By GINA KOLATA
October 23, 1992
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A group of expert scientists said yesterday that a provocative hypothesis that AIDS originated as a contaminant in polio vaccines was highly improbable.
The group nonetheless recommended that vaccine manufacturing be changed, just to be safe in the future. Viruses for vaccines are currently grown in tissues taken from newly killed animals. The group recommended that instead they be grown in cells that have been cultured in the laboratory and can be more easily checked for the presence of contaminating viruses.
The scientists were called together by the Wistar Institute, a research center in Philadelphia and an original maker of polio vaccines, to resolve a smoldering debate over a theory on the origin of AIDS. The hypothesis was advanced in the March 19 issue of Rolling Stone magazine by Tom Curtis, a freelance reporter, and has received widespread publicity. Theory Is Outlined
Mr. Curtis argued that some lots of live polio vaccines that were given to Africans in 1957 had been tainted with monkey viruses similar to the human immunodeficiency virus that causes AIDS. And the monkey viruses got into the vaccines, Mr. Curtis proposed, as a hidden contaminant of the monkey kidney cells used to grow batches of polio virus. Once the monkey viruses entered the human population, he said, they gradually evolved into the human immunodeficiency virus, known as H.I.V.
As supporting evidence, Mr. Curtis noted that many scientists believed that H.I.V. originated from a monkey virus in Africa and that the Congo, the very area where the AIDS epidemic first broke out, was the place where 300,000 Africans were given a live polio vaccine in 1957.
Dr. Clayton Buck, a panel member from the Wistar Institute, said the center had sought an independent scientific assessment of the hypothesis out of a sense of public duty. The Wistar's former director, Dr. Hilary Koprowski, developed the polio vaccine used in Africa. "We had to at least investigate the possibility," that the hypothesis was correct, Dr. Buck said.
Dr. Frank Lilly, a committee member from the Albert Einstein College of Medicine in the Bronx, said: "It was actually a plausible hypothesis. We were not hostile to it."
But Dr. Eckard Wimmer, a committee member from the State University of New York at Stony Brook, said that after examining the evidence, the group concluded that "the hypothesis is so unlikely that we don't have to take it seriously." 4 'Improbable' Conditions
Essentially, the scientists concluded that the only way the hypothesis could be correct was for a sequence of four improbable events to have occurred.
*The monkey AIDS virus grows in some kinds of cells of the animal, but not those of the kidney. The vaccine would have to be contaminated with these other cells. Furthermore, the fragile virus would have to survive unscathed after at least two cycles of freezing and thawing and a 300-fold dilution, the steps taken to make the vaccine.
*The virus would have to infect people through sores in the mouth, since it is not transmitted through intact skin.
*The virus, though used to living in monkeys, would then have to be able to multiply in humans.
*The virus would have to mutate into H.I.V., a process that many scientists think would take decades or even centuries. 'Extremely Low' Likelihood
The group concluded that the chances that this chain of unlikely events occurred and led the AIDS epidemic is "extremely low." They wrote that "almost every step in this hypothetical mode of transmission is problematic."
In addition, they noted, the first identified case of AIDS was in a merchant seaman who died of the disease in 1959. The man had traveled to Africa in the 1950's, but he was living in Manchester, England, by the first half of 1957, when the polio vaccinations began. "Therefore, it can be stated with almost certainty that the large polio vaccine trial begun in late 1957 in Congo was not the origin of AIDS," the committee wrote."
Mr. Curtis agreed that each of the steps in his hypothesis was unlikely. But he added: "Look at the numbers. There were 300,000 people inoculated. Let's say 50 had sores in their mouths or inhaled the virus deep into their lungs. If they get it and each person passes it on to another person every year, that's all you have to do to get the current 6.5 million Africans." He was referring to the number of Africans now infected with the virus.
Mr. Curtis suggested that the hypothesis could easily be tested. All that was needed was to examine lots of vaccine used in Africa in the 1950's. Although the group felt that such testing would be "laborious, expensive and may be inconclusive," it recommended that some testing be done anyway "so that no stone is left unturned." But Dr. Claudio Basilico, a committee member from the New York University School of Medicine, said there was only one vaccine sample in storage that the scientists could say for certain was used in Africa in 1957, making it very unlikely that anything conclusive could from the testing. Possibility of Contamination
While arguing against the vaccine hypothesis for the origin of AIDS, the committee acknowledged that polio vaccines could in theory become contaminated with other monkey viruses. Polio virus is still grown in African green monkey kidney cells, the group noted. And although the monkey cells can now be tested and certified free of the monkey AIDS virus, such tests cannot prove they are free of other monkey viruses that may not have been identified.
As an alternative, the group recommended that polio viruses be grown in cells that have been cultured in the laboratory and throughly tested for viral contaminants.
In addition to Dr. Buck, Dr. Basilico, and Dr. Wimmer, other scientists on the committee were Dr. Ronald Desrosiers of Harvard Medical School and Dr. David Ho of the Aaron Diamond AIDS Research Center in New York.