Pretreatment with thymus cell-conditioned medium enhances the whole-animal survival of mice exposed to ionizing radiation.

Pretreatment with cell-free supernatant of thymus cell-conditioned medium (TCCM) protects mice in a dose-dependent manner from the lethal effect of ionizing radiation. A single dose of TCCM injected i.p. in a volume of 1.2 ml 8 h before lethal gamma irradiation with a dose of 9 Gy (LD95/30) protected 36% of C57BL/6 mice. Four doses of TCCM injected i.p. in a volume of 0.8 ml once a day (i.e., during four days), protected 50% of C57BL/6 mice. Application of five-fold concentrated supernatant of conditioned medium (cTCCM) in a volume of 1 ml i.p. 8 h before irradiation with a dose of 9 Gy protected 75% of mice. On the other hand, no therapeutic effect of different doses of the supernatant fluids from thymus cell cultures was found. Our observations suggest that media conditioned by thymus cells can mediate a radioprotective effect.