Human cytomegalovirus (HCMV)-specific CD4+ and CD8+ T cells are both required for prevention of HCMV disease in seropositive solid-organ transplant recipients.

In solid-organ transplant recipients (SOTR) the protective role of human cytomegalovirus (HCMV)-specific CD4+, CD8+ and γδ T-cells vs. HCMV reactivation requires better definition. The aim of this study was to investigate the relevant role of HCMV-specific CD4+, CD8+ and γδ T-cells in different clinical presentations during the post-transplant period. Thirty-nine SOTR underwent virologic and immunologic follow-up for about 1 year after transplantation. Viral load was determined by real-time PCR, while immunologic monitoring was performed by measuring HCMV-specific CD4+ and CD8+ T cells (following stimulation with autologous HCMV-infected dendritic cells) and γδ T-cells by flow cytometry. Seven patients had no infection and 14 had a controlled infection, while both groups maintained CD4+ T-cell numbers above the established cut-off (0.4 cell/µL blood). Of the remaining patients, 9 controlled the infection temporarily in the presence of HCMV-specific CD8+ only, until CD4+ T-cell appearance; while 9 had to be treated preemptively due to a viral load greater than the established cut-off (3×10(5) DNA copies/mL blood) in the absence of specific CD4+ T-cells. Polyfunctional CD8+ T-cells as well as Vδ2- γδ T-cells were not associated with control of infection. In conclusion, in the absence of HCMV-specific CD4+ T-cells, no long-term protection is conferred to SOTR by either HCMV-specific CD8+ T-cells alone or Vδ2- γδ T-cell expansion.