Surface expression of HLA-DM on dendritic cells derived from CD34-positive bone 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. In 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 healthy donors were used to generate DCs with the recombinant human cytokines granulocyte-macrophage colony-stimulating factor (GM-CSF), tumour necrosis factor alpha (TNF-alpha) and stem cell factor (SCF), both with and without interleukin 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 culture respectively. The number of HLA-DM molecules expressed per HLA-DM+ cell on 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 commencement of culture increased the proportion of HLA-DM+ cells and increased the number of HLA-DM molecules per HLA-DM+ cell significantly (P < 0.05). Although most of the HLA-DM+ cells expressed CD1a, CD80 or CD86 antigen, only a small 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 morphological features of DCs. Primary mixed lymphocyte cultures demonstrated that the HLA-DM+ cells elicited a vigorous proliferation of allogeneic T cells. The level of antigen-specific T-cell activation induced by antigen-pulsed, chloroquine-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 characterization of DCs and human immunotherapy.