of responses appears to be dependent upon persistent exposure to HIV. Prediction of progression rates During the initial weeks after HIV infection, qualitative differences in the cell-mediated immune response are observed that correlate with different disease progression rates (i.e., rapid progression to WHO stage 4 and the rapid loss of CD4+ T cell levels versus normal to slow progression to WHO stage 4 and the maintenance of CD4+ T cell counts above 500/µl). The appearance of HIV-1-specific CD8+ cytotoxic T cells (CTLs) early after primo-infection has been correlated with the control of HIV-1 viremia. The virus which escapes this CTL response have been found to have mutations in specific CTL epitopes. Individuals with a broad expansion of the V-beta chain of the T cell receptor of CD8+ T cells during primo-infection appear to have low levels of virus six to twelve months later, which is predictive of relatively slow disease progression. In contrast, individuals with an expansion of only a single subset of the V-beta chain of the CD8+ T cells are not able to control HIV levels over time, and thus have high viral loads six to twelve months later. LTNP’s have also been shown to have a vigorous proliferation of circulating activated HIV-1-specific CD4+ T cell and CTL response against multiple epitopes with no detectable broadly cross-reactive neutralizing antibodies in the setting of an extremely low viral load. However, a few reports have correlated the presence of antibodies against Tat in LTNP status. HIV subtype variation and effect on progression rates The HIV-1 subtype that an individual becomes infected with can be a major factor in the rate of progression from sero-conversion to AIDS. Individuals infected with subtypes C, D and G are 8 times more likely to develop AIDS than individuals infected with subtype A. In Uganda, where subtypes A and D are most prevalent, subtype D is associated with faster disease progression compared with subtype A. Age has also been shown to be a major factor in determining survival and the rate of disease progression, with individuals over 40 years of age at sero-conversion being associated with rapid progression. Host genetic susceptibility The Centers for Disease Control and Prevention (CDC) has released findings that genes influence susceptibility to HIV infection and progression to AIDS. HIV enters cells through an interaction with both CD4 and a chemokine receptor of the 7 transmembrane family. They first reviewed the