The Concept of Mother cell or Bone Marrow Stem Cells
Although the concept of a common “mother cell” of all blood elements in the adult dates to Maximov in 1909, and its potential for participation in disease as proposed by Danchakoff in 1916, the basic concepts of a hierarchical organization of Bone Marrow Stem Cells and progenitor cells leading to mature blood cell production were congealed by Till and McCulloch using a spleen colonyforming assay, experimentally establishing the existence of multipotential hematopoietic cells.
The capacity to transplant Bone Marrow Stem Cells
The capacity to transplant Bone Marrow Stem Cells and reconstitute all aspects of hematopoiesis in myeloablated recipients provided an in vivo assay for the Bone Marrow Stem Cells, but it was not until the development of clonal in vitro assays of lineage committed progenitors that a coherent model of blood cell production began to emerge. The pioneering work of Pluznik and Sachs and of Bradley and Metcalf provided methods to enumerate and characterize Bone Marrow Stem Cells committed to the hematopoietic lineage. These investigators independently developed culture conditions that allowed colonies of leukocytes to develop from single progenitors. However, as a result of the more fastidious conditions required for erythropoiesis and megakaryopoiesis in vitro, the description of methods to culture these progenitors did not occur for another decade or more.
Bone Marrow Stem Cells Kinetics
Based on transplantation data indicating that there are a remarkably similar total-body number of Bone Marrow Stem Cells in mice and cats, it has been estimated that all mammals, including humans, possess 2 x 10 stem cells,and because only a small fraction of these are cycling (and therefore contributing to blood cell production) at any given time, it is also clear that daily blood cell development from the few cycling Bone Marrow Stem Cells to produce the approximately 4 x 10 mature blood cells represents a massive amplification process.