More than 13 million people around the world have been infected with HIV, a virus which causes AIDS, and the number is expected to grow to 30 to 40 million by the year 2000, according to U.S. government estimates. But while researchers isolated HIV a decade ago, an AIDS vaccine remains elusive.
One obstacle to creating a vaccine against the virus, says Dr. Martin S. Hirsch, a professor of medicine at the Medical School and director of AIDS research at Massachusetts General Hospital (MGH), is the rapid rate at which the virus mutates. "A single vaccine won't be effective against all the active strains that are out there," says Hirsch.
In addition, creating valuable animal models for HIV infection is difficult, says Hirsch, because the virus does not infect any organism but humans.
One Harvard researcher, Professor of Microbiology and Molecular Genetics Ronald C. Desrosiers, has been trying to develop such an animal model in monkeys with SIV, a rough equivalent of HIV in the animals. Desrosiers has been able to delete certain portions of SIV to create a live but weakened form of the virus which won't cause disease. Despite initial success with the strategy, later results have been disappointing.
Because of the uniqueness of the virus, syas Hirsch, researchers are forced to use two distinct strategies to create a vaccine. The first approach is the classical one, the strategy used for polio, mumps and measles (please see main story).
MGH researchers are pursuing a different strategy, using vaccines to stimulate the immune response of patients already sick with AIDS. Following a similar track is MicroGeneSys, a Connecticut biotechnology firm. The company initially secured $20 million in government funding for clinical trials of its vaccine GP-160, modeled on a recombinant protein found in the coat which covers HIV.
But Congress may soon halt funding amid protests from scientists and advocacy groups that the drug received the go-ahead because of lobbying rather than sound scientific evidence.
So when do researchers expect an AIDS vaccine to be developed? Hirsch's call is positively within 20 years. "I think you'll find a whole range [of predictions] from people who say we'll never have a vaccine effective against AIDS to those who say we'll have one within the next five to 10 years," he says.
But skepticism remains. "There's still very little evidence that any of [the prospective vaccines] are going to do anything in terms of preventing the disease," says Dr. Bernard N. Fields, Lehman professor of microbiology and molecular genetics.
"So in this case you have to do an awful lot of research on how the virus works and how it infects the host to really build the groundwork for trying to make an effective vaccine," says Fields.