Abstract 1840: Methylmalonic acid accumulation suppresses CD8+ T cell activation and contributes to age-induced immunosuppression

Abstract Deregulation of cytotoxic CD8+ T cells is a feature of the aging process with important consequences for anti-tumor immunity and consequently affects tumor initiation, progression, and response to immunotherapies. However, our understanding of how the aging process affects CD8+ T cells remains incomplete. Vitamin B12 deficiency is also a feature of old age caused by a well-recognized decrease in vitamin absorption. Interestingly, clinical studies have reported a significant decline in CD8+ T cells in individuals with vitamin B12 deficiency, suggesting that vitamin B12 levels might be a mechanistic link between aging and deregulation of CD8+ T cells. An important and often overlooked consequence of vitamin B12 deficiency is an elevation of methylmalonic acid (MMA) in circulation. Our laboratory has previously established a critical role for age-induced MMA in promoting progression into metastatic disease of breast and lung cancers, which coincided with a robust immunosuppressive signature. Here, we demonstrate that exposure of CD8+ T cells to MMA or culture of CD8+ T cells in the absence of vitamin B12 reduces T cell activation, thereby decreasing T cell numbers and effector function. Conversely, supplementation of vitamin B12 on CD8+ T cells isolated from old mice enhances their ability to activate and increases T cell numbers. Evaluation of the effects of MMA on the CD8+ T cells metabolome revealed a decrease in antioxidant levels, including a pronounced reduction in vitamin C and reduced glutathione, which were accompanied by an increase in both superoxide and hydrogen peroxide, suggesting that an increase in reactive oxygen species might be the link between MMA and CD8+ T cell dysfunction. Together, these results put forward the idea that MMA is an important regulator of immune cell function and that supplementation of vitamin B12 in older people and individuals diagnosed with vitamin B12 deficiency may function as an important strategy to improve immune cytotoxic responses and thereby increase anti-cancer immunosurveillance and the effectiveness of certain immunotherapies. Citation Format: Joanne D. Tejero, Stanislav Drapela, Juan Fernandez-Garcia, Sarah-Maria Fendt, Didem Ilter, Ana P. Gomes. Methylmalonic acid accumulation suppresses CD8+ T cell activation and contributes to age-induced immunosuppression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1840.