BOSTON (AP) _ An exquisitely targeted drug has been found to kill renegade immune cells and clear up stubborn psoriasis, suggesting a promising new approach to other diseases that occur when the body's defenses run amok.
Those diseases include arthritis, multiple sclerosis and inflammatory bowel disease.
``I think it's really exciting,'' said Cornell University dermatologist Dr. Richard D. Granstein. He said it is one of several psoriasis drugs in testing that are ``opening up a whole new approach to treatment'' of autoimmune diseases.
The research was paid for in part by the drug's manufacturer, Biogen, which expects to seek federal approval for the medication later this year.
Findings on the new drug, a fusion of two proteins known as alefacept, were published Thursday in The New England Journal of Medicine.
Later testing, which is still unpublished, reinforces evidence that the drug is generally safe and effective for some patients, said New York University dermatologist Dr. Mark Lebwohl, who took part in those experiments.
About 2 percent of people suffer from red patches, silvery scales or other symptoms of psoriasis. It is usually mild but persists for a long time. In severe cases, it can cover large expanses of skin and lead to a form of arthritis.
There is no outright cure but there are many treatments, including ointments, sunlight or ultraviolet treatments, and stronger drugs that can damage the liver or kidneys.
The disease is suspected to stem from an immune reaction to an unknown irritant made by the body. Immune fighters known as memory effector T cells marshal an attack and prompt inflammation of skin tissue.
The new drug targets the overactive T cells while leaving the rest of the immune system largely intact. Existing treatments launch more broad-based attacks on immune cells, which can weaken the body's defenses against disease and cause other side effects.
``We're just going after the specific cells that we're most interested in stopping,'' said Dr. Charles Ellis, a University of Michigan dermatologist who co-wrote the New England Journal report on the drug.
His team tested it on 229 psoriasis patients, at 22 health centers, who had failed to respond to standard drugs. Those given the biggest injections improved an average of about 50 percent in their symptoms. The psoriasis vanished or nearly did so in a quarter of the patients.
People did not need more treatment for an average of 10 months, a longer time than with other therapies.
The researchers found no serious side effects.
The later tests on more than 1,000 patients arrived at similar findings, Lebwohl said. Almost three quarters of the patients improved by 50 percent or more, and many were left with little or no psoriasis, he said.
He predicted that the drug will replace other treatment for some patients.