To test the hypothesis that in vivo transgene expression mediated by single intra-articular injection of adeno-associated virus serotype 2 (AAV2) persists within intra-articular tissues 1 year post-injection and can be externally controlled using an AAV2-based tetracycline-inducible gene regulation system containing the tetracycline response element (TRE) promoter.
Sprague Dawley rats received intra-articular injections of AAV2-cytomegalovirus (CMV)-enhanced green fluorescent protein (GFP) and AAV2-CMV-luciferase (Luc) into their right and left knees, respectively. Luciferase expression was evaluated over 1 year using bioluminescence imaging. After sacrifice, tissues were analyzed for GFP+ cells by fluorescent microscopy. To study external control of intra-articular AAV-transgene expression, another set of rats was co-injected with AAV2-TRE-Luc and AAV2-CMV-reverse-tetracycline-controlled transactivator (rtTA) into the right knees, and AAV2-CMV-Luc and AAV2-CMV-rtTA into the left knees. Rats received oral doxycycline (Dox), an analog of tetracycline, for 7 days. Luciferase expression was assessed by bioluminescence imaging.
Luciferase expression was localized to the injected joint and persisted throughout the 1-year study period. Abundant GFP+ cells were observed within intra-articular soft tissues. Transgene expression in AAV2-TRE-Luc injected joints was upregulated by oral administration of Dox, and downregulated following its removal, at 14 days and 13 months post-AAV injection.
This longitudinal in vivo study shows that sustained and stable AAV-mediated intra-articular transgene expression can be achieved through a single intra-articular injection and can be controlled using a tetracycline-controlled inducible AAV system in a normal rat knee model. Highly regulatable long-term intra-articular transgene expression is of potential clinical utility for development of treatment strategies for chronic intra-articular disease processes such as inflammatory and degenerative arthritis.