5. Equity

July 2020 Stock Issuances

In July 2020, pursuant to the 2019 ATM Agreement, the Company issued 1,301,126 shares of common stock at an average price of $1.47 per share through the ATM Prospectus Supplement. The Company received total proceeds of $1.9 million, net of $0.1 million in transaction expenses. Previously, in April 2020, pursuant to the 2019 ATM Agreement, the Company issued 7,170,964 shares of common stock at an average price of $1.44 per share through the ATM Prospectus Supplement. The Company received total proceeds of $10.3 million, net of $0.3 million in transaction expenses.

February 2020 Stock Offering

In February 2020, the Company entered into subscription agreements with certain institutional investors for the sale by the Company of 7,500,000 shares of its common stock and warrants to purchase 5,625,000 shares of common stock at a combined public offering price of $0.80 per share and related warrant. The Company received total proceeds of $6.0 million, net of $0.7 million in transaction expenses. See Note 4 - Warrants for equity classified warrants granted during the nine months ended September 30, 2020.

Stock-based Compensation and Outstanding Awards

Under the terms of the Company’s 2015 Stock Plan, as amended, and approved by its stockholders in  June 2020, 10.5 million shares of the Company’s common stock were available for grant to employees, non-employee directors and consultants. The 2015 Stock Plan provides for the grant of stock options, stock awards, stock unit awards, or stock appreciation rights. As of September 30, 2020, there were 4,409,132 shares remaining to be issued under the 2015 Stock Plan.

Stock-based compensation for the three and nine months ended September 30, 2020 and 2019, respectively (in thousands):

Each of the Company's stock-based compensation arrangements are discussed below.

Stock Options

Stock option awards are generally granted with an exercise price equal to the market price of the Company’s stock at the date of grant. Stock option awards generally have a 10-year contractual term and vest over a 4-year period for employees and over a 1 to 3-year period for directors from the grant date on a straight-line basis over the requisite service period. The grant-date fair value of stock options is determined using the Black-Scholes option-pricing model. Additionally, the Company’s stock options provide for full vesting of unvested outstanding options, in the event of a change of control of the Company.

The fair value of each stock option is estimated on the date of grant using the Black-Scholes option valuation model that uses the assumptions noted below. The expected term of the stock option awards was computed using the “plain vanilla” method as prescribed by the Securities and Exchange Commission Staff Accounting Bulletin 107 because the Company does not have sufficient data regarding employee exercise behavior to estimate the expected term. Beginning in 2020, the Company used the volatility of its own stock in the BSM as it now has sufficient historic data in its stock price. Prior to 2020, the volatility was determined by referring to the average historical volatility of a peer group of public companies combined with its own due to the lack of sufficient historical data of its stock price. The risk-free rate for periods within the contractual life of the option is based on the U.S. Treasury yield curve in effect at the time of grant.

The fair value of the option grants has been estimated, with the following weighted-average assumptions:

Stock option activity for the nine months ended September 30, 2020 is as follows:

Options granted during 2020 have an aggregated fair value of $1.3 million that was calculated using the Black-Scholes option-pricing model. At September 30, 2020, total compensation cost not yet recognized was $3.0 million and the weighted average period over which this amount is expected to be recognized is 2.65 years. The aggregate fair value of options vesting in the nine months ended September 30, 2020 and 2019, respectively, was $1.2 million and $1.0 million, respectively. In July 2020, the Company granted 1,349,750 employee stock options. In August 2020, the Company issued 100,000 options to Dr. Waldemar Priebe, one of the Company's founders and chair of our Scientific Advisory Board. In October 2020, the Company granted 40,000 stock options, with 3-year annual vesting upon appointment of Elizabeth Cermak to the Company's Board of Director's.

Restricted Stock

Restricted stock units are granted with a grant date fair value determined using the closing price of the Company's common stock on the grant date. Restricted stock units vest annually in four equal installments. Additionally, the Company’s restricted stock unit agreements provide for full vesting of the restricted stock award in the event of a change of control of the Company.

Restricted stock unit activity for the nine months ended September 30, 2020 is as follows:

 As of September 30, 2020, total compensation cost not yet recognized was $0.6 million and the weighted average period over which this amount is expected to be recognized is 3.3 years.