Abstract C009: Disruption of tumor-promoting desmoplasia by adoptive transfer of fibroblast activation protein targeted chimeric antigen receptor (CAR) T cells enhances anti-tumor immunity and immunotherapy

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal disease due to the poor response to current therapeutic treatments. A major barrier to effective treatment of PDAC is the extensive remodeling of tumor stroma characterized by accumulation of cancer associated fibroblasts (CAFs) and extracellular matrix which forms a physical barrier that limits access of the drugs to the cancer cells, suppresses the immune system, and attenuates efficacy of immunotherapies. Fibroblast activation protein (FAP) is highly expressed in a pro-tumorigenic subset of CAFs in PDAC. We hypothesized that depletion of FAP+-CAFs would deplete extracellular matrix (ECM) and reduce the immune suppressive function of the stroma and thereby enhance the efficacy of tumor antigen targeted CAR T cell therapy in PDAC. Using real-time tumor fragment-based 2-photon microscopy, multiparametric flow cytometry and multiplexed immunofluorescence staining, we showed that FAP targeted CAR T cells (FAP-CAR T) efficiently traffic into tumors compared with tumor-antigen (mesothelin) targeted CAR (Meso-CAR) T cells which were trapped in the stroma-rich or matrix-dense areas and led to depletion of immunosuppressive FAP+ cells and reprogrammed the fibrillar collagen network surrounding tumor nests, advancing the infiltration of FAP-CAR T cells into tumor nests. Strikingly, FAP-CAR T cell-mediated depletion for FAP+ cells also rendered the tumor microenvironment permissive to the infiltration and anti-tumor activity of tumor antigen meso-CAR T cells. Moreover, ablation of FAP+ cells markedly enhanced endogenous T cell infiltration which further enhanced anti-tumor immunity and immunotherapy in PDAC models. Thus, our findings established that FAP-CAR T cell-mediated ablation of immunosuppressive FAP+-CAFs and disruption of the desmoplastic stroma they generate, can enhance accumulation and functionality of endogenous anti-tumor immunity and CAR-T cell therapy in the context of highly desmoplastic solid tumors. Citation Format: Zebin Xiao, Leslie A. Hopper, Meghan C. Kopp, Emily McMillan, Yue Li, Richard L Barrett, Ellen Puré. Disruption of tumor-promoting desmoplasia by adoptive transfer of fibroblast activation protein targeted chimeric antigen receptor (CAR) T cells enhances anti-tumor immunity and immunotherapy [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C009.