CD20-Specific Immunoligands Engaging NKG2D Enhance γδ T Cell-Mediated Lysis of Lymphoma Cells

Human γδ T cells are innate-like T cells which are able to kill a broad range of tumor cells and thus may have potential for cancer immunotherapy. The activating receptor natural killer group 2 member D (NKG2D) plays a key role in regulating immune responses driven by γδ T cells. Here, we explored whether recombinant immunoligands consisting of a CD20 single-chain fragment variable (scFv) linked to a NKG2D ligand, either MHC class I chain–related protein A (MICA) or UL16 binding protein 2 (ULBP2), could be employed to engage γδ T cells for tumor cell killing. The two immunoligands, designated MICA:7D8 and ULBP2:7D8, respectively, enhanced cytotoxicity of ex vivo expanded γδ T cells against CD20-positive lymphoma cells. Both Vδ1 and Vδ2 γδ T cells were triggered by MICA:7D8 or ULBP2:7D8. Killing of CD20-negative tumor cells was not induced by the immunoligands, indicating their antigen-specificity. MICA:7D8 and ULBP2:7D8 acted in a dose-dependent manner and induced cytotoxicity at nanomolar concentrations. Importantly, chronic lymphocytic leukemia (CLL) cells isolated from patients were sensitized by the two immunoligands for γδ T cell-cytotoxicity. In a combination approach the immunoligands were combined with bromohydrin pyrophosphate (BrHPP), an agonist for Vδ2 γδ T cells, which further enhanced the efficacy in target cell killing. Thus, employing tumor-directed recombinant immunoligands which engage NKG2D may represent an attractive strategy to enhance anti-tumor cytotoxicity of γδ T cells. This article is protected by copyright. All rights reserved.