Cytotoxicity assay of patient’s γδ T cells. Specific lysis of sorted γδ T cells versus (A) CMV-infected human foreskin cells or (B) versus patient’s B-CLL. Total γδ T cells were sorted from patient’s blood samples using PE-conjugated anti pan γδ TCR (clone 11 F2) after Ficoll separation using a FACS Aria cell sorter 9 months after transplantation. At the same time, B-CLL cells were sorted according to size and for positive signals using PerCPCy5.5-conjugated CD19 (clone 5J25C1) and PE-Cy7-conjugated CD20 (clone L27). Cytotoxicity assay: 51chromium (51Cr) release cytotoxicity assay was performed by using sorted γδ T cells as effectors and either (A) CMV-infected primary human foreskin fibroblasts or (B) autologous tumor cells as targets. After 51Cr-labeling, target cells were washed and resuspended in medium (RPMI1640 supplemented with 10% foetal calf serum, 100 U/ml penicillin/streptomycin, 1 mM sodium pyruvate, and 2 mM glutamine). 100 μl of effector cells (1×106/ml – 1.25×105/ml) were pipetted in triplicates at three effector to target (E/T) ratios (20:1, 10:1, and 2.5:1) in V-bottom microtiter plates containing 50 μl of target cell solution (1×105/ml). The assay was incubated for 20 hours. The plates were centrifuged and 25 μl of cell-free supernatants were harvested. Specific cytotoxicity was measured by determining released 51Cr. Background values were determined by incubating target cells without effector cells. Maximal values were obtained by lysing target cells with Triton X-100. Specific lysis was calculated by: experimental release - spontaneous release / maximum release - spontaneous release x 100. Generation of positive control target cells by HFF infection: HFF were cultured in Dulbecco’s modified Eagle’s medium supplemented with 10% fetal calf serum (FCS) and antibiotics. Cells were infected with HCMV TB40/E UL11-V5 mutant  at an m.o.i. of 1 for 120 h prior to in vitro killing assay.