[Identification of primitive hematopoietic stem cells in mice by the limiting dilution method]

An absolute number of the primitive stem cells (PSC) providing for prolonged maintenance of hemopoiesis in culture was measured with the aid of the limiting dilution method. The number of the PSC was determined according to the magnitude of the "zero" class cultures, i. e. of the cultures in which CFUs could not be demonstrated after 5-8 weeks. The fitness of the method can be proved by the presence of the linear relations between the number of the explanted stem cells and the number of the PSC as well as by the passage of the regression curve through the origin of coordinates. The data on the content of the PSC functioning in vivo and in vitro turned out similar, amounting to about 100 cells per mouse femur.