HHV6B-specific T cells are detected in the peripheral blood of HSCT recipients. PBMCs isolated from a HSCT recipient at the time of acute HHV6 infection were tested for specificity against our panel of HHV6 antigens, using IFN-γ ELISPOT as a readout. Unstimulated PBMCs were used as a negative control, whereas stimulation with a cocktail of CMV-pp65 and Adv-Hexon pepmixes was used to assess the relative frequency of circulating T cells directed against other ubiquitous viruses. Results are expressed as SFCs/1 × 105 input PBMCs (A). PBMCs from 4 other HSCT recipients with recently controlled HHV6 reactivations were stimulated with HHV6B antigen-spanning pepmixes and expanded for 9-10 days in presence of IL-4 + IL-7. (B) Phenotype of the expanded cells assessed by flow cytometry (mean ± SD expression). (C) Specificity by IFN-γ ELISPOT assay; results are expressed as SFCs/1 × 105 input cells.
