Present status of vaccination against HIV-1 infection.

The development of an effective vaccine against the acquired immunodeficiency syndrome (AIDS) is a formidable task. The absence of any documented case of natural recovery from the disease raises the question of whether any vaccine against human immunodeficiency virus (HIV) could possibly be effective in preventing natural transmission of the virus. It also raises the issue of which type of immune response a vaccine should elicit to be protective. Many obstacles have to be overcome, including the considerable antigenic variability of the virus, its intracellular mode of transmission, its mucosal port of entry, and the persistent nature of the infection. The only animal model available for the development of prototype HIV-1 vaccines is the chimpanzee model. Chimpanzees infected with HIV-1 do not develop AIDS but remain persistently infected. This model, therefore, allows one to test for protection from infection, but not for protection from disease.