Background Achieving biologically effective yet safe levels of recombinant anti-inflammatory proteins by gene therapy may require three regulatory features: 1) a basal level that is sufficiently low to avoid or minimise chronic immunosuppression 2) transcriptional regulation over a wide dynamic range, and 3) induced expression levels that are sufficiently high to achieve the desired biological effects. The C3-Tat/HIV promoter construct seems to have these properties.¹ In this two-component expression system the complement factor 3 (C3) promoter regulates production of the HIV transactivator of transcription, and the Tat protein then stimulates expression of the desired transgene, which is regulated by the HIV-LTR promoter. Both C3 and HIV LTR promoters are inducible by proinflammatory cytokines.

Objectives To achieve disease-inducible expression of recombinant anti-inflammatory proteins in order to allow autoregulation of drug dose by natural homeostatic mechanisms.

Methods We compared a disease-inducible, two component expression system (C3-Tat/HIV) with the constitutive immediate early cytomegalovirus (ieCMV) promoter in the polyarticular Collagen-Induced Arthritis (CIA) model in mice. DBA/I mice were immunised with bovine type II collagen and boostered on day 22. On day 22, mice without any clinical signs of arthritis were selected and adenoviral vectors (Ad. CMV-Luc, Ad. CMV-IL-1Ra, or Ad. C3-Tat/HIV-IL-1Ra) that contained luciferase or the human IL-1Ra gene under control of one of the two promoters were used to transfect the synovial lining of both knees. The injected knee joints and ipsilateral paws were then scored for signs of arthritis and at the end histology was taken.

Results Inducible promoter-driven IL-1Ra expression resulted in significantly improved inhibition of CIA than did CMV-driven IL-1Ra production. Moreover, overexpression of IL-1Ra in the knee joints also prevented CIA in the ipsilateral paws.

Conclusion Our data (1) demonstrate the feasibility of an inducible expression system for producing a recombinant transgene for treatment of arthritis and (2) show that this system is more effective than strong, constitutive transgene expression for preventing collagen-induced arthritis in mice.

Reference

1. Varley AW, Geiszler SM, Gaynor RB, Munford RS. A two-component expression system that responds to inflammatory stimuli in vivoin vivo. Nat Biotechnol. 1997;15(10):1002–6