P-CD19CD20-ALLO1: Potent Fully Allogeneic CAR-T Therapy Targeting CD19 and CD20 with Superior Efficacy over Single-Target Products

Autologous Chimeric Antigen Receptor (CAR) T cells targeting CD19 have revolutionized the treatment of relapsed or chemotherapy-refractory B cell malignancies. However, many patients experience disease progression due to the loss or reduced expression of CD19. Autologous therapies also pose challenges for access, as each CAR-T dose requires patient apheresis and individual manufacture, leading to associated wait times and the need for bridging therapy. Here, we describe P-CD19CD20-ALLO1, a fully allogeneic CAR-T product expressing two full-length CARs targeting CD19 and CD20, respectively. P-CD19CD20-ALLO1 is currently being investigated in an open-label, multicenter Phase 1 study in subjects with relapsed/refractory B cell malignancies (NCT06014762) and is the most advanced allogeneic dual-targeting CAR-T in clinical development.

P-CD19CD20-ALLO1 is a T stem cell (T_SCM)-rich product derived from healthy donor pan-T cells using a nonviral transposon-based system for transgene delivery, with knockout of TRBC1/2 and B2M. Clinical data from Poseida and others have demonstrated safety and efficacy advantages associated with T_SCM CAR-T, including for P-BCMA-ALLO1, our BCMA-targeting allogeneic CAR-T for Relapsed/Refractory Multiple Myeloma (NCT04960579). Both the CD19 and CD20-targeting CARs employ novel fully human single-domain VH binders.

In nonclinical studies, P-CD19CD20-ALLO1 demonstrated potent antigen-specific anti-tumor activity against multiple tumor models in vivo, across multiple healthy donors and dose levels. Beyond expected advantages of targeting two antigens to prevent antigen escape, we also observed potency advantages for P-CD19CD20-ALLO1 compared to its CD19- and CD20-single targeting counterparts. In vitro potency was evaluated using serial restimulation against the CD19- and CD20-positive RAJI cell line, as well as RAJI cells engineered to express only CD19 or CD20. In these assays, P-CD19CD20-ALLO1 CAR-T cells showed superior potency against WT (CD19+CD20+) RAJI cells compared to the CD19- or CD20-single targeting products. Interestingly, this superiority was also observed against Raji cells expressing only one of the two target antigens, CD19 or CD20, suggesting that the increased potency of P-CD19CD20-ALLO1 is not solely due to the dual binding of CAR molecules to more antigens on the same target cell. Mechanistically, we observed that over three restimulations with WT (CD19+CD20+) RAJI cells, P-CD19CD20-ALLO1 CAR-T cells expressed and/or sustained higher expression of effector cytokines such as IFNγ, FasL, Granzyme A, and Granulysin than either CD19 or CD20 single-antigen targeting CAR-T cells.

In addition to improved in vitro potency, we assessed the in vivo efficacy of the dual-targeting product in comparison with the single-targeting products in a stress xenograft model of WT (CD19+CD20+) RAJI. P-CD19CD20-ALLO1 CAR-T cells were superior to the CD19-targeting CAR-T product.

P-CD19CD20-ALLO1, a dual-targeting, fully allogeneic T_SCM-rich CAR-T product for CD19 and CD20-positive B-cell malignancies, demonstrates robust antigen-specific activity against DLBCL and CLL models and outperforms its single-targeting counterparts even in the presence of only a single antigen on target cells.

Jambon:Poseida Therapeutics: Current Employment, Current equity holder in publicly-traded company. Ruiz:Poseida Therapeutics: Current Employment, Current equity holder in publicly-traded company. Garcia-Maldonado:Poseida Therapeutics: Current Employment, Current equity holder in publicly-traded company. Chen:Poseida Therapeutics: Current Employment, Current equity holder in publicly-traded company. Mendoza:Poseida Therapeutics: Current Employment, Current equity holder in publicly-traded company. Arauz:Poseida Therapeutics: Current Employment, Current equity holder in publicly-traded company. DeMarco:Poseida Therapeutics: Current Employment, Current equity holder in publicly-traded company. Connerney:Poseida Therapeutics: Current Employment, Current equity holder in publicly-traded company. Eskew:Poseida Therapeutics: Current Employment, Current equity holder in publicly-traded company. Belani:Poseida Therapeutics: Current Employment, Current equity holder in publicly-traded company. Cranert:Poseida Therapeutics: Current Employment, Current equity holder in publicly-traded company. Coronella:Poseida Therapeutics: Current Employment, Current equity holder in publicly-traded company. Shedlock:Poseida Therapeutics: Current Employment, Current equity holder in publicly-traded company.