Very small embryonic-like cells in the mirror of regenerative medicine.

Regenerative medicine with the promise of complete organ restoration could change the treatment paradigm for various degenerative disorders. In order to develop successful, safe and efficient regenerative therapies, appropriate amount of pluripotent autologous cells are desired. Pluripotent stem cell lines, such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), offer a unique opportunity to derive various cell types that can be exploited for regenerative medicine. However, their application in therapies is limited due to inherent potential tumorigenesis, problems with immune-rejection, applied reprogramming methods, and ethical considerations. Recent reports on the establishment of very small embryonic-like cells (VSELs) are pointing to a way out of this dilemma, since it is proposed that these cells have similar characteristics as ESCs and could serve as basis for therapeutic applications. A careful scientific comparison of VSELs is now needed in order to make judgments about their capabilities and characteristics. In any case, the development of successful, safe and efficient regenerative therapies based on human pluripotent cells requires additional quality assessments of critical parameters that are also summarized within the review.