Immune regulatory activity of CD34+ progenitor cells: evidence for a deletion-based mechanism mediated by TNF-α

Previous studies suggest that cells within the CD34+ hematopoietic stem cell compartment are endowed with immune regulatory activity. Furthermore, it is possible to expand the human regulatory cells upon short-term culture of purified CD34+ cells with an early-acting cytokine cocktail. We now show that addition of anti-CD28, anti-CD2, interleukin-2 (IL-2), anti–IL-10, or IL-12 to the bulk mixed lymphocyte reaction (MLR) cannot reverse the inhibitory activity of the CD34+ cells, ruling out anergy-based mechanisms or mechanisms involving Th1-Th2 skewing. Furthermore, phenotyping of cells present after addition of CD34+ cells to the bulk MLR ruled out potential induction of plasmacytoid dendritic precursors, known to be endowed with regulatory activity. In contrast, the inhibitory activity of CD34+ cells could be reversed by adding the caspase inhibitor BD-FMK to the bulk MLR, indicating a deletion-based mechanism. The deletion can be inhibited by anti–tumor necrosis factor-α (anti–TNF-α) and not by anti–transforming growth factor-β (anti–TGF-β), suggesting a potential role for TNF-α in the regulatory activity of CD34+ cells.

Synthesis of hyperbranched glycodendrimers incorporating α-thiosialosides based on a gallic acid core

Hyperbranched glycodendrimers containing sialic acid residues were synthesized in order to further understand the multivalency effect and its role in carbohydrate–protein interactions. Gallic acid 7 as trivalent core and oligoethylene glycol derivatives as hydrophilic spacers were used to scaffold the dendritic backbones. α-Thiosialoside 16 was conjugated onto N-chloroacetylated dendritic precursors 13,14, and 26 by nucleophilic substitution to afford trivalent 17,18, and nonavalent 27 sialodendrimers. Complete sugar deprotection furnished water-soluble α-thiosialodendrimers 21,22, and 29, which were used in protein-binding studies. Turbidimetric analysis confirmed the strong potential of sialodendrimers 29 having nine readily accessible sialic acid residues to bind, cross-link, and precipitate two different lectins. Preliminary results indicated that nonavalent α-sialodendrimer 29 had a greater affinity towards dimeric wheat germ agglutinin (WGA) and the lectin from the slug Limaxflavus (LFA) than the corresponding trivalent glycodendrimers 21 and 22. Keywords: carbohydrate, dendrimer, sialic acid, gallic acid, lectin, wheat germ agglutinin, Limaxflavus.