Washington, D.C., resident Bob Hoff has been HIV positive for more than 25 years, but has no detectable viral load and has never had to take medication. Over the years he has seen many friends die of AIDS, but his disease has never progressed.

He is now part of several studies looking at these HIV "elite controllers" for immune clues that could help lead to an HIV vaccine, part of an area of AIDS research we investigated as part of our series this week on Peru.

Source:PBS