Over the last three decades, interest in the field of gene therapy seems to have fluctuated between hot and cold. Encouraging pre-clinical and clinical data has demonstrated the potential of genetic therapies and yet setbacks in clinical trials have cast doubts in some minds over the clinical future of gene therapy [1-3]. In the last two years, a number of studies have demonstrated therapeutic benefits in clinical trials aimed towards specific monogenetic disorders [4-6], and this has brought renewed optimism to the field. [...]