Inflammation repsonsive delivery of Anti-Inflammatory Cytokines by Gene Transfer
Rheumatoid arthritis is characterized by an overabundance of pro-inflammatory cytokines, and inadequate anti-inflammatory cytokines. Gene therapy has been proposed as a means of correcting the imbalance, by the delivery of anti-inflammatory molecules to arthritic joints. One challenge in administering gene therapy is that articular inflammation waxes and wanes, therefore necessitating the levels of a therapeutic protein to be dynamic. In this experiment Miagkov, et al (J. Clin. Invest. 109:1223-1229, 2002) explored the feasibility of physiologically responsive gene therapy (PRGT) for treatment of recurrent arthritis in which severity of inflammation controls production of the gene product.
Methods: An adenoviral vector carrying the cDNA of an anti-inflammatory cytokine, human IL-10 (hIL-10), regulated by an inflammation-inducible promoter was developed. A two-component inflammation-inducible expression system was used. In the construct, the promoter region of the complement factor 3 (C3) acute-phase protein regulated the expression of the HIV Tat protein. In the same construct, the HIV promoter region was positioned upstream of the human IL-10 (hIL-10) gene. When expressed the Tat protein transactivated the expression of hIL-10 by binding to the HIV promoter. Both the HIV and C3 promoters are inducible by cytokines, allowing for both the trans and cis activation of the system.
Acute arthritis was induced in female Lewis rats by intraarticular injection of streptococcal cell wall (SCW) fragments. The adenoviral construct containing the inducible IL-10 gene was injected intraarticularly after resolution of the acute arthritis and two days before recurrent SCW arthritis was induced. Synovial fibroblasts were also transfected in vitro with the gene construct.
Results: In vitro, transfected synovial fibroblasts exhibited a low level of basal activity. When exposed to various inflammatory stimuli, including TNF-alpha, IL-1 beta, IL-6 and LPS, IL-10 production (measured as luciferase activity) increased four to five orders of magnitude. When introduced to rats with SCW-induced arthritis, hIL-10 activity increased commensurately with the recurrence of arthritis. This response prevented the influx of inflammatory cells to the synovium and the resultant swelling of the joint.
Conclusion: In sum, hIL-10 levels can be regulated in response to waxing and waning arthritis. In a broader sense, this study shows that physiologically regulated gene therapy approach is a viable therapeutic approach. It should be possible to regulate the production of many different proteins in this way employing a variety of promoter systems. Safer vectors will need to be identified, however, since adenovirus can itself induce arthritis.
Editorial Comment: Controlled delivery of therapeutic proteins, in response to need, is desirable for some clinical situations in which disease activity waxes and wanes. Although the investigators argue that rheumatoid arthritis is such a condition, this is debatable since chronic (constant) inflammation is more typically observed. Nonetheless, the concept introduced here is valid and this vector appears to be more sensitive to inflammatory cytokines than previously reported vectors with inflammationresponsive, inducible genes. In a condition such as RA in which many joints are inflamed, intraarticular introduction of the vector is a less feasible approach than systemic gene therapy.
