Lysis of a broad range of epithelial tumour cells by human γδ T cells:: Involvement of NK62D ligands and T-cell receptor- versus NKG2D-dependent recognition

Human gamma delta T cells expressing a V gamma 9V delta 2 T-cell receptor (TCR) kill various turnout cells including autologous tumours. In addition to TCR-dependent recognition, activation of NKG2D-positive gamma delta T cells by turnout cell-expressed NKG2D ligands can also trigger cytotoxic effector function. In this study, we investigated the involvement of TCR versus NKG2D in turnout cell recognition as a prerequisite to identify turnout types suitable for gamma delta T-cell-based immunotherapy. We have characterized epithelial turnout cells of different origin with respect to cell surface expression of the known NKG2D ligands MHC class I-chain-related antigens (MIC) A/B and UL16-binding proteins (ULBP), and susceptibility to 6 T-cell killing. Most turnout cells expressed comparable levels of MICA and MICB as well as ULBP with the exception of ULBP-1 which was absent or only weakly expressed. Most epithelial tumours were susceptible to allogeneic 6 T-cell lysis and in the case of an established ovarian carcinoma to autologous gamma delta T-cell killing. Lysis of resistant cells was enhanced by pre-treatment of turnout cells with aminobisphosphonates or pre-activation of gamma delta T cells with phosphoantigens. A potential involvement of TCR and/or NKG2D was investigated by antibody blockade. These experiments revealed three patterns of inhibition, i.e. preferential inhibition by anti-TCR antibody, preferential inhibition by anti-NKG2D antibody, or additive blockade by anti-TCR plus anti-NKG2D antibodies. Our results indicate for the first time that the NKG2D pathway is involved in the lysis of different melanomas, pancreatic adenocarcinomas, squameous cell carcinomas of the head and neck, and lung carcinoma.