PRIMITIVE STEM-CELLS ALONE MEDIATE RAPID MARROW-RECOVERY AND MULTILINEAGE ENGRAFTMENT AFTER TRANSPLANTATION

The engraftment of hematopoietic stem and progenitor cells in lethally irradiated mice was evaluated following transplants of enriched hemat opoietic cell populations which were defined by surface antigen and rh odamine-123 staining, Phenotypically defined long-term repopulating st em cells, short-term pluripotent progenitors, and committed myeloeryth roid progenitors all rapidly reconstituted splenic cellularity and per ipheral red blood cells after transplant into myeloablated animals, In contrast, marrow cellularity was reconstituted only after transplant of long-term repopulating stem cells, In addition, peripheral blood pl atelet and lymphocyte counts increased only after transplantation of t he longterm repopulating population, Transplantation of highly enriche d multipotent progenitors resulted in a transient increase in peripher al blood myeloid cells that occurred with kinetics similar to that see n after transplant of the primitive stem cell population, Erythroid re constitution was similar in all groups, suggesting that the effect of myeloerythroid progenitor cells in mouse marrow transplants is primari ly on reconstitution of the erythroid lineage due to splenic hematopoi esis. Collectively, these results suggest that the cells which functio n to rapidly reconstitute the nucleated blood cells in a transplant se tting are more closely related to primitive, marrow-homing stem cells than to committed progenitor cells.