Degranulation of T-Cells Specific for the CMV-Proteins pp65 and IE-1 in Allogeneic Stem Cell Recipients.

Infection and disease with human cytomegalovirus (HCMV) is still an important cause for morbidity and mortality after allogeneic stem cell transplantation (allo SCT). Specific T-cells (CTL) are crucial for the control of CMV infection. In addition to cytokine production, degranulation is an interesting marker of T-cell function. Recent studies in patients after solid organ transplantation revealed that high levels of IE-1-specific CTL correlate with a protection from CMV disease. However, the functionality of these cells is less clear. As demonstrated in AIDS suffering patients, CTL activity is more related to a protection than to a cytokine secretion. Here we address the question, whether CD4 and CD8 T-cells have different abilities to degranulate or to produce cytokines depending on the type of immunosuppression and the CMV target protein.

Material and Methods: T-cells from 6 healthy CMV exposed donors and 16 allografted patients (11 AML, 3 ALL, 1 NHL, 1 MPS) were stimulated with peptide pools representing the pp65 (UL83) and IE-1 (UL123) proteins. Mobilized CD107 (marker of CTL activity), TNF, IFN-g, and IL-2 production was analyzed by 8-color flowcytometry. Immunosuppression consisted of CSA/MMF (n=4), CSA alone (n=4) and CSA/MTX (n=8), 4/8 patients additionally received ATG for GvHD-prophylaxis as part of the conditioning regimen. In all transplanted patients CMV antigenemia was assessed twice a week.

Results and Conclusion: The responding T-cell population mainly demonstrated an effector phenotype with a low expression of CD28. Frequency of reactive CTL did not correlate with CMV antigenemia. Interestingly, there was no impairment of degranulation or cytokine production found in any of the allogeneic transplanted patients compared with healthy CMV exposed controls, showing that immunosuppression does not target the function of the specific CTL.