Rapid and efficient homing of human CD34+CD38−/lowCXCR4+stem and progenitor cells to the bone marrow and spleen of NOD/SCID and NOD/SCID/B2mnull mice

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Abstract
Stem cell homing into the bone microenvironment is the first step in the initiation of marrow-derived blood cells. It is reported that human severe combined immunodeficient (SCID) repopulating cells home and accumulate rapidly, within a few hours, in the bone marrow and spleen of immunodeficient mice previously conditioned with total body irradiation. Primitive CD34+CD38−/lowCXCR4+ cells capable of engrafting primary and secondary recipient mice selectively homed to the bone marrow and spleen, whereas CD34−CD38−/lowLin− cells were not detected. Moreover, whereas freshly isolated CD34+CD38+/high cells did not home, in vivo stimulation with granulocyte colony-stimulating factor as part of the mobilization process, or in vitro stem cell factor stimulation for 2 to 4 days, potentiated the homing capabilities of cytokine-stimulated CD34+CD38+ cells. Homing of enriched human CD34+ cells was inhibited by pretreatment with anti-CXCR4 antibodies. Moreover, primitive CD34+CD38−/lowCXCR4+cells also homed in response to a gradient of human stromal cell-derived factor 1 (SDF-1), directly injected into the bone marrow or spleen of nonirradiated NOD/SCID mice. Homing was also inhibited by pretreatment of CD34+ cells with antibodies for the major integrins VLA-4, VLA-5, and LFA-1. Pertussis toxin, an inhibitor of signals mediated by Gαiproteins, inhibited SDF-1–mediated in vitro transwell migration but not adhesion or in vivo homing of CD34+ cells. Homing of human CD34+ cells was also blocked by chelerythrine chloride, a broad-range protein kinase C inhibitor. This study reveals rapid and efficient homing to the murine bone marrow by primitive human CD34+CD38−/lowCXCR4+cells that is integrin mediated and depends on activation of the protein kinase C signal transduction pathway by SDF-1.