ARTHRITIS & RHEUMATISM Vol. 46, No. 6, June 2002, pp 1661–1670 DOI 10.1002/art.10481 © 2002, American College of Rheumatology C3-Tat/HIV–Regulated Intraarticular Human Interleukin-1 Receptor Antagonist Gene Therapy Results in Efficient Inhibition of Collagen-Induced Arthritis Superior to Cytomegalovirus-Regulated Expression of the Same Transgene A. C. Bakker, 1 F. A. J. van de Loo, 1 L. A. B. Joosten, 1 O. J. Arntz, 1 A. W. Varley, 2 R. S. Munford, 2 and W. B. van den Berg 1 Objective. To achieve disease-inducible expres- sion of recombinant antiinflammatory proteins in order to allow autoregulation of drug dose by natural homeo- static mechanisms. Methods. We compared the inducible 2-component expression system (C3–human immunode- ficiency virus/transactivator of transcription [C3-Tat/ HIV]) with the constitutive cytomegalovirus (CMV) promoter in the polyarticular collagen-induced arthritis (CIA) model in mice. DBA/1 mice were immunized with bovine type II collagen and were given boosters on day 21. On day 22, mice were injected intraarticularly with the adenoviral vectors AdCMVLuc, AdCMVhIL-1Ra, AdC3-Tat/HIV-Luc, or AdC3-Tat/HIV-hIL-1Ra. The in- jected knee joints and hind paws were then scored for signs of arthritis, and knee joint histology was com- pared. Results. The CMV-driven interleukin-1 receptor antagonist (IL-1Ra) expression resulted in a high con- stitutive expression and amelioration of CIA. C3-Tat/ HIV–driven IL-1Ra expression could be detected only on days 24, 29, and 35. Fourteen days after injection of the vectors, CIA was significantly better inhibited by the C3-Tat/HIV–driven IL-1Ra expression compared with the CMV-driven IL-1Ra expression. Moreover, preven- tion of CIA in the knee joints also prevented CIA in the untreated hind paws. Conclusion. Our data demonstrate for the first time the feasibility of an inducible expression system for local production of IL-1Ra for treatment of arthritis in the CIA model. Rheumatoid arthritis (RA), which affects 1% of the world’s population, is a chronic progressive auto- immune disease. Ideally, treatment of RA would parallel the intermittent course of the disease and be limited to the affected joints. Constant high levels of antiinflam- matory mediators could be undesirable; they might increase the risk of infection (1,2) or have other unde- sirable effects (2), and the homeostatic balance might adapt to the constant high concentration of antiinflam- matory protein so as to reduce its therapeutic efficacy (tachyphylaxis). Gene therapy has the potential for disease-regulated expression of a recombinant protein drug to meet these variable physiologic demands. To our knowledge, this potential has not yet been developed for application in inflammatory diseases. Varley and Mun- ford (3) have developed a 2-component expression system that responds to inflammatory stimuli in vivo. We have tested this system for its efficiency in achieving disease-inducible expression of a therapeutic protein drug in arthritis. In this 2-component expression system, the com- plement factor 3 (C3) promoter regulates production of the human immunodeficiency virus (HIV) transactivator of transcription (Tat; only the first exon of the Tat gene is included in the vector). The Tat protein then stimu- lates expression of the desired transgene, which is reg- Supported by the Dutch Rheumatism Association (grant 941), the Dutch Organization for Scientific Research (project 902-27-218), and the National Institute for Allergy and Infectious Diseases (grant AI-38596). 1 A. C. Bakker, MSc, F. A. J. van de Loo, PhD, L. A. B. Joosten, PhD, O. J. Arntz, W. B. van den Berg, PhD: University Medical Center Nijmegen, Nijmegen, The Netherlands; 2 A. W. Varley, PhD, R. S. Munford, PhD: University of Texas Southwestern Medical Center at Dallas. Address correspondence and reprint requests to F. A. J. van de Loo, PhD, Department of Rheumatology, University Medical Center Nijmegen, Geert Grooteplein 26-28, PO Box 9101, 6500 HB Nijmegen, The Netherlands. E-mail: A.vandeloo@reuma.azn.nl. Submitted for publication January 24, 2001; accepted in revised form January 31, 2002. 1661