The typical course of HIV infection is characterized by multiple phases that occur over a period of eight to ten years. A critical event in the initial establishment of HIV infection is the localization of HIV in lymphoid organs that serve as major reservoirs for HIV and as primary sites for virus replication. Despite the fact that the majority of HIV-infected individuals do not show any clinical signs of disease activity for extended periods of time, HIV disease is active and progressive in lymphoid organs during this clinically latent period. Persistence of virus in lymphoid organs causes a chronic stimulation of the immune system that ultimately leads to destruction of the lymphoid tissue and loss of the ability to respond to HIV and/or other pathogens.