Granulocyte colony-stimulating factor (G-CSF) transiently suppresses mitogen-stimulated T-cell proliferative response

Granulocyte colony-stimulation factor (G-CSF) is a cytokine that selectivel y promotes growth and maturation of neutrophils and may modulate the cytoki ne response to inflammatory stimuli. The purpose of this study was to exami ne the effect of G-CSF on ex vivo peripheral blood mononuclear cell (PBMC) functions. Ten patients with breast cancer were included in a clinical tria l in which r-metHuG-CSF was administered daily for 5 days to mobilize perip heral blood stem cells. Ten healthy women were also included as controls. O ur data show that G-CSF treatment induces an increase in peripheral blood l eucocyte, neutrophil, lymphocyte and monocyte counts. We have found a modul ation in the percentages of CD19+, CD45+CD14+, CD4+CD45RA+ and CD4+CD45ROcells in PBMC fractions during G-CSF treatment. We have also found a signif icant reduction in the proliferative response of PBMC to mitogenic stimulat ion that reverted 14 days after the fifth and the last dose of G-CSF. Furth ermore, it was not associated with significant changes in the pattern of cy tokine production. The mechanism of this immunoregulatory effect is probabl y indirect since G-CSF receptor has not been found in T lymphocytes. This m echanism and its potential clinical applications remain to be elucidated.