Neurotoxicity with CAR T cells in myeloma deciphered?

Novel immunotherapies, including B-cell maturation antigen (BCMA)-directed chimeric antigen receptor (CAR) T cells, have changed the treatment landscape for multiple myeloma (MM) and are widely used today.In this issue of Blood, Hosoya et al 1 identified that absolute lymphocyte count (ALC) may serve as a surrogate marker for CAR T-cell expansion during the first months after treatment and can be used to implement therapeutic precautions, if exceedingly elevated.Their findings are relevant for CAR T-cell centers as we strive to avoid CAR T-cell-induced complications and learn more as to why these evolve.The key results, based on assessment of peripheral blood (PB) CAR T-cell expansion in a test cohort using flow cytometry (FC) and evaluation of ALC as a surrogate in a validation cohort, were that ciltacabtagen autoleucel (cilta-cel) was associated with higher CAR T-cell expansion than idecabtagenvicleucel (ide-cel) and that ALC were good alternatives to CAR T-cell expansion.The higher the expansion of BCMA-CAR T cells or ALC, the more frequently neurotoxicity (NT) was observed, such as immune effector cellassociated neurotoxicity syndrome (ICANS), delayed neurotoxicity (DNT), and parkinsonism.1