future commercialization efforts. To meet our capital needs, we are considering multiple alternatives, including, but not limited to, additional equity financings, which include sales of our common stock under at-the-market offerings, if available, debt financings, partnerships, collaborations and other funding transactions. This is based on our current estimates, and we could use our available capital resources sooner than we currently expect. We will need to generate significant revenues to achieve profitability, and we may never do so. As of March 31, 2021, we had approximately $132.0 million in cash and cash equivalents and short-term investments.
Cash Flows
Operating activities. The use of cash in both periods resulted primarily from our net losses adjusted for non-cash charges and changes in components of working capital. Net cash used in operating activities during the three months ended March 31, 2021 was $4.8 million compared to $5.8 million during the same period in 2020. The decrease was primarily due to a increased net loss of $1.2 million, a decrease in change in fair value of common stock warrants of $1.0 million and deferred revenue of $0.4 million offset by an increase in stock based compensation expense of $1.9 million.
Investing activities. Net cash used in investing activities was $0.6 million during the three months ended March 31, 2021 compared to $0.05 million during the same period in 2020. The increase is from the net purchase of short-term investments of $0.2 million and lab equipment of $0.3 million.
Financing activities. Net cash provided by financing activities was $25.6 million during the three months ended March 31, 2021 compared to $17.6 million during the three months ended March 31, 2020. The increase was primarily due to net increased sales of our common stock through an at-the-market Common Stock Sales Agreement with B. Riley FBR, Inc. and Cantor Fitzgerald & Co. for $14.9 million, net of related stock issuance costs of $0.2 million, partially offset by a public offering of shares only occurring in 2020 of $6.6 million.
Current and Future Financing Needs
We have incurred an accumulated deficit of $138.2 million through March 31, 2021. We have incurred negative cash flows from operations since we started our business. We have spent, and expect to continue to spend, substantial amounts in connection with implementing our business strategy, including our planned product development efforts, our clinical trials, and our research and discovery efforts.
In order to promote efficiency and reduce our reliance on third-party vendors, we plan to enhance our in-house development of bioanalytic, process development and manufacturing capabilities and offer such services to third parties for fees. We have identified a 20,441 square foot facility in San Antonio, TX to conduct such services and are currently negotiating lease terms. Our proposed expansion in Texas is part of a company-wide-growth strategy to enhance efficiency and decrease our dependence on third-party vendors as we advance our clinical trials and general research and development. We estimate that the investment to build out the facility with labs, equipment, and staff will be approximately $26 million, without taking into account federal new market tax credits based on the location in San Antonio, federal and state historical tax credits based on the historical designation of the facility, and city and county tax abatement incentives which have been applied for with the City of San Antonio and Bexar County, respectively. We intend to fund this initiative with current working capital. The potential value of tax credits and tax incentives are estimated to be up to approximately $4.5 million based on the total cost of the build out, employees hired, real property, and other factors. Operations at the facility are projected to commence by second quarter of 2022, and we expect to fill production capacity by transitioning our outsourced manufacturing and development to in-house immediately and followed by contracting with external customers. However, there can be no assurance that we will be successful in these new operations. As of April 28, 2021 we have spent $1.8 million on laboratory related manufacturing equipment.
We intend to meet our financing needs through multiple alternatives, including, but not limited to, cash on hand, additional equity financings, debt financings and/or funding from partnerships or collaborations and potential revenue, if any, from our planned development and manufacturing facility.
However, the actual amount of funds we will need to operate is subject to many factors, some of which are beyond our control. These factors include the following: