Answer:
Embryonic stem cells are pluripotent stem cells derived from the inner cell mass of a blastocyst, an early-stage pre-implantation embryo. Human embryos reach the blastocyst stage 4–5 days post fertilization, at which time they consist of 50–150 cells.
Step-by-step explanation:
Adult Stem Cells
Embryonic Stem Cells
Induced Pluripotent Stem Cells
Pros
Trans differentiate and and reprogramming of these cells is possible but is not well studied
Thought to be less likely to be rejected if used in transplants
Success has already been demonstrated in various clinical applications
Can maintain and grow for 1 year or more in culture
Established protocols for maintenance in culture
ESCs are pluripotent cells that can generate most cell types
By studying ESCs, more can be learned about the process of development
Abundant somatic cells of donor can be used
Issues of histocompatibility with donor/recipient transplants can be avoided
Very useful for drug development and developmental studies
Information learned from the “reprogramming” process may be transferable for in vivo therapies to reprogram damaged or diseased cells/tissues
Cons
Limitations on ASC ability to differentiate are still uncertain; currently thought to be multi or unipotent.
Cannot be grown for long periods of time in culture
Usually a very small number in each tissue making them difficult to find and purify
Currently there is no technology available to generate large quantities of stem cells in culture
Process to generate ESC lines is inefficient
Unsure whether they would be rejected if used in transplants.
Therapies using ESC avenues are largely new and much more research and testing is needed
If used directly from the ESC undifferentiated culture prep for tissue transplants, they can cause tumors (teratomas) or cancer development
Methods for ensured reproducibility and maintenance, as differentiated tissues are not certain.
Viruses are currently used to introduce embryonic genes and has been shown to cause cancers in mouse studies