Efficacy and Safety of Fully Human Bcma Targeting CAR T Cell Therapy in Relapsed/Refractory Multiple Myeloma

Background: Previous studies indicate that patients with relapsed/refractory multiple myeloma (RRMM) who receive BCMA-targeting CAR-T cells may achieve better remission but have a higher relapse rate. Persistence of CAR T cells post-infusion may be one determinant of the duration of response. Moreover, once the disease progresses again, the re-infusion of CAR-T cells is not effective. To solve this dilemma, we have developed a novel BCMA-targeting CAR-T (CT103A) with a lentiviral vector containing a CAR structure with a fully human scFv, CD8a hinger, and transmembrane, 4-1BB co-stimulatory and CD3z activation domains.

Methods: ChiCTR1800018137 is a single-center and single-arm trial of CT103A in patients with RRMM (≥ 3 prior lines, including a proteasome inhibitor and an IMiD, or double refractory). The primary objectives are the incidence of adverse events (AEs), including dose-limiting toxicities (DLTs). The secondary objectives are the duration of clinical response, evaluation of minimal residual disease (MRD), progression-free and overall survival, and CAR-T cell persistence in blood. Between September 21, 2018, and August 1st, 2019, sixteen patients (including 4 patients having relapsed after being given a murine BCMA CAR-T and 5 patients having extramedullary disease and/or plasma cell leukemia) received CT103A in 3+3 dose-escalation trial (four doses at 1, 3, 6, 8 ×10⁶/kg) after a conditioning chemotherapy regimen of cyclophosphamide and fludarabine. Median follow-up after CT103A infusion was 195 days (23 to 314 days) and all 16 patients were evaluable for initial (14 days) clinical response.

Results: As of August 1st, 2019, the objective response rate was 100%, 6/16 patients achieved CR/sCR within two weeks post-infusion and all 8 patients surpassing 6 months achieved VGPR/CR/sCR. CR/sCR was 75%, and VGPR was 25% for these 8 patients, according to the IMWG Uniform Response Criteria for MM. In 4 patients who have participated in a prior CAR-T trial, three have achieved sCR, and 1 achieved VGPR. All 15 patients who could be evaluated for minimal residual disease (MRD) had MRD-negative status (≤10^-4 nucleated cells by flow). The circulating CT103A cells were detected in the blood by flow and digital polymerase chain reaction, peaking at 14 days (ranging from 9 to 25), and remaining detectable in 12/16 patients, at the time of their last evaluation. Patient #1 (the first patient treated) has now exceeded 314 days of CART persistence, post-infusion. All sixteen patients developed cytokine release syndrome (according to ASBMT Consensus Grading for Cytokine Release Syndrome and Neurological Toxicity Associated with Immune Effector Cells: 10 Grade 1-2, 5 Grade 3,1 Grade 4). A grade 4 CRS appeared at the 6×10⁶ /kg dose level and was considered as a dose-limiting toxicity DLT. No neurotoxicity was observed in all dose groups. One patient died of a lung infection 19 days post-infusion.

Conclusions: Data from this early-stage clinical study showed the unparalleled safety and efficacy of CT103A in heavily pretreated R/R multiple myeloma patients. Highly active (ORR 100%) and rapid response within two weeks, suggests CT103A could be developed as a competitive therapy to treat patients with RRMM.