Chimpanzees inoculated with an experimental AIDS vaccine have successfully fought off repeated exposures to the AIDS virus up to a year after they were vaccinated, a research team reported Sunday.
Scientists cautioned that other vaccines have looked similarly effective in chimpanzees, only to fail in human clinical trials. But researchers said they were encouraged by the strength of the immune response triggered by this vaccine.
In previous tests of AIDS vaccines, chimps or monkeys have been exposed to the AIDS virus, HIV, soon after they were vaccinated - an unrealistic scenario.
The new vaccine worked even when chimps were challenged with a big HIV dose 50 weeks after they were vaccinated - longer than has worked in any other study.
Representatives of Wyeth-Ayerst Laboratories, which helped develop the vaccine, could not be reached for comment. But study leader Marjorie Robert-Guroff, of the National Cancer Institute, said the possibility of working toward a small safety trial in people was “under discussion.”
The new vaccine is made from an adenovirus - a kind of virus that can cause colds in people - that was genetically engineered to contain an extra gene called gp160, normally found only in HIV. When sprayed into the nasal passages of chimps, the virus settled into the animals’ upper respiratory tracts and intestines.
During the next week or so, the viruses multiplied in the chimps’ mucous membranes and spewed out gp160 proteins. As predicted, the chimps’ immune systems responded to the proteins by making antibodies and white blood cells programmed to attack HIV.
The researchers boosted that protective immune response by giving the chimps a shot in the arm containing laboratory-made versions of a different HIV protein, gp120. More than 11 months later, they subjected the chimps to intravenous infusions of HIV.
Robert-Guroff and her colleagues reported in the June issue of Nature Medicine, released Sunday, that vaccinated chimps remained healthy until the study ended, almost a year later.