Late-onset relapsing neurotoxicity after Brexucabtagene autoleucel associated with high chimeric antigen receptor T cells in cerebrospinal fluid

Background aims: Mounting evidence suggests that persistent cell expansion is the main driver for both efficacy and toxicity of chimeric antigen receptor (CAR) T-cell therapy. Hereby, we describe a case of delayed recurrent neurotoxicity associated with late CAR T-cells re-expansion. Case description: A 44-year-old man suffering from mantle cell lymphoma received brexu-cel. After infusion, he developed grade 2 cytokine release syndrome. On day +11, grade 3 neurotoxicity was reported and high-dose methylprednisolone was started with a complete resolution of neurological manifestations. On day +30, he experienced a late-onset CAR T-cell toxicity associated with CAR T-cell re-expansion. The patient was treated with tocilizumab and dexamethasone, with resolution of symptoms. On day +58, he was readmitted for new onset of neurotoxicity. Notably, a new CAR T-cell expansion was observed, with an unexpectedly elevated cerebrospinal fluid/blood ratio. The patient was promptly treated with dexamethasone and then escalated to high-dose methylprednisolone and anakinra, with resolution of his neurologic condition noted. Conclusions: CAR T-cell-related neurotoxicity usually has an early monophasic course. To our knowledge, this is the first case of late-onset, recurrent neurotoxicity. Moreover, an elevated level of cerebrospinal fluid CAR T cells was observed, which may suggest that the delayed neurotoxicity was primarily caused by the brain infiltration of CAR T cells rather than driven by cytokine-mediated neuroinflammation.