Recombinant adeno-associated viral vectors (rAAV) have now been used in several 
clinical trials to treat a variety of diseases, and are currently the preferred 
choice of many investigators in the field, due to both their low pathogenicity 
and immunogenicity compared with other viral vectors, as well as localized 
long-term gene expression, despite their limitations of DNA size packaging and 
speed of expression. Recently, a number of advances have led to new generations 
of rAAV vectors, with improved features. This review addresses the various 
strategies employed to such effect, namely exploring distinct serotype tropisms, 
the production of mosaic and chimeric capsids, the selection of vectors through 
directed evolution, the development of self-complementary vectors, the use of 
pharmacological adjuvants and the induction of specific capsid mutations. Such 
approaches are expected to help the establishment of rAAV-based clinical gene 
therapy in the near future.