Although HIV-1 infection is characterized by progressive depletion of CD4+ T cells that eventually leads to clinically significant immunodeficiency, a chronic generalized immune activation is now being recognized to be the main driving force for T cell depletion, loss of anti-HIV-1 immunity and disease progression during chronic HIV-1 infection. In particular, this immune activation has been identified as a disease determinant independent of viral load or cell death in HIV-1 infection. A series of clinical evidences have indicated that activated CD8 T cells may attack body cells infected with viruses. Because of this, CD4 cells infected with HIV are frequently destroyed by CD8 cells.