While immunotherapies have had a striking efficacy in melanoma patients, significant proportions of melanoma patients exhibit poor responsiveness to immunotherapies. Further understanding of immunoregulatory mechanisms is needed to improve immunotherapies. Previously, we discovered increasing tumor fucosylation in melanomas reduces tumor growth and metastasis (Lau et al., 2015). To identify tumor-infiltrating lymphocytes (TILs) affected by L-fucose, we profiled lymphocytes from syngeneic tumors of control- or fucose-fed mice tumors. Dietary supplementation of L-fucose increased TILs by ~10-50-fold. Of total TILs, CD3+ T cells (including CD4+ and CD8+ T cells) doubled. L-fucose did not trigger tumor suppression in immune-deficient mouse melanoma models, indicating the immune system’s requirement for L-fucose-triggered suppression. Immunodepletion of CD4+ or CD8+ T cells during L-fucose treatment revealed that CD4+ T cells are crucial for tumor suppression. CD4+ T-cell depletion abrogated infiltration of NK, dendritic, and CD8+ T cells in the tumors, implicating these populations as downstream effectors of fucosylation- and CD4+ T cell-triggered tumor suppression. To identify proteins on melanomas contributing to fucosylation-triggered immune responses, we performed mass spectrometric analysis of all fucosylated proteins in melanoma and identified 2 MHC proteins, HLA-A and HLA-DRB1, as fucosylated. Knockdown of HLA- DRB1 and HLA-A in vivo revealed HLA-DRB1 is required for L-fucose-mediated tumor suppression, and notably, for recruitment of CD4+ T cells. We further investigated how fucosylation affects CD4+ T-cell biology using CD4+ T cells isolated from healthy donors, which we pharmacologically modulated fucosylation. The roles of fucosylation on tumor vs. CD4+ T cells and clinical utility/implications for melanoma patients will be discussed. Our data show how increased fucosylation drives tumor suppression through CD4+ T cells, and support the potential of dietary L-fucose to boost immunity in melanomas.

Citation Format: Daniel K. Lester, Pasquale Innamarato, Krithika Kodumudi, Gregory Watson, Matt Mercurio, Shari Pilon-Thomas, Jane Messina, Susan McCarthy, Eric Lau. Fucosylation in CD4+ T cell-mediated melanoma suppression [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A73.