Induction of allogeneic unresponsiveness in adult dogs by irradiation and bone marrow transplantation: Implication of Ia-positive bone marrow stem cells

A number of investigators have suggested in recent years that placement of hemopoietic cells into an irradiated host milieu may trigger such cells to undergo a transient cycle of replication and differentiation which recapitulates the events of immunological ontogeny-including fetal erythropoiesis, production of newborn Υ-chains in adults, and generation of fetal and newborn-type lymphoid cells. In an extension of this hypothesis to transplantation, supralethally irradiated dogs were reconstituted with their own stored marrow, followed within 12 to 18 hr by the transplanation of a kidney allograft obtained from a DLA identical donor. This sequence resulted in long-term unresponsiveness to the transplanted kidneys in the recipients without further treatment. The 60% incidence of success obtained with this procedure could be improved further if the host's own stored marrow was treated in vitro with methylprednisolone (MPd) prior to replacement of the marrow following irradiation. In an attempt to analyze the possible changes in the cellular composition of marrow that might have been associated with this result, a serial cytofluorographic analysis of marrow before and after treatment with MPd was performed. For this purpose, cell samples obtained before and after exposure of bone marrow to MPd were studied in an Ortho 50H Cell Sorter after staining with acridine orange by using green fluorescence for DNA and red fluroescence for RNA, or, alternatively, using 900 scatter for the X axis and a narrow forward scatter for the Y axis, without addition of any stain