1. ¹Rheumatology Research and Advanced Therapeutic, University Medical Center Nijmegen, Nijmegen, The Netherlands
2. ²Molecular Host Defense Lab, Division of Infectious Diseases, Department of Internal Medicine, University of Texas Southwestern Medical Center at Dallas, Texas, USA

Correspondence: Dr FAJ van de Loo, Rheumatology Research and Advanced Therapeutics, University Medical Center Nijmegen, Nijmegen Center for Molecular Life Sciences, Geert Grooteplein 26-28, 6500 HB Nijmegen, The Netherlands

Received 28 January 2003; Accepted 19 September 2003; Published online 19 February 2004.

Abstract

To achieve a disease-regulated transgene expression for physiologically responsive gene therapy of arthritis, a hybrid promoter was constructed. The human IL-1 enhancer region (-3690 to -2720) upstream of the human IL-6 promoter region (-163 to +12) was essential in mounting a robust response in HIG-82 synovial fibroblasts and in RAW 264,7 macrophages. A replication-deficient adenovirus was engineered with luciferase (Luc) controlled by the IL-1/IL-6 promoter (Ad5.IL-1/IL-6-Luc). LPS caused a 23- and 4.6-fold induction of Luc. activity in RAW cells infected with Ad5.IL-1/IL-6-Luc or the conventional Ad5.CMV-Luc construct, respectively. Next, adenoviruses (10⁶ ffu) were injected into the knees of C57Bl/6 mice. An intra-articular injection of zymosan, 3 days after Ad5.IL-1/IL-6-Luc, increased Luc. activity by 39-fold but had no effect in the Ad5.CMV-Luc joints. The constitutive CMV promoter was rapidly silenced and could not be reactivated in vivo. In contrast, the IL-1/IL-6 promoter could be reactivated by Streptococcal cell wall (SCW)-induced arthritis up to 21 days after infection. Next the IL-1/IL-6 promoter was compared to the C3-Tat/HIV-LTR two-component system in wild-type, IL-6^-/- and IL-1^-/- gene knockout mice. Both systems responded well to LPS-, zymosan- and SCW-induced arthritis. However, the basal activity of the IL-1/IL-6 promoter was lower and IL-6 independent. This study showed that the IL-1/IL-6 promoter is feasible to achieve disease-regulated transgene expression for treatment of arthritis.