Patients undergoing chimeric antigen receptor T (CAR T)-cell therapy are at risk of developing immune effector cell-associated neurotoxicity syndrome (ICANS). We observed an upregulation of CCR5 and CCR2 expression in CD4+ T cells among patients who developed ICANS. Notably, increased CCR5 expression was detectable as early as day one post-infusion, but only in those who eventually developed ICANS, suggesting a potential role for CCR5 as an early biomarker for ICANS onset.