Chimeric Antigen Receptor-Modified T Cells for the Treatment of Acute Myeloid Leukemia Expressing CD33

Relapsed acute myeloid leukemia (AML) is an aggressive disease with very poor outcomes. Redirection of T-cell specificity via chimeric antigen receptor (CAR) has shown promising anti-tumor activity in clinical trials, particularly for B cell linage malignancies. CD33 is a transmembrane protein expressed on normal and malignant myeloid-derived cells as well (as on subsets of activated T cells and NK cells). Since this protein is commonly expressed on AML cells, we sought to evaluate the efficacy of targeting AML with CD33-specific CAR-T cells. We generated a lentiviral construct to co-express CD33-specific CAR and a kill switch based on a tag derived from the epidermal growth factor receptor. The latter allows for the conditional elimination of CAR-T cells in vivo. Following transduction of primary T cells, we confirmed CAR and kill switch co-expression by flow cytometry and western blot analyses. Elimination of genetically modified T cells was demonstrated using the clinically-available antibody, cetuximab. CD33 CAR-T cells demonstrated specific cytotoxicity to CD33⁺ target cell lines. CD33 CAR-T cells were also activated to produce IFNg, TNF, and IL-2 cytokines in response to CD33⁺ target cells. Furthermore, adoptive transfer of CD33 CAR-T in immunocompromised (NSG) mice bearing established CD33⁺(CD19^neg) AML (MOLM-13) tumor resulted in reduction of tumor burden and improvement of overall survival, compared to control mice receiving CD19 CAR-T cells or no immunotherapy (Figure). Sampling of blood demonstrated the persistence of the CD33 CAR-T cells with no detection of AML (MOLM-13) tumor cells. These pre-clinical data demonstrate the effectiveness of CD33 CAR-T cells in targeting CD33⁺ AML tumor cells and provide a rationale for future clinical evaluation in AML patients with unmet medical need.

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