Types and sources of stem cells Stem cells niches are spatially distributed across various tissues of the body since the early developmental stages of life till the maturation of an organism into adult form. In humans the early developmental stages of embryo, amniotic fluid, placenta and umbilical cord blood are conclusively the richest sources of undifferentiated stem cells. There are diverse types of stem cells like embryonic stem cell, tissue specific or adult stem cell, cancer stem cell, mesenchymal stem cell and induced pluripotent stem cells. These cells are much prevalent due to their prominence in medical domain with each having potential to treat gamut of diseases which were considered incurable so far in the medical era . Embryonic stem cells are pluripotent in nature due to their ability to differentiate into every single type of cell forming the adult body except the placenta and umbilical cord. These cells are derived from a 200-300 early embryonic cell stage called the blastocyst or a hollow ball of cells formed at the fifth day post fertilization in humans. Human embryonic stem cells are procured primarily from blastocysts created that were no longer needed for assisted reproduction by in vitro fertilization (IVF). The cells of the inner cell mass of the blastocyst eventually gives rise to specialized cells organizing itself into various tissues and organs of the body. Embryonic
stem cell and embryonic germ cell lines from the human blastocyst and
embryonic gonad respectively can differentiate into multiple forms of
somatic cell. However, it is reported that under in-vitro growth conditions the isolated inner cell mass preserves the native properties of embryonic stem cells. The infinite potential of these stem cells suggests enormous prospects for disease research and new therapies. Characterization of these cells are essential for prior to employing them in clinical trials or drug development which remains as one of the major limitation. Current challenges stirring up the ESC research includes the ethical considerations. In transplantation procedures the prime necessity to ensure the terminal differentiation of embryonic stem cells into the desired tissue specific cells prior to grafting on patients.