[Study of abscopal effect and cellular infiltration of tumor nests using less-fractionated, large-dose radiation]

As reported by several authors, abscopal effect and favorable cellular infiltrations into the tumor nest caused by irradiation suggest the existence of cell immunity in the host. In our present study, as first step to elucidate the mechanism of the fact mentioned above, effects of radiation with a single dose irradiation was estimated in terms of the increase of survival rate and the inhibition of pulmonary metastasis, i.e. abscopal effect in the mice of irradiated tumor burden. Therefore, we examined the resected and pulmonary specimen after irradiation histopathologically. We also examined the effects of the administration of immune modulator PSK and OK-432. Results; 1) Increase of survival rate and inhibition of pulmonary metastasis were observed in groups of mice with inoculated tumor and with again inoculated tumor treated by a single dose irradiation, compared to either the control groups. 2) Also administration of immune potentiator with radiation enhanced the survival rate and inhibition of pulmonary metastasis in all experimental protocols. 3) Remarkable cellular infiltrations of tumor nest after irradiation were observed, and these cellular infiltrations suggest participation of immunoreaction. In the group of using immune modulator, the cellular infiltrations were observed more remarkable than the other groups. 4) Optimal radiation dose was proved to be 30 Gy in this study.