Effect of Host Immune Capability on Radiocurability and Subsequent Transplantability of a Murine Fibrosarcoma<xref ref-type="fn" rid="FN2">2</xref>

The dose-response relationships for local control by radiation of a highly immunogenic 3-methylcholanthrene-induced fibrosarcoma, FSa, were studied in normal syngeneic C3Hf/Bu mice, in mice immunosuppressed temporarily by 600 rads of whole-body irradiation (WBI) or immunosuppressed permanently by thymectomy plus 900 rads WBI followed by reconstitution with syngeneic bone marrow (TxIR), and in mice treated with Corynebacterium parvum, a nonspecific stimulator of the reticuloendothelial system. The radiation dose required to control the tumor in 50% of the mice (TCD50) was lowest (1,530 rads) in mice treated with C. parvum prior to irradiation. Increasing values of the TCD50 were observed in normal mice, in those given 600 rads WBI before tumor transplantation, and in TxIR mice: 3,040 rads, 5,080 rads, and 6,450 rads, respectively. The shallow slopes of the dose-response curves for tumor control suggested considerable heterogeneity of response in normal and C. parvum-treated mice. This heterogeneity was confirmed in assays of tumor transplantability in mice in which the primary tumor had been controlled by irradiation 4 months previously. Four subcutaneous sites per mouse were injected with equal numbers of FSa cells. In many animals, tumors became palpable and subsequently regressed; some mice developed tumors at all four sites, whereas others receiving the same inoculum developed no tumors. in several instances, individual mice were able to reject large inocula, whereas others were unable to reject small inocula. These phenomena were not observed in “naive” (control) mice, either normal or those Immunosuppressed by 600 rads WBI.