Stem cells are undifferentiated cells that have the ability to start from a single cell and differentiate into a variety of cells, and are being recognized as the key to curing incurable diseases and extending human life. There are various types of stem cells, including adult stem cells, embryonic stem cells, and reverse differentiation stem cells, each of which is under active research and ethical debate.
Humans are differentiated from a single fertilized egg when a sperm and egg meet, and by the time we reach adulthood, we have an average of 70 trillion to 100 trillion cells. It’s important to note that a complex body is created from a single cell. The various cells that make up our blood vessels, muscles, nervous system, etc. eventually differentiated from a single cell, which means that the cell has the ability and information to become any cell. These cells are called stem cells.
A stem cell is an undifferentiated cell that has not yet differentiated and can become any other cell or tissue. All of a cell’s information is contained in its DNA, and all cells have the same DNA. DNA is often analogized to a blueprint, and stem cells are the raw materials that can become anything, depending on which part of the blueprint is consulted, before being built according to the blueprint.
The term stem cell has been used since the early 20th century, but it wasn’t until the 1950s that the existence of stem cells was proven. Since then, research has been conducted to create and utilize stem cells at will, including artificial insemination, nuclear replacement, and transcription factors, and has gone through the following stages: cloning using fertilized eggs, cloning sheep through somatic cell cloning, and culturing stem cells. Recently, a breakthrough technology called reverse differentiation stem cells has been developed, which has opened up a huge horizon for stem cell research.
Stem cells are often categorized according to the way they are obtained: adult stem cells, which are stem cells that remain in the adult body; embryonic stem cells, which are derived from fertilized eggs, as in the previous example; and reverse differentiation stem cells, which are derived from the reverse process of differentiation.
Adult stem cells, which were first discovered in bone marrow in the 1950s and paved the way for stem cell research, are undifferentiated cells that are obtained from adults at the end of their development. A typical example is hematopoietic stem cells, which can be obtained from bone marrow or umbilical cord blood, and have the ability to differentiate into blood cells as well as the lymphatic system. Since stem cells are extracted from their natural state and used directly for treatment, they are less likely to be rejected by the body and are free from ethical and religious issues. However, they are difficult to isolate because they exist in small quantities, and it is impossible to differentiate them into cells of all tissues.
To solve these problems, embryonic stem cells emerged as the next best option in 1998, when they successfully differentiated into different tissues. Embryonic stem cells are stem cells obtained from the embryonic stage of development. A fertilized egg undergoes cell division and cleavage to form an embryo, and it is during the blastocyst stage that most of the differentiation of the tissues that make up our body occurs. By extracting the mass of differentiating cells inside the blastocyst and stopping them from differentiating, we can obtain highly differentiated stem cells. There are two main ways to derive embryonic stem cells to create a specific human organ or tissue. One is fertilized embryonic stem cells, which are derived from a blastocyst created from an egg and in vitro fertilization, and the other is cloned embryonic stem cells, which are derived from a blastocyst cultured from an egg by nuclear transfer of the nucleus of a somatic cell into the nucleus of an egg. These embryonic stem cells are pluripotent, meaning they can differentiate into any tissue, but they are bioethically problematic because they destroy the embryo, which is considered life by the Catholic Church. There are also technical and economic challenges, so they are less studied than the more practical adult stem cells.
However, these two types of stem cells are not yet practical to use due to the problems mentioned above. In 2012, the Nobel Prize was awarded to reverse differentiation stem cells, and reverse differentiation stem cells were recognized as a new way to manipulate stem cells. Reverse-differentiated stem cells are stem cells that are obtained by stimulating certain parts of a differentiated body cell to reverse differentiation. Stem cells differentiate by expressing specific transcription factors that are controlled by key regulatory genes that control differentiation. Transcription factors determine which genes will be expressed, for example, a cell that needs to differentiate into a liver will only express transcription factor A, which means that only genes needed for the liver will be expressed, and a cell that needs to differentiate into a heart will only express transcription factor B, which means that only genes needed for the heart will be expressed. In this case, reverse differentiation of liver cells with transcription factor B using reverse differentiation stem cell technology would result in heart cells. Reverse differentiation stem cells are currently receiving a lot of attention because they can be used to create genetically identical embryonic stem cells, so they are highly versatile, free from physical rejection and ethical and religious issues. However, the risk of cancerous cells and the lack of technology to manipulate genes carefully make it difficult to use stem cells under control.
Stem cells have attracted many scientists and medical practitioners because they have the potential to cure many incurable diseases, physical disabilities, and even old age. It is clear that stem cells will continue to be one of humanity’s greatest research challenges. However, there are still many challenges before stem cells can be put to practical use.
First, we are still at a very basic stage of understanding how to induce specific differentiation. The key regulatory genes, the mechanisms by which they trigger differentiation, and how they can be finely tuned still need to be discovered. The ability to fine-tune stem cells to differentiate into the tissues we need will be critical to practical therapies and reduce the likelihood of stem cells getting out of control and turning into abnormally differentiated tumors, called teratomas, or cancer cells. Beyond differentiating specific cells and tissues, much work remains to be done on how to systematically create the organs we need and how to integrate them into the body so they can be used as needed.
Stem cell research also raises many ethical questions. There needs to be a societal consensus on the beginning and end of life and artificial intervention, which could change the direction and methods of research. Therefore, stem cell research must be closely linked not only to scientific advances but also to social and ethical discussions.
Finally, the legal and economic framework for the commercial utilization of stem cells needs to be in place. In order for stem cell therapies to be commercialized, it is essential to have the relevant laws and regulations in place, as well as economic support to reduce the cost of research and treatment. Considering these points, we can see that stem cell research is not just a scientific endeavor, but a complex area of research that requires cooperation and discussion with various fields.
As such, stem cells hold great promise for the future of medicine, but there are still many challenges ahead of their practical application. It is hoped that through continued research and social discussion, stem cells can contribute significantly to human health and welfare.
