Immunological responsiveness against tumors induced by avian sarcoma virus: reduced expression of pp60src kinase activity in regressing tumors

Abstract

Tumors which are induced in chickens by avian sarcoma virus frequently grow progressively for several weeks and then regress. We showed that tumor cells which are derived from the progressively growing phase of tumor growth produce large quantities of progeny-transforming virus, are reactive with antiviral antibody, and are susceptible to lysis in cell-mediated cytotoxicity assays by splenic lymphocytes of sensitized hosts. In contrast, tumor cells derived from regressing sarcomas are poor producers of progeny virus and are relatively unreactive with both antiviral antibody and sensitized lymphocytes. We further found that pp6OSrc kinase activity was reduced by about 75% in regressing compared with progressively growing tumor cells. The half-lives of directly precipitable pp60`in tumor cells derived from progressively growing and regressing neoplasn.s were 6 and 1.5 h, respectively. Studies on each of three other cellular enzymes did not reveal any regressio.li-associated decreases in enzyme activity. These data support the notion that expression of adequate levels of long-lived pp60 kinase activity s essential to progressive tumor growth.