London--A controversial theory that a contaminated polio vaccine tested in Africa more than 40 years ago sparked the AIDS epidemic took a severe hit yesterday. At a spirited, sometimes raucous Royal Society meeting, researchers revealed that tests of old samples of the vaccine contained no traces of HIV or a closely related chimp virus. But the theory's main proponent, British writer Edward Hooper, claims the results don't disprove his scenario.
Most AIDS researchers believe that HIV infected humans through the hunting and handling of chimpanzees, some of which have been found to harbor a closely related virus called SIVcpz. This "natural transfer" theory holds that a "cut hunter" was infected, and then urbanization, the use of dirty needles in medical campaigns, increased geographic mobility, and other effects of modernization in Africa caused the epidemic to explode.
Hooper last year laid out a challenge to this conventional wisdom in a thick tome, The River, that pins the genesis of the AIDS epidemic on a long-forgotten oral polio vaccine made by Hilary Koprowski and colleagues. Between 1957 and 1960, Koprowski, former head of the Wistar Institute in Philadelphia, tested his vaccine on a million people in what is now the Democratic Republic of Congo, Burundi, and Rwanda. Hooper posits that the vaccine became contaminated with SIVcpz because researchers used kidney cells from infected chimpanzees during the manufacturing process. As circumstantial evidence, Hooper contends that the earliest cases of AIDS closely match the sites of these vaccinations. And he argues in The River that the Wistar Institute could help settle the case by testing the few remaining samples of the vaccine.
Now, three independent labs have done just that. At the Royal Society meeting, Claudio Basilico, the head of the expert committee and chairman of microbiology at New York University Medical Center, described the results of tests on seven old vaccine samples found in Wistar's freezers. Koprowski has insisted that he used kidneys from monkeys, not chimpanzees, to make the vaccine, so one lab analyzed primate mitochondrial DNA in the samples. Another looked for SIV or HIV genetic material. And the third lab, headed by Simon Wain-Hobson of the Pasteur Institute--who has been sympathetic to Hooper's point of view and even helped do some research for him--ran tests for both virus and mitochondrial DNA. All the samples tested negative for simian and human viruses, and the mitochondrial DNA clearly came from monkey, not chimpanzee, cells.
Hooper did not challenge the results; he simply dismissed them. "This means nothing at all for the polio vaccine theory," he said at a jam-packed press conference held a few minutes later. Hooper noted that the samples didn't come from the exact lots of the polio vaccines tested in Africa. Indeed, Koprowski himself has acknowledged that no such samples still exist. Hooper added that he recently had discovered "two smoking guns": Two people who worked in Africa on the project whose first-hand accounts support the idea that Koprowski or his collaborators used chimpanzee kidney cells to make the vaccine.
But Stanley Plotkin, an emeritus professor at the University of Pennsylvania who helped Koprowski make and test the vaccine, says he has spent the past year contacting former collaborators, and 16 scientists have testified, in writing, that they never worked with chimpanzee cells. "I'm sure Mr. Hooper will be disappointed by the results of this meeting," said Plotkin. "There is no gun. There is no bullet. There is no shooter. There is no motive. There is only smoke created by Mr. Hooper."
Supporters of Hooper's theory remained unconvinced. Brian Martin, a social scientist from Australia's University of Wollongong, argued that if people scrutinized the natural transfer theory as closely as they have examined Hooper's scenario, it would prove to be just as unsatisfying. "There is one thing I will predict as a social scientist," said Martin. "Whatever happens at this conference, this controversy will continue."