Two teams of scientists with strong ties to the Bay Area are racing to develop a stem cell therapy that would provide a practical cure for people living with HIV infection, leaving them with an immune system capable of keeping them healthy without daily medication even as some virus remains circulating in their bloodstream.

Both groups of researchers are trying to capitalize on the DNA of so-called elite controllers - people who are naturally resistant to HIV due to a genetic mutation that prevents the virus from latching on to their immune cells. It was an elite controller who donated bone marrow to Timothy Brown, the "Berlin patient," who was the first in the world to be cured of HIV. Doctors attribute Brown's rebuilt HIV-resistant immune system to the genetic mutation in the bone marrow.

Bone marrow transplants are not an effective cure for HIV for the general population because they're risky and expensive. But stem cells, drawn from a patient's own bone marrow and altered to be HIV-resistant, may be able to do the job using the same premise.

"If you could make a person's immune system mutated in a way that HIV could not infect it, then you may be able to cure the HIV," said Dr. John Zaia, a virologist with the Beckman Research Institute near Los Angeles, who's working with Sangamo Biosciences in Richmond on a technique to engineer and transplant stem cells.

"That's the premise anyway," he said. "And it's based on that one case in the Berlin, that one transplant."

The teams at the forefront of stem cell HIV therapy are led by Sangamo and Calimmune, a San Diego company that is testing its treatment in patients in Los Angeles and San Francisco.

Calimmune was the first to start human clinical trials, in July 2013, and last month reported that the first group of patients was doing well enough that they were ready to begin treating a second group. Sangamo expects to start clinical trials as early as this fall.

Both groups are being funded in part by the California Institute for Regenerative Medicine, the state's stem cell agency.

The research is based on the discovery in the mid-1990s of a specific genetic mutation that blocks a protein called CCR5. The protein is found on the surface of some cells where it acts as a receptor, allowing HIV to attach and ultimately fuse with the cell. Without CCR5, it's much more difficult, although not impossible, for the virus to infect a cell.

In elite controllers, the CCR5 receptor is mutated in such a way that HIV cannot latch onto it. Scientists believe that only about 1 percent of people worldwide have the CCR5 genetic mutation.

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Stem cell therapy could lead to HIV cure - SFGate