Radioprotection of Mice by the Bacterial Extract Broncho-Vaxom^R: Haemopoietic Stem Cells and Survival Enhancement

Abstract

Pretreatment of mice with 50–1000 µg of the bacterial extract Broncho-Vaxom^R (BV, free of endotoxin) before sublethal irradiation induced an increase in the number of endogenous haemopoietic stem cells (E-CFU). The degree of radioprotection was dependent on both the time of administration and the dose of BV. An optimal E-CFU survival was observed when 500 µg of BV was administered i.p. 24 h before irradiation.

BV did not affect the day 9 CFU-S survival in the bone marrow directly after irradiation. However, 5, 9 and 12 days after irradiation, the number of day 9 CFU-S was almost 2-fold higher in the bone marrow of BV injected mice. Pretreatment with BV protected C57B1/6 mice in a dose-dependent manner from the lethal effect of ionizing radiation. A single dose (50, 100, 250, or 500 µg) of bacterial lysate injected i.p. 24 h before 9·5 Gy γ-rays (LD_100/21) protected 16%, 25%, 80%, and 94% of C57B1/6 mice, respectively. The dose reduction factor in the case when the BV (500 µg per mouse) was administered at that time was 1·18 (95% CL 1·12, 1·25).