In this blog post, we will look at how stem cell research is contributing to the treatment of incurable diseases and extending life, and what possibilities and challenges lie ahead.
Can you believe that the day is not far off when we will be able to treat Parkinson’s disease and leukemia with ease? Can you believe that there is a patient who has had his eyes treated using his own skin tissue cells? It is none other than stem cells that make such miraculous things possible. Stem cells have been continuously developed since they were discovered in the early 1900s, and they have become the most popular topic in biology and medicine, showing their potential for application in treatment and research. Despite the problems that stem cell treatment can bring, such as cancer development and immune rejection, the fact that numerous scientists are working to eliminate these side effects shows the value of stem cell research.
In the body, normal cells perform only limited roles within the organs in which they exist. This is called differentiation, in which cells perform only the roles that fit the organs. However, stem cells are undifferentiated cells that do not perform specific roles within organs but can turn into any cell in the body, that is, cells that can differentiate. Stem cells have two major characteristics that distinguish them from normal cells. The first is self-replication, which allows cells to replicate themselves infinitely while remaining undifferentiated, and the second is the ability to differentiate into specific cells in the body. Stem cells are first created when a fertilized egg divides, and after numerous self-replications, those stem cells differentiate into the cells that make up all of the organs and tissues in our bodies. Stem cells, which are created when a fertilized egg divides, are the mother of all the cells in our bodies.
Stem cells are usually classified into adult stem cells, which are stem cells that produce cells in tissues in the body of an adult, embryonic stem cells, which are stem cells that exist in fertilized eggs, and induced pluripotent stem cells, which have already completely differentiated and returned to stem cells.
Adult stem cells are the cells that exist in the minimum amount needed for various tissues such as the bone marrow, skin, and nerves, which we commonly know produce blood, and differentiate into the corresponding tissue when the tissue is damaged, enabling self-healing. Unlike embryonic stem cells, adult stem cells have a very high and stable potential to differentiate only into cells in the corresponding tissue. Adult stem cells are currently being used more actively in clinical trials than embryonic stem cells because they are so stable that they rarely have side effects such as cancer mutations. However, adult stem cells are very scarce and difficult to culture, making it difficult to collect the required amount. And unlike embryonic stem cells, adult stem cells are known to be able to differentiate into specific cells only, and crucially, they show immune rejection when transplanted into another person, making them less useful. However, recent studies have shown that adult stem cells can also differentiate into cells in various tissues like embryonic stem cells, and as culture technology advances, treatment and research using adult stem cells is again attracting attention.
Embryonic stem cells are cells derived from fertilized eggs, which are the source of life. Unlike adult stem cells, they have the flexibility to differentiate into almost all tissues in the body. Embryonic stem cells can be divided into three types according to their differentiation ability: totipotent stem cells, pluripotent stem cells, and multipotent stem cells. First, totipotent stem cells can differentiate into all cells, allowing them to create a complete individual. In the development of life, it can be seen as an early stage, including the first stage of fertilized eggs. Next, pluripotent stem cells can differentiate into most cells, but they cannot create a new individual because they do not differentiate into the placenta necessary for fetal development. In development, pluripotent stem cells can be seen as having differentiated into pluripotent stem cells, and then pluripotent stem cells form the organs and tissues of our body. Finally, pluripotent stem cells are cells that are limited in their differentiation into specific cells, just as adult stem cells can only differentiate into cells within a specific tissue.
Embryonic stem cells are being actively researched as a means of treatment due to their wide range of differentiation, but there are practical limitations. First, they are not very stable, and differentiation can occur during culture, and there is also the possibility of cancer mutations. In addition, since embryonic stem cells are obtained from fertilized eggs, there is an ethical issue that has been criticized by those who view fertilized eggs as life, saying that the collection and culture of embryonic stem cells is an act of using life. To solve these ethical issues, we sometimes use leftover artificial fertilized eggs for infertile couples with their permission, or use stem cells in cord blood. Despite ethical controversies, stem cell research remains a field that gives hope to many people.
More recently, the creation of new stem cells has opened up new horizons in stem cell research. It is an induced pluripotent stem cell (iPSC) developed by Professor Shinya Yamanaka of Japan. While normal stem cells differentiate into specialized cells, these induced pluripotent stem cells are reprogrammed stem cells that return functioning somatic cells to their stem cell state. Induced pluripotent stem cells can be made from one’s own somatic cells, so there is no immune rejection. Even stem cells made from other people’s somatic cells can suppress immune rejection, and a technology is under development that can suppress immune rejection. This will make it possible to prepare stem cells in advance and use them immediately in case of emergency. Also, the process of making induced pluripotent stem cells involves converting cells into cells, so there is no ethical problem. In addition, since they are made from somatic cells, they can be easily made into stem cells, and through culture, they can be used for various research purposes, such as experiments on side effects of new drugs, physiology of tissue and organ development, and modeling human diseases, in addition to treatment, which further increases the value of induced pluripotent stem cells. However, the possibility of cancer remains due to the instability of differentiation, and the difficulty of controlling differentiation into various tissues outside the body remains as a challenge.
The common feature of these various stem cells is that they can differentiate into somatic cells that perform functions in the human body, and this is why there is a huge investment in medical research using stem cells. Just as we repair a machine by grinding down old parts, we can use stem cells to generate cells to treat most diseases caused by dysfunction of cells and tissues. It has opened up the possibility of treating a number of incurable diseases, including leukemia, in which blood is not produced properly in the bone marrow, Parkinson’s disease, which is caused by the destruction of nerve cells that produce dopamine, diabetes, which is caused by the inability to produce insulin, and heart disease and cirrhosis, which are caused by the narrowing or destruction of blood vessels. In the case of leukemia, Parkinson’s disease, and diabetes, treatment can be performed by transplanting differentiated stem cells instead of cells that cannot perform the corresponding function, and in the case of heart disease and cirrhosis, stem cells can be injected to treat them using the homing effect of adult stem cells, which differentiate spontaneously in abnormal parts of the body. It even shows potential for treating chronic diseases such as asthma and atopic dermatitis, and there are actually patients who have improved after treatment using stem cells. And since it can replace aged cells, the possibilities of stem cells are endless, as they can be used to treat wrinkles and hair loss.
In addition, stem cells can be cultured and differentiated in vitro in addition to being directly transplanted or injected into the body, suggesting the possibility of in vitro experiments. Even now, experiments on drug side effects and disease mechanisms are being conducted using tissues cultured and differentiated from stem cells in vitro, and the field of in vitro applications is expanding.
However, despite efforts to improve the production capacity of stem cells, such as the development of stem cell culture technology and iPSCs, the reason why it is difficult to see stem cell-based treatments around us is that there are still problems with stem cells. Methods to avoid immune rejection 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 to reduce the risk of cancer is steadily progressing, the day will come when we can receive stem cell therapy without worrying about side effects, and at that time, medical care will be a step above the existing medical care.
The future of stem cell research is thus promising. If the day comes when the potential of stem cells is realized along with the development of life science technology, we will be able to escape the fear of disease and enjoy a healthier and more abundant life. Furthermore, it is expected to make a significant contribution to extending human lifespan, which will be an opportunity to dramatically change the paradigm of medical care. Stem cell research will not only improve current treatment methods, but will also be the key to opening a new era that humans have never experienced before.
