Time-dependent prognostic value of serological and measurable residual disease assessments after idecabtagene vicleucel.

The role of MRD in multiple myeloma patients treated with CAR T cells is uncertain. We analyzed MRD kinetics during the first year after idecabtagene vicleucel (ide-cel) infusion in 125 relapsed/refractory multiple myeloma patients enrolled in KarMMa. At month 1 after ide-cel, there were no differences in progression-free survival (PFS) between patients in less than complete response (CR) vs those in CR; only MRD status was predictive of significantly different PFS at this landmark. In patients with undetectable MRD at 3 months and beyond, PFS was longer in those achieving CR vs <CR. Persistent MRD in the 10-6 logarithmic range and reappearance of normal plasma cells in MRD negative patients associated with inferior PFS. This study unveiled different prognostic implications of serological and MRD response dynamics after ide-cel and suggests potential value of studying the reappearance of normal plasma cells as a surrogate of loss of CAR T cell functionality.