Immune-based therapies are being explored on the presumption that host response to HIV is central to the pathogenesis and progression of HIV infection. Specific immune responses in most individuals serve to limit the acute stage of infection and induce a more chronic form of viral infection. Thus, immune response to HIV appears to be critical to virus control. On the other hand, HIV infection induces widespread activation of immune cells, which in turn contributes to further HIV production. Also, immune dysfunction contributes to the development of a number of clinical disorders of AIDS, including opportunistic infections, wasting syndrome, AIDS dementia complex, Kaposi’s sarcoma and lymphoproliferative disorders.