Interactions of Tumor Necrosis Factor with Granulocyte-macrophage Colony-stimulating Factor and Other Cytokines in the Regulation of Dendritic Cell Growth in Vitro from Early Bipotent CD34+ Progenitors in Human Bone Marrow

Colonies of CD1a+ HLA-DR+/DQ+ CD4+ cells with the functional and some of the structural attributes of Langerhans cells are observed in human bone marrow cultures in semi-solid media and are assumed to be the progeny of an early progenitor, the dendritic/Langerhans cell CFU (CFU-DL). The cytokine-regulated growth of these cells has been studied using a chemically defined serum-free system to culture both unfractionated and highly enriched bone marrow progenitor cell populations. Although unfractionated cell growth was optimal in serum replete cultures with PHA-stimulated leukocyte-conditioned medium (PHA-LCM) suboptimal proliferation of CFU-DL was observed in serum even in the absence of PHA-LCM. No colonies were observed under serum-free conditions when granulocyte-macrophage CSF (GM-CSF), IL-3, granulocyte CSF (G-CSF), and macrophage CSF (M-CSF) were present at levels optimal for granulocyte colony-forming unit (CFU-G) and macrophage colony-forming unit (CFU-M) growth. Addition of IL-1 alpha to these cytokines stimulated a small number of CFU-DL. However, in the presence of GM-CSF and IL-3, TNF-alpha or TNF-beta (5 U/ml) were both highly effective in promoting growth up to 82% of optimal and CFU-G growth was also enhanced at these concentrations. TNF was only active during the first 3 days of culture and higher concentrations of TNF-alpha but not TNF-beta were inhibitory for both CFU-DL and CFU-G. CD34+ cell-enriched populations were also enriched for both myeloid progenitors (CFU-G + CFU-M) and CFU-DL to 36- and 48-fold, respectively, and single cell cultures of CD34+ cells yielded single colonies containing both CD1a+ dendritic cells and CD1a- macrophages. Thus dendritic/Langerhans progenitors in the bone marrow expresses CD34, have a capacity for both macrophage and dendritic cell differentiation, and depend on hemopoietic growth factors and TNF for their further development in vitro.