In this blog post, we will examine the role and limitations of stem cells in future medicine, focusing on their types and characteristics, therapeutic potential, and ethical controversies.
In 2004, Professor Hwang Woo-suk announced that he had successfully cloned embryonic stem cells using human eggs in South Korea. Although this research was eventually proven to be false, the incident sparked widespread public interest in stem cells in Korea. However, interest in stem cells had actually been growing for a long time before that. Since Russian scientist Alexander Maximov first coined the term in 1908 and McCullough and James Till proved their existence in 1963, research on stem cells and their potential for treating diseases has been conducted in various fields.
In particular, stem cell research has advanced rapidly since the latter half of the 20th century, along with the development of biotechnology. For example, in 1981, Martin Evans and Gale Martin succeeded in isolating embryonic stem cells from mice, and this research became the basis for human embryonic stem cell research. Subsequently, in 1998, James Thomson succeeded in culturing human embryonic stem cells for the first time, and human stem cell research began in earnest. Although stem cell research has steadily progressed, it has faced various limitations, such as the difficulty of controlling stem cell differentiation and ethical issues, and has not made much progress. However, in 2007, Shinya Yamanaka succeeded in iPS stem cell research, which overcame all these limitations, reigniting stem cell research, which continues to be studied with the potential for various treatments.
In this article, we will discuss what stem cells are, what characteristics they have, what types of stem cells exist, what advantages and disadvantages each type has in research and treatment, and how they can be applied to treatment and research.
Our bodies are made up of hundreds of different types of cells, each performing specific functions. For example, skin cells isolate our bodies from the external environment, lung cells expel carbon dioxide and absorb oxygen, and small intestine cells absorb nutrients into the body. The cells that produce these various types of cells are called stem cells. In other words, stem cells are cells that have the ability to differentiate into various types of cells, and are undifferentiated cells that have not yet differentiated. Therefore, in a broad sense, fertilized eggs are also cells that have the ability to divide repeatedly and differentiate into the entire body, and are therefore included in stem cells. However, when the term “stem cell” is used in general, it refers to cells that have the ability to differentiate into cells other than themselves, excluding fertilized eggs.
All stem cells have two properties: the ability to self-replicate and the ability to differentiate. First, the ability to self-replicate is the ability to replicate itself through somatic cell division, just like other cells. However, unlike other cells, in order to maintain their numbers within the body, when stem cells differentiate into two cells, only one differentiates into a cell with a new function, and the other is replicated in the same form as the original stem cell. If one stem cell differentiates into two new cells within the body, other stem cells maintain their number by producing two identical stem cells through somatic cell division. The second property is the ability to differentiate into various cells, or differentiation potential. Stem cells are classified as totipotent, pluripotent, or multipotent stem cells according to the range of their differentiation potential. Totipotent stem cells are stem cells with the differentiation capacity to produce a complete organism, and include fertilized eggs and the cells that undergo cell division to form a morula-like structure. Pluripotent stem cells are stem cells found at a slightly more differentiated stage than totipotent stem cells. Although they cannot form a complete organism because they cannot form a placenta, they have the differentiation ability to differentiate into almost all types of cells. The cells of the endoderm, mesoderm, and ectoderm, which are formed by further differentiation from the blastula stage, belong to this category. Finally, multipotent stem cells are limited in the types of cells they can differentiate into from stem cells, and mainly differentiate into cells with similar functions. For example, NSCs (Neural Stem Cells) can only differentiate into cells such as neurons, astrocytes, and oligodendrocytes in the nervous system, and these are multipotent stem cells.
As explained above, stem cells have the ability to differentiate into other cells, making them highly valuable in the field of medicine. In order for stem cells to be used in various medical treatments, they must have good differentiation ability, their differentiation speed must be controllable, there must be no ethical issues, and they must not cause immune rejection in patients. Stem cells can be broadly divided into three types: embryonic stem cells, adult stem cells, and induced pluripotent stem cells (iPS cells). Each type has different characteristics, as described above. The following is a look at the three types of stem cells and their advantages and disadvantages for therapeutic use in relation to the characteristics mentioned above.
First, embryonic stem cells are stem cells that play a role in creating cells that perform various functions during the process of forming tissues and organs and developing into a fetus through repeated cell division called fertilization. An embryo refers to the period of about eight weeks after a male sperm and a female egg meet and become a fertilized egg, when differentiation into various tissues and organs is complete. Embryonic stem cells play an important role during this period, and since they are stem cells involved in creating all the cells that make up the fetus’s tissues and organs, they theoretically have the potential to differentiate into all the cells in our bodies. For this reason, embryonic stem cells are classified as totipotent and pluripotent stem cells, as explained above. However, in the case of embryonic stem cells, if the embryo is considered a living organism, experimenting with it is equivalent to killing a life, which raises ethical issues. In addition, embryonic stem cells differentiate very quickly, making it difficult to artificially control the differentiation rate and differentiate them into specific cells, and there is a risk that they may develop into cancer cells. Furthermore, when embryonic stem cells from another person must be transplanted, there is a risk of immune rejection. To solve the problem of immune rejection, patient-specific embryonic stem cells have been developed. Patient-specific embryonic stem cells are created by removing the nucleus from a fertilized egg during the process of creating embryonic stem cells, injecting the patient’s somatic cell nucleus into the fertilized egg, and then culturing the fertilized egg. Stem cells created in this way do not cause an immune rejection response in the patient’s body. However, these patient-specific embryonic stem cells also raise ethical issues because they use fertilized eggs, and they are not suitable for use in research or treatment because they have the potential to develop into cancer cells.
Second, there are adult stem cells. Adult stem cells are stem cells found in mature adults. They exist in various tissues throughout the body and can differentiate into cells that make up specific tissues. Currently known adult stem cells include bone marrow, adipose, and blood stem cells. Unlike embryonic stem cells, adult stem cells have stable differentiation and do not have the potential to become cancer cells, which is an ethical advantage. Therefore, they are more suitable for research and therapeutic purposes than embryonic stem cells. A representative example of their use in therapy is bone marrow transplantation. However, adult stem cells are found in small quantities in tissues, so the number of stem cells that can be obtained is limited. Compared to embryonic stem cells, adult stem cells can differentiate into a limited number of cell types, which makes them suitable for culturing specific cells but limits their application in many fields.
Induced pluripotent stem cells were developed to overcome the problems and limitations of these two types of stem cells. Induced pluripotent stem cells are stem cells created from somatic cells in our bodies by inducing them to revert to their original stem cell state, i.e., by inducing the dedifferentiation of somatic cells. Like embryonic stem cells, these stem cells have the advantage of being able to differentiate into any cell in the body, but unlike embryonic stem cells, they do not pose ethical issues. However, since the factor introduced into somatic cells for dedifferentiation is part of a cancer gene, there is a risk that it may cause cancer if not done correctly, and these stem cells are still in the development stage and cannot yet be used clinically. Therefore, the stem cells currently used in research and treatment are mainly adult stem cells, while induced pluripotent stem cells are attracting attention as a potential future cell therapy.
Currently, stem cells are used in some areas of treatment. Bone marrow transplantation is a representative example, but stem cell therapy is not yet widely used in areas other than bone marrow transplantation. However, efforts are underway to find treatments using stem cells in various fields, such as diabetes, rheumatoid arthritis, Parkinson’s disease, Alzheimer’s disease, cerebral infarction, myocardial infarction, spinal cord recovery, and cancer treatment. Stem cells are also used in basic medical research, such as experimenting with pharmacological responses using tissues and organs created from stem cells. Recently, research is being conducted on technology to create artificial organs using 3D printers by combining stem cells and 3D printing technology to make the process of creating organs for treatment or research more sophisticated and easier.
Stem cell research is advancing rapidly with advances in science and technology. For example, recent research is focusing on increasing the possibility of treating specific diseases by precisely editing the genes of stem cells using CRISPR-Cas9 gene editing technology. In addition, research is actively underway to cultivate mini-organs called organoids from stem cells and use them to study the development process of human organs and test the effects of drugs. These studies show that stem cells are becoming an important tool for understanding human biology and diseases, going beyond their role as cell therapies.
Like seeds necessary for trees to grow, stem cells are the source of the countless cells that make up our bodies, and they have various differentiation abilities depending on their type. Embryonic stem cells and induced pluripotent stem cells can differentiate into almost all types of cells, while adult stem cells have the ability to differentiate into cells that make up specific tissues. Among these, adult stem cells are widely studied because they are safe, pose no ethical issues, and have no potential to cause cancer, and are actually used for therapeutic purposes in clinical practice. Although stem cells still have many possibilities but have not been widely applied in practice, they are a subject of interest to many people who are considering their future potential.
