Microenvironment and Immunology Cancer Immunotherapy Using a Bispecific NK Receptor Fusion Protein that Engages both T Cells and Tumor Cells

T-cell immunotherapy is a promising strategy to treat cancer, but its efficacy, complexity, and costs may pose challenges. In this study, we report the results of an investigation of a new approach to selectively activate a Tcell attack against tumor cells. The immunotherapeutic approach we developed utilizes a bifunctional fusion protein that binds tumor cells through NK (natural killer)–activating receptor NKG2D and that recruits and stimulates T cells through an anti-CD3 single-chain variable fragment (scFv-NKG2D). In vitro, this scFv-NKG2D fusion protein engaged both T cells and tumor cells, stimulating T cells to produce IFN-g , and cytotoxicity against NKG2D ligand–positive tumor cells. In vivo, expression of scFv-NKG2D by NKG2D ligand–positive tumor cells reduced tumor burden and, in some cases, led to tumor-free survival. Administration of scFv-NKG2D in vivo also promoted survival in a murine lymphoma model. Tumor-free mice were resistant to rechallenge with cognate tumor cells, suggesting that a host-specific immunologic memory response had been generated. Host adaptive immunity including gd T cells was required for scFv-NKG2D–mediated therapeutic efficacy. ScFvNKG2D also inhibited the growth of NKG2D ligand–negative B16F10 tumors, reduced the percentage of myeloidderived suppressor cells and regulatory T cells, and increased the infiltration of T cells, suggesting that scFvNKG2Dmay target these immune suppressive cells. Together, these results establish scFv-NKG2D as a promising biological fusion protein to induce effective antitumor immunity. Cancer Res; 71(6); 2066–76. 2011 AACR.