Studies dismiss polio-vaccine hypothesis for HIV's origin

THE CONTROVERSIAL theory that researchers developing polio vaccines in Africa in the 1950s accidentally triggered today's global AIDS epidemic has today been dealt what could finally be a fatal blow. Three new studies have found no evidence for the main claims of the theory published in Nature.

In his 1999 book The River: A Journey to the Source of HIV and AIDS, journalist Edward Hooper promulgated a disturbing theory about the origins of AIDS. Hooper's assertions threatened to capture the public's imagination until they were largely discredited by preliminary investigations presented at the Royal Society in September last year. At the time, Hooper dismissed the results as "irrelevant" to his hypothesis.

Hooper claimed that by using chimpanzee kidney tissues infected with human immunodeficiency virus (HIV) when developing an oral polio vaccine (OPV), researchers at the Wistar Institute in Philadelphia, Pennsylvania inadvertently contaminated their vaccine stocks with the virus. He alleges that when these vaccines were tested in as many as one million people in the Congo between 1957 and 1959 they seeded the human population with HIV-1 the strain that most commonly causes AIDS.

Three independent research groups have now found no trace of chimpanzee tissue in any of the remaining stocks of the original vaccine, including a vial of the stock used to create the OPV tested in the Congo. They also detected neither HIV nor its primate form and closest ancestor, simian immunodeficiency virus (SIV). Furthermore, they present evidence that the virus emerged in human populations before the Congo vaccine trial.

The researchers admit that their findings cannot disprove Hooper's theory. "It's the old problem of proving a negative," says Neil Berry of the National institute for Biological Standards and Control (NISBC) in Potters Bar, U.K. "But the data really don't provide any support for his hypothesis."

Out in the cold

Perhaps the most compelling evidence against Hooper's theory comes from Berry's group. They analysed a vial of the same vaccine stock as was used to treat people in the Congo and is directly blamed in The River for the outbreak of HIV in humans. When the River was published, the Wistar Institute could not produce a sample of that vaccine; the one that has now been tested was later found in a freezer at the NISBC.

Berry's team did not detect HIV or SIV in the suspect vaccine. What's more, the only tissue identified was from macaque monkeys - which Wistar researchers insisted that they had used - and not from chimpanzees. "We used a sensitive assay for both tissues and only one was positive," says Berry. Philippe Blancou at the Pasteur Institute in Paris and his colleagues looked at the remaining samples of the original vaccine stock from the Wistar Institute. They too found only evidence of macaque tissue and no HIV.

Finally, having examined samples of HIV collected in the Congo in 1997, Edward Holmes at the University of Oxford and his colleagues conclude that the multiple sub-types that characterize modern-day HIV could not have originatd from contamination with chimpanzee tissue in the 1950s. According to Holmes' team, the last common ancestor of the variants knownin the Congo today was present in a human host and was not, as Hooperalleges, transferred from a primate.

Proof positive

The genetic history of HIV-1 strains, says Holmes, "fits a classic exponential epidemiological spread and says nothing at all about multiple transfer" from vaccination with a contaminated oral polio vaccine. "It's appealing to point the finger at someone rather than admit it may be a natural, ecological process, which is what I believe it is," Holmes adds.

Edward Hooper was not available for comment but has so far stood firmly in support of his theory. He has said that the only evidence he will accept is proof that HIV existed in humans before 1957. "He's going to fight until someone finds a blood sample from the 1940s that's HIV-positive," says Holmes.

Simon Wain-Hobson, a member of the Blancou team at the Pasteur Institute sympathizes with Hooper's "compelling" theory. "Such an outrageous thing as HIV0 requires an outrageous explanation." But, he argues, the scientific evidence for the origins of HIV tell a less dramatic tale. "You can play conspiracy theories 'til you're blue in the face, but the onus is now on Hooper0 to provide proof," he says.

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