Alpine Immune Sciences (ALPN) 10-K 28 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Mar. 20, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	ALPN
Entity Registrant Name	Alpine Immune Sciences, Inc.
Entity Central Index Key	1,626,199
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		13,846,084
Entity Public Float			$ 28.4

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 8,000,000	$ 11,819,000
Short-term investments	73,240,000
Prepaid expenses and other current assets	1,308,000	36,000
Total current assets	82,548,000	11,855,000
Restricted cash	132,000
Property and equipment, net	1,089,000	740,000
Intangible assets	1,453,000
Total assets	85,222,000	12,595,000
Current liabilities:
Accounts payable	193,000	127,000
Accrued liabilities	382,000	170,000
Income taxes payable		66,000
Deferred revenue	277,000	2,008,000
Deferred rent, current portion	48,000	33,000
Current portion of long-term debt	995,000
Total current liabilities	1,895,000	2,404,000
Deferred rent, long-term portion	66,000
Deferred tax liability	305,000
Long-term debt	4,039,000	113,000
Total liabilities	6,305,000	2,517,000
Commitments and contingencies
Convertible preferred stock, $0.001 par value, 10,000,000 shares authorized and zero shares issued and outstanding at December 31, 2017; $0.0001 par value, 22,081,852 shares authorized and 4,311,770 shares issued and outstanding at December 31, 2016; aggregate liquidation preference of zero and $11,583 at December 31, 2017 and 2016, respectively		11,535,000
Stockholders' equity (deficit):
Common stock, $0.001 par value, 200,000,000 shares authorized, 13,881,645 shares issued and 13,831,178 shares outstanding at December 31, 2017; $0.0001 par value, 46,500,000 shares authorized, 608,701 shares issued and outstanding at December 31, 2016	14,000
Additional paid-in capital	88,346,000	144,000
Accumulated other comprehensive loss	(59,000)
Accumulated deficit	(9,384,000)	(1,601,000)
Total stockholders' equity (deficit)	78,917,000	(1,457,000)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$ 85,222,000	$ 12,595,000

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Convertible preferred stock, par value	$ 0.001	$ 0.0001
Convertible preferred stock, shares authorized	10,000,000	22,081,852
Convertible preferred stock, shares issued	0	4,311,770
Convertible preferred stock, shares outstanding	0	4,311,770
Convertible preferred stock, liquidation preference	$ 0	$ 11,583
Common stock, par value	$ 0.001	$ 0.0001
Common stock, shares authorized	200,000,000	46,500,000
Common stock, shares issued	13,881,645	608,701
Common stock, shares outstanding	13,831,178	608,701
Treasury stock, shares	50,467	0

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Collaboration revenue	$ 1,731,000	$ 2,950,000	$ 492,000
Operating expenses:
Research and development	10,626,000	2,989,000	422,000
General and administrative	6,079,000	1,149,000	441,000
Total operating expenses	16,705,000	4,138,000	863,000
Loss from operations	(14,974,000)	(1,188,000)	(371,000)
Other income (expense):
Bargain purchase gain	6,601,000
Interest expense	(152,000)
Interest and other income	542,000	22,000	2,000
Loss before taxes	(7,983,000)	(1,166,000)	(369,000)
Income tax benefit (expense)	200,000	(66,000)
Basic and diluted net loss attributable to common stockholders	(7,783,000)	(1,232,000)	(369,000)
Comprehensive loss:
Unrealized loss on investments	(59,000)
Comprehensive loss	$ (7,842,000)	$ (1,232,000)	$ (369,000)
Basic and diluted net loss per share applicable to common stockholders	$ (1.20)	$ (2.18)	$ (0.74)
Weighted-average shares used to compute basic and diluted net loss per share attributable to common stockholders	6,481,665	564,816	496,900

Consolidated Statement of Conve

Consolidated Statement of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Series A-1 Convertible Preferred Stock	Common Stock	Treasury	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Retained Earnings
Balance, convertible preferred stock at Dec. 31, 2014		$ 0
Balance, convertible preferred stock, shares at Dec. 31, 2014		0
Balance at Dec. 31, 2014	$ 0			$ 0	$ 0	$ 0	$ 0	$ 0
Balance, shares at Dec. 31, 2014				0
Issuance common stock	1					1
Issuance common stock, shares				496,900
Issuance of convertible preferred stock		$ 610
Issuance of convertible preferred stock, shares		1,212,436
Stock-based compensation and warrant expense	16					16
Net loss	(369)							(369)
Balance, convertible preferred stock at Dec. 31, 2015		$ 610
Balance, convertible preferred stock, shares at Dec. 31, 2015		1,212,436
Balance at Dec. 31, 2015	(352)					17		(369)
Balance, shares at Dec. 31, 2015				496,900
Issuance of convertible preferred stock		$ 10,925
Issuance of convertible preferred stock, shares		3,099,334
Exercise of stock options	50					50
Exercise of stock options, shares				111,801
Stock-based compensation	77					77
Net loss	(1,232)							(1,232)
Balance, convertible preferred stock at Dec. 31, 2016	$ 11,535	$ 11,535
Balance, convertible preferred stock, shares at Dec. 31, 2016	4,311,770	4,311,770
Balance at Dec. 31, 2016	$ (1,457)					144		(1,601)
Balance, shares at Dec. 31, 2016				608,701
Issuance of convertible preferred stock			$ 37,666
Issuance of convertible preferred stock, shares			4,989,663
Conversion of convertible preferred stock to common stock	49,201			$ 1		49,200
Conversion of convertible preferred stock to common stock, shares		(9,301,433)
Conversion of convertible preferred stock to common stock		$ (49,201)
Conversion of convertible preferred stock to common stock, shares				9,301,433
Common stock acquired in business combination	38,103					38,103
Common stock acquired in business combination, shares				3,914,058
Adjustment of par value from $0.0001 per share to $0.001 per share				$ 13		(13)
Conversion of warrant liability to equity	52					52
Exercise of stock options and common stock warrants	22					22
Exercise of stock options and common stock warrants, shares				57,453
Repurchase of common stock				(50,467)	50,467
Stock-based compensation	838					838
Unrealized loss on investments	(59)						(59)
Net loss	$ (7,783)							(7,783)
Balance, convertible preferred stock, shares at Dec. 31, 2017	0
Balance at Dec. 31, 2017	$ 78,917			$ 14	$ 50,467	$ 88,346	$ (59)	$ (9,384)
Balance, shares at Dec. 31, 2017				13,831,178

Consolidated Statement of Conv6

Consolidated Statement of Convertible Preferred Stock and Stockholders' Equity (Deficit) - (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement Of Stockholders Equity [Abstract]
Common stock, par value	$ 0.001	$ 0.0001

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net loss	$ (7,783)	$ (1,232)	$ (369)
Adjustments to reconcile net loss to net cash used in operating activities:
Bargain purchase gain	(6,601)
Depreciation expense	241	69	1
Non-cash interest expense	87
Common stock issued for intellectual property			1
Stock-based compensation expense	838	77	16
Changes in operating assets and liabilities:
Prepaid expenses	(1,193)	(26)	(10)
Accounts payable	66	80	47
Deferred revenue	(1,731)	(2,950)	4,958
Accrued liabilities	(259)	39	176
Deferred income tax	(204)
Deferred rent and other	(33)	146
Net cash (used in) provided by operating activities	(16,572)	(3,797)	4,820
Investing activities:
Purchase of property and equipment	(586)	(782)	(7)
Purchase of short-term investments	(88,307)
Proceeds from sale short-term investments	27,960
Cash and cash equivalents acquired in connection with merger	31,130
Net cash used in investing activities	(29,803)	(782)	(7)
Financing activities:
Proceeds from sale of preferred stock	37,666	10,925	610
Proceeds from borrowings	5,000
Proceeds from exercise of stock options and common stock warrants	22	50
Net cash provided by financing activities	42,688	10,975	610
Net (decrease) increase in cash and cash equivalents and restricted cash	(3,687)	6,396	5,423
Cash and cash equivalents and restricted cash at beginning of period	11,819	5,423
Cash and cash equivalents and restricted cash at end of period	8,132	$ 11,819	$ 5,423
Supplemental Information
Convertible preferred stock exchanged for common stock	49,201
Discount in connection with issuance of debt	428
Cash paid for income taxes	76
Cash paid for interest	53
Reclass of preferred stock warrant liability to equity	$ 52

Description of Business

Description of Business	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Description of Business	1. Description of Business Alpine Immune Sciences, Inc. (the “Company”, “Alpine”, “we”, “us”, or “our”) is focused on discovering and developing modern, protein-based immunotherapies targeting the immune synapse to treat cancer, inflammation, and other diseases. Our proprietary scientific platform uses a process known as directed evolution, or an iterative scientific engineering process purposefully conducted to “evolve” a protein to create therapeutics potentially capable of modulating immune system interactions. In our pre-clinical animal studies, our platform has proven capable of identifying novel molecules, including single domains capable of modulating multiple targets. We were incorporated under the laws of the State of Delaware and are headquartered in Seattle, Washington. Significant estimates inherent in the preparation of the accompanying consolidated financial statements include recoverability and useful lives of intangible assets and the fair value of equity based awards. Reverse Merger and Subscription Agreement On April 18, 2017, we entered into a merger agreement with Nivalis Therapeutics, Inc. (“Nivalis”), a public biotechnology company, and one of its wholly-owned subsidiaries pursuant to which, the subsidiary merged with and into Alpine, with Alpine continuing as a wholly owned subsidiary of Nivalis and the surviving corporation of the merger (the “Merger Agreement”). Nivalis Therapeutics, Inc. was incorporated in Delaware in March 2007. Alpine Immune Sciences, Inc. (prior to its business combination with Nivalis Therapeutics, Inc.) was incorporated in Delaware on December 30, 2014. The merger is intended to qualify for federal income tax purposes as a tax-free reorganization under the provisions of Section 368(a) of the Internal Revenue Code of 1986, as amended. At the closing of the merger, each outstanding share of our capital stock (common stock and preferred stock) was converted into the right to receive shares of Nivalis common stock (subject to the payment of cash in lieu of fractional shares and after giving effect to a 1:4 reverse stock split of Nivalis common stock) such that, immediately following the effective time of the merger, preexisting Nivalis stockholders, optionholders, and warrantholders owned, or held rights to acquire, approximately 26% of the fully-diluted common stock of Nivalis, which changed its name to “Alpine Immune Sciences, Inc.” following the completion of the merger and Alpine’s preexisting stockholders, optionholders, and warrantholders owned, or held rights to acquire approximately 74% of the fully-diluted common stock of Nivalis. The issuance of the shares to our pre-existing stockholders was registered under the Securities Act of 1933, as amended, pursuant to a registration statement on Form S-4 (No. 333-218134) (the “Registration Statement”) declared effective by the Securities and Exchange Commission (the “SEC”) on June 6, 2017. Contemporaneously with the execution and delivery of the Merger Agreement, certain of our pre-existing stockholders entered into a subscription agreement with us pursuant to which such stockholders purchased, immediately prior to the closing of the merger, 1,335,118 shares of our capital stock at a purchase price of $12.74 per share for an aggregate purchase price of approximately $17.0 million. The merger and the subscription described above were consummated on July 24, 2017.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation and Use of Estimates The accompanying consolidated financial statements have been prepared in accordance with the rules and regulations of the SEC and generally accepted accounting principles in the United States of America (“GAAP”). The preparation of financial statements in conformity with GAAP requires management to make judgments, estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. We base our estimates and assumptions on historical experience when available and on various factors we believe to be reasonable under the circumstances. Actual results could differ materially from those estimates. Principles of Consolidation Our consolidated financial statements include the financial position and results of operations of Alpine and AIS Operating Co., Inc., our wholly owned subsidiary and operating company. On July 24, 2017, we closed the merger on the terms described in more detail in Note 1. In connection with the merger, Nivalis effected a 1:4 reverse stock split of its common stock. Upon the closing of the merger, (1) a wholly-owned subsidiary of Nivalis merged with and into Alpine, with Alpine (renamed as “AIS Operating Co., Inc.”) remaining as the surviving entity; and (2) Nivalis was renamed as “Alpine Immune Sciences, Inc.” Segments We operate in one segment and use cash flow as the primary measure to manage our business and do not segment the business for internal reporting or decision-making purposes. Business Combination We use our best estimates and assumptions to accurately assign fair value to the tangible and intangible assets acquired and liabilities assumed at the acquisition date. Our estimates are inherently uncertain and subject to refinement. During the measurement period, which may be up to one year from the acquisition date, we may record adjustments to the fair value of these tangible and intangible assets acquired and liabilities assumed, with the corresponding offset to bargain purchase gain. In addition, uncertain tax positions and tax-related valuation allowances are initially established in connection with a business combination as of the acquisition date. Our management collects new information and reevaluates these estimates and assumptions quarterly and records any adjustments to our preliminary estimates to bargain purchase gain during the measurement period. Upon the conclusion of the measurement period or final determination of the fair value of assets acquired or liabilities assumed, whichever comes first, any subsequent adjustments are recorded to our consolidated statements of operations and comprehensive income (loss). We allocated the preliminary purchase price to the acquired tangible and intangible assets and assumed liabilities of Nivalis based on their estimated fair values as of the acquisition date. The fair value of our identifiable intangible asset is based on detailed valuations using information and assumptions provided by management. The allocation of the purchase consideration to the assets acquired and liabilities assumed in our financial statements was finalized as of December 31, 2017. Cash and cash equivalents We consider all highly liquid investments with an original maturity of 90 days or less at the time of purchase to be cash equivalents. Cash and cash equivalents consist of deposits with commercial banks in checking and interest-bearing accounts, and highly liquid money market funds. Concentrations of Credit Risk Cash and cash equivalents, receivables, accounts payable and accrued liabilities, which are recorded at invoiced amount or cost, approximate fair value based on the short-term nature of these financial instruments. The fair value of short-term investments is based on quoted market prices. Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash and cash equivalents and short-term investments. Periodically, we maintain deposits in financial institutions in excess of government insured limits. We believe we are not exposed to significant credit risk as our deposits are held at financial institutions we believe to be of high credit quality securities such as money market funds, U.S. Treasury securities, and commercial paper. To date, we have not realized any losses on these deposits. Short-Term Investments Our short-term investments include funds invested in highly liquid money market funds, U.S. Treasury securities, commercial paper, and corporate debt securities with a final maturity of each security of less than one year. All investments are classified as available-for-sale securities and are recorded at fair value based on quoted prices in active markets, with unrealized gains and losses excluded from earnings and reported in other comprehensive income (loss). Purchase premiums and discounts are recognized as interest income using the interest method over the terms of the securities. Realized gains and losses and declines in fair value deemed to be other than temporary are reflected in the consolidated statements of operations and comprehensive income (loss) using the specific-identification method. Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation. Depreciation is recorded using the straight-line method the estimated useful lives of the assets, generally three to five years, while leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is credited or charged to operations. Maintenance and repairs are expensed as incurred. Major improvements are capitalized as additions to property and equipment. Intangible Asset Our intangible asset is our indefinite-life GSNOR inhibitor in-process research and development asset (“IPR&D”) acquired from Nivalis. The IPR&D represents the processes, expertise, and technology employed in the development of S-nitrosoglutathione reductase (“GSNOR”) inhibitors and Nivalis’ lead product candidate, cavosonstat. The IPR&D represents the estimated fair value as of the acquisition date of substantive in-process projects that have not reached technological feasibility. The primary basis for determining technological feasibility of these projects is obtaining regulatory approval. The valuation of IPR&D is determined using a discounted cash flow method. In determining the value of IPR&D, management considers, among other factors, the stage of completion of the projects, the technological feasibility of the projects, whether the projects have an alternative future use, and the estimated residual cash flows that could be generated from the various projects and technologies over their respective projected economic lives. The discount rate used is determined at the time of acquisition and includes a rate of return which accounts for the time value of money, as well as risk factors reflecting the economic risk that the projected cash flows may not be realized. We review our IPR&D at least annually for possible impairment. IPR&D is reviewed for possible impairment between annual tests if an event occurs or circumstances change that would more likely than not reduce the fair value of the IPR&D below their carrying values. We test our IPR&D each year on October 1. Our IPR&D asset totaled $1.5 million at December 31, 2017. Impairment of Long-lived Assets We evaluate our long-lived tangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. If the carrying value exceeds the undiscounted future cash flows estimated to result from the use and eventual disposition of the asset, we write down the asset to its estimated fair value. Impairment is assessed by comparing the undiscounted cash flows expected to be generated by the asset to its carrying value. We did not record any impairments in the years ended December 31, 2017, 2016 and 2015. Accrued Liabilities As part of the process of preparing our consolidated financial statements, we are required to estimate accruals for professional services and research and development expenses. This process involves reviewing contracts and vendor agreements, and communicating with applicable personnel to identify services that have been performed on our behalf. We estimate the level of service performed and the associated cost incurred for the service when we have not yet been invoiced or otherwise notified of the actual cost. We estimate accrued liabilities as of each balance sheet date based on known facts and circumstances. Although we do not expect our estimates to be materially different from amounts actually incurred, if our estimates of the status and timing of services performed differ from the actual status and timing of services performed, we may report amounts that are too high or too low in any particular period. To date, we have not experienced any significant adjustments to our estimates. Leases and Deferred Rent We have entered into lease agreements for office and laboratory space. These leases are classified as operating leases. Rent payments, rent-free periods and rent increases are recognized as rent expense on a straight-line basis over the lease term. The difference between rent expense recognized and rental payments is recorded as deferred rent in the accompanying consolidated balance sheets. Common Stock Warrants We granted common stock warrants to certain non-employee professional advisers. We account for our warrants at fair value, with changes in fair value recognized in operating expenses. Common stock warrants are initially recorded at their issuance date fair value and are subsequently remeasured at each balance sheet date. These warrants are valued using the Black-Scholes option pricing model based on the estimated market value of the underlying common stock at the valuation measurement dates, the remaining contractual term of the warrant, risk-free interest rates, expected dividends, and expected volatility of the price of the underlying common stock. Derivative Financial Instruments We evaluate all of our financial instruments, including issued stock purchase warrants, to determine if such instruments are derivatives or contain features qualifying as embedded derivatives. For derivative financial instruments accounted for as liabilities, the derivative instrument is initially recorded at its fair value and is then re-valued at each reporting date, with changes in the fair value reported in the consolidated statement of operations and comprehensive income (loss). We use the Black-Scholes option-pricing model to value the derivative instruments at inception and subsequent valuation dates. The classification of derivative instruments, including whether such instruments should be recorded as liabilities or as equity, is re-assessed at the end of each reporting period. We do not use derivative instruments to hedge exposures to cash flow, market, or foreign currency risks. Revenue Recognition We derive our revenue from collaboration and licensing agreements. We recognize revenue when each of the following four criteria are met: (1) persuasive evidence of an arrangement exists; (2) products have been delivered or services have been rendered; (3) the sales price is fixed or determinable; and (4) collectability is reasonably assured. We recognize revenue under our License and Research Agreement (the “Collaboration Agreement”) with Kite Pharma, Inc. (“Kite”) in accordance with the guidance on multiple element arrangements. Multiple elements or deliverables may include (1) grants of, or options to obtain, intellectual property licenses; (2) research and development services; and/or (3) manufacturing or supply services. Payments typically received under these arrangements include one or more of the following: non-refundable upfront license fees, option exercise fees, payment for research and/or development efforts, amounts due upon the achievement of specified objectives, and/or royalties on future product sales. The evaluation of multiple-element arrangements requires management to make judgments about (1) the identification of deliverables; (2) whether such deliverables are separable from other aspects of the contractual relationship; (3) the estimated selling price of each deliverable; and (4) the expected period of performance for each deliverable. To determine the units of accounting under a multiple-element arrangement, management evaluates certain separation criteria, including whether the deliverables have stand-alone value, based on the relevant facts and circumstances for each arrangement. Management then estimates the selling price for each unit of accounting and allocates the arrangement consideration to each unit using the relative selling price method. The allocated consideration for each unit of accounting is recognized based on the method most appropriate for that unit of account and in accordance with the revenue recognition criteria detailed above. If there are deliverables in an arrangement that are not separable from other aspects of the contractual relationship, they are treated as a combined unit of accounting, with the allocated revenue for the combined unit recognized in a manner consistent with the revenue recognition criteria applicable to the final deliverable in the combined unit. Payments received prior to satisfying the relevant revenue recognition criteria are recorded as deferred revenue in the accompanying consolidated balance sheets and recognized as revenue when the related revenue recognition criteria are met. The Collaboration Agreement provides for non-refundable milestone payments. We recognize revenue that is contingent upon the achievement of a substantive milestone in its entirety in the period in which the milestone is achieved. A milestone is considered substantive when the consideration payable to us for such milestone (1) is consistent with our performance necessary to achieve the milestone or the increase in value to the collaboration resulting from our performance; (2) relates solely to our past performance; and (3) is reasonable relative to all of the other deliverables and payments within the arrangement. In making this assessment, we consider all facts and circumstances relevant to the arrangement, including factors such as the scientific, regulatory, commercial, and other risks that must be overcome to achieve the milestone, the level of effort and investment required to achieve the milestone and whether any portion of the milestone consideration is related to future performance or deliverables. We will periodically review the estimated performance periods under the Collaboration Agreement which provides for non-refundable upfront payments and fees. We will adjust the periods over which revenue should be recognized when appropriate to reflect changes in assumptions relating to the estimated performance periods. We could accelerate revenue recognition in the event of early termination of programs or if our expectations change. Alternatively, we could decelerate revenue recognition if programs are extended or delayed. While such changes to our estimates have no impact on our reported cash flows, the timing of revenue recorded in future periods could be materially impacted. Research and Development Research and development costs are expensed as incurred. Research and development costs include payroll and personnel expense, consulting costs, external contract research and development expenses, raw materials, drug product manufacturing costs and allocated overhead – including depreciation, rent and utilities. Research and development costs that are paid in advance of performance are capitalized as a prepaid expense and amortized over the service period as the services are provided. Stock-based Compensation We account for all stock-based compensation granted to employees and non-employees using a fair value method. Stock-based compensation awarded to employees and non-employees is measured at the grant date fair value for stock option grants. We use the Black-Scholes option pricing model to estimate the fair value of stock options at the grant date. Stock-based compensation to employees is recognized over the requisite service period of the awards, usually the vesting period, on a straight-line basis. Stock-based compensation awarded to non-employees is revalued over its vesting period using a Black-Sholes option pricing model. For performance-based awards where the vesting of the options may be accelerated upon the achievement of certain milestones, vesting and the related stock-based compensation is recognized as an expense when it is probable the milestone will be met. We recognize forfeiture of awards as they occur rather than estimating the expected forfeiture rate. When awards are modified, we compare the fair value of the affected award measured immediately prior to modification to its value after modification. To the extent that the fair value of the modified award exceeds the original award, the incremental fair value of the modified award is recognized as compensation on the date of modification for vested awards, and over the remaining vesting period for unvested awards. Income Taxes Income taxes are accounted for using an asset and liability approach that requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the consolidated financial statement and tax bases of assets and liabilities at the applicable enacted tax rates. We will establish a valuation allowance for deferred tax assets if it is more likely than not that these items will expire before we are able to realize their benefits or that future deductibility is uncertain. We recognize the tax benefit from uncertain tax positions only if it is more likely than not that the tax position will be sustained on examination by the tax authorities, based on the technical merits of the position. The tax position is measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. We recognize interest and penalties related to income tax matters in income tax expense if incurred. Comprehensive Income (Loss) Comprehensive income (loss) is comprised of net income (loss) and certain changes in equity excluded from net income (loss). For the year ended December 31, 2017, other comprehensive loss consists of unrealized losses on our short-term investments. There was no difference between comprehensive income (loss) and net income (loss) for the years ended December 31, 2016 and 2015. Recently Issued Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers, as amended, which amends the guidance for revenue recognition to replace numerous industry specific requirements. ASU 2014-09, as amended, implements a five-step process for customer contract revenue recognition focusing on transfer of control, as opposed to transfer of risk and rewards. ASU 2014-09, as amended, also requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenues and cash flows from contracts with customers. Other major provisions include ensuring the time value of money is considered in the transaction price, and allowing estimates of variable consideration to be recognized before contingencies are resolved in certain circumstances. ASU 2014-09, as amended, is effective for reporting periods beginning after December 15, 2017. Early adoption is permitted, but not before December 15, 2016. Entities can transition to the standard either retrospectively or as a cumulative-effect adjustment as of the date of adoption. We adopted this new standard effective January 1, 2018, on a modified retrospective basis, which requires the cumulative effect of the adoption to be recognized as an adjustment to opening retained earnings in the first period of adoption. The adoption of ASU No. 2014-09 did not have a material impact on recorded amounts when applied to the opening balance sheet as of January 1, 2018, and is not expected to have a material impact on the amount or timing of the future amounts of net income. Additional impacts could still result when the standard is first applied to revenue transactions during the first quarter of 2018. In February 2016, the FASB issued ASU No. 2016-02, Leases. ASU 2016-02 requires a lessee to separate the lease components from the non-lease components in a contract and recognize in the statement of financial position a liability to make lease payments (the lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term. It also aligns lease accounting for lessors with the revenue recognition guidance in ASU 2014-09. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, and is to be applied at the beginning of the earliest period presented using a modified retrospective approach. We are continuing to evaluate the effect the standard will have on our financial statements and related disclosures. In August 2016, the FASB issued ASU No. 2016-15 which provides new guidance on the classification of certain cash receipts and payments in the statement of cash flows. The new guidance is intended to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. We will be required to adopt the new guidance beginning with the first fiscal quarter of 2018; early adoption is permitted. We are currently assessing the impact the new guidance will have on our consolidated statements of cash flows. In May 2017, the FASB issued ASU No. 2017-09 to provide clarity and reduce both diversity in practice and cost and complexity when applying the guidance in Compensation - Stock Compensation ( Recently Adopted Accounting Pronouncements In August 2014, the FASB issued ASU No.2014-15, Disclosures of Uncertainties about an Entity’s Ability to Continue as a Going Concern. Under the new guidance, management is required to assess an entity’s ability to continue as a going concern and to provide related footnote disclosures in certain circumstances. The provisions of this standard are effective for annual periods ending after December 31, 2016, and for annual and interim periods thereafter. We adopted this guidance this year and management believes our existing cash and cash equivalents as of December 31, 2017 are sufficient to fund our operations and do not raise substantial doubt about our ability to continue as a going concern. In March 2016, the FASB issued ASU No. 2016-09- Improvements to Employee Share-Based Payment Accounting, wh ich simplified the accounting for share-based payment transactions, including the income tax consequences, the calculation of diluted earnings per share, the treatment of forfeitures, the classification of awards as either equity or liabilities, and the classification on the statement of cash flows. For public business entities, the amendments in this update are effective for annual periods beginning after December 15, 2016 and interim periods within those annual periods. Early adoption is permitted for any entity in any interim or annual period. We adopted ASU 2016-09 with effect from January 1, 2015. The adoption of this standard did not have an impact on our financial statements. In November 2016, the FASB issued ASU No. 2016-18 relating to restricted cash. The new guidance requires amounts generally described as restricted cash and restricted cash equivalents to be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the consolidated statement of cash flows. This guidance is required to be adopted beginning with the first fiscal quarter of 2018; early adoption is permitted. We adopted this guidance effective June 30, 2017, which required us to include restricted cash within the beginning and ending balance of cash and cash equivalents for the year ended December 31, 2017. We had no restricted cash prior to adopting this guidance, thus we were not required to revise prior period statements of cash flows. The adoption of this guidance does not impact our financial position or results of operations.

Business Combination

Business Combination	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Business Combination	3. Business Combination On July 24, 2017, we closed the merger on the terms described in more detail in Note 1. In connection with the merger, Nivalis effected a 1:4 reverse stock split of its common stock. Upon the closing of the merger, (1) a wholly-owned subsidiary of Nivalis merged with and into Alpine, with Alpine (renamed as “AIS Operating Co., Inc.”) remaining as the surviving entity; and (2) Nivalis was renamed as “Alpine Immune Sciences, Inc.” Under the terms of the Merger Agreement, Nivalis issued shares of its common stock to Alpine’s stockholders, at an exchange rate of 0.4969 shares of Nivalis common stock, after taking into account the 1:4 reverse stock split, for each share of Alpine’s common stock and preferred stock outstanding immediately prior to the merger. The exchange rate was determined through arms’-length negotiations between Nivalis and Alpine. Nivalis also assumed all of the stock options outstanding under Alpine’s Amended and Restated 2015 Stock Plan, as amended (the “Alpine Plan”), and stock warrants for Alpine’s capital stock outstanding immediately prior to the merger, with such stock options and warrants henceforth representing the right to purchase a number of shares of the Nivalis common stock equal to 0.4969 multiplied by the number of shares of Alpine’s common stock or preferred stock previously represented by such options and warrants. Nivalis also assumed the Alpine Plan. Immediately after the merger, there were 13,881,645 shares of common stock outstanding. Immediately after the merger, Alpine’s former stockholders, warrantholders, and optionholders owned, or held rights to acquire, approximately 74% of the fully-diluted common stock of Nivalis, which for these purposes is defined as the outstanding common stock of Nivalis, plus “in the money” options and warrants to purchase shares of Nivalis’ common stock, assuming all “in the money” options and warrants of Nivalis outstanding immediately prior to the merger are exercised on a cashless basis immediately prior to the closing of the merger, with Nivalis’ stockholders, optionholders, and warrantholders immediately prior to the merger owning, or holding rights to acquire, approximately 26% of the fully diluted common stock of Nivalis. More than 74% of Nivalis’ common stock outstanding immediately after the merger was held by stockholders party to lock-up agreements, pursuant to which such stockholders have agreed, except in limited circumstances, not to sell, transfer, or engage in swap or similar transactions with respect to shares of Nivalis’ common stock, including, as applicable, shares received in the merger and issuable upon exercise of certain warrants and options, for a period of 180 days following the completion of the merger. The issuance of shares of Nivalis’ common stock to our pre-existing stockholders was registered with the SEC pursuant to the Registration Statement. Immediately prior to the merger, we issued and sold an aggregate of approximately $17.0 million of shares of our capital stock to certain existing stockholders. For accounting purposes, our historical financial statements were not adjusted to reflect the merger, other than adjustments to the capital structure to reflect the historical capital structure of Nivalis. No other adjustments to our historical assets and liabilities were made as a result of the merger. In addition to the operating assets and liabilities of Nivalis, we also acquired Nivalis’ tax attributes, which primarily consisted of net operating losses which begin to expire in 2032. Our ability to utilization the tax attributes of Nivalis may be limited under Section 382 of the U.S. Internal Revenue Service and as such, have been reserved. We recorded a deferred tax liability related to future tax benefits arising from IPR&D acquired in the Merger. The combined organization is focusing on the development and commercialization of our innovative immunotherapies. Following the merger, the increased cash resources and increased access to capital of the combined organization will help to support the clinical development of our products. Consideration Transferred The fair value of the consideration transferred was based on the most reliable measure, which was determined to be the market price of Nivalis shares of common stock as of the acquisition date. The fair value of the consideration transferred consisted of the following (in thousands except share and per share amounts): Outstanding Nivalis common stock 3,914,058 Per share fair value of Nivalis common stock $ 9.60 Outstanding Nivalis stock options 421,992 Weighted average per share fair value of Nivalis stock options $ 1.25 Total fair value of consideration $ 38,103 Pursuant to the Merger Agreement, unvested Nivalis stock options immediately vested as of the closing of the business combination and were adjusted to give effect to the recapitalization. Purchase Price Allocation As Alpine was the accounting acquirer in the merger, we allocated the purchase price to the acquired tangible and intangible assets and assumed liabilities of Nivalis based on their estimated fair values as of the acquisition date. The excess of the estimated fair values of net assets acquired over the acquisition consideration paid was recorded as a bargain purchase gain in the consolidated statements of operations and comprehensive income (loss). The determination of the fair values of the assets acquired and liabilities assumed requires significant judgment, including third party valuation estimates relating to the value of the acquired IPR&D. The allocation of the purchase consideration to the assets acquired and liabilities assumed in our financial statements was finalized as of December 31, 2017. Since the acquisition date, we have recorded adjustments to the allocation of the purchase consideration that included increases of $77,000 and $15,000 to other receivables and accrued liabilities, respectively, which resulted in a decrease of $62,000 in our bargain purchase gain. These purchase price adjustments are reflected in the accompanying consolidated balance sheet as of December 31, 2017. The final allocation of the purchase consideration is as follows (in thousands): Assets: Cash and cash equivalents $ 31,130 Marketable securities 12,952 Other receivables 79 IPR&D 1,453 Total assets acquired 45,614 Liabilities: Accrued liabilities (401 ) Deferred tax liability (509 ) Total liabilities assumed (910 ) Bargain purchase gain (6,601 ) Total $ 38,103 We relied on significant Level 3 unobservable inputs to estimate the fair value of our acquired IPR&D using management’s estimate of future royalties and expected earnings of the assets after taking into account an estimate of future expenses necessary to bring the products to completion. These projected cash flows were then discounted to their present values using a discount rate of 17%, which was considered commensurate with the risks and stages of development of the IPR&D. The bargain purchase gain resulted from expenses incurred by Nivalis between the time the purchase price was negotiated and the close of the transaction, and changes in the Nivalis stock price during that period as the exchange ratio was fixed when the purchase price was negotiated. We recognized acquisition-related costs of $1.5 million for the year ended December 31, 2017. These costs are included within general and administrative expense in our consolidated statements operations and of comprehensive income (loss). Pro Forma Financial Information The following pro forma consolidated results of net loss for the years ended December 31, 2017 and 2016 assume the business combination was completed as of January 1, 2016 (in thousands, except per share amounts): Years Ended December 31, 2017 2016 Pro forma revenues $ 1,731 $ 2,950 Pro forma net loss (18,327 ) (32,695 ) Pro forma basic and diluted net loss per share $ (1.32 ) $ (2.37 ) For purposes of the pro forma disclosures above, the primary adjustments for the years ended December 31, 2017 include the elimination of acquisition related costs and acceleration of stock compensation expense upon the change in control.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Net Loss Per Share	4. Net Loss Per Share We compute net loss per share attributable to common stockholders using the two-class method required for participating securities. We consider our convertible preferred stock to be participating securities. In accordance with the two-class method, earnings allocated to these participating securities, which include participation rights in undistributed earnings, are subtracted from net income to determine total undistributed earnings to be allocated to common stockholders. Net loss is not allocated to participating securities as there is no contractual obligation to share in net losses. Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. All participating securities are excluded from basic weighted-average common shares outstanding. Because of net losses recognized in each period, potential common shares issuable upon the exercise of outstanding stock options and warrants and the conversion of preferred shares into common shares have not been reflected in the calculation of diluted net loss per share due to the anti-dilutive effect. Diluted net loss per share, therefore, does not differ from basic net loss per share. The basic and diluted net loss per share for the years ended December 31, 2017, 2016, and 2015 were computed based on the shares of common stock outstanding during the respective periods. The net loss per share for the year ended December 31, 2017 includes the conversion 9,301,433 shares of our convertible preferred stock into common stock, and 3,914,058 shares acquired in connection with the merger. The significant number of shares issued has affected the year-over-year comparability of our net loss per share calculations. The common stock issuable upon the conversion or exercise of the following dilutive securities has been excluded from the diluted net loss per share attributable to common stockholders calculation because their effect would have been antidilutive for the periods presented: December 31, 2017 2016 2015 Convertible preferred stock — 4,311,770 1,212,436 Warrants to purchase common stock 24,123 12,422 12,422 Options to purchase common stock 1,611,996 520,739 401,688 Total 1,636,119 4,844,931 1,626,546

Cash Equivalents and Short-Term

Cash Equivalents and Short-Term Investments	12 Months Ended
	Dec. 31, 2017
Cash Cash Equivalents And Short Term Investments [Abstract]
Cash Equivalents and Short-term Investments	5. Cash Equivalents and Short-Term Investments The amortized cost and fair value of our cash equivalents and short-term investments are as follows (in thousands): Assets: December 31, 2017 Amortized Cost Gross unrealized gains Gross unrealized losses Fair market value Money market funds $ 5,680 $ — $ — $ 5,680 U.S. treasury bills 19,909 — (21 ) 19,888 Corporate debt securities and commercial paper 53,390 — (38 ) 53,352 Total $ 78,979 $ — $ (59 ) $ 78,920 All short-term investments held as of December 31, 2017 were classified as available-for-sale securities and had contractual maturities of less than one year. There were no realized gains and losses on these securities for the periods presented. There were no short-term investments as of December 31, 2016.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	6. Fair Value Measurements Fair value is defined as the exchange price received for an asset or paid to transfer a liability, or an exit price, 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 three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value, is as follows: Level 1 : Quoted prices in active markets for identical assets or liabilities. Level : Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in inactive markets, 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 supported by little or no market activity and significant to the fair value of the assets or liabilities. At December 31, 2016, we had cash of $11.8 million and no assets measured using Level 1, Level 2, or Level 3 inputs. As of December 31, 2017, cash of $2.3 million is excluded from the fair value table below. The following table summarizes our financial assets and liabilities measured at fair value on a recurring basis (in thousands): Assets: December 31, 2017 Level 1 Level 2 Level 3 Total Money market funds $ 5,680 $ — $ — $ 5,680 U.S. treasury bills 19,888 — — 19,888 Corporate debt securities and commercial paper — 53,352 — 53,352 Total $ 25,568 $ 53,352 $ — $ 78,920 Our Level 2 assets consist of commercial paper and corporate debt securities. W e review trading activity and pricing for our available-for-sale securities as of the measurement date. When sufficient quoted pricing for identical securities is not available, we use market pricing and other observable market inputs for similar securities obtained from various third-party data providers. These inputs either represent quoted prices for similar assets in active markets or have been derived from observable market data. On June 30, 2017, we issued Series A-1 preferred stock warrants in connection with long-term debt. The warrant liability was classified as a Level 3 liability and the fair value was determined using the Black-Scholes option-pricing model with the following key assumptions: (1) stock price of $9.64; (2) a risk-free rate of 2.31%; (3) an expected volatility of 78%; and (4) a term of 9.5 years. Both observable and unobservable inputs are used to determine the fair value of the warrant liability. As a result, the unrealized gains and losses of the warrant liability may include changes in fair value attributable to both observable inputs (e.g., changes in market interest rates) and unobservable inputs (e.g., probabilities of the occurrence of an early termination event). In July 2017, in connection with the closing of the merger, our preferred stock warrants converted to common stock warrants. As a result of the change in the underlying shares, the warrants were equity-classified beginning on July 24, 2017. As of the date of conversion, we remeasured the fair value of the warrants, which resulted in a $1,000 decrease in fair value, which was recorded as other income in our accompanying consolidated statements of operations and comprehensive income (loss). See Note 10 for additional discussion of the warrants. The following table shows the reconciliation of the Level 3 warrant liability measured and recorded at fair value on a recurring basis, using significant unobservable inputs (in thousands): Estimated Fair Value Balance as of January 1, 2017 $ — Fair value of warrants at issuance (June 30, 2017) 53,000 Change in fair value of warrant liability in connection with merger (1,000 ) Conversion of warrant liability to equity (52,000 ) Balance as of December 31, 2017 $ —

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	12 Months Ended
	Dec. 31, 2017
Prepaid Expense Current [Abstract]
Prepaid Expenses and Other Current Assets	7. Prepaid expenses and other current assets Prepaid expenses and other current assets consists of the following (in thousands): December 31, 2017 2016 Prepaid research and development $ 791 $ — Prepaid insurance 298 8 Prepaid other 91 28 Other receivables 128 — Prepaid expenses and other current assets $ 1,308 $ 36

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Property and Equipment	8. Property and Equipment Property and equipment consist of the following (in thousands): December 31, 2017 2016 Laboratory equipment $ 1,161 $ 660 General equipment and furniture 110 74 Computer equipment and software 82 70 Leasehold improvements 47 6 Property and equipment, at cost 1,400 810 Less accumulated depreciation and amortization (311 ) (70 ) Property and equipment, net $ 1,089 $ 740 Depreciation expense was $241,000, $69,000 and 1,000 for the years ended December 31, 2017, 2016 and 2015, respectively.

Accrued Liabilities

Accrued Liabilities	12 Months Ended
	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued Liabilities	9. Accrued Liabilities Accrued liabilities and other current liabilities consisted of the following (in thousands): December 31, 2017 2016 Accrued research and development $ 197 $ — Accrued professional fees 112 5 Deferred compensation — 61 Accrued taxes and licenses 30 61 Accrued other 43 43 Total $ 382 $ 170

Long-term Debt

Long-term Debt	12 Months Ended
	Dec. 31, 2017
Debt Instruments [Abstract]
Long-term Debt	10. Long-term Debt On June 30, 2017, we drew down a term loan of $5.0 million from Silicon Valley Bank with whom we had entered into a long-term financing arrangement on December 16, 2016. The loan has an interest-only period that expires on July 1, 2018, at which point we will be obligated to make thirty consecutive equal monthly payments of principal (each in an amount that will fully amortize the loan), plus accrued interest. Interest accrues at a floating per annum rate equal to the lender’s prime rate minus 1.75%. As a condition to the loan, we agreed to pay a final payment fee of 7.5%, or $375,000, upon repayment of the loan. The final payment fee was recorded in long-term debt with an offsetting reduction in long-term debt and was accounted for as a debt discount. Pursuant to the loan agreement we have pledged substantially all of our assets, excluding intellectual property, as collateral. The obligations under the loan agreement are subject to acceleration upon the occurrence of specified events of default, including a material adverse change in our business, operations, financial, or other condition. We assessed the likelihood of the lender accelerating payment of the loan due to a material adverse change in our business, operations, financial, or other condition as remote. As such, as of December 31, 2017, the classification of the loan is split between current and noncurrent based on the timing of payment obligations. The term loan agreement contains customary conditions to borrowings, events of default and negative covenants, including covenants that could limit our ability to, among other things, incur additional indebtedness, liens or other encumbrances; make dividends or other distributions; buy, sell or transfer assets; engage in any new line of business; and enter into certain transactions with affiliates. We were in compliance with our covenants as of December 31, 2017. Also, in connection with the drawdown of the loan, we also granted the financial institution 7,069 Series A-1 Preferred Stock warrants at an exercise price of $12.38 per share. The fair value of the warrants on the date of issuance was $53,000, determined using the Black-Scholes option-pricing model, and was recorded as a discount to the note and as a warrant liability on the accompanying consolidated balance sheets. In connection with the merger and conversion of all outstanding Series A-1 preferred stock, the warrants became exercisable for 7,069 fully vested shares of our common stock. As a result of the change in the underlying shares, the warrants were equity-classified beginning on July 24, 2017. The debt discount is being amortized to interest expense using the effective interest method over the repayment term of the initial loan amount. Non-cash interest expense associated with the amortization of the discount was $87,000, for year ended December 31, 2017. The unamortized discount was $341,000 as of December 31, 2017.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and Contingencies Operating Lease In 2016, we entered into a non-cancelable operating lease to rent office and laboratory space in Seattle, Washington. In April 2016, we amended the agreement to lease additional premises adjacent to our existing leased premises. Under our lease agreements, w e lease approximately 11,158 square feet of office and laboratory space with an annual base rent of $566,000 in the first year, which will increase by 3% each year thereafter. As required by the terms of the lease, in May 2017, we entered into a line of credit to establish collateral to support the security deposit in an amount of $132,000. This is recorded as restricted cash in the accompanying consolidated balance sheets. We recognize rent expense on a straight-line basis over the lease period and accrue for rent expense incurred but not paid. The lease also requires us to pay additional amounts for operating and maintenance expenses. Rent expense was for the years ended December 31, 2017, 2016 and 2015, respectively. Future minimum lease payments for our non-cancelable operating leases at December 31, 2017 are as follows (in thousands): Minimum Lease Payments 2018 $ 605 2019 606 2020 — 2021 — 2022 — Total future minimum lease payments $ 1,211 In January 2018, we entered into a lease amendment for approximately 6,184 square feet of additional office and laboratory space adjacent to our existing leased premises in Seattle, Washington. The lease expires on December 31, 2019 and has two options to extend the lease term with each option enabling us to extend the lease term by twelve months. The annual base rent due under the lease is $295,000 for the first year and will increase by 3.0% each year thereafter. Lease payments in connection with this amendment are not included in the table above.

License and Collaboration Agree

License and Collaboration Agreement	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
License and Collaboration Agreement	12. License and Collaboration Agreement In October 2015, we entered into a Collaboration and Licensing Agreement with Kite Pharma, Inc. to discover and develop protein-based immunotherapies targeting the immune synapse to treat cancer. Under our agreement, we are to perform certain research services and grant to Kite an exclusive license to two programs from our transmembrane immunomodulatory protein (TIP™) technology, which Kite is planning to further engineer into chimeric antigen receptor (“CAR”) and T cell receptor (“TCR”) product candidates. Under the terms of the Collaboration Agreement, Kite made upfront payments to us of $5.5 million, which were initially recorded as deferred revenue. We will also be eligible to receive milestone payments based upon the successful achievement of pre-specified research, clinical, and regulatory milestones totaling up to $530.0 million plus royalty payments on product sales, if any. Kite will receive an exclusive, worldwide license to research, develop, and commercialize engineered autologous T cell therapies incorporating two programs coming from our platform. On October 20, 2017, we entered into an amendment with Kite to extend the research term of the Collaboration Agreement. Under the amended agreement, we are eligible to receive an additional $450,000 research support payment from Kite in two tranches (instead of a single tranche as previously contemplated by the original Collaboration Agreement) (the “Amendment”). The Amendment also amended and restated the original research plan. We adjusted our estimated service period over the extended term and have adjusted the revenue recognition accordingly. We recorded revenue of $1.7 million, $2.9 million and $492,000 for the years ended December 31, 2017, 2016 and 2015, respectively.

Convertible Preferred Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2017
Temporary Equity Disclosure [Abstract]
Convertible Preferred Stock	13. Convertible Preferred Stock Between January 2015 and November 2015, we issued and sold 1,212,436 shares of Series Seed convertible preferred stock and received a total of $610,000. In April 2016, we issued and sold an additional 1,272,064 shares of Series Seed convertible preferred stock and received a total of $640,000. In June 2016, the we issued and sold 1,827,270 shares of Series A convertible preferred stock and received $10.3 million. We incurred $48,000 of issuance costs related to the June 2016 issuance. In March 2017, we issued and sold 707,330 shares of Series A convertible preferred stock and received a total of $4.0 million. In April 2017, prior to the execution and delivery of the Merger Agreement certain holders of our Series A-1 convertible preferred stock purchased 2,947,211 shares of Series A-1 preferred stock for $16.7 million in proceeds. Contemporaneously with the execution and delivery of the Merger Agreement certain of our pre-existing stockholders entered into a subscription agreement with us pursuant to which such stockholders purchased immediately prior to the closing of the merger 1,335,118 shares of our convertible preferred stock at a purchase price of $12.74 per share for an aggregate purchase price of approximately $17.0 million. Upon the closing of the merger, all outstanding shares of our convertible preferred stock converted into 9,301,433 shares of common stock. As of December 31, 2017, we do not have any convertible preferred stock outstanding. A summary of convertible preferred stock as of December 31, 2016 is as follows (amounts in thousands, except share and per share data): December 31, 2016 Issued Price per Share Shares Authorized Shares Issued and Outstanding Aggregate Liquidation Preference Carrying Value Series Seed $ 0.51 5,000,000 2,484,500 $ 1,250 $ 1,250 Series A $ 5.66 17,081,852 1,827,270 10,333 10,285 Total 22,081,852 4,311,770 $ 11,583 $ 11,535 The convertible preferred stock had the following rights, preferences and privileges: full voting rights and powers as common stock on an as-converted basis, dividends at a rate of six percent of the original issue price per share per annum, rights and obligations to participate in future tranches, optional conversion features, mandatory conversion features, special conversion features and a liquidation preference of $5.66 per share plus any declared but unpaid dividends. Preferred Stock Warrants In connection with our drawdown of a term loan on June 30, 2017, we granted the lender 7,069 of fully vested Series A-1 preferred stock warrants at an exercise price of $12.38 per share and a term of ten years. The fair value of the warrants on the date of issuance was $53,000 and was recorded as a discount to the note and as a warrant liability within the accompanying consolidated balance sheets. The warrants were initially classified as a liability because the underlying to the warrants were puttable shares. On July 24, 2017, in connection with the merger and conversion of all outstanding Series A-1 preferred stock, the warrants became exercisable for 7,069 fully vested shares of our common stock. As a result of the change in the underlying shares, the warrants were equity-classified beginning on July 24, 2017. As a result of the equity classification, the warrant liability was remeasured as of July 24, 2017 and the change in fair value was recognized within other (income) expense in our consolidated statements of operations and comprehensive income (loss) and the carrying value of the revised warrant liability was reclassified to additional paid-in capital within stockholders’ deficit.

Stockholders' Deficit

Stockholders' Deficit	12 Months Ended
	Dec. 31, 2017
Stockholders Equity Note [Abstract]
Stockholders’ Deficit	14. Stockholders’ Deficit Common Stock We had 13,831,178 and 608,701 shares of common stock outstanding as of December 31, 2017 and 2016, respectively. Shares of common stock reserved for future issuance were as follows: December 31, 2017 2016 Shares to be issued upon conversion of convertible preferred stock — 4,311,770 Shares to be issued upon exercise of outstanding stock options 1,611,996 520,739 Shares to be issued upon conversion of common stock warrants 24,123 12,422 Shares available for future stock grants 576,722 545,078 Shares to be issued under employee stock purchase plan 45,211 — Shares of common stock reserved for future issuance 2,258,052 5,390,009 In December 2017, we repurchased 50,467 shares of unvested common stock issued to one of our former employees for the original purchase price of $0.002 per share. Common Stock Warrants In connection with our drawdown of a term loan on June 30, 2017, we granted the lender 7,069 of fully vested Series A-1 preferred stock warrants at an exercise price of $12.38 per share and a term of ten years. On July 24, 2017, in connection with the merger and conversion of all outstanding Series A-1 preferred stock, the warrants became exercisable for 7,069 fully vested shares of our common stock. Additionally, in connection with the merger, we assumed 4,632 fully vested warrants to purchase common stock at an exercise price of $97.12. We have also issued common stock warrants on two occasions to certain non-employee professional advisers. On each occasion, the warrants were convertible into 12,422 shares of common stock. The warrants issued on April 24, 2015 had an exercise price of $0.11 per share, a vesting commencement date of October 1, 2014, and vested ratably over 24 months. These warrants were exercised in full on March 20, 2017. The warrants issued on April 12, 2017 have an exercise price of $5.02 per share, a vesting commencement date of March 29, 2017, and vest ratably over 48 months. Stock-based compensation expense related to these warrants is included in general and administrative expenses for all periods presented Equity Incentive Plans In July 2017, in connection with the merger, we assumed Nivalis’ Employee Stock Purchase Plan (the ESPP). Upon assumption of the ESPP, there were 45,211 shares available for issuance under the ESPP. As of December 31, 2017, we have not activated the ESPP. In July 2017, in connection with the merger, we assumed Nivalis’ 2015 Equity Incentive Plan (the “2015 EIP”). The 2015 EIP provides for the granting of incentive and nonqualified stock options, stock appreciation rights, restricted stock, restricted stock units, performance-based awards and other stock-based awards to our employees, directors and consultants. Upon assumption of the 2015 EIP, a total of 658,275 shares of common stock were authorized for issuance. The 2015 EIP provides that an additional number of shares will automatically be added to the shares authorized for issuance under the 2015 EIP on January 1 of each calendar year, through January 1, 2025. The number of shares added each year will be equal to: (a) 5% of the total number of shares of common stock issued and outstanding on December 31 of the preceding calendar year; or (b) such lesser number of shares of common stock approved by the Board of Directors on or prior to such immediately preceding December 31. On January 1, 2018 a total of 691,558 additional shares were automatically added to the shares authorized for issuance under the 2015 EIP. In February 2015, our board of directors approved the 2015 Stock Plan (the “2015 Plan”) to provide incentive stock options and non-qualified stock options to employees, non-qualified stock options to members of the board of directors and advisory board, and non-employees. The terms of the stock awards, including vesting requirements, are determined by the board of directors, subject to the provisions of the 2015 Plan. Stock options granted under the 2015 Plan generally vest within four years and vested options are exercisable from the grant date until ten years after the date of grant. Vesting of certain employee options may be accelerated in the event of a change in control of the Company. We grant stock options to employees with exercise prices equal to the fair value of our common stock on the date of grant. The term of incentive stock options may not exceed ten years from the date of grant. As of December 31, 2017, a total of 2,370,395 shares of common stock were authorized for issuance under our 2015 Plan and 2015 EIP, of which 576,722 shares were available for future grants. A summary of stock option activity under our plans is presented below: Options Outstanding Weighted- average Exercise Price Weighted- average Remaining Contract Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2015 401,688 $ 0.42 Granted 512,844 $ 0.53 Exercised (111,802 ) $ 0.45 Forfeited/Expired (281,991 ) $ 0.45 Outstanding at December 31, 2016 520,739 $ 0.51 9.22 $ 179 Options assumed in the merger 421,992 $ 22.97 Options assumed in the merger, expired during period (253,194 ) $ 30.66 Granted 997,368 $ 4.94 Exercised (45,031 ) $ 0.45 Forfeited/Expired (29,878 ) $ 4.72 Outstanding at December 31, 2017 1,611,996 $ 4.32 8.35 $ 11,525 Vested and expected to vest after December 31, 2017 1,611,996 $ 4.32 8.35 $ 11,525 Exercisable at December 31, 2017 377,550 $ 5.39 5.70 $ 2,600 As of December 31, 2017 there was $4.1 million of unrecognized stock-based compensation expense related to nonvested stock options that is expected to be recognized over a weighted-average period of 3.3 years. The aggregate intrinsic value of stock options exercised during the year ended December 31, 2017 was $18,000. The total fair value of shares vested during the year ended December 31, 2017 was $139,000. Stock-Based Compensation Expense We use the Black-Scholes option pricing model to estimate the fair value of stock options at the grant date. The Black-Scholes option pricing model requires us to make certain estimates and assumptions, including assumptions related to the expected price volatility of our stock, the period during which the options will be outstanding, the rate of return on risk-free investments, and the expected dividend yield of our stock. The fair values of stock options granted to employees were calculated using the following assumptions: Years Ended December 31, 2017 2016 2015 Weighted-average estimated fair value $ 4.69 $ 0.42 $ 0.38 Risk-free interest rate (1) 1.90% - 2.26% 1.14% - 2.24% 1.79% - 2.24% Expected term of options (in years) (2) 5.69 - 6.32 5.22 – 7.00 5.21 - 10.00 Expected stock price volatility (3) 72% - 83% 72% - 79% 70% - 85% Expected dividend yield (4) —% —% —% (1) The risk-free interest rate assumption was based on zero-coupon U.S. Treasury instruments that had terms consistent with the expected term of our stock option grants. (2) We used the “simplified method” for options to determine the expected term of stock option granted to employees. Under this approach, the weighted-average expected life is presumed to be the average of the vesting term and the contractual term of the option. (3) Volatility is a measure of the amount by which a financial variable, such as share price, has fluctuated or is expected to fluctuate during a period. We analyzed the stock price volatility of companies at a similar stage of development to estimate expected volatility of our stock price. (4) We have never declared or paid any cash dividends and do not presently plan to pay cash dividends in the foreseeable future. The fair value of each non-employee stock option is estimated at the date of grant using the Black-Scholes option pricing model and are remeasured over the vesting term, as earned. Assumptions used in valuing non-employee stock options are generally consistent with those used for employee stock options with the exception that the expected term is over the contractual life. Stock-based compensation expense is classified in the statements of operations as follows (amounts in thousands): Years Ended December 31, 2017 2016 2015 Employee: Research and development $ 183 $ 14 $ — General and administrative 588 53 10 Non-Employee: Research and development 52 5 2 General and administrative 15 5 4 Total stock-based compensation expense $ 838 $ 77 $ 16 In May 2016 we extended the vesting period of 567,500 unvested share options held by 5 employees. As a result of this modification, we recognized additional compensation expense of $4,000 for the year ended December 31, 2016.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	15. Income Taxes On December 22, 2017, the U.S. government enacted comprehensive tax legislation commonly referred to as the Tax Cuts and Jobs Act (the “Tax Act”). The Tax Act incorporates broad and complex changes to the U.S. tax code. The main provision of the Tax Act that is applicable to us is the reduction of a maximum federal tax rate of 35% to a flat tax rate of 21%, effective January 1, 2018. We incorporated the change in federal tax rates in our annual tax provision. As a result of the rate change, we reduced our net deferred tax asset balance by $2.0 million, with a corresponding reduction to our valuation allowance of $2.2 million, resulting in a deferred income tax benefit of $200,000. At December 31, 2017, we have not completed accounting for the tax effects of Tax Act. We have made reasonable estimates of the effects of the Tax Act on existing deferred tax balances. We will continue to refine our calculations as additional analysis is completed. Our estimates may be affected as we gain a more thorough understanding of the Tax Act. Our entire income (loss) before taxes is considered domestic (United States) as we have no foreign operations. We received $5.5 million in advanced payments from Kite in 2015. As of December 31, 2016, $2.0 million of this $5.5 million was deferred for financial reporting purposes but was included in taxable income for the year ended December 31, 2016. As a result of this timing difference, we incurred current federal and state income tax expense in the year ended December 31, 2016. We expect to be in a loss position for tax purposes in 2017 and thereafter for the foreseeable future. The provision for income taxes is composed of the following (in thousands): Years Ended December 31, 2017 2016 Current: U.S. - Federal $ (1 ) $ 4 U.S. - State 5 62 Total current 4 66 Deferred: U.S. - Federal (204 ) — U.S. - State — — Total deferred (204 ) — Total income tax expense $ (200 ) $ 66 The effective tax rate of the provision for income taxes differs from the federal statutory rate as follows: Years Ended December 31, 2017 2016 U.S. Statutory rate 35.0 % 34.0 % Effect of: State taxes (net of federal benefit) (1.6 %) 5.6 % Permanent differences (0.1 %) (0.3 %) Federal research and development credit 4.4 % 9.4 % Change in valuation allowance (19.4 %) (54.0 %) Benefit of a lower tax rate 0.2 % 0.9 % Stock-based compensation (2.6 %) (1.2 %) Non-deductible merger costs (17.6 %) (— %) Bargain purchase gain 28.9 % (— %) Tax rate change (24.7 %) (— %) Effective income tax rate 2.5 % (5.6 %) We recorded a tax benefit of $200,000 for the year ended December 31, 2017 and tax expense of $66,000 for the year ended December 31, 2016, representing effective tax rates of 2.5% and (5.6)% for the years ended December 31, 2017 and 2016, respectively. The difference between the U.S. federal statutory tax rate of 35% and our effective tax rate in all periods is primarily due to a full valuation allowance related to our deferred tax assets, the generation, and consumption of, federal R&D tax credits, and, specific to 2017, a change in future federal income tax rates due to tax reform, non-deductible transaction costs, and the non-taxable bargain purchase gain recorded on the Nivalis merger. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The following table represents the significant components of our deferred tax assets and liabilities for the periods presented (in thousands): December 31, 2017 2016 Deferred tax assets: Net operating loss $ 2,475 $ — Deferred compensation — 24 Research and development credits 458 103 Intangible asset basis — 16 Deferred revenue 58 800 Deferred rent 24 58 Stock based compensation 810 3 Other 12 — Gross deferred tax assets 3,837 1,004 Valuation allowance (3,722 ) (786 ) Total deferred tax assets, net of valuation allowance 115 218 Deferred tax liabilities: Prepaid expenses (63 ) (12 ) Fixed asset basis (110 ) (206 ) Intangible asset basis (247 ) Total deferred tax liability (420 ) (218 ) Net deferred tax assets and liabilities $ (305 ) $ — As part of the merger with Nivalis, we identified $1.5 million of acquired IPR&D. IPR&D acquired in a business combination is an indefinite-lived intangible asset until the completion or abandonment of the associated R&D efforts. Once the R&D efforts are completed or abandoned, the IPR&D will either be impaired or amortized over the asset life as a finite-lived intangible. As the acquired IPR&D is not completed, and has not been abandoned, it is considered indefinite-lived for accounting purposes. Any future reversal of a deferred tax liability resulting from IPR&D costs cannot be scheduled for tax purposes and therefore cannot be considered as a source of future taxable income. Thus, we have recorded a deferred tax liability of $305,000 as a result of the acquired IPR&D having a financial reporting basis of $1.5 million and a tax basis of zero. A valuation allowance is provided for deferred tax assets where the recoverability of the assets is uncertain. The determination to provide a valuation allowance is dependent upon the assessment of whether it is more likely than not that sufficient taxable income will be generated to utilize the deferred tax assets. Based on the weight of the available evidence, which includes our historical operating losses, uncertainty of future taxable income, and the accumulated deficit, we provided a full valuation allowance against our deferred tax assets. The valuation allowance increased by $2.9 million and $629,000 during the year ended December 31, 2017 and December 31, 2016, respectively. We have net operating loss carryforwards as follows (in thousands): December 31, 2017 2016 Federal $ 11,784 $ — Federal and state net operating loss carryforwards would begin to expire in 2037. We have net research and development tax credit carryforwards as follows (in thousands): December 31, 2017 2016 Federal $ 458 $ 103 Federal research and development tax credit carryforwards begin to expire in 2035. Current tax laws impose substantial restrictions on the utilization of R&D credit and net operating loss carryforwards in the event of an ownership change, as defined by the Internal Revenue Code Section 382 and 383. Such an event may limit our ability to utilize our net operating losses and R&D tax credit carryforwards. Under Internal Revenue Code Section 382 and 383, the Q3 2017 merger with Nivalis is likely considered an ownership change with respect to the potential limitation of the Nivalis federal tax credits and net operating losses. As such, it is likely that any future utilization of Nivalis federal tax credits and net operating losses is substantially limited. Therefore, as of December 31, 2017, all Nivalis tax credit and net operating loss carryforwards have been reduced to zero. We account for uncertainty in income taxes in accordance with ASC 740. Tax positions are evaluated in a two-step process, whereby we first determine whether it is more likely than not that a tax position will be sustained upon examination by the tax authority, including resolutions of any related appeals or litigation processes, based on technical merit. If a tax position meets the more-likely-than-not recognition threshold it is then measured to determine the amount of benefit to recognize in the financial statements. The tax position is measured as the largest amount of benefit that is greater than 50% likely of being realized upon ultimate settlement. The following table summarized the activity related to unrecognized tax benefits (in thousands): December 31, 2017 2016 Unrecognized benefits – beginning of year $ 34 $ 7 Gross decreases – prior year tax positions (4 ) — Gross increases – current year tax positions 84 27 Unrecognized benefit – end of year $ 114 $ 34 All of the unrecognized tax benefits as of December 31, 2017 are accounted for as a reduction in our deferred tax assets. Due to our valuation allowance, none of the $114,000 of unrecognized tax benefits would affect our effective tax rate, if recognized. We do not believe it is reasonably possible that our unrecognized tax benefits will significantly change in the next twelve months. We recognize interest and penalties related to unrecognized tax benefits as income tax expense. There were no accrued interest or penalties related to unrecognized tax benefits for 2017 and 2016. We do not expect any significant change in our unrecognized tax benefits during the next twelve months. Our material income tax jurisdictions are the United States (federal), and California (state). We are subject to audit for tax years 2012 and forward for federal purposes, and 2015 and forward for California.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	16. Related Party Transactions We have a shared services agreement with Alpine BioVentures GP, LLC, pursuant to which we incurred costs of $0, $17,000 and $47,000 years ended December 31, 2017, 2016 and 2015, respectively. We had an accrual of $5,000 related to the shared services agreement at December 31, 2016, which was paid in April 2017.

401(k) Retirement Plan

401(k) Retirement Plan	12 Months Ended
	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
401(k) Retirement Plan	17. 401(k) Retirement Plan We have adopted a 401(k) plan. To date, we have not matched employee contributions to the plan. All employees are eligible to participate, provided they meet the requirements of the plan.

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation and Use of Estimates	Basis of Presentation and Use of Estimates The accompanying consolidated financial statements have been prepared in accordance with the rules and regulations of the SEC and generally accepted accounting principles in the United States of America (“GAAP”). The preparation of financial statements in conformity with GAAP requires management to make judgments, estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. We base our estimates and assumptions on historical experience when available and on various factors we believe to be reasonable under the circumstances. Actual results could differ materially from those estimates.
Principles of Consolidation	Principles of Consolidation Our consolidated financial statements include the financial position and results of operations of Alpine and AIS Operating Co., Inc., our wholly owned subsidiary and operating company. On July 24, 2017, we closed the merger on the terms described in more detail in Note 1. In connection with the merger, Nivalis effected a 1:4 reverse stock split of its common stock. Upon the closing of the merger, (1) a wholly-owned subsidiary of Nivalis merged with and into Alpine, with Alpine (renamed as “AIS Operating Co., Inc.”) remaining as the surviving entity; and (2) Nivalis was renamed as “Alpine Immune Sciences, Inc.”
Segments	Segments We operate in one segment and use cash flow as the primary measure to manage our business and do not segment the business for internal reporting or decision-making purposes.
Business Combination	Business Combination We use our best estimates and assumptions to accurately assign fair value to the tangible and intangible assets acquired and liabilities assumed at the acquisition date. Our estimates are inherently uncertain and subject to refinement. During the measurement period, which may be up to one year from the acquisition date, we may record adjustments to the fair value of these tangible and intangible assets acquired and liabilities assumed, with the corresponding offset to bargain purchase gain. In addition, uncertain tax positions and tax-related valuation allowances are initially established in connection with a business combination as of the acquisition date. Our management collects new information and reevaluates these estimates and assumptions quarterly and records any adjustments to our preliminary estimates to bargain purchase gain during the measurement period. Upon the conclusion of the measurement period or final determination of the fair value of assets acquired or liabilities assumed, whichever comes first, any subsequent adjustments are recorded to our consolidated statements of operations and comprehensive income (loss). We allocated the preliminary purchase price to the acquired tangible and intangible assets and assumed liabilities of Nivalis based on their estimated fair values as of the acquisition date. The fair value of our identifiable intangible asset is based on detailed valuations using information and assumptions provided by management. The allocation of the purchase consideration to the assets acquired and liabilities assumed in our financial statements was finalized as of December 31, 2017.
Cash and cash equivalents	Cash and cash equivalents We consider all highly liquid investments with an original maturity of 90 days or less at the time of purchase to be cash equivalents. Cash and cash equivalents consist of deposits with commercial banks in checking and interest-bearing accounts, and highly liquid money market funds.
Concentration of Credit Risk	Concentrations of Credit Risk Cash and cash equivalents, receivables, accounts payable and accrued liabilities, which are recorded at invoiced amount or cost, approximate fair value based on the short-term nature of these financial instruments. The fair value of short-term investments is based on quoted market prices. Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash and cash equivalents and short-term investments. Periodically, we maintain deposits in financial institutions in excess of government insured limits. We believe we are not exposed to significant credit risk as our deposits are held at financial institutions we believe to be of high credit quality securities such as money market funds, U.S. Treasury securities, and commercial paper. To date, we have not realized any losses on these deposits.
Short-Term Investments	Short-Term Investments Our short-term investments include funds invested in highly liquid money market funds, U.S. Treasury securities, commercial paper, and corporate debt securities with a final maturity of each security of less than one year. All investments are classified as available-for-sale securities and are recorded at fair value based on quoted prices in active markets, with unrealized gains and losses excluded from earnings and reported in other comprehensive income (loss). Purchase premiums and discounts are recognized as interest income using the interest method over the terms of the securities. Realized gains and losses and declines in fair value deemed to be other than temporary are reflected in the consolidated statements of operations and comprehensive income (loss) using the specific-identification method.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation. Depreciation is recorded using the straight-line method the estimated useful lives of the assets, generally three to five years, while leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is credited or charged to operations. Maintenance and repairs are expensed as incurred. Major improvements are capitalized as additions to property and equipment.
Intangible Asset	Intangible Asset Our intangible asset is our indefinite-life GSNOR inhibitor in-process research and development asset (“IPR&D”) acquired from Nivalis. The IPR&D represents the processes, expertise, and technology employed in the development of S-nitrosoglutathione reductase (“GSNOR”) inhibitors and Nivalis’ lead product candidate, cavosonstat. The IPR&D represents the estimated fair value as of the acquisition date of substantive in-process projects that have not reached technological feasibility. The primary basis for determining technological feasibility of these projects is obtaining regulatory approval. The valuation of IPR&D is determined using a discounted cash flow method. In determining the value of IPR&D, management considers, among other factors, the stage of completion of the projects, the technological feasibility of the projects, whether the projects have an alternative future use, and the estimated residual cash flows that could be generated from the various projects and technologies over their respective projected economic lives. The discount rate used is determined at the time of acquisition and includes a rate of return which accounts for the time value of money, as well as risk factors reflecting the economic risk that the projected cash flows may not be realized. We review our IPR&D at least annually for possible impairment. IPR&D is reviewed for possible impairment between annual tests if an event occurs or circumstances change that would more likely than not reduce the fair value of the IPR&D below their carrying values. We test our IPR&D each year on October 1. Our IPR&D asset totaled $1.5 million at December 31, 2017.
Impairment of Long-Lived Assets	Impairment of Long-lived Assets We evaluate our long-lived tangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. If the carrying value exceeds the undiscounted future cash flows estimated to result from the use and eventual disposition of the asset, we write down the asset to its estimated fair value. Impairment is assessed by comparing the undiscounted cash flows expected to be generated by the asset to its carrying value. We did not record any impairments in the years ended December 31, 2017, 2016 and 2015.
Accrued Liabilities	Accrued Liabilities As part of the process of preparing our consolidated financial statements, we are required to estimate accruals for professional services and research and development expenses. This process involves reviewing contracts and vendor agreements, and communicating with applicable personnel to identify services that have been performed on our behalf. We estimate the level of service performed and the associated cost incurred for the service when we have not yet been invoiced or otherwise notified of the actual cost. We estimate accrued liabilities as of each balance sheet date based on known facts and circumstances. Although we do not expect our estimates to be materially different from amounts actually incurred, if our estimates of the status and timing of services performed differ from the actual status and timing of services performed, we may report amounts that are too high or too low in any particular period. To date, we have not experienced any significant adjustments to our estimates.
Leases and Deferred Rent	Leases and Deferred Rent We have entered into lease agreements for office and laboratory space. These leases are classified as operating leases. Rent payments, rent-free periods and rent increases are recognized as rent expense on a straight-line basis over the lease term. The difference between rent expense recognized and rental payments is recorded as deferred rent in the accompanying consolidated balance sheets.
Common Stock Warrants	Common Stock Warrants We granted common stock warrants to certain non-employee professional advisers. We account for our warrants at fair value, with changes in fair value recognized in operating expenses. Common stock warrants are initially recorded at their issuance date fair value and are subsequently remeasured at each balance sheet date. These warrants are valued using the Black-Scholes option pricing model based on the estimated market value of the underlying common stock at the valuation measurement dates, the remaining contractual term of the warrant, risk-free interest rates, expected dividends, and expected volatility of the price of the underlying common stock.
Derivative Financial Instruments	Derivative Financial Instruments We evaluate all of our financial instruments, including issued stock purchase warrants, to determine if such instruments are derivatives or contain features qualifying as embedded derivatives. For derivative financial instruments accounted for as liabilities, the derivative instrument is initially recorded at its fair value and is then re-valued at each reporting date, with changes in the fair value reported in the consolidated statement of operations and comprehensive income (loss). We use the Black-Scholes option-pricing model to value the derivative instruments at inception and subsequent valuation dates. The classification of derivative instruments, including whether such instruments should be recorded as liabilities or as equity, is re-assessed at the end of each reporting period. We do not use derivative instruments to hedge exposures to cash flow, market, or foreign currency risks.
Revenue Recognition	Revenue Recognition We derive our revenue from collaboration and licensing agreements. We recognize revenue when each of the following four criteria are met: (1) persuasive evidence of an arrangement exists; (2) products have been delivered or services have been rendered; (3) the sales price is fixed or determinable; and (4) collectability is reasonably assured. We recognize revenue under our License and Research Agreement (the “Collaboration Agreement”) with Kite Pharma, Inc. (“Kite”) in accordance with the guidance on multiple element arrangements. Multiple elements or deliverables may include (1) grants of, or options to obtain, intellectual property licenses; (2) research and development services; and/or (3) manufacturing or supply services. Payments typically received under these arrangements include one or more of the following: non-refundable upfront license fees, option exercise fees, payment for research and/or development efforts, amounts due upon the achievement of specified objectives, and/or royalties on future product sales. The evaluation of multiple-element arrangements requires management to make judgments about (1) the identification of deliverables; (2) whether such deliverables are separable from other aspects of the contractual relationship; (3) the estimated selling price of each deliverable; and (4) the expected period of performance for each deliverable. To determine the units of accounting under a multiple-element arrangement, management evaluates certain separation criteria, including whether the deliverables have stand-alone value, based on the relevant facts and circumstances for each arrangement. Management then estimates the selling price for each unit of accounting and allocates the arrangement consideration to each unit using the relative selling price method. The allocated consideration for each unit of accounting is recognized based on the method most appropriate for that unit of account and in accordance with the revenue recognition criteria detailed above. If there are deliverables in an arrangement that are not separable from other aspects of the contractual relationship, they are treated as a combined unit of accounting, with the allocated revenue for the combined unit recognized in a manner consistent with the revenue recognition criteria applicable to the final deliverable in the combined unit. Payments received prior to satisfying the relevant revenue recognition criteria are recorded as deferred revenue in the accompanying consolidated balance sheets and recognized as revenue when the related revenue recognition criteria are met. The Collaboration Agreement provides for non-refundable milestone payments. We recognize revenue that is contingent upon the achievement of a substantive milestone in its entirety in the period in which the milestone is achieved. A milestone is considered substantive when the consideration payable to us for such milestone (1) is consistent with our performance necessary to achieve the milestone or the increase in value to the collaboration resulting from our performance; (2) relates solely to our past performance; and (3) is reasonable relative to all of the other deliverables and payments within the arrangement. In making this assessment, we consider all facts and circumstances relevant to the arrangement, including factors such as the scientific, regulatory, commercial, and other risks that must be overcome to achieve the milestone, the level of effort and investment required to achieve the milestone and whether any portion of the milestone consideration is related to future performance or deliverables. We will periodically review the estimated performance periods under the Collaboration Agreement which provides for non-refundable upfront payments and fees. We will adjust the periods over which revenue should be recognized when appropriate to reflect changes in assumptions relating to the estimated performance periods. We could accelerate revenue recognition in the event of early termination of programs or if our expectations change. Alternatively, we could decelerate revenue recognition if programs are extended or delayed. While such changes to our estimates have no impact on our reported cash flows, the timing of revenue recorded in future periods could be materially impacted.
Research and Development	Research and Development Research and development costs are expensed as incurred. Research and development costs include payroll and personnel expense, consulting costs, external contract research and development expenses, raw materials, drug product manufacturing costs and allocated overhead – including depreciation, rent and utilities. Research and development costs that are paid in advance of performance are capitalized as a prepaid expense and amortized over the service period as the services are provided.
Stock-based Compensation	Stock-based Compensation We account for all stock-based compensation granted to employees and non-employees using a fair value method. Stock-based compensation awarded to employees and non-employees is measured at the grant date fair value for stock option grants. We use the Black-Scholes option pricing model to estimate the fair value of stock options at the grant date. Stock-based compensation to employees is recognized over the requisite service period of the awards, usually the vesting period, on a straight-line basis. Stock-based compensation awarded to non-employees is revalued over its vesting period using a Black-Sholes option pricing model. For performance-based awards where the vesting of the options may be accelerated upon the achievement of certain milestones, vesting and the related stock-based compensation is recognized as an expense when it is probable the milestone will be met. We recognize forfeiture of awards as they occur rather than estimating the expected forfeiture rate. When awards are modified, we compare the fair value of the affected award measured immediately prior to modification to its value after modification. To the extent that the fair value of the modified award exceeds the original award, the incremental fair value of the modified award is recognized as compensation on the date of modification for vested awards, and over the remaining vesting period for unvested awards.
Income Taxes	Income Taxes Income taxes are accounted for using an asset and liability approach that requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the consolidated financial statement and tax bases of assets and liabilities at the applicable enacted tax rates. We will establish a valuation allowance for deferred tax assets if it is more likely than not that these items will expire before we are able to realize their benefits or that future deductibility is uncertain. We recognize the tax benefit from uncertain tax positions only if it is more likely than not that the tax position will be sustained on examination by the tax authorities, based on the technical merits of the position. The tax position is measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. We recognize interest and penalties related to income tax matters in income tax expense if incurred.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) is comprised of net income (loss) and certain changes in equity excluded from net income (loss). For the year ended December 31, 2017, other comprehensive loss consists of unrealized losses on our short-term investments. There was no difference between comprehensive income (loss) and net income (loss) for the years ended December 31, 2016 and 2015.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers, as amended, which amends the guidance for revenue recognition to replace numerous industry specific requirements. ASU 2014-09, as amended, implements a five-step process for customer contract revenue recognition focusing on transfer of control, as opposed to transfer of risk and rewards. ASU 2014-09, as amended, also requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenues and cash flows from contracts with customers. Other major provisions include ensuring the time value of money is considered in the transaction price, and allowing estimates of variable consideration to be recognized before contingencies are resolved in certain circumstances. ASU 2014-09, as amended, is effective for reporting periods beginning after December 15, 2017. Early adoption is permitted, but not before December 15, 2016. Entities can transition to the standard either retrospectively or as a cumulative-effect adjustment as of the date of adoption. We adopted this new standard effective January 1, 2018, on a modified retrospective basis, which requires the cumulative effect of the adoption to be recognized as an adjustment to opening retained earnings in the first period of adoption. The adoption of ASU No. 2014-09 did not have a material impact on recorded amounts when applied to the opening balance sheet as of January 1, 2018, and is not expected to have a material impact on the amount or timing of the future amounts of net income. Additional impacts could still result when the standard is first applied to revenue transactions during the first quarter of 2018. In February 2016, the FASB issued ASU No. 2016-02, Leases. ASU 2016-02 requires a lessee to separate the lease components from the non-lease components in a contract and recognize in the statement of financial position a liability to make lease payments (the lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term. It also aligns lease accounting for lessors with the revenue recognition guidance in ASU 2014-09. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, and is to be applied at the beginning of the earliest period presented using a modified retrospective approach. We are continuing to evaluate the effect the standard will have on our financial statements and related disclosures. In August 2016, the FASB issued ASU No. 2016-15 which provides new guidance on the classification of certain cash receipts and payments in the statement of cash flows. The new guidance is intended to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. We will be required to adopt the new guidance beginning with the first fiscal quarter of 2018; early adoption is permitted. We are currently assessing the impact the new guidance will have on our consolidated statements of cash flows. In May 2017, the FASB issued ASU No. 2017-09 to provide clarity and reduce both diversity in practice and cost and complexity when applying the guidance in Compensation - Stock Compensation (
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In August 2014, the FASB issued ASU No.2014-15, Disclosures of Uncertainties about an Entity’s Ability to Continue as a Going Concern. Under the new guidance, management is required to assess an entity’s ability to continue as a going concern and to provide related footnote disclosures in certain circumstances. The provisions of this standard are effective for annual periods ending after December 31, 2016, and for annual and interim periods thereafter. We adopted this guidance this year and management believes our existing cash and cash equivalents as of December 31, 2017 are sufficient to fund our operations and do not raise substantial doubt about our ability to continue as a going concern. In March 2016, the FASB issued ASU No. 2016-09- Improvements to Employee Share-Based Payment Accounting, wh ich simplified the accounting for share-based payment transactions, including the income tax consequences, the calculation of diluted earnings per share, the treatment of forfeitures, the classification of awards as either equity or liabilities, and the classification on the statement of cash flows. For public business entities, the amendments in this update are effective for annual periods beginning after December 15, 2016 and interim periods within those annual periods. Early adoption is permitted for any entity in any interim or annual period. We adopted ASU 2016-09 with effect from January 1, 2015. The adoption of this standard did not have an impact on our financial statements. In November 2016, the FASB issued ASU No. 2016-18 relating to restricted cash. The new guidance requires amounts generally described as restricted cash and restricted cash equivalents to be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the consolidated statement of cash flows. This guidance is required to be adopted beginning with the first fiscal quarter of 2018; early adoption is permitted. We adopted this guidance effective June 30, 2017, which required us to include restricted cash within the beginning and ending balance of cash and cash equivalents for the year ended December 31, 2017. We had no restricted cash prior to adopting this guidance, thus we were not required to revise prior period statements of cash flows. The adoption of this guidance does not impact our financial position or results of operations.
Net Loss Per Share	We compute net loss per share attributable to common stockholders using the two-class method required for participating securities. We consider our convertible preferred stock to be participating securities. In accordance with the two-class method, earnings allocated to these participating securities, which include participation rights in undistributed earnings, are subtracted from net income to determine total undistributed earnings to be allocated to common stockholders. Net loss is not allocated to participating securities as there is no contractual obligation to share in net losses. Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. All participating securities are excluded from basic weighted-average common shares outstanding. Because of net losses recognized in each period, potential common shares issuable upon the exercise of outstanding stock options and warrants and the conversion of preferred shares into common shares have not been reflected in the calculation of diluted net loss per share due to the anti-dilutive effect. Diluted net loss per share, therefore, does not differ from basic net loss per share.
Fair Value Measurements	Fair value is defined as the exchange price received for an asset or paid to transfer a liability, or an exit price, 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 three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value, is as follows: Level 1 : Quoted prices in active markets for identical assets or liabilities. Level : Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in inactive markets, 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 supported by little or no market activity and significant to the fair value of the assets or liabilities.

Business Combination (Tables)

Business Combination (Tables) - Nivalis Therapeutics, Inc.	12 Months Ended
	Dec. 31, 2017
Business Acquisition [Line Items]
Schedule of Fair Value of Consideration Transferred	The fair value of the consideration transferred was based on the most reliable measure, which was determined to be the market price of Nivalis shares of common stock as of the acquisition date. The fair value of the consideration transferred consisted of the following (in thousands except share and per share amounts): Outstanding Nivalis common stock 3,914,058 Per share fair value of Nivalis common stock $ 9.60 Outstanding Nivalis stock options 421,992 Weighted average per share fair value of Nivalis stock options $ 1.25 Total fair value of consideration $ 38,103
Schedule of Adjusted Allocation of Purchase Consideration	The final allocation of the purchase consideration is as follows (in thousands): Assets: Cash and cash equivalents $ 31,130 Marketable securities 12,952 Other receivables 79 IPR&D 1,453 Total assets acquired 45,614 Liabilities: Accrued liabilities (401 ) Deferred tax liability (509 ) Total liabilities assumed (910 ) Bargain purchase gain (6,601 ) Total $ 38,103
Schedule of Pro Forma Financial Information	The following pro forma consolidated results of net loss for the years ended December 31, 2017 and 2016 assume the business combination was completed as of January 1, 2016 (in thousands, except per share amounts): Years Ended December 31, 2017 2016 Pro forma revenues $ 1,731 $ 2,950 Pro forma net loss (18,327 ) (32,695 ) Pro forma basic and diluted net loss per share $ (1.32 ) $ (2.37 )

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Schedule of Anti-dilutive Securities Excluded from Diluted Net Loss Per Share Attributable to Common Stockholders Calculation	The common stock issuable upon the conversion or exercise of the following dilutive securities has been excluded from the diluted net loss per share attributable to common stockholders calculation because their effect would have been antidilutive for the periods presented: December 31, 2017 2016 2015 Convertible preferred stock — 4,311,770 1,212,436 Warrants to purchase common stock 24,123 12,422 12,422 Options to purchase common stock 1,611,996 520,739 401,688 Total 1,636,119 4,844,931 1,626,546

Cash Equivalents and Short-Te28

Cash Equivalents and Short-Term Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Cash Cash Equivalents And Short Term Investments [Abstract]
Summary of Amortized Cost and Fair Value of Cash Equivalents and Short Term Investments	The amortized cost and fair value of our cash equivalents and short-term investments are as follows (in thousands): Assets: December 31, 2017 Amortized Cost Gross unrealized gains Gross unrealized losses Fair market value Money market funds $ 5,680 $ — $ — $ 5,680 U.S. treasury bills 19,909 — (21 ) 19,888 Corporate debt securities and commercial paper 53,390 — (38 ) 53,352 Total $ 78,979 $ — $ (59 ) $ 78,920

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis	The following table summarizes our financial assets and liabilities measured at fair value on a recurring basis (in thousands): Assets: December 31, 2017 Level 1 Level 2 Level 3 Total Money market funds $ 5,680 $ — $ — $ 5,680 U.S. treasury bills 19,888 — — 19,888 Corporate debt securities and commercial paper — 53,352 — 53,352 Total $ 25,568 $ 53,352 $ — $ 78,920
Reconciliation of Level 3 Warrant Liability Measured and Recorded at Fair Value on Recurring Basis, Using Significant Unobservable Inputs	The following table shows the reconciliation of the Level 3 warrant liability measured and recorded at fair value on a recurring basis, using significant unobservable inputs (in thousands): Estimated Fair Value Balance as of January 1, 2017 $ — Fair value of warrants at issuance (June 30, 2017) 53,000 Change in fair value of warrant liability in connection with merger (1,000 ) Conversion of warrant liability to equity (52,000 ) Balance as of December 31, 2017 $ —

Prepaid Expenses and Other Cu30

Prepaid Expenses and Other Current Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Prepaid Expense Current [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consists of the following (in thousands): December 31, 2017 2016 Prepaid research and development $ 791 $ — Prepaid insurance 298 8 Prepaid other 91 28 Other receivables 128 — Prepaid expenses and other current assets $ 1,308 $ 36

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Schedule of property and equipment	Property and equipment consist of the following (in thousands): December 31, 2017 2016 Laboratory equipment $ 1,161 $ 660 General equipment and furniture 110 74 Computer equipment and software 82 70 Leasehold improvements 47 6 Property and equipment, at cost 1,400 810 Less accumulated depreciation and amortization (311 ) (70 ) Property and equipment, net $ 1,089 $ 740

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Payables And Accruals [Abstract]
Summary of Accrued Liabilities and Current Liabilities	Accrued liabilities and other current liabilities consisted of the following (in thousands): December 31, 2017 2016 Accrued research and development $ 197 $ — Accrued professional fees 112 5 Deferred compensation — 61 Accrued taxes and licenses 30 61 Accrued other 43 43 Total $ 382 $ 170

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Summary of Future Minimum Lease Payments for Non-cancelable Operating Leases	Future minimum lease payments for our non-cancelable operating leases at December 31, 2017 are as follows (in thousands): Minimum Lease Payments 2018 $ 605 2019 606 2020 — 2021 — 2022 — Total future minimum lease payments $ 1,211

Convertible Preferred Stock (Ta

Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2017
Temporary Equity Disclosure [Abstract]
Summary of Convertible Preferred Stock	A summary of convertible preferred stock as of December 31, 2016 is as follows (amounts in thousands, except share and per share data): December 31, 2016 Issued Price per Share Shares Authorized Shares Issued and Outstanding Aggregate Liquidation Preference Carrying Value Series Seed $ 0.51 5,000,000 2,484,500 $ 1,250 $ 1,250 Series A $ 5.66 17,081,852 1,827,270 10,333 10,285 Total 22,081,852 4,311,770 $ 11,583 $ 11,535

Stockholders' Deficit (Tables)

Stockholders' Deficit (Tables)	12 Months Ended
	Dec. 31, 2017
Stockholders Equity Note [Abstract]
Schedule of Shares of Common Stock Reserved for Future Issuance	Shares of common stock reserved for future issuance were as follows: December 31, 2017 2016 Shares to be issued upon conversion of convertible preferred stock — 4,311,770 Shares to be issued upon exercise of outstanding stock options 1,611,996 520,739 Shares to be issued upon conversion of common stock warrants 24,123 12,422 Shares available for future stock grants 576,722 545,078 Shares to be issued under employee stock purchase plan 45,211 — Shares of common stock reserved for future issuance 2,258,052 5,390,009
Schedule of Stock Option Activity	A summary of stock option activity under our plans is presented below: Options Outstanding Weighted- average Exercise Price Weighted- average Remaining Contract Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2015 401,688 $ 0.42 Granted 512,844 $ 0.53 Exercised (111,802 ) $ 0.45 Forfeited/Expired (281,991 ) $ 0.45 Outstanding at December 31, 2016 520,739 $ 0.51 9.22 $ 179 Options assumed in the merger 421,992 $ 22.97 Options assumed in the merger, expired during period (253,194 ) $ 30.66 Granted 997,368 $ 4.94 Exercised (45,031 ) $ 0.45 Forfeited/Expired (29,878 ) $ 4.72 Outstanding at December 31, 2017 1,611,996 $ 4.32 8.35 $ 11,525 Vested and expected to vest after December 31, 2017 1,611,996 $ 4.32 8.35 $ 11,525 Exercisable at December 31, 2017 377,550 $ 5.39 5.70 $ 2,600
Schedule of Stock Option Assumptions	. The fair values of stock options granted to employees were calculated using the following assumptions: Years Ended December 31, 2017 2016 2015 Weighted-average estimated fair value $ 4.69 $ 0.42 $ 0.38 Risk-free interest rate (1) 1.90% - 2.26% 1.14% - 2.24% 1.79% - 2.24% Expected term of options (in years) (2) 5.69 - 6.32 5.22 – 7.00 5.21 - 10.00 Expected stock price volatility (3) 72% - 83% 72% - 79% 70% - 85% Expected dividend yield (4) —% —% —% (1) The risk-free interest rate assumption was based on zero-coupon U.S. Treasury instruments that had terms consistent with the expected term of our stock option grants. (2) We used the “simplified method” for options to determine the expected term of stock option granted to employees. Under this approach, the weighted-average expected life is presumed to be the average of the vesting term and the contractual term of the option. (3) Volatility is a measure of the amount by which a financial variable, such as share price, has fluctuated or is expected to fluctuate during a period. We analyzed the stock price volatility of companies at a similar stage of development to estimate expected volatility of our stock price. (4) We have never declared or paid any cash dividends and do not presently plan to pay cash dividends in the foreseeable future.
Schedule of Stock-based Compensation Expense	Stock-based compensation expense is classified in the statements of operations as follows (amounts in thousands): Years Ended December 31, 2017 2016 2015 Employee: Research and development $ 183 $ 14 $ — General and administrative 588 53 10 Non-Employee: Research and development 52 5 2 General and administrative 15 5 4 Total stock-based compensation expense $ 838 $ 77 $ 16

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Summary of Provision for Income Taxes	The provision for income taxes is composed of the following (in thousands): Years Ended December 31, 2017 2016 Current: U.S. - Federal $ (1 ) $ 4 U.S. - State 5 62 Total current 4 66 Deferred: U.S. - Federal (204 ) — U.S. - State — — Total deferred (204 ) — Total income tax expense $ (200 ) $ 66
Summary of Effective Tax Rate of Provision for Income Taxes Differs from Federal Statutory Rate	The effective tax rate of the provision for income taxes differs from the federal statutory rate as follows: Years Ended December 31, 2017 2016 U.S. Statutory rate 35.0 % 34.0 % Effect of: State taxes (net of federal benefit) (1.6 %) 5.6 % Permanent differences (0.1 %) (0.3 %) Federal research and development credit 4.4 % 9.4 % Change in valuation allowance (19.4 %) (54.0 %) Benefit of a lower tax rate 0.2 % 0.9 % Stock-based compensation (2.6 %) (1.2 %) Non-deductible merger costs (17.6 %) (— %) Bargain purchase gain 28.9 % (— %) Tax rate change (24.7 %) (— %) Effective income tax rate 2.5 % (5.6 %)
Schedule of Significant Components of Deferred Tax Assets and Liabilities	The following table represents the significant components of our deferred tax assets and liabilities for the periods presented (in thousands): December 31, 2017 2016 Deferred tax assets: Net operating loss $ 2,475 $ — Deferred compensation — 24 Research and development credits 458 103 Intangible asset basis — 16 Deferred revenue 58 800 Deferred rent 24 58 Stock based compensation 810 3 Other 12 — Gross deferred tax assets 3,837 1,004 Valuation allowance (3,722 ) (786 ) Total deferred tax assets, net of valuation allowance 115 218 Deferred tax liabilities: Prepaid expenses (63 ) (12 ) Fixed asset basis (110 ) (206 ) Intangible asset basis (247 ) Total deferred tax liability (420 ) (218 ) Net deferred tax assets and liabilities $ (305 ) $ —
Summary of Net Operating Loss Carryforwards	We have net operating loss carryforwards as follows (in thousands): December 31, 2017 2016 Federal $ 11,784 $ —
Summary of Net Research and Development Tax Credit Carryforwards	We have net research and development tax credit carryforwards as follows (in thousands): December 31, 2017 2016 Federal $ 458 $ 103
Summary of Activity Related to Unrecognized Tax benefits	The following table summarized the activity related to unrecognized tax benefits (in thousands): December 31, 2017 2016 Unrecognized benefits – beginning of year $ 34 $ 7 Gross decreases – prior year tax positions (4 ) — Gross increases – current year tax positions 84 27 Unrecognized benefit – end of year $ 114 $ 34

Description of Business - Addit

Description of Business - Additional Information (Details) $ / shares in Units, $ in Thousands	Jul. 24, 2017USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)
Description Of Business [Line Items]
Convertible preferred stock, shares issued | shares		0	4,311,770
Convertible preferred stock, purchase price per share | $ / shares		$ 0.001	$ 0.0001
Aggregate purchase price | $		$ 37,666	$ 10,925	$ 610
Convertible Preferred Stock
Description Of Business [Line Items]
Convertible preferred stock, shares issued | shares	1,335,118
Convertible preferred stock, purchase price per share | $ / shares	$ 12.74
Aggregate purchase price | $	$ 17,000
AIS Operating Co Inc Preexisting Stockholders, Optionholders, and Warrantholders
Description Of Business [Line Items]
Ownership percentage immediately following merger consummation	74.00%
Nivalis Therapeutics, Inc.
Description Of Business [Line Items]
Stock split conversion ratio	0.25
Ownership percentage immediately following merger consummation	26.00%
Effective date of merger	Jul. 24, 2017

Summary of Significant Accoun38

Summary of Significant Accounting Policies - Additional Information (Details)	Jul. 24, 2017	Dec. 31, 2017USD ($)Segment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Jun. 29, 2017USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | Segment		1
IPR&D intangible assets		$ 1,453,000
Impairment of long-lived tangible assets		$ 0	$ 0	$ 0
Minimum percentage of income tax benefit realized upon ultimate settlement		50.00%
Restricted cash		$ 132,000			$ 0
Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets		3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets		5 years
Nivalis Therapeutics, Inc.
Summary Of Significant Accounting Policies [Line Items]
Effective date of merger	Jul. 24, 2017
Stock split conversion ratio	0.25

Business Combination - Addition

Business Combination - Additional Information (Details)	Jul. 24, 2017USD ($)shares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)	Jul. 25, 2017shares
Business Acquisition [Line Items]
Common stock, shares outstanding | shares		13,831,178	608,701		13,881,645
Aggregate purchase price		$ 37,666,000	$ 10,925,000	$ 610,000
Net operating loss carryforward expiration beginning year		2,032
Percenatge of projected cash flows discounted to their present value using discount rate		17.00%
General and Administrative Expense
Business Acquisition [Line Items]
Acquisition-related costs		$ 1,500,000
Convertible Preferred Stock
Business Acquisition [Line Items]
Aggregate purchase price	$ 17,000,000
Minimum
Business Acquisition [Line Items]
Percentage of shares outstanding after merger	74.00%
Common Stock
Business Acquisition [Line Items]
Lock out period of shares issued in merger	180 days
AIS Operating Co Inc Preexisting Stockholders, Optionholders, and Warrantholders
Business Acquisition [Line Items]
Ownership percentage immediately following merger consummation	74.00%
AIS Operating Co Inc Preexisting Stockholders, Optionholders, and Warrantholders | Common Stock
Business Acquisition [Line Items]
Stock split conversion ratio	0.4969
Nivalis Therapeutics, Inc.
Business Acquisition [Line Items]
Effective date of merger	Jul. 24, 2017
Description of Reverse stock split		1:4 reverse stock split
Stock split conversion ratio	0.25
Common stock, shares outstanding | shares	3,914,058
Ownership percentage immediately following merger consummation	26.00%
Adjustments to the allocation of the purchase consideration included increase of other receivables		$ 77,000
Adjustments to the allocation of the purchase consideration included increase of accrued liabilities		15,000
Ajustments to the allocation of the purchase consideration resulted decrease in bargain purchase gain		$ 62,000

Business Combination - Schedule

Business Combination - Schedule of Fair Value of Consideration Transferred (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 24, 2017	Dec. 31, 2017	Jul. 25, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Outstanding Nivalis common stock		13,831,178	13,881,645	608,701
Nivalis Therapeutics, Inc.
Business Acquisition [Line Items]
Outstanding Nivalis common stock	3,914,058
Per share fair value of Nivalis common stock	$ 9.60
Outstanding Nivalis stock options	421,992
Weighted average per share fair value of Nivalis stock options	$ 1.25
Total fair value of consideration	$ 38,103

Business Combination - Schedu41

Business Combination - Schedule of Adjusted Allocation of Purchase Consideration (Details) - USD ($) $ in Thousands	Jul. 24, 2017	Dec. 31, 2017
Bargain Purchase gain [Abstract]
Bargain purchase gain		$ (6,601)
Nivalis Therapeutics, Inc.
Assets:
Cash and cash equivalents	$ 31,130
Marketable securities	12,952
Other receivables	79
IPR&D	1,453
Total assets acquired	45,614
Liabilities:
Accrued liabilities	(401)
Deferred tax liability	(509)
Total liabilities assumed	(910)
Bargain Purchase gain [Abstract]
Bargain purchase gain	(6,601)
Total	$ 38,103

Business Combination - Schedu42

Business Combination - Schedule of Pro Forma Financial Information (Details) - Alpine Immune Sciences, Inc - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Pro forma revenues	$ 1,731	$ 2,950
Pro forma net loss	$ (18,327)	$ (32,695)
Pro forma basic and diluted net loss per share	$ (1.32)	$ (2.37)

Net Loss Per Share - Additional

Net Loss Per Share - Additional Information (Details) - Common Stock - shares	Jul. 24, 2017	Dec. 31, 2017
Earnings Per Share [Line Items]
Convertible preferred stock converted to common stock	9,301,433
Common stock acquired in business combination, shares	3,914,058	3,914,058

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Anti-dilutive Securities Excluded from Diluted Net Loss Per Share Attributable to Common Stockholders Calculation (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	1,636,119	4,844,931	1,626,546
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)		4,311,770	1,212,436
Warrants to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	24,123	12,422	12,422
Options to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	1,611,996	520,739	401,688

Cash Equivalents and Short-Te45

Cash Equivalents and Short-Term Investments - Summary of Amortized Cost and Fair Value of CashEquivalents and Short Term Investments (Details) $ in Thousands	Dec. 31, 2017USD ($)
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 78,979
Gross unrealized losses	(59)
Fair market value	78,920
Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,680
Fair market value	5,680
U.S. Treasury Bills
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	19,909
Gross unrealized losses	(21)
Fair market value	19,888
Corporate Debt Securities and Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	53,390
Gross unrealized losses	(38)
Fair market value	$ 53,352

Cash Equivalents and Short-Te46

Cash Equivalents and Short-Term Investments - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Realized gains on securities	$ 0
Realized losses on securities	$ 0
Short-term investments		$ 0
Maximum
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities, contractual maturity period	1 year

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 24, 2017	Jun. 30, 2017	Jul. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash				$ 2,300	$ 11,800
Common Stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Date of conversion of preferred stock warrants to common stock warrants	Jul. 24, 2017
Other Income
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Decrease in fair value of warrant			$ (1,000)
Warrant Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Stock price		$ 9.64
Risk-free rate		2.31%
Expected volatility		78.00%
Term		9 years 6 months
Decrease in fair value of warrant				$ (1,000)

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) $ in Thousands	Dec. 31, 2017USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets disclosure	$ 78,920
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets disclosure	5,680
Corporate Debt Securities and Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets disclosure	53,352
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets disclosure	78,920
Fair Value, Measurements, Recurring | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets disclosure	25,568
Fair Value, Measurements, Recurring | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets disclosure	53,352
Fair Value, Measurements, Recurring | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets disclosure	5,680
Fair Value, Measurements, Recurring | Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets disclosure	5,680
Fair Value, Measurements, Recurring | U.S. Treasury Bills
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets disclosure	19,888
Fair Value, Measurements, Recurring | U.S. Treasury Bills | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets disclosure	19,888
Fair Value, Measurements, Recurring | Corporate Debt Securities and Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets disclosure	53,352
Fair Value, Measurements, Recurring | Corporate Debt Securities and Commercial Paper | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets disclosure	$ 53,352

Fair Value Measurements - Recon

Fair Value Measurements - Reconciliation of Level 3 Warrant Liability Measured and Recorded at Fair Value on Recurring Basis, Using Significant Unobservable Inputs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Conversion of warrant liability to equity	$ (52)
Warrant Liability
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance as of January 1, 2017	0
Fair value of warrants at issuance (June 30, 2017)	53,000
Change in fair value of warrant liability in connection with merger	(1,000)
Conversion of warrant liability to equity	(52,000)
Balance as of December 31, 2017	$ 0

Prepaid Expenses and Other Cu50

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Prepaid Expense Current [Abstract]
Prepaid research and development	$ 791
Prepaid insurance	298	$ 8
Prepaid other	91	28
Other receivables	128
Prepaid expenses and other current assets	$ 1,308	$ 36

Property and Equipment (Details

Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 1,400	$ 810
Less accumulated depreciation and amortization	(311)	(70)
Property and equipment, net	1,089	740
Laboratory equipment
Property Plant And Equipment [Line Items]
Property and equipment, at cost	1,161	660
General equipment and furniture
Property Plant And Equipment [Line Items]
Property and equipment, at cost	110	74
Computer equipment and software
Property Plant And Equipment [Line Items]
Property and equipment, at cost	82	70
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 47	$ 6

Property and Equipment - Additi

Property and Equipment - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Abstract]
Depreciation expenses	$ 241,000	$ 69,000	$ 1,000

Accrued Liabilities - Summary o

Accrued Liabilities - Summary of Accrued Liabilities and Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Accrued research and development	$ 197
Accrued professional fees	112	$ 5
Deferred compensation		61
Accrued taxes and licenses	30	61
Accrued other	43	43
Total	$ 382	$ 170

Long-term Debt - Additional Inf

Long-term Debt - Additional Information (Details)	Jul. 24, 2017shares	Jun. 30, 2017USD ($)$ / sharesshares	Dec. 31, 2017USD ($)Installmentshares
Debt Instrument [Line Items]
Term loan drew down			$ 5,000,000
Number of equal monthly payments | Installment			30
Amortization of debt discount			$ 87,000
Unamortized debt discount			$ 341,000
Common Stock
Debt Instrument [Line Items]
Warrants exercisable for shares of common stock | shares			7,069
Date of conversion of preferred stock warrants to common stock warrants	Jul. 24, 2017
Series A-1 Preferred Stock Warrants
Debt Instrument [Line Items]
Class of warrant or rights, granted | shares	7,069	7,069
Warrants issued, exercise price | $ / shares		$ 12.38
Fair value of warrant liability		$ 53,000
Warrants exercisable for shares of common stock | shares		7,069
Term Loan
Debt Instrument [Line Items]
Term loan drew down		$ 5,000,000
Interest-only period expiration date			Jul. 1, 2018
Long-term debt final payment fee percentage			7.50%
Long-term debt final payment fee			$ 375,000
Term Loan | Prime Rate
Debt Instrument [Line Items]
Debt instrument variable interest rate			1.75%

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	1 Months Ended	12 Months Ended
	Jan. 31, 2018USD ($)ft²Option	Dec. 31, 2017USD ($)ft²Option	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Operating Leased Assets [Line Items]
Office and laboratory space | ft²		11,158
Operating lease, annual base rent		$ 566,000
Number of option to extend term lease | Option		2
Operating lease, Expiry date		Dec. 31, 2019
Operating lease, annual base rent increasing percentage		3.00%
Operating lease renewal term		12 months
Rent expense		$ 529,000	$ 267,000	$ 43,000
Subsequent Event
Operating Leased Assets [Line Items]
Operating lease, annual base rent	$ 295,000
Number of option to extend term lease | Option	2
Operating lease, Expiry date	Dec. 31, 2019
Operating lease, annual base rent increasing percentage	3.00%
Operating lease renewal term	12 months
Additional office and laboratory space | ft²	6,184
Restricted cash
Operating Leased Assets [Line Items]
Security deposit		$ 132,000

Commitments and Contingencies56

Commitments and Contingencies - Summary of Future Minimum Lease Payments for Non-cancelable Operating Leases (Details) $ in Thousands	Dec. 31, 2017USD ($)
Commitments And Contingencies Disclosure [Abstract]
2,018	$ 605
2,019	606
Total future minimum lease payments	$ 1,211

License and Collaboration Agr57

License and Collaboration Agreement - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Oct. 20, 2017USD ($)Tranche	Oct. 31, 2015USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized	$ 1,731,000	$ 2,950,000	$ 492,000
Kite Pharma, Inc. | Collaboration and Licensing Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue					$ 5,500,000
Revenue recognized	1,700,000	$ 2,900,000	$ 492,000
Kite Pharma, Inc. | Collaboration and Licensing Agreement | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future milestones receivable	$ 530,000,000
Kite Pharma, Inc. | Amended Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Eligible to receive additional research support payment				$ 450,000
Number of tranches | Tranche				2

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Details) - USD ($)	Jul. 24, 2017	Jun. 30, 2017	Apr. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Apr. 30, 2016	Nov. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Temporary Equity [Line Items]
Convertible preferred stock, shares issued								0	4,311,770
Proceeds from issuance of convertible preferred stock								$ 37,666,000	$ 10,925,000	$ 610,000
Convertible preferred stock, purchase price per share								$ 0.001	$ 0.0001
Convertible preferred stock, shares outstanding								0	4,311,770
Series A-1 Preferred Stock Warrants
Temporary Equity [Line Items]
Class of warrant or rights, granted	7,069	7,069
Warrants issued, exercise price		$ 12.38
Fair value of warrant liability		$ 53,000
Warrants issued, term for exercise		10 years
Common Stock
Temporary Equity [Line Items]
Convertible preferred stock converted to common stock	9,301,433
Date of conversion of preferred stock warrants to common stock warrants	Jul. 24, 2017
Conversion of preferred stock warrants to common stock warrants	7,069
Series Seed Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares issued						1,272,064	1,212,436
Proceeds from issuance of convertible preferred stock						$ 640,000	$ 610,000
Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares issued				707,330	1,827,270
Proceeds from issuance of convertible preferred stock				$ 4,000,000	$ 10,300,000
Stock issuance costs incurred					$ 48,000
Series A-1 Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares issued			2,947,211
Proceeds from issuance of convertible preferred stock			$ 16,700,000
Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares issued	1,335,118
Proceeds from issuance of convertible preferred stock	$ 17,000,000
Convertible preferred stock, purchase price per share	$ 12.74
Convertible preferred stock, shares outstanding									4,311,770	1,212,436	0
Convertible preferred stock, entitled to dividend rate percentage									6.00%
Liquidation preference, price per share to convertible preferred stock holders									$ 5.66

Convertible Preferred Stock - S

Convertible Preferred Stock - Summary of Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Temporary Equity [Line Items]
Shares Authorized	10,000,000	22,081,852
Shares Issued and Outstanding		4,311,770
Aggregate Liquidation Preference	$ 0	$ 11,583
Carrying Value		$ 11,535
Series Seed
Temporary Equity [Line Items]
Issued Price per Share		$ 0.51
Shares Authorized		5,000,000
Shares Issued and Outstanding		2,484,500
Aggregate Liquidation Preference		$ 1,250
Carrying Value		$ 1,250
Series A
Temporary Equity [Line Items]
Issued Price per Share		$ 5.66
Shares Authorized		17,081,852
Shares Issued and Outstanding		1,827,270
Aggregate Liquidation Preference		$ 10,333
Carrying Value		$ 10,285

Stockholders' Deficit - Additio

Stockholders' Deficit - Additional Information (Details)

Jan. 02, 2018shares

Jul. 24, 2017

Jun. 30, 2017$ / sharesshares

Apr. 12, 2017$ / sharesshares

Apr. 24, 2015$ / sharesshares

Dec. 31, 2017USD ($)$ / sharesshares

Jul. 31, 2017shares

May 31, 2016Employeeshares

Feb. 28, 2015

Dec. 31, 2017USD ($)$ / sharesshares

Dec. 31, 2016USD ($)shares

Jul. 25, 2017shares

Class Of Stock [Line Items]

Common stock, shares outstanding

13,831,178

13,831,178

608,701

13,881,645

Repurchase of unvested common stock

50,467

50,467

0

Original purchase price | $ / shares

$ 0.002

Shares available for future issuance

2,258,052

2,258,052

5,390,009

Extended vesting period of number of unvested share options

567,500

Number of employees | Employee

5

Additional compensation expense | $

$ 4,000

Options to purchase common stock

Class Of Stock [Line Items]

Unrecognized compensation cost related to nonvested stock options | $

$ 4,100,000

$ 4,100,000

Weighted-average period over which unrecognized compensation expense related to nonvested stock options is expected to be recognized

3 years 3 months 18 days

Aggregate intrinsic value of stock options exercised | $

$ 18,000

Fair value of shares vested | $

$ 139,000

ESPP

Class Of Stock [Line Items]

Shares available for future issuance

45,211

2015 Plan

Class Of Stock [Line Items]

Vesting period (in years)

4 years

Term (in years)

10 years

2015 EIP

Class Of Stock [Line Items]

Number of shares authorized (in shares)

658,275

Annual percentage increase, authorized shares (as a percent)

5.00%

2015 EIP | Subsequent Event

Class Of Stock [Line Items]

Additional number of shares authorized (in shares)

691,558

2015 Plan and 2015 EIP

Class Of Stock [Line Items]

Shares available for future issuance

576,722

576,722

Number of shares authorized (in shares)

2,370,395

2,370,395

Series A-1 Preferred Stock Warrants

Class Of Stock [Line Items]

Warrants exercisable for shares of common stock

7,069

Warrants issued, exercise price | $ / shares

$ 12.38

Warrants issued, term for exercise

10 years

Warrants Assumed in Merger

Class Of Stock [Line Items]

Warrants exercisable for shares of common stock

4,632

4,632

Warrants issued, exercise price | $ / shares

$ 97.12

$ 97.12

Common Stock

Class Of Stock [Line Items]

Warrants exercisable for shares of common stock

7,069

7,069

Date of conversion of preferred stock warrants to common stock warrants

Jul. 24, 2017

Non-Employee Professional Advisers

Class Of Stock [Line Items]

Warrants exercisable for shares of common stock

12,422

12,422

Warrants issued, exercise price | $ / shares

$ 5.02

$ 0.11

Warrants exercisable for shares of common stock, vesting period

48 months

24 months

Options to purchase common stock | Maximum | 2015 Plan

Class Of Stock [Line Items]

Term (in years)

10 years

Stockholders' Deficit - Schedul

Stockholders' Deficit - Schedule of Shares of Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2017	Dec. 31, 2016
Class Of Stock [Line Items]
Shares of common stock reserved for future issuance	2,258,052	5,390,009
Shares to be Issued Upon Conversion of Convertible Preferred Stock
Class Of Stock [Line Items]
Shares of common stock reserved for future issuance		4,311,770
Shares to be Issued Upon Exercise of Outstanding Stock Options
Class Of Stock [Line Items]
Shares of common stock reserved for future issuance	1,611,996	520,739
Shares to be Issued Upon Conversion of Common Stock Warrants
Class Of Stock [Line Items]
Shares of common stock reserved for future issuance	24,123	12,422
Shares Available For Future Stock Grants
Class Of Stock [Line Items]
Shares of common stock reserved for future issuance	576,722	545,078
Shares to be Issued under Employee Stock Purchase Plan
Class Of Stock [Line Items]
Shares of common stock reserved for future issuance	45,211

Stockholders' Deflicit - Summar

Stockholders' Deflicit - Summary of Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Weighted-Average Remaining Contractual Life (In Years)
Outstanding (in years)	8 years 4 months 6 days	9 years 2 months 19 days
Vested and expected to vest after December 31, 2017 (in years)	8 years 4 months 6 days
Exercisable (in years)	5 years 8 months 12 days
Aggregate Intrinsic Value
Outstanding at beginning of period		$ 179
Outstanding at ending of period	$ 11,525
Vested and expected to vest after December 31, 2017	11,525
Exercisable at December 31, 2017	$ 2,600
Options to purchase common stock
Options Outstanding
Outstanding at beginning of period	520,739	401,688
Options assumed in the merger	421,992
Options assumed in the merger, expired during period	(253,194)
Granted	997,368	512,844
Exercised	(45,031)	(111,802)
Forfeited/Expired	(29,878)	(281,991)
Outstanding at ending of period	1,611,996	520,739
Vested and expected to vest after December 31, 2017	1,611,996
Exercisable at December 31, 2017	377,550
Weighted Average Exercise Price
Outstanding at beginning of period	$ 0.51	$ 0.42
Options assumed in the merger	22.97
Options assumed in the merger, expired during period	30.66
Granted	4.94	0.53
Exercised	0.45	0.45
Forfeited/Expired	4.72	0.45
Outstanding at ending of period	4.32	$ 0.51
Vested and expected to vest after December 31, 2017	4.32
Exercisable at December 31, 2017	$ 5.39

Stockholders' Deficit - Sched63

Stockholders' Deficit - Schedule of Stock Option Assumptions (Details) - $ / shares		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average estimated fair value		$ 4.69	$ 0.42	$ 0.38
Risk-free interest rate, minimum	[1]	1.90%	1.14%	1.79%
Risk-free interest rate, maximum	[1]	2.26%	2.24%	2.24%
Expected stock price volatility, minimum	[2]	72.00%	72.00%	70.00%
Expected stock price volatility, maximum	[2]	83.00%	79.00%	85.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term of options (in years)	[3]	5 years 8 months 8 days	5 years 2 months 19 days	5 years 2 months 15 days
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term of options (in years)	[3]	6 years 3 months 25 days	7 years	10 years
[1]	The risk-free interest rate assumption was based on zero-coupon U.S. Treasury instruments that had terms consistent with the expected term of our stock option grants.
[2]	Volatility is a measure of the amount by which a financial variable, such as share price, has fluctuated or is expected to fluctuate during a period. We analyzed the stock price volatility of companies at a similar stage of development to estimate expected volatility of our stock price.
[3]	We used the “simplified method” for options to determine the expected term of stock option granted to employees. Under this approach, the weighted-average expected life is presumed to be the average of the vesting term and the contractual term of the option.

Stockholders' Deficit - Sched64

Stockholders' Deficit - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 838	$ 77	$ 16
Employee | Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	183	14
Employee | General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	588	53	10
Non-Employee | Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	52	5	2
Non-Employee | General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 15	$ 5	$ 4

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	Jul. 24, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
U.S. federal statutory rate			35.00%	34.00%
Change in tax rate, reduction in deferred tax asset			$ 2,000,000
Change in tax rate, reduction in valuation allowance			2,200,000
Change in tax rate, resulting in deferred income tax benefit			200,000
Tax benefit and expense			$ (200,000)	$ 66,000
Effective tax rate			2.50%	(5.60%)
Increase in valuation allowance			$ 2,900,000	$ 629,000
Net operating loss carryforward expiration beginning year			2,032
Description of the likelihood that an uncertainty in income taxes will not be sustained upon audit by taxing authority			greater than 50% likely
Unrecognized tax benefits			$ 114,000	34,000	$ 7,000
Unrecognized tax benefits that would impact effective tax rate, if recognized			0
Accrued interest or penalties related to unrecognized tax benefits			$ 0	0
Federal and State
Income Taxes [Line Items]
Net operating loss carryforward expiration beginning year			2,037
Federal
Income Taxes [Line Items]
Research and development tax credit carryforwards expiration beginning year			2,035
Nivalis Therapeutics, Inc.
Income Taxes [Line Items]
IPR&D acquired in business combination	$ 1,453,000
Deferred tax liability, IPR&D	305,000
IPR&D acquired in business combination, tax basis	$ 0
Tax credit and net operating loss carryforwards			$ 0
Kite Pharma, Inc.
Income Taxes [Line Items]
Deferred revenue				$ 2,000,000	$ 5,500,000
Scenario, Plan [Member]
Income Taxes [Line Items]
U.S. federal statutory rate		21.00%

Income Taxes - Summary of Provi

Income Taxes - Summary of Provision for Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Current:
U.S. - Federal	$ (1,000)	$ 4,000
U.S. - State	5,000	62,000
Total current	4,000	66,000
Deferred:
U.S. - Federal	(204,000)
Total deferred	(204,000)
Total income tax expense	$ (200,000)	$ 66,000

Income Taxes - Summary of Effec

Income Taxes - Summary of Effective Tax Rate of Provision for Income Taxes Differs from Federal Statutory Rate (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
U.S. Statutory rate	35.00%	34.00%
State taxes (net of federal benefit)	(1.60%)	5.60%
Permanent differences	(0.10%)	(0.30%)
Federal research and development credit	4.40%	9.40%
Change in valuation allowance	(19.40%)	(54.00%)
Benefit of a lower tax rate	0.20%	0.90%
Stock-based compensation	(2.60%)	(1.20%)
Non-deductible merger costs	(17.60%)
Bargain purchase gain	28.90%
Tax rate change	(24.70%)
Effective income tax rate	2.50%	(5.60%)

Income Taxes - Schedule of Sign

Income Taxes - Schedule of Significant Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss	$ 2,475
Deferred compensation		$ 24
Research and development credits	458	103
Intangible asset basis		16
Deferred revenue	58	800
Deferred rent	24	58
Stock based compensation	810	3
Other	12
Gross deferred tax assets	3,837	1,004
Valuation allowance	(3,722)	(786)
Total deferred tax assets, net of valuation allowance	115	218
Deferred tax liabilities:
Prepaid expenses	(63)	(12)
Fixed asset basis	(110)	(206)
Intangible asset basis	(247)
Total deferred tax liability	(420)	$ (218)
Net deferred tax assets and liabilities	$ (305)

Income Taxes - Summary of Net O

Income Taxes - Summary of Net Operating Loss Carryforwards (Details) $ in Thousands	Dec. 31, 2017USD ($)
Federal
Income Taxes [Line Items]
Net operating loss carryforwards	$ 11,784

Income Taxes - Summary of Net R

Income Taxes - Summary of Net Research and Development Tax Credit Carryforwards (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Research and development credits	$ 458	$ 103
Federal
Income Taxes [Line Items]
Research and development credits	$ 458	$ 103

Income Taxes - Summary of Activ

Income Taxes - Summary of Activity Related to Unrecognized Tax Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Unrecognized benefits – beginning of year	$ 34,000	$ 7,000
Gross decreases – prior year tax positions	(4,000)
Gross increases – current year tax positions	84,000	27,000
Unrecognized benefit – end of year	$ 114,000	$ 34,000

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - Alpine BioVentures GP, LLC - USD ($)	1 Months Ended	12 Months Ended
	Apr. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Expenses related to shared services agreement		$ 0	$ 17,000	$ 47,000
Accrued expenses related to shared services agreement			$ 5,000
Payment of accumulated expenses related to shared services agreement	$ 5,000