HHV6B antigen-specific T cells can be expanded from peripheral blood. (A) The frequency of antigen-specific T cells in peripheral blood was determined by IFN-γ ELISPOT assay after overnight stimulation of PBMCs with CMV (pp65 and IE1) and HHV6 (U11, U14, U54, U71, and U90) antigen-spanning pepmixes in 4 donors. Stimulation with Staphylococcus aureus was used as positive control, and unstimulated PBMCs served as a negative control. Results are expressed as SFCs/4 × 105 input cells (median SFCs). (B) PBMCs were stimulated with the HHV6 pepmixes in the presence of IL-4 + IL-7. On day 9 after stimulation, the phenotype (mean expression ± SD) was assessed (n = 14). (C) PBMCs from 14 donors were stimulated with HHV6 pepmixes in the presence of IL-4 + IL-7, and specificity on day 9 was measured by IFN-γ ELISPOT. Results are expressed as SFCs/1 × 105 input cells. (D) Specificity of CTLs generated from 6 CMV-seronegative donors. IFN-γ production was assessed on day 9 after stimulation, and results are expressed as SFCs/1 × 105 input cells. The negative control was IFN-γ release detected in response to stimulation with an irrelevant pepmix.
