Surface expression of HLA-DM on dendritic cells derived from CD34-positivebone marrow haematopoietic stem cells

HLA-DM has been known to be largely absent from the cell surface of antigen -presenting cells, accumulating instead in the intracellular compartment. I n this study, we demonstrated that a population of HLA-DM-positive (HLA-DM) dendritic cells (DCs) can be identified in an in vitro culture of CD34(+) bone marrow haematopoietic stem cells. CD34(+) bone marrow cells of health y donors were used to generate DCs with the recombinant human cytokines gra nulocyte-macrophage colony-stimulating factor (GMCSF), tumour necrosis fact or alpha (TNF-alpha) and stem cell factor (SCF), both with and without inte rleukin 4 (IL-4). Flow cytometric analysis demonstrated that HLA-DM+ cells comprised 2.5 +/- 0.9% and 1.8 +/- 0.4% of the CD34(+) cell-derived progeny in the presence of GM-CSF, TNF-alpha, and SCF after 7 d and 14 d of cultur e respectively. The number of HLA-DM molecules expressed per HLA-DM+ cell o n d 7 was significantly higher than that on d 14 (1410 +/- 47 versus 370 +/ - 25, P < 0.05). The addition of IL-4 to the cytokines from the commencemen t of culture increased the proportion of HLA-DM+ cells and increased the nu mber of HLA-DM molecules per HLA-DM+ cell significantly (P < 0.05). Althoug h most of the HLA-DM+ cells expressed CD1a, CD80 or CD86 antigen, only a sm all proportion of CD1a(+), CD80(+) or CD86(+) cells expressed HLA-DM. About half the HLA-DM+ cells expressed CD83. The addition of IL-4 resulted in a decrease in the expression of CD83 on the HLA-DM+ cells on d 7. Microscopic evaluations of sorted HLA-DM+ cells revealed the characteristic morphologi cal features of DCs. Primary mixed lymphocyte cultures demonstrated that th e HLA-DM+ cells elicited a vigorous proliferation of allogeneic T cells. Th e level of antigen-specific T-cell activation induced by antigen-pulsed, ch loroquine-treated HLA-DM+ cells was substantially higher than that induced by HLA-DM- cells (P < 0.05). These results show that HLA-DM can be used as a useful DC lineage-specific marker, as well as a tool for the characteriza tion of DCs and human immunotherapy.