Doctors have used gene therapy to upgrade the immune system of 12 patients suffering from HIV to help shield them from the virus's onslaught.
Researchers at the University of Pennsylvania are adapting patients' own immune systems to help them defend against HIV.
Millions of T-cells were taken out from the patient's blood and grown in the laboratory until the doctors had billions of cells, the BBC reported.
Researchers 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 injected back in, although only around 20 per cent were successfully modified.
When patients were taken off their meds for four weeks, the number of unprotected T-cells still in the body fell dramatically, whereas the modified T-cells appeared protected and could still be found in the blood several months later.
The study has been published in the New England Journal of Medicine.