Triple checkpoint blockade, but not anti-PD1 alone, enhances the efficacy of engineered adoptive T cell therapy in advanced ovarian cancer

Abstract

Abstract Less than 50% of ovarian cancer patients survive five years after diagnosis. This rate has changed little in the last 30 years, highlighting the need for novel therapies. A promising strategy employs T cells engineered to target tumor-expressed proteins. Mesothelin (Msln) is overexpressed in ovarian cancers, contributes to the malignant and invasive phenotype and has limited expression in healthy cells, making it a candidate immunotherapy target. We used the immune-competent ID8 VEGFmouse model of advanced ovarian cancer to show that T cells engineered to express a Msln-specific T cell receptor (TCR Msln) can preferentially accumulate within established tumors, delay tumor growth and significantly prolong mouse survival. However, elements in the tumor microenvironment limited engineered T cell function. Tumor-bearing mice were therefore treated with TCR MslnT cells plus PD1, Tim-3 and/or Lag-3 checkpoint-blocking antibodies, alone or in combination. Triple checkpoint blockade, but not single- or double-agent treatments, dramatically increased effector cytokine production by intratumoral TCR MslnT cells. Single cell RNA-sequencing revealed gene expression changes in intratumoral TCR MslnT cells and myeloid cells consistent with immune activation and inflammation. Moreover, combining adoptive immunotherapy with triple checkpoint blockade prolonged survival in treated mice, relative to TCR Mslnwith or without single- or double-agent checkpoint blockade. These results suggest that disrupting multiple immune-inhibitory pathways simultaneously, which can be more safely pursued in a cell intrinsic form through genetic engineering, may be necessary to improve outcomes for ovarian cancer patients.