Step 2: Finding the Right Type of Stem Cell

To replace the dead cells, the researchers needed to find stem cells that could differentiate into dopamine neurons.

Which types of stem cells could they use? Let's evaluate their possible choices:

Possible Stem Cell Choices

Blastocyst embryonic stem cells. These pluripotent cells are thought to be the most versatile type of stem cell, because they can become almost any type of cell in the body. Although their plasticity would have made them excellent candidates for the proposed therapy, researchers had not yet grown human embryonic stem cells in culture. The first success at culturing human embryonic stem cells was reported in 1998.

Therefore, although embryonic stem cells held promise for this type of therapy, they were not a feasible option at the time.

Fetal stem cells. The pluripotent stem cells found in fetal brain tissue are the natural source of dopamine neurons in the adult brain. Biologically, they were excellent candidates for the treatment.

This approach came with its own challenges, however: the tissue needed for the treatment came from prematurely terminated human fetuses or late-stage embryos. (Technically, a human embryo is considered a fetus eight weeks after the egg is fertilized by a sperm cell.) This raised a valid ethical issue for consideration.

Umbilical cord blood stem cells. The multipotent stem cells from umbilical cord blood have the potential to turn into many different types of cells, but their natural fate is to become blood and immune cells. Also, at the time that the treatment was designed, not much was known about umbilical cord blood stem cells. Thus, they were not an option for the treatment.

Adult stem cells. There are many different types of multipotent adult stem cells, each of which is responsible for developing into the cells of a certain type of tissue. The best adult stem cell candidates for the Parkinson's disease treatment would be those that can differentiate into dopamine neurons. At the time this treatment was being developed, however, researchers knew little about adult stem cells in the human brain. Therefore, they were not an option for the treatment.

Which cells to use? Of the candidates, the best choice at the time was fetal stem cells, due to both their high potential for success and their availability.

Step 3: Match the Stem Cells with the Transplant Recipient Go
Want more background information about stem cell types?

See What are Some Different Types of Stem Cells?


Obtaining stem cells for research

Stem cells are not plentiful resources, and obtaining them can pose a challenge. Much of the current work in stem cell research is focused on developing reliable and safe ways to obtain and grow enough stem cells for research and treatments. Find more details about this in Creating Stem Cells for Research.


Is human embryonic stem cell research illegal?

Federal funding has historically not been permitted for human embryo research. Does this mean that human embryonic stem cell research is illegal in the United States?

No, human embryonic stem cell research is not illegal in the United States. This only means that funding provided through federal research grants could not be used for research involving human embryos. Research using privately supplied funds was permitted, however. Therefore, human embryo research has typically been performed by private companies using non-government funds.

Regulation of human embryo research has been critically reviewed and revised in recent years. For the latest news on regulation, see Additional Resources.