nsGSLs on tumors impair anti-tumor immune responses by OT-I T cells in vitro and support tumor growth in vivo

Tumors often evolve to engage numerous strategies to circumvent detection by the immune system. Our group recently discovered elevated neolacto-series glycosphingolipids (nsGSL) surface levels as a possible immune evasion mechanism of tumors. We demonstrated a direct disruption of both innate and adaptive anti-tumor immunity in vitro when expression of nsGSLs was upregulated on established target cells. It remains unclear however, whether in vivo nsGSLs play an active role in tumor development and can aid tumors in evading immune responses. To investigate whether nsGSLs facilitate tumor progression in vivo, we first established a murine model system using MC38-OVA cell lines with varying cell surface levels of nsGSLs. In vitro analysis revealed reduced MHC-I accessibility on tumor cells with elevated nsGSLs profiles, leading to diminished activation of OVA-specific OT-I T cells as evidenced by decreased expression of CD25, CD69, and production of IFN{gamma}, which subsequently resulted in decreased tumor cell death. Subsequent in vivo experiments investigating tumor outgrowth after engraftment of subcutaneously injected MC38-OVA cell lines with low or high cell surface levels of nsGSLs demonstrated better growth of nsGSL-rich tumor cells compared to nsGSL-poor tumors which could be controlled. Together these results suggest that nsGSLs expressed by tumors can facilitate immune evasion and subsequent tumor progression. These data pave the way to explore whether targeting of the GSL pathway with specific inhibitors could be advantageous as a therapy against tumors with high nsGSL levels.