005 Novel cutaneous squamous cell carcinoma cell lines constrained by T cell-mediated immune responses

Abstract

T cell-mediated immune responses can control in vivo cutaneous squamous cell carcinoma (cSCC) growth, but the determinants of anti-tumor T cell responses are not fully understood. To address this need, we developed a murine model of cSCC induced by the same etiologic factor as human disease which allows for evaluation of tumor-specific T cell responses. Solar simulated light induced cSCC tumors from BALB/c mice were used to create a panel of six clonal cSCC cell lines. Athymic mice, lacking mature T cells, and immunocompetent wild-type mice were injected with 1e6 cells of each cSCC cell line. Each cSCC cell line generated tumors in all athymic mice, demonstrating that, in the absence of T cells, the cSCC cell lines reliably form tumors. However, in wild-type mice all cSCC cell lines formed small tumors and then regressed, demonstrating that T cells constrain cSCC tumor growth. In four of the cSCC cell lines, injection of a higher cell number (5e6) resulted in immune evasion and tumor formation in a portion of mice, while no mice injected with the other two cSCC cell lines developed tumors. The cSCC cell lines express BALB/c-specific MHC class I alleles (H2Kd, H2Dd, H2Ld) in vitro. Whole exome and RNA sequencing was performed on the cSCC cell lines. In each cSCC cell line, there were >4000 missense mutations and >400 predicted MHC class I neoantigens, with 2-5 predicted to be immunogenic. Immunogenicity was predicted based on high affinity of the peptide:MHC class I interaction and high mRNA expression in the tumor cell. This cSCC model can be used to identify determinants of tumor-specific T cell responses.