Durable Remission Achieved from Bcma-Directed CAR-T Therapy Against Relapsed or Refractory Multiple Myeloma

Background: Promising results are seen from several early phase clinical trials on the cellular immunotherapy based on chimeric antigen receptor (CAR)-engineered T (CAR-T) targeting B cell maturation antigen (BCMA) for the treatment of relapsed/refractory (RR) multiple myeloma (MM). We developed an anti-BCMA CAR-T cell product manufactured via gamma-retrovirus-mediated transduction of activated T cells to express a second-generation CAR with the 4-1BB costimulatory domain along with a truncated epidermal growth factor receptor (tEGFR) as a safety switch. The preclinical study confirmed its high reactivity against MM cells.

Methods: We initiated a phase 1 clinical trial (NCT03093168) to evaluate the safety and feasibility of this BCMA CAR-T autologous cellular therapy for treating RRMM. The enrolled RRMM patients either had received at least 3 prior treatment regimens, including a proteasome inhibitor and an immunomodulatory agent, or were double-refractory, and have over 5% BCMA expression on plasma cells (One patient with extramedullary plasmacytoma does not express BCMA). Patients were subjected to a lymphodepleting regimen with Cy (300 mg/m², d-5 to d-3) and Flu daily for 3 days (25 mg/m², d-5 to d-3) prior to the CAR-T infusion (d0) at a dose of 9´10⁶ CAR⁺ cells/kg. The efficacy was assessed by the International Uniform Response Criteria for Multiple Myeloma, and the toxicity was graded by CTCAE 4.03.

Results: As of July 6th, 2018, 17patients had been infused with this intended dose of the autologous BCMA CAR-T cells, and 14 patients had reached at least 1 month of follow-up. As of this data cut-off, the most common non-haematologicalgrade 3 adverse events were pneumonia, hypophosphatemiaand hypocalcemia(two[14%] of 14patients), and fever, cytokine release syndrome,and neurotoxicities (one[7%]of 14patients).All toxicities were fully reversible. The overall response rate (ORR) for the 14 evaluable patients was 79%, including 3 sCRs, 4 CRs and 2 MRD-negative responses (2 VGPR). The CAR-T cell expansion and persistence were consistently observed throughout these patients.The durable remission was observed for two early enrolled patients, with the ongoing objective response (1 sCR and 1 VGPR) lasting more than 15 months.

Conclusions: Our result demonstrates the high potential of this single CAR-T infusion therapy for RRMM, including 3 sCRs and ongoing durable clinical responses, with only mild and manageable CRS to date. These initial data provide strong evidence to support the further development of this anti-myeloma cellular immunotherapy.