officers, employees and agents against any liability, whether or not we would have the power to indemnify such person against such liability under the DGCL or the bylaws.
We have entered into indemnification agreements with each of our directors and our executive officers. These agreements will provide that we will indemnify each of our directors and such officers to the fullest extent permitted by law and our certificate of incorporation.
We also maintain a general liability insurance policy which covers certain liabilities of directors and officers of our company arising out of claims based on acts or omissions in their capacities as directors or officers.
In any underwriting agreement we will enter into in connection with the sale of the common stock being registered hereby, the underwriters will agree to indemnify, under certain conditions, us, our directors, our officers and persons who control us within the meaning of the Securities Act, against certain liabilities.
Item 15. Recent Sales of Unregistered Securities
Since December 31, 2015, we have issued the following unregistered securities:
Preferred Stock Issuances
In April 2016, we sold an aggregate of 13,586,946 shares of our Series E preferred stock to 23 accredited investors at a purchase price of $2.944 per share, for an aggregate purchase price of $40.0 million.
In May 2017, we sold an aggregate of 12,956,724 shares of our Series F preferred stock to two accredited investors at a purchase price of $3.859 per share, for an aggregate purchase price of $50.0 million.
In June 2018, we issued an aggregate of 3,065,259 shares of Series G preferred stock to 15 accredited investors, upon conversion of convertible notes at a purchase price of $4.7565 for an aggregate purchase price of $14.6 million. In June and July 2018, we sold an aggregate of 18,921,474 shares of Series G preferred stock to six accredited investors at a purchase price of $5.2850 for an aggregate purchase price of $100.0 million.
In March 2019, we sold an aggregate of 10,182,111 shares of our Series H preferred stock to 15 accredited investors at a purchase price of $6.8748 per share, for an aggregate purchase price of $70.0 million.
The preferred stock issuances described above were exempt from registration under the Securities Act (or Regulation D promulgated thereunder) by virtue of Section 4(a)(2) of the Securities Act as transactions by an issuer not involving a public offering. The recipients of the securities in each of these transactions represented their intentions to acquire the securities for investment only and not with a view to or for sale in connection with any distribution thereof, and appropriate legends were placed upon the stock certificates issued in these transactions. All recipients had adequate access, through their relationships with us, to information about us. The sales of these securities were made without any general solicitation or advertising.
Warrant Issuances
In September 2016, we issued a warrant to purchase 25,597 shares of our Series E preferred stock to Pacific Western Bank in connection with an increase to the outstanding principal under the existing loan and security agreement, as amended, with Square 1 Bank, a division of Pacific Western Bank, at an exercise price of $2.93 per share. The warrant has not been exercised.
In August 2017, we issued a warrant to purchase 45,833 shares of our common stock to an accredited investor in connection with an executive search consulting agreement at an exercise price of $1.34 per share. The warrant has been exercised in full.
II-3