Suspended Gene Therapy Test Had Drawn Early Questions

They acknowledged that some animals had shown improvement in joints on the opposite side of the body from those injected -- an observation that had raised reviewers' concerns that the viruses might be spreading throughout the body, with possible ill effects in the long run. But Carter said that phenomenon has been seen with many kinds of arthritis treatments and remains unexplained.

Most important, both said, tests on animals -- and more recently on some patients -- have all failed to find evidence that the viruses, which produce a protein that can block the arthritis-related inflammation, escape from the joint where they are injected.

Mark A. Kay, a Stanford University professor who has led gene therapy trials that, like the arthritis study, used "adeno-associated viruses," said he was surprised by the death, given the virus's safety record.

In the one instance of trouble in his studies, he said, a patient's immune system attacked his own liver cells after those cells became infected with the virus, causing a "mild and self-limited" decline in liver function.

"I don't think people should panic," Kay said. "It's devastating, and my heart goes out to the family. But people have to sit back and see what happened before jumping to conclusions."

Theodore Friedmann, director of the gene therapy program at the University of California at San Diego School of Medicine, chaired the committee that reviewed the initial 2003 arthritis proposal. He said he does not recall the meeting, but he said the field, despite its occasional setbacks, needs to get over its long-standing "hangdog attitude."

"It's a difficult technology. It's early. It's immature still. But it is attacking some very nasty diseases," Friedmann said, "and in some cases, it is having a benefit."

On a day when all stocks dropped sharply, shares of Targeted Genetics fell 42 cents yesterday to $1.65 in Nasdaq Stock Market composite trading, the lowest price since the stock was first sold to the public in May 1994.