Stem cell kinetics: correlation of in vivo and in vitro data

Comparisons have been made along three parameters between the observations of a number of workers regarding in vivo the transitional cell compartment, and in vitro observations of colony-forming units. The parameters used were size changes when the stem cell requirements are increased, the existence of three size groups in both the transitional cell compartment and in the colony-forming units examined, and the relation between cell size and the percentage of cells in DNA synthesis. On all these parameters there appears to be close correlation between the in vitro properties of stem cells and progenitor cells and the in vivo properties of the transitional cell compartment. Transitional cells appear to be the only cells in the marrow that can match the kinetic properties of a number of colony-forming units.