In this blog post, we’ll explore the types and characteristics of stem cells, their medical potential, ethical issues, and the latest research trends.
“Stem cells” is a term that anyone interested in life sciences has likely heard at least once. Stem cells are gaining attention as a key technology capable of treating various intractable diseases, and their importance is growing alongside advancements in regenerative medicine, tissue engineering, and cell therapy. However, not many people have a detailed understanding of exactly what stem cells are, what types exist, and what characteristics and limitations each type possesses. In this post, we’ll explore what stem cells are, how they are classified, and what possibilities and limitations have been identified so far.
Early-stage cells undergo several processes to develop into mature cells with diverse characteristics, and the most important of these processes is differentiation. After differentiation, cells acquire unique characteristics that enable them to perform the necessary functions within their respective tissues. Through this process, early-stage cells develop into the various types of cells that make up our bodies, such as bone, skin, blood vessels, nerves, and muscles. Our bodies contain not only cells that have already completed differentiation but also undifferentiated cells that have not yet differentiated into specific tissues; these cells are known as stem cells. Because stem cells have not yet differentiated into cells with specific functions, they possess the ability to differentiate into various types of cells when provided with the appropriate environment and signals. They also possess the ability to self-renew by continuously replicating themselves to produce identical stem cells.
Stem cells can be broadly classified into adult stem cells, embryonic stem cells, and induced pluripotent stem cells (iPS cells). Adult stem cells are found in various tissues of adults; while they cannot differentiate into every type of tissue, they can differentiate into a certain range of cell types. These stem cells are called multipotent stem cells. Typical examples include hematopoietic stem cells found in bone marrow and mesenchymal stem cells obtained from bone marrow and adipose tissue. Hematopoietic stem cells produce red blood cells, various types of white blood cells, and platelets, while mesenchymal stem cells can differentiate into various tissues such as bone, cartilage, and fat cells. These multipotent stem cells differentiate into the necessary tissues in response to various biological signals, such as those from surrounding cells or growth factors. In fact, the process by which blood cells are produced in the bone marrow is also precisely regulated by various signals transmitted from the surrounding environment.
Embryonic stem cells are stem cells obtained from the inner cell mass of a blastocyst, approximately 5 to 7 days after fertilization. Because these cells have the ability to differentiate into nearly every type of cell that makes up the human body, they are referred to as pluripotent stem cells. Embryonic stem cells can proliferate for long periods under appropriate conditions and can be induced to differentiate into various tissues, making them a crucial foundation for regenerative medicine research. However, since obtaining embryonic stem cells requires the use of blastocysts, ethical debates regarding where to define the beginning of life continue to persist. Furthermore, when using cells derived from another person’s embryo, there is a possibility of an immune rejection reaction occurring during the transplantation process. In the past, research was actively conducted to address these issues using somatic cell nuclear transfer technology, and currently, research utilizing various immunological approaches and gene-editing technologies is also being carried out.
The technology developed to address these issues is induced pluripotent stem cells (iPS cells). Professor Shinya Yamanaka and his research team at Kyoto University in Japan succeeded in reintroducing specific genes into somatic cells—such as adult skin cells—to reprogram them into pluripotent stem cells.
This research marked a new turning point in stem cell research, and Professor Yamanaka was jointly awarded the 2012 Nobel Prize in Physiology or Medicine in recognition of this achievement. Since induced pluripotent stem cells do not use embryos, they significantly reduce ethical controversies; furthermore, when generated from the patient’s own cells, they can relatively lower the risk of immune rejection. Currently, iPSCs are being used not only for developing disease models, evaluating new drug candidates, and conducting regenerative medicine research, but also for clinical applications in certain diseases, with various clinical trials underway in countries around the world.
As discussed earlier, stem cells are classified into adult stem cells, embryonic stem cells, and induced pluripotent stem cells, each with distinct advantages and limitations. Adult stem cells have the advantage of posing almost no ethical issues and carrying a relatively low risk of immune rejection, but their range of differentiation is limited. Embryonic stem cells can differentiate into almost any tissue, but they are subject to ethical controversy and carry a risk of immune rejection. Induced pluripotent stem cells are regarded as a technology that largely resolves these two issues while maintaining high differentiation potential. However, both embryonic stem cells and induced pluripotent stem cells carry the potential to form tumors or teratomas if the differentiation process is not fully controlled, so research to enhance safety is ongoing.
In addition, there are still many challenges to be addressed. During the process of culturing stem cells in large quantities, cells may differentiate in undesirable directions or exhibit inconsistent quality. Furthermore, accurately delivering stem cells to the target tissue, ensuring long-lasting therapeutic effects, and guaranteeing long-term safety are also critical challenges. Recently, research has been actively conducted not only on direct stem cell injection but also on the therapeutic use of substances secreted by stem cells, such as exosomes, while culture and production technologies to maintain consistent stem cell quality are rapidly advancing.
Despite these various limitations, stem cell research continues to attract steady attention because it offers new possibilities for treating intractable diseases and regenerating damaged tissues. Currently, research and clinical trials involving stem cells are underway in various fields, including not only the treatment of blood disorders but also neurological disorders, retinal diseases, cardiovascular diseases, spinal cord injuries, and diabetes. If we can further enhance the safety and efficacy of stem cells and reasonably resolve ethical issues in the future, stem cells are expected to establish themselves as a core technology in regenerative medicine, providing new treatment opportunities to more patients. The progress of stem cell research serves as a prime example of how medical technology can advance in a healthier direction when scientific and technological development goes hand in hand with ethical reflection.
