This blog post looks at the types and possibilities of stem cells and the balance between ethical issues.
Stem cells are a word that anyone interested in the life sciences has heard at least once. Stem cells are attracting attention as the key to solving many incurable diseases, and their importance is growing day by day. However, few people know much about stem cells, and even fewer can explain them. This article will address what stem cells are, how they are distinguished, and what their limitations are.
Early-stage cells go through various processes to develop into mature cells with different characteristics, one of which is differentiation. Cells that have undergone differentiation have characteristics suitable for functioning in each tissue. Through this process, the initial cells develop into cells that make up various tissues such as bones, skin, and blood vessels. Among the many cells in our bodies, there are undifferentiated cells that have not undergone the process of differentiation. These undifferentiated cells are called stem cells. Since stem cells have not yet differentiated, they have the ability to differentiate into various body tissues under the right conditions.
Stem cells can be broadly classified into adult stem cells, embryonic stem cells, and induced pluripotent stem cells (iPS cells). Adult stem cells are stem cells that exist in specific mammalian tissues and can differentiate into a limited number of tissues, although they cannot differentiate into all tissues. These stem cells are called multipotent stem cells. Examples of adult stem cells include hematopoietic stem cells in the bone marrow and mesenchymal stem cells. Hematopoietic stem cells are responsible for producing red blood cells and various white blood cells, while mesenchymal stem cells are responsible for producing bones and the connective tissue that surrounds them. These pluripotent stem cells differentiate according to need. In fact, blood cells that differentiate in the bone marrow differentiate according to signals from adjacent cells or the circulatory system.
Embryonic stem cells are stem cells found in early embryos and have the ability to form entirely new individuals. In humans, a mass of cells called a blastocyst forms in the early stages of the embryo, and the cells of this blastocyst have the ability to differentiate into all kinds of cells that make up the body. Embryonic stem cells can be isolated from this blastocyst and can be propagated almost infinitely under appropriate conditions, and can be differentiated in a specific manner when given the appropriate signal. Such stem cells are called pluripotent stem cells. However, the process of obtaining embryonic stem cells is accompanied by ethical issues. In order to obtain embryonic stem cells, the blastocyst must be destroyed because this blastocyst is a stage with the potential to develop into a life. This causes ethical controversy. In addition, there is a problem that the embryonic stem cells and tissues derived from them can cause an immune response in the recipient when transplanted. However, this problem can be solved by replacing the nucleus of the fertilized egg with the recipient’s somatic cell nucleus.
Fortunately, a new method has been developed to create pluripotent stem cells while solving both of these problems. Professor Shinya Yamanaka and his research team at Kyoto University in Japan created pluripotent stem cells using the patient’s skin cells instead of isolating embryonic stem cells from the blastocyst. The stem cells created in this way are called induced pluripotent stem cells (iPS cells). The research team examined the differences in the genes expressed in embryonic stem cells and non-stem cells, and then found genes that are uniquely expressed at a high level only in embryonic stem cells. The research team, which determined that these genes are essential for the undifferentiated state of stem cells and the function of embryonic stem cells, created induced pluripotent stem cells by introducing these genes into the skin cells of patients. Since these cells are derived from the patient’s own skin cells, they do not cause an immune response. They have already been used for cell therapy in animals with diseases and will soon be applied to humans as well.
As we have seen, stem cells are divided into three types: adult stem cells, embryonic stem cells, and induced pluripotent stem cells, each with its own advantages and disadvantages. Adult stem cells have the advantage of not causing an immune response, but they have the disadvantage of having a limited range of differentiation. Embryonic stem cells, which were studied to solve this problem, have the advantage of being able to differentiate into a wide range of cells, but they have the disadvantage of causing an immune response and ethical issues. Induced pluripotent stem cells were created through research to solve the disadvantages of embryonic stem cells while maintaining their advantages. However, both embryonic stem cells and induced pluripotent stem cells are unstable and have the disadvantage of having the potential to develop into cancer.
There are other problems to be solved. In the process of culturing stem cells, it often happens that they differentiate into cells with different functions. In order to inject stem cells into the blood and induce them to differentiate to reach the desired target, a considerable amount of stem cells is required. However, with the current technology, even if a small amount of stem cells are obtained, most of them differentiate into cells with different functions during the differentiation process, making it difficult to obtain the desired amount of stem cells.
Despite these shortcomings, many people are paying attention to stem cells because they have a lot of potential and can offer hope for the treatment of incurable diseases. If we find ways to overcome the shortcomings of each type of stem cell and the common shortcomings, stem cells may become the key to solving incurable diseases. Stem cell research is more hopeful when looking at the process that leads from the discovery of stem cells to the development of induced pluripotent stem cells. If many people continue to be interested in and conduct research, the day may come when stem cells will solve intractable diseases.
