Transplanted tumor growth and the incidence of T-lymphocyte populations in the spleen of newcastle virus-treated mice.

C3Hf/HZgr mice were transplanted with SCCVII carcinoma cells and treated with Newcastle disease virus (NDV). The treatment slows down the growth of transplanted tumor. Furthermore, by using specific monoclonal antibodies, the frequencies of CD4+, CD8+, and CD4+CD25+ T lymphocytes were determined in the spleen of tumorous mice at particular times following tumor transplantation and/or NDV application. The incidence of lymphocytes CD4+ and CD8+ decreased and of CD4+CD25+ increased in the spleen of mice during the time following tumor transplantation. However, the frequency of regulatory CD4+CD25+ T lymphocytes in the spleen is very low, while CD4+ and CD8+ increased to normal level following intraperitoneal (i.p.) NDV injection in tumor-bearing mice. Thus, besides directly destroying transplanted tumor, NDV seems to be involved against growing tumor by reducing the frequency of regulatory T lymphocytes maintaining the frequency of CD4+ and CD8+ T lymphocytes within the control values pointing to its role in immunomodulation.