Abstract B119: Generation of an Endogenous PDAC-Specific TCR Transgenic Mouse

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is among the deadliest malignancies and remains largely refractory to chemotherapy and immunotherapy. Although KRAS inhibitors show promising initial efficacy, resistance rapidly emerges, and immunotherapy responses are mostly restricted to the rare subset of patients with microsatellite instability-high tumors. Together, these findings underscore the potential of immune-based strategies, while highlighting our incomplete understanding of the immune regulatory mechanisms in pancreatic cancer. Using orthotopically implanted KPCY (6694c2) tumors, we have demonstrated that a stabilized IL-21 variant (21h10) combined with the KRAS inhibitor MRTX1133 cured resistant PDAC through a CD4+ T cell–dependent, but CD8+ T cell–independent, mechanism. Using single cell TCR clonotype tracking from mice treated with combination 21h10 and MRTX1133, we identified clonally expanded Th1-polarized CD4+ T cells that we hypothesized were responding to tumor antigens. TCRs derived from these expanded CD4 T cell populations were cloned and expressed in 58α-/-β-/- T cells for antigen screening, leading to the identification of two tumor-specific CD4+ TCRs, TCR33 and TCR125. These TCRs recognize an endogenous PDAC antigen shared across KPC cell lines and do not recognize Cre recombinase or YFP. We subsequently generated a TCR33 transgenic mouse and confirmed the development of TCR33-expressing CD4+ T cells on a RAG2-/- background. This model will enable mechanistic studies of antigen-specific CD4+ T cell–mediated tumor control and immune regulation in PDAC.