Rapid induction of CD40 on a subset of granulocyte colony-stimulating factor-mobilized CD34(+) blood cells identifies myeloid committed progenitors and permits selection of nonimmunogenic CD40(-) progenitor cells.

CD40 antigen is a costimulatory molecule highly expressed on dendritic cells (DC) and activated B cells, which induces T-cell proliferation through the binding with CD40L receptor. In this study, we evaluated CD40 expression on normal CD34(+) blood cells and functionally characterized CD34(+)CD40(+) and CD34(+)CD40(-) cell subsets. CD40, CD80, and CD86 antigens were constitutively expressed on 3.2% +/- 4.5%, 0%, and 1.8% +/- 1.2% CD34(+) blood cells, respectively. However, after 24 hours in liquid culture with medium alone, or with tumor-necrosis-factor-alpha (TNF-alpha), or with allogeneic mononuclear cells 10.8% +/- 3.8%, 75.3% +/- 15.0% and 53. 7% +/- 17.0% CD34(+) blood cells, respectively, became CD40(+). After incubation for 24 hours with TNF-alpha CD34(+)CD40(+) blood cells expressed only myeloid markers and contained less than 5% CD86(+) and CD80(+) cells. Also, a 24-hour priming with TNF-alpha or ligation of CD40 significantly increased the CD34(+) blood cells alloantigen presenting function. Finally, purified CD34(+)CD40(+) blood cells stimulated an alloreactive T-cell response in MLC, were enriched in granulocytic, monocytic, and dendritic precursors, and generated high numbers of DC in 11-14 d liquid cultures with GM-CSF, SCF, TNF-alpha and FLT-3L. In contrast, CD34(+)CD40(-) cells were poorly immunogenic, contained committed granulocytic and erythroid precursors and early progenitors, and differentiated poorly toward the DC lineage. In conclusion, a short incubation with TNF-alpha allows the selection of CD40(+) blood progenitors, which may be a useful source of DC precursors for antitumor vaccine studies, and also a CD34(+)CD40(-) blood cell fraction that could be exploited in innovative strategies of allogeneic transplantation across HLA barriers.