Baboons offer promising model for AIDS.

Baboons injected intravenously with one type of HIV, the AIDS-causing virus, show persistent infection and eventually develop the disease. These findings may lead to the first primate model for AIDS, say the researchers who conducted the study.

"We're very excited," says molecular biologist Susan W. Barnett of Chiron Corp. in Emeryville, Calif. "It's a very powerful model." Barnett worked with a team of scientists led by Jay A. Levy of the University of California, San Francisco.

Levy, Barnett, and their colleagues turned to HIV-2, a type of HIV first discovered in West Africa. They had failed to cause AIDS in baboons with HIV-1. HIV-2 is considered less aggressive than HIV-1, the dominant AIDS-causing virus in the United States (SN: 9/17/94, p.187).

In 1988, the researchers injected a single baboon with a strain of HIV-2 isolated from a West African patient. Within a few weeks, the animal developed antibodies to the virus, a sign of infection. Within 18 months, the baboon's blood showed a decline in CD4 T lymphocytes, the white blood cells whose destruction signals the onset of AIDS in humans.

In January 1992, the team gave four additional baboons the same strain of HIV-2. Like humans infected with this virus, the animals developed swollen lymph nodes and showed persistent evidence of antibodies circulating in the bloodstream.

After 2 years, one of the four baboons went on to develop severe weight loss and AIDS. The animal suffered from a type of pneumonia that often afflicts children with AIDS and from skin tumors that resemble those seen in Kaposi's sarcoma, the bluish-colored growths that often afflict people with AIDS.

Another baboon in that group is progressing toward AIDS. It already has skin tumors and is losing CD4 T lymphocytes, Levy points out.

In January 1993, Levy's group injected three more baboons with a different strain of HIV-2, this one taken from a patient in Gambia. All three show signs of ongoing viral infection. That finding suggests that baboons will prove vulnerable to many different strains of HIV-2, a key requirement if researchers are to use this model to test AIDS vaccines. The researchers describe their results in the Oct. 28 SCIENCE.

The team has since injected three healthy baboons with blood taken from a previously infected animal. By cycling the virus through the baboons' bodies, the researchers hope to create a more vicious HIV-2.

"There's been a real need to find a model [on which we] can test the human virus," Levy says. Researchers had successfully inoculated chimps and monkeys with HIV-1, but those mild infections do not lead to AIDS.

In addition to vaccine research, the team says, the baboon model might help doctors find better therapies for Kaposi's sarcoma and other ailments that plague humans with AIDS.