Nef-mediated downregulation of CD4 enhances human immunodeficiency virus type 1 replication in primary T lymphocytes

The accessory protein Nef plays a crucial role in primate lentivirus pathogenesis. Nef enhances human immunodeficiency virus type 1 (HIV-1) infectivity in culture and stimulates viral replication in primary T cells. In this study, we investigated the relationship between HIV-1 replication efficiency in CD4(+) T cells purified from human blood and two various known activities of Nef, CD4 downregulation and single-cycle infectivity enhancement. Using a battery of reporter viruses containing point mutations in nef, we observed a strong genetic correlation between CD4 downregulation by Nef during acute HIV-1 infection of activated T cells and HIV-1 replication efficiency in T cells. In contrast, HIV-1 replication ability was not significantly correlated with the ability of Nef to enhance single-cycle virion infectivity, as determined by using viruses produced in cells lacking CD4. These results demonstrate that CD4 downregulation by Nef plays a crucial role in HIV-1 replication in activated T cells and underscore the potential for the development of therapies targeting this conserved activity of Nef.