4.2 – Overview of Stem Cells and Their Potential as a Therapeutic
At the core of the cellular therapy discussed in this chapter are stem cells. Stem cells are undifferentiated cells of the body that have regenerative abilities like no other cells of the body.
(TedEd)
Of the trillions of cells in the body, stem cells are unique for two cardinal characteristics: the ability to self-renew, meaning making more of themselves, and the ability to differentiate into specialized cells (Essentials of Stem Cell Biology). In order for a stem cell to expand in numbers it undergoes symmetrical division. While on the other hand, asymmetrical division typically accompanies differentiation because it helps to maintain the existing stem cell pool and at the same time generate differentiated cells. While stem cells do not have a single defined function, like myocytes or neurons, they are crucial to the function of the body as a whole. The body naturally uses stem cells to replace the worn-out cells. For example, the average lifespan of a erythrocytes is around 120 days and without the self renewing capability of hematopoietic stem cells, the body would run out of red blood cells within 2 months. Thus, the stem cells’ natural repair and replace mechanism is vital to maintaining normal bodily function.
SELF-RENEWAL
- one of the key abilities of a stem cell in order to increases the stem cell pool
- involves symmetrical division
DIFFERENTIATION
- a unique property of stem cells used to replace worn-out tissue
- involves asymmetrical division
The three types of stem cells
There are also multiple kinds of stem cells that interest scientists. Adult stem cells are tissue-specific undifferentiated cells and have limited potency (Essentials of Stem Cell Biology). Embryonic stem cells are, as the name suggests, derived from the inner cell mass of the embryo and capable of differentiating into all non-placental cell type (Embryonic Stem Cells). Induced-pluripotent stem cells (iPSCs) are derived from differentiated cells that have been reprogrammed to be pluripotent. They can be made in a dish through using transcription factors to reverse a differentiated cell, such as a fibroblast, back into its previously undifferentiated state (Essentials of Stem Cell Biology). The most famous of these factors is a set of four transcription factors, the Yamanaka factors (Oct4, Sox2, Klf4, and c-Myc), which allow for somatic cells to be turned into iPSCs that can then differentiate into other cell types from various tissues (Okita and Yamanaka).
With the many ways that stem cells can be derived and their unlimited potential, it is an appealing method of treatment for many diseases. Studies are constantly exploring ways stem cells can be used to generate and replace defective cells in diseases such as Diabetes, Alzheimer’s, and Macular Degeneration.
Associated risks of using stem cells and potential ethical concerns
Like many treatments, the use of stem cells in clinical settings is not without risks. In fact, the Food and drug Administration (FDA) has approved only a handful of stem cell treatments, most of which relates to hematopoietic stem cells (FDA) which has been around for over 50 years (Henig and Zuckerman). This is in part because of limited knowledge in how to generate a controlled population of stem cells and other safety-associated risks. In addition to the technical difficulties, ethical concerns, particularly regarding the use of embryonic stem cells is also a controversial topic. Considerations of whether stem cells may possess personhood are still widely discussed today. With that in mind, although stem cells seem promising in many fields of study, there are possible heath, political, and social risks that are associated with it.
Potential benefits of iPSCs in treatment
The reason that stem cell therapies remain a popular topic in research despite its risks is in part due to the discovery of iPSCs. With the ability to generate iPSCs in laboratory settings, large numbers of tissue-specific cell types can be generated from a single lineage. This is unlike adult stem cells where only a limited number of cells can be retrieved and purified from the body. In addition, since iPSCs can divide indefinitely from a single cell, the resulting iPSC cultures are homogenized and therefore make them more uniform and phenotypically stable (Soontararak et al.).
Compared to traditional stem cell therapies that involve transplantation of cells from a donor to a recipient, iPSCs can be derived from the patient themselves and serve as a unified source of treatment. This would eliminate concerns of immune rejection due to transplantation. Furthermore, since iPSCs are patient derived and do not go through an embryonic stage, this would also eliminate the ethical concerns surrounding the use of embryonic cells.
These characteristics of iPSCs suggest that it is a safer and a more viable therapeutic in comparison to other sources of stem cells.
KEY TAKEAWAYS
- Stem cells have two cardinal characteristics are self-renewal and differentiation
- There are three types of stem cells: adult stem cells, embryonic stem cells, and induced pluripotent stem cells (iPSCs)
- iPSCs are derived from fibroblasts of the skin via Yamanaka factors
- iPSCs are better alternatives to adult stem cells and embryonic stem cells because they have more sustainable production and are less controversial
- Stem cell therapies are promising but still lots to be learned