Neoplasia in adoptively immunosuppressed rats. A possible model for tumorigenesis in transplant recipients.

An extremely high incidence of malignant tumors was observed in groups of rats that had previously been exposed to whole body irradiation, grafted with allogeneic tissue, and injected with lymphocytes capable of specifically suppressing the rejection of the grafted tissue. Neoplasia in these adoptively immunosuppressed rats had features in common with that in therapeutically immunosuppressed transplant recipients. Increased tumor incidence could not be accounted for on the basis of the effects of whole body irradiation or failure of immune surveillance, nor could it be a direct effect of lymphoid tissue stimulation. It is suggested that cell mediated suppressor responses play a critical role in tumorigenesis. The mechanism of this is not simply direct stimulation of lymphoid tissue proliferation.