203 - ATA3219: A Potent Next-Generation Allogeneic Off-the-Shelf CD19 CAR-T Therapy without the Need for Gene Editing

Abstract

INTRODUCTION The development of allogeneic CD19 chimeric antigen receptor (CAR) T cells from healthy donors is a significant focus in cell therapy and is anticipated to overcome the technical and logistical challenges associated with autologous CAR-T cells. Unlike gene-edited approaches, which require inactivation of the endogenous αβ T cell receptor to reduce the risk of Graft-versus-Host Disease (GvHD), allogeneic Epstein-Barr Virus (EBV)-targeted T cells represent a clinically-advanced treatment modality that, to-date, has demonstrated a favorable safety profile with limited risks of GvHD or cytokine release syndrome [Prockop et al. JCI, 2020; Prockop et al. Blood, 2019] . As an allogeneic CAR T cell platform, EBV T cells represent a unique composition that retains critical transducibility and function, and minimizes risks for GvHD and other host interactions, without requiring complex gene editing or other cell engineering approaches to facilitate use in the allogeneic setting. Recent clinical experience with allogeneic CD19 CAR-modified EBV T cells have further supported safe and effective clinical experience in the context of B cell malignancies [Curran KJ et al. TCT 2020]. Recent advances in next-generation stimulatory domains also represent potential for improvement on current CAR-T therapies. Specifically, a modified CD3ζ domain retaining signaling capacity in 1 of 3 immune-receptor-tyrosine-based-activation-motif (ITAM) regions (referred to as 1XX) is designed to extend functional persistence without compromising potency via calibration of antigen induced CAR signaling intensity to more physiologic levels [Feucht et al. Science Trans Med 2018]. Here, we describe the first preclinical evaluation of ATA3219, a next-generation allogeneic CD19 CAR T cell therapy, combining a non-edited allogeneic EBV T cell approach with a CAR signaling domain designed to improve upon the currently clinically validated CD19 targeted CAR therapies. METHODS and RESULTS We generated EBV T cells engineered with a CD19-targeted CAR containing a modified CD3ζ signaling domain, 1XX (CD19-1XX CAR+ EBV T cells). CD19-1XX CAR+ EBV T cells demonstrate high CAR expression, polyfunctionality, expansion and in vitro potency through HLA-independent killing of CD19+ targets. Furthermore, CD19-1XX CAR+ EBV T cells demonstrate highly potent antitumor activity in an established disseminated tumor model of acute lymphoblastic leukemia and is associated with long-term persistence of the product. No treatment-related toxicities were observed in this animal model. CONCLUSIONS This preclinical dataset for CD19-1XX CAR+ EBV T cells demonstrate, persistence, polyfunctional phenotype and efficient targeting of CD19-expressing tumor cells, both in vitro and in vivo, with limited allocytoxicity against antigen-negative, HLA-mismatched targets. These findings support advancing ATA3219 to clinical evaluation. Disclosures Pham: Atara Biotherapeutics: Current Employment, Current equity holder in publicly-traded company. Spindler: Atara Biotherapeutics: Current Employment, Current equity holder in publicly-traded company. Hwang: Atara Biotherapeutics: Current Employment, Current equity holder in publicly-traded company. Brito: Atara Biotherapeutics: Current Employment, Current equity holder in publicly-traded company. Bulliard: Atara Biotherapeutics: Current Employment, Current equity holder in publicly-traded company. Aftab: Atara Biotherapeutics: Current Employment, Current equity holder in publicly-traded company.