A PIONEERING treatment to thwart HIV by genetically altering blood cells so the virus cannot invade them has shown promisein the first nine people to receive it.

The treatment involves taking the white blood cells most prone to infection by HIV, called CD4+ cells, from someone with HIV. These are then altered in the lab to sabotage a gene called CCR5, before being returned to the patient. Because CCR5makes the molecular “door-handle” by which HIV enters cells, treated cells become impossible for the virus to infect. “This is the first example of genetic editing to introduce a disease-resistant gene in patients,” says lead investigator Carl June at the University of Pennsylvania School of Medicine.

Preliminary results presented this week at a virus conference in Boston reveal that a year after the treatment, the altered cells had increased in number. In some patients, the cells had colonised areas of the gut and rectum mucosal linings where HIV multiplies, and where native CD4+ cells are usually depleted.