Rheumatoid arthritis (RA) is a multifactorial polygenic disease that is both common (about 0.5% among adults) and severe. It is a systemic inflammatory and autoimmune disease where clinical manifestations predominate in the joints. Although the trigger is unknown, the cascade of immunological and inflammatory responses has been documented in detail [1]. These responses lead to inflammatory synovitis with angiogenesis and infiltration by mononuclear and polynuclear cells within the joint. Synovial inflammation also heralds irreversible bone and joint destruction. Studies highlighting the key role of proinflammatory cytokines in RA have allowed the development of treatment targeting those
molecules [2]. IL-1b and TNF inhibitors are the first step toward targeted therapies in RA. However, despite the high efficiency of these molecules, primary or acquired unresponsiveness are not uncommon, thus highlighting the necessity to elaborate alternate therapeutic means.
In polygenic diseases such as RA, gene therapy can be used, to transfer a DNA fragment that encodes an anti-inflammatory medi- ator. Advantages of this strategy over direct administration of the protein include the possibility to obtain long term protein expres- sion in vivo [3,4] and to control the kinetics and spatial distribution of protein delivery. In this context, we previously established the feasibility of electrotransfer (ET) of plasmids in collagen-induced arthritis (CIA), a model of RA, using IL-10 gene [5] or type I soluble receptor for TNF (sTNFRI) gene [6,7].
Among anti-inflammatory candidates, IL-35 belongs to the IL-12 family of heterodimeric cytokines and is composed by two subunits, IL-12a and Epstein–Barr virus induced gene 3 (Ebi3). It was recently identified as an additional anti-inflammatory and immunosuppressive cytokine [8]. There is still relatively limited knowledge of this molecule which has been shown to induce the differentiation of CD4+ effector T cells into regulatory T cell