On September 27, 2024 Poseida Therapeutics, Inc. (the "Company") reported new interim clinical data from its ongoing Phase 1 trial of P-BCMA-ALLO1 in patients with relapsed/refractory multiple myeloma ("RRMM") (Press release, Poseida Therapeutics, SEP 27, 2024, View Source [SID1234646929]).
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P-BCMA-ALLO1 is an investigational non-viral, stem cell memory T cell ("TSCM")-rich allogeneic CAR-T cell therapy in Phase 1/1b clinical development for the treatment of patients with RRMM. The Company is developing this investigational off-the-shelf allogeneic CAR-T cell therapy with F. Hoffmann-La Roche Ltd and Hoffmann-La Roche Inc. (collectively, "Roche") as part of a broader collaboration focused on addressing blood cancers with the Company’s TSCM-rich CAR-T platform.
Data, based on an efficacy cutoff date of September 6, 2024 and a safety cutoff date of July 31, 2024, demonstrated a 91% overall response rate ("ORR") and compelling safety results in the 23 heavily pretreated patients in Arm C, an optimized lymphodepletion arm. The new clinical data were presented on September 27, 2024 in an oral session at the 21st International Myeloma Society Annual Meeting ("IMS") in Rio de Janeiro.
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 July 31, 2024, 72 unique patients were enrolled and had at least 4 weeks of follow-up 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 B-cell maturation antigen ("BCMA")- and/or G protein-coupled receptor class C group 5 member D ("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.
In the ITT population, 100% of patients enrolled 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, including patients 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.
Results from 23 study participants in Arm C were highlighted in the oral session at IMS. Patients received cyclophosphamide 750 mg/m2/day and fludarabine 30 mg/m2/day and approximately 2×106 cells/kg P-BCMA-ALLO1. Some patients were treated in an outpatient setting. Arm C patient details include:
•Nearly half (48%) were age 65 or older
•All were heavily pretreated, with a median of six prior lines of anti-myeloma therapy and a maximum of 14
•62% of patients had received prior BCMA-targeting therapy
•29% had failed both a BCMA CAR-T and a bispecific TCE, and 29% had failed both a BCMA-targeting therapy and the GPRC5D-targeting TCE, talquetamab
•Approximately two-thirds of patients (62%) had high-risk disease by cytogenetics and 38% had extramedullary disease
Efficacy results, which are still evolving, for the 23 patients in Arm C showed:
•An ORR of 91%, with a 100% ORR in BCMA-naïve patients, an 86% ORR in those who had received at least one prior BCMA-targeting treatment (all had received prior CAR-T and/or TCE), and an 86% ORR in those who had received at least one prior BCMA-targeting treatment and/or talquetamab
•22% achieved a CR or an sCR
•48% achieved VGPR+
•Median DoR could not be estimated at the time of data cut-off because the current median follow-up is less than 3.5 months (for pooled arms A and B, the median DoR was more than seven months (estimated range of five-10 months), with a median time to response of only 16 days)
P-BCMA-ALLO1 was well-tolerated with key safety results from Arm C, including:
•No dose-limiting toxicities, Grade 3 or higher cytokine release syndrome ("CRS") or immune effector cell neurotoxicity syndrome ("ICANS"). The incidence of Grade 1 or 2 CRS was 39% and the incidence of Grade 1 or 2 ICANS was 13%
•The incidence of infections was 48%, including 30% that were Grade 1 or 2 and 17% that were Grade 3
•Rapid cytopenia recovery in the vast majority of cases
•No graft-vs-host disease (GvHD), hemophagocytic lymphohistiocytosis (HLH), Parkinsonism or cranial neuropathies observed
•The safety results of P-BCMA-ALLO1 in arm C have been consistent with those observed in the other three arms of the Phase 1 trial, with a total safety database, including 72 unique patients
The ongoing P-BCMA-ALLO1 Phase 1/1b trial is enrolling patients using the Arm C lymphodepletion regimen described above, across two dosing cohorts, with dose optimization ongoing in Arm C.
Roche Collaboration
Under that certain Collaboration and License Agreement, dated July 30, 2022, as amended (the "Roche Agreement"), by and between the Company and Roche, Roche did not timely exercise its option to acquire an exclusive license to the Company’s BCMA/CD19 Allo CAR T-cell therapy program for the development of hematological malignancies (the "BCMA/CD19 Program"), and, as a result, the rights held by Roche with respect to the BCMA/CD19 Program under the Roche Agreement have been deemed terminated. The Company plans to continue development of the BCMA/CD19 Program internally.