Robust CD4⁺ CAR T cell Expansion Is Associated with Non-ICANS Neurotoxicities Following Ciltacabtagene Autoleucel

Non-ICANS neurotoxicities (NINTs) are serious, atypical toxicities associated with ciltacabtagene autoleucel, a commercial chimeric antigen receptor (CAR) T cell therapy approved for relapsed/refractory multiple myeloma. Risk factors contributing to the development of NINTs are poorly understood. In a cohort of 109 patients, we identify predisposing risk factors and propose strategies to mitigate NINTs. We show that high peak absolute lymphocyte count is a strong NINT predictor which directly correlates with flow cytometry-based peripheral blood CAR T cell quantitation. The observed CAR lymphocytosis was polyclonal with a bias towards CD4⁺ CAR T cells rich in memory marker expression. We then identified CAR lymphocytosis associated CD4⁺ CAR T cell populations which exhibited increased inflammatory pathway gene expression. Finally, we characterize NINT associated CD4⁺ CAR T cell populations which are potential therapeutic targets for future exploration.