VIRUS-INDUCED TRANSPLANTABLE SARCOMA IN R ATS AS A MODEL FOR STUDYINGOF NEOPLASTIC PROGRESSION AND SPONTANEOUS REGRESSION

The growth and spontaneous regression of transplantable sarcoma, induc ed by SR-RSV, were studied in Wistar rats. The age of the animals and the quantity of implanted cells are of Importance for the emergence an d development of the SR-RSV-induced transplantable tumour in the rats. Sarcoma cells inoculated in newborns or in x-irradiated adult Fats de veloped progressively growing tumours. Transplantable sarcoma in rats, induced by SR-RSV, heve a definitive tendency to regress spontaneousl y. The rats undergone spontaneous resolution of transplantable sarcoma remain unresponsive to an additional transplantation of syngeneic tum our cells. The degree of unresponsiveness is not constant throughout t he entire time following termination of regression. Moreover the resis tance to the additional trantsplant is not typical of all animals unde rgone spontaneous regression. The atenuation of the transplantation un responsiveness in rats undergone spontaneous regression to syngeneic t umour cells following their irradiation with gamma-rays or their treat ment with antithymocyte serum was observed. We suppose that the immune system plays an important and perheps caused role in the spontaneous regression of the transplantable sarcoma, induced by SR-RSV in rat.