[Studies on viral immunotherapy of ascitic tumors in mice. II. Preliminary studies on the mechanism of treatment of S 180 ascitic tumors in mice by PR8 strain of influenza virus].

Present paper reports on the preliminary studies of the mechanism of virus therapy. In the untreated group, after ip transplant of 7.5 X 10(5) S 180 cells into healthy mice, the number of tumor cells increased rapidly and reached 3 X 10(8) cells/ml on day 9 and the death rate of cells was under 5%, except day 1 and 2. However, in the virus treated group, the PR 8 virus was given ip 48 hours after transplant of S 180 cells. The growth rate of tumor cells was significantly suppressed (maintained at about 3 X 10(5) cells/ml) and the death rate averaged 58.6%. In the antiPR 8 antibody treated group, the antibody was given ip 24 hours after injection of virus. The number of tumor cells decreased to the average of 1.5 X 10(5) cells/ml and the death rate reached 72.8% which is comparable with the virus treated group at day 6-9 after transplant of S 180 cells, suggesting in this period the oncolysis be antibody related (ADCC). In vitro test, the death rate of the tumor cells caused by PR 8 virus was only 6.9% in 24 hours after virus infection and 7.8% after 72 hours. The increased death rate of tumor cells after virus treatment in vivo and in vitro shows that the immune system is the main factor which eliminates the tumor cells in vivo.