On March 11, 2020, we sold 16,000,000 shares of our common stock in an underwritten offering pursuant to the 2018 Shelf Registration at a public offering price of $7.89 per share, resulting in net proceeds of $118.2 million, after underwriting discounts, commissions, and offering expenses. In addition, the underwriters of the offering were granted the option for a period of 30 days to purchase up to an additional 2,400,000 shares of common stock offered in the public offering at the public offering price, less underwriting discounts, commissions and offering expenses. On April 3, 2020, the underwriters exercised their option and purchased an additional 979,371 shares of common stock at $7.89 per share, resulting in net proceeds to us of $7.2 million, after underwriting discounts, commissions, and offering expenses. The total number of shares sold by us in the offering was 16,979,371, resulting in total net proceeds to us, after underwriting discounts, commissions and offering expenses, of $125.4 million.
Under the 2018 Shelf Registration, we have issued an aggregate of 30,549,976 shares of common stock, including under the ATM Offering, resulting in aggregate gross proceeds to us of $231.7 million. There was $18.3 million of securities available to be issued under the 2018 Shelf Registration as of June 30, 2021.
On May 7, 2020, we filed our shelf registration statement on Form S-3 that was declared effective by the SEC on May 7, 2020, or the 2020 Shelf Registration, under which we may offer and sell up to $350.0 million of a variety of securities including common stock, preferred stock, warrants, depositary shares, debt securities or units during the three-year period that commenced upon the 2020 Shelf Registration becoming effective. In connection with the filing of the 2020 Shelf Registration, we entered into an amended and restated sales agreement with Jefferies, pursuant to which we may issue and sell, from time to time, up to an aggregate of $75.0 million of our common stock under our ATM Offering. During the fourth quarter of 2020, we issued an aggregate of 2,821,059 shares of our common stock under the ATM Offering, resulting in net proceeds to us of $20.6 million. In the three and six months ended June 30, 2021, we issued and sold an additional 837,257 and 5,583,329 shares of our common stock under our ATM Offering, respectively, resulting in net proceeds to us of $6.0 million and $40.7 million, respectively. As of June 30, 2021, there was $11.9 million of shares of common stock remaining under the ATM Offering that we may issue and sell in the future and, excluding the shares of common stock that may be offered under our ATM Offering, there was $275.0 million of securities available to be issued under the 2020 Shelf Registration.
On May 4, 2021, we entered into the Loan Agreement with Oxford Finance, in its capacity as lender, or the Lender, and in its capacity as collateral agent (in such capacity, the “Agent”), pursuant to which a term loan of up to an aggregate principal amount of $125.0 million is available to us, consisting of (i) a tranche A term loan that was disbursed on the closing date of the Loan Agreement in the aggregate principal amount of $80.0 million; (ii) a contingent tranche B term loan in the aggregate principal amount of $20.0 million available to us through June 30, 2023 and within 90 days of our achieving trailing 6-month product revenue equal to or greater than $75.0 million, subject to certain other terms and conditions; and (iii) a contingent tranche C term loan in the aggregate principal amount of $25.0 million available to us through December 31, 2023 and within 90 days of our achieving trailing 6-month product revenue equal to or greater than $100 million, subject to certain other terms and conditions. The term loans bear interest at a floating rate equal to the greater of 30-day LIBOR and 0.11%, plus 7.89%. Certain of the customary negative covenants limit our and certain of our subsidiaries’ ability, among other things, to incur future debt, grant liens, make investments, make acquisitions, distribute dividends, make certain restricted payments and sell assets, subject in each case to certain exceptions. The Loan Agreement provides for interest-only payments until December 1, 2024 if neither the tranche B term loan nor the tranche C term loan are made, and until June 1, 2025 if either the tranche B term loan or the tranche C term loan is made, or the Amortization Date. The aggregate outstanding principal balance of the term loans are required to be repaid in monthly installments starting on the Amortization Date based on a repayment schedule equal to (i) 18 months if neither the tranche B term loan nor the tranche C term loan is made and (ii) 12 months if either the tranche B term loan or the tranche C term loan is made. All unpaid principal and accrued and unpaid interest with respect to each term loan is due and payable in full on May 1, 2026, or the Maturity Date.
We paid a facility fee of $400,000 on the closing date of the Loan Agreement and have agreed to pay a facility fee of $100,000 upon closing of the tranche B term loan and a $125,000 facility fee upon the closing of the tranche C term loan. We will be required to make a final payment fee of 7.00% of the original principal amount of any funded term loan payable on the earlier of (i) the prepayment of the term loan in full or (ii) the Maturity Date. At our option, the we may elect to prepay all, but not less than all, of the outstanding loans, subject to a prepayment fee equal to the following percentage of the principal amount being prepaid: 3.00% if an advance is prepaid during the first 12 months following