Forty Seven (FTSV) 10-Q 13 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Nov. 02, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Trading Symbol	FTSV
Entity Registrant Name	Forty Seven, Inc.
Entity Central Index Key	1,667,633
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		31,064,600

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents		$ 23,426	$ 24,417	[1]
Short-term investments		130,592	63,694	[1]
Prepaid expenses and other current assets		6,622	4,450	[1]
Total current assets		160,640	92,561	[1]
Property and equipment, net		1,175	1,358	[1]
Other assets		1,477	1,546	[1]
Total assets		163,292	95,465	[1]
Current liabilities:
Accounts payable		3,890	3,705	[1]
Accrued liabilities		5,500	4,808	[1]
Deferred grant funding, current		4,134	2,759	[1]
Total current liabilities		13,524	11,272	[1]
Lease-related liabilities, noncurrent		376	476	[1]
Other long-term liabilities		157	255	[1]
Total liabilities		14,057	12,003	[1]
Commitments and Contingencies				[1]
Stockholders’ equity:
Convertible preferred stock	[1]		149,397
Common stock		3	1	[1]
Additional paid-in capital		271,819	3,507	[1]
Accumulated other comprehensive loss		(32)	(44)	[1]
Accumulated deficit		(122,555)	(69,399)	[1]
Total stockholders’ equity		149,235	83,462	[1]
Total liabilities and stockholders’ equity		$ 163,292	$ 95,465	[1]
[1]	The balance sheet as of December 31, 2017 is derived from the audited financial statements as of that date.

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating expenses:
Research and development	$ 17,984	$ 8,842	$ 42,733	$ 27,212
General and administrative	4,383	2,051	11,588	5,509
Total operating expenses	22,367	10,893	54,321	32,721
Loss from operations	(22,367)	(10,893)	(54,321)	(32,721)
Interest and other income, net	708	60	1,165	153
Net loss	(21,659)	(10,833)	(53,156)	(32,568)
Unrealized (loss) gain on available-for-sale securities	(4)	13	12	(4)
Comprehensive loss	$ (21,663)	$ (10,820)	$ (53,144)	$ (32,572)
Net loss per share, basic and diluted	$ (0.71)	$ (1.67)	$ (3.63)	$ (5.06)
Shares used in computing net loss per share, basic and diluted	30,430,898	6,504,467	14,643,348	6,438,138

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net loss	$ (53,156)	$ (32,568)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	2,318	413
Depreciation and amortization	289	276
Amortization (accretion) of premiums (discounts) on marketable securities	(293)	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,172)	1,146
Other assets	69	20
Accounts payable	185	(231)
Accrued liabilities	554	1,536
Deferred grant funding	1,375	2,478
Lease-related liabilities	(86)	(62)
Other long-term liabilities	(1)	(16)
Net cash used in operating activities	(50,918)	(27,008)
Cash flows from investing activities:
Purchases of property and equipment	(106)	(68)
Purchases of available-for-sale securities	(138,071)	(27,000)
Proceeds from maturities of available-for-sale securities	71,478	17,000
Net cash used in investing activities	(66,699)	(10,068)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs	0	40,377
Proceeds from issuance of common stock upon exercise of stock options	166	247
Proceeds from initial public offering, net of issuance costs	116,460	0
Net cash provided by financing activities	116,626	40,624
Net (decrease) increase in cash and cash equivalents	(991)	3,548
Cash and cash equivalents — beginning of period	24,417	9,742
Cash and cash equivalents — end of period	23,426	13,290
Supplemental disclosures of cash flow information:
Conversion of convertible preferred stock to common stock at close of initial public offering	149,397	0
Deferred offering costs included in accounts payable and accrued liabilities	$ 124	$ 0

Description of Business

Description of Business	9 Months Ended
	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	1. Description of Business The Company is a clinical-stage immuno-oncology company focused on developing novel checkpoint therapies to activate macrophages in the fight against cancer. Forty Seven was founded based on the insight that blocking CD47, a key signaling molecule that is over-expressed on cancer cells, renders tumors susceptible to macrophages and the innate immune system. By harnessing macrophages, the Company believes that its lead product candidate, 5F9, dosed as a monotherapy and in combination with marketed cancer therapies, can transform the treatment of cancer. Liquidity In the course of its development activities, the Company has sustained operating losses and expects to continue to generate operating losses for the foreseeable future. The Company’s ultimate success depends on the outcome of its research and development activities. The Company had cash, cash equivalents and short-term investments of $154.0 million as of September 30, 2018. Since inception through September 30, 2018, the Company has incurred cumulative net losses of $122.6 million. Management expects to incur additional losses in the future to conduct product research and development and recognizes the need to raise additional capital to fully implement its business plan. The Company intends to raise such capital through the issuance of additional equity financing and/or third-party collaboration funding. However, if such financing is not available at adequate levels, the Company will need to reevaluate its operating plan and may be required to delay the development of its products. The Company expects that its cash, cash equivalents and short-term investments will be sufficient to fund operating expenses and capital expenditure requirements for a period of at least one year from the date the unaudited financial statements are filed with the Securities and Exchange Commission (“SEC”). Reverse Stock Split In June 2018, the Company’s board of directors approved an amended and restated certificate of incorporation to effect a reverse split of shares of the Company’s common stock and convertible preferred stock on a 1-for-7.75 basis (the “Reverse Stock Split”). The par values of the common stock and convertible preferred stock were not adjusted as a result of the Reverse Stock Split. All references to common stock, options to purchase common stock, restricted stock, share data, per share data, convertible preferred stock and related information contained in the financial statements have been retroactively adjusted to reflect this Reverse Stock Split for all periods presented. The Reverse Stock Split was effected on June 14, 2018. Initial Public Offering On July 2, 2018, the Company completed its initial public offering (“IPO”) of 7,035,000 shares of common stock, and subsequently on July 27, 2018, the Company issued and sold an additional 1,055,250 shares upon the exercise of the underwriters’ over-allotment option. In connection with the IPO, including the over-allotment option, the Company issued and sold an aggregate of 8,090,250 shares of common stock at $16.00 per share, raising $116.3 million in proceeds, net of underwriting discounts and commissions of $9.1 million and offering expenses of $4.1 million. U pon the closing of the IPO, all outstanding shares of convertible preferred stock were automatically converted into 16,215,896 shares of common stock.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The interim condensed balance sheet as of September 30, 2018, the condensed statements of operations and comprehensive loss for the three and nine months ended September 30, 2018 and 2017, and the statements of cash flows for the nine months ended September 30, 2018 and 2017 are unaudited. The unaudited interim condensed financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s financial position as of September 30, 2018, its results of operations for the three and nine months ended September 30, 2018 and 2017, and cash flows for the nine months ended September 30, 2018 and 2017. The financial data and the other financial information contained in these notes to the condensed financial statements related to the three month and nine month periods are also unaudited. The results of operations for the three and nine months ended September 30, 2018 are not necessarily indicative of the results to be expected for the year ending December 31, 2018 or for any other future annual or interim period. The condensed balance sheet as of December 31, 2017 included herein was derived from the audited financial statements as of that date. These condensed financial statements should be read in conjunction with the Company's audited financial statements included in the prospectus dated June 27, 2018 (“Prospectus”) that forms a part of the Company's Registration Statements on Form S-1 (File Nos. 333-2225390 and 333-225933), as filed with the SEC pursuant to Rule 424 promulgated under the Securities Act of 1933, as amended. Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying financial statements include but are not limited to the fair value of common stock, the fair value of stock options, income tax uncertainties, 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. Fair Value Measurement Assets and liabilities recorded at fair value on a recurring basis in the 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. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2—Inputs (other than quoted prices included in Level 1) are either directly or indirectly observable for the asset or liability. These include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active; 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. Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update No. 2016-02, Leases

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The Company measures and reports its cash equivalents and short-term investments at fair value. Money market funds are measured at fair value on a recurring basis using quoted prices and are classified as a Level 1 input. Short-term investments are measured at fair value based on inputs other than quoted prices that are derived from observable market data and are classified as Level 2 inputs. There were no transfers between Levels 1, 2 or 3 for any of the periods presented. All of the investments held as of September 30, 2018 and December 31, 2017 had maturities of less than one year. There were no realized gains or losses on investments for the three and nine months ended September 30, 2018 and 2017. The fair value and amortized cost of cash equivalents and available-for-sale securities by major security type as of September 30, 2018 and December 31, 2017 are presented in the following tables: As of September 30, 2018 Fair Value Hierarchy Amortized Cost Unrealized Gains Unrealized Losses Market Value (In thousands) Money market funds Level 1 $ 20,726 $ — $ — $ 20,726 Commercial paper Level 2 39,046 — — 39,046 Corporate debt securities Level 2 48,166 — (20 ) 48,146 Asset-backed securities Level 2 23,542 — (10 ) 23,532 US government debt securities Level 2 19,870 — (2 ) 19,868 Total cash equivalents and available-for-sale securities $ 151,350 $ — $ (32 ) $ 151,318 As of December 31, 2017 Fair Value Hierarchy Amortized Cost Unrealized Gains Unrealized Losses Market Value (In thousands) Money market funds Level 1 $ 19,052 $ — $ — $ 19,052 Commercial paper Level 2 31,467 — — 31,467 Corporate debt securities Level 2 24,556 — (35 ) 24,521 Asset-backed securities Level 2 7,717 — (7 ) 7,710 US government debt securities Level 2 1,993 — (2 ) 1,991 Total cash equivalents and available-for-sale securities $ 84,785 $ — $ (44 ) $ 84,741

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2018
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	4. Balance Sheet Components Accrued Liabilities Accrued liabilities consist of the following: September 30, 2018 December 31, 2017 (In thousands) Accrued research and development expenses $ 3,044 $ 4,096 Accrued bonus 1,165 — Lease-related liabilities, current 147 133 Other 1,144 579 Total accrued liabilities $ 5,500 $ 4,808

Research and License Agreements

Research and License Agreements	9 Months Ended
	Sep. 30, 2018
Research And License Agreements [Abstract]
Research and License Agreements	5. Research and License Agreements Stanford License Agreement In November 2015, the Company entered into a technology license agreement with The Board of Trustees of the Leland Stanford Junior University (“Stanford”) under which Stanford granted to the Company exclusive licenses under certain patents and other intellectual property rights relating to the Company’s current product candidates and non-exclusive licenses under certain other patents and intellectual property rights to develop, manufacture and commercialize products for use in certain licensed fields, the scope of which would include the application of the licensed intellectual property in oncology. With respect to these licenses, the Company could be required to pay Stanford up to $5.6 million in milestone payments based on the achievement of certain development and regulatory approval milestones. The first such milestone payment of $75,000 was paid to Stanford in February 2018 and included in research and development expense for the nine months ended September 30, 2018. In addition, the m a n i q ir e t a m i i m u n u f e and a royalty of single digit percentage on e s l li c e s s reimburse patent-related expenses, s a r n non-royalty s bl i c e s i i c m c i v e l t h l i c n s n l og y n a c a g c n f e California Institute of Regenerative Medicine (CIRM) Grants In J u r 1 t m n a w d a research grant I T R s t u t v m l s e - b s a y m n w t h t a w 0 ov r f y rs As of September 30, 2018 and December 31, 2017, the Company had received $7.2 million and $3.8 million under the award In November 2017, the Company was awarded a second research grant from CIRM for a separate clinical trial study. The total amount of the research grant awarded was $5.0 million in various milestone-based payments over a period of five years. As of September 30, 2018 and December 31, 2017, the Company had received $1.6 million and $1.1 million under the award t C m a n is obligated t a o y a l i n li c e s i f e a s o p ce a g e s a l RM - f n e product candidates I M - f n e e c n l g y Leukemia & Lymphoma Society Grant In The Company recognizes research grants as a reduction of research and development expense when the eligible costs are incurred. For the three months ended September 30, 2018 and 2017, the Company recognized $2.2 million and $0.9 million as a reduction to research and development expenses for research grants. For the nine months ended September 30, 2018 and 2017, the Company recognized $5.6 million and $2.3 million as a reduction to research and development expenses for research grants. Merck Collaboration Agreement In BliNK Purchase Agreement In m a n could be q ir e t a a royalty of single digit percentage on e s l li c e s s Synthon License Agreement In July 2018, the Company entered into a settlement and license agreement with Synthon Biopharmaceuticals B.V. (“Synthon”). Under the agreement, the Company agreed to discontinue its ongoing oppositions and challenges at the European Patent Office (“EPO”) and the U.S. Patent and Trademark Office (“USPTO”) directed towards certain patents licensed by Synthon from Stichting Sanquin Bloedvoorziening (“SSB”) that In exchange, for these sublicenses and option rights, the Company agreed to pay Synthon an aggregate of up to approximately 40.0 million Euros (approximately $47 million US Dollar based on the exchange rate at July 16, 2018) comprising an upfront payment upon grant of sublicense and the achievement of future regulatory and commercial milestones which comprise the significant majority of the aggregate payments. If the Company exercises its option right, the Company will pay Synthon additional amounts upon the achievement of certain regulatory and commercial milestones related to such follow-on anti-CD47 product. In addition, the Company will be required to pay Synthon an annual license fee and a royalty of a tiered, low single digit percentage on net sales of any approved licensed products. The Company has the right to buy out its royalty obligations for each licensed product in full by paying Synthon specified lump sum amounts prior to the occurrence of certain defined events.

Convertible Preferred Stock

Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Convertible Preferred Stock	6. Convertible Preferred Stock On the completion of the IPO on July 2, 2018, all outstanding shares of convertible preferred stock were automatically converted into 16,215,896 shares of common stock and the related carrying value was reclassified to common stock and additional paid-in capital. Accordingly, there were no shares of convertible preferred stock outstanding as of September 30, 2018.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	7. Stock-Based Compensation 2015 and 2018 Equity Incentive Plans In November 2015, the Company adopted the 2015 Equity Incentive Plan (“2015 Plan”). The 2015 Plan provides for the Company to sell or issue common stock or restricted common stock, or to grant incentive stock options or nonqualified stock options for the purchase of common stock, to employees, members of the board of directors and consultants of the Company under terms and provisions established by the board of directors. As of September 30, 2018, there were 3,322,805 shares of the Company’s common stock reserved for future issuance under the 2015 Plan upon the exercise of outstanding stock options. In June 2018, the Company adopted the 2018 Equity Incentive Plan (“2018 Plan”), which became effective upon the execution of the underwriting agreement related to the IPO. As a result, the Company will not grant any additional awards under the 2015 Plan. The terms of the 2015 Plan and applicable award agreements will continue to govern any outstanding awards thereunder. The Company has initially reserved 3,000,000 shares of common stock for issuance under the 2018 Plan. In addition, the number of shares of common stock reserved for issuance under the 2018 Plan will automatically increase on the first day of January for a period of up to ten years, commencing on January 1, 2019, in an amount equal to 5% of the total number of shares of the Company’s capital stock outstanding on the last day of the preceding year, or a lesser number of shares determined by the Company’s board of directors. As of September 30, 2018, there were 2,977,650 shares available for future grants under the 2018 Plan. The following summarizes option activity for the nine months ended September 30, 2018: Shares Issuable Under Options Weighted- Average Exercise Price Weighted- Average Remaining Contract Term Aggregate Intrinsic Value (In years) (In thousands) Balance, December 31, 2017 2,102,528 $ 4.47 9.43 $ 1,672 Options granted 1,335,138 8.94 Options exercised (32,736 ) 5.06 Options forfeited (59,775 ) 4.97 Balance outstanding September 30, 2018 3,345,155 6.24 9.04 29,030 Exercisable, September 30, 2018 2,051,733 5.99 8.98 18,312 Vested and expected to vest, September 30, 2018 3,345,155 6.24 9.04 29,030 Total stock-based compensation was as follows: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) (In thousands) Research and development $ 477 $ 51 $ 774 $ 116 General and administrative 794 160 1,544 297 Total $ 1,271 $ 211 $ 2,318 $ 413 Restricted Stock As of September 30, 2018 and December 31, 2017, there was $157,000 and $255,000 recorded in other long-term liabilities related to shares held by employees and directors that were subject to repurchase. A summary of restricted stock activity follows: Number of Restricted Shares Outstanding Unvested shares—December 31, 2017 156,988 Early exercised options 11,418 Restricted shares vested (66,129 ) Repurchased by the Company (41,935 ) Unvested shares—September 30, 2018 60,342 Employees Share Purchase Plan (ESPP) In June 2018, the Company adopted the 2018 Employee Stock Purchase Plan (“ESPP”), which became effective upon the execution of the underwriting agreement related to the IPO. The Company has initially reserved 450,000 shares of common stock for purchase under the ESPP. The initial offering period began June 27, 2018 and will end on August 15, 2020 with purchase dates of February 25, 2019, August 15, 2019, February 15, 2020, and August 15, 2020. Each subsequent offering will be approximately 24 months long and will consist of four purchase periods with purchase dates occurring on February 15 and August 15 of each year. On each purchase date, ESPP participants will purchase shares of common stock at a price per share equal to 85% of the lesser of (1) the fair market value per share of the common stock on the offering date or (2) the fair market value of the common stock on the purchase date.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Net Loss Per Share	8. Net Loss Per Share The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect: As of September 30, 2018 2017 Convertible preferred stock — 8,626,388 Stock options to purchase common stock 3,345,155 1,326,319 Restricted stock subject to future vesting 60,342 182,795 Shares committed under ESPP 18,728 — Total 3,424,225 10,135,502

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes In December 2017, the Tax Cuts and Jobs Act of 2017 (the “Tax Act”) was signed into law. The Tax Act, among other changes, lowers the Company’s federal tax rate from 34% to 21%. Based on provisions of the Tax Act, the Company remeasured its deferred tax assets and liabilities as of December 31, 2017 to reflect the lower statutory tax rate. However, since the Company established a valuation allowance to offset its deferred tax assets, there was no impact to the effective tax rate, as any changes to deferred taxes would be offset by the valuation allowance. The deferred tax remeasurement is provisional and is subject to revision as the Company completes its analysis of the Tax Act, collects and prepares necessary data and interprets any additional guidance issued by standard-setting bodies. The Company currently anticipates finalizing and recording any resulting adjustments related to the tax effects of the Tax Act in the fourth quarter of 2018.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The interim condensed balance sheet as of September 30, 2018, the condensed statements of operations and comprehensive loss for the three and nine months ended September 30, 2018 and 2017, and the statements of cash flows for the nine months ended September 30, 2018 and 2017 are unaudited. The unaudited interim condensed financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s financial position as of September 30, 2018, its results of operations for the three and nine months ended September 30, 2018 and 2017, and cash flows for the nine months ended September 30, 2018 and 2017. The financial data and the other financial information contained in these notes to the condensed financial statements related to the three month and nine month periods are also unaudited. The results of operations for the three and nine months ended September 30, 2018 are not necessarily indicative of the results to be expected for the year ending December 31, 2018 or for any other future annual or interim period. The condensed balance sheet as of December 31, 2017 included herein was derived from the audited financial statements as of that date. These condensed financial statements should be read in conjunction with the Company's audited financial statements included in the prospectus dated June 27, 2018 (“Prospectus”) that forms a part of the Company's Registration Statements on Form S-1 (File Nos. 333-2225390 and 333-225933), as filed with the SEC pursuant to Rule 424 promulgated under the Securities Act of 1933, as amended.
Use of Estimate	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying financial statements include but are not limited to the fair value of common stock, the fair value of stock options, income tax uncertainties, 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.
Fair Value Measurement	Fair Value Measurement Assets and liabilities recorded at fair value on a recurring basis in the 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. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2—Inputs (other than quoted prices included in Level 1) are either directly or indirectly observable for the asset or liability. These include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active; 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.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update No. 2016-02, Leases

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis	The fair value and amortized cost of cash equivalents and available-for-sale securities by major security type as of September 30, 2018 and December 31, 2017 are presented in the following tables: As of September 30, 2018 Fair Value Hierarchy Amortized Cost Unrealized Gains Unrealized Losses Market Value (In thousands) Money market funds Level 1 $ 20,726 $ — $ — $ 20,726 Commercial paper Level 2 39,046 — — 39,046 Corporate debt securities Level 2 48,166 — (20 ) 48,146 Asset-backed securities Level 2 23,542 — (10 ) 23,532 US government debt securities Level 2 19,870 — (2 ) 19,868 Total cash equivalents and available-for-sale securities $ 151,350 $ — $ (32 ) $ 151,318 As of December 31, 2017 Fair Value Hierarchy Amortized Cost Unrealized Gains Unrealized Losses Market Value (In thousands) Money market funds Level 1 $ 19,052 $ — $ — $ 19,052 Commercial paper Level 2 31,467 — — 31,467 Corporate debt securities Level 2 24,556 — (35 ) 24,521 Asset-backed securities Level 2 7,717 — (7 ) 7,710 US government debt securities Level 2 1,993 — (2 ) 1,991 Total cash equivalents and available-for-sale securities $ 84,785 $ — $ (44 ) $ 84,741

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2018
Balance Sheet Related Disclosures [Abstract]
Schedule of Accrued Liabilities	Accrued liabilities consist of the following: September 30, 2018 December 31, 2017 (In thousands) Accrued research and development expenses $ 3,044 $ 4,096 Accrued bonus 1,165 — Lease-related liabilities, current 147 133 Other 1,144 579 Total accrued liabilities $ 5,500 $ 4,808

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Option Activity	The following summarizes option activity for the nine months ended September 30, 2018: Shares Issuable Under Options Weighted- Average Exercise Price Weighted- Average Remaining Contract Term Aggregate Intrinsic Value (In years) (In thousands) Balance, December 31, 2017 2,102,528 $ 4.47 9.43 $ 1,672 Options granted 1,335,138 8.94 Options exercised (32,736 ) 5.06 Options forfeited (59,775 ) 4.97 Balance outstanding September 30, 2018 3,345,155 6.24 9.04 29,030 Exercisable, September 30, 2018 2,051,733 5.99 8.98 18,312 Vested and expected to vest, September 30, 2018 3,345,155 6.24 9.04 29,030
Schedule of Total Stock-Based Compensation	Total stock-based compensation was as follows: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (In thousands) (In thousands) Research and development $ 477 $ 51 $ 774 $ 116 General and administrative 794 160 1,544 297 Total $ 1,271 $ 211 $ 2,318 $ 413
Summary of Restricted Stock Activity	A summary of restricted stock activity follows: Number of Restricted Shares Outstanding Unvested shares—December 31, 2017 156,988 Early exercised options 11,418 Restricted shares vested (66,129 ) Repurchased by the Company (41,935 ) Unvested shares—September 30, 2018 60,342

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Summary of Outstanding Potentially Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share	The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect: As of September 30, 2018 2017 Convertible preferred stock — 8,626,388 Stock options to purchase common stock 3,345,155 1,326,319 Restricted stock subject to future vesting 60,342 182,795 Shares committed under ESPP 18,728 — Total 3,424,225 10,135,502

Description of Business - Addit

Description of Business - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 27, 2018	Jul. 02, 2018	Jun. 30, 2018	Sep. 30, 2018	Dec. 31, 2017	[1]
Description Of Business [Line Items]
Cash, cash equivalents and short-term investments				$ 154,000
Cumulative net losses				$ 122,555	$ 69,399
Reverse stock split			1-for-7.75
Convertible preferred stock automatically converted into common stock		16,215,896
Intial Public Offering
Description Of Business [Line Items]
Common stock shares, issued		7,035,000
Convertible preferred stock automatically converted into common stock		16,215,896
Over-Allotment Option
Description Of Business [Line Items]
Common stock shares, issued	1,055,250
IPO and Over-Allotment
Description Of Business [Line Items]
Common stock shares, issued	8,090,250
Common stock price per share	$ 16
Proceeds from issuance of common stock	$ 116,300
Underwriting discounts and commissions	9,100
Offering expenses	$ 4,100
[1]	The balance sheet as of December 31, 2017 is derived from the audited financial statements as of that date.

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers between level 1 to Level 2 and Level 3 amount	$ 0		$ 0
Realized gains (losses) on investments	$ 0	$ 0	$ 0	$ 0
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity of investments			1 year

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value and Amortized Cost of Cash Equivalents and Available for Sale Securities by Major Security Type (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 151,350	$ 84,785
Unrealized Losses	(32)	(44)
Market Value	151,318	84,741
Level 1
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	20,726	19,052
Market Value	20,726	19,052
Commercial Paper | Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	39,046	31,467
Market Value	39,046	31,467
Corporate Debt Securities | Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	48,166	24,556
Unrealized Losses	(20)	(35)
Market Value	48,146	24,521
Asset-backed Securities | Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	23,542	7,717
Unrealized Losses	(10)	(7)
Market Value	23,532	7,710
US Government Debt Securities | Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	19,870	1,993
Unrealized Losses	(2)	(2)
Market Value	$ 19,868	$ 1,991

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accrued Liabilities Current [Abstract]
Accrued research and development expenses	$ 3,044	$ 4,096
Accrued bonus	1,165
Lease-related liabilities, current	147	133
Other	1,144	579
Total accrued liabilities	$ 5,500	$ 4,808	[1]
[1]	The balance sheet as of December 31, 2017 is derived from the audited financial statements as of that date.

Research and License Agreemen_2

Research and License Agreements - Additional Information (Details) € in Millions

1 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

Jul. 31, 2018USD ($)

Jun. 30, 2018USD ($)

Feb. 28, 2018USD ($)

Nov. 30, 2017USD ($)

Jan. 31, 2017USD ($)

Sep. 30, 2018USD ($)

Sep. 30, 2017USD ($)

Sep. 30, 2018USD ($)

Sep. 30, 2018EUR (€)

Sep. 30, 2017USD ($)

Dec. 31, 2017USD ($)

Mar. 31, 2017USD ($)

Nov. 30, 2015USD ($)

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Research and development

$ 17,984,000

$ 8,842,000

$ 42,733,000

$ 27,212,000

Technology License Agreement | Leland Stanford Junior University

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone payments

$ 75,000

Technology License Agreement | Leland Stanford Junior University | Research and Development

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone payments

75,000

Technology License Agreement | Leland Stanford Junior University | Maximum

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone payments to be paid upon achievement of development and regulatory approval milestones

$ 5,600,000

Research Grant | California Institute of Regenerative Medicine (CIRM)

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaborative arrangement research grant receivable

$ 10,200,000

Collaborative arrangement milestone payments receivable period

4 years

Proceeds from collaborators

7,200,000

$ 3,800,000

Research Grant | Leukemia & Lymphoma Society, Inc. ("LLS")

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaborative arrangement research grant receivable

$ 4,200,000

Proceeds from collaborators

3,900,000

1,000,000

Reduction to research and development expenses for research grants

2,200,000

$ 900,000

5,600,000

$ 2,300,000

Research Grant | Leukemia & Lymphoma Society, Inc. ("LLS") | Maximum

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone payments to be paid upon achievement of development and regulatory approval milestones

15,000,000

15,000,000

Second Research Grant | California Institute of Regenerative Medicine (CIRM)

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaborative arrangement research grant receivable

$ 5,000,000

Collaborative arrangement milestone payments receivable period

5 years

Proceeds from collaborators

1,600,000

$ 1,100,000

Merck Collaboration Agreement | Ares Trading S.A

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Reduction to research and development expenses for research grants

400,000

1,000,000

Receivable for reimbursement of research and development costs incurred

1,000,000

1,000,000

BliNK Purchase Agreement | Blink

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone payments

0

Initial upfront fee payment

$ 500,000

$ 2,500,000

Additional annual payment for license fee

300,000

Research and development

500,000

3,000,000

BliNK Purchase Agreement | Blink | Intellectual Property Rights and Know-How

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Initial upfront fee payment

$ 500,000

BliNK Purchase Agreement | Blink | Maximum

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone payments to be paid upon achievement of development and regulatory approval milestones

$ 43,000,000

43,000,000

License and Settlement Agreement | Synthon Biopharmaceuticals B.V.

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Payments comprising upfront payment, achievement of future regulatory and commercial milestones

$ 47,000,000

€ 40

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Details) - shares	Sep. 30, 2018	Jul. 02, 2018
Class Of Stock [Line Items]
Convertible preferred stock automatically converted into common stock		16,215,896
Intial Public Offering
Class Of Stock [Line Items]
Convertible preferred stock automatically converted into common stock		16,215,896
Preferred Stock, Shares Outstanding	0

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employees share purchase plan description	The initial offering period began June 27, 2018 and will end on August 15, 2020 with purchase dates of February 25, 2019, August 15, 2019, February 15, 2020, and August 15, 2020. Each subsequent offering will be approximately 24 months long and will consist of four purchase periods with purchase dates occurring on February 15 and August 15 of each year. On each purchase date, ESPP participants will purchase shares of common stock at a price per share equal to 85% of the lesser of (1) the fair market value per share of the common stock on the offering date or (2) the fair market value of the common stock on the purchase date.
Employees share purchase plan purchase price percentage	85.00%
Restricted Stock | Other Long-term Liabilities
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares held by employees and directors subject to repurchase	$ 157,000	$ 255,000
2015 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock reserved for future issuance	3,322,805
2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock reserved for future issuance	3,000,000
Number of shares available for future grants	2,977,650
Increase in number of shares of common stock reserved for issuance, description	Number of shares of common stock reserved for issuance under the 2018 Plan will automatically increase on the first day of January for a period of up to ten years, commencing on January 1, 2019, in an amount equal to 5% of the total number of shares of the Company?s capital stock outstanding on the last day of the preceding year, or a lesser number of shares determined by the Company?s board of directors.
Percentage of increase in number of shares of common stock reserved for issuance	5.00%
Maximum period to increase common stock reserved for issuance	10 years
Employees Share Purchase Plan (ESPP)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock reserved for future issuance	450,000

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Option Activity (Details) - 2015 and 2018 Stock Plan - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issuable Under Options, Beginning balance	2,102,528
Shares Issuable Under Options, Options granted	1,335,138
Shares Issuable Under Options, Options exercised	(32,736)
Shares Issuable Under Options, Options forfeited	(59,775)
Shares Issuable Under Options, Ending balance	3,345,155	2,102,528
Shares Issuable Under Options, Exercisable	2,051,733
Shares Issuable Under Options, Vested and expected to vest	3,345,155
Weighted-Average Exercise Price, Beginning balance	$ 4.47
Weighted-Average Exercise Price, Options granted	8.94
Weighted-Average Exercise Price, Options exercised	5.06
Weighted-Average Exercise Price, Options forfeited	4.97
Weighted-Average Exercise Price, Ending balance	6.24	$ 4.47
Weighted-Average Exercise Price, Exercisable	5.99
Weighted-Average Exercise Price, Vested and expected to vest	$ 6.24
Weighted-Average Remaining Contract Term	9 years 14 days	9 years 5 months 4 days
Weighted-Average Remaining Contract Term Exercisable	8 years 11 months 23 days
Weighted-Average Remaining Contract Term Vested and expected to vest	9 years 14 days
Aggregate Intrinsic Value	$ 29,030	$ 1,672
Aggregate Intrinsic Value Exercisable	18,312
Aggregate Intrinsic Value Vested and expected to vest	$ 29,030

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Total Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 1,271	$ 211	$ 2,318	$ 413
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	477	51	774	116
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 794	$ 160	$ 1,544	$ 297

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Restricted Stock Activity (Details)	9 Months Ended
	Sep. 30, 2018shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Restricted Shares Outstanding, Beginning balance	156,988
Number of Restricted Shares Outstanding, Early exercised options	11,418
Number of Restricted Shares Outstanding, Restricted shares vested	(66,129)
Number of Restricted Shares Outstanding, Repurchased by the Company	(41,935)
Number of Restricted Shares Outstanding, Ending balance	60,342

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Outstanding Potentially Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	3,424,225	10,135,502
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total		8,626,388
Stock Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	3,345,155	1,326,319
Restricted Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	60,342	182,795
Shares Committed under ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	18,728

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal tax rate	21.00%	34.00%