Radiation-induced augmentation of host resistance to histocompatible tumor in mice: Detection of a graft antitumor effect of syngeneic bone marrow transplantation

Lethally irradiated and syngeneic bone marrow-re- constituted (C57BL/6JxDBA/2J) F₁female mice dem-onstrated prolonged survival following challenge with the DBA/2 mastocytoma P815-X2 compared with non- irradiated littermate controls. This radiation-induced augmentation of host resistance to P815-X2 was not abolished by the adoptive transfer of normal syngeneic spleen cells. In addition, this phenomenon was not detectable in adult thymectomized recipients, suggesting the requirement for an intact host thymus. This effect was also absent in syngeneic F₁male recipients. We suggest that lethal irradiation and marrow reconstitution may result in activation of a nonspecific immune effector mechanism against tumor cells-and, as such, may serve as a model to explore the graft-antitumor effect of bone marrow transplantation.