Chronic inflammation and tissue breakdown are the major pathophysiological lesions in many connective tissue diseases. Treatment of these conditions remains unsatisfactory, partly because existing drugs are intrinsically inadequate and partly because these drugs cannot be specifically targeted to sites of disease. Furthermore, present therapeutic strategies fail to address the chronicity of these diseases. We propose to use gene therapy as a radical new approach to treating such conditions. In this approach, a gene, or gene(s) coding for protein(s) with anti-inflammatory or anti-erosive properties are stably introduced into resident, mesenchymal, connective tissue cells at the disease site. This procedure permits selective, local synthesis of the therapeutic agent(s) just at sites of disease activity. In this way, systemic ef- fects are minimized. Furthermore, stable incorporation and expression of the transduced genes ensures prolonged synthesis of their products, as is necessary for the treatment of chronic diseases. These ideas will be tested experimentally in a step-wise fashion with the rabbit knee as a model system. In short-term experiments, we have successfully transplanted lac Z+, neo+ synovial fibroblasts into the knee joint of recipient rabbits, where they survive for at least two weeks, and possibly as long as three months. During the present proposal, we will further refine this ex vivo procedure, attempting to achieve per- manent gene transfer to the synovium for the lifetime of the animal. As an alternative, in vivo approach, the possibility of direct, in situ transfection of synovial cells will be evaluated with emphasis on adenoassociated virus, herpes virus and liposomes as vectors. Having thus established a system of gene delivery to synovial fibroblasts, this delivery method will be used to antagonize the actions of interleukin-1 (IL-1), a cytokine which produces inflammation and tissue destruction. To do this, a gene coding for an IL-1 receptor antagonist (IRAP) will be transduced into the synovial cells lining the knee joint. The in situ production of IRAP will be confirmed, steps taken to maximize its in vivo expression. The ability of endogenously synthesized IRAP to block the actions of intraarticularly administered IL-1 will be tested. Finally, the therapeutic effect of transducing IRAP genes into synovium will be tested in an experimental model of articular inflammation and tissue destruction.