Poseida Therapeutics highlights interim Phase 1 results for P-BCMA-ALLO1

Poseida Therapeutics (PSTX) will highlight interim clinical data from its Phase 1 trial of P-BCMA-ALLO1 in patients with relapsed/refractory multiple myeloma, including new profiling of patient responses from Arm C, an optimized lymphodepletion arm. The P-BCMA-ALLO1 data are being presented, along with two additional Company poster presentations covering new preclinical data for P-CD19CD20-ALLO1 and a patient case study demonstrating the reactivation of a Poseida autologous CAR-T therapy with a T-cell engager, at the 66th ASH Annual Meeting and Exposition being held in San Diego on December 7-10, 2024. P-BCMA-ALLO1 is an investigational non-viral, stem cell memory T cell-rich allogeneic CAR-T cell therapy in Phase 1/1b clinical development for the treatment of patients with RRMM. P-CD19CD20-ALLO1 is an investigational, non-viral TSCM-rich allogeneic CAR-T cell therapy in Phase 1 clinical development for the treatment of patients with B-cell malignancies and is the Company’s first dual CAR-T program. P-BCMA-ALLO1 and P-CD19CD20-ALLO1 are being developed in collaboration with Roche. P-BCMA-ALLO1 Phase 1 Data: The poster presentation will highlight Phase 1 clinical data first presented at the 21st International Myeloma Society Annual Meeting in September 2024. The data showed a 91% overall response rate in Arm C, including a 100% ORR in B-cell maturation antigen-naive patients, and an 86% ORR in those who had received at least one prior BCMA- and/or G protein-coupled receptor class C group 5 member D-targeting treatment modality, along with differentiated safety results with no dose-limiting toxicities, low rates of cytokine release syndrome and immune effector cell neurotoxicity syndrome, all Grade 2 or less, and no graft vs. host disease or Parkinsonism. No patients required anti-myeloma bridging therapy or prophylaxis with steroids or tocilizumab, and there was no invasive apheresis; an average manufacturing wait time, from treatment decision to clinical response, was only 3.5 weeks. The patients in this study had more advanced disease than the myeloma patients studied in clinical trials of approved autologous CAR-T therapies, and in the intent-to-treat population, 100% of patients were infused with P-BCMA-ALLO1. New profiling of patient responses from Arm C are included in the ASH poster presentation. The data from this analysis show consistent P-BCMA-ALLO1 cellular expansion and persistence across different subgroups, including patients that are typically more challenging to treat. Key highlights suggest that P-BCMA-ALLO1: Cellular kinetics were not impacted by prior BCMA/GPRC5D-targeted therapy Expands and persists in patients with extramedullary disease P-CD19CD20-ALLO1 Preclinical Data Preclinical data has demonstrated that P-CD19CD20-ALLO1 delivers high in vitro potency and strong in vivo antitumor activity for either CD19 or CD20 single-positive target cells, as well as double-positive targets. New preclinical data included in the poster presentation show that compared to CD19-single targeting or CD20-single targeting CAR-T cells, P-CD19CD20-ALLO1: Achieved higher and more durable killing of tumor cells over three rechallenges, even in the presence of only one tumor antigen Exhibited higher cytotoxicity Produced higher and more sustained levels of effector cytokines that play an important role mediating the immune system response to cancers Showed higher in vivo antitumor efficacy than the CD19-single targeting CAR-T cells The Company’s P-CD19CD20-ALLO1 Phase 1 clinical trial is enrolling patients with selected B-cell malignancies, with initial clinical data anticipated in 2025. CAR-T Reactivation with T-cell Engager Case Study The case study highlights the reactivation of an autologous Poseida CAR-T therapy with a T-cell engager in a patient with relapsed multiple myeloma. The patient attained and remained in stringent complete response over 12 months after CAR-T reactivation. This case highlights the potential of Poseida’s TSCM-based CAR-T therapies to deliver a strong anti-myeloma response with long-term remission and CAR-T cell persistence. The Company believes this is the first time that a T-cell engager has been seen to reactivate a CAR-T therapy.