Monocytes from mobilized stem cells inhibit T cell function

Granulocyte-macrophage colony-stimulating factor, mobilized peripheral blood stem cell (PSC) products, and peripheral blood leukocytes posttransplantation contain cells that cause allogeneic and autologous T cell apoptosis, Isolation and characterization of these cells demonstrated that they were low-density (Percoll fractionation) CD14(+) monocytes. T cells in PSC products have a depressed phytohemagglutinin (PHA) mitogenic response; however, purified CD4(+) or CD8(+) T cells exhibit a statistically normal mitogenic function, Furthermore, no T cell inhibitory activity was observed in CD14(+), CD4(+), and CD8(+) cell-depleted fractions enriched in CD4(-)CD8(-)TCR alpha/beta(+) T cells, Inhibition of T cell function by CD14(+) monocytes required cell-cell contact, and the analyses of DNA fragmentation by Southern and TUNEL analysis demonstrates an activation-induced T cell apoptosis in the presence of CD14(+) monocytes. Reverse-transcriptase polymerase chain reaction studies suggested that high levels of interleukin-10 or tumor necrosis factor gene transcripts in the PSC products may contribute to the inhibition of T cell function.