In vivo blocking of SV40 virus-induced antitumor resistance by Syrian hamster sera from early stages of primary SV40 carcinogenesis.

The blocking of specific SV40-induced resistance of hamsters by the sera collected from 12 individual hamsters infected with SV40 when newborn was studied at different periods of primary virus-induced carcinogenesis. The serum samples were collected at the following periods of primary carcinogenesis: during the latent period (60 days after virus inoculation), at the day of primary tumor appearance, and 19-36 and 45-57 days after primary tumor appearance. For detection of the blocking activity of the collected sera the cells of transplantable SV40 test-tumor were pretreated in vitro with these sera and with control normal hamster sera, and then used for challenge in vivo in SV40-immunized and normal hamsters. With the use of such method, as a rule, no blocking activity of the serum samples collected at any time after the tumor appearance was observed. However, the sera obtained from 7 out of 12 of these hamsters during the latent period significantly decreased the resistance index of animals challenged in transplantation test with the serum pretreated tumor cells. Possible explanations of these findings are discussed.