Does the prospect of developing an effective AIDS vaccine justify condemning chimpanzees to death? That's the stark question dividing biomedical researchers in the US, now that virologists know that some strains of HIV cause the same fatal illness in chimps as they do in people.
Already, several chimps have been deliberately infected with HIV strains that can kill them. And the researcher who discovered that chimps can develop AIDS plans to expose up to four more animals to his lethal virus.
These experiments could be the prelude to vaccine experiments involving larger numbers of apes. That prospect has outraged animal welfare campaigners-and many researchers. No scientist would infect a person with HIV deliberately, they point out. Being our closest living relatives, they argue, chimps should be treated with similar respect.
"You can compare a chimp to a mildly retarded child. Just because it's mildly retarded doesn't mean you abuse it," says Alfred Prince, a virologist at the New York Blood Center. Along with 11 other scientists, he has sent a letter to the journal Science raising ethical and scientific objections to the use of lethal HIV strains in chimps. Another of the signatories is primatologist Jane Goodall, famous for her studies of wild chimps in Tanzania.
Chimps are no longer used in research in many countries, including Britain and Australia. But in the US, more than 100 of the apes have been infected with different strains of HIV since the early 1980s. Until recently, it seemed that HIV never causes AIDS in chimps. This meant that chimps fell from favour as an animal model for AIDS research and limited the controversy surrounding the experiments.
But that all changed in 1997, when Frank Novembre of the Yerkes Regional Primate Research Center in Atlanta reported a single case of HIV causing AIDS in a chimp (Journal of Virology, vol 71, p 4086). Since then, the virus responsible has been deliberately passed on to a handful of other chimps. None of these animals has yet developed AIDS, but some have extremely low levels of CD4 cells, the white blood cells that are destroyed by HIV. This suggests that it is only a matter of time before they become sick and die.
"The good news is that we now have a pathogenic HIV model in a chimp," says Alan Schultz, head of preclinical research in the AIDS vaccine programme of the National Institute of Allergy and Infectious Diseases (NIAID) near Washington DC. "The bad news is that to do meaningful vaccine experiments, we will have to put chimps' lives at risk."
The NIAID is now funding Novembre to expose up to four more chimps to lethal HIV strains, with the aim of working out the smallest dose needed to establish an infection via the rectum. Novembre and virologist Patricia Fultz of the University of Alabama at Birmingham have already exposed chimps with good immune responses to less virulent strains of HIV to one of the new aggressive strains. The existing infection appeared to offer some protection.
Hopes for a vaccine that can completely prevent HIV infection are fading, however, so attention is shifting towards vaccines that might slow the progression to AIDS. These could be tested in chimps infected with the lethal strains. The alternative-going straight into tests on people with HIV-is complicated by the widespread use of anti-retroviral drugs, which also delay the progression to AIDS. This would make it difficult to distinguish the effect of the vaccine from that of the drugs.
Fultz argues that terminal experiments involving chimps are a necessary evil. "With 40 million people infected in the world, there is a great need for a vaccine" she says.
But Prince claims the chimp experiments are flawed. The virulent HIV strains are more aggressive than the strains that usually infect people, he says, so potentially effective vaccines could get overlooked. Fultz disagrees: "The strain I have is very much like HIV in humans."
Irrespective of the scientific arguments, however, many people would oppose the experiments on ethical grounds-particularly in the light of current efforts to grant legal rights to chimps and other great apes (This Week, 13 February, p 20). Prince hopes his letter to Science will provoke sufficient public outcry to prompt a moratorium on potentially terminal AIDSexperiments involving chimps.
Author: Rachel Nowak, Washington DC
New Scientist magazine issue 20 February 1999
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