Immunotherapies targeting neoantigens are effective in PD-1 blockade-resistant tumors.

Only a small fraction of tumor-infiltrating lymphocytes can specifically recognize and attack cancer cells in PD-1/PD-L1 blockade therapy. Here, we investigate approaches to expand the neoantigen-specific CD8 T cells to overcome the difficulties in treating PD-1/PD-L1 blockade-resistant tumors. Mutation-associated neoepitopes of murine nonsmall cell lung cancer ASB-XIV were estimated by whole-exome and RNA sequencing and predicted by MHC-I binding affinity (FPKM >1) in silico. Using ASB-XIV-specific CD8 T cells, we screened a panel of 257 neoepitope peptides derived from ASB-XIV missense and indel mutations. Mutated Phf3 peptide (mPhf3) was successfully identified as an immunogenic neoepitope. Prophylactic mPhf3-DC vaccination inhibited ASB-XIV tumor growth through CD8 T cell-mediated antitumor immunity. Combining the mPhf3-DC vaccine and anti-PD-1 treatment elicited robust antitumor activity through the induction of mPhf3-specific CD8 T cells in the tumor microenvironment. Furthermore, the adoptive transfer of mPhf3-specific CD8 T cells eradicated ASB-XIV tumors. Likewise, the combination of mutated Cdt1 peptide (mCdt1)-DC vaccine and anti-PD-1 treatment or adoptive transfer of mCdt1-specific CD8 T cells also led to significant regression of PD-1 blockade-resistant murine gastric YTN16 tumors. In conclusion, a novel immunogenic neoepitope of ASB-XIV was identified for immunotherapy targeting neoantigens. Identification of immunogenic neoantigens can extend the therapeutic strategies by increasing the frequency of neoantigen-specific T cells, even for PD-1/PD-L1 blockade-resistant tumors.