CD8A and viral infectious disease: Functional impairments of CD8+ T cells have been characterized in several persistent viral infections, including human immunodeficiency virus (HIV) and hepatitis C virus (HCV) infection in humans, simian immunodeficiency virus (SIV) infection in macaques, and lymphocytic choriomeningitis virus (LCMV) infection in mice (Ahmed and Rouse, 2006).