Toolbox for retrovectorologists.

Retroviral vectors have actively contributed to the advent of gene therapy as a realistic approach in human therapeutics. At the beginning, the use of retroviral vectors was thought to be as simple as the collection of a viral supernatant that was applied to the desired cell. Rapidly, target resistance to transduction appeared in various conditions, ex vivo as well as in vivo. At that time, retrovectorologists entered an active "back to the bench" era. This phase was thought to have reached its conclusion with the generation of theoretically safe lentiviral vectors and when, in 2000, a first clinical trial using retroviral vectors proved to be successful. Unfortunately, recent developments have shown that we still need to improve our knowledge of several steps in the retroviral life cycle before we can accurately adapt vectors to target specific cells. In this review we will first briefly detail key features of the life cycle of wild-type retroviruses. Thereafter, an overview of the minimal requirements needed to generate retroviral vectors will be followed by the relevant developments in this rapidly moving field. Of note, we have highlighted the crucial biosafety issues in a specific section.