To evaluate the recombinant adeno‐associated virus vector encoding interleukin‐1 receptor antagonist (rAAV–IL‐1Ra) complementary DNA for its potential in the treatment and prevention of lipopolysaccharide (LPS)–induced arthritis.

The therapeutic effect of rAAV–IL‐1Ra on arthritis was studied by injecting knees of Sprague‐Dawley rats with LPS and rAAV–IL‐1Ra and then evaluating the severity of arthritis by leukocyte counts in synovial fluid, histologic changes of synovium, and uptake of ⁶⁷Ga citrate in joint tissue. To study the therapeutic effect on recurrent arthritis, we induced recurrent arthritis by a second injection of LPS 80 days after primary LPS and rAAV–IL‐1Ra injections and then evaluated the severity of recurrent arthritis. To study the prevention of arthritis, rAAV–IL‐1Ra was injected into normal joints. After 100 days, LPS was used to induce arthritis, and the severity of arthritis was evaluated.

The production of the rAAV–IL‐1Ra transgene was up‐regulated by LPS‐induced joint inflammation and proved to be efficacious in the therapeutic and preventative protocols. Not only primary but also recurrent arthritis could be suppressed by a single injection of rAAV–IL‐1Ra. We found that the transgene expression of IL‐1Ra could be reactivated by a second challenge with LPS delayed for 80 days after rAAV administration. The therapeutic level of IL‐1Ra protein reached a mean ± SD of 5.8 ± 0.5 ng/ml in synovial fluid. In addition, the rAAV transgene persisted within normal joints for at least 100 days and could still be induced to express, after LPS insult, a high level of IL‐1Ra (mean ± SD 5.2 ± 0.8 ng/ml) that prevented the occurrence of arthritis.

This gene therapy, by combining highly efficient and stable rAAV gene delivery, disease‐regulated gene expression, and the antiinflammatory effect of IL‐1Ra, provides a valuable approach for long‐term protection against, and prevention of, arthritis.