Abstract A021: The role of MGAT5 in sex-dependent regulation of CD8+ T cells in muscle-invasive bladder cancer

Abstract Biological sex significantly affects bladder cancer incidence and outcome. Although men have much greater incidence of bladder cancer than women, females tend to be diagnosed with more advanced tumors and have worse outcomes. The mechanisms driving these differences are likely multifactorial, with biological factors playing an important role, however, much of the biology underlying these differences is unknown. The immune system is a critical regulator of cancer biology, and immune features have been associated with bladder cancer grade, stage, progression, and response to therapies. Sex dramatically affects the immune system including anti-tumor immunity. However, how sex and immunity intersect to affect clinical outcomes in bladder cancer patients remains unclear. CD8+ T cells are a key part of anti-tumor immune responses and the importance of inhibitory receptors such as programmed cell death-1 (PD-1), is now well established as a mechanism restricting T cell responses in MIBC. However, there are a variety of other regulatory pathways that restrict their anti-tumor function, which have yet to be investigated. One such pathway involves alterations in protein glycosylation, which can affect T cell function at many levels. The activity of the glycosyltransferase N-acetylglucosaminyltransferase V (MGAT5), responsible for complex N-glycan branching, has been shown to regulate T cell function in autoimmunity and chronic viral infections, however, its role in regulating anti-tumor CD8+ T cell responses has yet to be explored. We assessed the activity of MGAT5 in circulating and tumor-infiltrating CD8+ T cells in mice using a panel of cell lines in a syngeneic orthotopic model of muscle-invasive bladder cancer (MIBC). We found that in all tumor models, MGAT5 activity was upregulated in tumor infiltrating CD8+ T cells compared with circulating cells. Furthermore, using high parameter flow cytometry, we assessed the activity of MGAT5 in CD8+ T cells from mice with bladder cancer induced by the carcinogen N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN), and in patients with MIBC. In both mice and humans, we found that sex affects MGAT5 activity in memory CD8+ T cells, with females exhibiting decreased MGAT5 activity in these cells compared to males. The functional significance of altering MGAT5 activity in T cells was also assessed in vivo. To do this, chimeric mice were generated by mixed bone-marrow transplant resulting in mice with loss of Mgat5 in T cells. Bladder cancer was then induced using BBN, and morbidity (defined as either 10% weight loss in one week, 10% weight loss post-BBN, or humane endpoint), as a proxy for mortality, was assessed over time. In this model, male mice were protected from BBN-induced morbidity compared to female mice, and this protection was abrogated by homozygous or heterozygous loss of Mgat5 in T cells. Overall, our data suggest that sex-dependent regulation of MGAT5 activity in CD8+ T cells may be an important underlying factor affecting outcomes in bladder cancer. Citation Format: Morgan E. Roberts, Igor Moskalev, Peter C. Black. The role of MGAT5 in sex-dependent regulation of CD8+ T cells in muscle-invasive bladder cancer [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2024 May 17-20; Charlotte, NC. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(10_Suppl):Abstract nr A021.