Abstract 644: Cytokine-induced memory-like NK cells with tafasitamab show efficacy against B-cell acute lymphoblastic leukemia

Abstract Introduction: While chimeric antigen receptor (CAR)-T cells can be effective in treating B-cell acute lymphoblastic leukemia (B-ALL), Natural Killer (NK) cell therapies are showing promise as an easier to manufacture product with potent activity in early studies. Cytokine-induced memory-like NK cells (CIMLNK) are generated by brief stimulation with the cytokines IL-12, IL-15, and IL-18 and demonstrate enhanced anti-cancer responses. Tafasitamab (TAFA) is an Fc-enhanced humanized anti-CD19 monoclonal antibody designed to enhance anti-tumor activity through antibody-derived cellular cytotoxicity (ADCC), a function primarily mediated by NK cells. Therefore, we hypothesized that combining TAFA with CIMLNK can augment responses against B-ALL. Methods: NK cells were isolated from peripheral blood mononuclear cells (PBMCs) of healthy volunteers. For the generation of CIMLNK, NK cells were incubated overnight with IL-12, IL-15, and IL-18. For flow cytotoxicity assays, target cells (NALM-6, a B-ALL cell line) were co-incubated with the effectors (NK or CIMLNK) at 2.5:1 effector: target (E: T) ratio, with or without TAFA (1 μg/ml). Degranulation and IFN-γ release assays were performed to examine mechanistic differences between effector responses. CD16 blocking assays were done using a purified anti-CD16 mAb to assess the role of CD16 binding in TAFA-induced ADCC. In vivo, irradiated NSG mice received 1 x 104 Nalm6-luc intravenously (i.v.). The next day, 1 x 106 CIMLNK were injected i.v., with TAFA given at 0.3 - 0.5 mg/kg, i.v. or intraperitoneally (i.p.) respectively. Statistical analyses were performed using GraphPad Prism v10. P values of < 0.05 were considered significant. Results: Cytotoxicity assays showed that CIMLNK + TAFA resulted in significantly higher killing of NALM6 compared with CIMLNK alone 84.4% vs 22.7%, (p=0.0005) and NK+TAFA 84.4% vs 38.3%, (p=0.0006). CIMLNK alone demonstrated significantly higher cytotoxicity against NALM6 compared to NK cells, 22.7% vs 1.2% (p=0.02). Cytotoxicity was not observed when TAFA was used alone. Mechanistically, we observed that combining TAFA with CIMLNK led to a significant increase in degranulation, 55.4% vs 13.3%, (p=0.02) and IFN-γ release, 26.7% vs 3.6%, (p=0.03) compared to CIMLNK monotherapy. Moreover, in the presence of TAFA, CIMLNK degranulated significantly more compared to unstimulated NK cells, 55.4% vs 27.7% (p=0.04). The addition of anti-CD16 mAb to CIMLNK abrogated TAFA-induced ADCC. In vivo, combining CIMLNK with TAFA resulted in a median survival of 35 days, which was significantly higher than that seen in untreated mice (28 days, p= 0.01), TAFA monotherapy (28 days, p= 0.003) and CIMLNK monotherapy (26.5 days, p=0.009). Conclusion: The combination of CIMLNK and TAFA exerts synergistic effects against B-ALL both in vitro and in vivo. Citation Format: Dimitrios Filioglou, Geovana Leite, Helena Batatinha, Nina Santa-Cruz, Dan Davini, Richard Simpson, Emmanuel Katsanis. Cytokine-induced memory-like NK cells with tafasitamab show efficacy against B-cell acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 644