HIV-1 variation: consequences for disease progression and vaccine strategies.

HIV-1 displays a high degree of biological heterogeneity in vitro, differing in tropism, kinetics of replication, cytopathogenicity, resistance to antiviral drugs and susceptibility to serum neutralization. Some of these properties can be linked to pathogenesis in the host. HIV variation is a major challenge to the development of effective vaccine or antiviral therapies.