Feline leukaemia virus: protective immunity is mediated by virus-specific cytotoxic T lymphocytes

Feline leukaemia virus (FeLV) nucleic acid vaccination of domestic cats aff ords protection against viraemia and the development of latency without ind ucing antiviral antibodies.(1) To determine the contribution of cell-mediat ed immunity to the control of virus replication and clearance from the host , FeLV-specific cytotoxic T lymphocyte (CTL) responses were compared in vac cine-protected, transiently viraemic, and persistently viraemic cats. Vacci nal immunity was associated with the detection of higher levels of virus-sp ecific effector CTL in the peripheral blood and lymphoid organs to FeLV Gag /Pro and Env antigens than those observed in unvaccinated control, persiste ntly viraemic cats (P < 0.001). Likewise, higher levels of virus-specific C TLs were also observed in transiently viraemic cats which recovered followi ng exposure to FeLV. In cats that controlled their infection, recognition o f Gag/Pro antigens was significantly higher than the recognition of Env ant igens. This is the first report highlighting the very significant role that virus-specific CTL have in determining the outcome of FeLV infection in ei ther vaccinated cats or cats recovering naturally from FeLV exposure.