NEW YORK (AP) _ Drugs designed to teach the body to accept transplanted organs have remained effective for up to a year in monkeys that received kidneys, according to researchers.

Scientists hope the experimental treatment will one day free some transplant patients from having to take anti-rejection drugs for the rest of their lives. The standard drugs suppress the immune system and leave patients vulnerable to infections and tumors.

Researchers are planning studies of the experimental treatment in people, said Dr. Allan Kirk of the Naval Medical Research Center in Bethesda, Md.

He and co-authors describe the monkey study in the June issue of the journal Nature Medicine. Two years ago, Kirk and colleagues reported on a similar treatment that staved off rejection for more than nine months in monkeys. The new treatment includes only one of the two substances administered in the prior work.

The goal is to teach the immune system to accept the transplanted tissue rather than attack it. To do that, researchers injected the monkeys with a protein to prevent certain blood cells from delivering a ``danger'' signal to other cells, an initial event in rejection.

The protein is called hu5C8. The researchers gave it to nine monkeys the morning of the kidney transplant, just after the surgery, about once a week for four weeks after that, and finally once a month for five months.

Eight of the nine treated monkeys remain alive and well with no organ rejection. Two have lived about a year so far since the end of treatment, and another more than six months. The ninth monkey died from an unrelated cause.

In a commentary accompanying the article, immune-system expert Polly Matzinger of the National Institutes of Health said a 1996 study had shown the approach works in mice. But transplant researchers largely overlooked that report, she said.

``Well,'' she wrote, ``it is time to pay attention!''