The morphological equivalent of the hematopoietic stem cell compartment I: Transplantation studies

Asynchronous restoration of the spleen colony forming units (CFU S) and nucleated cellularity of mouse bone marrow following the administration of nitrogen mustard led to a relative increase in the proportion of stem cells. Stem cell assays indicated that the proportion of stem cells was increased about nineteen fold. This increase was balanced by a decrease in the number of nucleated cells in the medullary cavity of the femoral diaphysis, so that the absolute number of stem cells was not altered appreciably. These assays then established criteria for the behavior of the morphological equivalent of the hematopoietic stem cell compartment. Morphological analysis of smears of this marrow demonstrated that these criteria were met by only one cell population, the leptochromatic mononuclear cell compartment. Autoradiographic studies suggested that cell production was occurring in this cell compartment but the growth fraction was very low (0.02 to 0.03), indicating a high proportion of non cycling cells.