Researchers Grow Stem Cells in a Laboratory. These stem cells are manipulated to specialize in specific types of cells, such as heart muscle cells, blood cells, or nerve cells. Specialized cells can be implanted into a person. Doctors now routinely use adult hematopoietic stem cells to treat diseases, such as leukemia, sickle cell disease, and other immunodeficiency problems.
At this time, the most commonly used stem cell-based therapy is bone marrow transplantation. Blood-forming stem cells in bone marrow were the first stem cells identified and were the first to be used in the clinic. This life-saving technique has helped thousands of people around the world who had had blood cancers, such as leukemia. In addition to their current use in cancer treatments, research suggests that bone marrow transplants will be useful in treating autoimmune diseases and helping people tolerate transplanted organs.
Other adult stem cell-based therapies are currently in clinical trials. Until those trials are completed, we will not know which type of stem cell is most effective in treating different diseases. The general designation “stem cell” covers many different cell types. Commonly, “embryonic” and “adult” modifiers are used to distinguish stem cells by the developmental stage of the animal they come from, but these terms are becoming insufficient as new research has discovered how to convert fully differentiated adult cells back into stem cells embryonic and, conversely, adult stem cells, more correctly referred to as “somatic stem cells”, which means “from the body”, are found in the fetus, placenta, cord blood and infants.
2 Therefore, this review will classify stem cells into two categories according to their biological properties: pluripotent stem cells and multipotent stem cells. Its sources, characteristics, differentiation and therapeutic applications are discussed. During the natural development of the embryo, cells undergo proliferation and specialization from the fertilized egg to the blastocyst and the gastula during the natural development of the embryo (left side of the panel). Pluripotent embryonic stem cells are derived from the inner cell mass of the blastocyst (shaded slightly).
Multipotent stem cells (rhomboid pattern, diagonal lines and darker hue) are found in the developing gastula or are derived from pluripotent stem cells and are restricted to give rise only to cells of their respective germ layer. The pluripotent stem cells used in current research come mainly from embryos, hence the name “embryonic stem cells”. Pre-implanted embryos a few days old contain only 10-15% pluripotent cells in the “inner cell mass” (Figure. Those pluripotent cells can be isolated and then cultured in a layer of “feeder cells” that provide unknown signals for many rounds of proliferation, while maintaining their pluripotency.
Multipotent stem cells may be a viable option for clinical use. These cells have the plasticity to become all progenitor cells of a particular germ layer or can be restricted to become only one or two types of specialized cells of a particular tissue. Multipotent stem cells with the highest differentiation potential are found in the developing embryo during gastrulation (days 14-15 in humans, day 6.5-7 in mice). These cells give rise to all the cells of their particular germ layer, so they still have flexibility in their ability to differentiate.
They are not pluripotent stem cells because they have lost the ability to become cells of the three germ layers (Figure. At the lower end of the plasticity spectrum are unipotent cells that can become a single specialized cell type, such as skin stem cells or muscle stem cells. These stem cells are typically found within their organ and, although their ability to differentiate is restricted, these limited progenitor cells play a vital role in maintaining tissue integrity by replenishing aging or injured cells. There are many other subtypes of multipotent stem cells that occupy a range of differentiation capacities.
For example, multipotent cells derived from the mesoderm of the gastrula undergo a differentiation step that limits them to muscle and connective tissue; however, greater differentiation results in greater specialization only towards connective tissue and so on until cells can give rise only to cartilage or just bone. Pluripotent stem cells have not yet been used therapeutically in humans because many of the early animal studies resulted in the undesirable formation of unusual solid tumors, called teratomas. Teratomas are composed of a mixture of cell types from all early germ layers. Subsequent successful animal studies used pluripotent cells modified to a more mature phenotype, limiting this proliferative capacity.
Cells derived from pluripotent cells have been used to successfully treat animals. For example, animals with diabetes have been treated by creating insulin-producing cells that respond to glucose levels. In addition, animals with acute spinal cord injury or visual impairment have been treated by creating new myelinated neurons or retinal epithelial cells, respectively. Commercial companies are currently negotiating with the FDA on the possibility of advancing to human trials.
Other animal studies have been conducted to treat several diseases, such as Parkinson's disease, muscular dystrophy and heart failure, 18,22,23 Promises of stem cell cures for human ailments have been highly promoted, but many obstacles still need to be overcome. First, more research on human pluripotent and multipotent cells is needed, since stem cell biology differs in mice and men. Second, the common characteristic of unlimited cell division shared by cancer cells and pluripotent stem cells should be better understood to prevent cancer formation. Thirdly, one must master the ability to acquire large quantities of the right cells at the right stage of differentiation.
Fourth, specific protocols should be developed to improve the production, survival and integration of transplanted cells. Finally, clinical trials must be completed to ensure the safety and effectiveness of stem cell therapy. When it comes to stem cells, knowing that they exist is far from using them therapeutically. A stem cell is a cell with the unique ability to become specialized cell types in the body.
In the future, they can be used to replace cells and tissues that have been damaged or lost due to disease. Stem cells are the basis of all organs and tissues in the body. There are many different types of stem cells that come from different places in the body or form at different times in our lives. These include embryonic stem cells that exist only in the early stages of development, and various types of tissue-specific stem cells (or adults) that appear during fetal development and remain in our body throughout life.
Embryonic stem cells are obtained from the inner cell mass of the blastocyst, a mainly hollow ball of cells that, in humans, forms three to five days after an egg is fertilized by a sperm cell. A human blastocyst is approximately the size of the spot above this “i”. In normal development, cells within the inner cell mass will give rise to the most specialized cells that give rise to the entire body, all our tissues and organs. However, when scientists extract the inner cell mass and grow them under special laboratory conditions, they retain the properties of embryonic stem cells.
Embryonic stem cells are pluripotent, meaning they can give rise to all types of cells in the fully formed body, but not to the placenta or umbilical cord. These cells are incredibly valuable because they provide a renewable resource for studying normal development and disease, and for testing drugs and other therapies. Human embryonic stem cells have been derived mainly from blastocysts created by in vitro fertilization (IVF) for assisted reproduction that were no longer needed. Tissue-specific stem cells (also called somatic or adult stem cells) are more specialized than embryonic stem cells.
Usually, these stem cells can generate different types of cells for the specific tissue or organ in which they live. Some tissues and organs in the body contain small deposits of tissue-specific stem cells whose function is to replace cells in that tissue that are lost in normal daily life or in injuries, such as those in the skin, blood, and lining of the intestine. Tissue-specific stem cells can be difficult to find in the human body, and they don't seem to self-renew in culture as easily as embryonic stem cells do. However, the study of these cells has increased our general knowledge about normal development, changes in aging, and what happens with injuries and diseases.
Induced pluripotent stem (iPS) cells are cells that have been designed in the laboratory by converting tissue-specific cells, such as skin cells, into cells that behave like embryonic stem cells. IPS cells are critical tools to help scientists learn more about normal development and the onset and progression of disease, and are also useful for developing and testing new drugs and therapies. While iPS cells share many of the same characteristics as embryonic stem cells, including the ability to give rise to all types of cells in the body, they are not exactly the same. Scientists are exploring what these differences are and what they mean.
On the one hand, the first iPS cells were produced by using viruses to insert additional copies of genes into tissue-specific cells. Researchers are experimenting with many alternative ways to create iPS cells so that they can ultimately be used as a source of cells or tissues for medical treatments. iPSCs derived from stem cells and adult tissues have great potential for regenerative medicine and disease therapy. This does not result in differentiated progeny, but it does increase the pool of stem cells from which specialized cells can develop in later divisions.
Human embryonic stem cell-derived cardiac myocyte patches may form a viable human myocardium after transplantation into animals24, and some show evidence of electrical integration. A number of MSCs are thought to have stem cell, and even immunomodulatory properties, and are being tested as treatments for many disorders, but there is little evidence to date that they are beneficial. Intravitreal injection of adipose-derived stem cells (ADSC) into the eye restores the microvascular capillary bed in mice. Some people consider working with human embryonic stem cells to be ethically problematic, while very few people have reservations when it comes to working with mouse models.
Hematopoietic stem cells are found in the blood and bone marrow and can produce all types of blood cells, including red blood cells that carry oxygen and white blood cells that fight disease. The argument against the use of embryonic stem cells is that it destroys a human blastocyst and the fertilized egg cannot become a person. Also called somatic or tissue-specific stem cells, adult stem cells exist throughout the body from the moment the embryo develops. In addition to commercial cell therapy products, a multitude of cell therapies have been investigated to treat cancer in clinical settings.
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