The immunopathology of rheumatoid arthritis (RA) is associated with the production of inflammatory cytokines (IL-1, TNF-α, IL-6), synovial proliferation, and cartilage invasion. A sustained increase in the amounts of cytokine antagonists obtained through gene therapy should inhibit the process. Targeting of a single molecule, however, is unlikely to be sufficient for the reversal of the complex molecular and cellular events that lead to the progressive destruction of cartilage and bone in RA. Several groups have developed efficient gene transfer of therapeutic molecules in experimental arthritis (IRAP, TNF-R, IL-10, TGF-β) through retrovirus (ex vivo procedure) or intra articular (i.a) or systemic adenoviral delivery (in vivo procedure).
To increase the efficiency of gene transfer, new targets have been identified. They include transduction signal inhibitors (super repressor Iκ Ba), synovial-cell activation cascade (c-Jun, Ras antagonist), and synovial apoptosis (fas ligand, p53 or Rb gene transfer). Suicide gene (HSV tk) may also be administered i.a. and induces a `genetic synovectomy' after IV gancyclovir treatment. Angiogenesis may also be inhibited after gene transfer (antagonist of α Vβ 3 or plasminogen activator [PA], PF4, angiostatin). We will present new data showing a decrease in arthritic severity after adenoviral transfer of PA antagonist. All of these targets may be combined with the cytokine approach.
Progress in the development of safe nonviral gene delivery has been made in recent years. Liposome HVJ is efficient to deliver DNA in chondrocytes and synoviocytes without systemic diffusion. Efficient HSV tk gene transfer has been achieved in the synovium by local injection of naked DNA plasmids. Plasmid injection in the muscle combined with electroporation increases by 1000 the serum concentration of cytokine.
AAV vectors are parvoviruses designed to be gutless and efficient for direct gene transfer in vivo. Interestingly, only a weak immune response against the transgene product is detected in animals following AAV-mediated gene transfer, allowing long-term expression (> 18 months). These vectors are suitable to transfer genes in the synovial tissue. Using the SCID mouse model, we showed the feasibility of gene transfer in human tissue with AAV recombinant vectors.
For gene therapy to be an effective and safe approach for the clinical management of disease, gene expression must be highly regulated. The design of safe vectors to enhance the duration of transgene expression and to co-transfer regulatory genes is an active area of research.