Effect of Small Doses of Syngeneic Bone Marrow on the 30- and 90-Day LD 50 of X-Irradiated Mice

The effects of very small doses of syngeneic bone marrow cells on 30- and 90-day survival of x-irradiated female (C57BL/Cum ♀ × C3H/Anf ♂) F1 mice were studied, principally in the LD₁₀- LD₁₀₀ range. As few as 0.01× 106 cells improved survival of mice exposed to an LD₁₀₀ or less, and a smaller cell dose was required to obtain good survival at mid-lethal exposures than at or above the LD₁₀₀ . The data, together with previous results, indicate a triphasic response of the LD₅₀₍₃₀₎ to the dose of syngeneic marrow cells. The LD₅₀₍₉₀₎ and LD₅₀₍₃₀₎ values are essentially the same, except for mice exposed to 1100, 1150, and 1200 R. In these groups 90-day survival percentages were about one-half those scored at 30 days. It was also found that slopes of survival curves for mice treated with marrow were about one-half tho...