InVitro Culture of Human Cord Blood Hematopoietic Stem/Progenitor Cells Interfered with Their Distribution to Other Bone Marrow Compartments after Intra-Bone Marrow Transplantation.

Intra-bone marrow transplantation (IBMT) is a novel strategy for transplantation of hematopoietic stem cells because it can transfer various types of cells to bone marrow regardless of their homing capacity. However, reconstitution process of these cells after IBMT remains to be fully elucidated. Here, we investigated whether in vitro culture of cord blood hematopoietic stem/progenitor cells affects their reconstitution in bone marrow after IBMT. Freshly isolated AC133⁺ cells (5x10⁴ cells/mouse) or all cells derived from AC133⁺ cells cultured with growth factors (stem cell factor, flt-3 ligand, and thrombopoietin) for 5 days were injected into the bone marrow of the left tibia in irradiated NOD/SCID mice. In the bone marrow of the injected left tibia, the engraftment levels of human CD45⁺ cells at 6 weeks after transplantation was not considerably different between transplantation of noncultured and cytokine-cultured cells (54±28% vs. 69±13%). However, the migration of transplanted cells to the bone marrow of other noninjected bones was extremely lower for cytokine-treated cells compared with noncultured cells (2±2% vs. 36±10%). Similar findings were observed for engraftment of CD34⁺ cells. To enhance the migration of cytokine-cultured cells after IBMT, we similarly transplanted cultured AC133⁺ cells into the bone marrow of the left tibia, assessed the engraftment in the injected and noninjected tibiae at 7 days after transplantation, and then subcutaneously administered G-CSF (250 μg/kg/d) for 5 days. Administration of G-CSF stimulated the migration of cytokine-cultured cells to the bone marrow of previously-aspirated right tibia but failed to induce their migration to intact bone marrow of femur. These data indicate that ex vivo manipulation of hematopoietic progenitor/stem cells adversely influences their migration properties to other bone marrow compartments after IBMT. Our data raise caution for future clinical applications of the IBMT method using ex vivo-manipulated hematopoietic stem cells.