Abstract 2561: Fully human immunoglobulin heavy chain only-derived CD33 CAR for the treatment of acute myeloid leukemia

Abstract

Abstract CD33 antigen is a promising target expressed on non-solid cancers, including acute myeloid leukemia (AML). Present investigative approaches to treatment of CD33-positive AML include antibody drug conjugates (My96, Mylotarg®) and CART cells incorporating CD33-targeting domains derived from a humanized scFv. Here, we designed a chimeric antigen receptor utilizing targeting domain derived from a fully human CD33 fragment variable heavy chain sequence, termed CAR33VH, and examined its in vitro and in vivo potency against AML. Primary human CD4+ CD8+ T cells derived from three healthy donors were transduced with lentiviral constructs (LV) encoding CAR33VH, or control CAR construct based on scFv My96 (My96CAR). Flow cytometric analysis revealed expression of CAR33VH at 32%-45%, and expression of My96CAR at 77% - 86%. When challenged with CD33+ AML tumor lines HL60 and MOLM-14 in vitro, both constructs demonstrated efficient target killing. CD33- tumor lines K562 and Reh were not sensitive to CAR killing, underscoring CAR specificity to CD33 antigen. Pro-inflammatory cytokines IFN gamma, TNF alpha and IL-2 in culture supernatants of CART cells incubated with CD33+ HL-60 and MOLM-14 tumors, but not with CD33- K562 cells overnight, were induced, as measured by ELISA. Long-term co-incubation assay of CART cells with HL-60 leukemia at E:T ratios 1:5 to 1: 0.04, suggested similar killing potency and persistence of CAR33VH to the positive control scFv-based CAR. In in vivo AML model, NSG mice engrafted with MOLM-14 cells stably expressing firefly luciferase, both CAR33VH, and My96CAR control were equally efficient in tumor elimination. In conclusion, CAR33VH, comprised of a fully human heavy-chain variable fragment only antigen binding domain, was efficient in tumor killing in vitro and in vivo, and may be used clinically for treatment of CD33+ hematologic malignancies. To our knowledge, this is one of the first instances demonstrating the feasibility of employing heavy chain only binder sequence in CART design. Citation Format: Dina Schneider, Ying Xiong, Weizao Chen, Zhongyu Zhu, Darong Wu, Jennifer Hwang, Dimiter S. Dimitrov, Boro Dropulic, Rimas J. Orentas. Fully human immunoglobulin heavy chain only-derived CD33 CAR for the treatment of acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2561.