Possible mechanism of hematopietic stem cells homing to the bone marrow microenvironment

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We found that the stromal cell derived factor-1/pre-B cell growth stimulating factor (SDF1/PBSF) receptor, CXCR4, is expressed on human CD34^+ bone marrow (BM) cells. Stringently FACS-sorted CD34^+CXCR4^+ BM cells completely lack myeloid, erythroid, megakaryocytic, and mixed colony forming potential (myeloid progenitors), but give rise to B and T lymphoid progenitors, whereas CD34^+CXCR4^- BM cells can generate colonies formed by myeloid progenitors and can also develop into these lymphoid progenitors. Therefore, expression of CXCR4 on CD34^+ BM cells can allow lymphoid progenitors to be discriminated from myeloid progenitors. Since CD34^+CXCR4^+ cells are differentiated from CD34^+CXCR4^- cells, multipotential progenitors located in the BM are likely to be negative for CXCR4 expression. CXCR4 seems to be expressed earlier than the interleukin-7 receptor and terminal deoxynucleotidyl transferase during early lymphohemopoiesis. These results suggest that the expression of CXCR4 on CD34^+ BM cells is one of the phenotypic alterations for committed lymphoid progenitors.