1. Introduction
For the last few decades, we have heard a lot about the term “Stem cell”. The first time I came across these magical words was in a science fiction film. However, nowadays, “Stem cell” is not a fictional term but an applicable therapy. In this article, I will review some main features of stem cells as well as their classification which relates to the application of these magical cells.
(Source: Scientific American)
Stem cells are undifferentiated cells which are endowed with the ability to extensively proliferate (self-renewal), usually arise from a single cell (clonal) and differentiate into a wide range of cell types and tissues (potency). [1]
2. Classification
According to their differentiation potential and origins, stem cells are divided into
different types:
● Totipotent or omnipotent cells are the most undifferentiated cells. They can differentiate into both embryonic and extraembryonic tissues, thereby forming the embryo and the placenta.
● Pluripotent stem cells are able to differentiate into cells that arise from the 3 germ layers – ectoderm, endoderm, and mesoderm – from which all tissues and organs develop.
● Multipotent stem cells can differentiate into cells from a single germ layer. For example, mesenchymal stem cells (MSCs) are multipotent cells that can be derived from bone marrow, adipose tissue, bone, Wharton’s jelly, umbilical cord blood, and peripheral blood. They can differentiate into mesoderm-derived tissue such as adipose tissue, bone, cartilage, and muscle. MSCs can also differentiate into neuronal tissue which is derived from the ectoderm.
● Oligopotent stem cells are able to self-renew and form 2 or more lineages within a specific tissue, for instance, hematopoietic stem cells.
● Unipotent stem cells can self-renew and differentiate into only one specific cell type such as muscle stem cells.
Source: [1]
2.2. Stem Cell Classification Based on Origin
● Embryonic Stem Cells (ESCs) are pluripotent cells derived from the inner cell mass of the blastocyst. Most embryonic stem cells are developed from eggs that have been fertilized in an in vitro clinic, not from eggs fertilized in vivo. [2]
● Induced Pluripotent Stem Cells (iPSCs) are adult somatic cells that are reprogrammed to possess the same features as human ESCs. [1]
● Somatic or adult stem cells are undifferentiated and found among differentiated cells in the whole body after development. The function of these cells is to enable the healing, growth, and replacement of cells that are lost each day. These cells have a restricted range of differentiation options.
Among many types, there are the following:
- Mesenchymal stem cells
- Neural cells
- Haematopoietic stem cells
- Skin stem cells
(Source: YourGenome)
3. Application
The most popular applicable stem cells are pluripotent stem cells, multipotent stem cells, and Oligopotent stem cells.
Pluripotent stem cells possess a greater potential for differentiation, being able to develop into cells from all three germinal layers. Due to ethical reasons, however, the use of pluripotent, or embryonic stem cells is strictly limited to research, with a recent shift to induced pluripotent stem cells (iPSCs).
Multipotent stem cells are at the center of research in tissue regeneration thanks
to their immunomodulatory function and paracrine (cell-signaling) effect, which implicates a wide range of applications.
Oligopotent stem cells are famous for their application in acute myeloid leukemia treatment by hematopoietic stem cell transplantation. [3]
Overall, stem cell’s applications are currently under research in 3 main areas:
3.1. Stem cell for dermatological and cosmetic applications, which include skin rejuvenation, scar healing and wound healing acceleration, among others [4-6]. An emerging promising therapy is called fat grafting, in which the cosmetic surgeon obtains the required stem cells by extracting fat tissues from your own body, killing two birds with one stone: giving you a stem cell beauty patch while eliminating some of those unwanted fats.
3.2. Stem cell in treatment of degenerative (age-related) or chronic diseases, for example, osteoarthritis [7]; heart failure due to dilated cardiomyopathy [8]; neurodegenerative diseases such as Alzheimer’s or Parkinson’s [9]; and a much more prevalent disease: Diabetes [10].
3.3. Stem cell in treatment of disease which used to be considered as “terminal” such as Cancer (typically leukemia (blood cancer) as mentioned above) or HIV [11]. At the moment this article is written, a total of 5 cases of HIV patients being completely cured by stem cell therapy have been reported around the world. [12] In addition, stem cell therapy has also shown potentials in treating other sophisticated dysfunctions of the human body, such as infertility or male erectile dysfunction.
That being said, Stem cell remains a rather novel therapy, with many of its applications still in trial stage, requires advanced technology and costs extravagantly. Patients and consumers should beware of scams that employ fake stem cells or shabby technology.
4. Conclusions
At the moment, stem cell therapy still remains a controversy among the medical community due to two major reasons: the ethical questions of harvesting embryos as well as the potential risks of stem cell hyperplasia and/or carcinogenesis if the stem cells’ growth becomes uncontrollable [1]. However, with their ability to self-renew indefinitely and differentiate into practically any developed tissue or organ of the human body, one cannot deny the tremendous potential of stem cells. They promise amazing breakthroughs in the medical field in general, and in regenerative medicine in particular.
References
[1] Kolios, G., & Moodley, Y. (2013). Introduction to stem cells and regenerative
medicine. Respiration; international review of thoracic diseases, 85(1), 3–10.
[2] Zakrzewski, W., Dobrzyński, M., Szymonowicz, M., & Rybak, Z. (2019). Stem cells: past, present, and future. Stem cell research & therapy, 10(1), 68.
[3] Takami A. (2018). Hematopoietic stem cell transplantation for acute myeloid leukemia. International journal of hematology, 107(5), 513–518.
[4] Jo, H., Brito, S., Kwak, B. M., Park, S., Lee, M.-G., & Bin, B.-H. (2021). Applications of Mesenchymal Stem Cells in Skin Regeneration and Rejuvenation. International Journal of Molecular Sciences, 22(5), 2410.
[5] Bojanic, C., To, K., Hatoum, A., Shea, J., Seah, K. M., Khan, W., & Malata, C. M.
(2021). Mesenchymal stem cell therapy in hypertrophic and keloid scars. Cell and Tissue Research, 383(3), 915–930.
[6] Jeon, Y. K., Jang, Y. H., Yoo, D. G., Kim, S. N., Lee, S. K., & Nam, M. J. (2010). Mesenchymal stem cells’ interaction with skin: Wound-healing effect on fibroblast cells and skin tissue. Wound Repair and Regeneration, 18(6), 655–661.
[7] Wiggers, T. G., Winters, M., Van Den Boom, N. A., Haisma, H. J., & Moen, M. H. (2021). Autologous stem cell therapy in knee osteoarthritis: a systematic review of randomised controlled trials. British Journal of Sports Medicine, 55(20), 1161–1169.
[8] Meng, H., Cheng, W., Wang, L., Chen, S., Teng, Y., Lu, Z., Li, Y., & Zhao, M. (2021). Mesenchymal Stem Cell Exosomes in the Treatment of Myocardial Infarction: a Systematic Review of Preclinical In Vivo Studies. Journal of Cardiovascular Translational Research, 15(2), 317–339.
[9] Liu, X. Y., Yang, L. P., & Zhao, L. (2020). Stem cell therapy for Alzheimer's disease. World journal of stem cells, 12(8), 787–802.
[10] Hogrebe, N. J., Ishahak, M., & Millman, J. R. (2023). Developments in stem cell-derived islet replacement therapy for treating type 1 diabetes. Cell Stem Cell, 30(5), 530–548.
[11] Kiem, H. P., Jerome, K. R., Deeks, S. G., & McCune, J. M. (2012). Hematopoietic-Stem-Cell-Based gene therapy for HIV disease. Cell Stem Cell, 10(2),
137–147.
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