Kenneth I. Berns, Nicholas Muzyczka

Today AAV is one of the most promising and successful gene therapy vectors. AAV vectors have been successful in the treatment of several monogenic diseases in early clinical trials1. Although work in the past has focused primarily on gene replacement, many investigators are now adapting the vector system to new clinical modalities including RNAi and gene modifying strategies such as Crisper/cas91. Moreover, Glybera2 has been licensed for clinical use in the European Union for treatment of a lysosomal storage disease. To reach this level of success has taken more than thirty years from the initial isolation of an infectious AAV clone and the development of AAV vectors for long term expression3-5. This has included the development of so-called scalable production systems that promise to deliver large quantities of vector for both clinical trials and eventually for patient therapies6. We have been studying AAV for 55 years and developing it as a vector for about 35 years. By now we have a fairly good idea of the dimensions of what would be useful to know to optimally employ AAV as a vector, but there are still many unanswered questions within the system. Like all biological systems, each good experiment raises further questions to answer. We will devote this paper to an overview of those areas in which we can identify information we don't know, and those questions which we haven't yet recognized. Some of these are touched on in the six review articles in this issue of Human Gene Therapy.