Monocytes from mobilized stem cells inhibit C 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^- TCRα/β⁺ T cells. Inhibition of T cell function by CD14⁺ monocytes required cell-cell contact, and the analyses of DNAS 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.