Long-term hemopoietic repopulation by Thy-1lo, Lin-, Ly6A/E+ cells.

Murine bone marrow Thy-1lo, Lin-, Ly6A/E+ cells have been isolated by fluorescence-activated cell sorting (FACS). This population contained up to 27% in vitro colony-forming cells (CFC) when stimulated by interleukin 3 (IL-3) and 5% day-12 spleen colony-forming units (CFU-S) (uncorrected for seeding efficiency). As few as 100 cells were able to reconstitute the myeloid and lymphoid compartments of lethally irradiated recipients for periods of up to 72 weeks. Over the range of 30-560 transplanted cells, three patterns of engraftment were observed; the proportion of donor cells increased gradually to values of > 90%, gradually declined, or remained static over the 72-week observation period. When the donor cell percentage in the peripheral blood exceeded 60%, both myeloid (neutrophils and monocytes) and lymphoid (T- and B-lymphocytes) cells were of donor origin. Primary animals containing > 60% donor cells in their peripheral blood were able to engraft secondary recipients with donor cells of both myeloid and lymphoid lineages. Primary animals with < 20% donor cells in their peripheral blood contained bone marrow cells that were only able to produce lymphoid cells in the peripheral blood of secondary recipients. With > 90% of animals, including both primary and secondary recipients, there were no large fluctuations in the proportion of donor myeloid or lymphoid cells in the peripheral blood. Where changes occurred, with three exceptions, these were gradual. These data suggest that the Thy-1lo, Lin-, Ly6A/E+ population is heterogeneous and contains in vitro CFC, day-12 CFU-S, and long-term repopulating cells for both the myeloid and lymphoid lineages and cells capable of long-term repopulation of only the lymphoid lineage.