Abstract 4004: Fine-tuning affinity/avidity of anti-CAIX CAR T cells to mitigate on-target off-tumor toxicity in clear cell renal cell carcinoma

Abstract On-target off-tumor toxicity (OTOT) is one of the major hurdles preventing tumor-associated antigen (TAA) targeted therapy from effectively treating patients with solid tumors due to the shared presence of the same TAA on normal tissues. We have previously demonstrated high expression of carbonic anhydrase IX (CAIX) in ccRCC patient samples and low-density expression on healthy bile duct epithelium. In 2006, a clinical trial was stopped due to OTOT bile duct toxicity observed in patients infused with anti-CAIX CAR T cell therapy. To address the issue of OTOT in the bile duct, we performed affinity/avidity fine-tuning of the anti-CAIX CAR G36 to specifically target ccRCC tumor cells with high CAIX expression while sparing cholangiocytes with low CAIX expression. We generated a complementarity-determining region (CDR) single variant mutagenesis library of G36 and displayed the library on yeast for screening. Using flow cytometry, we were able to identify six populations based on antigen-binding affinity: high, med-high, med, med-low, low, and loss of binding. These libraries were sequenced via PacBio, a next generation sequencing (NGS) platform that excels in long-read sequencing, providing a powerful tool to detect single mutations in the scFv. The results were analyzed to identify enriched mutations compared to the wild-type G36, and inspected using in silico modeling and docking. Furthermore, enriched mutants from med-low and low populations were tested in CAR-T format for their cytotoxic capacity on tumor cells and bile duct cholangiocytes, as well as their avidity. We demonstrate that mutations in CDR2 and CDR3 of the heavy chain successfully mitigate OTOT toxicity on cholangiocytes with physiological levels of CAIX expression while maintaining tumor-killing capacity, shedding light on CDR mutagenesis as a useful tool to mitigate OTOT toxicity. Citation Format: Stephen Hsien-Chi Yuan, Yufei Wang, Rabia Abbas, Peterson Mathenge, Charles Chien, Christian D. Coherd, Branson Bajoua, Matthew R. Chang, Nithyassree Murugan, Gabriella M. Kastrunes, Guilin Wang, Song-My Hoang, Wayne A. Marasco. Fine-tuning affinity/avidity of anti-CAIX CAR T cells to mitigate on-target off-tumor toxicity in clear cell renal cell carcinoma [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 4004.