The field of stem cells research is one of the most exciting and fast developing fields with a great potential to heal different degenerative diseases and to improve quality of human life. In spite of great enthusiasm and effort, there are several general obstacles and questions about stem cells, which still need to be resolved to enable safe and efficient treatment of degenerative diseases in the future. There are several interesting types of stem cells in humans including embryonic stem cells (ESCs), parthenogenetic embryonic stem cells (pESCs), female and male germinal stem cells (GSCs), and very small embryonic-like stem cells (VSELs). There is still no general consensus about the most promising type of stem cells and the best approach to cell therapy in regenerative medicine. Moreover, there is great effort taken to regenerate the nonfunctional ovaries or testicles using stem cell transplantation and to treat the infertility in this way, especially after cancer therapy. Most of these studies are performed in animal models but with tendency to be translated to human studies. At present, there are several attempts of in vitro gametogenesis but several issues still need to be resolved. Using established markers, the limits between different groups of stem cells including germinal stem cells are not clear and it has been proven that different groups of stem cells can express a degree of pluripotency/multipotency and plasticity. Our tendency is to better elucidate the links between germ line and presence of VSELs in adult tissues and between germ line and adult postnatal stem cells. One of the main tasks is to better predict behavior of transplanted stem cells in the body and their possible relation to tumorigenesis. The aim of this special issue is to answer some aspects of these important questions and to summarize the most recent and advanced developments, approaches, and new ideas in the field. For this special issue we invite both basic scientists and clinicians to submit their original research articles or concise reviews to further elucidate the basic scientific questions about stem cells and to inspire the clinicians to use stem cells in their clinical practice.

Potential topics include, but are not limited to:

• Different stem cell types in humans and in the animal models such as
  • embryonic stem cells (ESCs)
  • parthenogenetic embryonic stem cells (pESCs)
  • gynogenetic and androgenetic ESCs
  • ESCs derived from maturing oocytes
  • female and male germinal stem cells (GSCs)
  • very small embryonic-like stem cells (VSELs)
  • link between germ line and presence of VSELs in adult tissues
  • link between germ line and adult postnatal stem cells
• Culture and cryopreservation of stem cells
• Purification and characterization of stem cells
• Stem cell plasticity and differentiation
• Regeneration of ovaries and testicles by stem cell transplantation
• In vitro gametogenesis (oogenesis and spermatogenesis) and in vitro development of germ cells from stem cells
• Clinical use of stem cells for cell therapies
• Stem cells and ethics