Eleven prominent AIDS researchers, primatologists, and animal conservationists are urging vaccine developers not to inject chimpanzees with strains of HIV that can cause AIDS-like disease in the animals. In a letter published in tomorrow's Science, they raise scientific and ethical objections to such experiments.
Until recently, chimps were considered poor models for testing vaccines, because HIV doesn't replicate well in the animals or appear to make them sick. But that changed when researchers at Emory University's Yerkes Regional Primate Research Center in Atlanta, Georgia, discovered a strain of HIV that causes a steep drop in the animals' CD4 cells and an increase of virus in their blood. In a review published in the 19 June 1998 Science, Norman Letvin of Harvard's Beth Israel Deaconess Medical Center in Boston pointed out that the strain could be useful for testing vaccine candidates, and many AIDS researchers agree.
But not virologist Alfred Prince of the New York Blood Center, who runs a chimp colony in Liberia, and his co-worker Linda Andrus. "The prospect of causing a rapidly progressive and fatal disease in this near-human species is abhorrent," they wrote in a letter in the 18 December 1998 Science. A more acceptable test for a candidate vaccine, they say, is whether it can prevent a virus from establishing a chronic infection; if so, the disease will not occur. And several nonvirulent strains appear to replicate well enough in chimps to provide a realistic challenge, they wrote.
In the new letter, Prince, Andrus, and nine others, including chimpanzee advocate Jane Goodall, raise a new objection: The virulent HIV strain may be too "hot." It destroys a chimp's immune system in a few weeks, while in humans the same process typically takes years. This could "seriously jeopardize the HIV vaccine effort" by ruling out vaccines that fail to protect against this strain, but which but might be effective against wild-type HIV, they write.
But Patricia Fultz of the University of Alabama at Birmingham doesn't believe the Emory strains of HIV are too hot, noting that infected animals have lived up to 4 years. And Letvin says that focusing only on a vaccine's ability to stave off chronic infection, rather than its effect on the disease process, might lead researchers to overlook a useful vaccine: "If we have a vaccine that can make people live decades longer, we need to know that."