Hematopoietic reconstitution of irradiated, stem cell-injected mice: early dynamics of restoration of the cell lineages of the spleen and bone marrow.

Hematopoietic stem cells, numbering approximately 1/100,000 cells in mammalian bone marrow, are capable of complete hematopoietic and immune reconstitution upon injection into a myeloablated host. The present study aimed to analyze the earliest events in reconstitution of lethally irradiated, host murine bone marrow and spleen, after injecting purified Thy 1loLin-Sca-1+ stem cells. Thy-1loLin-Sca-1+ cells were isolated by fluorescence-activated cell sorting (FACS) from the bone marrow of 4-week-old C57BL(Thy1.1, Ly5.1) mice and injected into preirradiated, syngeneic hosts. These stem cells were also injected into congenic hosts, i.e., C57BL(Thy1.2, Ly5.2), and confirmed the donor origin of hematopoietic cells in the reconstituted host mice. Hematologically stained smears of the spleen and bone marrow of stem cell-injected recipients were prepared at 11, 14, 17, 21, 24, and 28 days after stem cell injection, and nucleated erythroid cells, mature granulocytes, and their myeloid precursors, monocytes, and la...