Protagonist Therapeutics (PTGX) 10-K 12 Mar 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 28, 2019	Jun. 30, 2018
Document And Entity Information
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Entity Registrant Name	Protagonist Therapeutics, Inc
Entity Central Index Key	0001377121
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		23,347,066
Entity Public Float			$ 96

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 82,233	$ 106,029
Restricted cash - current	10	10
Available-for-sale securities - current	46,620	37,972
Receivable from collaboration partner and contract asset - related party	4,587	1,816
Research and development tax incentive receivable	1,429	1,347
Prepaid expenses and other current assets	2,624	3,773
Total current assets	137,503	150,947
Property and equipment, net	861	879
Restricted cash - noncurrent	450	450
Available-for-sale securities - noncurrent		11,458
Deferred tax asset - noncurrent	658
Total assets	139,472	163,734
Current liabilities:
Accounts payable	5,711	1,257
Payable to collaboration partner - related party	1,061
Accrued expenses and other payables	11,163	9,546
Deferred revenue - related party	8,223	31,752
Total current liabilities	26,158	42,555
Deferred rent - noncurrent	799	547
Total liabilities	26,957	43,102
Commitments and contingencies (Note 8)
Stockholders equity:
Preferred stock, $0.00001 par value, 10,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.00001 par value, 90,000,000 shares authorized; 23,187,219 and 21,088,306 shares issued and outstanding as of December 31, 2018 and December 31, 2017, respectively	0	0
Additional paid-in capital	253,222	222,188
Accumulated other comprehensive loss	(233)	(6)
Accumulated deficit	(140,474)	(101,550)
Total stockholders equity	112,515	120,632
Total liabilities and stockholders equity	$ 139,472	$ 163,734

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Consolidated Balance Sheets
Preferred stock, par value	$ 0.00001	$ 0.00001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, shares authorized	90,000,000	90,000,000
Common stock, shares issued	23,187,219	21,088,306
Common stock, shares outstanding	23,187,219	21,088,306

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidated Statements of Operations
License and collaboration revenue - related party	$ 30,925	$ 20,063
Operating expenses:
Research and development	59,497	46,181	$ 25,705
General and administrative	13,697	11,779	6,961
Total operating expenses	73,194	57,960	32,666
Loss from operations	(42,269)	(37,897)	(32,666)
Interest income	2,546	940	242
Change in fair value of redeemable convertible preferred stock tranche and warrant liabilities			(4,719)
Other expense			(34)
Loss before income tax benefit	(39,723)	(36,957)	(37,177)
Income tax benefit	799
Net loss	(38,924)	(36,957)	(37,177)
Net loss attributable to common stockholders	$ (38,924)	$ (36,957)	$ (37,735)
Net loss per share attributable to common stockholders, basic and diluted	$ (1.74)	$ (2.09)	$ (5.80)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted	22,364,515	17,694,505	6,501,796

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidated Statements of Comprehensive Loss
Net loss	$ (38,924)	$ (36,957)	$ (37,177)
Other comprehensive loss:
Gain (loss) on translation of foreign operations	(322)	298	(76)
Unrealized gain (loss) on available-for-sale securities	95	(59)	(67)
Comprehensive loss	$ (39,151)	$ (36,718)	$ (37,320)

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) - USD ($)	Common StockPrivate Placement	Common StockAt-the-market offering	Common Stock	Additional Paid-in Capital [Member]Private Placement	Additional Paid-in Capital [Member]At-the-market offering	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Redeemable Convertible Preferred Stock	Private Placement	At-the-market offering	Total
Balance at Dec. 31, 2015									$ 36,996,000			$ 36,996,000
Balance (in shares) at Dec. 31, 2015									77,185,117
Increase (Decrease) in Redeemable Convertible Preferred Stock
Issuance of Series C redeemable convertible preferred stock, net of issuance costs									$ 22,488,000
Issuance of Series C redeemable convertible preferred stock (in shares)									45,189,794
Settlement of fair value of redeemable convertible preferred stock tranche liability									$ 5,837,000
Exercise of redeemable convertible preferred stock warrant liability									$ 1,025,000
Exercise of redeemable convertible preferred stock warrant liability (in shares)									1,999,998
Accretion of redemption of convertible preferred stock to redemption value									$ 558,000			558,000
Conversion of redeemable convertible preferred stock to common stock at closing of initial public offering									$ (66,904,000)
Conversion of redeemable convertible preferred stock to common stock at closing of initial public offering (in shares)									(124,374,909)
Balance at Dec. 31, 2015						$ 118,000	$ (102,000)	$ (27,416,000)				(27,400,000)
Balance (in shares) at Dec. 31, 2015			272,409
Increase (Decrease) in Stockholders' Equity (Deficit)
Conversion of redeemable convertible preferred stock to common stock at closing of initial public offering						66,904,000						66,904,000
Conversion of redeemable convertible preferred stock to common stock at closing of initial public offering (in shares)			8,577,571
Issuance of common stock upon public offering, net of issuance costs						83,648,000						83,648,000
Issuance of common stock upon public offering, net of issuance costs (in shares)			7,752,972
Accretion of redeemable convertible preferred stock						(558,000)						(558,000)
Stock-based compensation expense						2,130,000						2,130,000
Issuance of common stock upon the exercise of options						151,000						151,000
Issuance of common stock upon the exercise of options (in shares)			119,328
Other comprehensive gain (loss)							(143,000)					(143,000)
Net loss								(37,177,000)				(37,177,000)
Balance at Dec. 31, 2016						152,393,000	(245,000)	(64,593,000)				87,555,000
Balance (in shares) at Dec. 31, 2016			16,722,280
Increase (Decrease) in Redeemable Convertible Preferred Stock
Accretion of redemption of convertible preferred stock to redemption value												$ 0
Balance (in shares) at Dec. 31, 2017									0			0
Increase (Decrease) in Stockholders' Equity (Deficit)
Issuance of common stock upon public offering, net of issuance costs						64,547,000						$ 64,547,000
Issuance of common stock upon public offering, net of issuance costs (in shares)			4,059,500
Stock-based compensation expense						4,241,000						4,241,000
Issuance of common stock upon the exercise of options and purchases under employee stock purchase plan						1,007,000						1,007,000
Issuance of common stock upon the exercise of options and purchases under employee stock purchase plan (in shares)			306,526
Other comprehensive gain (loss)							239,000					239,000
Net loss								(36,957,000)				(36,957,000)
Balance at Dec. 31, 2017						222,188,000	(6,000)	(101,550,000)				$ 120,632,000
Balance (in shares) at Dec. 31, 2017												21,088,306
Balance (in shares) at Dec. 31, 2017			21,088,306									21,088,306
Increase (Decrease) in Redeemable Convertible Preferred Stock
Accretion of redemption of convertible preferred stock to redemption value												$ 0
Balance (in shares) at Dec. 31, 2018									0			0
Increase (Decrease) in Stockholders' Equity (Deficit)
Issuance of common stock upon public offering, net of issuance costs					$ 1,508,000						$ 1,508,000
Issuance of common stock upon public offering, net of issuance costs (in shares)		151,273
Issuance of common stock and warrants upon private placement, net of issuance costs				$ 21,673,000						$ 21,673,000
Issuance of common stock and warrants upon private placement, net of issuance costs (in shares)	2,750,000
Retirement of common stock in exchange for common stock warrant						(6,670,000)						$ (6,670,000)
Retirement of common stock in exchange for common stock warrant (in shares)			(1,000,000)
Issuance of common stock warrant in exchange for retirement of common stock						6,670,000						6,670,000
Stock-based compensation expense						6,919,000						6,919,000
Issuance of common stock upon the exercise of options and purchases under employee stock purchase plan						934,000						934,000
Issuance of common stock upon the exercise of options and purchases under employee stock purchase plan (in shares)			197,640
Other comprehensive gain (loss)							(227,000)					(227,000)
Net loss								(38,924,000)				(38,924,000)
Balance at Dec. 31, 2018						$ 253,222,000	$ (233,000)	$ (140,474,000)				$ 112,515,000
Balance (in shares) at Dec. 31, 2018												23,187,219
Balance (in shares) at Dec. 31, 2018			23,187,219									23,187,219

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (38,924,000)	$ (36,957,000)	$ (37,177,000)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation	6,919,000	4,241,000	2,130,000
Depreciation and amortization	527,000	406,000	317,000
Net amortization of premium on available-for-sale securities	206,000	687,000	117,000
Change in deferred tax asset	(658,000)
(Loss) gain on disposal of property and equipment		(62,000)	34,000
Change in fair value associated with redeemable convertible preferred stock tranche liability			4,194,000
Change in fair value of redeemable convertible preferred stock warrant liability	0	0	525,000
Changes in operating assets and liabilities:
Research and development tax incentive receivable	(236,000)	1,070,000	(1,588,000)
Receivable from collaboration partner - related party	(2,771,000)	(1,816,000)
Prepaid expenses and other assets	1,117,000	(333,000)	(1,804,000)
Accounts payable	4,430,000	91,000	(115,000)
Payable to collaboration partner - related party	1,061,000
Accrued expenses and other payables	1,911,000	4,793,000	3,395,000
Deferred revenue - related party	(23,529,000)	31,752,000
Net cash provided by (used in) operating activities	(49,947,000)	3,872,000	(29,972,000)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of available-for-sale securities	(71,060,000)	(39,546,000)	(73,169,000)
Proceeds from maturities of available-for-sale securities	73,759,000	56,035,000	14,188,000
Purchases of property and equipment, net	(486,000)	(666,000)	(347,000)
Net cash provided by (used in) investing activities	2,213,000	15,823,000	(59,328,000)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of common stock and warrants in private placement, net of issuance costs	21,673,000	64,547,000	83,648,000
Proceeds from at-the-market offering, net of issuance costs	1,508,000
Proceeds from issuance of common stock upon exercise of stock options and purchases under employee stock purchase plan	934,000	1,007,000	151,000
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs			22,508,000
Net cash provided by financing activities	24,115,000	65,554,000	106,307,000
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(177,000)	146,000	22,000
Net (decrease) increase in cash, cash equivalents and restricted cash	(23,796,000)	85,395,000	17,029,000
Cash, cash equivalents and restricted cash, beginning of year	106,489,000	21,094,000	4,065,000
Cash, cash equivalents and restricted cash, end of period	82,693,000	106,489,000	21,094,000
SUPPLEMENTAL DISCLOSURES OF NON-CASH FINANCING AND INVESTING INFORMATION:
Fair value of common stock retired in exchange for issuance of common stock warrant	6,670,000
Purchases of property and equipment in accounts payable	24,000		21,000
Acquisition of new equipment upon trade-in for existing equipment		185,000
Deferred offering costs in accounts payable and accrued liabilities		66,000
Conversion of redeemable convertible preferred stock to common stock at closing of initial public offering			66,904,000
Settlement of fair value of redeemable convertible preferred stock liability			5,837,000
Reclassification of preferred stock warrant liability to equity			1,005,000
Accretion of redeemable convertible preferred stock	$ 0	$ 0	$ 558,000

Organization and Description of

Organization and Description of Business	12 Months Ended
	Dec. 31, 2018
Organization and Description of Business
Organization and Description of Business	Note 1. Organization and Description of Business Protagonist Therapeutics, Inc. (the “Company”) was incorporated in the state of Delaware on August 22, 2006 and is headquartered in Newark, California. The Company is a clinical-stage biopharmaceutical company with a proprietary technology platform that enables the discovery and development of novel constrained peptide-based drug candidates that address significant unmet medical needs. Protagonist Pty Limited (“Protagonist Australia”) is a wholly-owned subsidiary of the Company and is located in Brisbane, Queensland, Australia. Protagonist Australia was incorporated in Australia in September 2001. The Company became the parent of Protagonist Australia pursuant to a transaction in which all of the issued and outstanding capital stock of Protagonist Australia was exchanged for shares of the Company’s common stock and Series A preferred stock. The Company manages its operations as a single operating segment. Liquidity The Company has incurred net losses from operations since inception and has an accumulated deficit of $140.5 million as of December 31, 2018. The Company’s ultimate success depends on the outcome of its research and development activities. The Company expects to incur additional losses in the future and it anticipates the need to raise additional capital to fully implement its business plan. Through December 31, 2018, the Company has financed its operations through private placements of redeemable convertible preferred stock, offerings of common stock and payments received under a license and collaboration agreement. On August 10, 2016, the Company’s registration statement on Form S-1 (File Nos. 333-212476 and 333-213071) related to its initial public offering (“IPO”) became effective. The IPO closed on August 16, 2016, at which time the Company issued 7,500,000 shares of its common stock at a price of $12.00 per share. In addition, upon closing the IPO, all outstanding shares of the Company’s redeemable convertible preferred stock converted into 8,577,571 shares of common stock. There were no shares of redeemable convertible preferred stock outstanding at December 31, 2018 or 2017. In September 2016, the Company issued an additional 252,972 shares of its common stock at a price of $12.00 per share following the underwriters’ exercise of their option to purchase additional shares. The Company received an aggregate of $83.6 million in cash, net of underwriting discounts and commissions, after deducting offering costs paid by the Company. In September 2017, the Company filed a registration statement on Form S-3 with the Securities and Exchange Commission (File No. 333-220314), effective as of October 5, 2017, as amended, which permits the offering, issuance, and sale by the Company of up to a maximum aggregate offering price of $200.0 million of its common stock, including warrants. Up to a maximum of $50.0 million of the maximum aggregate offering price of $200.0 million may be issued and sold pursuant to an at-the-market (“ATM”) financing facility under a sales agreement with Cantor Fitzgerald & Co. (the “Sales Agreement”). The Company pays Cantor Fitzgerald & Co. up to 3% of gross proceeds for any common stock sold through the Sales Agreement. The Company sold 151,273 shares of its common stock pursuant to the Sales Agreement during the year ended December 31, 2018 for net proceeds of $1.5 million, after deducting commissions and offering costs. As of December 31, 2018, $48.3 million of common stock remained available for sale under the ATM financing facility. In October 2017, the Company completed an underwritten public offering of 3,530,000 shares of common stock at a public offering price of $17.00 per share. In November 2017, the Company issued an additional 529,500 shares of its common stock at a price of $17.00 per share following the underwriters’ exercise of their option to purchase additional shares. Net proceeds, after deducting underwriting commissions and offering costs paid by the Company, were $64.5 million. On August 6, 2018, the Company entered into a Securities Purchase Agreement with certain accredited investors (each, an “Investor” and, collectively, the “Investors”), pursuant to which the Company sold an aggregate of 2,750,000 shares of its common stock at a price of $8.00 per share, for aggregate net proceeds of $21.7 million, after deducting offering expenses payable by the Company. In a concurrent private placement, the Company issued the Investors warrants to purchase an aggregate of 2,750,000 shares of its common stock (each, a “Warrant” and, collectively, the “Warrants”). Each Warrant is exercisable from August 8, 2018 through August 8, 2023. Warrants to purchase 1,375,000 shares of the Company’s common stock have an exercise price of $10.00 per share and Warrants to purchase 1,375,000 shares of the Company’s common stock have an exercise price of $15.00 per share. The exercise price and number of shares of common stock issuable upon the exercise of the Warrants (the “Warrant Shares”) are subject to adjustment in the event of any stock dividends and splits, reverse stock split, recapitalization, reorganization or similar transaction, as described in the Warrants. Under certain circumstances, the Warrants may be exercisable on a “cashless” basis. In connection with the issuance and sale of the common stock and Warrants, the Company granted the Investors certain registration rights with respect to the Warrants and the Warrant Shares. The common stock and warrants are classified as equity in accordance with Accounting Standards Codification Topic 480 , Distinguishing Liabilities from Equity, and the net proceeds from the transaction were recorded as a credit to additional paid-in capital. As of December 31, 2018, none of the Warrants have been exercised. On December 21, 2018, the Company entered into an exchange agreement (the “Exchange Agreement”) with an Investor and its affiliates (the “Exchanging Stockholders”), pursuant to which the Company exchanged an aggregate of 1,000,000 shares of the Company’s common stock, par value $0.00001 per share, owned by the Exchanging Stockholders for pre-funded warrants (the “Exchange Warrants”) to purchase an aggregate of 1,000,000 shares of common stock (subject to adjustment in the event of any stock dividends and splits, reverse stock split, recapitalization, reorganization or similar transaction, as described in the Exchange Warrants), with an exercise price of $0.00001 per share. The Exchange Warrants will expire ten years from the date of issuance. The Exchange Warrants are exercisable at any time prior to expiration except that the Exchange Warrants cannot be exercised by the Exchanging Stockholders if, after giving effect thereto, the Exchanging Stockholders would beneficially own more than 9.99% of the Company’s common stock, subject to certain exceptions. In accordance with Accounting Standards Codification Topic 505, Equity , the Company recorded the retirement of the common stock exchanged as a reduction of common shares outstanding and a corresponding debit to additional paid-in-capital at the fair value of the Exchange Warrants on the issuance date. The Exchange Warrants are classified as equity in accordance with Accounting Standards Codification Topic 480 , Distinguishing Liabilities from Equity, and fair value of the Exchange Warrants was recorded as a credit to additional paid-in capital and is not subject to remeasurement. The Company determined that the fair value of the Exchange Warrants is substantially similar to the fair value of the retired shares on the issuance date due to the negligible exercise price for the Exchange Warrants. As of December 31, 2018, none of the Exchange Warrants have been exercised.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	Note 2. Summary of Significant Accounting Policies Basis of Presentation and Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiary, Protagonist Australia and have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). All intercompany balances and transactions have been eliminated in consolidation. The financial statements of Protagonist Australia use the Australian dollar as the functional currency since the majority of expense transactions occur in such currency. Gains and losses from foreign currency transactions were not material for all periods presented. The re-measurement from Australian dollar to U.S. dollars is outlined below: a. Equity accounts, except for the change in retained earnings during the year, have been translated using historical exchange rates. b. All other Australian dollar denominated assets and liabilities as of December 31, 2018 and 2017 have been translated using the year-end exchange rate. c. The consolidated statements of operations have been translated at the weighted average exchange rates in effect during each year. Foreign currency translation gains and losses are reported as a component of stockholders’ equity in accumulated other comprehensive loss on the consolidated balance sheets. Use of Estimates The preparation of the consolidated financial statements in conformity with GAAP requires management to make estimates, assumptions and judgments that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, accruals for research and development activities, fair value of redeemable convertible preferred stock tranche liability, fair value of redeemable convertible preferred stock warrant liability, fair value of common stock, stock-based compensation, income taxes and available-for-sale securities. Estimates related to revenue recognition include actual costs incurred versus total estimated budgeted cost of the Company’s deliverables, actual costs versus total estimated budget to determine percentage of completion, and application of constraint in the determination of transaction price under its license and collaboration agreement with Janssen Biotech Inc. (the “Janssen License and Collaboration Agreement”). Management bases these estimates on historical and anticipated results, trends, and various other assumptions that the Company believes are reasonable under the circumstances, including assumptions as to forecasted amounts and future events. Actual results may differ significantly from those estimates. Concentrations of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents and available-for-sale securities. Substantially all of the Company’s cash is held by three financial institutions that management believes are of high credit quality. Such deposits may, at times, exceed federally insured limits. The primary focus of the Company’s investment strategy is to preserve capital and to meet liquidity requirements. The Company’s cash equivalents and available-for-sale securities are managed by external managers within the guidelines of the Company’s investment policy. The Company’s investment policy addresses the level of credit exposure by limiting concentration in any one corporate issuer and establishing a minimum allowable credit rating. To manage its credit risk exposure, the Company maintains its portfolio of cash equivalents and available-for-sale securities in fixed income securities denominated and payable in U.S. dollars. Permissible investments of fixed income securities include obligations of the U.S. government and its agencies, money market instruments including commercial paper and negotiable certificates of deposit, and highly rated corporate debt obligations and money market funds. The Company has not experienced any material credit losses on its investments. Cash Equivalents Cash equivalents that are readily convertible to cash are stated at cost, which approximates fair value. The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. Restricted Cash Restricted cash consists of cash balances primarily held as security in connection with a letter of credit related to the Company’s facility lease entered into in March 2017 and the Company’s corporate credit card. Cash as Reported in Consolidated Statements of Cash Flows Cash as reported in the consolidated statements of cash flows includes the aggregate amounts of cash and cash equivalents and the restricted cash as presented on the consolidated balance sheets. Cash as reported in the consolidated statements of cash flows consists of (in thousands): December 31, 2018 2017 2016 Cash and cash equivalents $ 82,233 $ 106,029 $ 21,084 Restricted cash - current 10 10 10 Restricted cash - noncurrent 450 450 — Cash balance in consolidated statements of cash flows $ 82,693 $ 106,489 $ 21,094 Available-for-Sale Securities All marketable securities have been classified as “available-for-sale” and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its marketable securities at the time of purchase and reevaluates such designation as of each balance sheet date. Short-term marketable securities have maturities greater than three months but not longer than 365 days as of the balance sheet date. Long-term marketable securities have maturities of 365 days or longer as of the balance sheet date. Unrealized gains and losses are excluded from earnings and are reported as a component of comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in interest income. The cost of securities sold is based on the specific-identification method. Interest on marketable securities is included in interest income. Fair Value of Financial Instruments Fair value accounting is applied to all financial assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements on a recurring basis (at least annually). The carrying amount of the Company’s financial instruments, including cash equivalents, receivable from collaboration partner, accounts payable, payable to collaboration partner and accrued expenses and other payables approximate fair value due to their short-term maturities. See Note 4. to the Consolidated Financial Statements for additional information regarding the fair value of the Company’s other financial assets and liabilities. Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, ranging from three to five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful lives of the assets. Maintenance and repairs are charged to expense as incurred. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the consolidated balance sheet and any resulting gain or loss is reflected in operations in the period realized. Impairment of Long-Lived Assets The Company reviews long-lived assets, primarily comprised of property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amount to the future net cash flows which the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset. There have been no such impairments of long-lived assets for any of the periods presented. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those from stockholders. The Company’s foreign currency translation and unrealized gains and losses on available-for-sale securities represent the only components of other comprehensive loss that are excluded from reported net loss and that are presented in the consolidated statements of comprehensive loss. Income Taxes The Company uses the asset and liability method to account for income taxes in accordance with the authoritative guidance for income taxes. Under this method, deferred tax assets and liabilities are determined based on future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases, and tax loss and credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance is established when necessary to reduce deferred tax assets to the amount expected to be realized. The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained. Recognized income tax positions are measured at the largest amount that is greater than a 50% likelihood of being realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. The Company records interest and penalties related to unrecognized tax benefits in income tax expense. To date, there have been no interest or penalties recorded in relation to unrecognized tax benefits. Revenue Recognition Effective July 1, 2017, the Company early adopted Accounting Standards Codification Topic 606, Revenue from Contracts with Customers (“ASC 606”) using the full retrospective transition method. The Company did not have any effective contracts within the scope of this guidance prior to July 1, 2017. Accordingly, the Company did not elect to use any of the practical expedients permitted related to adoption, and the adoption of ASC 606 had no impact on the Company’s financial position, results of operations or liquidity. This standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements under Accounting Standards Codification Topic 808, and financial instruments. Under ASC 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. The Company entered into a license and collaboration agreement that became effective upon the resolution of regulatory requirements during the third quarter of 2017 which is within the scope of ASC 606, under which it has licensed certain rights to its PTG-200 product candidate to a third party, and may enter into other such arrangements in the future. The terms of the arrangement include payment to the Company of one or more of the following: non-refundable, up-front license fees, development and regulatory and commercial milestone payments, and royalties on net sales of licensed products. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgement to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring proportional performance for purposes of recognizing revenue from non-refundable, up-front fees. The Company evaluates the measure of proportional performance each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone payments: At the inception of each arrangement that includes development, regulatory or commercial milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price. ASC 606 suggests two alternatives to use when estimating the amount of variable consideration: the expected value method and the most likely amount method. Under the expected value method, an entity considers the sum of probability-weighted amounts in a range of possible consideration amounts. Under the most likely amount method, an entity considers the single most likely amount in a range of possible consideration amounts. Whichever method is used, it should be consistently applied throughout the life of the contract; however, it is not necessary for the Company to use the same approach for all contracts. The Company expects to use the most likely amount method for development and regulatory milestone payments. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis. The Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability or achievement of each such milestone and any related constraint and, if necessary, adjusts its estimates of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. To date, the Company has not recognized any milestone payments resulting from its collaboration arrangement. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from its collaboration arrangement. Up-front payments and fees are recorded as deferred revenue upon receipt or when due, and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. Research and Development Costs Research and development costs are expensed as incurred, unless there is an alternate future use in other research and development projects or otherwise. Research and development costs include salaries and benefits, stock-based compensation expense, laboratory supplies and facility-related overhead, outside contracted services including clinical trial costs, manufacturing and process development costs for both clinical and preclinical materials, research costs, development milestone payments under license and collaboration agreements, and other consulting services. The Company accrues for estimated costs of research and development activities conducted by third-party service providers, which include the conduct of pre-clinical studies and clinical trials, and contract manufacturing activities. The Company records the estimated costs of research and development activities based upon the estimated services provided but not yet invoiced and includes these costs in accrued expenses and other payables in the consolidated balance sheets and within research and development expense in the consolidated statements of operations. These costs are a significant component of the Company’s research and development expenses. The Company accrues for these costs based on factors such as estimates of the work completed and in accordance with agreements established with its third party service providers. The Company makes significant judgments and estimates in determining the accrued liabilities at each balance sheet date. As actual costs become known, the Company adjusts its accrued liabilities. The Company has not experienced any material differences between accrued liabilities and actual costs incurred. However, the status and timing of actual services performed, number of patients enrolled, and the rate of patient enrollment may vary from the Company’s estimates, resulting in adjustments to expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations. Research and Development Tax Incentive The Company is eligible under the AusIndustry research and development tax incentive program to obtain a cash amount from the Australian Taxation Office. The tax incentive is available to the Company on the basis of specific criteria with which the Company must comply. Specifically, the Company must have annual turnover of less than AUD 20.0 million and cannot be controlled by income tax exempt entities. The research and development tax incentive is recognized as a reduction to research and development expense when the right to receive has been attained and funds are considered to be collectible. The tax incentive is denominated in Australian dollars and, therefore, the related receivable is remeasured into U.S. dollars as of each reporting date. Under certain conditions, research and development activities conducted outside Australia (“overseas finding”) also qualify for the research and development tax incentive. Funds received for overseas finding are at a risk of clawback until substantiation that less than 50% of research and development expenditures for a project will be incurred overseas. A deferred tax incentive is recorded upon the cash receipt of the overseas finding funds and a reduction of research and development expenses is not recognized until the Company can substantiate that more than 50% of the total project expenditure will occur in Australia. When there is reasonable assurance that the grant will be received with remote risk of clawback, the relevant expenditure has been incurred, and the consideration can be reliably measured, the Company records the research and development incentive, including the overseas finding funds, as research and development tax incentive receivable and a reduction of research and development expenses to reflect that the funds are owed to the Company for the period the eligible costs are incurred. SBIR Grants The Company has been awarded Small Business Innovation Research (“SBIR”) grants from the National Institute of Diabetes and Digestive and Kidney Diseases (“NIDDK”) and the National Heart, Lungs and Blood Institute (“NHLBI”) of the National Institutes of Health (“NIH”) in support of its research activities. The Company records the eligible costs incurred under the SBIR grants as a reduction of research and development expenses. Redeemable Convertible Preferred Stock Tranche Liability The Company has determined that the Company’s obligation to issue additional shares of the Company’s redeemable convertible preferred stock represents a freestanding financial instrument, which was accounted for as a liability. The freestanding redeemable convertible preferred stock tranche liability was initially recorded at fair value, with fair value changes recognized in the consolidated statements of operations. During the year ended December 31, 2016, the fair value of the redeemable convertible preferred stock tranche liability was reclassified to redeemable convertible preferred stock with no further remeasurement required. Redeemable Convertible Preferred Stock Warrant Liability The Company has accounted for its freestanding warrants issued prior to 2016 to purchase shares of the Company’s redeemable convertible preferred stock as liabilities at fair value upon issuance. At the end of each reporting period, changes in estimated fair value during the period are recorded in the consolidated statements of operations. The Company continued to adjust the liability for these warrants for changes in fair value until the earlier of the exercise of the warrants or expiration on May 10, 2016, and no further remeasurement is required . Stock-based Compensation The Company measures its stock-based awards made to employees based on the estimated fair values of the awards as of the grant date. For stock option awards, the Company uses the Black-Scholes option-pricing model. For restricted stock unit awards, the estimated fair value is generally the fair market value of the underlying stock on the grant date. Stock-based compensation expense is recognized over the requisite service period and is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. The Company adopted Accounting Standards Update (“ASU”) No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting effective January 1, 2017 and has elected to recognize forfeitures of stock-based awards as they occur on a prospective basis. Prior to January 1, 2017, the Company’s stock-based compensation was reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differed from those estimates. Stock-based compensation expense for awards granted to non-employees as consideration for services received is measured on the date of performance at the fair value of the consideration received or the fair value of the equity instruments issued, whichever can be more reliably measured. Compensation expense for awards granted to non-employees is periodically remeasured as the underlying awards vest. Net Loss per Share Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding and Exchange Warrants outstanding during the period, without consideration of potentially dilutive securities. In accordance with Accounting Standards Codification Topic 260, Earnings Per Share , the Exchange Warrants are included in the computation of basic net loss per share because the exercise price is negligible and they are fully vested and exercisable at any time after the original issuance date. The net loss attributable to common stockholders is calculated by adjusting the net loss of the Company for the accretion on the redeemable convertible preferred stock, if applicable. Diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders for all periods presented since the effect of potentially dilutive securities is anti-dilutive given the net loss of the Company. Recently Issued Accounting Pronouncements Adopted During the Year Ended December 31, 2018 In August 2016, the FASB issued ASU No. 2016‑15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments , which clarifies the classification of certain cash receipts and cash payments in the statements of cash flow to eliminate the diversity in practice related to eight specific cash flow issues. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2017, with early adoption permitted. The Company adopted this guidance effective January 1, 2018. The adoption of this guidance had no effect on the Company’s consolidated financial statements and disclosures. In May 2017, the FASB issued ASU No. 2017‑09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting, which provides guidance on the types of changes to the terms and conditions of share-based payment awards to which an entity would be required to apply modification accounting. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions and classification of the awards are the same immediately before and after the modification. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2017, with early adoption permitted. The Company adopted this guidance effective January 1, 2018. The adoption of this guidance had no effect on the Company’s consolidated financial statements and disclosures. Recently Issued Accounting Pronouncements Not Yet Adopted as of December 31, 2018 In February 2016, the FASB issued ASU No. 2016‑02, Leases (Topic 842) . In July 2018, the FASB issued ASU No. 2018-10, Codification Improvements to Topic 842, Leases, which provides clarification to ASU 2016-02. These ASUs (collectively, the new lease standard) require an entity to recognize a lease liability and a right-of-use asset on the balance sheet for leases with lease terms of more than twelve months. Lessor accounting is largely unchanged, while lessees will no longer be provided with a source of off-balance sheet financing. This guidance is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Initial guidance required the adoption of the new lease standard using the modified retrospective transition method. In July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842) - Targeted Improvements , which allows entities to elect an optional transition method where entities may continue to apply the existing lease guidance during the comparative periods and apply the new lease requirements through a cumulative effect adjustment in the period of adoptions rather than in the earliest period presented. The Company will adopt the new standard on January 1, 2019 using the optional transition method. The Company established a cross-functional implementation team to review its lease portfolio and implement the new guidance. While the Company continues to review its current accounting policies and practices to identify potential differences that would result from applying the new guidance, the Company expects that its non-cancellable operating lease commitments with a term of more than twelve months will be subject to the new guidance and recognized as right-of-use assets and operating lease liabilities on the Company’s consolidated balance sheets upon adoption. The Company expects to elect transitional practical expedients such that the Company will not need to reassess whether contracts are leases and will retain lease classification and initial direct costs for leases existing prior to the adoption of the new lease standard. In June 2016, the FASB issued ASU No. 2016‑13, Financial Instruments - Credit Losses (Topic 326) , which is intended to provide financial statement users with more useful information about expected credit losses on financial assets held by a reporting entity at each reporting date. The new standard replaces the existing incurred loss impairment methodology with a methodology that requires consideration of a broader range of reasonable and supportable forward-looking information to estimate all expected credit losses. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2019 and early adoption is permitted for fiscal years and interim periods within those years beginning after December 15, 2018. The Company is currently evaluating the impact of this new guidance on its consolidated financial statements and disclosures. In June 2018, the FASB issued ASU No. 2018-07, Compensation – Stock Compensation (Topic 718), Improvements to Nonemployee Share-Based Payment Accounting , which is intended to simplify the accounting for nonemployee share-based payment transactions by expanding the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. The guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2018. The Company is currently evaluating the impact of this new guidance on its consolidated financial statements and disclosures. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820) – Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement , which modifies the disclosure requirements on fair value measurements and is intended to improve the effectiveness of disclosures, including the consideration of costs and benefits. The guidance is effective for the fiscal years and interim periods within those years beginning after January 1, 2020. Early adoption is permitted, and an entity is permitted to early adopt any removed or modified disclosures and delay adoption of additional disclosures until their effective date. The Company does not expect this new guidance to impact its consolidated financial statements and is currently evaluating the impact on its disclosures. In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606 , which is intended to clarify the circumstances under which certain transactions in collaborative arrangements should be accounted for under the revenue recognition standard. Certain transactions between collaboration arrangement participants should be accounted for as revenue under ASC Topic 606 when the collaborative arrangement participant is a customer in the context of a unit of account. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2020. Early adoption is permitted. The Company is in the process of assessing the impact of this new guidance on its consolidated financial statements and disclosures.

Janssen License and Collaborati

Janssen License and Collaboration Agreement	12 Months Ended
	Dec. 31, 2018
Janssen License and Collaboration Agreement
Collaboration and License Agreement
Collaboration Agreement	Note 3. Janssen License and Collaboration Agreement Agreement Terms On May 26, 2017, the Company and Janssen Biotech, Inc., (“Janssen”), one of the Janssen Pharmaceutical Companies of Johnson & Johnson, entered into an exclusive license and collaboration agreement for the development, manufacture and commercialization of PTG-200 worldwide for the treatment of Crohn’s disease (“CD”) and ulcerative colitis (“UC”). Janssen is a related party to the Company as Johnson & Johnson Innovation - JJDC, Inc., a significant stockholder of the Company, and Janssen are both subsidiaries of Johnson & Johnson. PTG-200 is the Company’s oral Interleukin 23 receptor (“IL-23R”) antagonist drug candidate currently in development. The Janssen License and Collaboration Agreement became effective on July 13, 2017. Upon the effectiveness of the agreement, the Company received a non-refundable, upfront cash payment of $50.0 million from Janssen. Under the Janssen License and Collaboration Agreement, the Company granted to Janssen an exclusive worldwide license to develop, manufacture and commercialize PTG-200 and related IL-23R compounds for all indications, including CD and UC. The Company is responsible, at its own expense, for the conduct of the Phase 1 clinical trial for PTG-200, and Janssen will be responsible for the conduct of a potential Phase 2 clinical trial for PTG-200 in CD, including filing the Investigational New Drug application (“IND”). All such clinical trials will be conducted in accordance with a mutually agreed upon clinical development plan and budget. Development costs for the Phase 2 clinical trial will be shared between the parties on an 80%/20% basis, with Janssen assuming the larger share. Should Janssen elect to retain its license following completion of the Phase 2 clinical trial, it will be responsible, at its own expense, for the manufacture, continued development of, seeking regulatory approval for, and commercialization of PTG-200 worldwide. The parties’ development activities under the Janssen License and Collaboration Agreement through the Phase 2 clinical trial will be overseen by a joint governance structure which will have equal representation by both parties unless both parties mutually agree to disband such structure or the Company has provided written notice to Janssen of its intention to disband and no longer participate in such structure. The Company is eligible to receive a $25.0 million payment upon Janssen’s filing of the IND. Following the conclusion of the planned Phase 2a portion of the Phase 2 clinical trial, if Janssen elects to maintain its license rights and continue the development of PTG-200 in the Phase 2b portion of such clinical trial (the “First Opt-in Election”), the Company would be eligible to receive a $125.0 million payment. Following the conclusion of the planned Phase 2b portion of the Phase 2 clinical trial, if Janssen elects again to maintain its license rights (the “Second Opt-in Election”), the Company would be eligible to receive a $200.0 million payment. In addition to the opt-in fees, the Company would be eligible to receive potential development, regulatory and sales milestone payments of up to an aggregate of $590.0 million, and tiered royalties paid as a percentage of Janssen’s worldwide net sales at rates ranging from ten to the mid-teens, with certain customary reductions under certain circumstances. If Janssen does not make either the First Opt-in Election or the Second Opt-in Election, the Janssen License and Collaboration Agreement will terminate. If Janssen does not make the Second Opt-in Election, or if at any time after the Second Opt-in Election, Janssen terminates the Janssen License and Collaboration Agreement, the Company would be obligated to pay Janssen a low single-digit royalty on worldwide net sales of PTG-200. The Company would also have an option to provide up to 30% of the required U.S. details for PTG-200 to prescribers, using its own sales force personnel, upon commercial launch in the United States. If such right is exercised by the Company, the Company’s detailing costs would be reimbursed by Janssen at a mutually agreed cost per primary detailing equivalent. The Janssen License and Collaboration Agreement contains customary representations, warranties and covenants by the Company and Janssen and includes an obligation by the Company not to develop or commercialize other compounds which also target IL-23R outside of the Janssen License and Collaboration Agreement until completion of the Phase 2b portion of the Phase 2 clinical trial. Each of the Company and Janssen is required to indemnify the other party against all losses and expenses related to breaches of its representations, warranties and covenants under the Janssen License and Collaboration Agreement. The Janssen License and Collaboration Agreement remains in effect until the royalty obligations cease following patent and regulatory expiry, unless terminated earlier. Either the Company or Janssen may terminate the Janssen License and Collaboration Agreement for uncured material breach. Janssen retains the right to terminate the Janssen License and Collaboration Agreement for convenience and without cause on written notice of a certain period to the Company. Upon a termination of the Janssen License and Collaboration Agreement, all rights revert back to the Company, and in certain circumstances, if such termination occurs during ongoing clinical trials, Janssen would, if requested, provide certain financial and operational support to the Company for the completion of such trials. Revenue Recognition The Company identified the following material promises under the Janssen License and Collaboration Agreement: (1) the license related to PTG-200, (2) the performance of development services, including regulatory support, during the Phase 1 clinical trial for PTG-200 through the filing of the IND by Janssen, and (3) compound supply services for Phase 1 and Phase 2 activities. The Company considered that the license has standalone functionality and is capable of being distinct. However, the Company determined that the license is not distinct from the development and compound supply services within the context of the agreement because the development and compound supply services significantly increase the utility of the intellectual property. Specifically, the Company’s development, manufacturing and commercialization license can only provide benefit to Janssen in combination with the Company’s development services in the Phase 1 study. The intellectual property (“IP”) related to the peptide technology platform, which is proprietary to the Company, is the foundation for the development activities related to the treatment for CD. The compound supply services are a necessary and integral part of the development services as they could only be conducted utilizing the outcomes of these services. Given the development services under the Janssen License and Collaboration Agreement are expected to involve significant further development of the initial IP, the Company has concluded that the development and compound supply services are not distinct from the license, and thus the license, development services and compound supply services are combined into a single performance obligation. The nature of the combined performance obligation is to provide development and compound supply services to Janssen under the arrangement. The Company also evaluated whether the fees related to the First Opt-in Election and Second Opt-in Election are options with material rights. These two options include additional sublicense rights and patent rights transferred to Janssen upon exercising both of these options. The Company concluded that Janssen’s opt in rights are not options with material rights because the $50.0 million upfront payment to the Company was not negotiated to provide incremental discount for the future opt in payments at the end of Phase 2a and Phase 2b. The option to “opt in” provides Janssen with a license for IP that has been improved from the license initially granted for a term in the case of the opt in after completion of Phase 2a and then a perpetual license in the case of opt in after completion of Phase 2b. Therefore, the First Opt-in Election and Second Opt-in Election options are not considered to be material rights. The option fees will be recognized as revenue when, and if, Janssen exercises its options because the Company has no further performance obligations at that point. For revenue recognition purposes, the Company determined that the duration of the contract begins on the effective date of July 13, 2017 and ends upon completion of Phase 2a activities. The contract duration is defined as the period in which parties to the contract have present enforceable rights and obligations. The Company analyzed the impact of Janssen terminating the agreement prior to the completion of Phase 2a and determined that there were significant economic penalties to Janssen for doing so. The Company believes that if Janssen terminates the agreement upon completion of Phase 2a, the forfeiture of the remaining license rights and payment of 50% of the remaining Phase 2 costs is not a significant economic penalty when compared to paying $125.0 million as an opt in license fee to continue the use of the License. Thus, the duration of the contract is limited to the end of Phase 2a. The Company determined that the transaction price of the Janssen License and Collaboration Agreement was $60.7 million as of December 31, 2018, an increase of $6.8 million from the transaction price of $53.9 million as of December 31, 2017. In order to determine the transaction price, the Company evaluated all the payments to be received during the duration of the contract. The Company determined that the $50.0 million upfront payment, the $25.0 million payment payable upon filing of the IND, which is fully constrained as of December 31, 2018 and December 31, 2017, and $10.7 million of estimated variable consideration for cost-sharing payments from Janssen for agreed upon services related to Phase 2 activities as of December 31, 2018 constituted consideration to be included in the transaction price, which is to be allocated to the combined performance obligation. The increase in the transaction price from December 31, 2017 was due to an increase in variable consideration related to compound supply services and was recognized as a cumulative catch-up adjustment. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. As part of the evaluation for determining that the $25.0 million payment upon filing of the IND is fully constrained as of December 31, 2018, the Company considered several factors, including the stage of development of PTG-200 and that achievement of the milestone is outside of the Company’s control, and concluded that the filing of the IND is not probable at December 31, 2018. If and when the filing of the IND becomes probable, the $25.0 million payment will be constrained by contra revenue amounts for payments that the Company expects to make for 20% of the cost of Phase 2 activities to be performed by Janssen. The additional potential development, regulatory and sales milestone payments of up to an aggregate of $590.0 million after the completion of Phase 2a activities that the Company is eligible to receive are outside the contract term and as such have been excluded from the transaction price. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur as they were determined to relate predominantly to the license granted to Janssen and therefore have also been excluded from the transaction price. At the end of each reporting period, the Company will update its assessment of whether an estimate of variable consideration is constrained and update the estimated transaction price accordingly. The Company uses the most likely amount method to determine variable consideration. Variable consideration for cost-sharing payments related to agreed upon services for Phase 2 activities that the Company performs within the duration of the contract are included in the transaction price at an amount equal to 80% of the estimated budgeted costs for these activities, including primarily internal full-time equivalent effort and third party contract costs. The Company is responsible for 20% of the development costs for the Phase 2 clinical trial. Accordingly, a significant portion of this work is expected to be performed by Janssen. Because the Phase 2 clinical trial activity is related to the license, it is not capable of being distinct. This is because both the Company and Janssen cannot benefit from these activities absent the Phase 1 activities. As the Phase 2 activities for which the Company will share 20% of the costs are not capable of being distinct and are not separately identifiable within the context of the contract, they are not a distinct service that Janssen transfers to the Company. Therefore, the consideration payable to Janssen is accounted for as a reduction in the transaction price. The Company and Janssen make quarterly cost-sharing payments to one another in amounts necessary to ensure that each party bears its contractual share of the overall shared costs incurred. The Company accounts for cost-sharing payments from Janssen as increases in license and collaboration revenue in its consolidated statements of operations, while cost-sharing payments to Janssen are accounted for as reductions in license and collaboration revenue, or contra-revenue. Costs incurred by the Company related to agreed upon services for Phase 2 activities under the Janssen License and Collaboration Agreement are recorded as research and development expenses in its consolidated statements of operations. In summary, the license, the development activities for Phase 1 activities and the agreed upon services for Phase 2 activities are combined as one performance obligation that will be performed over the duration of the contract, which is from the effective date of the Janssen License and Collaboration Agreement through to the completion of Phase 2a activities. Since the Company has determined that the combined performance obligation is satisfied over time, ASC 606 requires the Company to select a single revenue recognition method for the performance obligation that faithfully depicts the Company’s performance in transferring control of the services. The guidance allows entities to choose between two methods to measure progress toward complete satisfaction of a performance obligation: 1. Output methods - recognize revenue on the basis of direct measurements of the value to the customer of the goods or services transferred to date relative to the remaining goods or services promised under the contract (e.g. surveys of performance completed to date, appraisals of results achieved, milestones reached, time elapsed, and units of produced or units delivered); and 2. Input methods - recognize revenue on the basis of the entity’s efforts or inputs to the satisfaction of a performance obligation (e.g., resources consumed, labor hours expended, costs incurred, or time elapsed) relative to the total expected inputs to the satisfaction of that performance obligation. The Company concluded that it will utilize a cost-based input method to measure proportional performance and to calculate the corresponding amount of revenue to recognize. The Company believes this is the best measure of progress because other measures do not reflect how the Company transfers its performance obligation to Janssen. In applying the cost-based input methods of revenue recognition, the Company uses actual costs incurred relative to budgeted costs to fulfill the combined performance obligation. These costs consist primarily of internal full-time equivalent effort and third-party contract costs. Revenue will be recognized based on actual costs incurred as a percentage of total budgeted costs as the Company completes its performance obligations. A cost-based input method of revenue recognition requires management to make estimates of costs to complete the Company’s performance obligations. In making such estimates, significant judgment is required to evaluate assumptions related to cost estimates. The cumulative effect of revisions to estimated costs to complete the Company’s performance obligations will be recorded in the period in which changes are identified and amounts can be reasonably estimated. A significant change in these assumptions and estimates could have a material impact on the timing and amount of revenue recognized in future periods. For the year ended December 31, 2018, the Company recognized $30.9 million of license and collaboration revenue. This amount included $30.8 million of the transaction price for the Janssen License and Collaboration Agreement recognized based on proportional performance, and $0.1 million, net, for other services related to Phase 2 activities performed by the Company on behalf of Janssen that are not included in the performance obligations identified under the Janssen License and Collaboration Agreement. For the year ended December 31, 2017, the Company recognized $20.1 million of license and collaboration revenue. This amount included $19.0 million of the transaction price for the Janssen License and Collaboration Agreement recognized based on proportional performance, and $1.1 million for other services related to Phase 2 activities performed by the Company on behalf of Janssen that are not included in the performance obligations identified under the Janssen License and Collaboration Agreement. The following table presents changes in the Company’s contract assets and liabilities for the years ended December 31, 2018 and 2017 (in thousands): Balance at Balance at Beginning of End of Year Ended December 31, 2018 Period Additions Deductions Period Contract assets: Receivable from collaboration partner - related party $ 1,816 $ 6,665 $ (6,439) $ 2,042 Contract asset - related party $ — $ 2,545 $ — $ 2,545 Contract liabilities: Deferred revenue - related party $ 31,752 $ 7,296 $ (30,825) $ 8,223 Payable to collaboration partner - related party $ — $ 1,574 $ (513) $ 1,061 Balance at Balance at Beginning of End of Year Ended December 31, 2017 Period Additions Deductions Period Contract assets: Receivable from collaboration partner - related party $ — $ 51,816 $ (50,000) $ 1,816 Contract liabilities: Deferred revenue - related party $ — $ 50,708 $ (18,956) $ 31,752 Deferred revenue related to the Janssen License and Collaboration Agreement was $8.2 million as of December 31, 2018, and was comprised of the $50.0 million upfront payment and $8.0 million of cost sharing payments from Janssen for agreed upon services for Phase 2a activities, less $49.8 million of license and collaboration revenue recognized from the effective date of the contract. Deferred revenue will be recognized as the combined performance obligation is satisfied. The Company recorded a $2.0 million receivable from collaboration partner as of December 31, 2018 for cost sharing amounts payable from and billed to Janssen and a $2.5 million contract asset for unbilled cost sharing amounts payable from Janssen. The Company also recorded a $1.1 million payable to collaboration partner as of December 31, 2018 for cost sharing amounts payable to Janssen. Deferred revenue related to the Janssen License and Collaboration Agreement of $31.8 million as of December 31, 2017 was comprised of the $50.0 million upfront payment and $0.7 million of cost sharing payments from Janssen for agreed upon services for Phase 2 activities, less $19.0 million of license and collaboration revenue recognized from the effective date of the contract. The Company also recorded a $1.8 million receivable from collaboration partner as of December 31, 2017 for cost sharing amounts payable from Janssen. During the year ended December 31, 2018, the Company recognized $23.5 million in revenue from the deferred revenue contract liability balance at the beginning of the year. During the year ended December 31, 2017, the Company did not recognize any revenue from amounts included in the contract asset and the contract liability balances at the beginning of the year or from performance obligations satisfied in previous periods. None of the costs to obtain or fulfill the contract were capitalized.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
Fair Value Measurements
Fair Value Measurements	Note 4. Fair Value Measurements Financial assets and liabilities are recorded at fair value. The accounting guidance for fair value provides a framework for measuring fair value, clarifies the definition of fair value and expands disclosures regarding fair value measurements. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. The accounting guidance establishes a three-tiered hierarchy, which prioritizes the inputs used in the valuation methodologies in measuring fair value as follows: Level 1 —Inputs are unadjusted quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2— Inputs (other than quoted market prices included in Level 1) are either directly or indirectly observable for the asset or liability through correlation with market data at the measurement date and for the duration of the instrument’s anticipated life. Level 3 —Inputs reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model. In determining fair value, the Company utilizes quoted market prices, broker or dealer quotations, or valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible and considers counterparty credit risk in its assessment of fair value. The following table presents the fair value of the Company’s financial assets determined using the inputs defined above (in thousands). December 31, 2018 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 25,390 $ — $ — $ 25,390 Corporate bonds — 8,989 — 8,989 Commercial paper — 59,730 — 59,730 Government bonds — 33,394 — 33,394 Total financial assets $ 25,390 $ 102,113 $ — $ 127,503 December 31, 2017 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 48,704 $ — $ — $ 48,704 Corporate bonds — 6,247 — 6,247 Commercial paper — 58,524 — 58,524 Government bonds — 40,303 — 40,303 Total financial assets $ 48,704 $ 105,074 $ — $ 153,778 The Company’s corporate bonds, commercial paper and government bonds are classified as Level 2 as they were valued based upon quoted market prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant inputs are observable in the market or can be corroborated by observable market data for substantially the full term of the assets.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2018
Balance Sheet Components
Balance Sheet Components	Note 5. Balance Sheet Components Cash Equivalents and Available-for-sale Securities Cash equivalents and available-for-sale securities consisted of the following (in thousands): December 31, 2018 Amortized Gross Unrealized Cost Gains Losses Fair Value Money market funds $ 25,390 $ — $ — $ 25,390 Corporate bonds 8,997 — (8) 8,989 Commercial paper 59,730 — — 59,730 Government bonds 33,423 — (29) 33,394 Total cash equivalents and available-for-sale securities $ 127,540 $ — $ (37) $ 127,503 Classified as: Cash equivalents $ 80,883 Available-for-sale securities - current 46,620 Total cash equivalents and available-for-sale securities $ 127,503 December 31, 2017 Amortized Gross Unrealized Cost Gains Losses Fair Value Money market funds $ 48,704 $ — $ — $ 48,704 Corporate bonds 6,254 — (7) 6,247 Commercial paper 58,524 — — 58,524 Government bonds 40,428 — (125) 40,303 Total cash equivalents and available-for-sale securities $ 153,910 $ — $ (132) $ 153,778 Classified as: Cash equivalents $ 104,348 Available-for-sale securities - current 37,972 Available-for-sale securities - noncurrent 11,458 Total cash equivalents and available-for-sale securities $ 153,778 All available-for-sale securities - current held as of December 31, 2018 and 2017 had contractual maturities of less than one year. All available securities - noncurrent held as of December 31, 2017 had contractual maturities of at least one year but less than two years. There were no material realized gains or realized losses from sales of available-for-sale securities for the periods presented. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2018 2017 Prepaid clinical and research related expenses $ 686 $ 2,324 Prepaid insurance 438 378 Other prepaid expenses 1,005 936 Other receivable 495 135 Prepaid expenses and other current assets $ 2,624 $ 3,773 Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): December 31, 2018 2017 Laboratory equipment $ 2,533 $ 2,177 Furniture and computer equipment 338 270 Leasehold improvements 67 26 Total property and equipment 2,938 2,473 Less: accumulated depreciation and amortization (2,077) (1,594) Property and equipment, net $ 861 $ 879 Depreciation expense for the years ended December 31, 2018, 2017, and 2016 was $527,000, $406,000 and $317,000, respectively. As of December 31, 2018, 2017 and 2016, $200, $1,200 and $8,000, respectively, of property and equipment, net, was located in Australia. The remainder of the Company’s property and equipment is located in the United States. Accrued Expenses and Other Payables Accrued expenses and other payables consisted of the following (in thousands): December 31, 2018 2017 Accrued clinical and research related expenses $ 7,781 $ 6,437 Accrued employee related expenses 2,726 2,718 Accrued milestone payment to former collaboration partner 500 — Accrued professional service fees 61 267 Other 95 124 Total accrued expenses and other payables $ 11,163 $ 9,546

Research Collaboration and Lice

Research Collaboration and License Agreement	12 Months Ended
	Dec. 31, 2018
Research Collaboration and License Agreement
Collaboration and License Agreement
Collaboration Agreement	Note 6. Research Collaboration and License Agreement In October 2013, the Company’s former collaboration partner decided to abandon a collaboration program with the Company and, pursuant to the terms of the agreement between the Company and the former collaboration partner, the Company elected to assume responsibility for the development and commercialization of the product. Upon the former collaboration partner’s abandonment, it assigned to the Company certain intellectual property arising from the collaboration and also granted the Company an exclusive license to certain background intellectual property rights of the former collaboration partner that relate to the products acquired by the Company. The nomination of PTG‑300 as a development candidate triggered a $250,000 payment from the Company to the former collaboration partner. The initiation of a Phase 1 clinical trial for PTG‑300 triggered an additional $250,000 payment from the Company to the former collaboration partner. The initiation of a Phase 2 clinical trial for PTG-300 triggered an additional $500,000 payment obligation to the former collaboration partner. The Company has the right, but not the obligation, to further develop and commercialize the product and, if the Company successfully develops and commercializes PTG‑300 without a partner, the Company will pay to the former collaboration partner up to an additional aggregate of $128.0 million for the achievement of certain development, regulatory and sales milestone events. In addition, the Company will pay to the former collaboration partner a low single digit royalty on worldwide net sales of the product until the later of ten years from the first commercial sale of the product or the expiration of the last patent covering the product. For each of the years ended December 31, 2018, 2017 and 2016, the Company recorded research and development expense of $500,000, $250,000 and $250,000 under this agreement.

Government Programs

Government Programs	12 Months Ended
	Dec. 31, 2018
Government Programs
Government Programs	Note 7. Government Programs Research and Development Tax Incentive The Company recognized AUD 2.1 million ($1.6 million), AUD 1.7 million ($1.3 million) and AUD 5.3 million ($4.0 million) as a reduction of research and development expenses for the years ended December 31, 2018, 2017 and 2016, respectively, in connection with the research and development tax incentive from Australia. As of December 31, 2018 and 2017, the research and development tax incentive receivable was AUD 2.0 million ($1.4 million) and AUD 1.7 million ($1.3 million), respectively. In March 2016, the Company received AUD 237,000 ($182,000) for overseas findings and recorded the funds as deferred tax incentive in accrued expenses and other payables on the consolidated balance sheet due to the possibility that the funds could have to be repaid. In December 2016, the Company’s research and development project under the AusIndustry research and development tax incentive program was complete and the Company substantiated that more than 50% of the total project expenditures occurred in Australia. Therefore, the overseas finding related incentive amounts were no longer deemed to be at risk of clawback and the Company recognized such amounts in December 2016 as a reduction of research and development expenses for the overseas findings received in 2016. Based on the nature of the amounts received under the Janssen License and Collaboration Agreement, the Company has concluded that these amounts should be classified as statutory income for Australian taxation purposes. Accordingly, they should not be included in the calculation of annual turnover for the purposes of determining eligibility for the refundable research and development tax offset. SBIR Grant In September 2015, the Company was awarded a Phase 1 SBIR Grant from the NIDDK of the NIH in support of research on orally stable peptide antagonists of IL‑23R as potential treatments for IBD. The total grant award was $224,000 and was for the period from September 2015 to August 2016. In July 2016, the Company was awarded a Phase 1 SBIR Grant from the NHLBI of the NIH in support of preclinical research aimed at discovering and optimizing lead molecules as novel peptide mimetics of the hepcidin hormone. The total grant award was $219,000 and was for the period from August 2016 to January 2017. In May 2017, the Company was awarded a Phase 2 SBIR Grant from the NIDDK of the NIH in support of research aimed at developing biomarkers that define IL-23R target engagement by oral peptide antagonists and the effects of that engagement of downstream signaling. The total grant award was $1.3 million and is for the period from May 2017 to April 2019. In September 2018, the Company was awarded a Phase 2 SBIR Grant from the NHLBI of the NIH in support of research aimed at developing the Company’s novel hepcidin mimetic PTG-300 for the potential treatment of chronic anemia and iron overload in rare blood disorders, including beta-thalassemia. The total grant award was $1.5 million and is for the period from September 2018 to August 2020. The Company recognizes a reduction to research and development expenses when expenses related to the grants have been incurred and the grant funds become contractually due from NIH. The Company recorded $663,000, $182,000 and $169,000 as a reduction of research and development expenses for the years ended December 31, 2018, 2017 and 2016, respectively. The Company recorded a receivable for $309,000 and $58,000 as of December 31, 2018 and 2017, respectively, to reflect the eligible costs incurred under the grants that are contractually due to the Company, and such amounts are included in prepaid expenses and other current assets on the consolidated balance sheets.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies
Commitments and Contingencies	Note 8. Commitments and Contingencies Lease Arrangements In March 2017, the Company entered into a lease agreement for office and laboratory space located in Newark, California. The Company relocated its operations to the new facility in May 2017. The Company provided the landlord with a $450,000 letter of credit collateralized by restricted cash as security deposit for the lease, which expires in May 2024. The Company is entitled to tenant improvement allowances of approximately $469,000. The Company records tenant improvement allowances as deferred rent when funds are received and associated capital expenditures as leasehold improvements that will be amortized over the shorter of their useful life or the remaining term of the lease. The following table summarizes the Company’s future minimum lease payments related to the Newark facility as of December 31, 2018 (in thousands): Year Ending December 31: Amount 2019 $ 1,941 2020 2,000 2021 2,059 2022 2,121 2023 2,185 Thereafter 922 Total $ 11,228 The Company’s rent expense was $1.9 million, $1.4 million and $408,000 for the years ended December 31, 2018, 2017 and 2016, respectively. Rent expense is recognized on a straight-line basis over the term of the lease and accordingly, the Company records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Indemnifications In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has also entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by California corporate law. The Company currently has directors’ and officers’ insurance. To date, the Company has not incurred material costs to defend lawsuits or settle claims related to the indemnification agreements. The Company believes that the fair value of these indemnification agreements is minimal and has not accrued any amounts for the obligations.

Preferred Stock Warrants

Preferred Stock Warrants	12 Months Ended
	Dec. 31, 2018
Preferred Stock Warrants
Preferred Stock Warrants	Note 9. Preferred Stock Warrants In connection with its Series B redeemable convertible preferred stock financing, the Company issued warrants to purchase 4,000,000 shares of Series B redeemable convertible preferred stock at an exercise price of $0.01 per share. These warrants became exercisable only when certain milestones were met on programs begun as a result of collaborations entered into in 2011 and 2012. In March 2016, the Company made a public announcement related to a preclinical candidate which triggered the achievement of a milestone and warrants to purchase 2,000,000 shares of Series B redeemable convertible preferred stock became exercisable as of that date. In April 2016, 1,999,998 shares of Series B redeemable convertible preferred stock were issued for cash proceeds of $20,000 in connection with the exercise of warrants. Immediately prior to the exercise of the warrants, the fair value of the warrants was remeasured at $1.0 million, determined using a hybrid method of the Option Pricing Model with a 67% weighted value per share and the probability-weighted expected return method (“PWERM”) with a 33% weighted value per share.. Upon the exercise of warrants, the redeemable convertible preferred stock warrant liability of $1.0 million was reclassified to redeemable convertible preferred stock. In May 2016, the remaining warrants for the purchase of 2,000,000 shares of Series B redeemable convertible preferred stock expired unexercised. The Company recorded a charge of $525,000 for the year ended December 31, 2016, representing the increase in the fair value of the redeemable convertible preferred stock warrant liability in the consolidated statements of operations. There were no such charges incurred for the years ended December 31, 2018 and 2017.

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2018
Redeemable Convertible Preferred Stock.
Redeemable Convertible Preferred Stock	Note 10. Redeemable Convertible Preferred Stock In April 2016, 1,999,998 shares of Series B redeemable convertible preferred stock were issued in connection with the exercise of warrants for cash proceeds of $20,000. Following the closing of the IPO, all outstanding shares of the redeemable convertible preferred stock converted into 8,577,571 shares of common stock and the related carrying value was reclassified to common stock and additional paid-in capital. There were no shares of redeemable convertible preferred stock outstanding as of December 31, 2018 or 2017. The table below provides information on the Company’s redeemable convertible preferred stock as of December 31, 2015 (in thousands, except shares and original issue price): Shares Aggregate Original Issued and Carrying Liquidation Issue Price Authorized Outstanding Value Preference Series A $ 1.00 6,037,500 6,037,500 $ 1,751 $ 6,038 Series B $ 0.50 40,000,000 36,000,000 18,825 18,000 Series C $ 0.4979 80,337,411 35,147,617 16,420 17,500 Total redeemable convertible preferred stock 126,374,911 77,185,117 $ 36,996 $ 41,538 As only the passage of time was required for Series A, B and C to become redeemable, the Company was accreting the carrying value of Series A, B and C to their redemption value over the period from the respective date of issuance to July 2022, (the earliest redemption date) up to the IPO date. In the event of a change of control of the Company, proceeds would be distributed in accordance with the liquidation preferences set forth in the Company’s Amended and Restated Certificate of Incorporation unless the holders of redeemable convertible preferred stock had converted their redeemable convertible preferred stock into shares of common stock. Therefore, redeemable convertible preferred stock was classified outside of stockholders’ equity (deficit) on the consolidated balance sheets, as Series A, B and C redeemable convertible preferred stock can be redeemed and as events triggering the liquidation preferences were not solely within the Company’s control. The Company recorded $558,000 for the accretion of the redeemable convertible preferred stock during the year ended December 31, 2016. The accretion was recorded as an offset to the additional paid-in capital until such balance was depleted and any remaining accretion was recorded to accumulated deficit. There were no such charges incurred for the years ended December 31, 2018 and 2017.

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock Tranche Liability	12 Months Ended
	Dec. 31, 2018
Redeemable Convertible Preferred Stock Tranche Liability
Redeemable Convertible Preferred Stock Tranche Liability	Note 11. Redeemable Convertible Preferred Stock Tranche Liability In July 2015, the Company entered into the Series C Preferred Stock Purchase Agreement (“the Series C Agreement”) for the issuance of up to 80,337,411 shares of Series C redeemable convertible preferred stock at a price of $0.4979 per share, in multiple closings. The initial closing occurred on July 10, 2015, whereby 35,147,617 shares of Series C redeemable convertible preferred stock were issued for gross proceeds of $17.5 million. According to the initial terms of the Series C Agreement, the Company could issue 45,189,794 additional shares under the same terms as the initial closing, in a subsequent closing (“Series C Second Tranche”) contingent upon the achievement of certain development milestones. On the date of the initial closing, the Company recorded a Series C redeemable convertible preferred stock liability of $1.0 million, as the fair value of the obligation/right to complete the Series C Second Tranche. At December 31, 2015, the fair value of the Series C redeemable convertible preferred stock tranche liability was determined to be $1.6 million using a one-step binomial lattice model in combination with the Option Pricing Model. In March 2016, the Company completed the closing of the Series C Second Tranche and issued 45,189,794 shares of Series C redeemable convertible preferred stock for net cash proceeds of $22.5 million. At this time the Series C redeemable convertible preferred stock liability was remeasured at $5.8 million, determined using a hybrid method of the Option Pricing Model with a 67% weighted value per share and the PWERM with a 33% weighted value per share. Upon the closing of the Series C Second Tranche, the Series C redeemable convertible preferred stock tranche liability was terminated and the balance of the liability of $5.8 million was reclassified to redeemable convertible preferred stock. For the year ended December 31, 2016, the Company recorded a charge of $4.2 million for the change in the fair value of the redeemable convertible preferred stock liability in the consolidated statements of operations. There were no such charges incurred for the years ended December 31, 2018 and 2017.

Equity Plans

Equity Plans	12 Months Ended
	Dec. 31, 2018
Equity Plans
Equity Plans	Note 12. Equity Plans Equity Incentive Plan In May 2007, the Company established the 2007 Stock Option and Incentive Plan (“2007 Plan”) which provided for the granting of stock options to employees and consultants of the Company. Options granted under the 2007 Plan were either incentive stock options (“ISOs”) or nonqualified stock options (“NSOs”). ISOs were granted only to Company employees (including officers and directors who are also employees). NSOs were granted to Company employees and consultants. Options under the 2007 Plan have a term of ten years and generally vest over a four-year period with one-year cliff vesting. In July 2016, the Company’s board of directors and stockholders approved the 2016 Equity Incentive Plan (“2016 Plan”) to replace the 2007 Plan, which became effective upon the IPO. Under the 2016 Plan, 1,200,000 shares of the Company’s common stock were initially reserved for the issuance of stock options, restricted stock units and other awards to employees, directors and consultants. Pursuant to the “evergreen” provision contained in the 2016 Plan, the number of shares reserved for issuance under the 2016 Plan automatically increases on January 1 of each year, starting on January 1, 2017 and continuing through (and including) January 1, 2026, by 4% of the total number of shares of the Company’s capital stock outstanding on December 31 of the preceding fiscal year, or a lesser number of shares determined by the Company’s board of directors. Upon adoption of the 2016 Plan, no additional stock awards were issued under the 2007 Plan. Options granted under the 2007 Plan that were outstanding on the date the 2016 Plan became effective remain subject to the terms of the 2007 Plan. The number of options available for grant under the 2007 Plan was ceased and the number was added to the common stock reserved for issuance under the 2016 Plan. As of December 31, 2018, approximately 177,473 shares of common stock were available for issuance under the 2016 Plan. The 2016 Plan is administered by the board of directors or a committee appointed by the board of directors, which determines the types of awards to be granted, including the number of shares subject to the awards, the exercise price and the vesting schedule. Options granted under the 2016 Plan expire no later than ten years from the date of grant. The exercise price of each option may not be less than 100% of the fair market value of the common stock at the date of grant. Options may be granted to stockholders possessing more than 10% of the total combined voting power of all classes of stocks of the Company at an exercise price at least 110% of the fair value of the common stock at the date of grant and the options are not exercisable after the expiration of 10 years from the date of grant. Employee stock options generally vest 25% upon one year of continued service to the Company, with the remainder in monthly increments over three additional years. Non-employee director initial stock options generally vest monthly over a period of approximately three years, and non-employee director annual refresher stock options generally vest over a period of approximately one year. Inducement Plan In May 2018, the Company’s board of directors approved the 2018 Inducement Plan, a non-stockholder approved stock plan, under which it reserved and authorized up to 750,000 shares of the Company’s common stock in order to award options and restricted stock unit awards to persons that were not previously employees or directors of the Company, or following a bona fide period of non-employment, as an inducement material to such persons entering into employment with the Company, within the meaning of Rule 5635(c)(4) of the NASDAQ Listing Rules. The 2018 Inducement Plan is administered by the board of directors or the Compensation Committee of the board, which determines the types of awards to be granted, including the number of shares subject to the awards, the exercise price and the vesting schedule. Awards granted under the 2018 Inducement Plan expire no later than ten years from the date of grant. As of December 31, 2018, approximately 645,000 shares were available for issuance under the 2018 Inducement Plan. Stock Options Activity under the Company’s equity incentive plans is set forth below: Weighted- Weighted- Average Average Exercise Remaining Aggregate Options Price Per Contractual Intrinsic Outstanding Share Life (years) Value (1) (in millions) Balances at December 31, 2015 833,178 $ 1.33 8.56 Options granted 1,679,979 14.24 Options exercised (119,328) 1.28 Balances at December 31, 2016 2,393,829 10.39 8.79 Options granted 493,500 13.20 Options exercised (257,858) 1.84 Options forfeited (191,320) 15.00 Balances at December 31, 2017 2,438,151 11.51 8.26 Options granted 1,067,400 13.17 Options exercised (143,358) 2.78 Options forfeited (183,752) 15.46 Balances at December 31, 2018 3,178,441 $ 12.23 7.52 $ 3.5 Options exercisable – December 31, 2018 1,475,083 $ 11.07 6.98 $ 2.6 Options vested and expected to vest – December 31, 2018 3,178,441 $ 12.23 7.52 $ 3.5 ____________________ (1) The aggregate intrinsic values were calculated as the difference between the exercise price of the options and the closing price of the Company’s common stock on December 31, 2018. The calculation excludes options with an exercise price higher than the closing price of the Company’s common stock on December 31, 2018. The aggregate intrinsic value of options exercised was $1.3 million, $3.5 million and $169,000 for the years ended December 31, 2018, 2017 and 2016, respectively. During the years ended December 31, 2018, 2017 and 2016, the estimated weighted-average grant-date fair value of common stock underlying options granted was $8.12, $7.74 and $8.20 per share, respectively. Employee Stock Options Valuation The fair value of employee and non-employee director stock option awards was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2018 2017 2016 Expected term (in years) 5.49 - 6.08 5.50 - 6.08 4.16 - 5.95 Expected volatility 62.0% - 66.5% 61.6% - 65.4% 62.5% - 64.8% Risk-free interest rate 2.42% - 3.03% 1.88 - 2.24% 1.27% - 1.79% Dividend yield — — — In determining the fair value of the options granted, the Company uses the Black-Scholes option-pricing model and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment to determine. Expected Term —The Company’s expected term represents the period that the Company’s options granted are expected to be outstanding and is determined using the simplified method (based on the mid-point between the vesting date and the end of the contractual term). The Company has very limited historical information to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior for its stock option grants. Expected Volatility —Since the Company does not have a long trading history for its common stock, the expected volatility is estimated based on the average volatility for comparable publicly traded biopharmaceutical companies over a period equal to the expected term of the stock option grants. The comparable companies were chosen based on their similar size, stage in the life cycle or area of specialty. Risk-Free Interest Rate —The risk-free interest rate is based on the U.S. Treasury zero coupon issues in effect at the time of grant for periods corresponding with the expected term of option. Expected Dividend —The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero. Prior to the completion of the Company’s IPO, the fair value of the Company’s shares of common stock underlying its stock options had historically been determined by the Company’s board of directors. Because there had been no public market for the Company’s common stock prior to August 2016, the Company’s board of directors had determined fair value of the common stock at the time of grant of the option by considering a number of objective and subjective factors including important developments in the Company’s operations, valuations performed by an independent third party, sales of redeemable convertible preferred stock, actual operating results and financial performance, the conditions in the biotechnology industry and the economy in general, the stock price performance and volatility of comparable public companies, and the lack of liquidity of the Company’s common stock, among other factors. For stock options granted after the completion of the IPO, the Company’s board of directors determined the fair value of each share of underlying common stock based on the closing price of the Company’s common stock as reported on the date of grant. Stock Options Granted to Non-employees Stock-based compensation related to stock options granted to non-employees is recognized as the stock options are earned. The fair value of the stock options granted to non-employees was calculated at each reporting date using the Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2018 2017 2016 Expected term (in years) 7.48 - 7.67 6.97 - 7.40 6.59 - 9.97 Expected volatility 64.4% - 67.8% 61.7% - 65.4% 62.5% - 62.8% Risk-free interest rate 2.61% - 3.02% 2.17% - 2.33% 1.29% - 1.79% Dividend yield — — — During the years ended December 31, 2018 and 2016, the Company granted 42,950 and 59,647 shares, respectively, to non-employee consultants. No options were granted to non-employee consultants during the year ended December 31, 2017. The Company recorded stock-based compensation expense for non-employee awards during the years ended December 31, 2018, 2017 and 2016 of $36,000, $263,000 and $505,000, respectively. Restricted Stock Units During the year ended December 31, 2018, the Company began issuing restricted stock units under the 2016 Plan. A restricted stock unit is an agreement to issue shares of the Company’s common stock at the time of vesting. Restricted stock units annual refresher awards vest in four equal installments on approximately the first, second, third and fourth anniversaries of the grant date. Restricted stock unit incentive awards granted during 2018 vest in three equal installments at six months intervals over a period of 18 months. Restricted stock unit activity under the Company’s equity incentive plans is set forth below: Un Weighted- Average Number of Grant Date Shares Fair Value Unvested at December 31, 2017 — — Restricted stock units granted $ Restricted stock units forfeited (7,575) Unvested at December 31, 2018 $ Stock-based compensation expense associated with restricted stock units is based on the fair value of the Company’s common stock on the grant date, which equals the closing market price of the Company’s common stock on the grant date. For restricted stock units, the Company recognizes compensation expense over the vesting period of the awards that are ultimately expected to vest. Employee Stock Purchase Plan In July 2016, the Company’s board of directors and stockholders approved the 2016 Employee Stock Purchase Plan (“2016 ESPP”), which became effective upon the IPO. The 2016 ESPP is intended to qualify as an employee stock purchase plan under Section 423 of the Internal Revenue Code of 1986, as amended, and is administered by the Company’s board of directors and the Compensation Committee of the board of directors. Under the 2016 ESPP, 150,000 shares of the Company’s common stock were initially reserved for employee purchases of the Company’s common stock. Pursuant to the “evergreen” provision contained in the 2016 ESPP, the number of shares reserved for issuance automatically increases on January 1 of each year, starting on January 1, 2017 and continuing through (and including) January 1, 2026 by the lesser of (i) 1% of the total number of shares of common stock outstanding on December 31 of the preceding fiscal year (ii) 300,000 shares, or (iii) such other number of shares determined by the board of directors. The 2016 ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their eligible compensation. At the end of each offering period, eligible employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s common stock at the beginning of the offering period or at the end of each applicable purchase period. As of December 31, 2018, 102,950 shares have been issued, and 425,155 shares are available for issuance. The fair value of the rights granted under the 2016 ESPP was calculated using the Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2018 2017 2016 Expected term (in years) 0.50 0.50 0.60 Expected volatility 49.0% - 63.4% 52.4% 52.5% Risk-free interest rate 1.89% - 2.32% 0.89% - 1.16% 0.45% Dividend yield — — — Stock-Based Compensation Total stock-based compensation expense was as follows (in thousands): Year Ended December 31, 2018 2017 2016 Research and development $ 3,424 $ 2,008 $ 1,080 General and administrative 3,495 2,233 1,050 Total stock-based compensation expense $ 6,919 $ 4,241 $ 2,130 As of December 31, 2018, total unrecognized stock-based compensation expense was $15.6 million, which the Company expects to recognize over a period of approximately 2.1 years.

401(k) Plan

401(k) Plan	12 Months Ended
	Dec. 31, 2018
401(k) Plan
401(k) Plan	Note 13. 401(k) Plan In March 2012, the Company adopted a retirement and savings plan under Section of 401(k) of Internal Revenue Code (the “401(k) Plan”) covering all employees. The 401(k) Plan allows employees to make pre- and post-tax contributions up to the maximum allowable amount set by the Internal Revenue Service. The Company does not make matching contributions to the 401(k) Plan on behalf of participants.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Taxes
Income Taxes	Note 14. Income Taxes The Company recorded an income tax benefit of $0.8 million for the year ended December 31, 2018 from the recognition of deferred tax assets in Protagonist Australia, the Company’s Australian subsidiary. The Company believes these deferred tax assets will be realized in the future due to expected profitability for this subsidiary. No provision for income taxes was recorded for the years ended December 31, 2017 and 2016. The Company had incurred net operating losses and did not reflect any benefit of operating loss carryforwards in the consolidated financial statements for those years. The Company continues to maintain a valuation allowance against its U.S. deferred tax assets due to the uncertainty surrounding the realization of such assets. The following table presents domestic and foreign components of net loss before income taxes for the periods presented (in thousands): Year Ended December 31, 2018 2017 2016 Domestic $ (37,511) $ (34,556) $ (34,977) Foreign (2,212) (2,401) (2,200) Net loss before income taxes $ (39,723) $ (36,957) $ (37,177) The effective tax rate of the provision for income taxes differs from the federal statutory rate as follows: Year Ended December 31, 2018 2017 2016 Federal statutory income tax rate 21.0 % % 34.0 % State taxes, net of federal benefit 7.0 0.5 6.5 Warrant revaluation — — (4.3) Research credit (1.3) 2.6 1.8 Foreign tax rate difference 0.4 (1.2) (1.6) Change in tax law — (31.2) — Change in valuation allowance (22.2) (5.2) (36.0) Other (2.9) 0.5 (0.4) Provision for income taxes 2.0 % — % — % On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (“Tax Act”) was signed into law making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S. international taxation from a worldwide tax system to a territorial system, and a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings as of December 31, 2017. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118 (“SAB 118”), which provides guidance for the tax effect of the Tax Act. SAB 118 provides a measurement period that should not extend beyond one year from the Tax Act’s enactment date for companies to complete the accounting under Accounting Standards Codification Topic 740, Income Taxes (“ASC 740”). In accordance with SAB 118, the Company must reflect the income tax effects of those aspects of the Tax Act for which the accounting under ASC 740 is complete. The impact of the Tax Act was finalized during the year ended December 31, 2018 and no change was made from the previously reported provisional transition tax amount of zero. The components of the deferred tax assets are as follows (in thousands): December 31, 2018 2017 Deferred tax assets: Net operating loss carryforwards $ 27,704 $ 21,682 Depreciation and amortization 269 339 Accruals/other 2,455 1,322 Research and development credits 4,270 2,544 Total deferred tax assets 34,698 25,887 Valuation allowance (34,040) (25,887) Net deferred tax assets $ 658 $ — Realization of the deferred tax assets is dependent upon future taxable income, if any, the amount and timing of which are uncertain. The Company has established a valuation allowance to offset U.S. deferred tax assets as of December 31, 2018 and 2017 due to the uncertainty of realizing future tax benefits from its net operating loss carryforwards and other deferred tax assets. The valuation allowance increased by approximately $8.2 million, $1.9 million and $13.4 million during the years ended December 31, 2018, 2017 and 2016, respectively. The change in valuation is due to an increase in net operating loss carryforwards incurred during the year, partially offset by a release of the $1.5 million valuation allowance related to Protagonist Australia. The increases in the valuation allowance for the years ended December 2018 and 2016 primarily related to the increase in net operating loss carryforwards incurred during the respective taxable years. The increase in valuation allowance for the year ended December 31, 2017 was primarily related to the increase in net operating loss carryforwards generated during the year, partially offset by a decrease in the deferred tax assets related to the reduction of the U.S. corporate income tax rate as provided in the Tax Act. At December 31, 2018, the Company had net operating loss carryforwards for federal income tax purposes of approximately $109.1 million, $78.7 million of which are available to offset future taxable income, if any, through 2037 and $30.4 million of which do not expire. At December 31, 2018, the Company had net operating loss carryforwards for state income tax purposes of approximately $97.1 million which are available to offset future taxable income, if any, through 2038. At December 31, 2018, the Company also had accumulated Australian tax losses of AUD 13.9 million ($9.8 million) available for carry forward against future earnings which, under relevant tax laws, do not expire but may be limited under certain circumstances. As of December 31, 2018, the Company had $4.0 million of federal and $2.2 million of state research and development tax credit carryforwards available to reduce future income taxes. The federal research and development tax credits will begin to expire in 2035, if not utilized. The state research and development tax credits have no expiration date. Federal and state laws impose substantial restrictions on the utilization of net operating loss and tax credit carryforwards in the event of an ownership change for tax purposes, as defined in Section 382 of the Internal Revenue Code. As a result of such ownership changes, the Company’s ability to realize the potential future benefit of tax losses and tax credits that existed at the time of the ownership change may be significantly reduced. Based on a review of the Company’s equity transactions since inception, the Company believes a portion of its net operating loss carryforwards and credit carryforwards may be limited due to certain of its equity financing transactions. It is the Company’s policy to include penalties and interest expense related to income taxes as a component of other expense, as necessary. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands): Year Ended December 31, 2018 2017 2016 Balance at beginning of year $ 5,414 $ 2,131 $ 805 Increase based on tax positions related to prior years 108 — 707 Increase based on tax positions related to current year 3,944 3,283 619 Balance at end of year $ 9,466 $ 5,414 $ 2,131 At December 31, 2018, the Company had unrecognized tax benefits of $9.5 million, of which $2.7 million would affect the effective tax rate if recognized and $6.8 million is subject to a valuation allowance and would not affect the effective tax rate if recognized. The Company files income tax returns in the United States federal jurisdiction, the State of California and Australia. The Company is not currently under examination by income tax authorities in federal, state or other jurisdictions. The Company’s tax returns for 2014 through 2018 remain open for examination due to the carryover of unused net operating losses and tax credits.

Net Loss per Share Attributable

Net Loss per Share Attributable to Common Stockholders	12 Months Ended
	Dec. 31, 2018
Net Loss per Share Attributable to Common Stockholders
Net Loss per Share Attributable to Common Stockholders	Note 15. Net Loss per Share Attributable to Common Stockholders As the Company had net losses for the years ended December 31, 2018, 2017 and 2016, all potential common shares were determined to be anti-dilutive. The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Year Ended December 31, 2018 2017 2016 Numerator: Net loss $ (38,924) $ (36,957) $ (37,177) Accretion of redeemable convertible preferred stock — — (558) Net loss $ (38,924) $ (36,957) $ (37,735) Denominator: Weighted-average shares used to compute net loss per common share, basic and diluted 22,364,515 17,694,505 6,501,796 Net loss per shares, basic and diluted $ (1.74) $ (2.09) $ (5.80) The following outstanding shares of potentially dilutive securities have been excluded from diluted net loss per share calculations for the years ended December 31, 2018, 2017 and 2016 because their inclusion would be anti-dilutive: Year Ended December 31, 2018 2017 2016 Options to purchase common stock 3,178,441 2,438,151 2,393,829 Common stock warrants 2,750,000 — — Restricted stock units 418,450 — — ESPP shares 52,134 24,938 — Total 6,399,025 2,463,089 2,393,829

Supplementary Financial Data (u

Supplementary Financial Data (unaudited)	12 Months Ended
	Dec. 31, 2018
Supplementary Financial Data (unaudited)
Supplementary Financial Data (unaudited)	Note 16. Supplementary Financial Data (unaudited) The following table presents the selected quarterly financial data for the years ended December 31, 2018 and 2017 (in thousands, except per share amounts): Consolidated Statements of Operations Quarter Ended March 31 June 30 September 30 December 31 2018 License and collaboration revenue - related party $ 10,781 $ 11,674 $ 6,117 $ 2,353 Loss from operations $ (8,229) $ (9,239) $ (9,389) $ (15,412) Net loss $ (7,661) $ (8,663) $ (8,735) $ (13,865) Net loss per share of common stock, basic and diluted (1) $ (0.36) $ (0.41) $ (0.38) $ (0.57) 2017 License and collaboration revenue - related party $ — $ — $ 8,781 $ 11,282 Loss from operations $ (14,273) $ (15,131) $ (4,980) $ (3,513) Net loss $ (14,101) $ (14,979) $ (4,825) $ (3,052) Net loss per share of common stock, basic and diluted (1) $ (0.84) $ (0.89) $ (0.29) $ (0.15) _________________ (1) Net loss per share amounts for the 2018 and 2017 quarters and full years have been computed separately. Accordingly, quarterly amounts may not add to the annual amounts because of differences in the weighted average shares outstanding during each period .

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Summary of Significant Accounting Policies
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiary, Protagonist Australia and have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). All intercompany balances and transactions have been eliminated in consolidation. The financial statements of Protagonist Australia use the Australian dollar as the functional currency since the majority of expense transactions occur in such currency. Gains and losses from foreign currency transactions were not material for all periods presented. The re-measurement from Australian dollar to U.S. dollars is outlined below: a. Equity accounts, except for the change in retained earnings during the year, have been translated using historical exchange rates. b. All other Australian dollar denominated assets and liabilities as of December 31, 2018 and 2017 have been translated using the year-end exchange rate. c. The consolidated statements of operations have been translated at the weighted average exchange rates in effect during each year. Foreign currency translation gains and losses are reported as a component of stockholders’ equity in accumulated other comprehensive loss on the consolidated balance sheets.
Use of Estimates	Use of Estimates The preparation of the consolidated financial statements in conformity with GAAP requires management to make estimates, assumptions and judgments that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, accruals for research and development activities, fair value of redeemable convertible preferred stock tranche liability, fair value of redeemable convertible preferred stock warrant liability, fair value of common stock, stock-based compensation, income taxes and available-for-sale securities. Estimates related to revenue recognition include actual costs incurred versus total estimated budgeted cost of the Company’s deliverables, actual costs versus total estimated budget to determine percentage of completion, and application of constraint in the determination of transaction price under its license and collaboration agreement with Janssen Biotech Inc. (the “Janssen License and Collaboration Agreement”). Management bases these estimates on historical and anticipated results, trends, and various other assumptions that the Company believes are reasonable under the circumstances, including assumptions as to forecasted amounts and future events. Actual results may differ significantly from those estimates.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents and available-for-sale securities. Substantially all of the Company’s cash is held by three financial institutions that management believes are of high credit quality. Such deposits may, at times, exceed federally insured limits. The primary focus of the Company’s investment strategy is to preserve capital and to meet liquidity requirements. The Company’s cash equivalents and available-for-sale securities are managed by external managers within the guidelines of the Company’s investment policy. The Company’s investment policy addresses the level of credit exposure by limiting concentration in any one corporate issuer and establishing a minimum allowable credit rating. To manage its credit risk exposure, the Company maintains its portfolio of cash equivalents and available-for-sale securities in fixed income securities denominated and payable in U.S. dollars. Permissible investments of fixed income securities include obligations of the U.S. government and its agencies, money market instruments including commercial paper and negotiable certificates of deposit, and highly rated corporate debt obligations and money market funds. The Company has not experienced any material credit losses on its investments.
Cash Equivalents	Cash Equivalents Cash equivalents that are readily convertible to cash are stated at cost, which approximates fair value. The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents.
Restricted Cash	Restricted Cash Restricted cash consists of cash balances primarily held as security in connection with a letter of credit related to the Company’s facility lease entered into in March 2017 and the Company’s corporate credit card.
Cash as Reported in Consolidated Statements of Cash Flows	Cash as Reported in Consolidated Statements of Cash Flows Cash as reported in the consolidated statements of cash flows includes the aggregate amounts of cash and cash equivalents and the restricted cash as presented on the consolidated balance sheets. Cash as reported in the consolidated statements of cash flows consists of (in thousands): December 31, 2018 2017 2016 Cash and cash equivalents $ 82,233 $ 106,029 $ 21,084 Restricted cash - current 10 10 10 Restricted cash - noncurrent 450 450 — Cash balance in consolidated statements of cash flows $ 82,693 $ 106,489 $ 21,094
Available-for-Sale Securities	Available-for-Sale Securities All marketable securities have been classified as “available-for-sale” and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its marketable securities at the time of purchase and reevaluates such designation as of each balance sheet date. Short-term marketable securities have maturities greater than three months but not longer than 365 days as of the balance sheet date. Long-term marketable securities have maturities of 365 days or longer as of the balance sheet date. Unrealized gains and losses are excluded from earnings and are reported as a component of comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in interest income. The cost of securities sold is based on the specific-identification method. Interest on marketable securities is included in interest income.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Fair value accounting is applied to all financial assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements on a recurring basis (at least annually). The carrying amount of the Company’s financial instruments, including cash equivalents, receivable from collaboration partner, accounts payable, payable to collaboration partner and accrued expenses and other payables approximate fair value due to their short-term maturities. See Note 4. to the Consolidated Financial Statements for additional information regarding the fair value of the Company’s other financial assets and liabilities.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, ranging from three to five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful lives of the assets. Maintenance and repairs are charged to expense as incurred. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the consolidated balance sheet and any resulting gain or loss is reflected in operations in the period realized.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, primarily comprised of property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amount to the future net cash flows which the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset. There have been no such impairments of long-lived assets for any of the periods presented.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those from stockholders. The Company’s foreign currency translation and unrealized gains and losses on available-for-sale securities represent the only components of other comprehensive loss that are excluded from reported net loss and that are presented in the consolidated statements of comprehensive loss.
Income Taxes	Income Taxes The Company uses the asset and liability method to account for income taxes in accordance with the authoritative guidance for income taxes. Under this method, deferred tax assets and liabilities are determined based on future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases, and tax loss and credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance is established when necessary to reduce deferred tax assets to the amount expected to be realized. The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained. Recognized income tax positions are measured at the largest amount that is greater than a 50% likelihood of being realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. The Company records interest and penalties related to unrecognized tax benefits in income tax expense. To date, there have been no interest or penalties recorded in relation to unrecognized tax benefits.
Revenue Recognition	Revenue Recognition Effective July 1, 2017, the Company early adopted Accounting Standards Codification Topic 606, Revenue from Contracts with Customers (“ASC 606”) using the full retrospective transition method. The Company did not have any effective contracts within the scope of this guidance prior to July 1, 2017. Accordingly, the Company did not elect to use any of the practical expedients permitted related to adoption, and the adoption of ASC 606 had no impact on the Company’s financial position, results of operations or liquidity. This standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements under Accounting Standards Codification Topic 808, and financial instruments. Under ASC 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. The Company entered into a license and collaboration agreement that became effective upon the resolution of regulatory requirements during the third quarter of 2017 which is within the scope of ASC 606, under which it has licensed certain rights to its PTG-200 product candidate to a third party, and may enter into other such arrangements in the future. The terms of the arrangement include payment to the Company of one or more of the following: non-refundable, up-front license fees, development and regulatory and commercial milestone payments, and royalties on net sales of licensed products. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgement to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring proportional performance for purposes of recognizing revenue from non-refundable, up-front fees. The Company evaluates the measure of proportional performance each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone payments: At the inception of each arrangement that includes development, regulatory or commercial milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price. ASC 606 suggests two alternatives to use when estimating the amount of variable consideration: the expected value method and the most likely amount method. Under the expected value method, an entity considers the sum of probability-weighted amounts in a range of possible consideration amounts. Under the most likely amount method, an entity considers the single most likely amount in a range of possible consideration amounts. Whichever method is used, it should be consistently applied throughout the life of the contract; however, it is not necessary for the Company to use the same approach for all contracts. The Company expects to use the most likely amount method for development and regulatory milestone payments. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis. The Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability or achievement of each such milestone and any related constraint and, if necessary, adjusts its estimates of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. To date, the Company has not recognized any milestone payments resulting from its collaboration arrangement. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from its collaboration arrangement. Up-front payments and fees are recorded as deferred revenue upon receipt or when due, and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred, unless there is an alternate future use in other research and development projects or otherwise. Research and development costs include salaries and benefits, stock-based compensation expense, laboratory supplies and facility-related overhead, outside contracted services including clinical trial costs, manufacturing and process development costs for both clinical and preclinical materials, research costs, development milestone payments under license and collaboration agreements, and other consulting services. The Company accrues for estimated costs of research and development activities conducted by third-party service providers, which include the conduct of pre-clinical studies and clinical trials, and contract manufacturing activities. The Company records the estimated costs of research and development activities based upon the estimated services provided but not yet invoiced and includes these costs in accrued expenses and other payables in the consolidated balance sheets and within research and development expense in the consolidated statements of operations. These costs are a significant component of the Company’s research and development expenses. The Company accrues for these costs based on factors such as estimates of the work completed and in accordance with agreements established with its third party service providers. The Company makes significant judgments and estimates in determining the accrued liabilities at each balance sheet date. As actual costs become known, the Company adjusts its accrued liabilities. The Company has not experienced any material differences between accrued liabilities and actual costs incurred. However, the status and timing of actual services performed, number of patients enrolled, and the rate of patient enrollment may vary from the Company’s estimates, resulting in adjustments to expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations.
Research and Development Tax Incentive	Research and Development Tax Incentive The Company is eligible under the AusIndustry research and development tax incentive program to obtain a cash amount from the Australian Taxation Office. The tax incentive is available to the Company on the basis of specific criteria with which the Company must comply. Specifically, the Company must have annual turnover of less than AUD 20.0 million and cannot be controlled by income tax exempt entities. The research and development tax incentive is recognized as a reduction to research and development expense when the right to receive has been attained and funds are considered to be collectible. The tax incentive is denominated in Australian dollars and, therefore, the related receivable is remeasured into U.S. dollars as of each reporting date. Under certain conditions, research and development activities conducted outside Australia (“overseas finding”) also qualify for the research and development tax incentive. Funds received for overseas finding are at a risk of clawback until substantiation that less than 50% of research and development expenditures for a project will be incurred overseas. A deferred tax incentive is recorded upon the cash receipt of the overseas finding funds and a reduction of research and development expenses is not recognized until the Company can substantiate that more than 50% of the total project expenditure will occur in Australia. When there is reasonable assurance that the grant will be received with remote risk of clawback, the relevant expenditure has been incurred, and the consideration can be reliably measured, the Company records the research and development incentive, including the overseas finding funds, as research and development tax incentive receivable and a reduction of research and development expenses to reflect that the funds are owed to the Company for the period the eligible costs are incurred.
SBIR Grants	SBIR Grants The Company has been awarded Small Business Innovation Research (“SBIR”) grants from the National Institute of Diabetes and Digestive and Kidney Diseases (“NIDDK”) and the National Heart, Lungs and Blood Institute (“NHLBI”) of the National Institutes of Health (“NIH”) in support of its research activities. The Company records the eligible costs incurred under the SBIR grants as a reduction of research and development expenses.
Redeemable Convertible Preferred Stock Tranche Liability	Redeemable Convertible Preferred Stock Tranche Liability The Company has determined that the Company’s obligation to issue additional shares of the Company’s redeemable convertible preferred stock represents a freestanding financial instrument, which was accounted for as a liability. The freestanding redeemable convertible preferred stock tranche liability was initially recorded at fair value, with fair value changes recognized in the consolidated statements of operations. During the year ended December 31, 2016, the fair value of the redeemable convertible preferred stock tranche liability was reclassified to redeemable convertible preferred stock with no further remeasurement required.
Redeemable Convertible Preferred Stock Warrant Liability	Redeemable Convertible Preferred Stock Warrant Liability The Company has accounted for its freestanding warrants issued prior to 2016 to purchase shares of the Company’s redeemable convertible preferred stock as liabilities at fair value upon issuance. At the end of each reporting period, changes in estimated fair value during the period are recorded in the consolidated statements of operations. The Company continued to adjust the liability for these warrants for changes in fair value until the earlier of the exercise of the warrants or expiration on May 10, 2016, and no further remeasurement is required .
Stock-based Compensation	Stock-based Compensation The Company measures its stock-based awards made to employees based on the estimated fair values of the awards as of the grant date. For stock option awards, the Company uses the Black-Scholes option-pricing model. For restricted stock unit awards, the estimated fair value is generally the fair market value of the underlying stock on the grant date. Stock-based compensation expense is recognized over the requisite service period and is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. The Company adopted Accounting Standards Update (“ASU”) No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting effective January 1, 2017 and has elected to recognize forfeitures of stock-based awards as they occur on a prospective basis. Prior to January 1, 2017, the Company’s stock-based compensation was reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differed from those estimates. Stock-based compensation expense for awards granted to non-employees as consideration for services received is measured on the date of performance at the fair value of the consideration received or the fair value of the equity instruments issued, whichever can be more reliably measured. Compensation expense for awards granted to non-employees is periodically remeasured as the underlying awards vest.
Net Loss per Share Attributable to Common Stockholders	Net Loss per Share Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding and Exchange Warrants outstanding during the period, without consideration of potentially dilutive securities. In accordance with Accounting Standards Codification Topic 260, Earnings Per Share , the Exchange Warrants are included in the computation of basic net loss per share because the exercise price is negligible and they are fully vested and exercisable at any time after the original issuance date. The net loss attributable to common stockholders is calculated by adjusting the net loss of the Company for the accretion on the redeemable convertible preferred stock, if applicable. Diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders for all periods presented since the effect of potentially dilutive securities is anti-dilutive given the net loss of the Company.
Recently Adopted Accounting Pronouncements and Recently Issued Accounting Pronouncements Not Adopted	Recently Issued Accounting Pronouncements Adopted During the Year Ended December 31, 2018 In August 2016, the FASB issued ASU No. 2016‑15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments , which clarifies the classification of certain cash receipts and cash payments in the statements of cash flow to eliminate the diversity in practice related to eight specific cash flow issues. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2017, with early adoption permitted. The Company adopted this guidance effective January 1, 2018. The adoption of this guidance had no effect on the Company’s consolidated financial statements and disclosures. In May 2017, the FASB issued ASU No. 2017‑09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting, which provides guidance on the types of changes to the terms and conditions of share-based payment awards to which an entity would be required to apply modification accounting. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions and classification of the awards are the same immediately before and after the modification. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2017, with early adoption permitted. The Company adopted this guidance effective January 1, 2018. The adoption of this guidance had no effect on the Company’s consolidated financial statements and disclosures. Recently Issued Accounting Pronouncements Not Yet Adopted as of December 31, 2018 In February 2016, the FASB issued ASU No. 2016‑02, Leases (Topic 842) . In July 2018, the FASB issued ASU No. 2018-10, Codification Improvements to Topic 842, Leases, which provides clarification to ASU 2016-02. These ASUs (collectively, the new lease standard) require an entity to recognize a lease liability and a right-of-use asset on the balance sheet for leases with lease terms of more than twelve months. Lessor accounting is largely unchanged, while lessees will no longer be provided with a source of off-balance sheet financing. This guidance is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Initial guidance required the adoption of the new lease standard using the modified retrospective transition method. In July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842) - Targeted Improvements , which allows entities to elect an optional transition method where entities may continue to apply the existing lease guidance during the comparative periods and apply the new lease requirements through a cumulative effect adjustment in the period of adoptions rather than in the earliest period presented. The Company will adopt the new standard on January 1, 2019 using the optional transition method. The Company established a cross-functional implementation team to review its lease portfolio and implement the new guidance. While the Company continues to review its current accounting policies and practices to identify potential differences that would result from applying the new guidance, the Company expects that its non-cancellable operating lease commitments with a term of more than twelve months will be subject to the new guidance and recognized as right-of-use assets and operating lease liabilities on the Company’s consolidated balance sheets upon adoption. The Company expects to elect transitional practical expedients such that the Company will not need to reassess whether contracts are leases and will retain lease classification and initial direct costs for leases existing prior to the adoption of the new lease standard. In June 2016, the FASB issued ASU No. 2016‑13, Financial Instruments - Credit Losses (Topic 326) , which is intended to provide financial statement users with more useful information about expected credit losses on financial assets held by a reporting entity at each reporting date. The new standard replaces the existing incurred loss impairment methodology with a methodology that requires consideration of a broader range of reasonable and supportable forward-looking information to estimate all expected credit losses. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2019 and early adoption is permitted for fiscal years and interim periods within those years beginning after December 15, 2018. The Company is currently evaluating the impact of this new guidance on its consolidated financial statements and disclosures. In June 2018, the FASB issued ASU No. 2018-07, Compensation – Stock Compensation (Topic 718), Improvements to Nonemployee Share-Based Payment Accounting , which is intended to simplify the accounting for nonemployee share-based payment transactions by expanding the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. The guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2018. The Company is currently evaluating the impact of this new guidance on its consolidated financial statements and disclosures. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820) – Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement , which modifies the disclosure requirements on fair value measurements and is intended to improve the effectiveness of disclosures, including the consideration of costs and benefits. The guidance is effective for the fiscal years and interim periods within those years beginning after January 1, 2020. Early adoption is permitted, and an entity is permitted to early adopt any removed or modified disclosures and delay adoption of additional disclosures until their effective date. The Company does not expect this new guidance to impact its consolidated financial statements and is currently evaluating the impact on its disclosures. In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606 , which is intended to clarify the circumstances under which certain transactions in collaborative arrangements should be accounted for under the revenue recognition standard. Certain transactions between collaboration arrangement participants should be accounted for as revenue under ASC Topic 606 when the collaborative arrangement participant is a customer in the context of a unit of account. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2020. Early adoption is permitted. The Company is in the process of assessing the impact of this new guidance on its consolidated financial statements and disclosures.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Summary of Significant Accounting Policies
Schedule of cash as reported in the consolidated statements of cash flows	Cash as reported in the consolidated statements of cash flows consists of (in thousands): December 31, 2018 2017 2016 Cash and cash equivalents $ 82,233 $ 106,029 $ 21,084 Restricted cash - current 10 10 10 Restricted cash - noncurrent 450 450 — Cash balance in consolidated statements of cash flows $ 82,693 $ 106,489 $ 21,094

Janssen License and Collabora_2

Janssen License and Collaboration Agreement (Tables)	12 Months Ended
	Dec. 31, 2018
Janssen License and Collaboration Agreement
Schedule of changes in contract assets and liabilities	The following table presents changes in the Company’s contract assets and liabilities for the years ended December 31, 2018 and 2017 (in thousands): Balance at Balance at Beginning of End of Year Ended December 31, 2018 Period Additions Deductions Period Contract assets: Receivable from collaboration partner - related party $ 1,816 $ 6,665 $ (6,439) $ 2,042 Contract asset - related party $ — $ 2,545 $ — $ 2,545 Contract liabilities: Deferred revenue - related party $ 31,752 $ 7,296 $ (30,825) $ 8,223 Payable to collaboration partner - related party $ — $ 1,574 $ (513) $ 1,061 Balance at Balance at Beginning of End of Year Ended December 31, 2017 Period Additions Deductions Period Contract assets: Receivable from collaboration partner - related party $ — $ 51,816 $ (50,000) $ 1,816 Contract liabilities: Deferred revenue - related party $ — $ 50,708 $ (18,956) $ 31,752

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Measurements
Schedule of fair value of financial assets	The following table presents the fair value of the Company’s financial assets determined using the inputs defined above (in thousands). December 31, 2018 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 25,390 $ — $ — $ 25,390 Corporate bonds — 8,989 — 8,989 Commercial paper — 59,730 — 59,730 Government bonds — 33,394 — 33,394 Total financial assets $ 25,390 $ 102,113 $ — $ 127,503 December 31, 2017 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 48,704 $ — $ — $ 48,704 Corporate bonds — 6,247 — 6,247 Commercial paper — 58,524 — 58,524 Government bonds — 40,303 — 40,303 Total financial assets $ 48,704 $ 105,074 $ — $ 153,778

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2018
Balance Sheet Components
Schedule of cash equivalents and available-for-sale securities	Cash equivalents and available-for-sale securities consisted of the following (in thousands): December 31, 2018 Amortized Gross Unrealized Cost Gains Losses Fair Value Money market funds $ 25,390 $ — $ — $ 25,390 Corporate bonds 8,997 — (8) 8,989 Commercial paper 59,730 — — 59,730 Government bonds 33,423 — (29) 33,394 Total cash equivalents and available-for-sale securities $ 127,540 $ — $ (37) $ 127,503 Classified as: Cash equivalents $ 80,883 Available-for-sale securities - current 46,620 Total cash equivalents and available-for-sale securities $ 127,503 December 31, 2017 Amortized Gross Unrealized Cost Gains Losses Fair Value Money market funds $ 48,704 $ — $ — $ 48,704 Corporate bonds 6,254 — (7) 6,247 Commercial paper 58,524 — — 58,524 Government bonds 40,428 — (125) 40,303 Total cash equivalents and available-for-sale securities $ 153,910 $ — $ (132) $ 153,778 Classified as: Cash equivalents $ 104,348 Available-for-sale securities - current 37,972 Available-for-sale securities - noncurrent 11,458 Total cash equivalents and available-for-sale securities $ 153,778
Summary of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2018 2017 Prepaid clinical and research related expenses $ 686 $ 2,324 Prepaid insurance 438 378 Other prepaid expenses 1,005 936 Other receivable 495 135 Prepaid expenses and other current assets $ 2,624 $ 3,773
Summary of Property and Equipment Net	Property and equipment, net consisted of the following (in thousands): December 31, 2018 2017 Laboratory equipment $ 2,533 $ 2,177 Furniture and computer equipment 338 270 Leasehold improvements 67 26 Total property and equipment 2,938 2,473 Less: accumulated depreciation and amortization (2,077) (1,594) Property and equipment, net $ 861 $ 879
Summary of Accrued Expenses and Other Payables	Accrued expenses and other payables consisted of the following (in thousands): December 31, 2018 2017 Accrued clinical and research related expenses $ 7,781 $ 6,437 Accrued employee related expenses 2,726 2,718 Accrued milestone payment to former collaboration partner 500 — Accrued professional service fees 61 267 Other 95 124 Total accrued expenses and other payables $ 11,163 $ 9,546

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies
Summary of Future Minimum Lease Payments	The following table summarizes the Company’s future minimum lease payments related to the Newark facility as of December 31, 2018 (in thousands): Year Ending December 31: Amount 2019 $ 1,941 2020 2,000 2021 2,059 2022 2,121 2023 2,185 Thereafter 922 Total $ 11,228

Redeemable Convertible Prefer_3

Redeemable Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2018
Redeemable Convertible Preferred Stock.
Summary of Redeemable Convertible Preferred Stock	The table below provides information on the Company’s redeemable convertible preferred stock as of December 31, 2015 (in thousands, except shares and original issue price): Shares Aggregate Original Issued and Carrying Liquidation Issue Price Authorized Outstanding Value Preference Series A $ 1.00 6,037,500 6,037,500 $ 1,751 $ 6,038 Series B $ 0.50 40,000,000 36,000,000 18,825 18,000 Series C $ 0.4979 80,337,411 35,147,617 16,420 17,500 Total redeemable convertible preferred stock 126,374,911 77,185,117 $ 36,996 $ 41,538

Equity Plans (Tables)

Equity Plans (Tables)	12 Months Ended
	Dec. 31, 2018
Schedule of activity under equity incentive plans	Weighted- Weighted- Average Average Exercise Remaining Aggregate Options Price Per Contractual Intrinsic Outstanding Share Life (years) Value (1) (in millions) Balances at December 31, 2015 833,178 $ 1.33 8.56 Options granted 1,679,979 14.24 Options exercised (119,328) 1.28 Balances at December 31, 2016 2,393,829 10.39 8.79 Options granted 493,500 13.20 Options exercised (257,858) 1.84 Options forfeited (191,320) 15.00 Balances at December 31, 2017 2,438,151 11.51 8.26 Options granted 1,067,400 13.17 Options exercised (143,358) 2.78 Options forfeited (183,752) 15.46 Balances at December 31, 2018 3,178,441 $ 12.23 7.52 $ 3.5 Options exercisable – December 31, 2018 1,475,083 $ 11.07 6.98 $ 2.6 Options vested and expected to vest – December 31, 2018 3,178,441 $ 12.23 7.52 $ 3.5 ____________________ (1) The aggregate intrinsic values were calculated as the difference between the exercise price of the options and the closing price of the Company’s common stock on December 31, 2018. The calculation excludes options with an exercise price higher than the closing price of the Company’s common stock on December 31, 2018.
Schedule of stock-based compensation expense	Total stock-based compensation expense was as follows (in thousands): Year Ended December 31, 2018 2017 2016 Research and development $ 3,424 $ 2,008 $ 1,080 General and administrative 3,495 2,233 1,050 Total stock-based compensation expense $ 6,919 $ 4,241 $ 2,130
Employee stock options
Black-Scholes option-pricing model assumptions	Year Ended December 31, 2018 2017 2016 Expected term (in years) 5.49 - 6.08 5.50 - 6.08 4.16 - 5.95 Expected volatility 62.0% - 66.5% 61.6% - 65.4% 62.5% - 64.8% Risk-free interest rate 2.42% - 3.03% 1.88 - 2.24% 1.27% - 1.79% Dividend yield — — —
Non-employee stock options
Black-Scholes option-pricing model assumptions	Year Ended December 31, 2018 2017 2016 Expected term (in years) 7.48 - 7.67 6.97 - 7.40 6.59 - 9.97 Expected volatility 64.4% - 67.8% 61.7% - 65.4% 62.5% - 62.8% Risk-free interest rate 2.61% - 3.02% 2.17% - 2.33% 1.29% - 1.79% Dividend yield — — —
Restricted stock units
Schedule of activity under equity incentive plans	Un Weighted- Average Number of Grant Date Shares Fair Value Unvested at December 31, 2017 — — Restricted stock units granted $ Restricted stock units forfeited (7,575) Unvested at December 31, 2018 $
ESPP rights
Black-Scholes option-pricing model assumptions	Year Ended December 31, 2018 2017 2016 Expected term (in years) 0.50 0.50 0.60 Expected volatility 49.0% - 63.4% 52.4% 52.5% Risk-free interest rate 1.89% - 2.32% 0.89% - 1.16% 0.45% Dividend yield — — —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Taxes
Schedule of domestic and foreign components of net loss	The following table presents domestic and foreign components of net loss before income taxes for the periods presented (in thousands): Year Ended December 31, 2018 2017 2016 Domestic $ (37,511) $ (34,556) $ (34,977) Foreign (2,212) (2,401) (2,200) Net loss before income taxes $ (39,723) $ (36,957) $ (37,177)
Schedule of provision differences from federal statutory rate	Year Ended December 31, 2018 2017 2016 Federal statutory income tax rate 21.0 % % 34.0 % State taxes, net of federal benefit 7.0 0.5 6.5 Warrant revaluation — — (4.3) Research credit (1.3) 2.6 1.8 Foreign tax rate difference 0.4 (1.2) (1.6) Change in tax law — (31.2) — Change in valuation allowance (22.2) (5.2) (36.0) Other (2.9) 0.5 (0.4) Provision for income taxes 2.0 % — % — %
Schedule of components of deferred tax assets	The components of the deferred tax assets are as follows (in thousands): December 31, 2018 2017 Deferred tax assets: Net operating loss carryforwards $ 27,704 $ 21,682 Depreciation and amortization 269 339 Accruals/other 2,455 1,322 Research and development credits 4,270 2,544 Total deferred tax assets 34,698 25,887 Valuation allowance (34,040) (25,887) Net deferred tax assets $ 658 $ —
Schedule of reconciliation of beginning and ending unrecognized tax benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands): Year Ended December 31, 2018 2017 2016 Balance at beginning of year $ 5,414 $ 2,131 $ 805 Increase based on tax positions related to prior years 108 — 707 Increase based on tax positions related to current year 3,944 3,283 619 Balance at end of year $ 9,466 $ 5,414 $ 2,131

Net Loss per Share Attributab_2

Net Loss per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2018
Net Loss per Share Attributable to Common Stockholders
Schedule of computation of the basic and diluted net loss per share attributable to common stockholders	The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Year Ended December 31, 2018 2017 2016 Numerator: Net loss $ (38,924) $ (36,957) $ (37,177) Accretion of redeemable convertible preferred stock — — (558) Net loss $ (38,924) $ (36,957) $ (37,735) Denominator: Weighted-average shares used to compute net loss per common share, basic and diluted 22,364,515 17,694,505 6,501,796 Net loss per shares, basic and diluted $ (1.74) $ (2.09) $ (5.80)
Schedule of potentially dilutive securities excluded from diluted net loss per share calculations	Year Ended December 31, 2018 2017 2016 Options to purchase common stock 3,178,441 2,438,151 2,393,829 Common stock warrants 2,750,000 — — Restricted stock units 418,450 — — ESPP shares 52,134 24,938 — Total 6,399,025 2,463,089 2,393,829

Supplementary Financial Data _2

Supplementary Financial Data (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Supplementary Financial Data (unaudited)
Summary of Selected Quarterly Financial Data	Consolidated Statements of Operations Quarter Ended March 31 June 30 September 30 December 31 2018 License and collaboration revenue - related party $ 10,781 $ 11,674 $ 6,117 $ 2,353 Loss from operations $ (8,229) $ (9,239) $ (9,389) $ (15,412) Net loss $ (7,661) $ (8,663) $ (8,735) $ (13,865) Net loss per share of common stock, basic and diluted (1) $ (0.36) $ (0.41) $ (0.38) $ (0.57) 2017 License and collaboration revenue - related party $ — $ — $ 8,781 $ 11,282 Loss from operations $ (14,273) $ (15,131) $ (4,980) $ (3,513) Net loss $ (14,101) $ (14,979) $ (4,825) $ (3,052) Net loss per share of common stock, basic and diluted (1) $ (0.84) $ (0.89) $ (0.29) $ (0.15)

Organization and Description _2

Organization and Description of Business - Liquidity (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 21, 2018	Aug. 06, 2018	Aug. 16, 2016	Nov. 30, 2017	Oct. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net losses from operations since inception
Accumulated deficit								$ (140,474)	$ (101,550)
Stock transactions
Common stock sold								23,187,219	21,088,306
Net proceeds from sale of stock								$ 1,508
Redeemable convertible preferred stock, shares outstanding								0	0
Par value (per share)								$ 0.00001	$ 0.00001
Common Stock
Stock transactions
Stock issued (in shares)					3,530,000				4,059,500	7,752,972
Price (in dollars per share)					$ 17
Conversion of redeemable convertible preferred stock to common stock at closing of initial public offering (in shares)			8,577,571							8,577,571
Procceds from stock issuance, net of underwriting and offering costs				$ 64,500			$ 83,600
Initial Public Offering | Common Stock
Stock transactions
Stock issued (in shares)			7,500,000
Price (in dollars per share)			$ 12
Underwriter overallotment option | Common Stock
Stock transactions
Stock issued (in shares)				529,500			252,972
Price (in dollars per share)				$ 17			$ 12
Shelf offering | Common Stock
Stock transactions
Maximum aggregate offering price						$ 200,000
Private Placement | Common Stock
Stock transactions
Number of warrants exercised								0
Cantor Fitzgerald & Co. Sales Agreement | At-the-market offering
Stock transactions
Gross proceeds for any common stock sold, maximum percent payable								3.00%
Cantor Fitzgerald & Co. Sales Agreement | At-the-market offering | Common Stock
Stock transactions
Maximum aggregate offering price						$ 50,000
Common stock sold								151,273
Net proceeds from sale of stock								$ 1,500
Common stock available for sale								$ 48,300
Investors | Common Stock
Stock transactions
Stock issued (in shares)		2,750,000
Price (in dollars per share)		$ 8
Aggregate gross proceeds		$ 21,700
Investors | Private Placement | Common Stock
Stock transactions
Warrants to purchase common stock, number of shares		2,750,000
Purchase of common stock		2,750,000
Exchange Agreement | Exchanging Stockholders
Stock transactions
Warrants to purchase common stock, number of shares	1,000,000
Warrants exercise price	$ 0.00001
Number of warrants exercised								0
Common stock exchanged for pre-funded warrants	1,000,000
Par value (per share)	$ 0.00001
Purchase of common stock	1,000,000
Exercise Price (per share)	$ 0.00001
Duration of warrants from date of issuance (in years)	10 years
Equity Method Investment, Ownership Percentage	9.99%
Group one | Private Placement | Common Stock
Stock transactions
Number of shares to be converted for each warrant		1,375,000
Warrants exercise price		$ 10
Exercise Price (per share)		$ 10
Group two | Private Placement | Common Stock
Stock transactions
Number of shares to be converted for each warrant		1,375,000
Warrants exercise price		$ 15
Exercise Price (per share)		$ 15
Redeemable Convertible Preferred Stock
Stock transactions
Redeemable convertible preferred stock, shares outstanding								0	0		77,185,117

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Concentrations of Credit Risk (Details)	Dec. 31, 2018Institution
Summary of Significant Accounting Policies
Number of financial institutions at which cash is held	3

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Aggregate amounts of cash and cash equivalents and the restricted cash
Cash and cash equivalents	$ 82,233	$ 106,029	$ 21,084
Restricted cash - current	10	10	10
Restricted cash - noncurrent	450	450
Cash balance in consolidated statements of cash flows	$ 82,693	$ 106,489	$ 21,094	$ 4,065

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Property and Equipment and Impairment of Long-Lived Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and Equipment
Impairments of long-lived assets	$ 0	$ 0	$ 0
Minimum | Property and equipment
Property and Equipment
Useful lives	3 years
Maximum | Property and equipment
Property and Equipment
Useful lives	5 years

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Research and Development Tax Incentive (Details) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018AUD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Summary Of Significant Accounting Policy
Interest or penalties recorded in relation to unrecognized tax benefits			$ 0	$ 0	$ 0
Maximum | Australian
Summary Of Significant Accounting Policy
Revenue for availability of research and development tax incentive		$ 20
Percentage of research and development expenditures for a project incurred overseas for availability of research and development tax incentive		50.00%	50.00%
Minimum | Australian | Australia [Member]
Summary Of Significant Accounting Policy
Percentage of research and development expenditures for a project incurred in geographic area of tax incentive for availability of research and development tax incentive	50.00%	50.00%	50.00%

Janssen Collaboration Agreement

Janssen Collaboration Agreement (Details) - USD ($) $ in Thousands	Jul. 13, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue		$ 2,353	$ 6,117	$ 11,674	$ 10,781	$ 11,282	$ 8,781	$ 30,925	$ 20,063
Deferred revenue - related party		8,223				31,752		8,223	31,752	$ 8,223
Receivable from collaboration partner and contract asset - related party		4,587				1,816		4,587	1,816	4,587
Payable to collaboration partner - related party		1,061						$ 1,061		1,061
Transaction price						53,900			53,900
License and Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized									20,100
Development cost								20.00%
Phase 2 clinical trial | Other services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue								$ 100	1,100
First Opt-in Election
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Future opt-in revenue eligible to receive								125,000
Janssen Biotech, Inc. | License and Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue										49,800
Deferred revenue - related party		8,223				$ 31,752		8,223	31,752	8,223
Payable to collaboration partner - related party		1,061						1,061		1,061
Transaction price recognized based on proportional performance								30,825	$ 18,956
Transaction price		$ 60,700						$ 60,700		$ 60,700
Development cost								80.00%
Percentage of details provided for PTG-200 to prescribers upon commercial launch								30.00%
Increase in transaction price								$ 6,800
Janssen Biotech, Inc. | License and Collaboration Agreement | Upfront cash payment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue	$ 50,000
Janssen Biotech, Inc. | Phase 2 clinical trial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue								10,700
Future opt-in revenue eligible to receive								$ 25,000
Janssen Biotech, Inc. | First Opt-in Election
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Forfeiture of remaining rights and payment of cost, penalty percentage								50.00%
Janssen Biotech, Inc. | Second Opt-in Election
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Future opt-in revenue eligible to receive								$ 200,000
Janssen Biotech, Inc. | Second Opt-in Election | Development, regulatory and sales milestone payments
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential development, regulatory and sales milestone payments								$ 590,000

Janssen Collaboration Agreeme_2

Janssen Collaboration Agreement - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended						12 Months Ended		18 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018
Deferred revenue - related party
Balance at beginning of period				$ 31,752			$ 31,752
Balance at end of period	$ 8,223				$ 31,752		8,223	$ 31,752	$ 8,223
Payable to collaboration partner - related party
Balance at End of Period	1,061						1,061		1,061
License and collaboration revenue - related party	2,353	$ 6,117	$ 11,674	10,781	11,282	$ 8,781	30,925	20,063
License and Collaboration Agreement
Payable to collaboration partner - related party
Revenue recognized from contract liability balance at beginning of period								20,100
Janssen Biotech, Inc. | License and Collaboration Agreement
Receivable from collaboration partner - related party
Balance at beginning of period				1,816			1,816
Additions							6,665	51,816
Deductions							(6,439)	(50,000)
Balance at end of period	2,042				1,816		2,042	1,816	2,042
Contract asset - related party
Contract asset - related party, Additions							2,545
Contract asset - related party, Balance at end of Period	2,545						2,545		2,545
Deferred revenue - related party
Balance at beginning of period				$ 31,752			31,752
Additions							7,296	50,708
Deductions							(30,825)	(18,956)
Balance at end of period	8,223				$ 31,752		8,223	31,752	8,223
Payable to collaboration partner - related party
Additions							1,574
Deductions							(513)
Balance at End of Period	$ 1,061						$ 1,061		1,061
License and collaboration revenue - related party									$ 49,800
Collaboration Agreement Development Cost								$ 700

Fair Value Measurements (Detail

Fair Value Measurements (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	$ 127,503	$ 153,778
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	25,390	48,704
Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	8,989	6,247
Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	59,730	58,524
Government Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	33,394	40,303
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	25,390	48,704
Level 1 | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	25,390	48,704
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	102,113	105,074
Level 2 | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	8,989	6,247
Level 2 | Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	59,730	58,524
Level 2 | Government Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	$ 33,394	$ 40,303

Balance Sheet Components - Cash

Balance Sheet Components - Cash Equivalents and Available-for-sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Cash Equivalents and Available-for-sale Securities
Total cash equivalents and available-for-sale securities, Amortized Cost	$ 127,540	$ 153,910
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	(37)	(132)
Total cash equivalents and available-for-sale securities, Fair Value	127,503	153,778
Corporate Bonds
Cash Equivalents and Available-for-sale Securities
Total cash equivalents and available-for-sale securities, Amortized Cost	8,997	6,254
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	(8)	(7)
Total cash equivalents and available-for-sale securities, Fair Value	8,989	6,247
Government Bonds
Cash Equivalents and Available-for-sale Securities
Total cash equivalents and available-for-sale securities, Amortized Cost	33,423	40,428
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	(29)	(125)
Total cash equivalents and available-for-sale securities, Fair Value	33,394	40,303
Money Market Funds
Cash Equivalents and Available-for-sale Securities
Total cash equivalents and available-for-sale securities, Amortized Cost	25,390	48,704
Total cash equivalents and available-for-sale securities, Fair Value	25,390	48,704
Commercial Paper
Cash Equivalents and Available-for-sale Securities
Total cash equivalents and available-for-sale securities, Amortized Cost	59,730	58,524
Total cash equivalents and available-for-sale securities, Fair Value	$ 59,730	$ 58,524

Balance Sheet Components - Clas

Balance Sheet Components - Classification of Cash Equivalents and Available-for-sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Classified as:
Cash equivalents	$ 80,883	$ 104,348
Available-for-sale securities - current	46,620	37,972
Available-for-sale securities - noncurrent		11,458
Total cash equivalents and available-for-sale securities	127,503	153,778
Contractual maturities
Available-for-sale securities with contractual maturities of less than one year	$ 46,620	37,972
Available-for-sale securities with contractual maturities of at least one year but less than two years		$ 11,458

Balance Sheet Components - Prep

Balance Sheet Components - Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid clinical and research related expenses	$ 686	$ 2,324
Prepaid insurance	438	378
Other prepaid expenses	1,005	936
Other receivable	495	135
Prepaid expenses and other current assets	$ 2,624	$ 3,773

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment Net (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and Equipment
Total property and equipment	$ 2,938,000	$ 2,473,000
Less: accumulated depreciation and amortization	(2,077,000)	(1,594,000)
Property and equipment, net	861,000	879,000
Property and equipment income statement disclosure
Depreciation expense	527,000	406,000	$ 317,000
Laboratory Equipment [Member]
Property and Equipment
Total property and equipment	2,533,000	2,177,000
Furniture and Computer Equipment [Member]
Property and Equipment
Total property and equipment	338,000	270,000
Leasehold Improvements [Member]
Property and Equipment
Total property and equipment	67,000	26,000
Australia [Member]
Property and Equipment
Property and equipment, net	$ 200	$ 1,200	$ 8,000

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Expenses and Other Payables (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Balance Sheet Components
Accrued clinical and research related expenses	$ 7,781	$ 6,437
Accrued employee related expenses	2,726	2,718
Accrued milestone payment to former collaboration partner	500
Accrued professional service fees	61	267
Other	95	124
Total accrued expenses and other payables	$ 11,163	$ 9,546

Research Collaboration and Li_2

Research Collaboration and License Agreement (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Collaboration and License Agreement
Research and Development Expense	$ 59,497,000	$ 46,181,000	$ 25,705,000
Research Collaboration and License Agreement
Collaboration and License Agreement
Term	10 years
Research Collaboration and License Agreement | PTG-300
Collaboration and License Agreement
Upfront payment to the former collaboration partner			250,000
Research and Development Expense	$ 500,000	250,000	$ 250,000
Research Collaboration and License Agreement | PTG-300 | Maximum
Collaboration and License Agreement
Aggregate milestone payment	128,000,000
Research Collaboration and License Agreement | Phase 1
Collaboration and License Agreement
Potential obligation to former collaboration partner for development and commercialization of product		$ 250,000
Research Collaboration and License Agreement | Phase 2
Collaboration and License Agreement
Potential obligation to former collaboration partner for development and commercialization of product	$ 500,000

Government Programs (Details)

Government Programs (Details)	1 Months Ended							12 Months Ended
	Sep. 30, 2018USD ($)	May 31, 2017USD ($)	Dec. 31, 2016	Jul. 31, 2016USD ($)	Mar. 31, 2016AUD ($)	Mar. 31, 2016USD ($)	Sep. 30, 2015USD ($)	Dec. 31, 2018AUD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017AUD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016AUD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Government Programs
Research and development tax incentive receivable														$ 1,429,000	$ 1,347,000
SBIR Grant
Government Programs
Reduction of research and development expenses related to tax									$ 663,000		$ 182,000		$ 169,000
Research and development grants	$ 1,500,000	$ 1,300,000		$ 219,000			$ 224,000
Grants receivable														309,000	58,000
Australian
Government Programs
Reduction of research and development expenses related to tax								$ 2,100,000	$ 1,600,000	$ 1,700,000	$ 1,300,000	$ 5,300,000	$ 4,000,000
Australian | Australia [Member] | Minimum
Government Programs
Percentage of research and development expenditures for a project incurred in geographic area of tax incentive for availability of research and development tax incentive			50.00%					50.00%	50.00%
Overseas Findings | Australian
Government Programs
Research and development tax incentive receivable								$ 2,000,000		$ 1,700,000				$ 1,400,000	$ 1,300,000
Deferred tax incentive					$ 237,000	$ 182,000

Commitments and Contingencies -

Commitments and Contingencies - Lease Agreement (Details) - USD ($)	1 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Rent expense		$ 1,900,000	$ 1,400,000	$ 408,000
Newark, California
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Security deposit	$ 450,000
Tenant improvement allowances	$ 469,000

Commitments and Contingencies_2

Commitments and Contingencies - Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Leases
2019	$ 1,941
2020	2,000
2021	2,059
2022	2,121
2023	2,185
Thereafter	922
Total	$ 11,228

Preferred Stock Warrants (Detai

Preferred Stock Warrants (Details) - USD ($)	1 Months Ended		12 Months Ended
	Apr. 30, 2016	Aug. 31, 2013	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 31, 2016	Mar. 31, 2016
Preferred Stock Warrants
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants					$ 22,508,000
Remeasured fair value of warrants	$ 1,000,000
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock					1,005,000
Change in fair value of redeemable convertible preferred stock warrant liability			$ 0	$ 0	$ 525,000
Redeemable Convertible Preferred Stock Warrant Liability [Member]
Preferred Stock Warrants
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock			$ 1,000,000
Option Pricing Model
Preferred Stock Warrants
Percentage of weighted value per share	67.00%
PWERM
Preferred Stock Warrants
Percentage of weighted value per share	33.00%
Redeemable convertible preferred stock Series B
Preferred Stock Warrants
Number of convertible preferred stock issued upon exercise of stock warrants		4,000,000
Redeemable convertible preferred stock, shares issued	1,999,998
Warrants to purchase common stock, number of shares							2,000,000
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants	$ 20,000
Number of redeemable convertible preferred stock expired unexercised						2,000,000

Redeemable Convertible Prefer_4

Redeemable Convertible Preferred Stock - Description (Details) - USD ($)	Aug. 16, 2016	Apr. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Redeemable Convertible Preferred Stock
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants					$ 22,508,000
Redeemable convertible preferred stock, shares outstanding			0	0
Redeemable convertible preferred stock redemption date			2022-07
Redeemable convertible preferred stock, period accretion			$ 0	$ 0	$ 558,000
Common Stock
Redeemable Convertible Preferred Stock
Conversion of redeemable convertible preferred stock to common stock at closing of initial public offering (in shares)	8,577,571				8,577,571
Redeemable Convertible Preferred Stock
Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, shares outstanding			0	0		77,185,117
Redeemable convertible preferred stock, period accretion					$ 558,000
Redeemable convertible preferred stock Series B
Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, shares issued		1,999,998
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants		$ 20,000

Redeemable Convertible Prefer_5

Redeemable Convertible Preferred Stock - Summary Series (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2015	Jul. 31, 2015
Redeemable Convertible Preferred Stock
Convertible preferred stock, shares authorized	126,374,911
Convertible preferred stock, shares issued and outstanding	77,185,117
Convertible preferred stock, carrying value	$ 36,996
Convertible preferred stock, aggregate liquidation preference	$ 41,538
Series A Redeemable Convertible Preferred Stock [Member]
Redeemable Convertible Preferred Stock
Convertible preferred stock, original issue price	$ 1
Convertible preferred stock, shares authorized	6,037,500
Convertible preferred stock, shares issued and outstanding	6,037,500
Convertible preferred stock, carrying value	$ 1,751
Convertible preferred stock, aggregate liquidation preference	$ 6,038
Redeemable convertible preferred stock Series B
Redeemable Convertible Preferred Stock
Convertible preferred stock, original issue price	$ 0.50
Convertible preferred stock, shares authorized	40,000,000
Convertible preferred stock, shares issued and outstanding	36,000,000
Convertible preferred stock, carrying value	$ 18,825
Convertible preferred stock, aggregate liquidation preference	$ 18,000
Redeemable convertible preferred stock Series C
Redeemable Convertible Preferred Stock
Convertible preferred stock, original issue price	$ 0.4979	$ 0.4979
Convertible preferred stock, shares authorized	80,337,411	80,337,411
Convertible preferred stock, shares issued and outstanding	35,147,617
Convertible preferred stock, carrying value	$ 16,420
Convertible preferred stock, aggregate liquidation preference	$ 17,500

Redeemable Convertible Prefer_6

Redeemable Convertible Preferred Stock Tranche Liability (Details) - USD ($)	Jul. 10, 2015	Apr. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jul. 31, 2015
Redeemable Convertible Preferred Stock Tranche Liability [Line Items]
Redeemable convertible preferred stock, proceeds						$ 22,508,000
Fair value of redeemable convertible preferred stock liability reclassified			$ 5,800,000			5,837,000
Redeemable convertible preferred stock, authorized							126,374,911
Change in fair value of redeemable convertible preferred stock tranche liabilities						4,194,000
Redeemable convertible preferred stock Series C
Redeemable Convertible Preferred Stock Tranche Liability [Line Items]
Redeemable convertible preferred stock, shares issued	35,147,617		45,189,794
Redeemable convertible preferred stock, proceeds	$ 17,500,000		$ 22,500,000
Fair value of redeemable convertible preferred stock liability	$ 1,000,000		$ 5,800,000				$ 1,600,000
Redeemable convertible preferred stock, price per share							$ 0.4979	$ 0.4979
Redeemable convertible preferred stock, authorized							80,337,411	80,337,411
Change in fair value of redeemable convertible preferred stock tranche liabilities				$ 0	$ 0	$ 4,200,000
Redeemable convertible preferred stock Series C | Option Pricing Model
Redeemable Convertible Preferred Stock Tranche Liability [Line Items]
Fair value assumptions, weighted volatility rate			67.00%
Redeemable convertible preferred stock Series C | PWERM
Redeemable Convertible Preferred Stock Tranche Liability [Line Items]
Fair value assumptions, expected volatility			33.00%
Redeemable convertible preferred stock Series C | Second Tranche Warrants
Redeemable Convertible Preferred Stock Tranche Liability [Line Items]
Additional shares to be issued upon the achievement of certain development milestones	45,189,794
Redeemable convertible preferred stock Series B
Redeemable Convertible Preferred Stock Tranche Liability [Line Items]
Redeemable convertible preferred stock, shares issued		1,999,998
Redeemable convertible preferred stock, proceeds		$ 20,000
Redeemable convertible preferred stock, price per share							$ 0.50
Redeemable convertible preferred stock, authorized							40,000,000

Equity Plans - Description (Det

Equity Plans - Description (Details) - shares	1 Months Ended	12 Months Ended
	Jul. 31, 2016	Dec. 31, 2018	May 31, 2018	Jul. 31, 2017
2007 Stock Option and Incentive Plan
Equity Plans
Number of shares available for issuance	0
2016 Equity Incentive Plan
Equity Plans
Number of shares authorized				1,200,000
Maximum annual additional authorized shares as a percentage of outstanding shares		4.00%
Number of shares available for issuance		177,473
2016 Equity Incentive Plan | Stockholders possessing more than 10% of the total combined voting power | Minimum
Equity Plans
Exercise price as a percentage of the fair market value of common stock on grant date		110.00%
2016 Equity Incentive Plan | Tranche two
Equity Plans
Vesting period	3 years
2018 Inducement Plan
Equity Plans
Expiration period		10 years
Number of shares authorized			750,000
Number of shares available for issuance		645,000
Stock options - employees, consultants, directors | 2007 Stock Option and Incentive Plan
Equity Plans
Expiration period		10 years
Stock options - employees, consultants, directors | 2007 Stock Option and Incentive Plan | Minimum
Equity Plans
Vesting period		4 years
Stock options - employees, consultants, directors | 2007 Stock Option and Incentive Plan | Maximum
Equity Plans
Cliff vesting period		1 year
Stock options - employees, consultants, directors | 2016 Equity Incentive Plan
Equity Plans
Expiration period		10 years
Stock options - employees, consultants, directors | 2016 Equity Incentive Plan | Minimum
Equity Plans
Exercise price as a percentage of the fair market value of common stock on grant date		100.00%
Employee stock options | 2016 Equity Incentive Plan
Equity Plans
Vesting percentage of requisite service period	25.00%
Non Employee Director Initial Stock Options | 2016 Equity Incentive Plan | Maximum
Equity Plans
Vesting period		3 years
Nonemployee Director Annual Refresher Stock Options | 2016 Equity Incentive Plan | Minimum
Equity Plans
Vesting period		1 year

Equity Plans - Activity (Detail

Equity Plans - Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Options Outstanding
Options Outstanding, Options granted	42,950
2016 Plan
Options Outstanding
Options Outstanding, Beginning balance	2,438,151	2,393,829	833,178
Options Outstanding, Options granted	1,067,400	493,500	1,679,979
Options Outstanding, Options exercised	(143,358)	(257,858)	(119,328)
Options Outstanding, Options forfeited	(183,752)	(191,320)
Options Outstanding, Ending balance	3,178,441	2,438,151	2,393,829	833,178
Options Outstanding, Options exercisable	1,475,083
Options Outstanding, Options vested and expected to vest	3,178,441
Weighted-Average Exercise Price Per Share
Weighted-Average Exercise Price Per Share, Beginning balance	$ 11.51	$ 10.39	$ 1.33
Weighted-Average Exercise Price Per Share, Options granted	13.17	13.20	14.24
Weighted-Average Exercise Price Per Share, Options exercised	2.78	1.84	1.28
Weighted-Average Exercise Price Per Share, Options forfeited	15.46	15
Weighted-Average Exercise Price Per Share, Ending balance	12.23	$ 11.51	$ 10.39	$ 1.33
Weighted-Average Exercise Price Per Share, Options exercisable	11.07
Weighted-Average Exercise Price Per Share, Options vested and expected to vest	$ 12.23
Weighted-Average Remaining Contractual Life (years)
Weighted-Average Remaining Contractual Life (years)	7 years 6 months 7 days	8 years 3 months 4 days	8 years 9 months 15 days	8 years 6 months 22 days
Weighted-Average Remaining Contractual Life (years), Options exercisable	6 years 11 months 23 days
Weighted-Average Remaining Contractual Life (years), Options vested and expected to vest	7 years 6 months 7 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Options Outstanding	$ 3,500,000
Aggregate Intrinsic Value, Options exercisable	2,600,000
Aggregate Intrinsic Value, Options vested and expected to vest	3,500,000
Aggregate intrinsic value of options exercised	$ 1,300,000	$ 3,500,000	$ 169,000
Options, weighted-average grant-date fair value	$ 8.12	$ 7.74	$ 8.20

Equity Plans - Employee Stock O

Equity Plans - Employee Stock Options Valuation Assumptions (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity Plans
Expected volatility, Maximum			64.80%
Employee stock options
Equity Plans
Expected volatility, Minimum	62.00%	61.60%
Expected volatility, Maximum	66.50%	65.40%
Risk-free interest rate, Minimum	2.42%	1.88%	1.27%
Risk-free interest rate, Maximum	3.03%	2.24%	1.79%
Employee stock options | Minimum
Equity Plans
Expected term	5 years 5 months 27 days	5 years 6 months	4 years 1 month 28 days
Expected volatility, Minimum			62.50%
Employee stock options | Maximum
Equity Plans
Expected term	6 years 29 days	6 years 29 days	5 years 11 months 12 days

Equity Plans - Non-employees St

Equity Plans - Non-employees Stock Options Valuation Assumptions (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity Plans
Expected volatility, Maximum			64.80%
Options Outstanding, Options granted	42,950
Total stock-based compensation expense	$ 6,919,000	$ 4,241,000	$ 2,130,000
Non-employee stock options
Equity Plans
Expected volatility, Minimum	64.40%	61.70%	62.50%
Expected volatility, Maximum			62.80%
Risk-free interest rate, Minimum	2.61%	2.17%	1.29%
Risk-free interest rate, Maximum	3.02%	2.33%	1.79%
Options Outstanding, Options granted		0	59,647
Total stock-based compensation expense	$ 36,000	$ 263,000	$ 505,000
Non-employee stock options | Minimum
Equity Plans
Expected term	7 years 5 months 23 days	6 years 11 months 19 days	6 years 7 months 2 days
Non-employee stock options | Maximum
Equity Plans
Expected term	7 years 8 months 1 day	7 years 4 months 24 days	9 years 11 months 19 days
Expected volatility, Maximum	67.80%	65.40%

Equity Plans - Restricted Stock

Equity Plans - Restricted Stock Units - (Details)	12 Months Ended
	Dec. 31, 2018installment$ / sharesshares
Equity Plans
Restricted stock units vesting, number of equal installments | installment	4
2016 Plan
Number of Shares
Number of shares, Unvested, Beginning balance | shares	0
Number of shares, Granted | shares	426,025
Number of Shares, Forfeited | shares	(7,575)
Number of shares, Unvested, Ending balance | shares	418,450
Weighted-Average Grant Date Fair Value
Weighted-Average Grant Date Fair Value, Unvested, Beginning balance | $ / shares	$ 0
Weighted-Average Grant Date Fair Value, Granted | $ / shares	10.53
Weighted-Average Grant Date Fair Value, Forfeited | $ / shares	15.36
Weighted-Average Grant Date Fair Value, Unvested, Ending balance | $ / shares	$ 10.45

Equity Plans - ESPP Description

Equity Plans - ESPP Description and Rights Valuation Assumptions (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jul. 31, 2016
Equity Plans
Expected volatility, Maximum			64.80%
ESPP rights
Equity Plans
Expected term	6 months	6 months	7 months 6 days
Expected volatility, Minimum	49.00%	0.89%
Expected volatility, Maximum	63.40%	1.16%
Expected volatility		52.40%	52.50%
Risk-free interest rate, Minimum	1.89%
Risk-free interest rate, Maximum	2.32%
Risk-free interest rate			0.45%
2016 Employee Stock Purchase Plan
Equity Plans
Number of shares authorized				150,000
Shares issued in period	102,950
Number of shares available for issuance	425,155
Maximum annual additional authorized shares as a percentage of outstanding shares	1.00%
Maximum annual additional authorized shares (in shares)	300,000
Maximum payroll deduction for share purchases (as a percent)	15.00%
Purchase price of stock (as a percent)	85.00%

Equity Plans - Compensation Exp

Equity Plans - Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 6,919	$ 4,241	$ 2,130
Total unrecognized stock-based compensation costs related to stock options	$ 15,600
Period of unrecognized stock-based compensation costs to be recognized	2 years 1 month 6 days
Research and Development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 3,424	2,008	1,080
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 3,495	$ 2,233	$ 1,050

Income Taxes - Provision and Co

Income Taxes - Provision and Components of Net Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes
Provision for income taxes	$ 799
Domestic and foreign components of net loss
Domestic	(37,511)	$ (34,556)	$ (34,977)
Foreign	(2,212)	(2,401)	(2,200)
Loss before income tax benefit	$ (39,723)	$ (36,957)	$ (37,177)

Income Taxes - Provision Differ

Income Taxes - Provision Difference from Federal Statutory Rate (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective tax rate of provision for income taxes difference from federal statutory rate
Federal statutory income tax rate (as a percent)	21.00%	34.00%	34.00%
State taxes, net of federal benefit (as a percent)	7.00%	0.50%	6.50%
Warrant revaluation (as a percent)			(4.30%)
Research credit (as a percent)	(1.30%)	2.60%	1.80%
Foreign tax rate difference (as a percent)	0.40%	(1.20%)	(1.60%)
Change in tax law (as a percent)		(31.20%)
Change in valuation allowance (as a percent)	(22.20%)	(5.20%)	(36.00%)
Other (as a percent)	(2.90%)	0.50%	(0.40%)
Provision for income taxes (as a percent)	2.00%
Maximum
Effective tax rate of provision for income taxes difference from federal statutory rate
Federal statutory income tax rate (as a percent)		35.00%

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets and Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 27,704	$ 21,682
Depreciation and amortization	269	339
Accruals/other	2,455	1,322
Research and development credits	4,270	2,544
Total deferred tax assets	34,698	25,887
Valuation allowance	(34,040)	(25,887)
Net deferred tax assets	658
Valuation allowance
Increase in valuation allowance	8,200	$ 1,900	$ 13,400
Australian
Valuation allowance
Increase in valuation allowance	$ 1,500

Income Taxes - Net Operating Lo

Income Taxes - Net Operating Loss Carryforwards (Details) $ in Thousands, $ in Millions	Dec. 31, 2018AUD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Net operating loss carryforwards
Operating loss carryforwards available to offset future taxable income		$ 27,704	$ 21,682
Australian
Net operating loss carryforwards
Net operating loss carryforwards		9,800
State
Net operating loss carryforwards
Net operating loss carryforwards		97,100
Federal
Net operating loss carryforwards
Net operating loss carryforwards		109,100
Operating loss carryforwards available to offset future taxable income		78,700
Net operating loss carryforwards with no expiration		$ 30,400
Federal | Australian
Net operating loss carryforwards
Net operating loss carryforwards	$ 13.9

Income Taxes - Research and Dev

Income Taxes - Research and Development Tax Credit Carryforwards (Details) - Research and Development Tax Incentive [Member] $ in Millions	Dec. 31, 2018USD ($)
State
Tax credit carryforwards
Tax credit carryforwards available to reduce future income taxes	$ 2.2
Federal
Tax credit carryforwards
Tax credit carryforwards available to reduce future income taxes	$ 4

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of beginning and ending amount of unrecognized tax benefits
Balance at beginning of year	$ 5,414	$ 2,131	$ 805
Increase based on tax positions related to prior years	108		707
Increase based on tax positions related to current year	3,944	3,283	619
Balance at end of year	9,466	$ 5,414	$ 2,131
Unrecognized tax benefits, amount that would affect the effective tax rate	2,700
Unrecognized tax benefits subject to a valuation allowance and would not affect the effective tax rate	$ 6,800

Net Loss per Share Attributab_3

Net Loss per Share Attributable to Common Stockholders - Computation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net loss	$ (13,865)	$ (8,735)	$ (8,663)	$ (7,661)	$ (3,052)	$ (4,825)	$ (14,979)	$ (14,101)	$ (38,924)	$ (36,957)	$ (37,177)
Accretion of redeemable convertible preferred stock											(558)
Net loss									$ (38,924)	$ (36,957)	$ (37,735)
Denominator:
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted									22,364,515	17,694,505	6,501,796
Net loss per shares, basic and diluted	$ (0.57)	$ (0.38)	$ (0.41)	$ (0.36)	$ (0.15)	$ (0.29)	$ (0.89)	$ (0.84)	$ (1.74)	$ (2.09)	$ (5.80)

Net Loss per Share Attributab_4

Net Loss per Share Attributable to Common Stockholders - Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	6,399,025	2,463,089	2,393,829
Employee stock options
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	3,178,441	2,438,151	2,393,829
Common stock warrants
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	2,750,000
Restricted stock units
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	418,450
ESPP rights
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	52,134	24,938

Supplementary Financial Data _3

Supplementary Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected quarterly financial data
License and collaboration revenue - related party	$ 2,353	$ 6,117	$ 11,674	$ 10,781	$ 11,282	$ 8,781			$ 30,925	$ 20,063
Loss from operations	(15,412)	(9,389)	(9,239)	(8,229)	(3,513)	(4,980)	$ (15,131)	$ (14,273)	(42,269)	(37,897)	$ (32,666)
Net loss	$ (13,865)	$ (8,735)	$ (8,663)	$ (7,661)	$ (3,052)	$ (4,825)	$ (14,979)	$ (14,101)	$ (38,924)	$ (36,957)	$ (37,177)
Net loss per share of common stock, basic and diluted	$ (0.57)	$ (0.38)	$ (0.41)	$ (0.36)	$ (0.15)	$ (0.29)	$ (0.89)	$ (0.84)	$ (1.74)	$ (2.09)	$ (5.80)