Timothy Brown may be the only person cured of AIDS. Brown, who lives in San Francisco, in 2007 received a stem-cell transplant in Berlin that transferred genetic material to him from one of the up to 2 percent of humans with a natural immunity to the disease. He has been off treatment since then, and no traces of the AIDS virus have been found in his body, says his hematologist, Gero Hütter, now with the German Red Cross in Mannheim. His case has encouraged tiny Sangamo BioSciences (SGMO) to develop a new form of gene therapy that could offer others the same result.

While there's no guarantee Brown, 44, will remain virus-free, his case has spurred scientists to try to duplicate the result without a dangerous stem-cell transplant. Sangamo, a Richmond (Calif.) biotechnology company, will report data late this month on a gene therapy that's likely to be less risky. If the results are a success, and the method is eventually approved, it may generate $750 million a year in U.S. sales, says Liana Moussatos, a biotech analyst at Wedbush Securities. "It's high-risk, but definitely high-reward," she says. "If this is a cure for HIV that prevents or reduces the lifelong need for drugs, that's a huge accomplishment."

Sangamo's stock has more than doubled since July 6, when the company, with no products on the market, reported success of its gene therapy approach in mice in the journal Nature Biotechnology. One reason for the enthusiasm: The therapy, using a new technology that acts like biological scissors to cut into genes at precise points, may also treat other diseases, such as hemophilia, Parkinson's, and neuropathy, the nerve damage caused by diabetes, says Sangamo Chief Executive Officer Edward Lanphier. An approved treatment for neuropathy alone, which has no cure, may generate $6 billion a year, Moussatos says.