Stem cells are a population of undifferentiated cells with the ability to extensively proliferate. They differentiate to different types of cells and tissues. It has been discovered that there are different types of stem cells. These include pluripotent cells that are embryonic stem cells, Embryonic stem cells are derived from the inner mass of the embryo. Induced pluripotent cells are formed from reprogramming of somatic cells. Pluripotent cells have the ability to differentiate to all three types of tissues of the germ layer. These tissues of the germ layer are endoderm, mesoderm, and ectoderm. Multipotent stem cells can differentiate into tissues obtained from single germ layers which form adipose tissue, bones, and cartilages (Kolios & Moodley, 2012).
Stem cells can be used in cellular therapy to replace damaged cells and regenerate organs. Stem cells have been categorized based on the differentiation capacity. Totipotent cells are the most undifferentiated cells that are found in early development. Fertilized oocyte and cells of first two divisions are in this category of stem cells. These cells differentiate to form the embryo and the placenta. Pluripotent cells are the other category of stem cells based on differentiation ability. These cells are able to differentiate into cells that originate from the three germ layers. These gem layers form the basic foundation from which all organs and tissues develop. Multitpotent cells exist in many tissues and differentiate to cells originating from a single germ layer (Kolios & Moodley, 2012). These cells can be derived from a number of body tissues including bone marrow, adipose tissue, bone, Wharton’s jelly, umbilical cord blood, and peripheral blood. These cells have the ability to differentiate into mesoderm-derived tissue such as adipose tissue, bone, cartilage, and muscle. Oligopotent stem cells have the unique ability of self-renewal and forming two or more lineages within a specific tissue. Studies suggest that bronchoalveolar duct junction cells can produce bronchiolar epithelium and alveolar epithelium. The other category of stem cells that researchers have identified is unipotent cells. These cells can self-renew and differentiate into only one cell type. This implies that they can only form a single lineage for example the muscle stem cells that mature to give rise to mature muscle cells only (Kajstura, et al., 2011).
Researchers have also been able to classify cells based on origin. They have identified embryonic stem cells which are pluripotent and derived from the inner cells mass of the blastocyst. These cells are known to differentiate into tissues of three germ layers. They can also be maintained in an undifferentiated state for a long period in a culture. Adult stem cells have also been recently identified. This is contrary to what many researchers initially believed that stem cells could not be found in adults. Adult stem cells are extracted from adult tissues. These tissues have limited capacity to differentiate. Adult stem cells have a few advantages over embryonic stem cells because they are not rejected by the body and do not cause ethical controversies. Further studies on adult stem cells have revealed that if they are cultured they are able to secrete various molecular mediators with ant-apoptiotic, immunomodulatory, angiogenic, and chemoattractant properties known to promote repair of body tissues (By,2001). Tissues resident stem cells have been found to originate during ontogenesis and then remain in a quiescent state till local stimuli activate them to differentiate, proliferate or migrate. Tissue resident cells are critical in generation of tissue-specific, terminally differentiated cells. These stem cells reside in a microenvironment that controls their self renewal and differentiation. Most of these cells are dormant and are activated when an injury occurs or when tissues need repair. These cells need to be controlled because uncontrolled increase in stem cell proliferation can cause stem cell hyperplasia or carcinogenesis. Reduction in the stem cells can impair the tissues repair process. Researchers have also discovered induced pluripotent stem cells. These cells are generated from adult human dermal fibroblasts. Induced pluripotent stem cells have the same characteristics as human stem cells (Kolios & Moodley, 2012). The only difference is that human stem cells occur naturally while induced stem cells are induced.
Stem cells have extensive use in the restoration of human health. They have created myriad opportunities to further research on the human body and the healing process. Doctors have used stem cells to develop new therapeutic strategies to improve human health. Stem cells provide a valuable tool necessary to understand human development and organogenesis. There is still a lot that can be done in the use of stem cells in the medical field. These include setting up human models of diseases in order to understand the pathogenic mechanisms of human diseases. This will help in understanding the pathogenic mechanisms of human diseases and enable improvements in cell-based therapy for degenerative disorders. Immunorejection is an issue that still needs to be addressed for all stem cells to be efficiently used in medicine. There are also issues to do with genetic stability of stem cells especially the induced pluripotent stem cells (Conrad, et al., 2008). Their genetic stability is still to be resolved. Genetic instability causes tumor cells. Another issue that needs further research is overcoming carcinogenesis which results from plasticity and self-renewal. The ethical issue surrounding destruction of embryos is slowly being overcome through use of induced pluripotent stem cells. However, these induced stem cells are not yet fully adapted due to the few issues surrounding them. Further research is necessary to overcome their instability issues and use them extensively.
By, L. J. (2001, Aug 13). New findings point to huge potential of adult stem cells. Wall Street Journal.
Kolios, G., & Moodley, Y. (2012). Introduction to stem cells and regenerative medicine.
Conrad, S., Renninger, M., Hennenlotter, J., Wiesner, T., Just, L., Bonin, M., . . . Skutella, T. (2008). Generation of pluripotent stem cells from adult human testis. ., D’Amario, D., MD, Sanada, F., M.D., . . . Anversa, P., M.D. (2011). Evidence for human lung stem cells.