Embryonic stem cells are pluripotent cells derived from a 3 to 5 day old human embryo. They have the unique potential to develop into one of over 200 other human cell types and can greatly improve our understanding of human development and disease.
Embryonic stem cells also have important uses in drug development and may one day be used to treat currently incurable conditions.
What are stem cells?
Stem cells are cells that have the potential to differentiate and produce other types of body cells. They are the basic materials from which all of the body’s own special cells are made during whole-body development and are used in adulthood to maintain and repair body tissue. There are two types of human stem cells, embryonic stem cells and adult stem cells.
What are embryonic stem cells?
Embryonic stem cells (ESCs) are stem cells obtained from a 3 to 5 day old human embryo (AKA a Blastocyst). ESCs are pluripotent, This means that they have the potential to become one of the more than 200 types of cells found in the human body. As the embryo develops, the ESCs and divide distinguish to form the complete complement of human body cells, which are necessary for healthy function.
The first differentiation event in human embryos begins about 5 days after fertilization. Therefore, ESC must be harvested before this time if they are to be used in medicine and research. At this early stage of development, the cells of the embryo form an undifferentiated mass and have not yet assumed the properties or functions of specialized adult cells.
The importance of embryonic stem cells
The ability of ESCs to evolve into all other types of human cells makes them an invaluable research tool. Studies with ESC can improve our understanding of human development, disease treatment, and drug effectiveness.
ESCs can be bred (or cultivated) in a laboratory. Under the right conditions, stem cells grow and divide indefinitely without differentiating. However, they retain their ability to differentiate, making ESC culture a convenient and renewable reservoir of human cells. When used in research, ECS are converted into their desired cell types by manipulating the culture conditions.
Use for embryonic stem cells
Scientists can use stem cells to advance their understanding of human development and disease. By studying embryonic stem cells, the researchers want to find out how they differentiate into tissues and organs, how diseases and conditions develop in these tissues, and how age affects their function.
Scientists can also use ESCs to test and develop new drugs and to identify new potential therapies for diseases such as Parkinson’s, heart failure, and spinal cord injuries.
Treatment of diseases
ESCs have enormous potential in the development of restorative or regenerative Medicine that replaces damaged tissue with healthy ones. Several stem cell therapies are currently available and could be used to treat a wide variety of injuries and diseases. These include spinal cord injuries, retinal and macular degeneration, heart failure, type 1 diabetes, and tendon rupture.
However, research into the use of ESCs in regenerative medicine is ongoing and a better understanding is needed before modern medicine can reach its full potential. In the future, the scientists hope that stem cell therapies can be used to treat diseases that are currently incurable or difficult to treat, such as AIDS or certain types of cancer.
Currently, the most common stem cell therapy is multipotent hematopoietic stem cell (HSC) transplantation. This treatment involves the transplant of hematopoietic (or blood) Stem cells and is commonly used to treat blood cell disorders such as leukemia and anemia.
ESCs can also be used in the development of new drugs that need to be tested on living tissues to determine their effectiveness and possible side effects.
Stem cells grown in the laboratory can be stimulated to differentiate into any type of human tissue. Hence, they are commonly used in preclinical drug trials. Once the potential and risks of the new drug have been identified using stem cells, the treatment can be used in animal studies and ultimately human clinical trials.
The ethical controversy surrounding ESCs
The discovery of ESCs has led to numerous breakthroughs in medical research, and their potential as the basis for new therapies and drugs is enormous. However, there is ethical controversy surrounding the use of ESCs in research, mainly because harvesting these cells destroys a human embryo.
For those who believe that life begins at conception, this raises moral objections. Opponents of stem cell research believe that embryos have the same rights as everyone else and should not be disposed of in the name of science.
Those who support the use of ESCs in medical research could argue that the embryos are not yet considered human as they are destroyed at very early stages of development. ESCs are harvested around day 5 of development, when the embryo (or blastocyst) is nothing more than a mass of undifferentiated cells.
Embryos used as a source for ESCs are often obtained from IVF clinics where they have been frozen after fertilization. Guidelines created by the National Institute of Health state that embryos can only be used for this purpose when they are no longer needed (that is, they are never implanted in a woman’s uterus). Such embryos would eventually be thrown away anyway, so it can be argued that they would be better used to advance medical research.
What are adult stem cells?
Adult stem cells (AKA somatic Stem cells are stem cells found in most adult tissues.
They can develop into other cell types, but unlike ESCs, they cannot pluripotent (can develop into any other cell type). Adult stem cells are either multipotent (able to develop into a limited number of closely related cells) or unipotent (able to develop into only one type of cell).
Their main function is to maintain and repair the tissues in which they reside and to replace cells that die from injury or disease.
Examples of adult stem cells
Mesenchymal stem cells
Mesenchymal stem cells are found in many adult tissues, including the umbilical cord, bone marrow, and adipose tissue. In the bone marrow, mesenchymal stem cells differentiate into bone, cartilage and fat cells.
Neural stem cells
Neural stem cells are located in the brain and develop into nerve cells and their supporting cells (glial Cells).
Hematopoietic stem cells
Hematopoietic stem cells are found in the bone marrow and peripheral blood. They lead to all types of blood cells, including red blood cells, white blood cells, and platelets.
Skin stem cells
Skin stem cells are located in the base layer of the epidermis and form keratinocytes for the continuous regeneration of the epidermal layers.