Poseida Therapeutics Reports Positive Interim Phase 1 Results for Allogeneic CAR-T Therapy P-BCMA-ALLO1 with High Overall Response Rates in Heavily Pretreated Relapsed/Refractory Multiple Myeloma Patients
New Interim Clinical Data from Phase 1 P-BCMA-ALLO1 Trial
The ongoing open-label, multicenter Phase 1/1b dose-escalation and expansion trial in patients with RRMM is assessing the safety and maximum tolerated dose of P-BCMA-ALLO1 (primary objective) and its anti-myeloma activity (secondary objective). As of September 6, 2024, 72 unique patients were enrolled as an intent-to-treat (ITT) population and were treated across four study arms (S, A, B and C) that included different P-BCMA-ALLO1 doses and lymphodepletion regimen combinations. Study participants were required to have received three or more prior lines of therapy, including a prior proteasome inhibitor, immunomodulatory drug and anti-CD38 monoclonal antibody. The trial enrolled a heavily pretreated patient population with 43% of patients having received prior BCMA-and/or GPRC5D targeting therapy. Most prior BCMA therapies included autologous CAR-T and/or T-cell engagers (TCE). Additionally, 33% of study participants were racial minorities, demonstrating Poseida's commitment to underserved patient populations.
In the ITT population, 100% of patients enrolled as of the data cutoff were infused with P-BCMA-ALLO1. No patients required anti-myeloma bridging therapy or prophylaxis with steroids or tocilizumab, and there was no invasive apheresis or manufacturing wait time. The median time from enrollment to the start of study treatment was one day.
The ORR across all four study arms was 54%; 11% of patients achieved a complete response (CR) or a stringent complete response (sCR), and 33% achieved a very good partial response or higher (VGPR+). The median duration of response (DoR) was 232 days for study Arms A and B – the cohorts with six or more months of follow-up at the time of data cut-off. Expansion and persistence of the CAR-T cells in patients after infusion has been dependent upon the conditioning dose of cyclophosphamide. P-BCMA-ALLO1 levels measured in the peripheral blood and were much higher in patients in Arm C (cyclophosphamide 750 mg/m2/day) and Arm B (cyclophosphamide 1000 mg/m2/day) than in patients in Arm S (cyclophosphamide 300 mg/m2/day), and Arm A (cyclophosphamide 500 mg/m2/day). Arm C was identified as the optimized lymphodepletion arm based on cellular kinetics, safety and efficacy.