Combination epigenetic-targeted therapy increases the immunogenicity of poorly immunogenic sarcomas

Immunotherapy approaches have shown limited efficacy in pediatric sarcomas, partly because these tumors have low mutation burden and few neoantigens. We sought to increase the immunogenicity of low mutation sarcomas by inducing expression of epigenetically silenced genes using the hypomethylating agent decitabine and histone deacetylase inhibitor entinostat. Using a mutated Kras-driven murine sarcoma model KP Sarc, sequential treatment with decitabine and entinostat significantly increased expression of silenced genes, including cancer testis antigens, and enhanced antigen presentation, including MHC I expression, compared with either agent alone. Vaccination with irradiated, epigenetically treated KP Sarc cells in a GM-CSF-secreting whole-cell vaccine induced T cell immunity against a matched tumor challenge. The anti-tumor response was directed toward epigenetically upregulated antigens, was T cell dependent, was further potentiated by immune checkpoint inhibition, and conferred immunologic memory. We showed that epigenetically regulated antigens can be shared between tumors providing protective immunity against both epigenetically treated KP Sarc and a second murine sarcoma M-3-9M. Treatment of human sarcoma lines with decitabine and entinostat induced similar gene expression changes, including shared antigen targets, and increased MHC I expression. These findings demonstrate that epigenetically upregulated antigens can serve as effective tumor-specific targets and broaden immunotherapy strategies for low-mutation sarcomas.