Abstract A021: Adjuvant iC9.B7-H3 CAR T cell-based immunotherapy effectively eradicates local and distant metastases in pancreatic ductal adenocarcinoma

Abstract

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) has a poor prognosis. Despite negative margin resections of the cancer and systemic therapy, PDAC often recurs. Pancreatic cancer-associated fibroblasts (CAFs) contribute to a highly desmoplastic tumor microenvironment (TME), preventing T cell infiltration. Moreover, CAF-secreted factors suppress the anti-tumor activity of T cells and shift tumor cells toward invasive proliferative and mesenchymal phenotypes. Therefore, targeting CAFs can enhance T-cell infiltration and improve treatment outcomes. In this study, we investigate using Chimeric Antigen Receptor (CAR) T cells targeting B7-H3 to eliminate PDAC metastatic disease in a preclinical mouse model. B7-H3, an immune checkpoint molecule, is highly expressed on PDAC cells and CAFs. Our CART-B7-H3 construct includes an inducible caspase 9 (iC9) suicide gene, which allows for the controlled elimination of the CAR T cells in the event of overwhelming cytokine release syndrome. Methods: The efficacy of iC9.B7-H3 CAR T cells was tested in vitro against human PDAC and fibroblast cell lines at various ratios. The antitumor activity of iC9.B7-H3 CAR T cells was assessed in PDAC cells after exposure to CAF-conditioned media, simulating TME with immunosuppressive cytokines. To validate the therapeutic potential of iC9.B7-H3 CAR T cells in vivo, NSG mice were orthotopically engrafted with patient-derived PDAC6 cells and hCAF1 cells at a ratio of 1:9, reflecting a clinically relevant model. After three weeks, the mice underwent surgical resection of the primary tumor (distal pancreatectomy and splenectomy) and were subsequently treated systemically with iC9.B7-H3 CAR T cells. Results: In vitro, at a high effector-to-target (E:T) ratio, iC9.B7-H3 CAR T cells effectively eliminated PDAC cells and CAFs. However, their anti-tumor activity was diminished when the E:T ratio was lowered (PDAC6 tumor cell killing (TCK): 92±5% at 1:1, hCAF1 TCK: 81.67±5% at 1:1, compared to PDAC6 TCK: 26±5% at 1:10, hCAF1 TCK: 0% at 1:10, P<0.0001). PDAC cells co-cultured with CAF cells demonstrated reduced susceptibility to elimination by iC9.B7-H3 CAR T cells compared to PDAC cells alone (PDAC3 TCK: 92±5% at 1:1, PDAC3+hCAF1 (1:9 ratio) TCK: 81±5% at 1:1, P=0.002). However, incubation with CAF-conditioned media did not significantly affect the elimination of PDAC cells by iC9.B7-H3 CAR T cells, which may suggest that CAFs may require direct cell-cell contact to exert their effects. In vivo, iC9.B7-H3 CAR T cells effectively eradicated both local and distant PDAC metastases for the length of the experiment (160 days), indicating long-term efficacy in the treatment of PDAC metastases with no adverse side effects. Conclusion: These data suggest that iC9.B7-H3 CAR T cells may be an effective adjuvant treatment for the eradication of micro-metastases and the prevention of disease recurrence in PDAC patients. Citation Format: Shahrzad Arya, Seyed Amir Sanatkar, Cristina Martin, Marco Ventin, Jingyu Jia, Giulia Cattaneo, Gabriella Lionetto, David T. Ting, Xinhui Wang, Sandra Ryeom, Cristina R. Ferrone, Soldano Ferrone. Adjuvant iC9.B7-H3 CAR T cell-based immunotherapy effectively eradicates local and distant metastases in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr A021.