Here, we present the primary findings of part A of a phase 1 study (NCT04318327) of durcabtagene autoleucel in patients with relapsed/refractory multiple myeloma (r/r MM). The primary objective was safety; secondary objectives included response rates, cellular kinetics, immunogenicity, and manufacturing feasibility. Durcabtagene autoleucel was successfully manufactured for all 55 patients (median vein-to-vein time, 24 days) and given as a single infusion at one of four flat target doses (2.5 × 106 to 20 × 106 CAR T cells). Among all patients, the overall response rate was 98%, and the stringent complete response rate was 55%. Eighty percent of evaluable patients (35 of 44) achieved minimal residual disease negativity. There were no unexpected safety findings and no reports of delayed neurotoxicity. Immunophenotyping and transcriptomic analyses confirmed preservation of a stem-like phenotype in the manufactured final product. On the basis of the safety, efficacy, and cellular expansion results from the phase 1 trial, a phase 2 trial (NCT05172596) was initiated to further explore the efficacy and safety of durcabtagene autoleucel in heavily pretreated patients with aggressive r/r MM.