Selective Generation of Different Dendritic Cell Precursors from CD34+ Cells by Interleukin‐6 and Interleukin‐3

There is a growing interest in generating dendritic cells (DCs) for using as vaccines. Several cytokines, especially stem cell factor (SCF) and FLT3‐ligand (FL), have been identified as essential to produce large numbers of myeloid precursors and even to increase DC yield obtained by the action of granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) and tumor necrosis factor alpha (TNF‐α). However, there are few studies on the effect of the early‐acting cytokines, commonly used to expand CD34+ progenitor cells, on DC generation. We report here that in the absence of serum, SCF, FL, and thrombopoietin (TPO) plus interleukin‐6 (IL‐6) and SCF, FL, and TPO plus IL‐3 were able to generate CD14+CD1a− and CD14− CD1a+ myeloid DC precursors from CD34+ cells, but IL‐6 had an inhibitory effect on the generation of CD14− CD1a+ cells. Both DC precursors differentiated into mature DCs by GM‐CSF, IL‐4, and TNF‐α, and DCs obtained from both types of culture exhibited equal allostimulatory capacity. CD1a+ DCs generated could be identified on the basis of DC‐specific intracellular adhesion molecule–grabbing nonintegrin (DC‐SIGN) expression, a novel C‐type lectin receptor expressed on dermal DCs but not on Langerhans cells. In addition, the inclusion of IL‐3 to the culture medium induced the appearance of CD13− cells that differentiated into plasmacytoid DC (DC2) on the addition of TNF‐α, allowing the identification of developmental stages of DC2. Like true plasmacytoid DCs, these cells secreted interferon‐α after TLR9‐specific stimulation with a specific CpG nucleotide.