Identification of cells in primate bone marrow resembling the hemopoietic stem cell in the mouse.

The colony-forming unit culture (CFU-C) in the thin-layer agar colony technique is considered to be representative for hemo-poietic stem cells (HSC), according to our studies in mouse and monkey bone marrow. Using this in vitro assay as a guide, stem cell concentrates were prepared from monkey and human bone marrow by repeated density gradient centnfugation. The number of CFU-C could be enriched up to 70-100-fold. In such concentrated CFU-C suspensions, a cell, morphologically identical with the hemopoietic stem cell in the mouse (MSCLC, mouse stem cell-like cell) was frequently observed, using a May-Gr#{252}nwald-Giemsa (MGG) staining method and electron microscope techniques. In MGG-stained preparations, the MSCLC superficially resembles the small lympho-cyte; therefore, a staining method has been described, the polychrome procedure, by which both cell populations could be clearly distinguished. Since a fair correlation exists between the number of MSCLC and the number of CFU-C in a variety of primate hemopoietic suspen-sions, we concluded that the MSCLC might be a good candidate for being the HSC in monkeys and man. M ANY ATTEMPTS have been reported to identify the hemopoietic stem cell (HSC) by morphologic criteria. " " 3 The possibility to recognize and to enumerate this cell is of obvious importance in many hematologic disorders, as well as in the field of bone marrow transplantation, since by extrapolation from extensive mouse data it is held to generate all different hemopoietic cell lines including the lymphoid line. None of the above-mentioned investigations, which were carried out in rodents, has led to a convincing identification, since quantitative correlations between numbers of candidate stem cells and the results of functional HSC tests were not provided. The greatest difficulty encountered in its identification was its low concentration in hemopoietic tissues. The highest concentration of HSC as calculated for mouse bone marrow is 0.4%-0.6%, which percentage has been estimated by the spleen colony assay of Till and McCulloch.4 Spleen colonies arising from a single cell have been shown to produce erythropoietic, myelopoietic, and thrombopoietic cell populations .4 Moreover, Trentin and Fahlberg5 demonstrated that in lethally irradiated mice complete repopulation of the hemopoietic tissue, as well as of the lymphatic organs, can be effectuated by descendants from one spleen colony.