L-fucose-mediated enrichment of memory CD4+T cells and enhanced anti-melanoma immunity - The efficacy of current cancer immunotherapies is limited in terms of upfront responsiveness in subsets of treated patients and durability of responses. Significant efforts are being made to increase upfront responsiveness in more patients by combination therapies. However, enhancing the durability of responses continues to be a significant clinical challenge. The durability of responses to cancer immunotherapies is limited by the formation of immunological memory, and our understanding of immune cell biology is insufficient, lacking safe and effective ways to enhance T cells with memory phenotype. CD4+T cells play important roles in mediating anti-tumor immune responses, in terms of helper, cytotoxic, and importantly, memory functions. In particular, CD4+T subsets, such as central memory (cm) CD4+T cells, are well established for promoting immunological memory during pathological conditions such as infection or cancer. Low memory T cell populations are a major underlying reason for transient anti-tumor immunity and responses to immunotherapies. Efforts aimed at specifically increasing memory CD4+T cell populations include adoptive cell transfer, which involves ex vivo sorting of intratumoral memory T cells followed by reinfusion into the patient. However, this approach is limited by baseline paucity of intratumoral T cells. Safe and effective ways to increase abundance, fitness, and activity of memory CD4+T cells are lacking and represent an urgent unmet clinical need. We recently discovered that oral administration of the dietary sugar L-fucose (L-fuc) to melanoma-bearing mice increases intratumoral immune cells that suppress tumor growth (Lester et al. 2023 Nature Cancer). We delineated a key mechanism underlying this immune-mediated anti-tumor activity: oral L-fuc increases fucosylation of the tumor-expressed MHC-II protein HLA-DRB1, promoting its cell surface accumulation and triggering CD4+T cell-mediated increases in intratumoral immune cells and tumor suppression. Notably, oral L- fuc alters intratumoral CD4+T cell profiles, specifically increasing cmCD4+T cell populations that are required for tumor suppression. In eliciting these effects, when combined with the immune checkpoint blockade agent anti- PD1, L-fuc enhances the efficacy and durability of anti-PD1-mediated tumor suppression. Our data indicate that L-fuc stimulates potent anti-tumor immunity by increasing intratumoral cmCD4+T cell populations. We propose to test our hypothesis that L-fuc and fucosylation alters signaling in CD4+T cells, skewing intratumoral subpopulations toward cmCD4+T cells and promoting durable anti-tumor immune memory and responses. In this project, we will delineate how L-fuc alters the biology of CD4+T cells to increase the development and expansion of cmCD4+T cells by single-cell RNA sequencing. We will further determine if L-fuc indeed enhances immunological memory and blocks tumor recurrence in vivo.
