One man’s HIV infection over a decade ago is giving scientists their first evidence of the safety of an AIDS vaccine that has been considered too dangerous for people.
In a kind of unintended natural experiment, the man caught a genetically weakened form of the AIDS virus. It is virtually identical to the weakened virus used in the experimental vaccine, which works well on monkeys.
Typically, people fall ill within 10 years of contracting HIV. But this man, now 44, appears to be perfectly healthy at least 12 years after getting infected.
About 5 percent of HIV-infected people show no signs of immune system damage more than a decade after catching the virus. Understanding the factors that keep them healthy is a major goal of AIDS research.
The study is the first to show that long-term HIV survival clearly may result from catching a crippled version of the virus.
Certainly, one healthy patient does not prove safety. And it also does not demonstrate whether the vaccine wards off other HIV infections, although the researchers said it may have kept the man, a hemophiliac, from getting more lethal forms of the virus from his clotting material, which was produced before it was routinely screened for HIV.
Recently, doctors discovered that the man’s virus was crippled by a mutation in one of its nine genes. By coincidence, this mutation is identical to the one deliberately engineered into an experimental vaccine for SIV, the monkey form of the AIDS virus.
Scientists showed two years ago that giving monkeys this weakened form of the virus protects them from catching the lethal variety, despite deliberate exposure. Yet it does not make the monkeys sick.
The case of the man who was inadvertently vaccinated was described in today’s issue of the New England Journal of Medicine by researchers from the New England Regional Primate Research Center and the University of Massachusetts Medical School.
The search for a human AIDS vaccine has been disappointing. Giving dead fragments of the virus does not appear to stimulate the body enough to ward off infection. Yet giving a weakened but live virus - called an attenuated vaccine - is considered too risky because of the chance it will cause the disease it is intended to prevent.
Dr. Ronald Desrosiers of the primate center said many scientists agree that a live attenuated AIDS accine is likely to be the most effective at preventing infection.
“But the big concern is safety, safety, safety, safety,” he said. “This guy is doing fine. This is evidence of sorts that it can be safe.”
In an accompanying editorial in the journal, Dr. David Baltimore of Massachusetts Institute of Technology wrote that “continued study of an attenuated vaccine is reasonable.”
However, he noted that a still-unpublished study, conducted by Dr. Ruth Ruprecht of the Dana-Farber Cancer Institute in Boston, found that the crippled virus caused AIDS when given to baby monkeys.
Because infants’ immune defenses are immature, a virus that is harmless to grownups may be lethal to them. Her study raises the possibility that mothers who get an attenuated vaccine might pass the AIDS virus to their babies.
And Dr. Dani Bolognesi of Duke University is skeptical about the possibility of attenuated vaccines.
“This study in monkeys is scary,” he said.
However, Dr. John Sullivan of the University of Massachusetts, a co-author with Desrosiers, said he thinks researchers should try to test such a vaccine. “When there is a new person infected every 15 seconds, we can’t sit around and scratch our heads and say we need to think about this for 10 more years,” he said. “It’s time to move forward with the idea that an attenuated vaccine might in fact be used.”
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