Abstract A089: Improving Therapeutic Window of Claudin 18.2-Targeted CAR-T cells in Pancreatic Cancer

Abstract Claudin 18. 2 (CLDN18) targeted therapies, such the CAR-T cell, Satri-cel (CT041) are expanding access to immunotherapy in pancreatic cancer, however, high rates of nausea and vomiting were seen thought to be related to on target off tumor (OT/OT) toxicity in the stomach, a known site of normal CLDN18. 2 expression. Furthermore, their utility is limited by relatively short duration of response. Taking advantage of the high degree of homology of CLDN18. 2 between mouse and human we develop novel, fully-human, nanobody-based CARs with superior therapeutic window compared to CT041, extending efficacy and reducing OT/OT. We also demonstrate toxicity inversely correlates with CAR binder affinity. Following an antibody discovery campaign, novel fully-human heavy chain only binders (HCAb) specific to CLDN18. 2; cross reactive to both the human and mouse protein, were cloned into the 4-1BB containing CAR. In vitro screening identified CARs with two highly active binders, “5795-VH” and “5797-VH”. The binding kinetics of IgG reformatted versions of binders 5795, 5797 and CT041 were determined via SPR against both mouse and human CLDN18. 2. CT041-IgG had highest affinity to human CLDN18. 2 (KD=3. 64±0. 2 nM), 5797-IgG had slightly lower affinity (KD=4. 5±3nM) while 5795-IgG had ∼10-fold lower affinity (KD=21. 8±2nM). Using the human pancreatic cancer xenograft model of PATU8988s, cells were allowed to engraft and expand in NSG DKO mice, then treated with a single dose of either 3 x105 or 1 x106 5795-VH, 5797-VH, or CT041-scFv CAR-T and compared to 1 x106 BCMA-scFv irrelevantly targeted control treated animals. All animals treated with either CT041, or 5797 based CAR-T succumbed to toxicity, even at the lower dose, while 5795 based CAR-T had long term tumor control at both doses, with minimal toxicity in this tumor model (mOS 31-36d for CT041-scFv groups and mOS not reached by 60d for 5795-VH groups; p0. 01). Stomach was harvested from animals in this model and stained by multiplex immunofluorescence and H Boston, MA; 2025 Sep 28-Oct 1; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85 (18Suppl₃): Abstract nr A089.