Abstract B084: Triple checkpoint blockade, but not anti-PD1 alone, enhances the efficacy of engineered adoptive T cell therapy in advanced ovarian cancer

Abstract Background: Over 20, 000 women are diagnosed with ovarian cancer annually, and more than half will die within 5 years. This rate has changed little in the last 30 years, highlighting the need for therapy innovation. Although immunotherapy has revolutionized cancer treatment, efforts to harness endogenous patient immune responses have yielded limited therapeutic activity in ovarian cancer patients. T cells engineered to express a T cell receptor (TCR) targeting proteins uniquely overexpressed in tumors have the potential to control tumor growth without toxicity. Mesothelin (Msln) is over-expressed in ovarian cancer, contributes to the malignant and invasive phenotype, and has limited expression in healthy cells, making it a candidate immunotherapy target in these tumors. Methods: The ID8VEGF mouse cell line was used to evaluate if T cells engineered to express a mouse Msln-specific high-affinity T cell receptor (TCRMsln) can kill ovarian cancer. Tumor-bearing mice were treated with TCRMsln T cells plus anti-PD-1, anti-Tim-3 or anti-Lag-3 checkpoint-blocking antibodies alone or in combination, ultimately targeting up to three inhibitory receptors simultaneously. Single-cell RNA-sequencing (scRNAseq) was used to profile the impact of combination checkpoint blockade on engineered T cells and the tumor microenvironment (TME). Results: In a disseminated ID8 tumor model, adoptively transferred TCRMsln T cells preferentially accumulated in established tumors, delayed ovarian tumor growth, and prolonged mouse survival. However, elements in the TME limited engineered T cell persistence and cytolytic function. Triple checkpoint blockade, but not single- or double-agent treatment, dramatically increased antitumor function by intratumoral TCRMsln T cells. scRNAseq of tumor-infiltrating cells revealed distinct transcriptome changes in engineered and endogenous T cells and myeloid-derived cells. Engineered T cells, when combined with triple checkpoint blockade, increased expression of genes associated with effector and memory gene signatures, including proliferation and metabolic function, and reduced expression of genes associated with exhaustion. Moreover, combining adoptive immunotherapy with triple checkpoint blockade significantly prolonged survival in the cohort of treated tumor-bearing mice, relative to mice that received TCRMsln T cells alone or with anti-PD1 or double-agent treatments. Conclusions: Inhibitory receptor/ligand interactions within the TME can dramatically reduce T cell function, suggesting tumor cells may upregulate the ligands for PD-1, Tim-3 and Lag-3 for protection from tumor-infiltrating lymphocytes. In an advanced ovarian cancer model, triple checkpoint blockade significantly improved engineered T cell function and outcomes in mice in a setting where single checkpoint blockade had no significant activity. These results suggest that disrupting multiple inhibitory pathways simultaneously, which can be more safely pursed in a cell intrinsic form through genetic engineering, may be necessary for improved efficacy in patients. Citation Format: Kristin G. Anderson, Yapeng Su, Madison G. Burnett, Breanna M. Bates, Magdalia L. Rodgers Suarez, Susan L. Ruskin, Valentin Voillet, Raphael Gottardo, Philip D. Greenberg. Triple checkpoint blockade, but not anti-PD1 alone, enhances the efficacy of engineered adoptive T cell therapy in advanced ovarian cancer abstract. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84 (5 Suppl₂): Abstract nr B084.