Preclinical development of a single domain mesothelin-specific chimeric antigen receptor (CAR) T cell therapy for ovarian cancer and other solid tumours 3385

Abstract Description Immunotherapy has shown limited success against high-grade serous ovarian cancer (HGSC), with no FDA-approved checkpoint inhibitors or adoptive cell therapies currently available. Chimeric Antigen Receptor (CAR) T cells offer a promising approach but have demonstrated poor clinical success in solid tumors. Mesothelin, a cell surface glycoprotein overexpressed in many solid tumors, is an attractive target for CAR therapy; however, existing antibodies often have suboptimal binding or are commercially restricted. This study reports the preclinical evaluation of a novel nanobody-based CAR T cell therapy targeting mesothelin. Mesothelin-specific nanobody candidates, derived from single-domain antibodies (sdAbs) of an immunized Llama glama, were incorporated into second-generation CAR constructs. Primary human T cells were transduced with sdAb CAR lentiviral vectors, with a clinically validated SS1 scFv CAR serving as a benchmark control. The sdAb CAR T cells achieved high expression and efficient transduction, exhibiting specific recognition and potent cytotoxicity against mesothelin-positive tumor cells in vitro. In an HGSC xenograft model (OVCAR3), the lead sdAb CAR demonstrated robust persistence, expansion, and a 100% durable complete response rate, significantly outperforming the SS1-based CAR (∼10% response). These findings support advancing the lead Meso CAR to phase I clinical trials, offering a promising therapy for ovarian and other mesothelin-expressing cancers. Funding Sources BC Cancer Foundation National Research Council Canada Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)