CD34+ hematopoietic progenitors from human cord blood differentiate along two independent dendritic cell pathways in response to GM-CSF+TNF alpha.

TLDR

In vitro, cord blood CD34+ hematopoietic progenitors expanded with GM‑CSF and TNF‑α generate dendritic cells, and this study demonstrates that they differentiate along two distinct DC pathways with potential in vivo relevance. During 12‑day cultures, two precursor populations (CD1a+ and CD14+) emerge by day 5–7, mature into phenotypically distinct DC by day 12–14—CD1a+ cells become Langerhans‑like with Birbeck granules, Lag antigen, and E‑cadherin, while CD14+ cells become dermal‑like DC expressing CD2, CD9, CD68, and factor XIIIa—and both subsets equally stimulate naive T cells, with CD14+ precursors also capable of differentiating into macrophage‑like cells under M‑CSF.

Abstract

Human dendritic cells (DC) can now be generated in vitro in large numbers by culturing CD34+ hematopoietic progenitors in presence of GM-CSF+TNF alpha for 12 d. The present study demonstrates that cord blood CD34+ HPC indeed differentiate along two independent DC pathways. At early time points (day 5-7) during the culture, two subsets of DC precursors identified by the exclusive expression of CD1a and CD14 emerge independently. Both precursor subsets mature at day 12-14 into DC with typical morphology and phenotype (CD80, CD83, CD86, CD58, high HLA class II). CD1a+ precursors give rise to cells characterized by the expression of Birbeck granules, the Lag antigen and E-cadherin, three markers specifically expressed on Langerhans cells in the epidermis. In contrast, the CD14+ progenitors mature into CD1a+ DC lacking Birbeck granules, E-cadherin, and Lag antigen but expressing CD2, CD9, CD68, and the coagulation factor XIIIa described in dermal dendritic cells. The two mature DC were equally potent in stimulating allogeneic CD45RA+ naive T cells. Interestingly, the CD14+ precursors, but not the CD1a+ precursors, represent bipotent cells that can be induced to differentiate, in response to M-CSF, into macrophage-like cells, lacking accessory function for T cells. Altogether, these results demonstrate that different pathways of DC development exist: the Langerhans cells and the CD14(+)-derived DC related to dermal DC or circulating blood DC. The physiological relevance of these two pathways of DC development is discussed with regard to their potential in vivo counterparts.