Transplantation of Marrow to Extramedullary Sites

Autologous fragments of transplanted marrow have survived in various extramedullary sites in the rat, rabbit, and dog. Survival of the fragments occurs with a complete reconstitution of the hemopoietic and adventitial structures. The process originates from a network of surviving reticular cells which proliferate and differentiate into osteoblasts and give rise to trabecular bone. Later, the reticular cells reconstruct the marrow's microcirculation. Hemopoietic repopulation of the marrow implant takes place only after its sinusoidal microcirculation has been established.