Overall, numerous reprogramming methods exist which all have their own positive and negative aspects (all reprogramming strategies are reviewed in [23]). In particular, the nonintegrating, virus free protocols will become more and more important with the look towards clinical trials. These methods should be not only intensively propagated and further improved, but also be tested with different starting materials. In this review, the reprogramming protocols of the different somatic cells sources are compared on virus-based methods due to their higher efficiency and the well-established processes.
