Flow cytometric quantitation and characterization of the T-lymphocyte memory response to CMV in healthy donors

Background Levels of circulating Of V Ag-specific lymphocytes determine CMV reactivation risk in immunocompromised individuals. Methods Frequencies of T cells producing cytokines after stimulation by CMV Ag were measured in hematopoietic stem-cell donors using flow cytometry. Results In seropositive individuals (n = 75) the mean number of CD8(+) (CD8(bright), CD8(dim)) and CD4(+) cells producing IFN-gamma was respectively 3.1% (12.6 /muL) and 0.38% (3.2/muL), over 10-fold higher than in seronegative subjects (n = 22). CMV stimulation induced tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) in both CD4(+) and CD8(+) cells (usually together), with a shift from memory- to effector-cell phenotype, while only a small proportion of CD4(+) cells produced IL-4. Although the normal range was wide, neither age, sex nor HLA type affected the frequency. Discussion These quantitative studies and the recognition of CD4(+) cells as potential effectors of CMV immunity are of relevance for immunotherapeutic approaches to prevent CMV disease after stem-cell transplantation.