Stockholders' Equity

Common Stock

The following shares were reserved for future issuance:



	December 31, 2018
Common stock options outstanding and available for future grant	5,574,901
Warrants to purchase common stock	11,817,912
Employee Stock Purchase Plan	157,360
	17,550,173

Sale of Common Stock

In June 2018, the Company sold 3,162,500 shares of its common stock at a public offering price of $38.85 per share and sold warrants to purchase up to 421,650 shares of its common stock at a public offering price of $38.849 per warrant. After deducting underwriter discounts and offering expenses, the Company received net proceeds from the transaction of $130.7 million. These warrants were recorded as a component of stockholders’ equity within additional paid-in capital. Per their terms, the outstanding warrants to purchase shares of common stock may not be exercised if certain holders' ownership of the Company’s common stock would exceed 9.99 percent for certain holders, and 19.99 percent for other holders, following such exercise.

In November 2017, the Company sold 2,938,986 shares of its common stock at a public offering price of $13.00 per share and sold warrants to purchase up to 4,137,999 shares of its common stock at a public offering price of $12.999 per warrant share. After deducting underwriter discounts and offering expenses, the Company received net proceeds from the transaction of $86.7 million. In January 2017, the Company sold 5,002,702 shares of its common stock at a public offering price of $5.60 per share and sold warrants to purchase up to 7,258,263 shares of its common stock at a public offering price of $5.599 per warrant share. After deducting underwriter discounts and offering expenses, the Company received net proceeds from the transaction of $66.8 million. In all cases, the public offering price for the warrants was equal to the public offering price of the common stock, less the $0.001 per share exercise price of each warrant. These warrants were recorded as a component of stockholders’ equity within additional paid-in capital. Per their terms, the outstanding warrants to purchase shares of common stock may not be exercised if the holder’s ownership of the Company’s common stock would exceed 9.99 percent for certain holders, and 19.99 percent for other holders, following such exercise.

Warrants

As of December 31, 2018, the following warrants for common stock were issued and outstanding:



Issue date	Expiration date	Exercise price		Number of warrants outstanding
January 11, 2017	None	$	0.001	7,258,263
November 20, 2017	None	$	0.001	4,137,999
June 11, 2018	None	$	0.001	421,650
				11,817,912

During the year ended December 31, 2018, no warrants were exercised.

During the year ended December 31, 2017, warrants for 52,825 shares of the Company's common stock were exercised via cashless exercises and 585,729 shares were exercised for cash, generating proceeds of $4.6 million and resulting in the issuance of 638,554 shares of common stock.

During the year ended December 31, 2016, warrants for 289,789 shares of the Company's common stock were exercised via cashless exercises and 313,756 shares were exercised for cash, generating proceeds of $2.1 million and resulting in the issuance of 603,545 shares of common stock.