Doctors have used gene therapy to upgrade the immune system of 12 patients with HIV to help shield them from the virus's onslaught. It raises the prospect of patients no longer needing to take daily medication to control their infection.
The patients' white blood cells were taken out of the body, given HIV resistance and then injected back in. The small study, published in the New England Journal of Medicine, suggested the technique was safe.
Some people are born with a very rare mutation that protects them from HIV. It changes the structure of their T-cells, a part of the immune system, so that the virus cannot get inside and multiply.
The first person to recover from HIV, Timothy Ray Brown, had his immune system wiped out during leukaemia treatment and then replaced with a bone marrow transplant from someone with the mutation.
Now researchers at the University of Pennsylvania are adapting patients' own immune systems to give them that same defence. Millions of T-cells were taken from the blood and grown in the laboratory until the doctors had billions of cells to play with.
The team then edited the DNA inside the T-cells to give them the shielding mutation - known as CCR5-delta-32. About 10 billion cells were then infused back in, although only around 20% were successfully modified.
When patients were taken off their medication for four weeks, the number of unprotected T-cells still in the body fell dramatically, whereas the modified T-cells seemed to be protected and could still be found in the blood several months later.