Many AIDS researchers have suspected that the most common HIV strain, HIV-1, has been lurking in the human population since the 1950s or even earlier. Now scientists have confirmed that's the case: Fragments of HIV-1 from a 1959 blood sample represent the earliest known case of HIV infection. The findings, presented today at the 5th Conference on Retroviruses and Opportunistic Infections in Chicago, could offer a clue to how the virus might have spread from primates to people, and might help vaccine designers learn how to cope with the remarkable genetic diversity of modern HIV strains.
A team led by David Ho, director of the Aaron Diamond AIDS Research Center in New York City, analyzed plasma from a man who in 1959 was living in what is now Kinshasa, Democratic Republic of the Congo. The sample had been collected as part of a large study of immune system genetics, and in 1986 it tested positive for anti-HIV antibodies, indicating the possible presence of the virus.
Ho and his colleagues used an exquisitely sensitive technique called the polymerase chain reaction to detect and amplify small amounts of HIV's genetic material in the sample. They obtained four small fragments--just 15% of HIV-1's complete genome--which they then sequenced. When two experts in the evolutionary history of HIV compared the 1959 virus, dubbed ZR59, to modern HIV strains, they found it to be very closely related to the common ancestor of three strains found in Europe, North America, and Africa. The team believes that this common ancestor must have been introduced into humans from animals sometime in the 1940s or 1950s. Ho's group describes its results in this week's issue of Nature.
The 1959 sample "provides a possible missing link" to HIV's early origins, says Francine McCutchan, a molecular biologist at the Henry M. Jackson Foundation for the Advancement of Military Medicine in Rockville, Maryland. This information, McCutchan says, could help drug companies design a vaccine based on common features shared with HIV's early ancestors--highly conserved and thus probably crucial characteristics that may prove to be more universal targets for fighting the global epidemic than vaccines based on combining a cocktail of modern HIV strains, whose genetic codes differ from each other by 10% or more.