Session: 703. Cellular Immunotherapies: Basic and Translational: Poster II
Hematology Disease Topics & Pathways:
Biological therapies, Chimeric Antigen Receptor (CAR)-T Cell Therapies, Therapies, Immunotherapy
Methods: We generated a FOLR1-directed CAR using anti-FOLR1 binder (Farletuzumab), IgG4 intermediate spacer and 41-BB/CD3zeta signaling domains. The pre-clinical efficacy of FOLR1 CAR T cells was evaluated against CBF/GLIS AML cell lines in vitro and in vivo. CBF/GLIS AML models include CB CD34+ cells transduced with CBF/GLIS expression construct (CBF/GLIS-CB) and WSU-AML cell line. We also engineered Kasumi-1 cell line to express FOLR1 (Kasumi-1 FOLR1+) to evaluate target specificity (Figure 1A).
Results: We tested the target specificity of FOLR1-directed CAR T cells against FOLR1-positive (CBF/GLIS-CB, WSU-AML, Kasumi-1 FOLR1+) and FOLR1-negative (Kasumi-1) cells. CD8 FOLR1 CAR T cells demonstrated cytolytic activity against FOLR1 positive but not FOLR1 negative cells (Figure 1B). Furthermore, both CD8 and CD4 FOLR1 CAR T cells produced higher levels of IL-2, IFN-𝛄, and TNF-𝛂 and proliferated more robustly than did unmodified T cells when co-incubated with FOLR1 positive but not FOLR1 negative cells (Figure 1C). These results indicate highly specific reactivity of FOLR1 CAR T cells against AML cells expressing FOLR1. We next investigated the in vivo efficacy of FOLR1-directed CAR T cells. In CBF/GLIS-CB, WSU-AML, and Kasumi-1 FOLR1+ xenograft models, treatment with FOLR1 CAR T cells induced leukemia clearance, while disease progression occurred in all mice that received unmodified T cells (Figure 1D). Activity of FOLR1 CAR T cells in vivo was target specific, as they did not limit the leukemia progression nor extend the survival of Kasumi-1 xenografts (Figure 1D).
To determine whether FOLR1 is expressed on normal HSPCs, we characterized FOLR1 expression in normal CB CD34+ samples. FOLR1 expression was entirely silent in HSPC subsets (Figure 1E). Consistent with lack of expression, no cytolytic activity was detected against HPSCs Moreover, FOLR1 CAR T cells did not affect the self-renewal and multilineage differentiation capacity of normal HSPCs as compared to unmodified control T cells (Figure 1F), whereas significant eradication of colonies were detected in the CBF/GLIS-CB cells (Figure 1G).
Conclusion: In this study, we demonstrate that FOLR1 CAR T effectively eradicates CBF/GLIS AML cells without compromising normal HSPCs, providing a promising approach for the treatment of high-risk CBF/GLIS AML. Transition of this CAR T to clinical development for infant AML is underway.
Disclosures: Hylkema: Moderna: Current equity holder in publicly-traded company; Quest Diagnostics Inc: Current equity holder in publicly-traded company. Pardo: Hematologics, Inc.: Current Employment. Eidenschink Brodersen: Hematologics, Inc.: Current Employment, Other: Equity Ownership. Loken: Hematologics, Inc.: Current Employment, Other: current equity holder in a privately owned company.
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