Via EurekAlert!: "Originally conceived as a means of treating genetic diseases, such as cystic fibrosis and hemophilia, gene therapy involves implanting a normal gene to compensate for a defective gene in the patient. ... This study helps extend gene therapy research to nongenetic, nonlethal diseases. Rheumatoid arthritis [RA] is an extremely painful condition affecting multiple joints throughout the body. Arthritis is a good target for this treatment because the joint is a closed space into which we can inject genes ... Evans has spent many years studying the molecules responsible for the breakdown of cartilage in patients with arthritis, identifying interleukin-1 as a good target. But, he adds, once he had this answer, another question was not far behind: How could he effectively reach the joints to block the actions of this protein? Gene therapy provided the answer. By implanting a gene in the affected joint, he was able to stimulate production of a human interleukin-1 receptor antagonist protein, which serves to block actions of the interleukin-1 protein. ... The idea is that by remaining in place, the new gene can continuously block the action of the interleukin-1 within the joints. In essence, the gene becomes its own little factory, continuously working to alleviate pain and swelling."

Link: http://www.eurekalert.org/pub_releases/2009-01/bidm-gtd012609.php