Identification of cord blood dendritic cells as an immature CD11c(-) population

Dendritic cells (DC) are the main stimulators of primary T-cell responses a nd, thus, probably play a role in the immune reactions after stem cell tran splantation. Very little is known about DC in cord blood (CB) and about the ir potential involvement in the low incidence and severity of acute graft-v ersus-host disease after CB transplantation. Here, CBDC were identified as a HLA-DR+ cell population, lacking the CD3, CD11b, CD14, CD16, CD19, CD34, CD56, and glycophorin A lineage markers (lin). This lin(-)/HLA-DR+ populati on represented 0.3% +/- 0.1% (mean +/- SD; range, 0.1% to 0.6%; n = 15) of CB mononuclear cells, and CB contained 5.4 +/- 3.2 x 10(3) CBDC/mL (1.8 to 13.0 x 103; n = 15). CBDC expressed CD4, CD11a, CD18, CD45RA, CD50, CD54, a nd CD123, but showed no expression of CD1a, CD11c, CD33, CD40, CD45R0, CD80 , CD83, end CD86 and only limited expression of CD58, CD102, and CD116. Des pite this immature phenotype, immunomagnetically lin(-)-enriched CBDC were potent stimulators of allogeneic CB T cells. As few as 266 +/- 107 (193 to 530; n = 10) lin-/HLA-DR+ CBDC stimulated a significant response. However, CBDC failed to take up protein or peptide antigens. Thus, in CB there is a prevalence of a DC subpopulation, resembling the CD11c(-) DC identified in tonsils, the so-called plasmacytoid T cells, which may exert a function dis tinct from the CD11c(+) DC subpopulation. (C) 1999 by The American Society of Hematology.