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Salk Report on AIDS Vaccine Meets Skepticism at Convention : Science: Other researchers fault tests of experimental product. But the polio pioneer shrugs off attacks.

June 10, 1993|SHERYL STOLBERG | TIMES MEDICAL WRITER

BERLIN — Releasing long-awaited test results, polio pioneer Jonas Salk announced Wednesday that his experimental AIDS vaccine appears to boost the immune systems of people infected with the human immunodeficiency virus. But his work met with immediate skepticism from other scientists gathered here at the Ninth International Conference on AIDS.

"I'm less than enthusiastic," said David Ho of the Aaron Diamond AIDS Research Institute in New York. Robin Weiss, the renowned British virologist, said of the presentation by Salk's collaborators: "It was a dog-and-pony show."

And, in a sense, it was.

Wednesday in Berlin was a media jamboree that only Salk, with his love-hate relationship with the limelight, could attract. As cameras rolled and reporters scribbled during a news conference that was linked by satellite to the United States, the 78-year-old scientist simply smiled and shrugged off the attacks.

"We've been explorers," he declared. "We're like Columbus going to India and finding America and saying, 'That's not where I was headed,' and then he still didn't know that there was St. Louis and San Francisco."

He acknowledged that the results of his double-blind, placebo-controlled study--a tightly guarded secret until Wednesday--were far from conclusive: "It's the first whiff of spring, you might say."

Still, Salk and his commercial partners--Carlsbad-based Immune Response Corp. and Rhone-Poulenc Rorer, a Pennsylvania-based subsidiary of the French pharmaceutical giant Rhone-Poulenc--said their findings were encouraging enough to warrant a large-scale clinical trial, conducted over a long period, that would demonstrate whether the vaccine truly helps people live longer.

Unlike traditional vaccines, the so-called Salk Immunogen is a "therapeutic vaccine," designed to improve immune response in infected people rather than prevent infection.

Several preventive vaccines are also being tested in humans; in a plenary address at the conference Wednesday, AIDS expert Dani P. Bolognesi of Duke University said two of those vaccines look promising and could proceed to large-scale clinical trials next year.

While most experimental AIDS vaccines rely on modern genetic engineering techniques, Salk is using an old-fashioned approach that employs a killed form of the AIDS virus--the same approach that worked for him nearly 40 years ago with polio.

His critics have said that is far too blunt an instrument for such a sophisticated invader as HIV. But Salk, no stranger to criticism, has pushed ahead.

The vaccine was tested in three separate clinical trials over a six-year period. The first, conducted at County USC Hospital under the direction of noted AIDS researcher Dr. Alexandra Levine, involved 23 homosexual men and concluded that the vaccine was safe. The second, at the University of Pennsylvania, was designed to determine the correct dose.

The largest, most recent and most significant trial was a one-year study in which the vaccine was compared to a placebo in 103 HIV-infected volunteers, none of whom showed symptoms of AIDS at the outset.

The study's timetable was too short for researchers to measure their success in terms of health; the asymptomatic patients were unlikely to become ill within a year. Instead, the scientists examined "surrogate markers"--biological changes--including levels of HIV in the blood detected through an extremely sensitive test called polymerase chain reaction, or PCR.

According to Levine, the USC hematologist who presented the results, the tests revealed three statistically significant changes in those who took the vaccine versus those who did not:

Vaccinated patients developed more antibodies to a core protein of HIV. They also showed stable levels of "viral burden"--the amount of virus in the blood--while unvaccinated patients showed an increase. And their CD4 cells--the immune system cells that are the main targets of HIV--demonstrated improved function.

But several prominent researchers who attended Wednesday's talk were not persuaded. In instant analyses delivered in the corridors of the conference center after Levine gave her talk, they complained that the results showed only trends, rather than detailed data for individual patients, and they questioned the precision of the PCR tests used by Salk's group.

These scientists said that the biological changes the patients showed do not offer solid evidence, both because they were minor and because no one yet knows which surrogate markers correspond with immunity against AIDS. The real test, they said, will come when Salk can prove that the vaccine helps people live longer.

"We simply don't know what these markers mean," said Bolognesi, the Duke University expert. "They haven't been validated. . . . Those are small changes, and small changes that we don't know what they mean doesn't give you real confidence that this is beneficial."

The most gracious of the critics was Anthony Fauci, the top AIDS expert at the U.S. National Institutes of Health, who said that while the results were "not overly impressive," it is important for Salk to go ahead with his work.

When, or if, the Salk Immunogen might become available to patients remained unclear. Officials at Immune Response Corp. said late last year that they hoped that by the end of 1993 or early 1994, they would obtain government permission to market their product while continuing to test it in patients.

On Wednesday, officials would say only that they were talking to the U.S. Food and Drug Administration.

"We can't give a timetable on approval," said Dr. Elizabeth Corsi, vice president of the company formed when Immune Response joined with Rhone-Poulenc Rorer. "That's speculation, and we don't want to deal with speculation."

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