The morphological characterization of the haematopoietic stem cell (CFU-S)

Four days after the intravenous injection of 100 μg of mustine hydrochloride (HN₂), a pronounced decrease has been demonstrated in the number of murine femoral bone marrow cells which is required to establish a given number of macroscopic surface colonies in the spleen, a given mass of tissue in the spleen, or a cell population of given size in the medullary cavity of the femoral diaphysis, within 10 days of transplantation to a lethally irradiated recipient. This decrease has been attributed to an increase in the number of haematopoietic stem cells (CFU-S) included among a given number of nucleated cells, which is balanced by a decrease in the number of nucleated cells so that the absolute size of the stem cell population is not altered appreciably. These changes in the stem cell content of the bone marrow are paralleled by comparable changes in only one cell population. Cells similar to those which constitute this population have previously been classified as transitional cells. Four days after the intravenous injection of 100 μg of mustine hydrochloride (HN₂) most of the transitional cells in murine femoral bone marrow measure between 9 and 11 μm in diameter, have pale blue cytoplasm and exhibit a very high nuclear: cytoplasmic ratio, when observed in smears stained using a variation of the Jenner-Giemsa technique. These are the stem cells indicated by transplantation assay (SCIBTA).