Augmentation with serum thymic factor of suppressive effects on retroviral tumor development in hosts immune to v-onc product.

Inbred adult female rats were immunized against syngeneic ST-FeSV induced sarcoma cells. ST-FeSV was injected subcutaneously into 57 neonates (vaccinated) born from these immunized females and into 60 non-vaccinated syngeneic neonates. Serum thymic factor (FTS) was injected subcutaneously into 10 of vaccinated and 30 of non-vaccinated rats. Sarcomas developed in 40.4% (19/47) of vaccinated (A), 20.0% (2/10) of vaccinated FTS injected (B), 63.3% (19/30) of non-vaccinated FTS injected (C), and 76.7% (23/30) of nontreated (D) rats. By AB immunostaining using antibody to v-fes product (P85), sarcomas developed in 10 of 13 rats of group C tested. and 3 of 6 rats of group D tested were positive, but those in 7 rats of group A and 2 rats of group B tested were all negative. Lung metastasis was observed in rats of all groups except those of B group. All sera of animals that developed sarcomas were positive to P85 in Western blot analysis. These results showed that FTS augmented suppressive effects on sarcoma development in hosts immune to the viral oncogene product.