Virus variation, escape from cytotoxic T lymphocytes and human retroviral persistence

Viruses use a variety of mechanisms to escape recognition by cytotoxic T lymphocytes (CTL). The available evidence suggests that the main mechanisms of CTL escape caused by viral sequence variation are loss of epitope binding to MHC molecules or altered recognition by T cell receptors. These types of mutations occur in both human immunodeficiency virus type 1 (HIV-1) and human T cell leukaemia virus type 1 (HTLV-1) infections. In HIV-1, CTL escape is one factor that may cause progression of disease. In HTLV-1, however, CTL escape mutants never predominate in the viral population.