mAb 256 specifically inhibits cytolytic responses of Vδ2⁻ γδ T cells induced by human B lymphoid target cells. (A) Mice were immunized against human EBV⁺ B-LCLs. Cytolytic activity of the 73R9 γδ T-cell clone (Vγ8Vδ3) was measured by ⁵¹Cr release assay after a 4-hour coculture together with B cells from human B-LCL (Do#AD) at 10:1 and 2:1 γδ T cell-to-target ratios, in the presence of supernatants (dilution, 1:5) collected from 6 distinct cloned hybridomas. (B) Cytolytic activity of the G12 (Vγ9Vδ2) and 73R9 (Vγ8Vδ3) γδ T-cell clones was measured by ⁵¹Cr release assay after a 4-hour coculture together with Burkitt lymphoma cells (Daudi) at 10:1 and 1:1 γδ T cell-to-target ratios in the absence (Ctrl, filled bars) or in the presence of mAb 256 (ascites 1:1000 dilution, open bars; n > 3). Similar data were obtained using different Vγ9Vδ2 T-cell clones/lines from distinct donors. (C) Cytolytic activity of 7 human Vδ2⁻ γδ T-cell clones was measured by ⁵¹Cr release assay after a 4-hour coculture together with target cells from 2 different B-LCLs (Do#GR, left and Do#AD, right) at 10:1 and 3:1 γδ T cell-to-target ratios in the presence of mAb 256 (ascites 1:500, open bars). γδ T-cell clones 94–5-14, 73R3, 73R11, and 73R13 were derived from PBL of 2 distinct donors. Clones 18S3.1, 18S3.5, and 21S3.15 were derived from human fetal thymi of 2 distinct donors. (A-C) Data are the percentage of specific lysis (mean ± SD) and are representative of at least 3 independent experiments. *P < .05. **P < .005.