In this blog post, we will examine how stem cell research is contributing to the treatment of intractable diseases and life extension, as well as the possibilities and challenges that lie ahead.
Can you believe that the day when Parkinson’s disease and leukemia can be easily treated is just around the corner? Can you believe that a patient has been treated for eye conditions using their own skin cells? The answer to these miraculous achievements is none other than stem cells. Since their discovery in the early 1900s, stem cells have undergone continuous development and are now recognized as one of the most promising topics in biology and medicine, with potential applications in treatment and research. Despite the challenges posed by issues such as cancer development and immune rejection reactions associated with stem cell therapy, numerous scientists are striving to eliminate these side effects, demonstrating the value of stem cell research.
General cells in the body perform limited roles within specific organs. When cells perform roles specific to their organs, they are said to have differentiated. However, stem cells are undifferentiated cells that do not perform specific roles within organs but can differentiate into various types of cells in the body. Stem cells have two major characteristics that distinguish them from general cells. The first is self-renewal, which is the ability to maintain an undifferentiated state and replicate itself indefinitely. The second is differentiation potential, which is the ability to differentiate into specific cells within the body. Stem cells are first created when a zygote divides, and after numerous self-replications, these stem cells differentiate into cells that make up all the organs and tissues of our bodies. The stem cells created during the division of a fertilized egg are the mother of all cells in our body.
Stem cells are usually classified into adult stem cells, which are stem cells that produce cells within tissues in the adult body, embryonic stem cells, which are stem cells found in fertilized eggs, and induced pluripotent stem cells, which are completely differentiated somatic cells that have been reverted to stem cells.
Adult stem cells exist in very small quantities in tissues such as bone marrow, skin, and nerves, and are responsible for producing blood. They play a crucial role in self-repair by differentiating into the specific cells needed to repair damaged tissues. Unlike embryonic stem cells, adult stem cells have a very high probability of differentiating into cells specific to their tissue and are highly stable. They are so stable that they rarely cause side effects such as cancerous mutations, making them more actively used in clinical applications than embryonic stem cells to date. However, adult stem cells have the drawback of being extremely scarce and difficult to cultivate, making it challenging to collect sufficient quantities. Additionally, unlike embryonic stem cells, adult stem cells are known to differentiate only into specific cell types, and critically, they exhibit immune rejection when transplanted into others, limiting their applicability. However, recent studies have shown that adult stem cells can also differentiate into various cell types within tissues, similar to embryonic stem cells, and as culture techniques advance, treatments and research utilizing adult stem cells are once again gaining attention.
Embryonic stem cells are derived from the zygote, the origin of life, and unlike adult stem cells, they possess the flexibility to differentiate into almost all tissues in the body. Embryonic stem cells can be further classified into three types based on their differentiation potential: totipotent stem cells, pluripotent stem cells, and multipotent stem cells. Totipotent stem cells can differentiate into all types of cells and can form a complete individual. In the process of life, this stage can be considered the initial stage, including the first fertilized egg. Next, pluripotent stem cells can differentiate into most cell types but cannot differentiate into the placenta required for fetal development, so they cannot form a new individual. In development, totipotent stem cells differentiate into pluripotent stem cells, which then form the organs and tissues of the body.
Finally, pluripotent stem cells are cells whose differentiation is limited to specific cells, similar to adult stem cells, which can only differentiate into cells within a specific tissue. Embryonic stem cells are actively researched as a means of treatment due to their broad differentiation potential, but practical limitations exist. First, they lack stability and may undergo differentiation during culture, and there is also a risk of cancerous mutations.
Additionally, embryonic stem cells are derived from fertilized eggs, leading to ethical concerns from those who view fertilized eggs as living beings, criticizing the extraction and cultivation of embryonic stem cells as the use of a life form. To address these ethical issues, methods such as using remaining fertilized eggs from in vitro fertilization with the consent of infertile couples or utilizing stem cells found in umbilical cord blood have been explored. Despite ethical controversies, stem cell research remains a field that offers hope to many people.
Recently, a new type of stem cell has been created, opening up new horizons for stem cell research. This is the induced pluripotent stem cell (iPSC) developed by Professor Shinya Yamanaka of Japan. While ordinary stem cells differentiate into specialized cells with specific functions, induced pluripotent stem cells are reprogrammed to revert to their undifferentiated state, similar to stem cells before differentiation. Since iPSCs can be created from one’s own somatic cells, they do not trigger an immune rejection response. Additionally, technology is currently being developed to suppress immune rejection even in stem cells created from another person’s somatic cells, making it possible to prepare stem cells in advance and use them immediately in emergencies. Furthermore, the process of creating iPSCs involves converting cells into other cell types, which does not raise ethical concerns. Furthermore, since stem cells can be easily created from somatic cells, they can be used not only for treatment but also for various research purposes such as testing new drug side effects, studying physiology related to tissue and organ development, and modeling human diseases. This makes the value of induced pluripotent stem cells even higher. However, there are still challenges to overcome, such as the instability of differentiation, which leaves a risk of cancer development, and the difficulty of controlling differentiation into various tissues outside the body.
The common feature of these various stem cells is their ability to differentiate into somatic cells that perform functions in the human body, which is precisely why there is significant investment in medical research using stem cells. Just as replacing old parts can repair a machine, using stem cells, which have the ability to generate cells, can potentially treat most diseases caused by dysfunction in cells or tissues. This opens up the possibility of treating numerous incurable diseases, such as leukemia, where blood is not properly produced in the bone marrow; Parkinson’s disease, caused by the deterioration of neurons that produce dopamine; diabetes, resulting from the inability to produce insulin; and heart disease and cirrhosis, caused by narrowed or damaged blood vessels. For conditions like leukemia, Parkinson’s disease, and diabetes, treatment could involve transplanting differentiated stem cells to replace non-functioning cells. For heart disease and cirrhosis, stem cells could be injected to utilize the “homing effect” of adult stem cells, which naturally migrate to abnormal areas within the body and differentiate to repair them. Stem cells even show potential for treating chronic diseases such as asthma and atopic dermatitis, and there are already cases of patients showing improvement after stem cell therapy. Additionally, since stem cells can replace aged cells, they have the potential to be used for applications such as wrinkle reduction and hair loss treatment, making their possibilities virtually limitless.
Furthermore, stem cells can be cultured and differentiated outside the body, in addition to direct transplantation or injection into the body, suggesting the possibility of in vitro experiments. Currently, experiments such as drug side effect testing and disease mechanism investigations are being conducted using tissues cultured and differentiated from stem cells in vitro, and the field of in vitro applications is also expanding broadly.
However, despite efforts to enhance stem cell production capabilities, such as advancements in stem cell culture technology and the development of iPSCs, the reason why stem cell-based therapies are still rare in our daily lives is that stem cells still have unresolved issues. While methods to avoid immune rejection reactions are being researched and are in progress, the potential for cancer development remains a significant barrier to the practical application of stem cell therapy, except for adult stem cells.
Since research to reduce the risk of cancer is ongoing, there will come a time when stem cell therapy can be performed without concerns about side effects, and at that point, medicine will advance to a new level. The future of stem cell research is thus promising. If the potential of stem cells is realized alongside the advancement of life science technology, we will be able to escape the fear of disease and enjoy a healthier and more prosperous life.
Furthermore, it is expected to significantly contribute to extending human lifespan, which could serve as a groundbreaking turning point in the paradigm of medicine. Stem cell research is not merely about improving current treatment methods; it holds the key to opening a new era that humanity has never before experienced.
