Rwandan patients show unusual HIV. (Biomedicine).

Routine testing of people in Rwanda who have had human immunodeficiency virus (HIV) for many years without getting AIDS indicates that many are infected with a virus harboring a rare mutation.

Researchers tested the blood of 16 people who have had HIV for at least 12 years but haven't taken medicine for it and haven't developed AIDS. The concentrations of T cells in the patients' blood, which gauges viral destruction of these immune cells, didn't fall drastically during the years of testing.

Now, close inspection of the virus shows that seven of the people have a form of HIV with rare mutations in the gene encoding a glycoprotein called gp120 in the virus' outer surface.

"We found this quite surprising," says Francois Roman, a physician and researcher at the Center for Public Health Research in Luxembourg. The mutations lie in the part of the gene that encodes the so-called V3 loop of gp120. The researchers still don't know the importance, if any, of the structural differences that the mutation leads to in the glycoprotein. They might weaken the virus and enable the immune system to control it, Roman speculates. The immune system itself may even modify the gene encoding gp120, he says.

The patients tested in the study all live near the capital city Kigali in this central African country. --N.S.