June 30, 2019, respectively. The decrease in the six month ended June 30, 2020 was due to the drop in interest rates in the US. Interest income represents interest from cash and cash equivalents held in US dollars resulting from the proceeds from the issuance of Series D Preferred Stock, our IPO, and payments received under our collaboration with Gilead. During the three and six months ended June 30, 2020 our cash, cash equivalents and restricted cash were mainly held in dollars at US investment grade financial institutions or in money market funds. In addition smaller amounts were held in euros at our Austrian subsidiary which produced no material interest income due the low or zero interest rate policy in the European Monetary Union.
Interest expenses for loans from government agencies were $0.2 million for both the three months ended June 30, 2020 and 2019 and $0.4 million for both the six months ended June 30, 2020 and 2019. Interest expense was recorded at the market rate of interest, which exceeded the contractual interest.
Other Income and Expenses
In April 2020, we applied for support under the Corona Short-term Work Program in Austria to mitigate the financial impact of the COVID 19 pandemic. In the three months ended June 30, 2020, we recognized $0.2 million in other operating income from non-refundable subsidies under this support program.
Liquidity and Capital Resources
Since our inception in 2011, we have funded our operations primarily through private placements of our convertible preferred stock and proceeds from our IPO, from grants, research incentives and borrowings under various agreements with public funding agencies, from an upfront payment, milestone payments and reimbursement of research and development expenses pursuant to the Collaboration Agreement with Gilead.
We have raised gross proceeds of approximately $142.5 million from the issuance of our convertible preferred stock and $21.0 million from non-refundable upfront and milestone payments pursuant to the Collaboration Agreement with Gilead. On April 23, 2019, we completed our IPO by issuing 6.0 million shares of our common stock, at $14.00 per share, for gross proceeds of $84.0 million, or net proceeds of $74.6 million. As of June 30, 2020, the principal amount outstanding under loans from government agencies was $6.0 million and we had cash, cash equivalents and restricted cash of $93.3 million.
We have entered into various funding agreements with the FFG. The loans by FFG, or the FFG Loans, were made on a project-by-project basis and bear interest at rates ranging from 0.75% to 1.0% per annum. In the event that the underlying program research results in a scientific or technical failure, the principal then outstanding under any loan may be forgiven by FFG and converted to non-repayable grant funding on a project-by-project basis. The FFG Loans contain no financial covenants and are not secured by any of our assets.
Because the FFG Loans bear interest at below market rates we account for the imputed benefit arising from the difference between an estimated market rate of interest and the contractual interest rate as grant funding from FFG, which is included in grant income. On the date that FFG Loan proceeds are received, we recognize the portion of the loan proceeds allocated to grant funding as a discount to the carrying value of the loan and as unearned income. As of June 30, 2020, the unamortized debt discount related to FFG Loans was $2.2 million.
We do not expect positive cash flows from operations in the foreseeable future, if at all. Historically, we have incurred operating losses as a result of ongoing efforts to develop our arenavirus technology platform and our product candidates, including conducting ongoing research and development, preclinical studies, clinical trials, providing general and administrative support for these operations and developing our intellectual property portfolio. We expect to continue to incur net operating losses for at least the next several years as we progress clinical development, seek regulatory approval, prepare for and, if approved, proceed to commercialization of our most advanced product candidates HB-101, HB-201 and HB-202, continue our research and development efforts relating to our other and future product candidates, and invest in our manufacturing capabilities and our own manufacturing facility.