Abstract 4084: Radiation enhances efficacy of TEM1-specific cancer vaccination

Abstract

Tumor endothelial marker 1 (TEM1 or CD248) is a protein found in both tumor vasculature and stroma. In prior experiments, we showed that immunizing with Tem1-TT plasmid-DNA (Tem1 cDNA fused to the minimal domain of the C fragment of tetanus toxoid) was effective in controlling tumor progression in three mouse tumor models in a T cell-dependent manner. Moreover, effective Tem1-TT vaccination reduced tumor vascularity without impacting normal angiogenesis. Radiation therapy (RT) is an established curative and palliative cancer treatment regimen which uses high-energy radiation to kill cancer cells. RT modulates the tumor microenvironment - by increasing MHC-I expression, inducing immunological cell death, and damaging the tumor-associated vasculature - potentially synergizing with anti-cancer immunotherapies. Here, we combined RT and Tem1-TT heterologous vaccination and showed that combination of the two therapies was more effective in controlling CT26 and TC1 tumor progression than either single therapy alone. Interestingly adding RT to Tem1-TT vaccine resulted in a stronger vaccine-specific immune response and increased epitope spreading toward gp70, a TAA expressed by CT26 tumor cell line. Further analysis of the tumor microenvironment revealed a significant increment of PD-L1 expression in both tumor cells and tumor vasculature after single or either combination therapy. This led us to test whether blocking the PD1/PD-L1 axe would further improve the efficacy of RT plus Tem1-TT therapy. Our results demonstrate that administration of anti-PD-L1 antibody further synergized with RT plus Tem1-TT and improved mice survival. In conclusion, triple combination of Tem1-TT vaccine, RT and anti-PD-L1 can offer a therapeutic advantage for TEM1-positive tumors which also express PD-L1. Citation Format: Stefano Pierini, Mireia Uribe-Herranz, Renzo Perales-Linares, Silvia Beghi, Francesca Costabile, Sergei Pustylnikov, Andrea Facciabene. Radiation enhances efficacy of TEM1-specific cancer vaccination [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4084.