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 CD20/CD19 bispecific benchmark CAR T cells. No treatment-related toxicities were observed in animals treated with ATA3431.

CONCLUSIONS: Preclinical evaluations of ATA3431 show B-cell tumor growth inhibition without any treatment-related toxicities and thereby support advancing ATA3431 for clinical evaluation.

Curran KJ, Sauter CS, Kernan CS, et al. Durable remission following “off-the-shelf” chimeric antigen receptor (CAR) T-cells in patients with relapse/refractory (R/R) B-cell malignancies. 2020 Transplantation & Cellular Therapy Meetings. Orlando.

Larson SM, Walthers CM, Ji B, Ghafouri SN, et al. CD19/CD20 bispecific chimeric antigen receptor (CAR) in naive/memory T cells for the treatment of relapsed or refractory non-Hodgkin lymphoma. Cancer Discov. 2023 Mar 1;13(3):580-597. doi: 10.1158/2159-8290.CD-22-0964. PMID: 36416874; PMCID: PMC9992104.

Shah NN, Johnson BD, Schneider D, et al. Bispecific anti-CD20, anti-CD19 CAR T cells for relapsed B cell malignancies: a phase 1 dose escalation and expansion trial. Nat Med. 2020 Oct;26(10):1569-1575. doi: 10.1038/s41591-020-1081-3. Epub 2020 Oct 5. PMID: 33020647.