A T cell (top) interacting with a dendritic cell. Scientists in the U.S. announced Monday that immune T cells stop working in most HIV patients because they are "turned off" by HI virus. more photos>>

    A healthy body generates something called T-cells or "killer cells," which attack viruses, they said. But what they didn't know, until now, is why those killer cells stopped working in most HIV patients.

    "One hypothesis has been that they become inactivated. One hypothesis is that that they became destroyed," said Dr. Bruce Walker, head researcher at Massachusetts General Hospital, Boston.

    "What this study shows us is actually that those cells are there, that they fully function; it's just that they have been turned off."

    The cells are turned off by HIV, which disarms them by flicking off a molecular switch in the cells. But in the laboratory, researchers were able to block that switch and restore T-cell function.

    The findings raise the possibility that one day, doctors could switch a chronically ill patient's immune system back "on" so that it could resume its fight against HIV, cancer or even Hepatitis C.

    But there's one big concern. Manipulating the immune system could send it into overdrive, triggering an auto-immune disease, attacking healthy parts of the body.

    "We really don't know what happens when we try this with humans," Walker said. "But it opens a new pathway for us to pursue. But we really need to proceed with caution." Enditem

    (Agencies)