Stem cells are a daily feature of science news nowadays and related fields are creating an astonishing array of advancements within regenerative medicine. Unfortunately unless you have a scientific background the differences between types can be terribly confusing. We are here to help.
The term stem cell can encompass:
1. Embryonic stem cells
2. Tissue stem cells: found at specific niches in everyone's body
3. Induced pluripotent stem cells (IPSCs) which are created by ‘reprogramming’ other cells to behave more flexibly (sidestepping the ethical restrictions with embryos).
Pluripotency is a measure of how many different types of cells a stem cell can differentiate into; adult stem cells can usually only become specific types of tissue like skin and are often unsuitable for many areas in regenerative medicine, whereas embryonic types can become every cell type except those of the placenta. While induced varieties are often included in the umbrella term 'stem cells', regenerative research with stem cells really uses either embryonic or various tissue types with less potency. These effectively come 'pre-packaged' and don't require the same tinkering. Embryonic cells are desirable, but issues with sourcing them and ethical controversy has made using them difficult and has forced research to turn to alternatives.
If we leave IPSCs to one side for now, what can pre-existing stem cells be used for?
Bone marrow transplants are widespread and have been used since the 70s for leukemia and skin stem cells can be taken from healthy skin to partially heal burn damage. Transplants using tissue stem cells have limited potential because they have limited potency, but different ones have different properties, and this is being explored further as more different types are discovered. Taken from different areas of the body, they may be able to regenerate certain organs like the liver. These cells are often easier to source and quicker to implement, but are unlikely to offer the significant regeneration IPSCs could provide.
Embryonic stem cells have similar potential to IPSCs and even some advantages, but they're extremely difficult to obtain and have immune rejection issues. Research using ESCs has generally been toned down as IPSC research gains steam. Without control or greater understanding of differentiation regulation, injected ESCs can also form teratomas.
Stem cells are extremely useful tools for studying specific tissue in the lab and things like drug effects, but IPSCs enable more specific testing and require less invasive techniques to obtain (e.g obtaining bone marrow to test is less pleasant than taking a skin sample).
...And if you're a stem cell nut, here's a great little film introduction into the world of stem cell research by EuroStemCell: