ATA3431: Allogeneic CD19/CD20 Bispecific CAR EBV T Cells for the Treatment of B-Cell Malignancies

BACKGROUND: Chimeric antigen receptor (CAR) therapy targeted against CD19 has yielded remarkable clinical responses in the treatment of relapsed/refractory B-cell malignancies, but about a third of patients ultimately relapse due to the loss or downregulation of CD19. Furthermore, technical and logistical challenges associated with autologous CAR T therapy limits access for a majority of eligible patients. To help address these challenges, we have developed an allogeneic bispecific tandem CAR directed against both CD19 and CD20 (ATA3431) built on our Epstein-Barr virus (EBV) T-cell platform. EBV T cells maintain expression of endogenous T-cell receptors that have inherently low alloreactivity due to their recognition of defined viral antigens. CAR EBV T cells have demonstrated a favorable safety profile with no associated evidence for graft-versus-host disease or high-grade cytokine release syndrome (Curran KJ, 2020). The bispecific tandem CAR design allows either CD19 or CD20 target antigen recognition to activate the CAR EBV T cell, with the goal of extending durability of response and limiting antigen escape. In clinical trials, autologous bispecific CAR T cells were shown to be efficacious and safe (Larson 2023, Shah 2020). Additionally, a 1XX mutated CD3ζ signaling domain and our optimized CAR EBV T-cell platform preserve a central memory phenotype, robust expansion, functional persistence, and potent antitumor activity of ATA3431. METHODS: We generated CD20/CD19 bispecific CAR EBV T cells containing a modified CD3ζ signaling domain 1XX using our EBV T-cell platform. As a benchmark comparator, we generated autologous CD20/CD19 bispecific CAR T cells using a 12-day process derived from OKT3/CD28-activated T cells. The final products were characterized via immunophenotyping and evaluated for in vitro and in vivo response to antigen expressing targets. RESULTS: CD20/CD19 bispecific CAR EBV T cells generated from multiple healthy donors demonstrated stable CAR expression, a high proportion of T-cell memory populations, and consistent HLA-independent killing of CD19 + and/or CD20 + tumor cells over repeated in vitrochallenges. ATA3431 mediated highly potent antitumor activity in an established disseminated tumor model of Burkitt's lymphoma and correlated with long-term in vivo persistence of CAR T cells without additional cytokine support. Moreover, ATA3431-treated animals showed superior tumor growth inhibition compared to animals treated with autologous