A 42-year-old HIV patient with leukemia continues to show no signs of HIV in his blood, two years after a stem cell transplant from a donor with a gene mutation that confers natural resistance to the virus that causes AIDS.

The stunning findings were published Wednesday in The New England Journal of Medicine, according to CNN, but doctors caution that the stem cell treatment is too dangerous to be of routine use to most people infected with HIV.

In the study, reported CNN, “the team deliberately chose a compatible donor who has a naturally occurring gene mutation that confers resistance to HIV. The mutation cripples a receptor known as CCR5, which is normally found on the surface of T cells, the type of immune system cells attacked by HIV.

“The mutation is known as CCR5 delta32 and is found in 1 percent to 3 percent of white populations of European descent.

“HIV uses the CCR5 as a co-receptor (in addition to CD4 receptors) to latch on to and ultimately destroy immune system cells. Since the virus can't gain a foothold on cells that lack CCR5, people who have the mutation have natural protection. (There are other, less common HIV strains that use different co-receptors.)

“People who inherit one copy of CCR5 delta32 take longer to get sick or develop AIDS if infected with HIV. People with two copies (one from each parent) may not become infected at all. The stem cell donor had two copies.”

Doctors say that while the risky stem cell transplant option should not be routinely exercised, the findings point the way toward development of potentially safer CCR5-disabling gene therapies or treatments that can be injected into the body.