MHC II-restricted neoantigen vaccine reverses immune microenvironment and overcomes resistance to immune checkpoint inhibitors in cold tumors

Cold tumors are resistant to immune checkpoint inhibitors (ICIs) due to their poor T cell infiltration and immunosuppressive tumor microenvironment (TME). While the role of CD4+ T cell response in anti-tumor immunity has been emphasized, it remains unclear whether the MHC II-restricted neoantigen vaccines targeting CD4+ T cell can reverse the immune microenvironment and overcome resistance to ICIs. Here we observed an enrichment of immune inflammation-related signaling pathways in TME following administration of MHC II-restricted neoantigen vaccines, indicating their potent role in reversing immunosuppressive TME. An increase in the tumor infiltration of CD4+ T cells and CD8+ T cells, an enhancement of their effector functions, and a tendency towards exhaustion were observed, providing prerequisites for the effectiveness of ICI treatment. Furthermore, NicheNet analysis indicated an enrichment of the inhibitory immune checkpoint signaling axis PVR-TIGIT following vaccination. The combination of the vaccines and TIGIT blockade exhibited synergistic anti-tumor efficacy. Mechanistically, the combination therapy promoted the differentiation of CD8+ T cells into effector memory phenotypes while delaying their exhaustion. Our study demonstrates that MHC II-restricted neoantigen vaccines can remodel the inhibitory TME with insufficient T cell infiltration and synergistically inhibit tumor growth with TIGIT antibody, providing a novel strategy for treating cold tumors. Overall design: B16F10 tumor bearing mice were subcutaneously injected with two doses of saline, M44 vaccine (50 µg M44 peptide formulated with 20 µg CpG) or M44 vaccine and TIGIT antibody on day 2 and 8, and tumors were collected by euthanizing on day 10. CD45 (TIL) MicroBeads (Miltenyi Biotec, #130-110-618, DE) were used for isolating the CD45+ immune cells for scRNA-seq (n=6 mice per group, mixed sample detection).