Human Immunodeficiency Virus Type 2 (HIV-2)

HIV-1 and HIV-2 are genetically and antigenically related viruses with distinct epidemiologic and biologic properties. In West Africa, many populations are at risk for both HIV-1 and HIV-2. Since its discovery in 1985, research on HIV-2 conducted in large part by West African researchers has amply demonstrated the unique biologic properties of this virus. Various studies suggest differences between HIV-2 and HIV-1 in geographic distribution, distinct temporal trends in the epidemic spread, and dramatic differences in perinatal and sexual transmission. Studies of HIV-2 infected individuals have shown a significantly slower progression to AIDS. Whereas most HIV-1 cohort studies have found 5-15% of their subjects fit a definition of long-term non-progression, 86-95% of HIV-2 infected individuals would be similarly classified. This dramatic difference in pathogenicity provides a unique opportunity to identify viral and host immune mechanisms involved in a closely related and relevant virus system that is predicted to have a significantly slower course of progression. In similar settings, HIV-2 shows lower infectivity and pathogenicity in comparison to that of HIV-1, suggesting that it may be viewed as a virus that is attenuated with respect to HIV-1. This view gave rise to the hypothesis that infection with HIV-2 might provide protection against subsequent infection with the more pathogenic HIV-1. The striking conclusion was that HIV-2 did provide ~60% protection against subsequent infection with HIV-1, now evaluated for over 13 years of study. This hypothesis has now been tested in a number of studies in other parts of West Africa. The ‘natural experiment’ of HIV-2’s observed protection against HIV-1 infection represents an invaluable model in which important correlates of HIV-1 protection can be identified and characterized.We are hopeful that further comparative studies of these related immunodeficiency viruses will yield important information on the pathogenic mechanisms employed by HIV viruses and lead the way to the development of effective interventions for the prevention and control of the AIDS pandemic.