LEAD: In the most hopeful experimental finding yet on the question of whether scientists will be able make an AIDS vaccine, researchers in Louisiana today reported that they protected eight of nine monkeys against simian AIDS with a vaccine.
In the most hopeful experimental finding yet on the question of whether scientists will be able make an AIDS vaccine, researchers in Louisiana today reported that they protected eight of nine monkeys against simian AIDS with a vaccine.
The work makes it likely that a vaccine that protects against AIDS infection in humans will eventually be possible, experts said, and it points the direction for researchers to take in developing such a vaccine.
No one can be sure when or even if such a vaccine will be perfected. Many experts believe that a human vaccine is at least 5 to 10 years away.
But today's announcement, coupled with earlier findings in animal studies, has helped dispel the deep pessimism that afflicted AIDS researchers after initial animal work failed to protect chimpanzees against infection.
"Our success is unambiguous proof that a vaccine for AIDS is possible," said Dr. Michael Murphy-Corb, leader of the research team at the Delta Regional Primate Research Center in Covington, La., which is affiliated with Tulane University.
And Dr. Anthony Fauci, director of the National Institute of Allergies and Infectious Diseases, said: "It sounds simplistic, but we did not know whether protective immunity was even possible, because there are hundreds of thousands of people infected who have had immune responses, but those responses did not protect them. Now we know it can be done."
The new findings are to be reported Friday in the journal Science. The work improves on an earlier, more limited success by other researchers in protecting monkeys from infection with simian AIDS. The simian virus is related to the AIDS virus and inflicts a disease that closely parallels AIDS in humans.
The earlier work showed that two of six monkeys were protected against infections with the simian AIDS virus, but the work announced today protected eight of nine. Although the ninth became infected with the virus, it has remained free of disease symptoms for 14 months, Dr. Murphy-Corb said.
'We Can See a Direction Now'
Dr. Bernard R. Moss, a vaccine expert at the National Institute of Allergies and Infectious Diseases, said today's report was "the most positive result in animals so far" on the prospects for a vaccine against AIDS.
"We can see a direction now, the results are important and the follow-up can be rapid," he said. "Things look more hopeful than before."
But Dr. Ronald C. Desrosiers of the New England Regional Primate Center, who led the group that carried out the earlier work, was more cautious. "We should be careful not to think that a human vaccine is just around the corner," he said. "Let's not forget that this was done in an idealized laboratory setting.
"The question is still not so much when as whether we can make a vaccine that will work in humans."
But he added that the success in monkeys encouraged him to believe that it could happen, "and we are all back in the lab and working hard on it."
From the beginning of the AIDS epidemic, researchers have believed that a vaccine would be the best way to attack the disease. Drugs work only after people are infected, and while drug treatments work extremely well against bacteria, AIDS is caused by a virus. The successes against viral diseases like smallpox, measles, mumps and polio have all come through vaccines.
All these vaccines were of the type that was tried in the Louisiana experiments: viruses that are killed so they do not infect their hosts, but are injected into the body so the immune system may respond and build up its natural defenses against invasion by a live virus.
Vaccine, Then Virus
The first AIDS vaccines tested were only fragments of the AIDS virus. If they had succeeded, they would have been safer to use and quicker to make than whole killed viruses. But experiments with the fragments failed to protect chimpanzees from infection. The later experiment in New England, in which two of six monkeys were protected against simian AIDS, used whole killed viruses, but the viruses were killed in a different way.
Today's announcement reported on work begun more than two years ago. The monkeys were each given three shots of vaccine made from whole killed simian immunodeficiency virus, which causes simian AIDS.
Four monkeys that got the vaccine were injected with the live virus a month later. Three of the four have shown no infection. The fourth became infected but remains without symptoms.
Thirteen months later, another five were given vaccine followed two weeks later with doses of live virus. Those five are still free of infection.
The experimenters also gave no vaccine to 17 monkeys and injected them with live virus. All 17 became infected, and 12 died within seven months.
The obstacles in developing a human vaccine are numerous, researchers said. They cannot be overcome in less than five years and are more likely to take a decade or more.
One major problem is that the vaccine protected the monkeys against only one strain of the simian AIDS virus. But viruses can have many strains; the polio vaccine now in use must combat three strains, and the AIDS virus is known to have more than five. Researchers will soon be trying to protect monkeys against more than one strain.
Another problem is that in the laboratory, the live virus is given within weeks of the vaccination. But outside a laboratory, a vaccine would have to protect patients for months or years after vaccination.
A Host of Obstacles
Still another difficulty is the persistence of the virus in the body. Most vaccines against viral diseases do not completely prevent infection with virus particles, but block most of the particles and help the body protect itself against a small amount of residual infection.
But with AIDS, it may be that infection even with a few particles of virus will prove fatal.
Before vaccines can be tried against AIDS in humans, they must first be completely successful in monkeys under more realistic conditions and against many strains of virus.
Safety is also a serious issue, experts said, because with vaccines that contain killed virus, there is always a risk that the virus will somehow be reactivated and cause the disease rather than prevent it.
For this reason, much work must be done to assure that the virus is disabled. Or if the work with monkeys can show which parts of the virus make the body's own defenses start working, those parts alone may be made into a vaccine that has no chance of causing the disease.
Besides Dr. Murphy-Corb and her group at Tulane, other researchers included Dr. Deborah A. Eppstein at Syntex Research in California and Dr. Ron C. Montelaro at Louisiana State University.