Some rare patients infected for years with the AIDS virus without becoming ill make white blood cells of a type missing from most patients of the immune system disorder, researchers say.
An analysis of blood from a Boston man infected with HIV for 18 years but still healthy showed that he was protected by a large number of immune system cells, called helper T-cells, that specifically attack the AIDS virus.
Most patients with long-term HIV infection have a low supply of helper T-cells targeting the AIDS virus, which leaves the immune system defenseless against the virus, Dr. Bruce Walker of the Massachusetts General Hospital said. He is senior author of a study being published today in the journal Science.
“Our work provides an explanation of why a very small group of people have been able to avoid getting sick from this virus even though they are infected,” said Walker.
Helper T-cells direct the body’s immune system. A variety of the cells exist, and each type is primed to attack a specific virus or other invader. As these cells detect the presence of a target virus, they reproduce by the billions, flooding the bloodstream with defenders.
But HIV, the AIDS virus, has broken down this defense. For reasons not understood, helper T-cells specific for HIV often are at low levels in or absent from patients infected with the virus.
Experiments at Massachusetts General confirmed that high levels of HIV-specific T-cells may be essential for the body to hold the AIDS virus in check.
Walker said laboratory tests of blood from HIV patients found that those with the strongest T-cell response to the HIV antigen had the lowest amount of virus in their bloodstream, but those with weak T-cell responses had high virus loads.
The discovery suggested the body might be able to control HIV if helper T-cells that target the virus could somehow be protected.
To test this idea, researchers used powerful anti-viral drugs to treat patients recently infected with HIV. Walker said the drugs caused the virus load to drop quickly, and the patients’ immune systems then started producing T-cells that specifically attacked HIV.
Walker said the HIV-specific T-cells were not produced in the bodies of patients who had been infected with HIV for more than six months.