Role of gene therapy in tissue engineering procedures in rheumatology: the use of animal models.

Tissue engineering is not only the application of cells and scaffolds to generate a new tissue but should also bring into play biological principles to guide cellular behavior. A way to modify cellular behavior is genetic modification of the cells used for tissue engineering (gene therapy). In the field of rheumatic diseases, cellular modification by overexpressing anabolic factors, such as insulin-like growth factor-I or transforming growth factor beta, or inhibitors of catabolic cytokines or proteolytic enzymes can protect tissues form further destruction and stimulate tissue repair. To test the effect of transgenes on tissue engineering adequate test systems have to be available. Initial testing can be done in simple in vitro systems. However, animal models are unavoidable to study the interaction between the environment and tissue engineering. Optimal models to study gene therapy in combination with tissue engineering in the field of rheumatology are not available at this moment. Arthritis models are mainly developed in small animals while high-quality tissue engineering experiments ask for a large animal model. Development of animal models that can be used for tissue engineering experiments and mimic end stage arthritic diseases is needed.