Immunoediting restricts clonal neoantigens in primary, treatment-naive human tumors

T cell targeting of cancer cells alters the tumor antigen landscape in preclinical models. Here, we examined the impact of immunoediting on the antigenic landscape of primary, treatment-naive human tumors. Cutaneous squamous cell carcinoma tumors from immunocompetent and immunosuppressed patients revealed consistent tumor mutational signatures; however, high-immune-infiltrate tumors from immunocompetent patients had lower overall mutational burdens and lower clonal mutational burdens compared with low-infiltrate tumors from immunocompetent patients and tumors from immunosuppressed patients. The lower clonal mutational burden in high-immune-infiltrate tumors from immunocompetent patients persisted after accounting for tumor purity and growth rate. Predicted neoantigen: major histocompatibility complex (MHC) class I binding affinity decreased with increasing variant allele frequency, demonstrating restriction of mutations encoding MHC-binding neoantigens. Neoantigens with features shared with validated immunogenic neoantigens were decreased in clonal relative to subclonal cancer cell populations in high-immune-infiltrate tumors from immunocompetent patients. Thus, the immune system restricts cancer cells expressing immunogenic antigens from clonal populations in primary, treatment-naive human tumors.