Marrow Stromal Stem Cells for Repairing the Skeleton

A wound is a disruption of tissue integrity that is typically associated with a loss of substance. Its occurrence initiates a dynamic process of healing which aims at re-establishing tissue continuity. However, the degree of morphological and functional recovery that ensues will depend on the species, the organs and the amount of substance lost. For example, a bone fracture will heal through the formation of a soft callus that will gradually convert into a hard callus by endochondral ossification. Under favourable conditions, it will be remodelled and lead to a virtually complete restoration of the anatomical structure of the damaged bone. However, when a bone defect has reached a critical size, it heals through the formation of a non-functional scar tissue (Hollinger and Kleinschmidt, 1990). A key factor in the outcome of the healing process is the supply of a sufficient number of osteocompetent cells within the defect. The notion that bone marrow is a potential source of osteocompetent cells is not new. As early as 1968, Friedenstein established that when bone marrow is plated at low cell densities, it gives rise to pluripotent fibroblastic colonies clonal in origin which, upon appropriate culture conditions, differentiate into osteoblasts, chondroblasts, adipocytes, and myelosupportive phenotypes (Friedenstein etal., 1968). The cells, from which colonies originated, are fibroblastic in appearance and were initially termed colony-forming units-fibroblastic (CFU-F). Now, they are more often referred