A Phase I Study of a Novel Fully Human BCMA-Targeting CAR (CT103A) in Patients with Relapsed/Refractory Multiple Myeloma

B cell maturation antigen- (BCMA) specific chimeric antigen receptor (CAR) T-cell therapies have shown efficacy in relapsed, refractory multiple myeloma (RRMM). Since the non-human originated antigen-targeting domain may limit clinical efficacy, we developed a fully human BCMA-specific CAR, CT103A, and report its safety and efficacy in a phase I trial. Eighteen consecutive RRMM patients, including four patients with prior murine BCMA CAR exposures, were enrolled. CT103A was administered at 1, 3, and 6 × 106 CAR-positive T cells/kg in the dose-escalation phase, and 1 × 106 CAR-positive T cells/kg in the expansion cohort. The overall response rate (ORR) was 100%, with 72.2% of the patients achieving complete response or stringent complete response (sCR). For the four murine BCMA CAR-exposed patients, three achieved sCR, and one achieved a very good partial response. At one year, the progression-free survival rate was 58.3% for all cohorts and 79.1% for the patients without extramedullary myeloma. Hematologic toxicities were the most common adverse events. 70.6% of the patients experienced grade 1 or 2 cytokine release syndromes. No immune effector cell-associated neurotoxicity syndrome was observed. To the cutoff date, CAR transgenes were detectable in 77.8% of the patients. The median CAR transgene persistence was 307.5 days. Only one patient was positive for the anti-drug antibody. Altogether, CT103A is safe and highly active in RRMM patients and can be developed as a promising therapy for RRMM. Patients who relapsed from prior murine BCMA CAR T-cell therapy may still benefit from CT103A. (Chinese Clinical Trial Registry ChiCTR1800018137)