recognized from MorphoSys, royalty revenue from Alexion, and licensing revenue from Aimmune and Gilead.
Research and development expenditures for the first quarter ended March 31, 2021 were $41.4 million, compared to $33.9 million for the same period in 2020. Additional spending on research and development expenses for the first quarter of 2021 was primarily due to increased spending on XmAb306, XmAb564 and XmAb819 programs.
General and administrative expenses for the first quarter ended March 31, 2021 were $8.2 million, compared to $7.2 million in the same period in 2020. Additional spending on general and administrative expenses for the first quarter of 2021 reflects increased spending related to staffing.
Other income for the first quarter ended March 31, 2021 was $13.2 million and included a gain of $12.9 million from equity related to a licensing transaction, compared to $0.7 million for the same period in 2020, which was primarily net interest income earned for the period.
Non-cash, stock-based compensation expense for the first quarter ended March 31, 2021 was $8.3 million, compared to $6.5 million for same period in 2020.
Net loss for the first quarter ended March 31, 2021 was $2.5 million, or $(0.04) on a fully diluted per share basis, compared to net loss of $8.1 million, or $(0.14) on a fully diluted per share basis, for the same period in 2020. The lower net loss reported for first quarter of 2021 compared to the net loss for the same period in 2020 is primarily due to other income recognized related to equity received in the first quarter of 2021 in excess of increased spending on research and development.
The total shares outstanding were 58,221,953 as of March 31, 2021, compared to 57,001,253 as of March 31, 2020.
Financial Guidance
Based on current operating plans, Xencor expects to have cash to fund research and development programs and operations into 2024. Xencor expects to end 2021 with between $425 million and $475 million in cash, cash equivalents and marketable securities.
Conference Call and Webcast
Xencor will host a conference call today at 4:30 p.m. ET (1:30 p.m. PT) to discuss these first quarter 2021 financial results and provide a corporate update.
The live call may be accessed by dialing (877) 359-9508 for domestic callers or +1 (224) 357-2393 for international callers and referencing conference ID number 2378094. A live webcast of the conference call will be available online from the Investors section of Xencor's website at www.xencor.com. The webcast will be archived on Xencor's website for 30 days.
About Xencor, Inc.
Xencor is a clinical-stage biopharmaceutical company developing engineered monoclonal antibodies and cytokines for the treatment of cancer and autoimmune diseases. Currently, 21 candidates engineered with Xencor's XmAb® technology are in clinical development internally and with partners. Xencor's XmAb antibody engineering technology enables small changes to the structure of proteins resulting in new mechanisms of therapeutic action. For more information, please visit www.xencor.com.
Forward-Looking Statements
Certain statements contained in this press release may constitute forward-looking statements within the meaning of applicable securities laws. Forward-looking statements include statements that are not purely statements of historical fact, and can generally be identified by the use of words such as “potential,” “can,”