annual minimum amounts, (ii) make milestone payments to UCSB upon the occurrence of certain events, (iii) make a milestone payment to UCSB upon occurrence of an IPO or change of control, and (iv) reimburse UCSB for prosecution and maintenance of the licensed patents. If the Company sublicenses its rights under the UCSB Agreement, it is obligated to pay UCSB a percentage of the total sublicense revenue received, which total amount would be first reduced by the aggregate amount of certain research and development related expenses incurred by the Company and other permitted deductions. As part of the UCSB Agreement, the Company has annual minimum royalty obligations of $ 0.2 million under the terms of certain exclusive licensed patent rights. The royalty obligations are cancellable any time by giving notice to the licensor, with the termination being effective 60 days after giving notice. In April 2019, the Company entered into Amendment No.3 to the UCSB Agreement to adjust and clarify certain sublicense terms (“Amendment No.3”). In connection with the amendment, the Company issued to UCSB 150,000 shares of CytomX common stock with a fair value of $ 10.68 per share. Under the terms of Amendment No.3, the Company and UCSB agreed to modify the determination of sublicense revenues payable by the Company to UCSB on certain existing collaboration agreements and on collaboration agreements executed subsequent to Amendment No.3. In exchange, the Company agreed to make an upfront payment of $ 1.0 million as well as additional annual license maintenance fees of $ 0.8 million through 2031 . In the event that the Company terminates the agreement due to material concern of the safety or efficacy of the related technology, 50 % of all remaining maintenance fees will become due immediately. Otherwise, all remaining maintenance fees will become due immediately upon early termination of the agreement unless there is a material breach by UCSB. Pursuant to Amendment No.3, the Company recorded in research and development expense a charge of $ 3.4 million relating to sublicense and maintenance fees representing the 150,000 shares issued with a fair value of $ 1.6 million, the upfront payment of $ 1.0 million and the additional annual maintenance fee of $ 0.8 million during the second quarter of 2019. In June 2019, the Company incurred an additional $ 0.8 million of sublicense fees related to the $ 10.0 million milestone payment for the second target selected by AbbVie under the Discovery Agreement. In February 2020, the Company recorded $ 0.8 million of sublicense fees triggered by the $ 10.0 million milestone payment from Bristol Myers Squibb’s dosing of the first patient in the Part 2 cohort expansion portion of its ongoing BMS-986249 clinical study for the CTLA-4 program. In March 2020, the Company incurred additional sublicense fees of $ 6.0 million related to the $ 80.0 million upfront fee received pursuant to the Astellas Agreement entered into in March 2020, and $ 1.4 million related to the $ 40.0 million milestone payment from AbbVie for satisfying the CD71 dose escalation success criteria under the CD71 Agreement in March 2020. During the years ended December 31, 2021, 2020, and 2019, the Company incurred sublicense expenses of $ 1.0 million, $ 9.1 million, and $ 4.3 million, respectively, under the provisions of the UCSB Agreement. ImmunoGen In December 2019, the Company entered into a License Agreement (the “ImmunoGen 2019 License”) with ImmunoGen, Inc. to obtain an exclusive license with respect to epithelial cell adhesion molecule (“EPCAM”). Under the ImmunoGen 2019 License, ImmunoGen agreed to transfer its know-how, patents, intellectual property rights, and technology transfer materials and information related to its EpCAM program. The license gives the Company the sole ability to develop, manufacture, use and commercialize any licensed product that incorporates, is comprised of, or otherwise derived from a Probody that targets EpCAM in any human therapeutic field on a worldwide basis. In exchange, the Company agreed to make non-refundable and non-creditable payments including an upfront license payment of $ 7.5 million and certain clinical development, approval and commercialization milestone payments, if achieved and royalties on product sales. The upfront license fee of $ 7.5 million was recorded as research and development expense in December 2019.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and Contingencies Legal Proceedings On March 4, 2020 , Vytacera Bio, LLC filed a patent infringement lawsuit against the Company in the U.S. District Court for the District of Delaware. The lawsuit alleges that the Company's use, offers to sell, and/or sales of the Probody® technology platform for basic research applications constitutes infringement. The complaint seeks unspecified monetary damages. The Company filed an Answer, Affirmative Defenses, and Counterclaims on May 26, 2020 . Vytacera Bio, LLC filed its Answer to CytomX Therapeutics Inc.’s Counterclaims on June 5, 2020 . On October 13, 2021, the Court granted the parties’ stipulation to stay all pending case deadlines except for certain matters. All case deadlines are stayed until the Court resolves the parties’ claim construction disputes. The Company believes that the lawsuit is without merit and intends to vigorously defend itself , and has no t recorded any amount for claims associated with this lawsuit as of December 31, 2021. Indemnifications In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has never incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. The Company has also entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by Delaware corporate law. The Company currently has directors’ and officers’ insurance.

Leases

Leases	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Leases	12. Leases Operating Lease In December 2015, the Company entered into a lease (the “2016 Lease”) of office and laboratory space located in South San Francisco, California for the Company’s corporate headquarters. The 2016 Lease has an initial term of ten years through 2026 and the Company has an option to extend the initial term for an additional five years at the then fair rental value as determined pursuant to the 2016 Lease. In addition, the Company obtained a standby letter of credit (the “Letter of Credit”) in an amount of approximately $ 0.9 million, which may be drawn by the Landlord to be applied for certain purposes upon the Company’s breach of any provisions under the 2016 Lease. The Company has recorded the $ 0.9 million of cash securing the Letter of Credit as non-current restricted cash on its balance sheet as of December 31, 2021 and 2020. Rent expense during the years ended December 31, 2021, 2020, and 2019 was $ 5.1 million, $ 5.1 million and $ 4.8 million, respectively. Supplemental information related to leases are as follows: Year Ended December 31, 2021 December 31, 2020 (in thousands) Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating leases $ 5,129 $ 4,990 December 31, 2021 December 31, 2020 (in thousands) Supplemental balance sheet information related to leases: Operating lease right-of-use assets $ 19,362 $ 22,495 Current operating lease liabilities 3,618 3,195 Non-current operating lease liabilities 18,056 21,675 Total operating lease liabilities $ 21,674 $ 24,870 Weighted-average remaining lease term (in years) Operating lease 4.75 5.75 Weighted-average discount rate Operating lease 8.25 % 8.25 % December 31, 2021 (in thousands) Maturity of operating lease liabilities 2022 5,273 2023 5,420 2024 5,572 2025 5,729 2026 and beyond 4,387 Total lease payments 26,381 Less imputed interest ( 4,707 ) Present value of lease liabilities $ 21,674

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
Common Stock	13. Common Stock In February 2020, the Company entered into an Open Market Sale Agreement (the “Sales Agreement”) with Jefferies LLC (“Jefferies”), to sell shares of the Company’s common stock, par value $ 0.00001 per share, with aggregate gross sales proceeds of up to $ 75,000,000 , from time to time upon the Company’s request, through an at the market offering under which Jefferies will act as sales agent. Pursuant to the Sales Agreement, Jefferies as the sales agent will receive a commission of 3.0 % of the gross sales price for shares of common stock sold under the Sales Agreement. During December 2020, the Company sold 1,535,217 shares at an average price of $ 7.62 per shares and received net proceeds of approximately $ 11.3 million after deducting the 3.0 % sales commission and related issuance cost. In January 2021, the Company completed an underwritten public offering of 14,285,714 shares of common stock at a price of $ 7.00 per share. The aggregate net proceeds received by the Company from the offering were approximately $ 93.6 million, after deducting underwriting discounts and commissions and offering expenses of $ 6.4 million. The Company also granted the underwriters the option for 30 days to purchase up to 2,142,857 additional shares of common stock at the public offering price, less the underwriting discounts and commissions. In February 2021, the underwriters exercised the option in full which resulted in additional net proceeds of $ 14.1 million to the Company, after deducting the underwriting discounts and commissions of $ 0.9 million.

Stock-based Compensation

Stock-based Compensation	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Stock-based Compensation	14. Stock-based Compensation The 2010 Plan and 2011 Plan In 2010, the Company adopted its 2010 Stock Incentive Plan (the “2010 Plan”) which provided for the granting of stock options to employees, directors and consultants of the Company. Options granted under the 2010 Plan were either incentive stock options (“ISOs”) or nonqualified stock options (“NSOs”). In February 2012, the Company adopted its 2011 Stock Incentive Plan (the “2011 Plan”). The 2011 Plan is divided into two separate equity programs, an option and stock appreciation rights grant program and a stock award program. In conjunction with adopting the 2011 Plan, the Company discontinued the 2010 Plan and released the shares reserved and still available under that plan. In connection with the consummation of the IPO in October 2015, the board of directors adopted the Company’s 2015 Equity Incentive Plan (the “2015 Plan” and collectively with the 2010 Plan and 2011 Plan, the “Plans”). In conjunction with adopting the 2015 Plan, the Company discontinued the 2011 Plan with respect to new equity awards. The 2015 Plan The 2015 Plan authorized the board of directors to grant incentive stock options, non-statutory stock options and RSUs to employees, directors, non-employee directors and consultants of the Company. Sto ck options under the 2015 Plan may be granted for periods of up to ten years . All stock options issued to date have had a 10 -year life. Under the terms of the 2015 Plan, stock options may be granted at an exercise price not less than the estimated fair value of the Company’s common stock on the date of grant, as determined by the Company’s board of directors. For employees holding more than 10 % of the voting rights of all classes of stock, the exercise price of ISOs and NSOs may not be less than 110 % of the estimated fair value of the shares on the date of grant, as determined by the board of directors. To date, stock options granted under the 2015 Plan generally vest over four years and vest at a rate of 25 % upon the first anniversary of the issuance date and 1/48 th per month thereafter. The initial number of shares of common stock available for future issuance under the 2015 Plan was 2,444,735 . Beginning on January 1, 2016 and continuing until the expiration of the 2015 Plan, the total number of shares of common stock available for issuance under the 2015 Plan will automatically increase annually on January 1 by 4 % of the total number of issued and outstanding shares of common stock as of January 1 of the same year. As of December 31, 2021 and 2020, 2,276,341 shares and 2,698,798 shares of common stock, respectively, were available for future issuance under the 2015 Plan. The 2019 Plan In September 2019, the Board of Directors adopted the 2019 Employment Inducement Incentive Plan (the “2019 Plan”) which provides for the grant of stock options and other equity awards to any employee who has not previously been an employee or director of the Company or who is commencing employment with the Company following a bona fide period of nonemployment by the Company. Awards granted under the 2019 Plan are intended to constitute “employment inducement awards” under Nasdaq Listing Rule 5635(c)(4). Options granted under the 2019 Plan are nonqualified stock options (“NSOs”) which may be exercisable for periods of up to ten years and the options shall be granted at an exercise price of not less than 100 % of the fair market value of the Company’s common stock on the date of grant. The initial number of shares of common stock available for future issuance under the 2019 Plan was 1,815,000 . During 2021, t he total number of shares of common stock available for issuance under the 2019 Plan has increased by 1,000,000 shares. As of December 31, 2021 and 2020, 486,234 shares and 204,600 shares, respectively, of common stock were available for future issuance under the 2019 Plan. Activity under the Company’s stock option plans is set forth below: Options Outstanding Number of Weighted- Weighted- Aggregate (in thousands) Balances at December 31, 2020 10,929,530 $ 10.77 Options granted 5,178,897 7.10 Options exercised ( 528,503 ) 2.70 Options cancelled ( 3,387,708 ) 11.26 Balances at December 31, 2021 12,192,216 9.42 7.5 $ 1,182 Options Exercisable—December 31, 2021 6,054,635 11.46 6.1 $ 1,155 The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the quoted market price of the underlying common stock as of December 31, 2021. The aggregate intrinsic value of stock options exercised in the years ended December 31, 2021, 2020, and 2019 was $ 2.2 million, $ 4.4 million, and $ 0.9 million, respectively. The options granted in the years ended December 31, 2021, 2020, and 2019 had weighted-average per share grant-date fair values of $ 3.97 , $ 3.94 , and $ 7.03 respectively. As of December 31, 2021, the unrecognized compensation expense with respect to options granted was $ 23.6 million and is expected to be recognized over 2.9 years. Early Exercise of Employee Options Certain stock options granted under the Plans provide option holders the right to elect to exercise unvested options in exchange for restricted common stock. Such unvested restricted shares are subject to a repurchase right held by the Company at the original issuance price in the event the optionee’s service to the Company is terminated either voluntarily or involuntarily. The right usually lapses 25 % on the first anniversary of the vesting start date and in 36 equal monthly amounts thereafter. These repurchase terms are considered to be a forfeiture provision. The cash or full recourse notes received from employees for exercise of unvested options is treated as a refundable deposit and is classified as a liability on the balance sheets. Time-based RSUs ("TRSU") and Performance-based RSUs ("PSU") In October 2021, the Company granted 439,000 TRSUs as recognition awards to certain employees with an aggregated grant fair value of $ 2.3 million. 50% of the RSUs granted will vest at the end of the first year of the grant date and the remaining 50% will vest at the end of the second year provided the grantee continues to provide services to the Company. The Company recorded $ 0.2 million of stock-based compensation expense related to the TRSUs for the year end December 31, 2021. In conjunction with the TRSU grants, the Company also granted 435,000 performance-based RSUs (“PSUs”) as recognition awards to executive employees with an aggregated grant date fair value of $ 2.3 million. 50% of the PSUs granted will vest within one year of the grant date upon achievement of certain specific milestones and the remaining 50% will vest within two years of the grant date upon achievement of additional company objectives. As of December 31, 2021, the Company determined that it is not probable that the performance conditions will be satisfied and hence recorded no compensation cost for these awards as of and for the year ended December 31, 2021. As of December 31, 2021, the unrecognized compensation expense with respect to the TRSUs was $ 2.1 million which is expected to be recognized over 1.6 years. The fair value of RSUs, including time-based RSUs and performance-based RSUs is based on the market price of the Company's shares on the date of grant. The following table summarizes the Company's RSU activities: Number of Weighted- Aggregate Weighted Average Grant Date Fair Value (in thousands) (in thousands) Balances at December 31, 2020 — $ - RSU's awarded 874,000 5.34 RSU's vested — - RSU's cancelled ( 5,750 ) 5.34 Balances at December 31, 2021 868,250 1.31 $ 3,760 5.34 Ending Exercisable—December 31, 2021 - - $ - $ - Employee Stock Purchase Plan Concurrent with the completion of the IPO in October 2015, the Company’s Employee Stock Purchase Plan (“ESPP”) became effective. The ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15 % of their eligible compensation, subject to any plan limitations. The ESPP generally provides for six-month offering periods, and at the end of each offering period, employees are able to purchase shares at 85 % of the lower of the fair market value of the Company’s common stock on the first trading day of the offering period or on the last trading day of the offering period. The Company issued 183,865 shares and 128,684 shares of common stock under the ESPP in 2021 and 2020, respectively. Shares available for future purchase under the ESPP were 1,751,818 shares and 1,935,683 shares at December 31, 2021 and 2020, respectively. The compensation expense related to the ESPP was $ 0.4 million, $ 0.4 million, and $ 0.6 million for the years ended December 31, 2021, 2020 and 2019, respectively. As of December 31, 2021, there was $ 0.2 million of unrecognized compensation cost related to the ESPP, which the Company expects to recognize over 5 months. Stock Based Compensation Total stock-based compensation recorded related to options granted to employees and non-employees and employee stock purchase plan was as follows (in thousands): Year Ended December 31, 2021 2020 2019 Research and development $ 5,797 $ 6,825 $ 9,226 General and administrative 7,370 7,961 9,874 Total stock-based compensation expense $ 13,167 $ 14,786 $ 19,100 Stock-based compensation expense for employees was $ 13.1 million, $ 14.7 million, and $ 18.9 million for the years ended December 31, 2021, 2020, and 2019, respectively. Stock-based compensation expense for non-employees was $ 0.1 million, $ 0.1 million, and $ 0.2 million for the years ended December 31, 2021, 2020, and 2019, respectively. The Company estimated the fair value of employee stock options and ESPP using the Black-Scholes valuation model based on the date of grant with the following assumptions: Options ESPP Year Ended December 31, Year Ended December 31, 2021 2020 2019 2021 2020 2019 Expected volatility 69.6 % - 74.8 % 64.4 % - 73.3 % 64.4 % - 68.6 % 46.87 % - 69.58 % 47.3 % - 122.1 % 60.8 % - 71.9 % Risk-free interest rate 0.5 % - 1.3 % 0.2 % - 1.3 % 1.4 % - 2.5 % 0.04 % - 0.10 % 0.1 % - 0.2 % 1.6 % - 2.4 % Dividend yield — % — % — % — % — % — % Expected term 4.5 - 4.8 4.7 - 4.9 4.9 - 5.0 0.5 0.5 0.5 Expected term. The expected term of stock options represents the period that the stock options are expected to remain outstanding and is based on vesting terms, exercise term and contractual lives of the options. The expected term of the ESPP shares is equal to the six-month look-back period. Expected volatility. The expected stock price volatility for the Company’s stock options is based on the historical stock price volatility which is commensurate with the estimated expected term of the stock awards. Volatility for ESPP shares is equal to the Company’s historical volatility over a six-month offering period. Risk-free interest rate. The risk-free interest rate is based on the U.S. Treasury yield with a maturity equal to the expected term of the stock options in effect at the time of grant. Dividend yield. The expected dividend is assumed to be zero as the Company has never paid dividends and has no current plan to pay any dividends on its common stock.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	15. Inco me Taxes The Company derives its income only from the United States. The components of the benefit from income taxes are as follows (in thousands): Years Ended December 31, 2021 2020 2019 Current: Federal $ — $ ( 13,912 ) $ ( 390 ) State — 1 — Total current — ( 13,911 ) ( 390 ) Deferred: Federal — — ( 37 ) State — — — Total deferred — — ( 37 ) Benefit from income taxes $ — $ ( 13,911 ) $ ( 427 ) A reconciliation of the Company’s effective tax rate to the statutory U.S. federal rate is as follows: Years Ended December 31, 2021 2020 2019 U.S. federal taxes at statutory rate 21.0 % 21.0 % 21.0 % State tax, net of federal benefit 2.1 % 3.3 % 1.3 % Stock compensation ( 4.3 )% ( 2.2 )% ( 1.2 )% Tax credits 2.8 % 11.0 % 2.5 % Change in valuation allowance ( 21.6 )% ( 31.2 )% ( 22.8 )% Net operating loss carryback 0.0 % 27.9 % 0.0 % Return to provision adjustment 0.0 % 0.0 % ( 0.3 )% Other 0.0 % ( 0.1 )% ( 0.1 )% Total 0.0 % 29.7 % 0.4 % The types of temporary differences that give rise to significant portions of the Company’s deferred income tax assets and liabilities are set out below (in thousands): Year Ended December 31, 2021 2020 Net operating loss carryforwards $ 49,186 $ 37,099 Research and development credits 20,809 16,803 Lease liability 4,555 5,223 Intangible assets 3,804 3,923 Deferred revenue 41,291 38,832 Accrued liabilities 1,933 1,512 Stock-based compensation 7,480 8,578 Other 29 20 Total gross deferred income tax assets 129,087 111,990 Less: valuation allowance ( 124,477 ) ( 106,448 ) Deferred tax assets, net of valuation allowance 4,610 5,542 Fixed assets ( 253 ) ( 433 ) Right-of-use assets ( 4,069 ) ( 4,724 ) Prepaid expenses ( 288 ) ( 385 ) Deferred tax liabilities ( 4,610 ) ( 5,542 ) Net deferred income tax liabilities $ — $ — On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (“CARES Act”) was enacted in response to the COVID-19 pandemic. The tax relief measures under the CARES Act for businesses include a five-year net operating loss carryback, suspension of annual deduction limitation of 80 % of taxable income from net operating losses generated in a tax year beginning after December 31, 2017, changes in the deductibility of interest, acceleration of alternative minimum tax credit refunds, payroll tax relief, and a technical correction to allow accelerated deductions for qualified improvement property. The Company recognized income tax benefit of $ 13.9 million for the year ended December 31, 2020, through the net operating loss carryback under the CARES Act which generated a refund of income taxes paid for 2018. The Company has established a valuation allowance against all of its net deferred tax assets. Management considered all available evidence, both positive and negative, including but not limited to our historical operating results, income or loss in recent periods, cumulative losses in recent years, forecasted earnings, future taxable income, and significant risk and uncertainty related to forecasts, and concluded the deferred tax assets are not more likely than not to be realized. The net change in the total valuation allowance for the years ended December 31, 2021, 2020 and 2019 was an increase(decrease) of $ 18.0 million, $( 2.7 ) million, and $ 22.7 million, respectively. The Company had net operating loss carryforwards for federal and state income tax purposes of approximately $ 226.1 million and $ 24.2 million, respectively, as of December 31, 2021, available to reduce future taxable income. Of the federal net operating loss carryforwards, $ 65.6 million will begin to expire in 2034 , if not utilized and $ 160.5 million will carryforward indefinitely. The state net operating loss carryforwards will begin to expire in 2032 , if not utilized. The Company also has federal and state research and development tax credits carryforwards of $ 19.1 million and $ 11.2 million, respectively, as of December 31, 2021 available to reduce future income taxes. The federal research and development tax credits will begin to expire in 2031 if not utilized. The state research and development tax credits have no expiration date. Internal Revenue Code section 382 (“IRC Section 382”) places a limitation (the “Section 382 Limitation”) on the amount of taxable income that can be offset by net operating loss (“NOL”) carryforwards after a change in control (generally greater than 50 % change in ownership) of a loss corporation. California has similar rules. The Company has performed an IRC Section 382 analysis and determined there was an ownership change in 2017 that resulted in 382 limitations. When an ownership change occurs, IRC Section 382 limits the use of NOLs and credits in subsequent periods based on the annual 382 limitations. The annual 382 limitations may limit the full use of available tax attributes in one year but the identified ownership changes may not result in expiration of tax attributes for use prior to expiration of their respective carryforward periods. Accordingly, none of the tax attributes have been reduced but limited the full use in 2018. The Company has determined that, while an ownership change has occurred, the applicable limits would not impair the value or anticipated use of the Company’s federal and state net operating losses. Although realization is not assured, management believes it is more likely than not that any limitation under IRC Section 382 will not impair the realizability of the deferred income tax assets related to federal and state net operating loss carryforwards. The Company reviewed its stock ownership for the year ended December 31, 2021 and concluded no ownership changes occurred in current year which would result in a reduction of its net operating loss or in its research and development credits expiring unused. If additional ownership change occurs, the utilization of net operating loss and credit carryforwards could be significantly reduced. A reconciliation of the beginning and ending unrecognized tax benefit amount is as follows (in thousands): Year Ended December 31, 2021 2020 2019 Balance at the beginning of the year $ 6,454 $ 5,249 $ 3,756 Additions based on tax positions related to current year 1,326 1,205 1,403 Adjustment based on tax positions related to prior years — — 90 Balance at end of the year $ 7,780 $ 6,454 $ 5,249 Of the unrecognized tax benefits as of December 31, 2021, 2020 and 2019, approximately $ 0 , $ 0 , and $ 0.9 million, respectively, would affect the Company’s effective tax rate if recognized. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense. To the extent accrued interest and penalties do not ultimately become payable, amounts accrued will be reduced and reflected as a reduction of the provision for income taxes in the period that such determination is made. Interest and penalties have no t been accrued for 2021, 2020 and 2019. The Company files income tax returns in the U.S. federal and state jurisdictions. The tax years 2010 to 2020 remains open to U.S. federal and state examination to the extent of the utilization of net operating loss and credit carryovers. As of December 31, 2021, the Company is under examination by the State of California.

Defined Contribution Plan

Defined Contribution Plan	12 Months Ended
	Dec. 31, 2021
Retirement Benefits [Abstract]
Defined Contribution Plan	16. Defined Contribution Plan The Company sponsors a defined contribution plan under Section 401(k) of the Internal Revenue Code covering substantially all full-time U.S. employees. Employee contributions are voluntary and are determined on an individual basis subject to the maximum allowable under federal tax regulations. During the years ended December 31, 2021, 2020 and 2019, the Company made contributions to the plan of $ 0.9 million, $ 0.8 million, and $ 0.8 million, respectively.

Basis of Presentation and Sum_2

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”).
Use of Estimates	Use of Estimates The preparation of the financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties The Company is subject to a number of risks similar to other biopharmaceutical companies in the early stage, including, but not limited to, the need to obtain adequate additional funding, possible failure of preclinical testing or clinical trials, the need to obtain marketing approval for its product candidates, competitors developing new technological innovations, the need to successfully commercialize and gain market acceptance of the Company’s products, and protection of proprietary technology. If the Company does not successfully obtain regulatory approval, commercialize or partner any of its product candidates, it will be unable to generate revenue from product sales or achieve profitability. Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents, short-term investments and accounts receivable. Substantially all the Company’s cash is held by one financial institution. Such deposits may, at times, exceed federally insured limits. The Company invests its cash equivalents in highly rated money market funds and its short-term investments in U.S. Government Bonds. Customers and collaboration partners who represent 10% or more of the Company’s total revenue during each period presented or accounts receivable balance at each respective balance sheet date are as follows: Revenue Accounts Receivable, net Year Ended December 31, December 31, 2021 2020 2019 2021 2020 (in thousands) (in thousands) AbbVie Ireland Unlimited Company $ 11,845 $ 38,192 $ 5,878 $ — $ — Amgen, Inc. 8,744 * * — — Astellas Pharma Inc. 19,365 13,931 — 790 798 Bristol Myers Squibb Company 29,619 39,630 47,740 — — Total revenue from customers who represent 10% or more $ 69,573 $ 91,753 $ 53,618 $ 790 $ 798 * Less than 10% The Company’s customers are located in the United States of America, Ireland and Japan.
Segments	Segments Management has determined that it has one business activity and operates as one operating segment as it only reports financial information on an aggregate basis to its chief executive officer and chief financial officer, who are the Company’s chief operating decision makers. All long-lived assets are maintained in the United States of America.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents.
Restricted Cash	Restricted Cash Restricted cash represents a standby letter of credit issued pursuant to an office lease. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets that sum to the total of the amounts shown in the statement of cash flows: December 31 2021 2020 2019 (in thousands) Cash and cash equivalents $ 205,530 $ 191,859 $ 188,425 Restricted cash - non-current assets 917 917 917 Total $ 206,447 $ 192,776 $ 189,342
Investments	Investments All investments have been classified as available-for-sale (“AFS”) and are carried at fair value as determined based upon quoted market prices or pricing models for similar securities at period end. Investments that are required for use in current operations and that mature in less than 12 months are classified as short-term investments in the accompanying balance sheets. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. Dividend and interest income are recognized when earned. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold. The Company assesses impairment of its AFS debt securities investments at each reporting period. Unrealized gains resulting from the excess of the fair value over the amortized cost basis of an investment are reported as a component of accumulated other comprehensive income (loss), net of tax. Unrealized losses or impairments resulting from the fair value of the AFS debt security being below the amortized cost basis are evaluated, using the discounted cash flow model, for identification of credit losses and non-credit related losses. Any credit losses are charged to earnings against the allowance for credit losses of the security, limited to the difference between the fair value and the amortized cost basis of the security. Any difference between the fair value of the security and the amortized cost basis, less the allowance for credit losses, are reported in other comprehensive income (loss). Expected cash inflows due to improvements in credit are recognized through a reversal of the allowance for credit losses subject to the total allowance previously recognized. In the event of impairment of any security, if management (i) has the intent to sell such security or (ii) will more-likely-than-not be required to sell such security before recovery of its amortized cost basis, such AFS debt security’s amortized cost basis will be written down to its fair value through earnings along with any existing allowance for credit losses.
Property and Equipment, net	Property and Equipment, net Property and equipment are recorded at cost net of accumulated depreciation and amortization. Depreciation is provided using the straight-line method over the estimated useful lives of the respective assets. The useful lives of property and equipment are as follows: Machinery and equipment 5 years Computer equipment and software 3 years Furniture and fixtures 3 years Leasehold improvements Shorter of remaining lease term or estimated life of the assets Maintenance and repairs that do not extend the life or improve the asset are expensed when incurred.
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill represents the excess of the purchase price paid over the fair value of tangible and identifiable intangible assets acquired in business combinations. Goodwill and other intangible assets with indefinite lives are not amortized, but are assigned to reporting units and tested for impairment annually, or whenever there is an impairment indicator. Intangible assets are comprised of in-process research and development. The Company assesses impairment indicators annually as of December 31 or more frequently, if a change in circumstances or the occurrence of events suggests the remaining value may not be recoverable. Intangible assets that are not deemed to have an indefinite life are amortized over their estimated useful lives. There was no impairment of goodwill or intangible assets identified during the years ended December 31, 2021, 2020 and 2019.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset (or asset group) may not be recoverable and prior to any goodwill impairment test. An impairment loss is recognized when the total of estimated undiscounted future cash flows expected to result from the use of the asset (or asset group) and its eventual disposition is less than its carrying amount. Impairment, if any, would be assessed using discounted cash flows or other appropriate measures of fair value. There was no impairment of long-lived assets during the years ended December 31, 2021, 2020 and 2019.
Revenue Recognition	Revenue Recognition The Company’s revenues are primarily derived through its license, research, development and commercialization agreements. The terms of these types of agreements may include (i) licenses for the Company’s technology or programs, (ii) research and development services, and (iii) services or obligations in connection with participation in research or steering committees. Payments to the Company under these arrangements typically include one or more of the following: nonrefundable upfront and license fees, research funding, milestone and other contingent payments to the Company for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of any commercialized products. The Company assesses whether the promises in its arrangements with customers are distinct performance obligations that should be accounted for separately. Judgment is required to determine whether the license to the Company’s intellectual property is distinct from the research and development services or participation on steering committees. The Company’s collaboration and license agreements may include contingent payments related to specified research, development and regulatory milestones. Such milestone payments are typically payable under the collaborations when the collaboration partner claims or selects a target, or initiates or advances a covered product candidate in preclinical or clinical development, upon submission for marketing approval of a covered product with regulatory authorities, or upon receipt of actual marketing approvals of a covered product or for additional indications. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At each reporting date, the Company re-evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price by using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price in such period of determination. The Company’s collaboration and license agreements may also include contingent payments related to sales-based milestones. Sales-based milestones are typically payable when annual sales of a covered product reach specified levels. Sales-based milestones are recognized at the later of when the associated performance obligation has been satisfied or when the sales occur. Unlike other contingency payments, such as regulatory milestones, sales-based milestones are not included in the transaction price based on estimates at the inception of the contract; instead, are included when the sales or usage occur. The transaction price in each arrangement is allocated to the identified performance obligations based on the relative standalone selling price (“SSP”) of each distinct performance obligation, which requires judgment. In instances where SSP is not directly observable, such as when a license or service is not sold separately, SSP is determined using information that may include market conditions and other observable inputs. Due to the early stage of the Company’s licensed technology, the license of such technology is typically combined with research and development services and steering committee participation as one performance obligation. In the event that the Company receives non-cash consideration such as consideration in the form of a research license and research support services from the counterparty, the transaction price of a non-monetary exchange that has commercial substance is estimated based on the fair value of the non-cash consideration received, which may be determined through a valuation analysis. In certain cases, the Company’s performance creates an asset that does not have an alternative use to the customer and the Company has an enforceable right to payment at all times for performance completed to date. In these cases, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. AbbVie Ireland Unlimited Company (“AbbVie”), one of the Company’s collaboration partners, entered into a license agreement with Seagen Inc., formerly Seattle Genetics, Inc. (“SGEN”) to license certain intellectual property rights. As part of the Company’s collaboration agreement with AbbVie, the Company is required to pay SGEN sublicense fees for certain milestone achievements and an annual maintenance fee. These sublicense fees are treated as reductions to the transaction price and combined with the performance obligation to which they relate.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) represents all changes in stockholders’ equity except those resulting from distributions to stockholders. The Company’s non-credit related unrealized gains and losses on investments and impact of adoption of new accounting pronouncements during the period represent the components of other comprehensive income (loss) that is excluded from the reported net loss.
Contract Balances	Contract Balances Customer payments are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until the Company satisfies its performance obligations under these arrangements. Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional.
Stock-Based Compensation	Stock-based Compensation The Company measures compensation expense for all stock-based payment awards, including employee stock options, restricted stock units ("RSUs"), and employee stock purchases related to Employee Stock Purchase Plan ("ESPP") based on estimated fair values of the award at the grant date, and recognizes compensation expense over the requisite service vesting period. Stock options forfeitures are accounted for in the period in which they occur. To determine the fair value of a stock option award on the grant date, the Company uses the Black-Scholes option pricing model which consist of estimating variables such as: expected life, volatility, and risk-free interest rate. Expected life and volatility are estimated primarily from the Company's historical records, and the risk-free rate is based on the U.S. Treasury yield curve in effect at the time of grant commensurate with the expected life assumption. These estimates involve inherent uncertainties and the application of judgment. The Company measures its restricted stock unit awards based on the market price of the Company’s common shares on the date of grant. Share-based compensation expense for performance-based awards is recognized when it becomes probable that the performance condition will be met. The Company reassesses the estimated probability at each reporting period, and if it is determined at a future date that a performance condition is probable of being achieved, the Company will recognize a cumulative catch-up adjustment and record the remaining expense ratably over the remaining requisite service period.
Income Taxes	Income Taxes The Company accounts for income taxes using an asset and liability approach. Deferred tax assets and liabilities reflect the net tax effects of temporary differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The Company records a valuation allowance to reduce its deferred tax assets to reflect the net amount that it believes as more likely than not to be realized. Realization of the deferred tax assets is dependent on the generation of future taxable income, the amount and timing of which are uncertain. The valuation allowance requires an assessment of both positive and negative evidence when determining whether it is more likely than not that deferred tax assets are recoverable. Based upon the weight of available evidence at December 31, 2021, the Company continues to maintain a full valuation allowance against all of its deferred tax assets after management considered all available evidence, both positive and negative, including but not limited to its historical operating results, income or loss in recent periods, cumulative income in recent years, forecasted earnings, future taxable income, and significant risk and uncertainty related to forecasts. The Company recognizes the tax effects of an uncertain tax position only if it is more likely than not that it will be sustained based solely on its technical merits as of the reporting date and only in an amount more likely than not that it will be sustained upon review by the tax authorities. The Company evaluates uncertain tax positions on a quarterly basis and adjust the liability for changes in facts and circumstances, such as new regulations or interpretations by the taxing authorities, new information obtained during a tax examination, significant amendment to an existing tax law, or resolution of an examination. To the extent that the final tax outcome of these matters is different than the amounts recorded, such differences will impact the income tax provision in the period in which such determination is made. The resolution of its uncertain income tax positions is dependent on uncontrollable factors such as law changes, new case law, and the willingness of the income tax authorities to settle, including the timing thereof and other factors. Although the Company does not anticipate significant changes to its uncertain income tax positions in the next twelve months, items outside of its control could cause its uncertain income tax positions to change in the future, which would be recorded in its statements of operations. Interest and/or penalties related to income tax matters are recognized as a component of income tax expense.
Research and Development Expenses	Research and Development Expenses The Company records accrued liabilities for estimated costs of research and development activities conducted by third-party service providers, which include the conduct of preclinical and clinical studies, and contract manufacturing activities. The Company records the estimated costs of research and development activities based upon the estimated amount of services provided but not yet invoiced, and includes these costs in accrued liabilities in the balance sheets and within research and development expense in the statements of operations. These costs are a significant component of the Company’s research and development expenses. The Company accrues for these costs based on factors such as estimates of the work completed and in accordance with agreements established with its third-party service providers under the service agreements. The Company makes significant judgments and estimates in determining the accrued liabilities balance in each reporting period. As actual costs become known, the Company adjusts its accrued liabilities. The Company has not experienced any material differences between accrued costs and actual costs incurred. However, the status and timing of actual services performed may vary from the Company’s estimates, resulting in adjustments to expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations. Research and development expenses include costs directly attributable to the conduct of research and development programs, including the cost of salaries, payroll taxes, employee benefits, materials, supplies, depreciation on and maintenance of research equipment, the cost of services provided by outside contractors, and the allocated portions of facility costs, such as rent, utilities, insurance, repairs and maintenance, depreciation, and general support services. All costs associated with research and development are expensed as incurred. In January 2019, the Company acquired certain technology know-how that is complementary to the Company’s proprietary Probody technology from a third party for $ 5.0 million. The Company plans to use this technology in certain of the Company’s discovery stage projects, and has concluded that the technology acquired does not have an alternative future use. Accordingly, the $ 5.0 million has been recorded as research and development expense for 2019.
Leases	Leases The Company determines if an arrangement is or contains a lease at inception. Operating leases are recorded as operating lease right-of-use (“ROU”) assets and operating lease liabilities in the Company’s balance sheet. ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent its obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. The Company uses an implicit rate when readily available, or its incremental borrowing rate based on the information available at lease commencement date in determining the present value of lease payments. The operating lease ROU assets also include any lease prepayments made and reduced by lease incentives. The Company’s lease terms may include options to extend the lease when it is reasonably certain that such option will be exercised. Lease expenses are recognized on a straight-line basis over the lease term. The Company elected the short-term lease recognition exemption. The Company’s operating lease arrangement includes lease and non-lease components which are generally accounted for separately.
Adopted Accounting Pronouncements	In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The amendments in this ASU simplify the accounting for income taxes by removing certain exceptions to the general principles of ASC 740 in order to reduce cost and complexity of its application. The ASU removes the exception related to the incremental approach for intra-period tax allocation as well as two exceptions related to accounting for outside basis differences of equity method investments and foreign subsidiaries. The ASU also amends the scope of ASC 740 related to a franchise tax (or similar tax) that is partially based on income; clarifies when a step-up in the tax basis of goodwill should be considered part of the business combination in which the book goodwill was originally recognized and when it should be considered a separate transaction; specifies that an entity is not required to allocate income tax expense to a legal entity that is both not subject to tax and disregarded by the taxing authority; and clarifies that all tax effects, both deferred and current, should be accounted for in the interim period that includes the enactment date. The Company adopted this ASU on January 1, 2021 , and there was no material impact on the financial statements upon adoption of this ASU.

Basis of Presentation and Sum_3

Basis of Presentation and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Schedule of Customers and Collaboration Partners who Represent 10% or More of Total Revenue During Each Period Presented or Net Accounts Receivable Balance	Customers and collaboration partners who represent 10% or more of the Company’s total revenue during each period presented or accounts receivable balance at each respective balance sheet date are as follows: Revenue Accounts Receivable, net Year Ended December 31, December 31, 2021 2020 2019 2021 2020 (in thousands) (in thousands) AbbVie Ireland Unlimited Company $ 11,845 $ 38,192 $ 5,878 $ — $ — Amgen, Inc. 8,744 * * — — Astellas Pharma Inc. 19,365 13,931 — 790 798 Bristol Myers Squibb Company 29,619 39,630 47,740 — — Total revenue from customers who represent 10% or more $ 69,573 $ 91,753 $ 53,618 $ 790 $ 798
Schedule of Cash, Cash Equivalents, and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets that sum to the total of the amounts shown in the statement of cash flows: December 31 2021 2020 2019 (in thousands) Cash and cash equivalents $ 205,530 $ 191,859 $ 188,425 Restricted cash - non-current assets 917 917 917 Total $ 206,447 $ 192,776 $ 189,342
Schedule of Useful Lives of Property and Equipment	The useful lives of property and equipment are as follows: Machinery and equipment 5 years Computer equipment and software 3 years Furniture and fixtures 3 years Leasehold improvements Shorter of remaining lease term or estimated life of the assets

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share	The following weighted-average outstanding shares of potentially dilutive securities are excluded from the computation of diluted net loss per share for the periods presented, because including them would have been anti-dilutive: Year Ended December 31, 2021 2020 2019 Options, RSUs and ESPP to purchase common stock 11,987,362 11,388,691 9,687,844

Fair Value Measurements and I_2

Fair Value Measurements and Investments (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Investments Subject to Fair Value Measurements on a Recurring Basis	The following tables set forth the fair value of the Company’s investments subject to fair value measurements on a recurring basis and the level of inputs used in such measurements: December 31, 2021 Valuation Amortized Allowance for Credit Losses Gross Gross Aggregate (in thousands) Assets Money market funds Level I 165,736 $ — $ — $ — $ 165,736 Restricted cash (money market funds) Level I 917 — — — 917 U.S. Government bonds Level I 99,938 — — ( 242 ) 99,696 Total Securities 266,591 $ — $ — $ ( 242 ) $ 266,349 December 31, 2020 Valuation Amortized Allowance Gross Gross Aggregate (in thousands) Assets Money market funds Level I $ 131,121 $ — $ — $ — $ 131,121 Restricted cash (money market funds) Level I 917 — — — 917 U.S. Government bonds Level I 124,254 — 6 — 124,260 Total securities $ 256,292 $ — $ 6 $ — $ 256,298

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net consisted of the following: December 31 2021 2020 (in thousands) Machinery and equipment $ 15,086 $ 13,772 Computer equipment and software 1,608 1,600 Furniture and fixtures 1,054 1,024 Leasehold improvements 1,736 1,728 Construction in progress 308 252 19,792 18,376 Less: accumulated depreciation and amortization ( 13,832 ) ( 11,426 ) $ 5,960 $ 6,950

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets	December 31, 2021 2020 (in thousands) Probody platform intangible asset $ 1,750 $ 1,750 Less accumulated amortization ( 729 ) ( 583 ) $ 1,021 $ 1,167

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2021
Accrued Liabilities, Current [Abstract]
Schedule of Accrued Liabilities	Accrued liabilities consisted of the following: December 31, 2021 2020 (in thousands) Research and clinical expenses $ 18,861 $ 10,092 Payroll and related expenses 9,576 8,362 Legal and professional expenses 1,468 815 Operating lease liabilities - short term 3,618 3,195 Other accrued expenses 713 595 Total $ 34,236 $ 23,059

Research and Collaboration Ag_2

Research and Collaboration Agreements (Tables)	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Revenue by Collaboration Partners	The following table summarizes the revenue by collaboration partners: Year Ended December 31, 2021 2020 2019 (in thousands) AbbVie $ 11,845 $ 38,192 $ 5,878 Amgen 8,744 8,609 3,871 Astellas 19,365 13,931 — Bristol Myers Squibb 29,619 39,630 47,740 Total revenue $ 69,573 $ 100,362 $ 57,489
Summary of Contract Liabilities	The following table presents changes in the Company’s total contract liabilities for the year ended December 31, 2021 (in thousands): Balance at Additions Deductions Balance at (in thousands) Contract liabilities: Deferred revenue $ 261,130 $ - $ 66,208 $ 194,922

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Summary of Supplemental Information Related to Leases	Supplemental information related to leases are as follows: Year Ended December 31, 2021 December 31, 2020 (in thousands) Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating leases $ 5,129 $ 4,990 December 31, 2021 December 31, 2020 (in thousands) Supplemental balance sheet information related to leases: Operating lease right-of-use assets $ 19,362 $ 22,495 Current operating lease liabilities 3,618 3,195 Non-current operating lease liabilities 18,056 21,675 Total operating lease liabilities $ 21,674 $ 24,870 Weighted-average remaining lease term (in years) Operating lease 4.75 5.75 Weighted-average discount rate Operating lease 8.25 % 8.25 %
Schedule of Maturity of Operating Lease Liabilities	December 31, 2021 (in thousands) Maturity of operating lease liabilities 2022 5,273 2023 5,420 2024 5,572 2025 5,729 2026 and beyond 4,387 Total lease payments 26,381 Less imputed interest ( 4,707 ) Present value of lease liabilities $ 21,674

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Schedule of Activity Under Company's Stock Option Plans	Activity under the Company’s stock option plans is set forth below: Options Outstanding Number of Weighted- Weighted- Aggregate (in thousands) Balances at December 31, 2020 10,929,530 $ 10.77 Options granted 5,178,897 7.10 Options exercised ( 528,503 ) 2.70 Options cancelled ( 3,387,708 ) 11.26 Balances at December 31, 2021 12,192,216 9.42 7.5 $ 1,182 Options Exercisable—December 31, 2021 6,054,635 11.46 6.1 $ 1,155
Total Stock-based Compensation Recognized	Total stock-based compensation recorded related to options granted to employees and non-employees and employee stock purchase plan was as follows (in thousands): Year Ended December 31, 2021 2020 2019 Research and development $ 5,797 $ 6,825 $ 9,226 General and administrative 7,370 7,961 9,874 Total stock-based compensation expense $ 13,167 $ 14,786 $ 19,100
Schedule of Estimated Fair Value of Employee Stock Options and ESPP Using Black-Scholes Valuation Model	The Company estimated the fair value of employee stock options and ESPP using the Black-Scholes valuation model based on the date of grant with the following assumptions: Options ESPP Year Ended December 31, Year Ended December 31, 2021 2020 2019 2021 2020 2019 Expected volatility 69.6 % - 74.8 % 64.4 % - 73.3 % 64.4 % - 68.6 % 46.87 % - 69.58 % 47.3 % - 122.1 % 60.8 % - 71.9 % Risk-free interest rate 0.5 % - 1.3 % 0.2 % - 1.3 % 1.4 % - 2.5 % 0.04 % - 0.10 % 0.1 % - 0.2 % 1.6 % - 2.4 % Dividend yield — % — % — % — % — % — % Expected term 4.5 - 4.8 4.7 - 4.9 4.9 - 5.0 0.5 0.5 0.5
RSU's
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Schedule of Company's TRSU Activities	The following table summarizes the Company's RSU activities: Number of Weighted- Aggregate Weighted Average Grant Date Fair Value (in thousands) (in thousands) Balances at December 31, 2020 — $ - RSU's awarded 874,000 5.34 RSU's vested — - RSU's cancelled ( 5,750 ) 5.34 Balances at December 31, 2021 868,250 1.31 $ 3,760 5.34 Ending Exercisable—December 31, 2021 - - $ - $ -

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Schedule of Components of Benefit from Income Taxes	The Company derives its income only from the United States. The components of the benefit from income taxes are as follows (in thousands): Years Ended December 31, 2021 2020 2019 Current: Federal $ — $ ( 13,912 ) $ ( 390 ) State — 1 — Total current — ( 13,911 ) ( 390 ) Deferred: Federal — — ( 37 ) State — — — Total deferred — — ( 37 ) Benefit from income taxes $ — $ ( 13,911 ) $ ( 427 )
Schedule of Effective Tax Rate Reconciliation	A reconciliation of the Company’s effective tax rate to the statutory U.S. federal rate is as follows: Years Ended December 31, 2021 2020 2019 U.S. federal taxes at statutory rate 21.0 % 21.0 % 21.0 % State tax, net of federal benefit 2.1 % 3.3 % 1.3 % Stock compensation ( 4.3 )% ( 2.2 )% ( 1.2 )% Tax credits 2.8 % 11.0 % 2.5 % Change in valuation allowance ( 21.6 )% ( 31.2 )% ( 22.8 )% Net operating loss carryback 0.0 % 27.9 % 0.0 % Return to provision adjustment 0.0 % 0.0 % ( 0.3 )% Other 0.0 % ( 0.1 )% ( 0.1 )% Total 0.0 % 29.7 % 0.4 %
Schedule of Deferred Income Tax Assets and Liabilities	The types of temporary differences that give rise to significant portions of the Company’s deferred income tax assets and liabilities are set out below (in thousands): Year Ended December 31, 2021 2020 Net operating loss carryforwards $ 49,186 $ 37,099 Research and development credits 20,809 16,803 Lease liability 4,555 5,223 Intangible assets 3,804 3,923 Deferred revenue 41,291 38,832 Accrued liabilities 1,933 1,512 Stock-based compensation 7,480 8,578 Other 29 20 Total gross deferred income tax assets 129,087 111,990 Less: valuation allowance ( 124,477 ) ( 106,448 ) Deferred tax assets, net of valuation allowance 4,610 5,542 Fixed assets ( 253 ) ( 433 ) Right-of-use assets ( 4,069 ) ( 4,724 ) Prepaid expenses ( 288 ) ( 385 ) Deferred tax liabilities ( 4,610 ) ( 5,542 ) Net deferred income tax liabilities $ — $ —
Schedule of Reconciliation of Unrecognized Tax Benefits	A reconciliation of the beginning and ending unrecognized tax benefit amount is as follows (in thousands): Year Ended December 31, 2021 2020 2019 Balance at the beginning of the year $ 6,454 $ 5,249 $ 3,756 Additions based on tax positions related to current year 1,326 1,205 1,403 Adjustment based on tax positions related to prior years — — 90 Balance at end of the year $ 7,780 $ 6,454 $ 5,249

Basis of Presentation and Sum_4

Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Customers and Collaboration Partners who Represent 10% or More of Total Revenue During Each Period Presented or Net Accounts Receivable Balance (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Concentration Risk [Line Items]
Revenues		$ 69,573	$ 100,362	$ 57,489
Accounts receivable		790	798
AbbVie Ireland Unlimited Company
Concentration Risk [Line Items]
Revenues	$ 9,900
Major Customer
Concentration Risk [Line Items]
Revenues		69,573	91,753	53,618
Accounts receivable		790	798
Major Customer | AbbVie Ireland Unlimited Company
Concentration Risk [Line Items]
Revenues		11,845	38,192	5,878
Accounts receivable		0	0
Major Customer | Amgen Inc
Concentration Risk [Line Items]
Revenues		8,744
Accounts receivable		0	0
Major Customer | Bristol Myers Squibb Company
Concentration Risk [Line Items]
Revenues		29,619	39,630	$ 47,740
Accounts receivable		0	0
Major Customer | Astellas Pharma Inc.
Concentration Risk [Line Items]
Revenues		19,365	13,931
Accounts receivable		$ 790	$ 798

Basis of Presentation and Sum_5

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details)	1 Months Ended	12 Months Ended
	Jan. 31, 2019USD ($)	Dec. 31, 2021USD ($)SegmentActivity	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of business activities | Activity		1
Number of operating segments | Segment		1
Impairment of goodwill			$ 0	$ 0
Impairment of intangible assets		$ 0	0	0
Impairment of long-lived assets		0	0	0
Increase in accumulated deficit balance		(533,724,000)	(450,115,000)
Research and development expense		114,194,000	112,936,000	131,619,000
Operating Lease, Right-of-Use Asset		19,362,000	22,495,000
Operating Lease, Liability		$ 21,674,000	$ 24,870,000
Probody technology
Summary Of Significant Accounting Policies [Line Items]
Acquired, technology know-how	$ 5,000,000
Research and development expense				$ 5,000,000

Basis of Presentation and Sum_6

Basis of Presentation and Summary of Significant Accounting Policies - Summary of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 205,530	$ 191,859	$ 188,425
Restricted cash - non-current assets	917	917	917
Cash, cash equivalents, and restricted cash	$ 206,447	$ 192,776	$ 189,342	$ 248,494

Basis of Presentation and Sum_7

Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Useful Lives of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2021
Machinery and equipment
Property Plant And Equipment [Line Items]
Estimated useful life of property and equipment	5 years
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	3 years
Leasehold improvements
Property Plant And Equipment [Line Items]
Estimated useful life of leasehold improvements, description	Shorter of remaining lease term or estimated life of the assets

Adopted Accounting Pronouncem_2

Adopted Accounting Pronouncements - Additional Information (Details)	Dec. 31, 2021
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]	false
ASU 2019-12
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adoption date	Jan. 1, 2021
Change in accounting principle, accounting standards update, immaterial effect [true false]	true

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Options, RSUs and ESPP to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	11,987,362	11,388,691	9,687,844

Fair Value Measurements and I_3

Fair Value Measurements and Investments - Schedule of Investments Subject to Fair Value Measurements on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 266,591	$ 256,292
Gross Unrealized Holding Gains	0	6
Gross Unrealized Holding Losses	242
Aggregate Fair Value	266,349	256,298
Cash and cash equivalents	205,530	191,859	$ 188,425
Level I | Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	165,736	131,121
Level I | Restricted cash (money market funds)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Restricted cash	917	917
Level I | U.S. Government bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term Investments, Amortized Cost	99,938	124,254
Short-term Investments, Gross Unrealized Holding Gains	0	6
Short-term Investments, Gross Unrealized Holding Losses	(242)
Aggregate Fair Value	$ 99,696	$ 124,260

Fair Value Measurements and I_4

Fair Value Measurements and Investments - Additional Information (Details)	12 Months Ended
	Dec. 31, 2021
U.S. Government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available for sale, maturity period	12 months

Property and Equipment - Summar

Property and Equipment - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Machinery and equipment	$ 15,086	$ 13,772
Computer equipment and software	1,608	1,600
Furniture and fixtures	1,054	1,024
Leasehold improvements	1,736	1,728
Construction in progress	308	252
Total property and equipment	19,792	18,376
Less: accumulated depreciation and amortization	(13,832)	(11,426)
Property and equipment, net	$ 5,960	$ 6,950

Property and Equipment - Additi

Property and Equipment - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Depreciation and amortization	$ 2.6	$ 2.4	$ 2.5

Intangible Assets - Additional

Intangible Assets - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Finite Lived Intangible Assets [Line Items]
Amortization expense of intangible assets	$ 146	$ 146	$ 146
Probody Platform Intangible Asset
Finite Lived Intangible Assets [Line Items]
Average estimated lives of patents	12 years
Amortization expense of intangible assets	$ 100	$ 100	$ 100

Intangible Assets - Schedule of

Intangible Assets - Schedule of Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Goodwill
Goodwill	$ 949	$ 949
Probody Platform Intangible Asset
Intangible assets
Intangible assets, gross	1,750	1,750
Less accumulated amortization	729	583
Intangible assets, net	$ 1,021	$ 1,167

Accrued Liabilities - Summary o

Accrued Liabilities - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Accrued Liabilities, Current [Abstract]
Research and clinical expenses	$ 18,861	$ 10,092
Payroll and related expenses	9,576	8,362
Legal and professional expenses	1,468	815
Operating lease liabilities - short term	3,618	3,195
Other accrued expenses	713	595
Total	$ 34,236	$ 23,059

Research and Collaboration Ag_3

Research and Collaboration Agreements - Schedule of Revenue by Collaboration Partners (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue	$ 69,573	$ 100,362	$ 57,489
AbbVie
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue	11,845	38,192	5,878
Amgen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue	8,744	8,609	3,871
Bristol Myers Squibb Company
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue	29,619	39,630	47,740
Astellas
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue	$ 19,365	$ 13,931

Research and Collaboration Ag_4

Research and Collaboration Agreements - AbbVie Ireland Unlimited Company - Additional Information (Details) $ in Thousands	1 Months Ended				3 Months Ended	12 Months Ended
	Mar. 31, 2020USD ($)	Jun. 30, 2019USD ($)	May 31, 2018USD ($)	Apr. 30, 2016USD ($)AgreementAccountingUnitTarget	Jun. 30, 2018USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Mar. 31, 2017Target
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized from collaborative arrangement						$ 69,573	$ 100,362	$ 57,489
Type of Revenue [Extensible List]						us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Deferred revenue						$ 194,922	$ 261,130
AbbVie Ireland Unlimited Company
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment received						100,000
Milestone payment received			$ 21,000
Revenue recognized from collaborative arrangement					$ 9,900
AbbVie Ireland Unlimited Company | ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received				$ 30,000
Milestone payment received				14,000
Total transaction price				39,800
Estimated sublicense fees				$ 4,200
Number of accounting units | AccountingUnit				2
AbbVie Ireland Unlimited Company | Collaborative Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of collaboration agreements | Agreement				2
Percentage of net profits or net losses related to development and commercialization costs				35.00%
AbbVie Ireland Unlimited Company | CD71 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received				$ 20,000
Milestone payment received	$ 40,000
Milestone payment received			21,000
Deferred revenue						16,100	25,200
AbbVie Ireland Unlimited Company | CD71 Agreement | Transferred over Time
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized from collaborative arrangement	$ 26,600
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember
AbbVie Ireland Unlimited Company | CD71 Agreement | ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received				20,000
Total transaction price				29,800
Estimated sublicense fees				4,200
Milestone payment received				$ 14,000
AbbVie Ireland Unlimited Company | CD71 Agreement | U.S
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Profit split on U.S. sales				35.00%
AbbVie Ireland Unlimited Company | CD71 Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent payments receivable upon achieving development, regulatory and commercial milestones				$ 470,000
AbbVie Ireland Unlimited Company | Seattle Genetics Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sublicense fees paid			$ 4,000
AbbVie Ireland Unlimited Company | Seattle Genetics Agreement | ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sublicense fees paid				1,000
AbbVie Ireland Unlimited Company | Discovery Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received				10,000
Number of targets selected | Target									1
Revenue recognized from collaborative arrangement				10,000
Deferred revenue						$ 5,200	$ 8,000
AbbVie Ireland Unlimited Company | Discovery Agreement | ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received				10,000
Total transaction price				$ 10,000
AbbVie Ireland Unlimited Company | Discovery Agreement | Second Target
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments received		$ 10,000
AbbVie Ireland Unlimited Company | Discovery Agreement | Second Target | ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total transaction price		$ 10,000
Estimated research service period		5 years
AbbVie Ireland Unlimited Company | Discovery Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targets | Target				2
AbbVie Ireland Unlimited Company | Discovery Agreement | Maximum | Development, Regulatory and Commercial Milestone Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent milestone payments receivable				$ 265,000

Research and Collaboration Ag_5

Research and Collaboration Agreements - AbbVie Ireland Unlimited Company - Additional Information (Details 1)	Apr. 30, 2016
AbbVie Ireland Unlimited Company | Discovery Agreement | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2016-04-01
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognition upon performance obligation, service period	5 years

Research and Collaboration Ag_6

Research and Collaboration Agreements - Amgen, Inc - Additional Information (Details) $ / shares in Units, $ in Thousands	Sep. 29, 2017USD ($)Target	Oct. 31, 2017USD ($)$ / sharesshares	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, value of shares issued in connection with agreement					$ 107,712	$ 11,288	$ 0
Accrued liabilities					34,236	23,059
Revenue recognized from collaborative arrangement					$ 69,573	$ 100,362	$ 57,489
Type of Revenue [Extensible List]					us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Deferred revenue					$ 194,922	$ 261,130
Amgen Inc | EGFR Products
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue					21,800
Amgen Inc | Amgen Other Products
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue					1,400
Collaboration and License Agreement | Amgen Inc
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received	$ 40,000	$ 40,000
Common stock, shares issuable under agreement | shares		1,156,069
Common stock, shares issuable under agreement, price per share | $ / shares		$ 17.30
Common stock, value of shares issued in connection with agreement		$ 20,000
Number of targets selected | Target	1
Number of additional collaboration target | Target	2
Total transaction price	$ 51,200
Portion of transaction price allocated to premium on sale of common stock	500
Estimated fair value of products	10,700
Collaboration and License Agreement | Amgen Inc | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent payments payable	203,000
Collaboration and License Agreement | Amgen Inc | EGFR Products
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total transaction price	46,400
Estimated research service period			8 years	7 years
Deferred revenue					21,800	29,800
Collaboration and License Agreement | Amgen Inc | EGFR Products | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent milestone payments receivable	$ 460,000
Percentage share of profit and losses	50.00%
Collaboration and License Agreement | Amgen Inc | Amgen Products | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent milestone payments receivable	$ 950,000
Number of targets | Target	3
Collaboration and License Agreement | Amgen Inc | Amgen Other Products
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total transaction price	$ 4,800
Estimated research service period	6 years
Revenue recognition upon performance obligation	$ 4,800
Deferred revenue					$ 1,400	$ 2,200
Sublicense Agreement | Amgen Inc | Maximum | UC Regents
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sublicense payment percentage	7.50%

Research and Collaboration Ag_7

Research and Collaboration Agreements - Astellas Pharma Inc - Additional Information (Details) $ in Thousands	Mar. 23, 2020USD ($)Target	Mar. 31, 2020USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized from collaborative arrangement			$ 69,573	$ 100,362	$ 57,489
Deferred revenue			194,922	261,130
Astellas Pharma Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue			51,600
Collaboration and License Agreement | Astellas Pharma Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targets selected | Target	1
Number of additional collaboration target | Target	3
Upfront payment received	$ 80,000	$ 80,000
Total transaction price	90,000
Research and development service fees	$ 10,000
Estimated research service period	5 years
Estimated research service termination month & year	2025-03
Deferred revenue			51,600	67,600
Amount due from customer			$ 800	$ 800
Collaboration and License Agreement | Astellas Pharma Inc. | Additional Contingent Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent milestone payments receivable	$ 900,000
Collaboration and License Agreement | Astellas Pharma Inc. | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targets | Target	4
Right to expand the number of additional collaboration target | Target	5
Contingent milestone payments receivable	$ 1,600,000
Collaboration and License Agreement | Astellas Pharma Inc. | Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Right to expand the number of additional collaboration target | Target	3

Research and Collaboration Ag_8

Research and Collaboration Agreements - Bristol-Myers Squibb Company - Additional Information (Details)

Apr. 25, 2017USD ($)Target

Jul. 07, 2014USD ($)TargetTerm

Mar. 31, 2020USD ($)

Mar. 31, 2019USD ($)

Dec. 31, 2021USD ($)

Dec. 31, 2020USD ($)

Dec. 31, 2019USD ($)

Feb. 28, 2021USD ($)

Feb. 29, 2020USD ($)

Nov. 30, 2017USD ($)

Mar. 17, 2017Target

Dec. 31, 2016USD ($)

Jan. 31, 2016USD ($)

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Revenue recognized from collaborative arrangement

$ 69,573,000

$ 100,362,000

$ 57,489,000

Type of Revenue [Extensible List]

us-gaap:LicenseAndServiceMember

us-gaap:LicenseAndServiceMember

us-gaap:LicenseAndServiceMember

Deferred revenue

$ 194,922,000

$ 261,130,000

Bristol Myers Squibb Company

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Deferred revenue

$ 98,800,000

$ 128,300,000

Collaborative Arrangement | Bristol Myers Squibb Company

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaboration target research term

2 years

Number of additional collaboration target | Target

2

Research terms

Each collaboration target had a two-year research term and the two additional targets had to be nominated by Bristol Myers Squibb within five years of the effective date of the BMS Agreement. The research term for each collaboration target could be extended in one year increments up to three times.

Extension of research term for each collaboration target

1 year

Upfront payment received

$ 200,000,000

$ 50,000,000

Contingent milestone payments receivable

$ 1,779,000,000

$ 10,000,000

$ 15,000,000

$ 10,000,000

Number of research targets selected | Target

8

Total transaction price

272,800,000

Upfront payment received

250,000,000

Research and development service fees

10,800,000

Milestone payment received

$ 12,000,000

$ 10,000,000

Estimated research service termination date

Apr. 25, 2025

Deferred revenue

$ 98,800,000

Collaborative Arrangement | Bristol Myers Squibb Company | Pre Clinical Candidate

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Contingent milestone payments receivable

$ 2,000,000

Collaborative Arrangement | Bristol Myers Squibb Company | Third And Fourth Immuno-Oncology Targets

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Revenue recognized from collaborative arrangement

$ 18,100,000

Contingent milestone payments, no longer eligible to receive

894,000,000

Collaborative Arrangement | Bristol Myers Squibb Company | New Drug Application for CTLA-4

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Contingent milestone payments receivable

$ 10,000,000

Collaborative Arrangement | Bristol Myers Squibb Company | Accelerated Recognition of Deferred Revenue

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Revenue recognized from collaborative arrangement

$ 17,400,000

Collaborative Arrangement | Maximum | Bristol Myers Squibb Company

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Number of oncology target | Target

4

Number of collaboration target | Target

2

Period of nomination of additional target from effective date

5 years

Times of increments for extended collaboration target research time | Term

3

Contingent milestone payments receivable

$ 3,586,000,000

$ 1,192,000,000

Collaborative Arrangement | Maximum | Bristol Myers Squibb Company | Each Of Two Additional Targets

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Contingent milestone payments receivable

$ 25,000,000

Collaboration and License Agreement | Maximum | Bristol Myers Squibb Company

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Number of additional collaboration target | Target

8

Research and Collaboration Ag_9

Research and Collaboration Agreements - ImmunoGen, Inc - Additional Information (Details)	1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 31, 2014USD ($)Target	Mar. 31, 2020USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Feb. 29, 2020USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated total fair value consideration recorded as deferred revenue			$ 194,922,000	$ 261,130,000
Revenue recognized from collaborative arrangement			69,573,000	100,362,000	$ 57,489,000
Research and development expense			$ 114,194,000	$ 112,936,000	$ 131,619,000
Collaborative Arrangement | Immuno Gen Inc
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment	$ 0
Number of research targets selected | Target	2
Milestone payments payable						$ 3,000,000
Research and development expense		$ 3,000,000

Research and Collaboration A_10

Research and Collaboration Agreements - Summary of Contract Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)
Revenue from Contract with Customer [Abstract]
Balance at 12/31/2020	$ 261,130
Additional	0
Deductions	66,208
Balance at 12/31/2021	$ 194,922

Research and Collaboration A_11

Research and Collaboration Agreements - Contract Liabilities - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additions to deferred revenue	$ 0
Deductions to deferred revenue recognized during the period	66,208
Deferred revenue	194,922	$ 261,130
AbbVie Ireland Unlimited Company | CD71 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue	$ 16,100	25,200
Deferred Revenue Recognition Maturity Year	2023
AbbVie Ireland Unlimited Company | First Target under Discovery Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue	$ 200
Deferred Revenue Recognition Maturity Year	2022
AbbVie Ireland Unlimited Company | Second Target under Discovery Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue	$ 5,000
Deferred Revenue Recognition Maturity Year	2024
Astellas Pharma Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue	$ 51,600
Deferred Revenue Recognition Maturity Year	2025
Amgen Inc | EGFR Products
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue	$ 21,800
Deferred Revenue Recognition Maturity Year	2024
Amgen Inc | Amgen Other Products
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue	$ 1,400
Deferred Revenue Recognition Maturity Year	2023
Bristol Myers Squibb Company
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue	$ 98,800	$ 128,300
Deferred Revenue Recognition Maturity Year	2025

License Agreement - Additional

License Agreement - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands

Mar. 23, 2020

Apr. 25, 2017

Jul. 07, 2014

Mar. 31, 2020

Feb. 29, 2020

Jun. 30, 2019

Apr. 30, 2019

Apr. 30, 2016

Mar. 31, 2020

Jun. 30, 2019

Dec. 31, 2021

Dec. 31, 2020

Dec. 31, 2019

License Agreement [Line Items]

Annual minimum royalty obligations

$ 200

License termination period

60 days

Common stock, shares issued

65,392,758

48,251,819

Research and development

$ 114,194

$ 112,936

$ 131,619

Accrued Liabilities, Current

34,236

23,059

AbbVie | Discovery Agreement | Second Target

License Agreement [Line Items]

Additional sublicense fees

$ 800

Milestone payment receivable

$ 10,000

Bristol Myers Squibb Company | Collaboration and License Agreement

License Agreement [Line Items]

Milestone payment receivable

$ 10,000

Sublicense fees

$ 800

Bristol Myers Squibb Company | Collaborative Arrangement

License Agreement [Line Items]

Upfront payment received

$ 200,000

$ 50,000

Milestone payment received

$ 12,000

$ 10,000

Astellas Pharma Inc. | Collaboration and License Agreement

License Agreement [Line Items]

Additional sublicense fees

$ 6,000

Upfront payment received

$ 80,000

80,000

AbbVie Ireland Unlimited Company

License Agreement [Line Items]

Milestone payment received

100,000

AbbVie Ireland Unlimited Company | Discovery Agreement

License Agreement [Line Items]

Upfront payment received

$ 10,000

AbbVie Ireland Unlimited Company | CD71 Agreement

License Agreement [Line Items]

Additional sublicense fees

1,400

Upfront payment received

$ 20,000

Milestone payment received

$ 40,000

Immuno Gen Inc | Collaborative Arrangement

License Agreement [Line Items]

Research and development

$ 3,000

Upfront license payment

7,500

UCSB

License Agreement [Line Items]

Common stock, shares issued

150,000

Fair value of common stock price per share

$ 10.68

Payment of upfront fees

$ 1,000

$ 1,000

Annual license maintenance fees

$ 800

$ 800

License payment term

2031

Percentage of remaining maintenance fees outstanding

50.00%

Fair value of common stock issued

$ 1,600

Sublicense fees

$ 1,000

$ 9,100

$ 4,300

UCSB | Sublicense and Maintenance Fees

License Agreement [Line Items]

Research and development

$ 3,400

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - Patent Infringement Lawsuit - USD ($)	Mar. 04, 2020	Dec. 31, 2021
Loss Contingencies [Line Items]
Lawsuit filed date	March 4, 2020
Name of plaintiff		Vytacera Bio, LLC
Loss contingency, answer, affirmative defenses and counterclaims filing date	May 26, 2020
Loss contingency, answer and counterclaims by plaintiff filing date	Jun. 5, 2020
Loss contingency claim amount		$ 0

Leases - Additional Information

Leases - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2015
Operating Leased Assets [Line Items]
Restricted cash - non-current assets	$ 917	$ 917	$ 917
Rent expense	5,100	5,100	$ 4,800
Letter of Credit
Operating Leased Assets [Line Items]
Letter of credit outstanding, amount	900
Restricted cash - non-current assets	$ 900	$ 900
New Lease Agreement
Operating Leased Assets [Line Items]
Lease term description	The 2016 Lease has an initial term of ten years through 2026 and the Company has an option to extend the initial term for an additional five years at the then fair rental value as determined pursuant to the 2016 Lease.
Initial lease term				10 years
Extended lease term				5 years

Leases - Summary of Supplementa

Leases - Summary of Supplemental Information Related to Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	$ 5,129	$ 4,990
Supplemental balance sheet information related to leases:
Operating lease right-of-use asset	19,362	22,495
Current operating lease liabilities	$ 3,618	$ 3,195
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Liabilities, Current	Liabilities, Current
Non-current operating lease liabilities	$ 18,056	$ 21,675
Total operating lease liabilities	$ 21,674	$ 24,870
Weighted-average remaining lease term (in years)
Operating lease	4 years 9 months	5 years 9 months
Weighted-average discount rate
Operating lease	8.25%	8.25%

Leases - Schedule of Maturity o

Leases - Schedule of Maturity of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Maturity of operating lease liabilities
2022	$ 5,273
2023	5,420
2024	5,572
2025	5,729
2026 and beyond	4,387
Total lease payments	26,381
Less imputed interest	(4,707)
Present value of lease liabilities	$ 21,674	$ 24,870

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - USD ($)	1 Months Ended				12 Months Ended
	Feb. 28, 2021	Jan. 31, 2021	Dec. 31, 2020	Feb. 29, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Common stock, shares authorized			150,000,000		150,000,000	150,000,000
Common stock, par value			$ 0.00001		$ 0.00001	$ 0.00001
Proceeds from issuance of common stock, net of issuance costs					$ 107,712,000	$ 11,288,000	$ 0
Jefferies LLC
Class Of Stock [Line Items]
Common stock, par value				$ 0.00001
Issuance of common stock in follow-on offering, net of issuance costs, shares			1,535,217
Proceeds from issuance of common stock, net of issuance costs			$ 11,300,000
Percentage of sales commission				3.00%
Average price			$ 7.62
Percentage of sales commission and issuance cost			3.00%			3.00%
Jefferies LLC | Maximum
Class Of Stock [Line Items]
Proceeds from issuance of common stock, net of issuance costs				$ 75,000,000
Underwritten Public Offering
Class Of Stock [Line Items]
Proceeds from issuance of common stock, net of issuance costs		$ 93,600,000
Underwriters
Class Of Stock [Line Items]
Proceeds from issuance of common stock, net of issuance costs	$ 14,100,000
Common Stock
Class Of Stock [Line Items]
Issuance of common stock in follow-on offering, net of issuance costs, shares					16,428,571	1,535,217	150,000
Common Stock | Underwritten Public Offering
Class Of Stock [Line Items]
Issuance of common stock in follow-on offering, net of issuance costs, shares		14,285,714
Common stock price, per share		$ 7
Underwriting discounts and commissions and offering expenses	$ 900,000	$ 6,400,000
Common Stock | Underwriters
Class Of Stock [Line Items]
Issuance of common stock in follow-on offering, net of issuance costs, shares		2,142,857
Period granted to underwriters to purchase additional shares		30 days

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 01, 2016	Oct. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option expiration period			10 years
Options granted generally vest period				36 months
Options granted generally vest percent				2.08%
Aggregate intrinsic value of stock options exercised			$ 2,200	$ 4,400	$ 900
Weighted average grant date fair value, options granted			$ 3.97	$ 3.94	$ 7.03
Unrecognized compensation expense, options granted			$ 23,600
Number of shares issued during period			183,865	128,684
Stock-based compensation expense			$ 13,167	$ 14,786	$ 19,100
Share-based Payment Arrangement, Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation cost, period for recognition			2 years 10 months 24 days
Stock-based compensation expense			$ 13,100	$ 14,700	18,900
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Estimated fair value of the shares on the date of grant			85.00%
Common stock, capital shares reserved for future issuance				1,935,683
Unrecognized stock-based compensation cost, period for recognition			5 months
Plan maximum percentage of eligible compensation to purchase shares			15.00%
Stock-based compensation expense			$ 400	$ 400	600
Unrecognized stock-based compensation cost			200
Non Employees [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense			100	$ 100	$ 200
RSU's
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense, options granted			$ 2,100
Unrecognized stock-based compensation cost, period for recognition			1 year 7 months 6 days
Stock-based compensation expense			$ 200
RSU's Awarded		439,000	874,000
RSU's Awarded, Grant date fair value		$ 2,300	$ 3,760
Vesting rights, description			50% of the RSUs granted will vest at the end of the first year of the grant date and the remaining 50% will vest at the end of the second year provided the grantee continues to provide services to the Company.
PSU's
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
RSU's Awarded		435,000
RSU's Awarded, Grant date fair value		$ 2,300
Vesting rights, description			50% of the PSUs granted will vest within one year of the grant date upon achievement of certain specific milestones and the remaining 50% will vest within two years of the grant date upon achievement of additional company objectives.
Share-based Payment Arrangement, Tranche Two [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted generally vest percent			2.08%
Two Thousand Fifteen Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option expiration period			10 years
Employees holding voting rights of all classes of stock, percentage			10.00%
Common stock, capital shares reserved for future issuance			2,276,341	2,698,798			2,444,735
Increase in number of shares available for issuance, as proportion of issued and outstanding shares of common stock, percentage	4.00%
Two Thousand Fifteen Stock Incentive Plan [Member] | Share-based Payment Arrangement, Tranche One [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted generally vest period			4 years
Options granted generally vest percent			25.00%
Two Thousand Nineteen Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, capital shares reserved for future issuance			486,234	204,600		1,815,000
Increase in Common Stock Capital Shares Reserved For Future Issuance			1,000,000
Early Exercise Of Employee Options [Member] | Share-based Payment Arrangement, Tranche One [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted generally vest percent			25.00%
Minimum [Member] | Two Thousand Fifteen Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Estimated fair value of the shares on the date of grant			110.00%
Minimum [Member] | Two Thousand Nineteen Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Estimated fair value of the shares on the date of grant			100.00%
Maximum [Member] | Two Thousand Nineteen Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option expiration period			10 years

Stock-based Compensation - Sche

Stock-based Compensation - Schedule of Activity Under Company's Stock Option Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Number of Options
Balances, beginning of the period	10,929,530
Options granted	5,178,897
Options exercised	(528,503)
Options cancelled	(3,387,708)
Balances, end of the period	12,192,216	10,929,530
Options Exercisable, end of the period	6,054,635
Options Outstanding, Weighted-Average Exercise Price Per Share
Balances, beginning of the period	$ 10.77
Options granted	7.10
Options exercised	2.70
Options cancelled	11.26
Balances, end of the period	9.42	$ 10.77
Options Exercisable, end of the period	$ 11.46
Options Outstanding, Weighted- Average Remaining Contractual Life (years)
Balances, end of the period	7 years 6 months
Options Exercisable, end of the period	6 years 1 month 6 days
Aggregate Intrinsic Value
Options exercised	$ 2,200	$ 4,400	$ 900
Balances at December 31, 2020	1,182
Options Exercisable—December 31, 2020	$ 1,155

Stock-based Compensation - Sc_2

Stock-based Compensation - Schedule of Company's RSU Activities (Details) - RSU's - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2021	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Balances, beginning of the period		0
RSU's Awarded	439,000	874,000
RSU's Vested		0
RSU's Cancelled		(5,750)
Balances, end of the period		868,250
Weighted Average Remaining Contractual Life (years)
Balances, end of the period		1 year 3 months 21 days
Aggregate Intrinsic Value
Balances, end of the period	$ 2,300	$ 3,760
Weighted Average Grant Date Fair Value
RSU's Awarded		$ 5.34
RSU's Cancelled		5.34
Balances, end of the period		$ 5.34

Stock-based Compensation - Tota

Stock-based Compensation - Total Stock-based Compensation Recognized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-based compensation expense:
Stock-based compensation expense	$ 13,167	$ 14,786	$ 19,100
Research and Development Expense [Member]
Stock-based compensation expense:
Stock-based compensation expense	5,797	6,825	9,226
General and Administrative Expense [Member]
Stock-based compensation expense:
Stock-based compensation expense	$ 7,370	$ 7,961	$ 9,874

Stock-based Compensation - Sc_3

Stock-based Compensation - Schedule of Estimated Fair Value of Employee Stock Options and ESPP Using Black-Scholes Valuation Model (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	69.60%	64.40%	64.40%
Expected volatility, maximum	74.80%	73.30%	68.60%
Risk-free interest rate, minimum	0.50%	0.20%	1.40%
Risk-free interest rate, maximum	1.30%	1.30%	2.50%
Employee Stock Option | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield	0.00%	0.00%	0.00%
Expected term (in years)	4 years 6 months	4 years 8 months 12 days	4 years 10 months 24 days
Employee Stock Option | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	4 years 9 months 18 days	4 years 10 months 24 days	5 years
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	46.87%	47.30%	60.80%
Expected volatility, maximum	69.58%	122.10%	71.90%
Risk-free interest rate, minimum	0.04%	0.10%	1.60%
Risk-free interest rate, maximum	0.10%	0.20%	2.40%
Expected term (in years)	6 months	6 months	6 months

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	Mar. 27, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017
Income Tax Contingency [Line Items]
Net operating loss carryback	5 years
Percentage of taxable income from net operating losses for suspension of annual deduction limitation	80.00%
Deferred tax asset, net change in total valuation allowance increase during period		$ 18,000	$ (2,700,000)	$ 22,700,000
Unrecognized tax benefits would affect company's effective tax rate		0	0	900,000
Income tax expense (benefit)		0	13,911,000	427,000
Interest and penalties accrued		0	$ 0	$ 0
Minimum
Income Tax Contingency [Line Items]
Percentage of change in ownership					50.00%
Federal
Income Tax Contingency [Line Items]
Net operating loss carryforwards		$ 226,100,000
Operating loss carryforwards expiration year		2034
Operating loss carryforwards to expire if not utilized		$ 65,600,000
Operating loss carryforwards not subject to expiration		$ 160,500,000
Open tax year		2010 2011 2012 2013 2014 2015 2016 2017 2018
Federal | Research and Development Tax Credits
Income Tax Contingency [Line Items]
Tax credit carry forwards		$ 19,100,000
Tax credit carryforward, expiration		2031
State
Income Tax Contingency [Line Items]
Net operating loss carryforwards		$ 24,200,000
Operating loss carryforwards expiration year		2032
Open tax year		2010 2011 2012 2013 2014 2015 2016 2017 2018
State | Research and Development Tax Credits
Income Tax Contingency [Line Items]
Tax credit carry forwards		$ 11,200,000

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Benefit from Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current:
Federal	$ 0	$ (13,912)	$ 390
State	0	1
Total current	0	(13,911)	390
Deferred:
Federal	0		(37)
State	0
Total deferred	0		(37)
Benefit from income taxes	$ 0	$ (13,911)	$ (427)

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. federal taxes at statutory rate	21.00%	21.00%	21.00%
State tax, net of federal benefit	2.10%	3.30%	1.30%
Stock compensation	(4.30%)	(2.20%)	(1.20%)
Tax credits	2.80%	11.00%	2.50%
Change in valuation allowance	(21.60%)	(31.20%)	(22.80%)
Net operating loss carryback	0.00%	27.90%	0.00%
Return to provision adjustment	(0.00%)	0.00%	(0.30%)
Other	0.00%	(0.10%)	(0.10%)
Total	0.00%	29.70%	0.40%

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Components of Deferred Tax Assets and Liabilities [Abstract]
Net operating loss carryforwards	$ 49,186	$ 37,099
Research and development credits	20,809	16,803
Lease liability	4,555	5,223
Intangible assets	3,804	3,923
Deferred revenue	41,291	38,832
Accrued liabilities	1,933	1,512
Stock-based compensation	7,480	8,578
Other	29	20
Total gross deferred income tax assets	129,087	111,990
Less: valuation allowance	(124,477)	(106,448)
Deferred tax assets, net of valuation allowance	4,610	5,542
Fixed assets	(253)	(433)
Right-of-use assets	(4,069)	(4,724)
Prepaid expenses	(288)	(385)
Deferred tax liabilities	(4,610)	(5,542)
Net deferred income tax liabilities	$ 0	$ 0

Income Taxes- Schedule of Recon

Income Taxes- Schedule of Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at the beginning of the year	$ 6,454	$ 5,249	$ 3,756
Additions based on tax positions related to current year	1,326	1,205	1,403
Adjustment based on tax positions related to prior years	0		90
Balance at end of the year	$ 7,780	$ 6,454	$ 5,249

Defined Contribution Plan - Add

Defined Contribution Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Company contributions to defined contribution plan	$ 0.9	$ 0.8	$ 0.8