Kezar Life Sciences (KZR) 10-Q 7 Aug 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Aug. 02, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	KZR
Entity Registrant Name	Kezar Life Sciences, Inc.
Entity Central Index Key	0001645666
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	true
Entity Small Business	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		19,137,645
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-38542
Entity Tax Identification Number	473366145
Entity Address, Address Line One	4000 Shoreline Court
Entity Address, Address Line Two	Suite 300
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	822-5600

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 13,031	$ 24,182
Marketable securities	80,392	83,250
Prepaid expenses	1,653	1,884
Other current assets	1,160	489
Total current assets	96,236	109,805
Property and equipment, net	4,713	4,595
Operating lease right-of-use asset	4,036
Other assets	282	282
Total assets	105,267	114,682
Current liabilities:
Accounts payable	955	193
Accrued liabilities	2,858	2,678
Operating lease liabilities, current	835
Deferred rent, current		354
Other liabilities, current	87	112
Total current liabilities	4,735	3,337
Operating lease liabilities, noncurrent	5,929
Deferred rent		2,548
Total liabilities	10,664	5,885
Stockholders' equity:
Common stock, $0.001 par value, 125,000,000 shares authorized as of June 30, 2019 (unaudited) and December 31, 2018; 19,132,645 and 19,114,421 shares issued and outstanding as of June 30, 2019 (unaudited) and December 31, 2018, respectively	19	19
Preferred stock, $0.001 par value, 10,000,000 shares authorized as of June 30, 2019 (unaudited) and December 31, 2018; zero shares issued and outstanding as of June 30, 2019 (unaudited) and December 31, 2018
Additional paid-in capital	160,295	158,176
Accumulated other comprehensive loss	(156)	(203)
Accumulated deficit	(65,555)	(49,195)
Total stockholders' equity	94,603	108,797
Total liabilities and stockholders' equity	$ 105,267	$ 114,682

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	19,132,645	19,114,421
Common stock, shares outstanding	19,132,645	19,114,421
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating expenses:
Research and development	$ 6,925	$ 5,228	$ 12,852	$ 8,800
General and administrative	2,430	1,722	4,812	3,236
Total operating expenses	9,355	6,950	17,664	12,036
Loss from operations	(9,355)	(6,950)	(17,664)	(12,036)
Interest income	637	175	1,304	314
Net loss	$ (8,718)	$ (6,775)	$ (16,360)	$ (11,722)
Net loss per common share, basic and diluted	$ (0.46)	$ (3.31)	$ (0.86)	$ (8.35)
Weighted-average shares used to compute net loss per common share, basic and diluted	19,073,830	2,044,027	19,058,263	1,404,392

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (8,718)	$ (6,775)	$ (16,360)	$ (11,722)
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	(49)	14	(41)	(9)
Unrealized gain on marketable securities	23		88
Total other comprehensive income (loss), net of tax	(26)	14	47	(9)
Comprehensive loss	$ (8,744)	$ (6,761)	$ (16,313)	$ (11,731)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Balance at Dec. 31, 2017	$ (25,687)		$ 1	$ 451	$ (111)	$ (26,028)
Balance, shares at Dec. 31, 2017			948,578
Balance at Dec. 31, 2017		$ 77,931
Balance, shares at Dec. 31, 2017		12,263,126
Issuance of common stock upon exercise of stock options, net of amount related to early exercised options	25			25
Issuance of common stock upon exercise of stock options, net of amount related to early exercised options, shares			109,818
Vesting related to shares of common stock issued pursuant to early exercises	17			17
Stock-based compensation expense	126			126
Other comprehensive income (loss)	(23)				(23)
Net loss	(4,947)					(4,947)
Balance at Mar. 31, 2018	(30,489)		$ 1	619	(134)	(30,975)
Balance, shares at Mar. 31, 2018			1,058,396
Balance at Mar. 31, 2018		$ 77,931
Balance, shares at Mar. 31, 2018		12,263,126
Balance at Dec. 31, 2017	(25,687)		$ 1	451	(111)	(26,028)
Balance, shares at Dec. 31, 2017			948,578
Balance at Dec. 31, 2017		$ 77,931
Balance, shares at Dec. 31, 2017		12,263,126
Other comprehensive income (loss)	(9)
Net loss	(11,722)
Balance at Jun. 30, 2018	119,341		$ 19	157,192	(120)	(37,750)
Balance, shares at Jun. 30, 2018			19,108,221
Balance at Jun. 30, 2018		$ 0
Balance, shares at Jun. 30, 2018		0
Balance at Mar. 31, 2018	(30,489)		$ 1	619	(134)	(30,975)
Balance, shares at Mar. 31, 2018			1,058,396
Balance at Mar. 31, 2018		$ 77,931
Balance, shares at Mar. 31, 2018		12,263,126
Conversion of redeemable convertible preferred stock to common stock	77,931		$ 12	77,919
Conversion of redeemable convertible preferred stock to common stock, shares			12,263,126
Conversion of redeemable convertible preferred stock to common stock		$ (77,931)
Conversion of redeemable convertible preferred stock to common stock, shares		(12,263,126)
Issuance of common stock upon initial public offering, net of issuance costs	77,641		$ 6	77,635
Issuance of common stock upon initial public offering, net of issuance costs, shares			5,750,000
Issuance of common stock upon exercise of stock options, net of amount related to early exercised options	24			24
Issuance of common stock upon exercise of stock options, net of amount related to early exercised options, shares			26,510
Issuance of common stock upon vesting of restricted stock units			10,189
Vesting related to shares of common stock issued pursuant to early exercises	7			7
Stock-based compensation expense	988			988
Other comprehensive income (loss)	14				14
Net loss	(6,775)					(6,775)
Balance at Jun. 30, 2018	119,341		$ 19	157,192	(120)	(37,750)
Balance, shares at Jun. 30, 2018			19,108,221
Balance at Jun. 30, 2018		$ 0
Balance, shares at Jun. 30, 2018		0
Balance at Dec. 31, 2018	108,797		$ 19	158,176	(203)	(49,195)
Balance, shares at Dec. 31, 2018			19,114,421
Balance at Dec. 31, 2018		$ 0
Balance, shares at Dec. 31, 2018		0
Issuance of common stock upon exercise of stock options, net of amount related to early exercised options	4			4
Issuance of common stock upon exercise of stock options, net of amount related to early exercised options, shares			4,000
Vesting related to shares of common stock issued pursuant to early exercises	12			12
Stock-based compensation expense	901			901
Other comprehensive income (loss)	73				73
Net loss	(7,642)					(7,642)
Balance at Mar. 31, 2019	102,145		$ 19	159,093	(130)	(56,837)
Balance, shares at Mar. 31, 2019			19,118,421
Balance at Mar. 31, 2019		$ 0
Balance, shares at Mar. 31, 2019		0
Balance at Dec. 31, 2018	$ 108,797		$ 19	158,176	(203)	(49,195)
Balance, shares at Dec. 31, 2018			19,114,421
Balance at Dec. 31, 2018		$ 0
Balance, shares at Dec. 31, 2018		0
Issuance of common stock upon exercise of stock options, net of amount related to early exercised options, shares	8,000
Other comprehensive income (loss)	$ 47
Net loss	(16,360)
Balance at Jun. 30, 2019	94,603		$ 19	160,295	(156)	(65,555)
Balance, shares at Jun. 30, 2019			19,132,645
Balance at Jun. 30, 2019		$ 0
Balance, shares at Jun. 30, 2019		0
Balance at Mar. 31, 2019	102,145		$ 19	159,093	(130)	(56,837)
Balance, shares at Mar. 31, 2019			19,118,421
Balance at Mar. 31, 2019		$ 0
Balance, shares at Mar. 31, 2019		0
Issuance of common stock upon exercise of stock options, net of amount related to early exercised options	180			180
Issuance of common stock upon exercise of stock options, net of amount related to early exercised options, shares			14,224
Vesting related to shares of common stock issued pursuant to early exercises	13			13
Stock-based compensation expense	1,009			1,009
Other comprehensive income (loss)	(26)				(26)
Net loss	(8,718)					(8,718)
Balance at Jun. 30, 2019	$ 94,603		$ 19	$ 160,295	$ (156)	$ (65,555)
Balance, shares at Jun. 30, 2019			19,132,645
Balance at Jun. 30, 2019		$ 0
Balance, shares at Jun. 30, 2019		0

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net loss	$ (16,360)	$ (11,722)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	628	281
Stock-based compensation	1,910	1,114
Amortization of premiums and discounts on marketable securities	(695)
Loss on disposal of property and equipment		97
Changes in operating assets and liabilities
Prepaid expenses and other current assets	(440)	(949)
Other assets		61
Accounts payable and accrued liabilities	919	548
Other liabilities, current		(8)
Deferred rent		(137)
Operating lease liabilities	(374)
Net cash used in operating activities	(14,412)	(10,715)
Cash flows from investing activities:
Purchases of property and equipment	(523)	(915)
Purchases of marketable securities	(59,255)	(16,412)
Maturities of marketable securities	62,896
Proceeds from sale of property and equipment		10
Net cash provided by (used in) investing activities	3,118	(17,317)
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs		78,782
Proceeds from the exercise of stock options	184	213
Net cash provided by financing activities	184	78,995
Effect of exchange rate changes on cash and cash equivalents and restricted cash	(41)	(36)
Net (decrease) increase in cash, cash equivalents and restricted cash	(11,151)	50,927
Cash, cash equivalents and restricted cash at the beginning of period	24,182	51,046
Cash, cash equivalents and restricted cash at the end of period	13,031	101,973
Supplemental disclosures of noncash investing and financing information:
Reclassification of employee stock liability to equity upon vesting	25	24
Addition of tenant improvement paid by landlord		2,703
Purchase of property and equipment in accounts payable	$ 23	35
Conversion of redeemable convertible preferred stock into common stock		77,931
Deferred offering costs in accrued liabilities		$ 1,141

Organization and Description of

Organization and Description of the Business	6 Months Ended
	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Description of the Business	1. Organization and Description of the Business Description of Business Kezar Life Sciences, Inc. (the “Company,” Liquidity Since commencing operations in mid-2015, substantially all of the Company’s efforts have been focused on research, development, and the advancement of the Company’s lead product candidate, KZR-616. The Company’s ultimate success depends on the outcome of the ongoing research and development activities. The Company has not yet generated product sales and as a result has experienced operating losses since inception and had an accumulated deficit of $65.6 million as of June 30, 2019. The Company expects to incur additional losses in the future to conduct research and development and will need to raise additional capital to fully implement management’s business plan. The Company intends to raise such capital through the issuance of additional equity, and potentially through borrowings, strategic alliances with partner companies and other licensing transactions. However, if such financing is not available at adequate levels, the Company may need to reevaluate its operating plans. Management believes that its existing cash, cash equivalents and marketable securities will be sufficient to fund the Company’s cash requirements for at least 12 months following the issuance of these financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Significant Accounting Policies The Company’s significant accounting policies are disclosed in the audited consolidated financial statements for the year ended December 31, 2018 and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018, filed with the U.S. Securities and Exchange Commission (“SEC”) on March 26, 2019 and except for the adoption of the Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842), there ha ve been no material changes during the six months ended June 30, 2019. Basis of Presentation and Consolidation The condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the Company’s accounts and those of its wholly owned Australian subsidiary, Unaudited Interim Condensed Consolidated Financial Statements The accompanying financial information as of June 30, 2019 is unaudited. The condensed consolidated financial statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of the results of operations for the interim periods covered and of our financial condition at the date of the interim balance sheet. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with GAAP for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying condensed consolidated financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto included in our Annual Report. 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 amounts of expenses during the reporting period. Significant items subject to such estimates and assumptions include the useful lives of fixed assets, stock-based compensation, and accrued research and development costs. Management bases its estimates on historical experience and on various other market-specific relevant assumptions that management believes to be reasonable under the circumstances. Actual results may differ from those estimates. Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents are stated at fair value. Marketable Securities All marketable securities have been classified as “available-for-sale” in accordance with the Company’s investment policy and cash management strategy. Short-term marketable securities mature within one-year from the balance sheet date. Investments in marketable securities are recorded at fair value, with any unrealized gains and losses reported within accumulated other comprehensive income as a separate component of stockholders’ deficit until realized or until a determination is made that an other-than-temporary decline in market value has occurred. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion, together with interest on securities, are included in interest income on the Company’s condensed consolidated statements of operations. Leases The Company elected the short-term lease recognition exemption for all leases that qualify. This means, for those leases that qualify, the Company will not recognize ROU assets or lease liabilities, and this includes not recognizing ROU assets or lease liabilities for existing short-term leases of those assets in transition. The Company did not elect to apply the practical expedient to not separate lease and non-lease components for all of its leases. Accounting Pronouncements Adopted in 2019 Leases (Topic 842) In February 2016, the Leases (Topic 842) Leases (Topic 842): Targeted Improvements The Company adopted the new standard on January 1, 2019 and used the effective date as its date of initial application. Consequently, financial information will not be restated and the disclosures required under the new standard will not be provided for dates and periods before January 1, 2019. The Company elected the package of transition practical expedients that allows the Company not to reassess the lease classification for any expired or existing contracts, whether initial direct costs were incurred, or whether any expired or existing contracts contained leases. This standard had a material effect on the Company’s consolidated financial statements. The most significant effects relate to: (1) the recognition of new ROU asset and lease liabilities on the balance sheet for the operating lease for the Company’s headquarters at 4000 Shoreline Court, Suite 300, South San Francisco; and (2) providing significant new disclosures about its leasing activities. The following table discloses the impact on the Company’s balance sheet upon adoption (in thousands): January 1, 2019 December 31, 2018 Operating lease ROU asset $ 4,236 $ — Operating lease liabilities, current 774 — Operating lease liabilities, noncurrent 6,364 — Deferred rent, current — 354 Deferred rent, noncurrent — 2,548 Stock Compensation (Topic 718) In June 2018, the FASB issued ASU No. 2018-07, Compensation – Stock Compensation (Topic 718) The Company adopted the new standard on January 1, 2019 and determined that New Accounting Pronouncements Not Yet Adopted , Financial Instruments-Credit Losses (Topic 326) In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement The amendment of ASU No. 2018-13 removes disclosure requirements from Topic 820 in the areas of: (1) the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy; (2) the policy for timing of transfers between levels; and (3) the valuation processes for Level 3 fair value measurements.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements Financial assets and liabilities are recorded at fair value. The carrying amount of certain financial instruments, including cash and cash equivalents, restricted cash, accounts payable and accrued liabilities, approximate fair value due to their relatively short maturities. Assets and liabilities recorded at fair value on a recurring basis in the condensed consolidated balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1 : Quoted prices in active markets for identical assets or liabilities. Level 2 : Observable inputs other than Level 1 prices, 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 3 : Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. There were no transfers between Level 1 and Level 2 securities in the periods presented. In certain cases, where there is limited activity or less transparency around inputs to valuation, securities are classified as Level 3 within the valuation hierarchy. The Company does not have any assets or liabilities measured using Level 3 inputs as of June 30, 2019 or December 31, 2018. The following table summarizes our financial assets measured at fair value on a recurring basis and classified under the appropriate level of the fair value hierarchy as described above (in thousands): June 30, 2019 Total Level 1 Level 2 Level 3 Financial Assets: Money market funds $ 12,646 $ 12,646 $ — $ — U.S. Treasury securities 9,983 9,983 — — Commercial paper 16,899 — 16,899 — Corporate debt securities 17,891 — 17,891 — U.S. agency bonds 35,619 — 35,619 — Total $ 93,038 $ 22,629 $ 70,409 $ — December 31, 2018 Total Level 1 Level 2 Level 3 Financial Assets: Money market funds $ 23,156 $ 23,156 $ — $ — U.S. Treasury securities 25,692 25,692 — — Commercial paper 19,190 — 19,190 — Corporate debt securities 20,451 — 20,451 — U.S. agency bonds 17,917 — 17,917 — Total $ 106,406 $ 48,848 $ 57,558 $ —

Available-for-Sale Securities

Available-for-Sale Securities	6 Months Ended
	Jun. 30, 2019
Investments Debt And Equity Securities [Abstract]
Available-for-Sale Securities	4. Available-for-Sale Securities The following table is a summary of available-for-sale securities recorded in cash and cash equivalents or marketable securities in our condensed consolidated balance sheets (in thousands): June 30, 2019 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Financial Assets Money market funds 12,646 — — 12,646 U.S. Treasury securities 9,971 12 — 9,983 Commercial paper 16,880 19 — 16,899 Corporate debt securities 17,885 6 — 17,891 U.S. agency bonds 35,588 33 (2 ) 35,619 Total $ 92,970 $ 70 $ (2 ) $ 93,038 December 31, 2018 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Financial Assets Money market funds $ 23,156 $ — $ — $ 23,156 U.S. Treasury securities 25,698 — (6 ) 25,692 Commercial paper 19,203 — (13 ) 19,190 Corporate debt securities 20,449 4 (2 ) 20,451 U.S. agency bonds 17,921 — (4 ) 17,917 Total $ 106,427 $ 4 $ (25 ) $ 106,406 The Company believes that the individual unrealized losses represent temporary declines primarily resulting from interest rate changes, and intends to hold these marketable securities to their maturities. As of June 30, 2019, the amortized cost and estimated fair value of the Company’s available-for-sale securities by contractual maturity are shown below (in thousands): Amortized Estimated Cost Fair Value Marketable securities maturing: In one year or less $ 80,324 $ 80,392 Total marketable securities $ 80,324 $ 80,392

Balance Sheet Components

Balance Sheet Components	6 Months Ended
	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheet Components	5. Balance Sheet Components Property and Equipment, Net Property and equipment consists of the following (in thousands): June 30, 2019 December 31, 2018 Leasehold improvements $ 3,268 $ 3,268 Furniture, laboratory and office equipment 2,539 2,043 Computer equipment 269 219 Total property and equipment 6,076 5,530 Less accumulated depreciation and amortization (1,363 ) (935 ) Property and equipment, net $ 4,713 $ 4,595 Depreciation expense was $0.2 million and $0.4 million for the three and six months ended June 30, 2019, respectively, compared to $0.2 million and $0.3 million for the three and six months ended June 30, 2018, respectively. Accrued Liabilities Accrued liabilities consisted of the following (in thousands): June 30, 2019 December 31, 2018 Accrued preclinical and research costs $ 1,469 $ 1,146 Accrued clinical costs 505 434 Accrued employee-related costs 640 736 Accrued professional services 145 138 Other 99 224 Total accrued liabilities $ 2,858 $ 2,678

Operating Lease

Operating Lease	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Operating Lease	6. Operating Lease In August 2017, the Company entered into a lease agreement to lease 24,357 square feet of combination laboratory and office space in South San Francisco, California. This lease expires in February 2025. The contractually specified minimum rent and annual rent increases for the operating lease are included in the measurement of the ROU asset and related lease liabilities. Under the lease arrangement, we may be required to pay directly, or reimburse the lessor for real estate taxes, insurance, utilities, maintenance and other operating costs. Such amounts are generally variable and therefore not included in the measurement of the ROU asset and related lease liability but are instead recognized as variable lease expense in our Condensed Consolidated Statements of Operations when they are incurred. The option to extend the lease was not recognized as part of the Company’s lease liability and ROU asset. Because the rate implicit in the lease is not readily determinable, the Company uses its incremental borrowing rate to determine the present value of the lease payments. The Company recorded lease liabilities and ROU asset for its office lease based on the present value of lease payments over the expected lease term. As of June 30, 2019, the weighted average remaining lease term was 5.67 years and the weighted average discount rate used to determine the operating lease liability was 10.0%. Information related to the Company’s ROU asset and related lease liabilities were as follows (in thousands): Three months ended June 30, 2019 Six months ended June 30, 2019 Cash paid for operating lease liabilities $ 193 $ 374 Operating lease costs 275 550 Variable lease costs 122 244 ROU asset obtained in exchange for operating lease obligation — 4,236 Maturities of lease liabilities as of June 30, 2019 were as follows for the years ending December 31: 2019 $ 730 2020 1,497 2021 1,542 2022 1,588 2023 1,635 2024 1,684 Thereafter 282 Total undiscounted lease payments 8,958 Less: imputed interest (2,194 ) Total lease liabilities $ 6,764 Operating lease liabilities, current 835 Operating lease liabilities, noncurrent 5,929 Total operating lease liabilities $ 6,764 Future minimum lease payments are as follows as of December 31, 2018 (in thousands): Years ending December 31: 2019 $ 1,453 2020 1,497 2021 1,542 2022 1,588 2023 1,635 Thereafter 1,966 Total future minimum lease payments $ 9,681 For the three and six months ended June 30, 2018, the Company recognized $0.3 million and $0.4 million of rent expense, respectively. Variable lease costs were $0.1 million and $0.2 million for the three and six months ended June 30, 2018, respectively.

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	7. Stock-Based Compensation Stock Incentive Plans 2018 Equity Incentive Plan In June 2018, the Company’s board of directors adopted and its stockholders approved the 2018 Equity Incentive Plan (the “2018 Plan”), which became effective as of June 20, 2018, at which point no further grants could be made under the 2015 Equity Incentive Plan (the “2015 Plan”) described below. Under the 2018 Plan, the Company may grant incentive stock options (“ISOs”), nonstatutory stock options (“NSOs”), stock appreciation rights, restricted stock awards, restricted stock units (“RSUs”) and other stock-based awards. As of June 30, 2019, options to purchase 787,601 shares of common stock and 10,189 RSUs have been granted and 2,055,886 shares were available for future issuance under the 2018 Plan. Initially, subject to adjustment as provided in the 2018 Plan, the aggregate number of shares of the Company’s common stock that may be issued pursuant to stock awards under the 2018 Plan was 4,000,000 shares, which is the sum of (i) 1,600,692 shares plus (ii) the number of shares reserved and remaining available for issuance under the 2015 Plan at the time the 2018 Plan became effective and (iii) the number of shares subject to stock options or other stock awards granted under the 2015 Plan that expire, terminate are forfeited or otherwise not issued, or are withheld to satisfy a tax withholding obligation in connection with an award or to satisfy a purchase or exercise price of an award (such as upon the expiration or termination of a stock award prior to vesting). The number of shares of the Company’s common stock reserved for issuance under the 2018 Plan will automatically increase on January 1 of each year, beginning on January 1, 2019 and continuing through and including January 1, 2028, by 5% of the total number of shares of capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s board of directors prior to such increase. The maximum number of shares that may be issued upon the exercise of ISOs under the 2018 Plan is 12,500,000 shares. 2015 Equity Incentive Plan The Company’s 2015 Plan provided for the granting of ISOs and NSOs to employees, directors and consultants at the discretion of its board of directors. The 2015 Plan was terminated as to future awards in June 2018, although it continues to govern the terms of options that remain outstanding under the 2015 Plan. No additional stock awards will be granted under the 2015 Plan, and all outstanding stock awards granted under the 2015 Plan that are repurchased, forfeited, expire or are cancelled will become available for grant under the 2018 Plan in accordance with its terms. Options granted under the 2015 Plan expire no later than 10 years from the date of grant. Options granted under the 2015 Plan vest over periods determined by the Company’s board of directors, generally over four years. The 2015 Plan allows for early exercise of certain options prior to vesting. Upon termination of employment, the unvested shares are subject to repurchase at the original exercise price. As of June 30, 2019, options to purchase 2,087,845 shares of common stock were outstanding under the 2015 Plan. 2018 Employee Stock Purchase Plan In June 2018, the Company’s board of directors adopted and its stockholders approved the 2018 Employee Stock Purchase Plan (the “ESPP”), which became effective as of June 20, 2018. The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the U.S. Internal Revenue Code of 1986, as amended. The number of shares of common stock initially reserved for issuance under the ESPP was 200,000 shares. The ESPP provides for an annual increase on January 1 of each year, beginning on January 1, 2019 and continuing through and including January 1, 2028, equal to the lesser of (i) 1% of the shares of common stock outstanding on the last day of the prior fiscal year or (ii) 375,000 shares, or a lesser number of shares determined by the Company’s board of directors prior to such increase. As of June 30, 2019, 10,224 shares of common stock had been issued under the ESPP and 380,920 shares remained available for future issuance under the ESPP. The price per share of common stock to be paid by an ESPP participant on the applicable purchase date of an offering period shall be equal to 85% of the lesser of the fair market value of a share of common stock on (i) the applicable offering date or (ii) the applicable purchase date. The Company’s board of directors authorized an initial six-month offering period beginning on November 16, 2018 and ending on May 15, 2019. A new six-month offering period automatically began on the day that immediately followed the conclusion of the initial offering period. Stock Option Activity The following table summarizes activity under the Company’s stock option plans and related information (in thousands, except share and per share amounts): Number of Options Outstanding Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Outstanding at December 31, 2018 2,181,466 $ 3.80 8.5 $ 43,189 Options granted 701,980 $ 21.07 Options exercised (8,000 ) $ 0.90 $ 134 Options cancelled — $ — Outstanding at June 30, 2019 2,875,446 $ 8.02 8.4 $ 9,234 Vested and exercisable at June 30, 2019 1,323,030 $ 3.74 7.7 $ 6,198 The weighted average grant date fair value of options granted during the six months ended June 30, 2019 was $14.74 per share. The total intrinsic value of exercised stock options during the three and six months ended June 30, 2019 was $56,000 and $134,000, respectively. The aggregate intrinsic value is calculated as the difference between the exercise price and the estimated fair value of the Company’s common stock at the date of exercise. Early Exercise Stock Options The 2015 Plan allowed for early exercisable option grants, which permit the holder to exercise a stock option for the purchase of common stock before the requisite service is provided (i.e., before the award is vested under its original terms); however, such arrangements permit the Company to subsequently repurchase at the exercise price any shares of common stock for which the applicable vesting conditions have not been satisfied. Under the 2015 Plan, the Company only made such early exercisable option grants to non-employee members of our board of directors. As of June 30, 2019 and December 31, 2018, there were 45,287 and 68,349 shares, respectively, of nonvested common stock outstanding that were exercised early and remain subject to repurchase by the Company at the original issuance price upon termination of the stockholder’s services. The right to repurchase these shares generally lapses with respect to 25% of the shares underlying the option one year after the applicable vesting commencement date and 1/48 of the shares underlying the option each month for 36 months thereafter. The shares purchased pursuant to the early exercise of stock options are not deemed, for accounting purposes, to be issued until such shares vest. The cash received in exchange for exercised and nonvested shares related to stock options granted is recorded as a liability for the early exercise of stock options on the balance sheets with the corresponding par value in common stock and an offset in additional paid-in capital. Restricted Stock In addition to the nonvested common stock outstanding described above under the section titled “Early Exercise Stock Options,” the Company issued restricted stock to its founders. The fair value of restricted stock on the issuance date is deemed equal to the cash consideration paid by the founders. Restricted stock vests over a four-year period from the applicable vesting commencement date. The following summarizes the vesting activity of restricted stock: Number of Shares Nonvested—December 31, 2018 20,908 Vested (20,908 ) Nonvested—June 30, 2019 — Stock-Based Compensation Expense Total stock-based compensation recognized by function was as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Research and development $ 470 $ 430 $ 917 $ 489 General and administrative 539 558 993 625 Total stock-based compensation expense $ 1,009 $ 988 $ 1,910 $ 1,114 As of June 30, 2019, the unrecognized stock-based compensation cost was $12.5 million with an estimated weighted average amortization period of 2.7 years. The fair value of the employee stock options granted is calculated using the Black-Scholes option-pricing model with the following weighted-average assumptions: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Expected term (years) 5.9 5.5 - 6.1 5.9 5.5 - 6.1 Expected volatility 78.7 - 81.3 % 82.8 % 78.7 - 81.9 % 82.0 - 82.8 % Risk-free interest rate 1.9 - 2.4 % 2.8 % 1.9 - 2.6 % 2.6 - 2.8 % Expected dividend yield — — — —

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	8. Income Taxes No provision for income taxes was recorded for the three and six months ended June 30, 2019 and 2018, respectively. 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. In December 2015, the Protecting Americans from Tax Hikes Act of 2015 (the “PATH Act”) was signed into law, which created several new research and development (“R&D”) tax credit provisions, including allowing qualified small businesses to utilize the R&D credit against the employer’s portion of payroll tax up to a maximum of $250,000 per year. The Company qualified as a small business under the PATH Act for both 2016 and 2017. The Company has not yet filed its federal tax return for 2018 in which the Company will determine whether it qualifies as a small business under the PATH Act. During the three and six months ended June 30, 2019, the Company utilized $79,000 and $172,000 of R&D tax credits as a reduction of payroll expenses to offset its payroll tax liabilities. During the three and six months ended June 30, 2018, there were zero tax benefits utilized from the R&D tax credits. The remaining R&D tax credits available for future payroll tax liabilities have been recorded as deferred tax assets with a full valuation allowance.

Net Loss per Share

Net Loss per Share	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Net Loss Per Share	9. Net Loss Per Share Net Loss Per Share The following table sets forth the calculation of basic and diluted net loss per share during the periods presented (in thousands, except share and per share data): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Numerator: Net loss $ (8,718 ) $ (6,775 ) $ (16,360 ) $ (11,722 ) Denominator: Weighted-average shares of common stock outstanding 19,073,830 2,044,027 19,058,263 1,404,392 Net loss per share, basic and diluted $ (0.46 ) $ (3.31 ) $ (0.86 ) $ (8.35 ) The following outstanding shares of common stock equivalents were excluded from the computation of the diluted net loss per share for the periods presented because their effect would have been anti-dilutive: Three and Six Months Ended June 30, 2019 2018 Stock options to purchase common stock 2,875,446 2,177,666 Common stock subject to future vesting 45,287 190,680 Total 2,920,733 2,368,346

Subsequent Event

Subsequent Event	6 Months Ended
	Jun. 30, 2019
Subsequent Events [Abstract]
Subsequent Event	10. Subsequent Event On July 3, 2019, we entered into an Open Market Sale Agreement SM

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Basis of presentation and consolidation	Basis of Presentation and Consolidation The condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the Company’s accounts and those of its wholly owned Australian subsidiary,
Unaudited Interim Condensed Consolidated Financial Statements	Unaudited Interim Condensed Consolidated Financial Statements The accompanying financial information as of June 30, 2019 is unaudited. The condensed consolidated financial statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of the results of operations for the interim periods covered and of our financial condition at the date of the interim balance sheet. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with GAAP for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying condensed consolidated financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto included in our Annual Report.
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 amounts of expenses during the reporting period. Significant items subject to such estimates and assumptions include the useful lives of fixed assets, stock-based compensation, and accrued research and development costs. Management bases its estimates on historical experience and on various other market-specific relevant assumptions that management believes to be reasonable under the circumstances. Actual results may differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents are stated at fair value.
Marketable Securities	Marketable Securities All marketable securities have been classified as “available-for-sale” in accordance with the Company’s investment policy and cash management strategy. Short-term marketable securities mature within one-year from the balance sheet date. Investments in marketable securities are recorded at fair value, with any unrealized gains and losses reported within accumulated other comprehensive income as a separate component of stockholders’ deficit until realized or until a determination is made that an other-than-temporary decline in market value has occurred. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion, together with interest on securities, are included in interest income on the Company’s condensed consolidated statements of operations.
Leases	Leases The Company elected the short-term lease recognition exemption for all leases that qualify. This means, for those leases that qualify, the Company will not recognize ROU assets or lease liabilities, and this includes not recognizing ROU assets or lease liabilities for existing short-term leases of those assets in transition. The Company did not elect to apply the practical expedient to not separate lease and non-lease components for all of its leases.
Accounting Pronouncements Adopted in 2019 and New Accounting Pronouncements Not Yet Adopted	Accounting Pronouncements Adopted in 2019 Leases (Topic 842) In February 2016, the Leases (Topic 842) Leases (Topic 842): Targeted Improvements The Company adopted the new standard on January 1, 2019 and used the effective date as its date of initial application. Consequently, financial information will not be restated and the disclosures required under the new standard will not be provided for dates and periods before January 1, 2019. The Company elected the package of transition practical expedients that allows the Company not to reassess the lease classification for any expired or existing contracts, whether initial direct costs were incurred, or whether any expired or existing contracts contained leases. This standard had a material effect on the Company’s consolidated financial statements. The most significant effects relate to: (1) the recognition of new ROU asset and lease liabilities on the balance sheet for the operating lease for the Company’s headquarters at 4000 Shoreline Court, Suite 300, South San Francisco; and (2) providing significant new disclosures about its leasing activities. The following table discloses the impact on the Company’s balance sheet upon adoption (in thousands): January 1, 2019 December 31, 2018 Operating lease ROU asset $ 4,236 $ — Operating lease liabilities, current 774 — Operating lease liabilities, noncurrent 6,364 — Deferred rent, current — 354 Deferred rent, noncurrent — 2,548 Stock Compensation (Topic 718) In June 2018, the FASB issued ASU No. 2018-07, Compensation – Stock Compensation (Topic 718) The Company adopted the new standard on January 1, 2019 and determined that New Accounting Pronouncements Not Yet Adopted , Financial Instruments-Credit Losses (Topic 326) In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement The amendment of ASU No. 2018-13 removes disclosure requirements from Topic 820 in the areas of: (1) the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy; (2) the policy for timing of transfers between levels; and (3) the valuation processes for Level 3 fair value measurements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Impact of Accounting Pronouncements Adoption on Balance Sheet	The following table discloses the impact on the Company’s balance sheet upon adoption (in thousands): January 1, 2019 December 31, 2018 Operating lease ROU asset $ 4,236 $ — Operating lease liabilities, current 774 — Operating lease liabilities, noncurrent 6,364 — Deferred rent, current — 354 Deferred rent, noncurrent — 2,548

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured at Fair Value on a Recurring Basis	The following table summarizes our financial assets measured at fair value on a recurring basis and classified under the appropriate level of the fair value hierarchy as described above (in thousands): June 30, 2019 Total Level 1 Level 2 Level 3 Financial Assets: Money market funds $ 12,646 $ 12,646 $ — $ — U.S. Treasury securities 9,983 9,983 — — Commercial paper 16,899 — 16,899 — Corporate debt securities 17,891 — 17,891 — U.S. agency bonds 35,619 — 35,619 — Total $ 93,038 $ 22,629 $ 70,409 $ — December 31, 2018 Total Level 1 Level 2 Level 3 Financial Assets: Money market funds $ 23,156 $ 23,156 $ — $ — U.S. Treasury securities 25,692 25,692 — — Commercial paper 19,190 — 19,190 — Corporate debt securities 20,451 — 20,451 — U.S. agency bonds 17,917 — 17,917 — Total $ 106,406 $ 48,848 $ 57,558 $ —

Available-for-Sale Securities (

Available-for-Sale Securities (Tables)	6 Months Ended
	Jun. 30, 2019
Investments Debt And Equity Securities [Abstract]
Summary of Available-For-Sale Securities Recorded in Cash and Cash Equivalents or Marketable Securities	The following table is a summary of available-for-sale securities recorded in cash and cash equivalents or marketable securities in our condensed consolidated balance sheets (in thousands): June 30, 2019 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Financial Assets Money market funds 12,646 — — 12,646 U.S. Treasury securities 9,971 12 — 9,983 Commercial paper 16,880 19 — 16,899 Corporate debt securities 17,885 6 — 17,891 U.S. agency bonds 35,588 33 (2 ) 35,619 Total $ 92,970 $ 70 $ (2 ) $ 93,038 December 31, 2018 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Financial Assets Money market funds $ 23,156 $ — $ — $ 23,156 U.S. Treasury securities 25,698 — (6 ) 25,692 Commercial paper 19,203 — (13 ) 19,190 Corporate debt securities 20,449 4 (2 ) 20,451 U.S. agency bonds 17,921 — (4 ) 17,917 Total $ 106,427 $ 4 $ (25 ) $ 106,406 The Company believes that the individual unrealized losses represent temporary declines primarily resulting from interest rate changes, and intends to hold these marketable securities to their maturities.
Summary of Amortized Cost and Estimated Fair Value of Available-for-sale Securities by Contractual Maturity	As of June 30, 2019, the amortized cost and estimated fair value of the Company’s available-for-sale securities by contractual maturity are shown below (in thousands): Amortized Estimated Cost Fair Value Marketable securities maturing: In one year or less $ 80,324 $ 80,392 Total marketable securities $ 80,324 $ 80,392

Balance Sheet Components (Table

Balance Sheet Components (Tables)	6 Months Ended
	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Property and Equipment	Property and equipment consists of the following (in thousands): June 30, 2019 December 31, 2018 Leasehold improvements $ 3,268 $ 3,268 Furniture, laboratory and office equipment 2,539 2,043 Computer equipment 269 219 Total property and equipment 6,076 5,530 Less accumulated depreciation and amortization (1,363 ) (935 ) Property and equipment, net $ 4,713 $ 4,595
Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): June 30, 2019 December 31, 2018 Accrued preclinical and research costs $ 1,469 $ 1,146 Accrued clinical costs 505 434 Accrued employee-related costs 640 736 Accrued professional services 145 138 Other 99 224 Total accrued liabilities $ 2,858 $ 2,678

Operating Lease (Tables)

Operating Lease (Tables)	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Details of Right-of-Use Assets and Lease Liabilities	Information related to the Company’s ROU asset and related lease liabilities were as follows (in thousands): Three months ended June 30, 2019 Six months ended June 30, 2019 Cash paid for operating lease liabilities $ 193 $ 374 Operating lease costs 275 550 Variable lease costs 122 244 ROU asset obtained in exchange for operating lease obligation — 4,236 Maturities of lease liabilities as of June 30, 2019 were as follows for the years ending December 31: 2019 $ 730 2020 1,497 2021 1,542 2022 1,588 2023 1,635 2024 1,684 Thereafter 282 Total undiscounted lease payments 8,958 Less: imputed interest (2,194 ) Total lease liabilities $ 6,764 Operating lease liabilities, current 835 Operating lease liabilities, noncurrent 5,929 Total operating lease liabilities $ 6,764
Schedule of Future Minimum Lease Payments	Future minimum lease payments are as follows as of December 31, 2018 (in thousands): Years ending December 31: 2019 $ 1,453 2020 1,497 2021 1,542 2022 1,588 2023 1,635 Thereafter 1,966 Total future minimum lease payments $ 9,681

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Activity under Stock Option Plan and Related Information	The following table summarizes activity under the Company’s stock option plans and related information (in thousands, except share and per share amounts): Number of Options Outstanding Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Outstanding at December 31, 2018 2,181,466 $ 3.80 8.5 $ 43,189 Options granted 701,980 $ 21.07 Options exercised (8,000 ) $ 0.90 $ 134 Options cancelled — $ — Outstanding at June 30, 2019 2,875,446 $ 8.02 8.4 $ 9,234 Vested and exercisable at June 30, 2019 1,323,030 $ 3.74 7.7 $ 6,198
Summarizes of Activity of Nonvested Restricted Stock	The following summarizes the vesting activity of restricted stock: Number of Shares Nonvested—December 31, 2018 20,908 Vested (20,908 ) Nonvested—June 30, 2019 —
Stock-Based Compensation Recognized	Total stock-based compensation recognized by function was as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Research and development $ 470 $ 430 $ 917 $ 489 General and administrative 539 558 993 625 Total stock-based compensation expense $ 1,009 $ 988 $ 1,910 $ 1,114
Fair Value of Employee Stock Options Granted is Calculated Using Black Scholes Option Pricing Model with Weighted Average Assumptions	The fair value of the employee stock options granted is calculated using the Black-Scholes option-pricing model with the following weighted-average assumptions: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Expected term (years) 5.9 5.5 - 6.1 5.9 5.5 - 6.1 Expected volatility 78.7 - 81.3 % 82.8 % 78.7 - 81.9 % 82.0 - 82.8 % Risk-free interest rate 1.9 - 2.4 % 2.8 % 1.9 - 2.6 % 2.6 - 2.8 % Expected dividend yield — — — —

Net Loss per Share (Tables)

Net Loss per Share (Tables)	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Calculation of Basic and Diluted Net Loss per Share	The following table sets forth the calculation of basic and diluted net loss per share during the periods presented (in thousands, except share and per share data): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Numerator: Net loss $ (8,718 ) $ (6,775 ) $ (16,360 ) $ (11,722 ) Denominator: Weighted-average shares of common stock outstanding 19,073,830 2,044,027 19,058,263 1,404,392 Net loss per share, basic and diluted $ (0.46 ) $ (3.31 ) $ (0.86 ) $ (8.35 )
Anti-dilutive Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share	The following outstanding shares of common stock equivalents were excluded from the computation of the diluted net loss per share for the periods presented because their effect would have been anti-dilutive: Three and Six Months Ended June 30, 2019 2018 Stock options to purchase common stock 2,875,446 2,177,666 Common stock subject to future vesting 45,287 190,680 Total 2,920,733 2,368,346

Organization and Description _2

Organization and Description of the Business - Additional Information (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019USD ($)Segment	Dec. 31, 2018USD ($)
Organization And Description Of Business [Line Items]
Number of operating segments | Segment	1
Accumulated deficit | $	$ 65,555	$ 49,195
Minimum
Organization And Description Of Business [Line Items]
Sufficient cash and cash equivalents available period term	12 months

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Impact of Accounting Pronouncements Adoption on Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Operating lease ROU asset	$ 4,036	$ 4,236
Operating lease liabilities, current	835	774
Operating lease liabilities, noncurrent	$ 5,929	$ 6,364
Deferred rent, current			$ 354
Deferred rent, noncurrent			$ 2,548

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail)	Jun. 30, 2019USD ($)
Fair Value Disclosures [Abstract]
Transfers from Level 1 to Level 2	$ 0
Transfers from Level 2 to Level 1	$ 0

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	$ 93,038	$ 106,406
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	22,629	48,848
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	70,409	57,558
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	12,646	23,156
Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	12,646	23,156
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	9,983	25,692
U.S. Treasury Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	9,983	25,692
Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	16,899	19,190
Commercial paper | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	16,899	19,190
Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	17,891	20,451
Corporate debt securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	17,891	20,451
U.S. Agency Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	35,619	17,917
U.S. Agency Bonds | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	$ 35,619	$ 17,917

Available-for-Sale Securities -

Available-for-Sale Securities - Summary of Available-For-Sale Securities Recorded in Cash and Cash Equivalents or Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 80,324
Fair Value	80,392
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	92,970	$ 106,427
Unrealized Gains	70	4
Unrealized Losses	(2)	(25)
Fair Value	93,038	106,406
Fair Value, Measurements, Recurring | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	12,646	23,156
Fair Value	12,646	23,156
Fair Value, Measurements, Recurring | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	9,971	25,698
Unrealized Gains	12
Unrealized Losses		(6)
Fair Value	9,983	25,692
Fair Value, Measurements, Recurring | Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	16,880	19,203
Unrealized Gains	19
Unrealized Losses		(13)
Fair Value	16,899	19,190
Fair Value, Measurements, Recurring | Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	17,885	20,449
Unrealized Gains	6	4
Unrealized Losses		(2)
Fair Value	17,891	20,451
Fair Value, Measurements, Recurring | U.S. Agency Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	35,588	17,921
Unrealized Gains	33
Unrealized Losses	(2)	(4)
Fair Value	$ 35,619	$ 17,917

Available-for-Sale Securities_2

Available-for-Sale Securities - Summary of Amortized Cost and Estimated Fair Value of Available-for-sale Securities by Contractual Maturity (Details) $ in Thousands	Jun. 30, 2019USD ($)
Marketable securities maturing, Amortized Cost:
In one year or less, Amortized Cost	$ 80,324
Total marketable securities, Amortized Cost	80,324
Marketable securities maturing, Estimated Fair Value:
In one year or less, Estimated Fair Value	80,392
Total marketable securities, Estimated Fair Value	$ 80,392

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment	$ 6,076	$ 5,530
Less accumulated depreciation and amortization	(1,363)	(935)
Property and equipment, net	4,713	4,595
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	3,268	3,268
Furniture, Laboratory and Office Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	2,539	2,043
Computer Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 269	$ 219

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Depreciation expense	$ 0.2	$ 0.2	$ 0.4	$ 0.3

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accrued preclinical and research costs	$ 1,469	$ 1,146
Accrued clinical costs	505	434
Accrued employee-related costs	640	736
Accrued professional services	145	138
Other	99	224
Total accrued liabilities	$ 2,858	$ 2,678

Operating Lease - Additional In

Operating Lease - Additional Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019USD ($)ft²	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)ft²	Jun. 30, 2018USD ($)
Weighted average remaining lease term	5 years 8 months 1 day		5 years 8 months 1 day
Operating lease liability, weighted average discount rate	10.00%		10.00%
Rent expense		$ 300		$ 400
Variable lease costs	$ 122	$ 100	$ 244	$ 200
South San Francisco, California [Member]
Area of lease | ft²	24,357		24,357
Lease Expiration Date			Feb. 28, 2025

Operating Lease - Details of Ri

Operating Lease - Details of Right-of-Use Assets and Lease Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019
Lessee Disclosure [Abstract]
Cash paid for operating lease liabilities	$ 193		$ 374
Operating lease costs	275		550
Variable lease costs	122	$ 100	244	$ 200
ROU asset obtained in exchange for operating lease obligation			4,236
2019	730		730
2020	1,497		1,497
2021	1,542		1,542
2022	1,588		1,588
2023	1,635		1,635
2024	1,684		1,684
Thereafter	282		282
Total undiscounted lease payments	8,958		8,958
Less: imputed interest	(2,194)		(2,194)
Total lease liabilities	6,764		6,764
Operating lease liabilities, current	835		835		$ 774
Operating lease liabilities, noncurrent	5,929		5,929		$ 6,364
Total operating lease liabilities	$ 6,764		$ 6,764

Operating Lease - Schedule of F

Operating Lease - Schedule of Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Years ending December 31:
2019	$ 1,453
2020	1,497
2021	1,542
2022	1,588
2023	1,635
Thereafter	1,966
Total future minimum lease payments	$ 9,681

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended	13 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options granted		701,980
Maximum number of shares issued upon exercise of incentive stock options	1,323,030	1,323,030	1,323,030
Common stock, shares issued	19,132,645	19,132,645	19,132,645	19,114,421
Weighted average grant date fair value of options granted		$ 21.07
Total intrinsic value of exercised stock options		$ 134,000
Early Exercise Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		36 months
Nonvested common shares outstanding	45,287	45,287	45,287	68,349
Percentage of underlying option shares whose right to purchase lapses after applicable vesting commencement date		25.00%
Right to repurchase shares underlying shares		0.0208
Employee options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation cost	$ 12,500,000	$ 12,500,000	$ 12,500,000
Estimated weighted average amortization period		2 years 8 months 12 days
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		4 years
Nonvested common shares outstanding				20,908
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future issuance	2,055,886	2,055,886	2,055,886
Number of shares will increase automatically through every year on specified date		--01-01
Number of shares increase automatically continuing through maximum period		beginning on January 1, 2019 and continuing through and including January 1, 2028
2018 Equity Incentive Plan | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares available for issuance	1,600,692	1,600,692	1,600,692
Increase in number of shares reserved for issuance as percentage of total number of shares of capital stock outstanding on last date of preceding calendar year		5.00%
2018 Equity Incentive Plan | Maximum [Member] | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares available for issuance	4,000,000	4,000,000	4,000,000
2018 Equity Incentive Plan | Employee options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options granted			787,601
2018 Equity Incentive Plan | Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of RSU granted			10,189
2018 Equity Incentive Plan | Incentive Stock Options | Maximum [Member] | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares issued upon exercise of incentive stock options	12,500,000	12,500,000	12,500,000
2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		4 years
Options to purchase of common stock outstanding	2,087,845	2,087,845	2,087,845
Weighted average grant date fair value of options granted		$ 14.74
Total intrinsic value of exercised stock options	$ 56,000	$ 134,000
2015 Equity Incentive Plan | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted expiry period		10 years
2018 Employee Stock Purchase Plan | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future issuance	380,920	380,920	380,920		200,000
Common stock, shares issued	10,224	10,224	10,224
Authorized an offering beginning period		Nov. 16, 2018
Authorized an offering ending period		May 15, 2019
2018 Employee Stock Purchase Plan | Maximum [Member] | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of annual increase in number of common stock shares		1.00%
Annual increase in number of common stock shares		375,000
Option price per share of common stock at fair market value		85.00%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Activity under Stock Option Plan and Related Information (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of options outstanding, Outstanding, Beginning balance	2,181,466
Number of options outstanding, Options granted	701,980
Number of options outstanding, Options exercised	(8,000)
Number of options outstanding, Outstanding, Ending balance	2,875,446	2,181,466
Number of options outstanding, options vested and exercisable	1,323,030
Weighted average exercise price, Outstanding, Beginning balance	$ 3.80
Weighted average exercise price, Options granted	21.07
Weighted average exercise price, Options exercised	0.90
Weighted average exercise price, Outstanding, Ending balance	8.02	$ 3.80
Weighted average exercise price, options vested and exercisable	$ 3.74
Weighted average remaining contractual term, Outstanding, Beginning balance	8 years 4 months 24 days	8 years 6 months
Weighted average remaining contractual term,options vested and exercisable	7 years 8 months 12 days
Aggregate intrinsic value, Outstanding, Beginning balance	$ 43,189
Aggregate intrinsic value, Options exercised	134
Aggregate intrinsic value, Outstanding, Ending balance	9,234	$ 43,189
Aggregate intrinsic value, options vested and exercisable	$ 6,198

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summarizes of Activity of Nonvested Restricted Stock (Details) - Restricted Stock	6 Months Ended
	Jun. 30, 2019shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested beginning balance	20,908
Number of Shares Outstanding, Vested	(20,908)

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,009	$ 988	$ 1,910	$ 1,114
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	470	430	917	489
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 539	$ 558	$ 993	$ 625

Stock-Based Compensation - Fair

Stock-Based Compensation - Fair Value of Employee Stock Options Granted is Calculated Using Black Scholes Option Pricing Model with Weighted Average Assumptions (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 10 months 24 days		5 years 10 months 24 days
Expected volatility		82.80%
Expected volatility, Minimum	78.70%		78.70%	82.00%
Expected volatility, Maximum	81.30%		81.90%	82.80%
Risk-free interest rate		2.80%
Risk-free interest rate, Minimum	1.90%		1.90%	2.60%
Risk-free interest rate, Maximum	2.40%		2.60%	2.80%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		5 years 6 months		5 years 6 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		6 years 1 month 6 days		6 years 1 month 6 days

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income tax provision	$ 0	$ 0	$ 0	$ 0
Research and development tax credit as a reduction of payroll expenses	$ 79,000	$ 0	$ 172,000	$ 0

Net Loss Per Share - Calculatio

Net Loss Per Share - Calculation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net loss	$ (8,718)	$ (7,642)	$ (6,775)	$ (4,947)	$ (16,360)	$ (11,722)
Denominator:
Weighted-average shares of common stock outstanding	19,073,830		2,044,027		19,058,263	1,404,392
Net loss per common share, basic and diluted	$ (0.46)		$ (3.31)		$ (0.86)	$ (8.35)

Net Loss Per Share - Anti-dilut

Net Loss Per Share - Anti-dilutive Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	2,920,733	2,368,346	2,920,733	2,368,346
Stock Options 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	2,875,446	2,177,666	2,875,446	2,177,666
Common stock subject to future vesting [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	45,287	190,680	45,287	190,680

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - ATM Agreement - Jefferies, LLC - Subsequent Event	Jul. 03, 2019USD ($)shares
Subsequent Event [Line Items]
Issuance of common stock | shares	0
Maximum
Subsequent Event [Line Items]
Common stock aggregate offering price | $	$ 50,000,000
Sales commission percentage on common stock	3.00%