Stem cells have the potential to treat a variety of incurable diseases, including Parkinson’s disease and leukemia, and research into adult stem cells, embryonic stem cells, and induced pluripotent stem cells (iPSCs) is expanding the possibilities for treating diseases and extending human life. However, challenges such as immune rejection and cancer development still need to be addressed.
Would you believe that the day is just around the corner when we can easily treat Parkinson’s disease, leukemia, or a patient’s eyes using cells from their own skin tissue? Stem cells are making these miracles possible. Since their discovery in the early 1900s, stem cells have been constantly evolving and are now one of the hottest topics in biology and medicine, with potential applications in therapy and research. Despite the problems that stem cell therapy can bring, such as cancer development and immune rejection, the fact that so many scientists are working to eliminate these side effects shows the value of stem cell research.
Normal cells in the body fulfill a limited role within the organ in which they exist. When a cell becomes specialized, it is called differentiated. Stem cells, on the other hand, are undifferentiated cells that do not fulfill a specific role in an organ, but are capable of becoming any cell in the body, i.e., they can differentiate. Stem cells have two main characteristics that distinguish them from normal cells. The first is self-renewal, which means they can replicate themselves indefinitely while remaining undifferentiated, and the second is differentiation, which means they can become specific cells in the body. Stem cells are first created when a fertilized egg divides, and after numerous self-replications, the stem cells differentiate into the cells that make up every organ and tissue in the body. The stem cells created during the division of a fertilized egg are the mother of all cells in the body.
Stem cells are usually categorized into three types: adult stem cells, which are the stem cells that produce cells in tissues in the adult body; embryonic stem cells, which are the stem cells present in the fertilized egg; and induced pluripotent stem cells, which are already fully differentiated body cells that have reverted to stem cells.
Adult stem cells are the cells that are present in minimal amounts in various tissues, such as bone marrow, skin, nerves, and other tissues that we recognize as producing blood, and that can differentiate into those tissues when they are damaged, allowing for self-healing. Unlike embryonic stem cells, adult stem cells are very stable and likely to differentiate only into cells within their own tissue. Because they are stable enough to have few side effects, such as cancerous transformation, they are currently more widely used in clinical practice than embryonic stem cells. However, adult stem cells are very small in number and difficult to culture, making it difficult to collect the required amount. In addition, unlike embryonic stem cells, adult stem cells can only differentiate into specific cells, and crucially, they have shown immune rejection when transplanted into other people, making them less useful. However, recent studies have shown that adult stem cells can differentiate into cells in various tissues just like embryonic stem cells, and advances in culture technology have led to a resurgence of interest in treatments and research using adult stem cells.
Embryonic stem cells are cells that originate from a fertilized egg, the source of life, and unlike adult stem cells, they have the flexibility to differentiate into almost any tissue in the body. Embryonic stem cells can be further categorized into totipotent stem cells, pluripotent stem cells, and multipotent stem cells based on their differentiation capabilities. First, pluripotent stem cells can differentiate into any cell, creating a complete individual. In the development of life, they can be seen as the earliest stages, including the first fertilized egg. Next, pluripotent stem cells can differentiate into most cells, but they cannot differentiate into the placenta, which is necessary for fetal development, and thus cannot create a new individual. In development, pluripotent stem cells differentiate into multipotent stem cells, and then multipotent stem cells form the organs and tissues of the body. Finally, pluripotent stem cells are cells that are limited in their ability to differentiate into specific cells, just as adult stem cells can only differentiate into cells within specific tissues.
Embryonic stem cells are being actively researched as a therapeutic tool due to their wide range of differentiation, but there are practical limitations. First, they are unstable and can undergo differentiation in culture, and there is the potential for cancerous transformation. Also, since embryonic stem cells are obtained from fertilized eggs, there is an ethical issue that the collection and cultivation of embryonic stem cells is criticized by those who view fertilized eggs as life, as it is an act of using a life. To address these ethical issues, some researchers use leftover fertilized eggs from infertile couples with their permission, while others use stem cells from cord blood. Despite the ethical controversies, stem cell research remains a field that offers hope to many people.
More recently, the creation of new stem cells has opened up new horizons in stem cell research. Induced Pluripotent Stem Cells (iPSCs) were developed by Japanese professor Shinya Yamanaka. While normal stem cells differentiate to become specialized cells, iPSCs are reverse-differentiated stem cells that turn a functioning body cell back into the same stem cell it was before differentiation. Since induced pluripotent stem cells can be made from one’s own body cells, there is no immune rejection, and even stem cells made from other people’s body cells can suppress immune rejection, so it is expected that medical treatment will be possible to prepare stem cells in advance and use them immediately in case of emergency. In addition, the process of creating induced pluripotent stem cells is cell-to-cell conversion, so there are no ethical issues. In addition, induced pluripotent stem cells are as easy to create as somatic cells, and their value is increased by the fact that they can be cultured to conduct a variety of research in addition to treatment, such as testing the side effects of new drugs, physiology of tissue and organ development, and modeling human diseases. However, the potential for cancer remains due to their unstable differentiation, and the difficulty of controlling their differentiation into various tissues outside the body remains a challenge.
The common characteristic of all these different stem cells is their ability to differentiate into somatic cells that perform functions in the human body, which is why there is a huge investment in medical research using stem cells. Like repairing a machine by replacing old parts, the ability to generate new cells makes it possible to treat most diseases caused by malfunctioning cells and tissues. This opens up the possibility of treating many intractable diseases, such as leukemia, in which the bone marrow does not produce enough blood; Parkinson’s disease, in which the nerve cells that produce dopamine are damaged; diabetes, in which the body does not produce insulin; and heart disease and cirrhosis, in which the blood vessels are narrowed or damaged. Leukemia, Parkinson’s disease, and diabetes could be treated by transplanting differentiated stem cells in place of cells that are unable to perform their functions, while heart disease and cirrhosis could be treated by injecting stem cells to take advantage of the homing effect of adult stem cells, which differentiate and heal themselves in abnormal parts of the body. Even chronic diseases such as asthma and atopic dermatitis are showing promise, with some patients actually improving after treatment with stem cells. The possibilities are endless, as stem cells can also be used to replace aging cells, so they can be used to treat wrinkles and hair loss.
In addition, stem cells can be cultured and differentiated outside the body in addition to direct transplantation and injection in the body, suggesting the possibility of in vitro experiments. Currently, tissues cultured and differentiated from stem cells in vitro are being used to test drug side effects and investigate disease mechanisms, and the field of in vitro applications is expanding.
However, despite efforts to increase the production capacity of stem cells, such as the development of stem cell culture technology and the development of iPSCs, it is difficult to see treatments using stem cells around us because the problems of stem cells remain. In the case of immune rejection, methods to avoid it have been studied and are in progress, but the possibility of cancer development is still a barrier to the realization of stem cell treatment and utilization, except for adult stem cells. As research continues to be conducted to reduce the incidence of cancer, there will come a time when stem cell treatments can be administered without worrying about side effects, and healthcare will be elevated to the next level.
The future of stem cell research is promising. If the potential of stem cells is realized with the advancement of life science technology, we will be able to live a healthier and richer life, free from the fear of disease. It is also expected to contribute to the extension of human life span, which will be a paradigm shift in healthcare. Stem cell research is not just about improving current treatments, it is the key to unlocking a new era that humans have never experienced before.
