An ex vivo human model system to evaluate specificity of replicating and non-replicating gene therapy agents

Background Inefficiency, aspecificity and toxicity of gene transfer vectors hamper gene therapy from showing its full potential. On this basis significant research currently focuses on developing vectors with improved infection and/or expression profiles. Screening assays with validity to the clinical context to determine improved characteristics of such agents are not readily available since this requires a close relationship to the human situation. We present a clinically relevant tissue slice technology to preclinically test improved vector characteristics. Methods Slices were prepared from rat, mouse and human liver samples and from tumor tissue. Specificity of gene expression and replication was determined by infecting target and non‐target tissue slices with transcriptionally retargeted adenoviruses and oncolytic viruses. Results Using rat liver slices, we demonstrate efficient knob‐mediated adenoviral infectivity. A favorable tumor‐on/liver‐off profile, resembling in vitro and mouse in vivo data, was shown for a tumor‐specific transcriptionally retargeted adenovirus by infecting slices prepared from tumor or liver tissue. Similar liver‐off data were found for mouse, rat and human samples (over 3‐log lower activity of the tumor‐specific promoter compared to cytomegalovirus (CMV)). More importantly, we show that this technology when applied to human livers is a powerful tool to determine aspecific replication of oncolytic viruses in liver tissue. A 2‐ to 6‐log reduction in viral replication was observed for a tumor‐specific oncolytic virus compared to the wild‐type adenovirus. Conclusions The precision‐cut tissue slice technology is a powerful method to test specificity and efficiency of gene transfer as well as of viral replication using human tissue. Copyright © 2005 John Wiley & Sons, Ltd.