Protection from haemopoietic death by shielding versus grafting of bone marrow

In an attempt to clarify the conflicting data in the literature, the efficacy of shielded bone marrow cells versus injected bone marrow cells for hemopoietic restoration of lethally irradiated mice was reinvestigated. Three different end points were employed. Spleen weight at 10 days after irradiation was used instead of spleen colony count, because of the difficulty encountered in enumeration of endogenous spleen colonies. Repopulation of the unshielded femur at day 10 after irradiation was used as a second end point, since the colonization pattern of endogenous surviving cells might be directed to parts of the hemopoietic system other than the spleen. As a third end point, 30 day survival of lethally irradiated animals was used, which required a two phase irradiation to avoid changes in mortality pattern caused by the immobilization during irradiation. The results obtained by all 3 methods indicate that endogenous surviving cells are at least equally effective in repopulating the hemopoietic tissues as grafted bone marrow cells.