We constructed the prediction model for antigens presented on MHC molecules by using the dataset of RNAseq and MHC peptidome. We compared dataset of mouse bladder cancer MB49, cisplatin-resistant MB49-CR, and lymphoma RMA cell lines, all of which are refractory to ICI, with datasets of 26 normal mouse tissues. Subsequently tumor-specific antigens, such as tumor-associated antigen (TAA) and neoantigen, presented on MHC-I and -II molecules were identified by this prediction algorithms. MB49, MB49-CR, or RMA bearing mice were treated with these antigen vaccine and ICI. Finally, we investigated tumor-infiltrating immune cells by flow cytometry, T cell receptor (TCR) repertoire analysis, RNA-seq of inoculated tumors.
50-80% of mice pre-immunized with identified antigens rejected MB49 and RMA inoculated s.c. and those immunized mice also rejected re-transplanted tumors. Furthermore, combination therapy of cancer antigen vaccine and ICI synergistically inhibited tumor-growths of MB49-CR, MB49 and RMA indicating that the combination immunotherapy enhances therapeutic efficacy to treat refractory cancers. We also observed the combination therapy with MHC-I antigen vaccine and ICI synergistically increased limited CD8+ TCR genes in tumors, suggesting increased antigen-specific tumor-infiltrating CD8+ T cells. Furthermore, combination therapy with MHC-I/II antigen vaccine and ICI synergistically induced drastic changes of various types of tumor-infiltrating immune cells such as CD8+ T cells, CD4+ type 1 helper T cells, natural killer cells, regulatory CD4+ T cells and MDSCs.
