Abstract 62: Intra-tumor persistence of activated anti-mesothelin hYP218 CAR T cells is associated with increased efficacy in gastric and colorectal cancers

Abstract Purpose: Patients with gastric and colorectal cancers that have progressed after standard therapies have poor prognosis. Given the high expression of mesothelin in these tumor types, we examined the potential utility of the anti-mesothelin hYP218 CAR T cells to treat these cancers. Experimental Design: Cell surface mesothelin expression in a panel of gastric and colorectal cancer cell-lines was analyzed using flow cytometry. In vitro efficacy of hYP218 CAR T cells against these cell lines was evaluated using cytotoxicity and cytokine release assays. In vivo efficacy of hYP218 CAR T cells was studied using gastric (HGC27) and colorectal (SW48) tumor xenografts in NSG mice. NSG mice were injected with 1 × 106 cancer cells and the tumors were allowed to grow until they reached a volume of 80-100mm³, after which the mice were treated with either 5 × 106 hYP218 CAR T cells, 5 × 106 untransduced T cells, or saline and monitored over time. Persistence of CAR T cells in the tumor was evaluated over time and expression of activation and exhaustion markers were studied. Results: hYP218 CAR T cells demonstrated strong cytotoxic activity against mesothelin positive gastric and colorectal cancer cell lines and exhibited increased pro-inflammatory cytokine production. In both the HGC27 and SW48 tumor models hYP218 CAR T cells demonstrated significant reduction in tumor volume and overall survival compared to mice treated with untransduced T cells or saline. CAR T cells isolated from tumors of both the xenograft models, at day 40 after treatment, displayed higher expression levels of activation markers CD39 and CD69 when compared to the infused product. Furthermore, a concomitant elevation in the levels of effector cytokines, TNF-α and IFN-γ, was detected in the blood of treated mice demonstrating the functional capacity of the CAR T cells to not only persist but also to maintain an activated state. Conclusions: hYP218 CAR T cells show anti-tumor efficacy against gastric and colorectal tumor xenografts due to increased accumulation of activated CAR T cells in the tumor and warrants further investigation for treatment of patients with these cancers. Citation Format: Sameer A. Mir, Abhilash Venugopalan, Jingli Zhang, Mana Kamana Khanal, Chaido Stathopoulou, Manjistha Sengupta, Qun Jiang, Raffit Hassan. Intra-tumor persistence of activated anti-mesothelin hYP218 CAR T cells is associated with increased efficacy in gastric and colorectal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 62.