Abstract
Stem cell homing has been studied in syngeneic models and appears to be rapid (<1 h) and dependent on cellular adhesion and migration factors. We utilized a full H2-mismatched transplantation model to determine the basics of allogeneic homing. C57BL/6J Lin-Sca-1+ cells were labeled with CFSE and injected in non-myeloablated BALB/c mice. Fluorescent cell detection was via high-speed FACS analysis. Alternatively, B6.SJL whole bone marrow cells were injected in lethally irradiated BALB/c mice (10 Gy). One, 3, 6, and 24 h after transplant, marrow was harvested and cells were either plated for high proliferative potential colony-forming cell (HPP-CFC) assay or secondarily injected into myeloablated (8 Gy) C57BL/6J mice using 10% competing C57BL/6J marrow. Chimerism was evaluated at 8 weeks. CFSE+ cells were detected in the bone marrow 1, 3, and 6 h after injection. The numbers were moderately lower when compared to syngeneic homing possibly due to strain effect. Conversely, utilizing a surrogate or secondary assay, we observed a decline of secondary engraftment of harvested cells over time, but not of HPP-CFC. Combining experiments and normalizing the 1-h time point to 100% (to allow comparison), we observed a mean relative engraftment of 87 +/- 29%, 72 +/- 21%, 84 +/- 35% of the 1 h level at 3, 6, and 24 h respectively. HPP-CFC assay showed no significant variation as a homing surrogate over 1-6 h. These data indicate a rapid homing into allogeneic recipients with a plateau at 1 h. The decline of secondary engraftability over time may indicate a phenotype alteration of homed cells.