title: Human CD34(+)CXCR4(-) sorted cells harbor intracellular CXCR4, which can be functionally expressed and provide NOD/SCID repopulation.
abstract: Homing and repopulation of nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice by enriched human CD34(+) stem cells from cord blood, bone marrow, or mobilized peripheral blood are dependent on stromal cell-derived factor 1 (SDF-1)/CXCR4 interactions. Recently, human cord and fetal blood CD34(+)CD38(-)CXCR4(-) and CXCR4(+) cells, sorted with neutralizing anti-CXCR4 monoclonal antibody (mAb), were shown to have similar NOD/SCID repopulation potential. Herein we report that human cord blood CD34(+)CXCR4(+) (R4(+)) and CD34(+)CXCR4(-) (R4(-)) subsets, sorted with neutralizing anti-CXCR4 mAb, engrafted NOD/SCID mice with significantly lower levels of human cells compared with nonsorted and SDF-1-migrated CD34(+) cells. Coinjection of purified cells with 10 microg anti-CXCR4 mAb significantly reduced engraftment of all CD34(+) subsets, and 50 microg completely abrogated engraftment by R4(-) and CD34(+) cells. Importantly, R4(-) cells harbor intracellular CXCR4, which can be rapidly induced to cell surface expression within a few hours. Moreover, 48 hours of cytokine stimulation resulted in up-regulation of both cell surface and intracellular CXCR4, restoring migration capacities toward a gradient of SDF-1 and high-level NOD/SCID repopulation potential. In addition, homing of sorted R4(-) cells into the murine bone marrow and spleen was significantly slower and reduced compared to CD34(+) cells but yet CXCR4 dependent. In conclusion, R4(-) cells express intracellular CXCR4, which can be functionally expressed on the cell membrane to mediate SDF-1-dependent homing and repopulation. Our results suggest dynamic CXCR4 expression on CD34(+) stem and progenitor cells, regulating their motility and repopulation capacities.
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000032:analysis*; D018952:Antigens, CD34 / Q000032:analysis*; D002455:Cell Division / Q000276:immunology / Q000502:physiology; D005312:Fetal Blood / Q000166:cytology*; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000276:immunology / Q000502:physiology*; D006801:Humans; D007231:Infant, Newborn; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D019718:Receptors, CXCR4 / Q000032:analysis* / Q000235:genetics / Q000502:physiology; D033581:Stem Cell Transplantation / Q000379:methods*; D014183:Transplantation, Heterologous / Q000502:physiology*
chemical_list: D015703:Antigens, CD; D018952:Antigens, CD34; D019718:Receptors, CXCR4