In the biggest clinical trial to date, a group of scientists have found gene therapy to be a safe and beneficial option for HIV patients.
Ronald Mitsuyasu, of the University of California, Los Angeles, headed the trial for testing gene therapy against HIV.
"To our knowledge, our study was the first randomised, controlled study performed with gene therapy in HIV," New Scientist magazine quoted him as saying.
For the trial, patients temporarily stopped their usual regime of anti-retroviral treatment (ART), in order to see whether gene therapy would prove effective or not.
Half the 74 patients received the treatment, and half a placebo.
Despite the fact that gene therapy didn't work as well as ART, virus concentrations in blood were on average about a third lower in recipients of the treatment as compared to controls who received a placebo.
Besides, recipients had higher numbers of CD4+ white blood cells, the type that is attacked by the virus.
"It provides proof of concept and early indications are that, with more refinement, this approach may be a viable one for controlling HIV directly in people without the need for continuous HIV medication," said Mitsuyasu.
He added: "From a scientific standpoint, it represents a new and potentially important and long-lasting way of controlling diseases."
The researchers took blood samples from patients and isolated CD34+ stem cells, which can mature into many types of white blood cell, including the CD4+ cells attacked by HIV.
After that, they used a harmless virus to load the stem cells with an extra gene that makes a ribozyme - a pair of molecular "scissors" targeted at the virus.
It was found that the patients with more altered cells had comparatively correspondingly lower levels of virus and marginally more CD4+ cells.
But, there was a decrease in the number of altered cells towards the end of the 100-day "break" from ART treatment, which was quite opposite of what was expected.
"Work is ongoing to develop better and more effective ways of performing gene insertion and allowing these genes to be better expressed in patients for longer periods of time," said Mitsuyasu.
The altered stem cells might have worked better if existing stem cells from the bone marrow had all been destroyed prior to the therapy, as in earlier mouse experiments, allowing the altered cells to take over in the empty bone marrow.