United Press International; Thursday July 2 7:08 PM EDT
Michael Smith, UPI Science News

Charles Farthing, medical director of the AIDS Healthcare Foundation, dismissed animal studies that showed live vaccines resulted in the monkey equivalent of AIDS. He says: "You have to do safety tests in humans. I firmly believe we have to do this experiment."

Farthing is also a member of the International Association of Physicians in AIDS Care, which in August 1997 called for volunteers from among its physician members to take part in a live vaccine trial. Farthing said 300 volunteers said they'd be willing to take part.

He spoke before a symposium on vaccines at the 12th World AIDS Conference today.

The danger of using a live virus is that it may cause disease rather than preventing it and Harvard Medical School researcher Ruth Ruprecht said that's exactly what happened in her studies of a live vaccine against the simian immunodeficiency virus (SIV).

SIV is the monkey equivalent of the human immunodeficiency virus (HIV), which causes AIDS.

In a study in which nine infant rhesus monkeys were injected with the live SIV vaccine, she said, none is free of disease and five have died. In a similar study of 15 adult monkeys who got the live vaccine, she said, four now are showing signs of disease and one has died.

The idea behind a live vaccine is to use a version of the virus that has been crippled in the laboratory so that it can no longer cause disease. But, Ruprecht said, "We actually do not know what part of the HIV genome is responsible for causing disease."

Researchers had thought that deleting a gene called nef would prevent SIV from causing disease, based on the case of 10 Australian men who contracted an HIV strain 14 years ago that is naturally missing its nef gene. All of those men remain healthy.

Ruprecht said it's now clear that SIV can cause disease even without that gene. But Farthing said Ruprecht's data don't deter him. For one thing, he said, SIV is naturally more aggressive than HIV. As well, he said, the live HIV vaccine that's under consideration has not only nef, but three others of its nine genes deleted.

Farthing also said he's not worried about the results in Ruprecht's study of infant monkeys. "We never give live attenuated viruses to human infants," he said. "You have to wait until the immune system is mature."

Live attenuated viruses are used as vaccines against several human diseases, including polio.

"Her adult data are more concerning," he said. "But you have to remember it (SIV) is a more vicious disease."

Farthing said the live vaccine, developed by Ron Desrosiers of the Harvard Primate Center, has been licensed to a Massachusetts company, Therion Biologics, for development.

He said he's hoping it can go into the first stage of clinical trials _ testing for safety _ within a year and a half.

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