Anti-viral and anti-tumor effects induced by an attenuated Marek's diseasevirus in CD4-or CD8-deficient chickens

By vaccination with an attenuated Marek's disease virus (MDV), strain CVI98 8, chickens ape protected from the development of T cell lymphoma caused by an oncogenic MDV. To clarify the role of T lymphocyte subsets in the prote ction mechanisms of this vaccine, vaccinated chickens were depleted of T ce ll subsets by neonatal thymectomy and injections of monoclonal antibodies s pecific to chicken CD4 and CD8 molecules, and then challenged with an oncog enic MDV, strain Md5. The MDV titers rescued from CD8(+) T cells, which are the main targets for latent infection and subsequent transformation by MDV , was much higher in the CD8-deficient vaccinated chickens than in untreate d vaccinated chickens at the early stage of the latent phase. However, the neonatal vaccination prevented lymphoma formation by strain Md5 even in eit her CD4(+) or CD8(+) T cell-depleted chickens. These results suggest that s pecific CD8(+) T cell responses induced by the MD vaccine play a crucial ro le in the prevention of MDV infection during the latent phase, but may not be essential for the prevention of lymphoma formation by an oncogenic MDV.