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 – TCRα/β + 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. J. Leukoc. Biol. 61: 583–591; 1997.