Annexon (ANNX) 10-Q 8 Sep 20 2020 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Jun. 30, 2020	Aug. 31, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Trading Symbol	ANNX
Entity Registrant Name	Annexon, Inc.
Entity Central Index Key	0001528115
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Title of 12(b) Security	Common Stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Entity File Number	001-39402
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	27-5414423
Entity Address, Address Line One	180 Kimball Way
Entity Address, Address Line Two	Suite 200
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	822-5500
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		38,148,090

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 124,761	$ 43,931
Prepaid expenses and other current assets	907	1,475
Total current assets	125,668	45,406
Property and equipment, less accumulated depreciation of $1,566 and $1,304 as of June 30, 2020 and December 2019, respectively	2,048	2,138
Other long-term assets	3,371	2,354
Total assets	131,087	49,898
Current liabilities:
Accounts payable	3,064	2,371
Accrued liabilities	9,218	2,194
Deferred rent, current	378	366
Total current liabilities	12,660	4,931
Deferred rent	1,247	1,437
Total liabilities	13,907	6,368
Commitments and contingencies (Note 5)
Stockholders' Deficit:
Common stock, $0.001 par value; 239,100,000 and 150,000,000 shares authorized as of June 30, 2020 and December 31, 2019, respectively; 433,749 shares issued and outstanding as of June 30, 2020 and December 31, 2019, respectively	4	4
Additional paid-in capital	9,365	2,202
Accumulated other comprehensive loss	(82)	(80)
Accumulated deficit	(127,161)	(102,580)
Total stockholders' deficit	(117,874)	(100,454)
Total liabilities, redeemable convertible preferred stock and stockholders' deficit	131,087	49,898
Redeemable Convertible Preferred Stock [Member]
Current liabilities:
Redeemable convertible preferred stock, $0.001 par value, 183,467,924 and 119,155,472 shares authorized as of June 30, 2020 and December 31, 2019, respectively; 183,467,924 and 111,748,065 shares issued and outstanding as of June 30, 2020 and December 31, 2019, respectively; liquidation preference of $239,814 and $137,814 as of June 30, 2020 and December 31, 2019, respectively	$ 235,054	$ 143,984

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accumulated depreciation on propoerty plant and equipment	$ 1,566	$ 1,304
Common Stock, Par Value Per Share	$ 0.001	$ 0.001
Common Stock, Shares Authorized	239,100,000	150,000,000
Common Stock, Shares Issued	433,749	433,749
Common Stock, Shares Outstanding	433,749	433,749
Redeemable Convertible Preferred Stock [Member]
Temporary Equity, Par Value Per Share	$ 0.001	$ 0.001
Temporary Equity, Shares Authorized	183,467,924	119,155,472
Temporary Equity, Shares Issued	183,467,924	111,748,065
Temporary Equity, Shares Outstanding	183,467,924	111,748,065
Temporary Equity, Liquidation Preference	$ 239,814	$ 137,814

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating expenses:
Research and development	$ 9,287	$ 5,987	$ 19,504	$ 10,640
General and administrative	2,950	2,230	5,189	3,679
Total operating expenses	12,237	8,217	24,693	14,319
Loss from operations	(12,237)	(8,217)	(24,693)	(14,319)
Loss on remeasurement of redeemable convertible preferred stock liability		(1,560)		(4,330)
Other income, net	1	376	116	597
Net loss before taxes	(12,236)	(9,401)	(24,577)	(18,052)
Provision for income taxes	4		4	1
Net loss	(12,240)	(9,401)	(24,581)	(18,053)
Accretion on redeemable convertible preferred stock	281	272	560	534
Net loss attributable to common stockholders	$ (12,521)	$ (9,673)	$ (25,141)	$ (18,587)
Net loss per share attributable to common stockholders, basic and diluted	$ (28.87)	$ (22.30)	$ (57.96)	$ (42.90)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted	433,749	433,749	433,749	433,232

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Net loss	$ (12,240)	$ (9,401)	$ (24,581)	$ (18,053)
Other comprehensive gain (loss):
Foreign currency translation adjustment	9	(4)	(2)	(10)
Comprehensive loss	$ (12,231)	$ (9,405)	$ (24,583)	$ (18,063)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Deficit - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning Balance, Shares at Dec. 31, 2018		89,525,848
Beginning Balance, Values at Dec. 31, 2018		$ 102,082
Beginning Balance, Shares at Dec. 31, 2018			432,309
Beginning Balance, Values at Dec. 31, 2018	$ (64,202)		$ 4	$ 1,257	$ (66)	$ (65,397)
Accretion on redeemable convertible preferred stock		$ 262
Accretion on redeemable convertible preferred stock	(262)			(262)
Stock option exercises, Shares			1,440
Stock option exercises, Values	3			3
Stock-based compensation	466			466
Foreign currency translation adjustment	(6)				(6)
Net loss	(8,652)					(8,652)
Ending Balance, Shares at Mar. 31, 2019		89,525,848
Ending Balance, Values at Mar. 31, 2019		$ 102,344
Ending Balance, Shares at Mar. 31, 2019			433,749
Ending Balance, Values at Mar. 31, 2019	(72,653)		$ 4	1,464	(72)	(74,049)
Beginning Balance, Shares at Dec. 31, 2018		89,525,848
Beginning Balance, Values at Dec. 31, 2018		$ 102,082
Beginning Balance, Shares at Dec. 31, 2018			432,309
Beginning Balance, Values at Dec. 31, 2018	(64,202)		$ 4	1,257	(66)	(65,397)
Foreign currency translation adjustment	(10)
Net loss	(18,053)
Ending Balance, Shares at Jun. 30, 2019		89,525,848
Ending Balance, Values at Jun. 30, 2019		$ 102,616
Ending Balance, Shares at Jun. 30, 2019			433,749
Ending Balance, Values at Jun. 30, 2019	(81,893)		$ 4	1,629	(76)	(83,450)
Beginning Balance, Shares at Mar. 31, 2019		89,525,848
Beginning Balance, Values at Mar. 31, 2019		$ 102,344
Beginning Balance, Shares at Mar. 31, 2019			433,749
Beginning Balance, Values at Mar. 31, 2019	(72,653)		$ 4	1,464	(72)	(74,049)
Accretion on redeemable convertible preferred stock		$ 272
Accretion on redeemable convertible preferred stock	(272)			(272)
Stock-based compensation	437			437
Foreign currency translation adjustment	(4)				(4)
Net loss	(9,401)					(9,401)
Ending Balance, Shares at Jun. 30, 2019		89,525,848
Ending Balance, Values at Jun. 30, 2019		$ 102,616
Ending Balance, Shares at Jun. 30, 2019			433,749
Ending Balance, Values at Jun. 30, 2019	(81,893)		$ 4	1,629	(76)	(83,450)
Beginning Balance, Shares at Dec. 31, 2019		111,748,065
Beginning Balance, Values at Dec. 31, 2019		$ 143,984
Beginning Balance, Shares at Dec. 31, 2019			433,749
Beginning Balance, Values at Dec. 31, 2019	(100,454)		$ 4	2,202	(80)	(102,580)
Accretion on redeemable convertible preferred stock		$ 279
Accretion on redeemable convertible preferred stock	(279)			(279)
Stock-based compensation	663			663
Foreign currency translation adjustment	(11)				(11)
Net loss	(12,341)					(12,341)
Ending Balance, Shares at Mar. 31, 2020		111,748,065
Ending Balance, Values at Mar. 31, 2020		$ 144,263
Ending Balance, Shares at Mar. 31, 2020			433,749
Ending Balance, Values at Mar. 31, 2020	(112,422)		$ 4	2,586	(91)	(114,921)
Beginning Balance, Shares at Dec. 31, 2019		111,748,065
Beginning Balance, Values at Dec. 31, 2019		$ 143,984
Beginning Balance, Shares at Dec. 31, 2019			433,749
Beginning Balance, Values at Dec. 31, 2019	(100,454)		$ 4	2,202	(80)	(102,580)
Beneficial conversion feature on Series D redeemable convertible preferred stock	$ 6,297
Stock option exercises, Shares	0
Foreign currency translation adjustment	$ (2)
Net loss	(24,581)
Ending Balance, Shares at Jun. 30, 2020		183,467,924
Ending Balance, Values at Jun. 30, 2020		$ 235,054
Ending Balance, Shares at Jun. 30, 2020			433,749
Ending Balance, Values at Jun. 30, 2020	(117,874)		$ 4	9,365	(82)	(127,161)
Beginning Balance, Shares at Mar. 31, 2020		111,748,065
Beginning Balance, Values at Mar. 31, 2020		$ 144,263
Beginning Balance, Shares at Mar. 31, 2020			433,749
Beginning Balance, Values at Mar. 31, 2020	(112,422)		$ 4	2,586	(91)	(114,921)
Issuance of Series D redeemable convertible preferred stock, net of issuance costs of $5,193, Shares		71,719,859
Issuance of Series D redeemable convertible preferred stock, net of issuance costs of $5,193, Values		$ 96,807
Beneficial conversion feature on Series D redeemable convertible preferred stock		(6,297)
Beneficial conversion feature on Series D redeemable convertible preferred stock	6,297			6,297
Accretion on redeemable convertible preferred stock		$ 281
Accretion on redeemable convertible preferred stock	(281)			(281)
Stock-based compensation	763			763
Foreign currency translation adjustment	9				9
Net loss	(12,240)					(12,240)
Ending Balance, Shares at Jun. 30, 2020		183,467,924
Ending Balance, Values at Jun. 30, 2020		$ 235,054
Ending Balance, Shares at Jun. 30, 2020			433,749
Ending Balance, Values at Jun. 30, 2020	$ (117,874)		$ 4	$ 9,365	$ (82)	$ (127,161)

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Deficit (Parenthetical) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2020
Payments of stock issuance costs			$ 890
Series D Redeemable Convertible Preferred Stock
Payments of stock issuance costs	$ 5,200	$ 5,193

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities:
Net loss	$ (24,581)	$ (18,053)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	262	236
Stock-based compensation	1,426	903
Change in fair value of redeemable convertible preferred stock liability		4,330
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	568	(496)
Other long-term assets	44
Accounts payable	787	893
Accrued liabilities	1,425	(346)
Deferred rent	(178)	(166)
Net cash used in operating activities	(20,247)	(12,699)
Investing activities:
Purchases of property and equipment	(16)	(18)
Net cash used in investing activities	(16)	(18)
Financing activities:
Proceeds from the exercise common stock options		3
Proceeds from Paycheck Protection Program loan	500
Repayments of Paycheck Protection Program loan	(500)
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	101,985
Payment of deferred offering costs	(890)
Net cash provided by financing activities	101,095	3
Net increase (decrease) in cash and cash equivalents	80,832	(12,714)
Effect of exchange rate changes on cash and cash equivalents	(2)	(10)
Cash and cash equivalents at beginning of period	43,931	44,175
Cash and cash equivalents at end of period	124,761	31,451
Non-cash investing and financing activities:
Accretion on redeemable convertible preferred stock	560	$ 534
Deferred offering costs included in accounts payable and accrued liabilities	171
Purchase of property and equipment included in accounts payable	156
Beneficial conversion feature recognized upon issuance of redeemable convertible preferred stock	6,297
Issuance costs of redeemable convertible preferred stock included in accounts payable and accrued liabilities	$ 5,178

Organization

Organization	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Organization	1. Organization Annexon, Inc., or the Company, is a clinical-stage biopharmaceutical company targeting C1q and initiating molecules of the classical complement pathway to develop transformative therapies for autoimmune and neurodegenerative disorders of the body, brain and eye. The Company is located in South San Francisco, California and was incorporated in Delaware in March 2011. The Company’s wholly-owned subsidiary, Annexon Biosciences Australia Pty Ltd, or the Subsidiary, is a proprietary limited company incorporated in 2016 and domiciled in Australia. The Subsidiary is also engaged in research and development activities in support of its parent company. Initial Public Offering On July 23, 2020, the Company’s registration statement on Form S-1 The condensed consolidated financial statements as of June 30, 2020, including share and per share amounts, do not give effect to the IPO as it closed subsequent to June 30, 2020. Liquidity Since inception, the Company has been involved primarily in performing research and development activities, conducting clinical trials, hiring personnel, and raising capital to support and expand these activities. The Company has experienced losses and negative cash flows from operations since its inception and, as of June 30, 2020, had an accumulated deficit of $127.2 million and cash and cash equivalents of $124.8 million. The Company has historically funded its operations through the issuance of shares of its redeemable convertible preferred stock. Based on projected activities, management projects that cash on hand and the proceeds from the IPO are sufficient to support operations for at least the next 12 months following issuance of these condensed consolidated financial statements. Management expects to continue to incur losses and negative cash flows from operations for at least the next several years.

Basis Of Presentation And Signi

Basis Of Presentation And Significant Accounting Policies	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	2. Basis of Presentation and Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States, or GAAP, and applicable rules and regulations of the SEC regarding interim financial reporting. The interim condensed consolidated balance sheet as of June 30, 2020, the interim condensed consolidated statements of operations, comprehensive loss, changes in redeemable convertible preferred stock and stockholders’ deficit for the three and six months ended June 30, 2020 and 2019 and the condensed consolidated statements of cash flows for the six months ended June 30, 2020 and 2019 are unaudited. These unaudited condensed consolidated financial statements have been prepared on the same basis as the annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s consolidated financial position as of June 30, 2020 and its results of operations and cash flows for the six months ended June 30, 2020 and 2019. The financial data and the other financial information contained in these notes to the condensed consolidated financial statements related to the three- and six-month S-1 No. 333-239647), Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported expenses during the reporting period. On an ongoing basis, management evaluates its estimates, including but not limited to the fair value of common stock, redeemable convertible preferred stock, redeemable convertible preferred stock liability, stock options, income taxes and certain accruals. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates. Principles of Consolidation The consolidated financial statements include the operations of Annexon, Inc. and its wholly-owned subsidiary and include the results of operations and cash flows of these entities. All intercompany balances and transactions have been eliminated in consolidation. Deferred Offering Costs Deferred offering costs, consisting of legal, accounting, audit and filing fees relating to an IPO, are capitalized. The deferred offering costs will be offset against offering proceeds upon the completion of the offering. In the event the offering is terminated or delayed, deferred offering costs will be expensed. As of June 30, 2020 and December 31, 2019, $3.3 million and $2.3 million, respectively, of deferred offering costs were capitalized, which are included in other long-term assets in the accompanying consolidated balance sheets. In July 2020, upon the closing of the IPO, all deferred costs were offset against the Company’s IPO proceeds. Redeemable Convertible Preferred Stock Liability The obligation to issue additional shares of the Company’s Series C redeemable convertible preferred stock at a future date was determined to be a freestanding financial instrument that should be accounted for as a liability. At initial recognition, the Company recorded the redeemable convertible preferred stock liability on the balance sheet at its estimated fair value. The liability is subject to remeasurement at each balance sheet date, with changes in fair value recognized as gain (loss) on remeasurement of redeemable convertible preferred stock liability on the consolidated statement of operations. Upon settlement of the redeemable convertible preferred stock liability in August 2019, the Company remeasured the liability and reclassified the final value associated with the redeemable convertible preferred stock liability to the carrying value of the Series C redeemable convertible preferred stock. Foreign Currencies The Company’s reporting currency is the U.S. dollar. The functional currency of the Company’s subsidiary located in Australia is the Australian Dollar. Balance sheets prepared in the functional currencies are translated to the reporting currency at exchange rates in effect at the end of the accounting period, except for stockholders’ equity accounts, which are translated at rates in effect when these balances were originally recorded. Revenue and expense accounts are translated using a weighted-average rate during the year. The resulting foreign currency translation adjustments are recorded as a separate component of accumulated other comprehensive loss in the accompanying consolidated balance sheets. Foreign exchange translation gain (loss) for the three and six months ended June 30, 2020 and 2019 were not material. Gains and losses resulting from exchange rate changes on transactions denominated in a currency other than the local currency are included in earnings as incurred. Research and Development Expense Research and development expenses consist primarily of direct and indirect costs incurred for the development of the Company’s product candidates. Direct expenses include (i) preclinical and clinical outside service costs associated with discovery, preclinical and clinical testing of the Company’s product candidates; (ii) professional services agreements with third-party contract organizations, investigative clinical trial sites and consultants that conduct research and development activities on the Company’s behalf; (iii) contract manufacturing costs to produce clinical trial materials; and (iv) laboratory supplies and materials. Indirect expenses include (A) compensation and personnel-related expenses (including stock-based compensation), (B) allocated expenses for facilities and depreciation; and (C) other indirect costs. Research and development costs are expensed as incurred. Payments made to third parties are under agreements that are generally cancelable by the Company. Advance payments for research and development activities are deferred as prepaid expenses. The prepaid amounts are expensed as the related services are performed. The Company estimates preclinical studies and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on the Company’s behalf. In accruing service fees, the Company estimates the period over which services will be performed and the level of effort to be expended in each period. These estimates are based on the Company’s communications with the third-party service providers and on information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies significantly from the estimate, the Company will adjust the accrual accordingly to reflect the best information available at the time of the financial statement issuance. The Company has not experienced any material differences between accrued costs and actual costs incurred since its inception. Stock-Based Compensation The Company accounts for stock-based compensation arrangements using a fair value method which requires the recognition of compensation expense for costs related to all stock-based payments, including stock options. The fair value method requires the Company to estimate the fair value of stock-based payment awards to employees on the date of grant using the Black-Scholes option pricing model. The Company grants certain employees performance-based stock options. For awards that include performance conditions, no compensation cost is recognized until the performance goals are probable of being met, at which time the cumulative compensation expense from the service inception date would be recognized. Stock-based compensation costs are based on the fair value of the underlying option calculated using the Black-Scholes option pricing model and recognized as expense on a straight-line basis (for all but performance based awards for which the accelerated method is used) over the requisite service period, which is the vesting period. Determining the appropriate fair value model and related assumptions requires judgment, including estimating the fair value of the underlying common stock, expected term, expected stock price volatility, risk-free interest rate and dividend yield. The Company accounts for forfeitures as they occur. Net Loss Per Share Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period, without consideration for potential dilutive shares of common stock. As the Company was in a loss position for all periods presented, basic net loss per share attributable to common stockholders is the same as diluted net loss per share attributable to common stockholders because the effects of potentially dilutive securities are antidilutive. Recently Adopted Accounting Pronouncements In June 2018, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), , Leases right-of-use No. 2019-10, Financial Instruments — Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842) No. 2020-05 COVID-19 No. 2020-05, Revenue from Contracts with Customers (Topic 606) and Leases (Topic 842), 2016-02) 2019-10. No. 2020-05, In August 2018, the FASB issued ASU No. 2018-15, Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The Company determines fair value based on assumptions that market participants would use in pricing an asset or liability in the principal or most advantageous market. When considering market participant assumptions in fair value measurements, the following fair value hierarchy distinguishes between observable and unobservable inputs, which are categorized in one of the following levels: • Level 1 Inputs: • Level 2 Inputs: • Level 3 Inputs: On a recurring basis, the Company measures certain financial assets and liabilities at fair value. The following tables summarize the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): June 30, 2020 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 124,171 $ — $ — $ 124,171 Total assets $ 124,171 $ — $ — $ 124,171 December 31, 2019 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 43,621 $ — $ — $ 43,621 Total assets $ 43,621 $ — $ — $ 43,621 The Company has an operating account invested in money market funds with maturities of less than three months and is classified as cash and cash equivalents on the Company’s condensed consolidated balance sheet. The money market funds are valued using Level 1 inputs that are based on quoted prices in active markets for identical assets. For the three months ended June 30, 2020 and 2019 and for the six months ended June 30, 2020 and 2019, the Company recognized no material realized gains or losses on financial instruments. The Company’s Level 3 liabilities include the redeemable convertible preferred stock liability which was settled in August 2019 upon the completion of the second closing of the Company’s Series C redeemable convertible preferred stock financing. The liability was remeasured at June 30, 2019 using a probability-weighted expected return method, or PWERM, whereby the Company’s total equity value was estimated under various exit scenarios and allocated to the Company’s different classes of equity. The PWERM included two scenarios, IPO or staying private, that considered an estimate of the timing of each scenario and were weighted based on the Company’s estimate of the probability of each event occurring. The equity value under the IPO scenario was based on recent IPO values of comparable companies and weighted 40%. The equity value under the staying private scenario was based on the recent Series C redeemable convertible preferred stock financing and was weighted 60%. The liability was remeasured to its fair value of $9.5 million as of June 30, 2019. The Company recorded a loss of $1.6 million and $4.3 million in the condensed consolidated statements of operations for the three and six months ended June 30, 2019, respectively, for the change in the fair value of the liability. The changes in the carrying value of the liability were as follows (in thousands): Fair value as of December 31, 2018 $ 5,140 Change in fair value 4,330 Fair value as of June 30, 2019 $ 9,470 There were no transfers between Levels 1, 2 or 3 for the periods presented.

Balance Sheet Components

Balance Sheet Components	6 Months Ended
	Jun. 30, 2020
Disclosure Of Balance Sheet Components [Abstract]
Balance Sheet Component	4. Balance Sheet Components Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): June 30, 2020 December 31, Prepaid research and development costs $ 333 $ 1,086 Prepaid expenses 574 310 Other receivables — 79 Total prepaid expenses and other current assets $ 907 $ 1,475 Accrued Liabilities Accrued liabilities consisted of the following (in thousands): June 30, 2020 December 31, Accrued commission related to issuance of redeemable convertible preferred stock $ 5,055 $ — Accrued research and development expenses 1,610 459 Accrued professional services 1,002 733 Accrued compensation 904 926 Other accrued expenses 647 76 Total accrued liabilities $ 9,218 $ 2,194

Promissory Note

Promissory Note	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Promissory Note	5. Promissory Note Pursuant to the Coronavirus Aid, Relief, and Economic Security Act, the Company obtained a $0.5 million promissory note from the U.S. Small Business Administration on April 21, 2020, which was repaid in full on May 1, 2020.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Leases The Company leases its offices and laboratory in South San Francisco, California under a 7-year 5-year non-cancelable Rent expense for each of the three months ended June 30, 2020 and 2019 was $88,000. Rent expense for each of the six months ended June 30, 2020 and 2019 was $176,000. License and Other Agreements In November 2011, the Company entered into an exclusive licensing agreement, or the Stanford Agreement, with The Board of Trustees of the Leland Stanford Junior University, or Stanford, whereby the Company was granted an exclusive, worldwide, royalty-bearing, sublicensable license, under certain patent rights, or the Licensed Patents, to make, use, offer for sale, sell, import and otherwise commercialize products covered by the Licensed Patents for human or animal diseases, disorders or conditions. Under the Stanford Agreement, the Company made an upfront payment and is obligated to pay Stanford annual license maintenance fees, potential future milestone payments totaling up to $600,000, and royalty payments at a rate equal to a low single-digit percentage of worldwide net sales of licensed products. In December 2016, the Company entered into a Sponsored Research Agreement with a not-for-profit The Company received $190,000 representing the final amount received under the Sponsored Research Agreement, which was recorded as other income for the three and six months ended June 30, 2019. No funding was received for the three and six months ended June 30, 2020. Guarantees and Indemnifications In the normal course of business, the Company enters into agreements that contain a variety of representations and provide for general indemnification. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. As of June 30, 2020, the Company did not have any material indemnification claims that were probable or reasonably possible and consequently has not recorded related liabilities.

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock and Stockholder's Deficit	6 Months Ended
	Jun. 30, 2020
Temporary Equity [Abstract]
Redeemable Convertible Preferred Stock and Stockholder's Deficit	7. Redeemable Convertible Preferred Stock and Stockholder’s Deficit Redeemable Convertible Preferred Stock As of June 30, 2020, redeemable convertible preferred stock consisted of the following: Shares Shares Net Carrying Liquidation Series A 1,015,434 1,015,434 $ 1,000 $ 1,000 Series A-1 16,398,995 16,398,995 17,149 17,219 Series B 38,778,090 38,778,090 44,518 44,595 Series C 55,555,546 55,555,546 81,877 75,000 Series D 71,719,859 71,719,859 90,510 102,000 Total 183,467,924 183,467,924 $ 235,054 $ 239,814 As of December 31, 2019, redeemable convertible preferred stock consisted of the following: Shares Shares Net Carrying Liquidation Series A 1,015,434 1,015,434 $ 1,000 $ 1,000 Series A-1 16,398,995 16,398,995 17,144 17,219 Series B 38,778,091 38,778,090 44,505 44,595 Series C 62,962,952 55,555,546 81,335 75,000 Total 119,155,472 111,748,065 $ 143,984 $ 137,814 In June 2020, the Company completed its financing of Series D redeemable convertible preferred stock, which resulted in the Company issuing 71,719,859 shares of Series D redeemable convertible preferred stock, including 9,773,587 shares issued to related parties who were 10% or greater holders of the Company, at a price per share of $1.4222 for aggregate proceeds of $96.8 million, net of issuance costs of $5.2 million. The shares of Series D redeemable convertible preferred stock are convertible at any time, at the holders’ option, into shares of common stock. In connection with the issuance and sale of the Series D redeemable convertible preferred stock, the Company recognized a beneficial conversion feature of approximately $6.3 million. A beneficial conversion feature represents the intrinsic value of the conversion feature, as determined by comparing the effective conversion price at the commitment date with the estimated fair value of the Company’s common stock. The beneficial conversion feature was recorded in additional paid-in capital as of June 30, 2020 resulting in a discount to the carrying value of the Series D redeemable convertible preferred stock. The Company has presented all of its Series A, Series A-1, A-1, In July 2020, immediately prior to the completion of the IPO (see Note 1), all outstanding shares of redeemable convertible preferred stock were automatically converted into 20,824,938 shares of common stock. Common Stock The Company has reserved the following shares of common stock for issuance as follows: June 30, 2020 December 31, Redeemable convertible preferred stock outstanding on an as-converted 20,824,938 12,684,214 Options issued and outstanding 3,026,480 2,007,222 Options available for future grant 376,894 454,110 Total common stock reserved 24,228,312 15,145,546

Equity Incentive Plan

Equity Incentive Plan	6 Months Ended
	Jun. 30, 2020
Share-based Payment Arrangement [Abstract]
Equity Incentive Plan	8. Equity Incentive Plan Stock option activity under the Plan was as follows: Shares Number of Weighted- Weighted- Aggregate Balances as of December 31, 2019 454,110 2,007,222 $ 4.91 8.26 $ 21,623 Additional shares authorized 942,042 — Stock options granted (1,021,898 ) 1,021,898 13.39 Stock options cancelled 2,640 (2,640 ) 4.67 Balances as of June 30, 2020 376,894 3,026,480 $ 7.77 8.50 $ 16,828 Exercisable as of June 30, 2020 1,032,734 $ 3.39 6.87 $ 10,236 No options were exercised during the six months ended June 30, 2020. The total intrinsic value of options exercised during each of the three and six months ended June 30, 2019 was $8,000. The intrinsic value is the difference between the estimated fair value of the Company’s common stock at the time of exercise, as determined by the Board of Directors, and the exercise price of the stock option. Stock-Based Compensation Expense The total stock-based compensation expense recognized for options granted was as follows (in thousands): Three Months Ended Six Months Ended June 30, 2020 2019 2020 2019 Research and development $ 335 $ 135 $ 660 $ 232 General and administrative 428 302 766 671 Total stock-based compensation expense $ 763 $ 437 $ 1,426 $ 903 As of June 30, 2020, the total unrecognized stock-based compensation cost related to outstanding unvested stock options that are expected to vest was $15.4 million, which the Company expects to recognize over an estimated weighted-average period of 3.2 years. To determine the value of stock option awards for stock-based compensation purposes, the Company uses the Black-Scholes option pricing model and the assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment. Expected Term mid-point Expected Volatility Risk-Free Interest Rate Dividend Yield Fair Value of Common Stock The fair value of each award issued was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Expected term (in years) 5.00 – 6.08 6.02 – 6.08 5.00 – 6.08 6.02 – 6.08 Expected volatility 85% 76% 85% 76% – 77% Risk-free interest rate 0.33% – 0.45% 1.87% – 2.20% 0.33% – 1.45% 1.87% – 2.61% Dividend yield — — — —

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes For the six months ended June 30, 2019 and 2020, the Company incurred insignificant amounts for an income tax provision. The U.S. federal and California deferred tax assets generated from the Company’s net operating losses have been fully reserved, as the Company believes it is not more likely than not that the benefit will be realized.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	6 Months Ended
	Jun. 30, 2020
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Stockholders	10. Net Loss Per Share Attributable to Common Stockholders The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Redeemable convertible preferred stock on an as-converted 20,824,938 10,161,828 20,824,938 10,161,828 Stock options to purchase common stock 3,026,480 2,109,906 3,026,480 2,109,906 Total 23,851,418 12,271,734 23,851,418 12,271,734

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	11. Subsequent Events Reverse Stock Split In July 2020, the Company’s board of directors approved an amendment to the Company’s certificate of incorporation to effect a reverse split of shares of the Company’s common stock on a one-for-8.81 Initial Public Offering In July 2020, the Company completed an initial public offering of its common stock. As part of the IPO, the Company issued and sold 14,750,000 shares of its common stock at a public offering price of $17.00 per share and 2,139,403 shares of its common stock to the underwriters of the IPO pursuant to the partial exercise of their option to purchase additional shares at a price of $17.00 per share less the underwriting discounts and commissions. The Company received net proceeds of approximately $262.7 million from the IPO, after deducting underwriting discounts and commissions of $20.1 million and offering costs of $4.3 million, of which $3.3 million was incurred as of June 30, 2020. Prior to the completion of the IPO, all shares of redeemable convertible preferred stock then outstanding were converted into 20,824,938 shares of common stock. Upon conversion of the redeemable convertible preferred stock, the unamortized balance of $6.2 million of the discount from the beneficial conversion feature was recorded as a deemed dividend to the preferred stockholders resulting in an increase to the carrying value of redeemable convertible preferred stock. Upon conversion into common stock, the carrying value of the redeemable convertible preferred stock of $241.4 million was reclassified to equity. In July 2020, the Company adopted the 2020 Incentive Award Plan, or the 2020 Plan, and the Employee Stock Purchase Plan, or the ESPP, which became effective in connection with the IPO. The Company has reserved 3,600,868 shares of common stock for future issuance under the 2020 Plan and 360,086 shares under the ESPP, respectively.

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States, or GAAP, and applicable rules and regulations of the SEC regarding interim financial reporting. The interim condensed consolidated balance sheet as of June 30, 2020, the interim condensed consolidated statements of operations, comprehensive loss, changes in redeemable convertible preferred stock and stockholders’ deficit for the three and six months ended June 30, 2020 and 2019 and the condensed consolidated statements of cash flows for the six months ended June 30, 2020 and 2019 are unaudited. These unaudited condensed consolidated financial statements have been prepared on the same basis as the annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s consolidated financial position as of June 30, 2020 and its results of operations and cash flows for the six months ended June 30, 2020 and 2019. The financial data and the other financial information contained in these notes to the condensed consolidated financial statements related to the three- and six-month S-1 No. 333-239647),
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported expenses during the reporting period. On an ongoing basis, management evaluates its estimates, including but not limited to the fair value of common stock, redeemable convertible preferred stock, redeemable convertible preferred stock liability, stock options, income taxes and certain accruals. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates.
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the operations of Annexon, Inc. and its wholly-owned subsidiary and include the results of operations and cash flows of these entities. All intercompany balances and transactions have been eliminated in consolidation.
Deferred Offering Costs	Deferred Offering Costs Deferred offering costs, consisting of legal, accounting, audit and filing fees relating to an IPO, are capitalized. The deferred offering costs will be offset against offering proceeds upon the completion of the offering. In the event the offering is terminated or delayed, deferred offering costs will be expensed. As of June 30, 2020 and December 31, 2019, $3.3 million and $2.3 million, respectively, of deferred offering costs were capitalized, which are included in other long-term assets in the accompanying consolidated balance sheets. In July 2020, upon the closing of the IPO, all deferred costs were offset against the Company’s IPO proceeds.
Redeemable Convertible Preferred Stock Liability	Redeemable Convertible Preferred Stock Liability The obligation to issue additional shares of the Company’s Series C redeemable convertible preferred stock at a future date was determined to be a freestanding financial instrument that should be accounted for as a liability. At initial recognition, the Company recorded the redeemable convertible preferred stock liability on the balance sheet at its estimated fair value. The liability is subject to remeasurement at each balance sheet date, with changes in fair value recognized as gain (loss) on remeasurement of redeemable convertible preferred stock liability on the consolidated statement of operations. Upon settlement of the redeemable convertible preferred stock liability in August 2019, the Company remeasured the liability and reclassified the final value associated with the redeemable convertible preferred stock liability to the carrying value of the Series C redeemable convertible preferred stock.
Foreign Currencies	Foreign Currencies The Company’s reporting currency is the U.S. dollar. The functional currency of the Company’s subsidiary located in Australia is the Australian Dollar. Balance sheets prepared in the functional currencies are translated to the reporting currency at exchange rates in effect at the end of the accounting period, except for stockholders’ equity accounts, which are translated at rates in effect when these balances were originally recorded. Revenue and expense accounts are translated using a weighted-average rate during the year. The resulting foreign currency translation adjustments are recorded as a separate component of accumulated other comprehensive loss in the accompanying consolidated balance sheets. Foreign exchange translation gain (loss) for the three and six months ended June 30, 2020 and 2019 were not material. Gains and losses resulting from exchange rate changes on transactions denominated in a currency other than the local currency are included in earnings as incurred.
Research and Development Expense	Research and Development Expense Research and development expenses consist primarily of direct and indirect costs incurred for the development of the Company’s product candidates. Direct expenses include (i) preclinical and clinical outside service costs associated with discovery, preclinical and clinical testing of the Company’s product candidates; (ii) professional services agreements with third-party contract organizations, investigative clinical trial sites and consultants that conduct research and development activities on the Company’s behalf; (iii) contract manufacturing costs to produce clinical trial materials; and (iv) laboratory supplies and materials. Indirect expenses include (A) compensation and personnel-related expenses (including stock-based compensation), (B) allocated expenses for facilities and depreciation; and (C) other indirect costs. Research and development costs are expensed as incurred. Payments made to third parties are under agreements that are generally cancelable by the Company. Advance payments for research and development activities are deferred as prepaid expenses. The prepaid amounts are expensed as the related services are performed. The Company estimates preclinical studies and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on the Company’s behalf. In accruing service fees, the Company estimates the period over which services will be performed and the level of effort to be expended in each period. These estimates are based on the Company’s communications with the third-party service providers and on information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies significantly from the estimate, the Company will adjust the accrual accordingly to reflect the best information available at the time of the financial statement issuance. The Company has not experienced any material differences between accrued costs and actual costs incurred since its inception.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based compensation arrangements using a fair value method which requires the recognition of compensation expense for costs related to all stock-based payments, including stock options. The fair value method requires the Company to estimate the fair value of stock-based payment awards to employees on the date of grant using the Black-Scholes option pricing model. The Company grants certain employees performance-based stock options. For awards that include performance conditions, no compensation cost is recognized until the performance goals are probable of being met, at which time the cumulative compensation expense from the service inception date would be recognized. Stock-based compensation costs are based on the fair value of the underlying option calculated using the Black-Scholes option pricing model and recognized as expense on a straight-line basis (for all but performance based awards for which the accelerated method is used) over the requisite service period, which is the vesting period. Determining the appropriate fair value model and related assumptions requires judgment, including estimating the fair value of the underlying common stock, expected term, expected stock price volatility, risk-free interest rate and dividend yield. The Company accounts for forfeitures as they occur.
Net Loss Per Share Attributable to Common Stockholders	Net Loss Per Share Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period, without consideration for potential dilutive shares of common stock. As the Company was in a loss position for all periods presented, basic net loss per share attributable to common stockholders is the same as diluted net loss per share attributable to common stockholders because the effects of potentially dilutive securities are antidilutive.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In June 2018, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), , Leases right-of-use No. 2019-10, Financial Instruments — Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842) No. 2020-05 COVID-19 No. 2020-05, Revenue from Contracts with Customers (Topic 606) and Leases (Topic 842), 2016-02) 2019-10. No. 2020-05, In August 2018, the FASB issued ASU No. 2018-15, Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2020
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following tables summarize the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): June 30, 2020 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 124,171 $ — $ — $ 124,171 Total assets $ 124,171 $ — $ — $ 124,171 December 31, 2019 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 43,621 $ — $ — $ 43,621 Total assets $ 43,621 $ — $ — $ 43,621
Summary of Changes in the Carrying Value of the Liability	The changes in the carrying value of the liability were as follows (in thousands): Fair value as of December 31, 2018 $ 5,140 Change in fair value 4,330 Fair value as of June 30, 2019 $ 9,470

Balance Sheet Components (Table

Balance Sheet Components (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure Of Balance Sheet Components [Abstract]
Summary of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): June 30, 2020 December 31, Prepaid research and development costs $ 333 $ 1,086 Prepaid expenses 574 310 Other receivables — 79 Total prepaid expenses and other current assets $ 907 $ 1,475
Summary of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): June 30, 2020 December 31, Accrued commission related to issuance of redeemable convertible preferred stock $ 5,055 $ — Accrued research and development expenses 1,610 459 Accrued professional services 1,002 733 Accrued compensation 904 926 Other accrued expenses 647 76 Total accrued liabilities $ 9,218 $ 2,194

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock and Stockholder's Deficit (Tables)	6 Months Ended
	Jun. 30, 2020
Temporary Equity [Abstract]
Summary of Redeemable Convertible Preferred Stock	As of June 30, 2020, redeemable convertible preferred stock consisted of the following: Shares Shares Net Carrying Liquidation Series A 1,015,434 1,015,434 $ 1,000 $ 1,000 Series A-1 16,398,995 16,398,995 17,149 17,219 Series B 38,778,090 38,778,090 44,518 44,595 Series C 55,555,546 55,555,546 81,877 75,000 Series D 71,719,859 71,719,859 90,510 102,000 Total 183,467,924 183,467,924 $ 235,054 $ 239,814 As of December 31, 2019, redeemable convertible preferred stock consisted of the following: Shares Shares Net Carrying Liquidation Series A 1,015,434 1,015,434 $ 1,000 $ 1,000 Series A-1 16,398,995 16,398,995 17,144 17,219 Series B 38,778,091 38,778,090 44,505 44,595 Series C 62,962,952 55,555,546 81,335 75,000 Total 119,155,472 111,748,065 $ 143,984 $ 137,814
Schedule of Common Stock Reserved For Future Issuance	The Company has reserved the following shares of common stock for issuance as follows: June 30, 2020 December 31, Redeemable convertible preferred stock outstanding on an as-converted 20,824,938 12,684,214 Options issued and outstanding 3,026,480 2,007,222 Options available for future grant 376,894 454,110 Total common stock reserved 24,228,312 15,145,546

Equity Incentive Plan (Tables)

Equity Incentive Plan (Tables)	6 Months Ended
	Jun. 30, 2020
Share-based Payment Arrangement [Abstract]
Summary of stock option activity	Stock option activity under the Plan was as follows: Shares Number of Weighted- Weighted- Aggregate Balances as of December 31, 2019 454,110 2,007,222 $ 4.91 8.26 $ 21,623 Additional shares authorized 942,042 — Stock options granted (1,021,898 ) 1,021,898 13.39 Stock options cancelled 2,640 (2,640 ) 4.67 Balances as of June 30, 2020 376,894 3,026,480 $ 7.77 8.50 $ 16,828 Exercisable as of June 30, 2020 1,032,734 $ 3.39 6.87 $ 10,236
Summary of stock-based compensation expense	The total stock-based compensation expense recognized for options granted was as follows (in thousands): Three Months Ended Six Months Ended June 30, 2020 2019 2020 2019 Research and development $ 335 $ 135 $ 660 $ 232 General and administrative 428 302 766 671 Total stock-based compensation expense $ 763 $ 437 $ 1,426 $ 903
Summary of fair value assumptions estimated on the date of grant using the Black-Scholes option pricing model	The fair value of each award issued was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Expected term (in years) 5.00 – 6.08 6.02 – 6.08 5.00 – 6.08 6.02 – 6.08 Expected volatility 85% 76% 85% 76% – 77% Risk-free interest rate 0.33% – 0.45% 1.87% – 2.20% 0.33% – 1.45% 1.87% – 2.61% Dividend yield — — — —

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Stockholders (Tables)	6 Months Ended
	Jun. 30, 2020
Earnings Per Share [Abstract]
Summary of Net Loss Per Share Attributable to Common Stockholders	The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Redeemable convertible preferred stock on an as-converted 20,824,938 10,161,828 20,824,938 10,161,828 Stock options to purchase common stock 3,026,480 2,109,906 3,026,480 2,109,906 Total 23,851,418 12,271,734 23,851,418 12,271,734

Organization - Additional Infor

Organization - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Aug. 04, 2020	Jul. 24, 2020	Jul. 31, 2020	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Payment of Deferred Offering Costs				$ 890
Accumulated Deficit				(127,161)	$ (102,580)
Cash and Cash Equivalents				124,761	$ 43,931	$ 31,451	$ 44,175
Subsequent Event [Member]
Proceeds From Issuance Of IPO		$ 262,700
Redeemable Convertible Preferred Stock, Shares Issued Upon Conversion		20,824,938	20,824,938
IPO [Member]
Payment of Deferred Offering Costs				$ 3,300
IPO [Member] | Subsequent Event [Member]
Shares issued during the period		14,750,000	14,750,000
Shares Issued Price Per Share		$ 17	$ 17
Payments for Underwriting Expense		$ 20,100
Payment of Deferred Offering Costs		$ 4,300
Over-Allotment Option [Member] | Subsequent Event [Member]
Shares issued during the period	2,139,403		2,139,403
Shares Issued Price Per Share			$ 17

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Deferred Offering Costs	$ 3.3	$ 2.3

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Total assets	$ 124,171	$ 43,621
Level 1 [Member]
Assets:
Total assets	124,171	43,621
Money market funds [Member]
Assets:
Total assets	124,171	43,621
Money market funds [Member] | Level 1 [Member]
Assets:
Total assets	$ 124,171	$ 43,621

Fair Value Measurements - Addi

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liability remeasured to its fair value	$ 9,470	$ 9,470	$ 5,140
Operational loss		4,330
Redeemable Convertible Preferred Stock Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liability remeasured to its fair value	9,500	9,500
Operational loss	$ 1,600	$ 4,300
IPO Scenario [Member] | Redeemable Convertible Preferred Stock Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average equity value percentage		40.00%
Staying Private Scenario [Member] | Redeemable Convertible Preferred Stock Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average equity value percentage		60.00%

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary Of Changes In The Carrying Value Of The Liability (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2020USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Fair value as of December 31, 2018	$ 5,140
Change in fair value	4,330
Fair value as of June 30, 2019	$ 9,470

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule Of Prepaid Expenses And Other Current Asset [Line Items]
Prepaid research and development costs	$ 333	$ 1,086
Prepaid expenses	574	310
Other receivables		79
Total prepaid expenses and other current assets	$ 907	$ 1,475

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accrued Liabilities, Current [Abstract]
Accrued commission related to issuance of redeemable convertible preferred stock	$ 5,055	$ 0
Accrued research and development expenses	1,610	459
Accrued professional services	1,002	733
Accrued compensation	904	926
Other accrued expenses	647	76
Total accrued liabilities	$ 9,218	$ 2,194

Promissory Note - Additional In

Promissory Note - Additional Information (Detail) - USD ($) $ in Thousands	May 01, 2020	Apr. 21, 2020	Jun. 30, 2020
Short-term Debt [Line Items]
Proceeds from short term notes payable			$ 500
Repayment of short term notes payable			$ 500
U S Small Business Administration Loan [Member]
Short-term Debt [Line Items]
Proceeds from short term notes payable		$ 500
Repayment of short term notes payable	$ 500

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Mar. 31, 2019USD ($)	Nov. 30, 2011USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2020USD ($)	Dec. 31, 2016USD ($)
Gain Contingencies [Line Items]
operating lease, term of contract			7 years		7 years		7 years
Operating lease, expiration month and year					Jun. 30, 2024
Operating lease, renewal term			5 years		5 years		5 years
Operating leases, rent expense			$ 88,000	$ 88,000	$ 176,000	$ 176,000
Loss contingency accrual			$ 0		$ 0		$ 0
Indemnification agreement [Member]
Gain Contingencies [Line Items]
Loss contingency pending claims			0		0		0
Stanford Agreement [Member] | Research and development arrangement [Member]
Gain Contingencies [Line Items]
Sponsor research agreements, commitment amount		$ 600,000
Sponsored Research Agreement [Member]
Gain Contingencies [Line Items]
Maximum threshold period allowed for filing market authorisation	15 years
Proceeds from funding							$ 455,000
Sponsored Research Agreement [Member] | Other income [Member]
Gain Contingencies [Line Items]
Proceeds from funding			$ 0	$ 190,000	$ 0	$ 190,000
Sponsored Research Agreement [Member] | Research and development arrangement [Member]
Gain Contingencies [Line Items]
Maximum expected research funding	$ 651,000							$ 693,000

Redeemable Convertible Prefer_3

Redeemable Convertible Preferred Stock and Stockholder's Deficit - Summary Of Redeemable convertible preferred stock (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Series A [Member]
Temporary Equity [Line Items]
Shares Authorized	1,015,434		1,015,434
Shares Outstanding	1,015,434		1,015,434
Net Carrying Value	$ 1,000		$ 1,000
Liquidation Preference	$ 1,000		$ 1,000
Series A-1 [Member]
Temporary Equity [Line Items]
Shares Authorized	16,398,995		16,398,995
Shares Outstanding	16,398,995		16,398,995
Net Carrying Value	$ 17,149		$ 17,144
Liquidation Preference	$ 17,219		$ 17,219
Series B [Member]
Temporary Equity [Line Items]
Shares Authorized	38,778,090		38,778,091
Shares Outstanding	38,778,090		38,778,090
Net Carrying Value	$ 44,518		$ 44,505
Liquidation Preference	$ 44,595		$ 44,595
Series C [Member]
Temporary Equity [Line Items]
Shares Authorized	55,555,546		62,962,952
Shares Outstanding	55,555,546		55,555,546
Net Carrying Value	$ 81,877		$ 81,335
Liquidation Preference	$ 75,000		$ 75,000
Series D [Member]
Temporary Equity [Line Items]
Shares Authorized	71,719,859
Shares Outstanding	71,719,859
Net Carrying Value	$ 90,510
Liquidation Preference	$ 102,000
Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Shares Authorized	183,467,924		119,155,472
Shares Outstanding	183,467,924	111,748,065	111,748,065	89,525,848	89,525,848	89,525,848
Net Carrying Value	$ 235,054		$ 143,984
Liquidation Preference	$ 239,814		$ 137,814

Redeemable Convertible Prefer_4

Redeemable Convertible Preferred Stock and Stockholder's Deficit - Additional information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jul. 31, 2020	Jul. 24, 2020
Aggregate proceeds from redeemable convertible preferred stock				$ 101,985
Net issuance cost				890
Recognized a beneficial conversion feature		$ 281	$ 272	$ 560	$ 534
Subsequent Event [Member]
Conversion of redeemable preferred stock into common shares						20,824,938	20,824,938
Series D preferred stock [Member]
Redeemable convertible preferred stock issued	71,719,859
Redeemable convertible preferred stock issue price per share	$ 1.4222	$ 1.4222		$ 1.4222
Aggregate proceeds from redeemable convertible preferred stock	$ 96,800
Net issuance cost	$ 5,200	$ 5,193
Recognized a beneficial conversion feature				$ 6,300
Series D preferred stock [Member] | Principal Owner [Member]
Redeemable convertible preferred stock issued				9,773,587

Redeemable Convertible Prefer_5

Redeemable Convertible Preferred Stock and Stockholder's Deficit - Schedule Of Common Stock Reserved For Future Issuance (Detail) - shares	Jun. 30, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Options issued and outstanding	3,026,480	2,007,222
Options available for future grant	376,894	454,110
Total common stock reserved	24,228,312	15,145,546
Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Redeemable convertible preferred stock outstanding on an as-converted basis	20,824,938	12,684,214
Options issued and outstanding [Member]
Class of Stock [Line Items]
Options issued and outstanding	3,026,480	2,007,222
Options available for future grant [Member]
Class of Stock [Line Items]
Options available for future grant	376,894	454,110

Equity Incentive Plan - Summary

Equity Incentive Plan - Summary of stock option activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Shares available for grant, Beginning balance	454,110
Shares available for grant, Additional shares authorized	942,042
Shares available for grant, Stock options granted	(1,021,898)
Shares available for grant, Stock options cancelled	2,640
Shares available for grant, Ending balance	376,894	454,110
Number of shares, Beginning balance	2,007,222
Number of shares, Stock options granted	1,021,898
Number of shares, Stock options cancelled	(2,640)
Number of shares, Ending balance	3,026,480	2,007,222
Number of shares, Exercisable	1,032,734
Weighted- average exercise price per share, Beginning balance	$ 4.91
Weighted- average exercise price per share, Stock options granted	13.39
Weighted- average exercise price per share, Stock options cancelled	4.67
Weighted- average exercise price per share, Ending balance	7.77	$ 4.91
Weighted- average exercise price per share, Exercisable	$ 3.39
Weighted- average remaining contractual term	8 years 6 months	8 years 3 months 3 days
Weighted- average remaining contractual term, Exercisable	6 years 10 months 13 days
Aggregate intrinsic value	$ 16,828		$ 21,623
Aggregate intrinsic value, Exercisable	$ 10,236

Equity Incentive Plan - Summa_2

Equity Incentive Plan - Summary of stock-based compensation expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 763	$ 437	$ 1,426	$ 903
Research and development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	335	135	660	232
General and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 428	$ 302	$ 766	$ 671

Equity Incentive Plan - Summa_3

Equity Incentive Plan - Summary of fair value assumptions estimated on the date of grant using the Black-Scholes option pricing model (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	85.00%	76.00%	85.00%
Risk-free interest rate, Minimum	0.33%	1.87%	0.33%	1.87%
Risk-free interest rate, Maximum	0.45%	2.20%	1.45%	2.61%
Dividend yield
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	6 years 29 days	6 years 29 days	6 years 29 days	6 years 29 days
Expected volatility				77.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	5 years	6 years 7 days	5 years	6 years 7 days
Expected volatility				76.00%

Equity Incentive Plan - Additio

Equity Incentive Plan - Additional information (Detail) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options exercised		0
Intrinsic value of options exercised	$ 8,000		$ 8,000
Unrecognized stock-based compensation cost		$ 15,400,000
Unrecognized stock-based compensation cost expected Period For Recognition		3 years 2 months 12 days

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Stockholders - Summary of Net Loss Per Share Attributable to Common Stockholders (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	23,851,418	12,271,734	23,851,418	12,271,734
Redeemable convertible preferred stock on an as-converted basis [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	20,824,938	10,161,828	20,824,938	10,161,828
Stock options to purchase common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	3,026,480	2,109,906	3,026,480	2,109,906

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) $ / shares in Units, $ in Thousands	Aug. 04, 2020shares	Jul. 24, 2020USD ($)$ / sharesshares	Jul. 17, 2020	Jul. 31, 2020$ / sharesshares	Jun. 30, 2020USD ($)shares	Dec. 31, 2019shares
Subsequent Event [Line Items]
Payment of deferred offering costs					$ 890
Carrying value of the redeemable convertible preferred stock reclassified to equity					$ 6,297
Common stock reserved for future issuance | shares					24,228,312	15,145,546
IPO [Member]
Subsequent Event [Line Items]
Payment of deferred offering costs					$ 3,300
Subsequent Event [Member]
Subsequent Event [Line Items]
Proceeds from issuance of IPO		$ 262,700
Redeemable convertible preferred stock, shares issued upon conversion | shares		20,824,938		20,824,938
Increase in the carrying value of redeemable convertible preferred stock		$ 6,200
Carrying value of the redeemable convertible preferred stock reclassified to equity		$ 241,400
Subsequent Event [Member] | Two Thousand And Twenty Incentive Award Plan [Member]
Subsequent Event [Line Items]
Common stock reserved for future issuance | shares				3,600,868
Subsequent Event [Member] | Two Thousand And Twenty Employee Stock Purchase Plan [Member]
Subsequent Event [Line Items]
Common stock reserved for future issuance | shares				360,086
Subsequent Event [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Description of Reverse Stock Split			one-for-8.81 basis
Reverse Stock Split, Conversion ratio			8.81
Subsequent Event [Member] | IPO [Member]
Subsequent Event [Line Items]
Shares issued during the period | shares		14,750,000		14,750,000
Shares issued price per share | $ / shares		$ 17		$ 17
Payments for underwriting expense		$ 20,100
Payment of deferred offering costs		$ 4,300
Subsequent Event [Member] | Over-Allotment Option [Member]
Subsequent Event [Line Items]
Shares issued during the period | shares	2,139,403			2,139,403
Shares issued price per share | $ / shares				$ 17