Stockholders' Equity

3 Months Ended

Mar. 31, 2022

Equity [Abstract]

Stockholders' Equity

9. Stockholders’ Equity

Underwritten Public Offering

On January 31, 2022, the Company completed an underwritten public offering of 4,074,075 shares of common stock and pre-funded warrants to purchase up to 925,925 shares of common stock. As part of the underwritten public offering, on February 3, 2022, the Company issued an additional 750,000 shares of common stock representing the underwriters’ full exercise of their over-allotment option. The shares of common stock and the pre-funded warrants were offered by the Company at a price to the public of $27.00 and $26.999 per share, respectively. The aggregate net proceeds received by the Company from the offering were $145.3 million, net of underwriting discounts and commissions and offering expenses of $9.9 million.

At-The-Market Common Stock Offering

The Company filed prospectus supplements pursuant to which it can issue and sell an aggregate of up to $150.0 million of its common stock from time to time in At-The-Market (ATM) offerings. There were no ATM sales during the three months ended March 31, 2022. During the three months ended March 31, 2021, the Company sold 1,149,820 shares under the ATM program for net proceeds of $19.6 million, net of commissions and offering expenses. As of March 31, 2022, there was $59.6 million remaining available under the ATM program.

Common Stock Reserved for Issuance

The Company is required to reserve and keep available out of its authorized but unissued shares of common stock a number of shares sufficient to effect the conversion of all outstanding options granted and available for grant under the incentive plans, shares reserved for issuance under the employee stock purchase plan and issued warrants.

	March 31, 2022		December 31, 2021
Shares reserved under Series A warrant		7,771,951		7,790,879
Shares reserved under Series B warrant		212,477		2,524,732
Shares reserved for future option grants under equity plans		1,452,859		1,207,827
Outstanding stock options under equity incentive plans		5,466,822		4,937,189
Pre-funded warrants for common stock		925,925		—
Outstanding warrants		1,839		727,122
Shares reserved under the 2015 employee stock purchase plan		17,500		17,500
Total common stock reserved for issuance		15,849,373		17,205,249

Common Stock Warrants

In connection with the Company’s January 2022 public offering, the Company issued pre-funded warrants to purchase up to 925,925 shares of common stock. There were no pre-funded warrants exercised during the three months ended March 31, 2022.

In connection with the Company’s November 2019 public offering, the Company issued Series A warrants to purchase up to 7,802,241 shares of common stock at an exercise price equal to $13.20, and Series B warrants to purchase up to 2,574,727 shares of common stock at an exercise price equal to $13.20. The Series A warrants will expire five years from the date they first became exercisable or on January 22, 2025 and contain a cash and/or cashless exercise provision. During the three months ended March 31, 2022, the Company issued 2,312,257 shares of common stock for the exercise of Series B warrants and  18,937 shares of common stock for the exercise of Series A warrants for proceeds of $30.5 million and $0.2 million, respectively. During the three months ended March 31, 2021, the Company issued 49,995 shares of common stock for the exercise of Series B warrants for proceeds of $0.7 million. See Note 12 for information pertaining to the exercise of Series A and Series B warrants subsequent to March 31, 2022.

On September 8, 2021, the Company entered into Amendment No. 1 to Series A warrants and Amendment No. 1 to Series B warrants. These amendments clarified the methodology by which Series A warrants and Series B warrants would be assumed or settled in the event of a Fundamental Transaction, as defined under the warrant agreements, and provided for greater consistency in the treatment of these warrants by a publicly-traded or private buyer. The amendments did not result in changes to the fair value of these warrants. As such, no expense was recorded during 2021 relating to the modifications to the warrants.

In connection with obligations under the amendment to the Asset Purchase Agreement (See Note 8), on January 31, 2020, the Company issued to Gilead 725,283 shares of the Company’s common stock and a warrant to purchase 725,283 shares of common stock at a price per share of $13.20. During the three months ended March 31, 2022, the warrant was fully exercised in cash by Gilead. Accordingly, the Company issued  725,283 shares of common stock for proceeds of $9.6 million.

In August 2018, in connection with a Loan and Security Agreement (Loan Agreement) with Silicon Valley Bank (SVB), the Company issued a warrant to SVB to purchase 1,839 of the Company’s common stock at a price per share of $74.80. The warrant is immediately exercisable, will expire on August 21, 2028 and contains a cashless exercise provision.