Gene therapy that could immunize people against the most common type of HIV is ready to be tested on humans.

Recruiting for the trial began Tuesday, and the first people to receive the experimental treatment will be HIV patients with drug-resistance problems.

"We do have good treatments for HIV. That has been one of the most successful stories of the last 20 years in medicine," said Pablo Tebas, an infectious disease expert at the University of Pennsylvania.

"However, over time, if the medications are not taken properly, individuals develop resistance to the HIV treatments, so they tend to have more limited therapeutic options."

Since the discovery that a small portion of people who are exposed to HIV do not get infected, scientists have been working to discover the secret to those people's resistance and how to make others resistant as well.

It turns out that most people have a gene called CCR5, which makes them vulnerable to HIV infections. The naturally resistant people have mutant CCR5 genes that inhibit HIV.

Previously, scientists found that by cutting the CCR5 gene out of white blood cells involved in the immune response known as T-cells, they could protect a tube full of human cells from the virus. The gene editing technique relies on proteins called zinc finger nucleases that can delete any gene from a living cell.

In theory, zinc finger nucleases could give that immunity to anyone.

The procedure is simple: Take some healthy T-cells out of an HIV patient, clip out their CCR5 genes, grow more of these clipped T-cells in a dish, and then put them back in the patient.

"In this first study we will re-infuse approximately 10 billion of these cells back into the participants, and we will see if it is safe and if those cells inhibit HIV replication in vivo," said Tebas. "We know they do in the test tube."

Photo: adamjtaylor/Flickr

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