Generation and preclinical characterization of an NKp80-Fc fusion protein for redirected cytolysis of NK cells against leukemia [Immunology]

July 21st, 2015 by Deng, G., Zheng, X., Zhou, J., Wei, H., Tian, Z., Sun, R.

The capacity of NK cells to mediate Fc-receptor-dependent effector functions, such as ADCC, largely contributes to their clinical application. Given that AICL, an identified ligand for NK activating receptor NKp80, is frequently highly expressed on malignant leukemia cells in AML and CML, and given the current lack of therapeutic AICL-specific antibodies, we aimed to explore a strategy to reinforce NK anti-leukemia reactivity by combining targeting AICL-expressing leukemia cells with the induction of NK cell ADCC using NKp80-Fc fusion proteins. Binding tests using flow cytometry indicated that NKp80-Fc chimera specifically bound to leukemia cell lines in an AICL-specific and concentration-dependent manner. Moreover, cell binding assays between NK and leukemia cells showed that NKp80-Fc significantly increased NK-target cell conjugation. In functional analyses, treatment with NKp80-Fc clearly induced an NK cell ADCC effect. Cell apoptosis and lysis assays showed that NKp80-Fc not only promoted NK-mediated target cell apoptosis in the early stage of cell conjugation but also enhanced NK cell degranulation and cytotoxicity activity in an AICL-dependent manner in the relatively late stage of cell conjugation. The bifunctional NKp80-Fc re-directed NK cells toward the leukemia cells by binding to both the tumor cells and NK cells, and triggered NK cell-mediated target cell killing in vitro. Taken together, our results demonstrate that NKp80-Fc can effectively target AICL-expressing leukemia cells for tumor lysis by NK cells. This method will be potentially useful in further research on molecular targeted therapy, and the fusion proteins may thus constitute a promising means for immunotherapy of leukemia.