FL-mobilized peripheral blood but not FL-expanded bone marrow FC promote establishment of chimerism and tolerance

¹ Institute for Cellular Therapeutics, University of Louisville, Kentucky
² Stem Cell Biology Program, James Graham Brown Cancer Center, University of Louisville, Kentucky

^* To whom correspondence should be addressed. E-mail: suzanne.ildstad{at}louisville.edu.

	Abstract

Facilitating cells (CD8⁺/TCR^-) (FC) enhance engraftment of limiting numbers of hematopoietic stem cells (HSC). The primary component of FC is precursor-plasmacytoid dendritic cells (ppreDC), a tolerogenic cell expanded by Flt3-ligand (FL). In the present study, we evaluated the function and composition of FL-expanded FC. FL treatment resulted in a significant increase of FC in bone marrow (BM) and peripheral blood (PB). When FL-expanded FC were transplanted with c-Kit⁺/Sca-1⁺/Lin^- (KSL) cells into allogeneic recipients, BM-FC exhibited significantly impaired function while PB-FC were potently functional. A significant upregulation of P-selectin expression and downregulation of VCAM-1 was present on FL-expanded PB-FC compared with FL BM-FC. SDF-1 and CXCR4 transcripts were significantly increased in FL PB-FC and decreased in FL BM-FC. Supernatant from FL PB-FC primed HSC migration to SDF-1, confirming production of the protein product. The FL PB-FC contained a predominance of ppreDC and NK-FC, and NK-FC were lacking in FL BM-FC. The impaired function for BM-FC was restored within 5 days after cessation of treatment. Taken together, these data suggest that FC may enhance HSC homing and migration via the SDF-1/CXCR4 axis and adhesion molecule modulation. These findings may have implications in development of strategies for retaining function of ex vivo manipulated FC and HSC.