Inconsistent Responses of Cytomegalovirus‐Specific T Cells to pp65 and IE‐1 versus Infected Dendritic Cells in Organ Transplant Recipients

CD4+ and CD8+ T cells specific for human cytomegalovirus (HCMV) and two immunodominant HCMV antigens (pp65 and IE‐1) were monitored in 20 solid organ transplant recipients undergoing primary (n = 4) or reactivated (n = 16) HCMV infection during the first year after transplantation by using as a stimulator either HCMV‐infected autologous dendritic cells (DCs) or pp65‐ or IE‐1 peptide mixtures. Turnaround times for test performance were 7 days for infected DCs and 24 h for peptides. Using infected DCs, HCMV‐specific T‐cell restoration occurred in all patients for CD8+ and in 18/20 (90%) for CD4+ T‐cell subpopulations, resulting in virus clearance from blood. Using peptide mixtures, T‐cell responses were less frequently detected. In detail, 14 (70%) patients showed pp65‐specific CD8+ T cells and 10 (50%) patients IE‐1‐specific CD8+ T cells, whereas pp65‐specific CD4+ T cells were detected in 14 (70%) patients, and IE‐1‐specific CD4+ T cells in three (15%) patients only. Protection from HCMV infection was associated with the presence of a HCMV‐specific T‐cell response directed against multiple viral proteins, but not against pp65 or IE‐1 only. In conclusion, the use of pp65 and IE‐1 peptide mixtures for rapid monitoring of HCMV‐specific T‐cell responses in solid organ transplant recipients underestimates the actual T‐cell immune response against HCMV. Use of pp65 and IE‐1 peptide mixture instead of infected dendritic cells for monitoring of human cytomegalovirus specific T‐cell responses in solid organ transplant recipients underestimates the actual level of specific T‐cell immune response.