Abstract 3250: CD229-targeted CAR T cell therapy for the treatment of B cell lymphoma

Background: B cell lymphomas are the most common hematologic malignancy. Unfortunately, therapy-resistant relapses, even after CD19 CAR T cells, drive poor survival in certain lymphoma subtypes. CD229 is an immune receptor that is expressed on normal B cells as well as various B cell malignancies. In this study, we performed the first preclinical evaluation of CD229 as a therapeutic CAR T cell target in B cell lymphoma. Methods: We analyzed expression of CD229 in B cell lymphoma cell lines and primary patient material by semi-quantitative PCR, western blot and flow cytometry. We then generated CD229 CAR T cells using our own, previously described CD229-specific scFv (single-chain fragment variable) antibody and CD3ζ / 4-1BB signaling domains. We determined the efficacy of CD229 CAR T cells against B cell lymphoma cell lines and primary patient material in vitro using established cytotoxicity assays and cytometric bead arrays. Finally, we utilized B cell lymphoma cell line-derived xenograft mouse models to determine the in vivo efficacy of CD229 CAR T cells. Results: Expression analysis of 12 B cell lymphoma cell lines including diffuse large B cell lymphoma (DLBCL), Burkitt lymphoma, B cell acute lymphoblastic leukemia (B-ALL) and mantle cell lymphoma revealed consistent expression of CD229 transcript, total protein and surface protein. Similarly, expression analysis of primary material from patients with B cell lymphoma revealed CD229 surface expression in 16/16 cases of B cell chronic lymphoblastic leukemia (B-CLL), 13/13 mantle cell lymphomas, 6/6 follicular lymphomas and 4/4 DLBCLs. Next, we efficiently generated CAR T cells targeting CD229 and utilized these CAR T cells for in vitro cytotoxicity assays. Coculture of CD229 CAR T cells with B cell lymphoma cell lines resulted in effective eradication of B cell lymphoma cells (two DLBCL, two mantle cell lymphoma and two Burkitt lymphoma) at low effector-target ratios while control CAR T cells had no effect. In addition to robust killing of B cell lymphoma cell lines, CD229 CAR T cells were also able to effectively kill primary cells from 4/4 mantle cell lymphoma patients and 3/3 B-CLL patients. CD229 CAR T cells produced high amounts of proinflammatory type-1 cytokines including IFNγ, IL2, and TNFα upon exposure to B cell lymphoma cell lines and primary material. Finally, we observed efficient tumor control by CD229 CAR T cells, but not control CAR T cells, using multiple B cell lymphoma xenograft mouse models. Conclusions: Taken together, we demonstrate for the first time that CD229 CAR T cells are a promising candidate for the treatment of B cell lymphoma as evidenced by the consistent expression of CD229 on B cell lymphoma cells and the efficacy of CD229 CAR T cells against B cell lymphoma in vitro and in vivo. Citation Format: Michael L. Olson, Sabarinath V. Radhakrishnan, Tim C. Luetkens, Djordje Atanackovic. CD229-targeted CAR T cell therapy for the treatment of B cell lymphoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3250.