Flow cytometric analysis of virus-specific T lymphocytes: Practicability of detection of HCMV-specific T lymphocytes in whole blood in patients after stem cell transplantation

The detection and quantification of specific T lymphocytes against human cytomegalovirus (HCMV) has proven an important laboratory marker in the monitoring of patients after stem cell transplantation (SCT). In these patients HCMV infections may cause severe disease and death. However, the determination of HCMV-specific T lymphocytes may be limited by lymphopenia occurring after transplantation. We evaluated a commercial test kit for the reliable determination of HCMV-specific T lymphocyte development in lymphopenic patients after stem cell transplantation. Using a whole blood protocol for the flow cytometric detection of antigen-specific CD4+ T-helper and CD8+ cytotoxic T lymphocytes this test kit measures intracellular cytokine production after stimulation with HCMV antigen. The measurement of HCMV-specific T lymphocytes was feasible when at least 3000 CD4+ or 1000 CD8+ T cells could be counted by flow cytometry. Detection of HCMV-specific T lymphocytes was possible, on average, 67 (SD ± 61) days after transplantation for CD4+ cells and 27 (SD ± 13) days for CD8+ cells, thus being still within the critical time for HCMV reactivation. In conclusion, the use of modern test kits permits the measurement of HCMV-specific T lymphocytes in stem cell transplant recipients and may be included in the HCMV monitoring system after SCT.