Stem Cells: Current Research

Karena Peterson, 7/20/24

Quick Look: What do they do?

Stem cells are often called the “building blocks” of our bodies, as not only do they build our bodies, but maintain them by replacing damaged or dead cells. They possess two main qualities, the ability to self-renew, or to divide to make more stem cells, and the ability to differentiate, or to undergo a process in order to develop specialized structures and functions. Stem cells are the only cells within us that can differentiate- and are sometimes able to specialize into over 200 types. They are vital for our wellbeing and play a crucial role in tissue regeneration and repair. In this overview of these rather complex cells, we’ll dive into their properties, cell potency, grouping and uses. 

What makes them unique?

These cells have two characteristics that are used to define them, and that are universally possessed: the ability to self-renew, and the potential to differentiate into different types of cells. Let’s look closer at both. 

Self-renewal of stem cells is the ability to divide, creating daughter cells that, “may be: 1) both stem cells, 2) a stem cell and a more differentiated cell, or 3) both more differentiated cells.” (National Institute of Health, Stem Cell Basics). This is unique, as muscle cells, neural cells, and blood cells do not typically replicate, showing why this is a distinctive property of stem cells. 

Differentiation is said to be when a cell, “may undertake major changes in its size, shape, metabolic activity, and overall function,” in order to, “[become] more specialized,” according to Oregon State University. Stem cells are originally undifferentiated, but then may differentiate to become a specific type of cell. However, what cell they specialize into may change based on which stem cell it is. For example, “hematopoietic stem cells reside in the bone marrow and can produce all the cells that function in the blood,” (Mayo Clinic, Stem Cells: What they are and what they do). Differentiation is what allows for the recreation of functional tissue after injury, cell death or other issues. 

 Potency

Not all stem cells can differentiate into every type of cell. They can be totipotent (able to differentiate into any of the cells types found in the embryo as well as the placenta and umbilical cord), pluripotent (able to differentiate into all cell types found in the body, but not the placenta/umbilical cord), multipotent (able to differentiate into types of cells from a multiple lineages), oligopotent (able to differentiate into a few types of cells), and unipotent (able to differentiate into only one type of cell). This is referred to as a cell’s potency. 

Totipotent stem cells, as previously stated, are able to differentiate into all cells of the embryo as well as the placenta and umbilical cord. Some refer to them as, “entirely potent or all-powerful from a cellular perspective,” such as Professor Paul Knoepfler, PH.D., in his article, What are totipotent stem cells & what can they do? Despite their high potency, examples, such as the zygote (fertilized egg), and young embryonic cells are not permanently totipotent . Most totipotent cells lose this quality around the 8-cell stage of the embryo’s growth. 

After this stage, most cells become pluripotent, which is still the second highest on the hierarchy of potency. The difference between totipotent and pluripotent is simple- while they can both differentiate into cells of the developing body, pluripotent stem cells cannot specialize to become cells found in the umbilical cord or placenta. Usually when talking about pluripotent stem cells, you’ll hear about both embryonic stem cells (found after the 8-cell stage, as said above) and induced pluripotent stem cells. Induced pluripotent stem cells are stem cells grown in laboratories that are- as the name suggests, pluripotent, and often used for research. 

Multipotent cells are the middle ground between pluripotent stem cells and oligopotent; while they can differentiate into more cell types than oligopotent and below, they are limited to specific lineages, (lineage of cells refers to the, “pattern of cell divisions during its development.” (Science Direct, “Cell Lineage”). An example would be a, “haematopoietic stem cell, which can develop into several types of blood cells,” (National Center for Biotechnology Information, “Stem cells: past, present, and future”). These cells are limited into becoming any type of cell found within their tissue or organ, and are found in adult tissues.

An oligopotent stem cell is able to divide into a few cell types found along a specific lineage. For example, a myeloid stem cell is able to differentiate into white blood cells, yet not red. 

Finally, unipotent, as the same suggests, are only able to differentiate into one type of cell, labeling them with the narrowest ability to differentiate. 

Grouping

 Though there are many different stem cells found in different locations at different points of a human development, such as Neural Stem Cells (NSC, found in the Central Nervous System, or the brain and spinal cord), or Basal Stem Cells (BSC, found in the epidermis, or outermost layer of the skin), stem cells are usually grouped based on their characteristics.

One way stem cells are categorized is in two, “the ‘pluripotent’ stem cells (embryonic stem cells and induced pluripotent stem cells) and nonembryonic or somatic stem cells (commonly called “adult” stem cells),” according to National Institute of Health Article, Stem Cell Basics. This divides the different stem cells into a group that is able to differentiate into all cells of the body and stem cells which cannot. 

It’s also very common to classify stem cells by source, which would divide the listed pluripotent category into an embryonic class (these stem cells are typically sourced from umbilical cord blood or embryos in IVF), and an induced pluripotent stem cell class (lab-made cells that mimic embryonic stem cells, thus why these two can be grouped together but are also considered to be of another source). With this classification, adult stem cells, also known as nonembryonic or somatic stem cells, are left to their own class, as they are sourced from tissue and are not pluripotent, but multi or unipotent. 

All stem cells will fall into either one of the categories or one of the classes, based on their own characteristics. For example, the previously listed NSC and BSC would fall into the nonembryonic or somatic stem cells category and class. Overall, it is common to group stem cells both by potency or by source. 

Uses 

Besides the obvious uses of the body, stem cells have been and will continue to be used frequently in both research and medicine. A common way to utilize stem cells in health is with stem cell therapy or regenerative medicine. This, “promotes the repair response of diseased, dysfunctional or injured tissue using stem cells or their derivatives,” according to, “Stem Cells: What They Are And What They Do,” by MayoClinic. This is important as this therapy relies on cells rather than organ donations- which are rare and complicated, as well as limited. These therapies offer a potentially renewable source. This therapy has two main steps, the growth and manipulation of these cells in a lab, and the implantation into a person. While this is a very commonly talked about topic, that’s not to say this is stem cell’s only use. 

Stem cells can also be used in research. Not only do they help us further our understanding of how diseases occur by studying the maturation of stem cells, they also can be used to test new medicine, drugs and treatments. 

This is not to say that the use of stem cells is without limits; like everything, stem cell applications have issues, ethical dilemmas (mainly surrounding the usage of embryonic stem cells, seeing as they are harvested from human early stage embryos) and other challenges surrounding them. Furthermore, many exciting future uses are blocked by significant technical hurdles that will need extensive research to overcome.  

Stem cells are incredibly useful and special within our bodies and within the branches of medicine and research. Not only that, but they are incredibly complex, and will likely require much more research to fully understand the true depths of their self-renewal, differentiation and characteristics. 

References

Stem cells: What they are and what they do - Mayo Clinic

Stem Cell Basics | STEM Cell Information (nih.gov)

Stem cells: past, present, and future - PMC (nih.gov)Adult Stem Cells // Center for Stem Cells and Regenerative Medicine // University of Notre Dame

Cell Lineage - an overview | ScienceDirect Topics

What are totipotent stem cells & what can they do? - The Niche (ipscell.com)

Cell Potency: Totipotent vs Pluripotent vs Multipotent Stem Cells | Technology Networks

Stem Cells: Types, What They Are & What They Do (clevelandclinic.org)

Stem cell - Neural, Regeneration, Differentiation | Britannica

3.6 Cellular Differentiation – Anatomy & Physiology (oregonstate.education)

Multipotent Stem Cell - an overview | ScienceDirect Topics