Stem cell therapy has become a very promising and advanced scientific research topic. Stem cells are unspecialized cells of the human body. They are able to differentiate into any cell of an organism and have the ability of self-renewal. Stem cells exist both in embryos and adult cells. Stem cells are the body’s raw materials — cells from which all other cells with specialized functions are generated. Under the right conditions in the body or a laboratory, stem cells divide to form more cells called daughter cells.
These daughter cells either become new stem cells (self-renewal) or become specialized cells (differentiation) with a more specific function, such as blood cells, brain cells, heart muscle cells or bone cells. No other cell in the body has the natural ability to generate new cell types.
Sources of Stem Cells:
Embryonic stem cells.
These stem cells come from embryos that are three to five days old. At this stage, an embryo is called a blastocyst and has about 150 cells. These are pluripotent stem cells, meaning they can divide into more stem cells or can become any type of cell in the body. This allows embryonic stem cells to be used to regenerate or repair diseased tissue and organs.
The embryos being used in embryonic stem cell research come from eggs that were fertilized at in vitro fertilization clinics but never implanted in a woman’s uterus. The stem cells are donated with informed consent from donors. Most embryonic stem cells are developed from eggs that have been fertilized in an in vitro clinic, not from eggs fertilized in vivo. The stem cells can live and grow in special solutions in test tubes or petri dishes in laboratories.
Adult stem cells.
These stem cells are found in small numbers in most adult tissues, such as bone marrow or fat. Compared with embryonic stem cells, adult stem cells have a more limited ability to give rise to various cells of the body. The function of these cells is to enable the healing, growth, and replacement of cells that are lost each day.
Emerging evidence suggests that adult stem cells may be able to create various types of cells. For instance, bone marrow stem cells may be able to create bone or heart muscle cells. This research has led to early-stage clinical trials to test usefulness and safety in people. For example, adult stem cells are currently being tested in people with neurological or heart disease. The proliferation time of adult stem cells is longer than that of embryonic stem cell. It is possible to reprogram adult stem cells back to their pluripotent state. This can be performed by transferring the adult nucleus into
the cytoplasm of an oocyte (cell that form ovum) or by fusion with the pluripotent cell. The same technique was used during cloning of the famous Dolly sheep.
Adult cells altered to have properties of embryonic stem cells (induced pluripotent stem cells).
Scientists have successfully transformed regular adult cells into stem cells using genetic reprogramming. By altering the genes in the adult cells, researchers can reprogram the cells to act similarly to embryonic stem cells. This new technique may allow researchers to use reprogrammed cells instead of embryonic stem cells and prevent immune system rejection of the new stem cells. Because pluripotent cells can propagate indefinitely and differentiate into any kind of cell, they can be an unlimited source, either for replacing lost or diseased tissues. iPSCs bypass the need for embryos in stem cell therapy. Because they are made from the patient’s own cells, they are autologous and no longer generate any risk of immune rejection.
Researchers have been able to take regular connective tissue cells and reprogram them to become functional heart cells. In studies, animals with heart failure that were injected with new heart cells experienced improved heart function and survival time. One of the arguments that limit the use of iPSCs is their infamous role in tumourigenicity. There is a risk that the expression of oncogenes (cancer genes) may increase when cells are being reprogrammed.
Perinatal stem cells.
Researchers have discovered stem cells in amniotic fluid as well as umbilical cord blood. These stem cells also have the ability to change into specialized cells. Amniotic fluid fills the sac that surrounds and protects a developing fetus in the uterus. Researchers have identified stem cells in samples of amniotic fluid drawn from pregnant women to test for abnormalities — a procedure called amniocentesis. More study of amniotic fluid stem cells is needed to understand their potential.
The umbilical cord is known to be rich in mesenchymal stem cells. Due to its cryopreservation immediately after birth, its stem cells can be successfully stored and used in therapies to prevent the future life-threatening diseases of a given patient.
Stem cells also act as internal repair systems of the body. The replenishment and formation of new cells are unlimited as long as an organism is alive. Various functions and uses of stem cells are:
- grow new cells in a laboratory to replace damaged organs or tissues
- correct parts of organs that don’t work properly
- research causes of genetic defects in cells
- research how diseases occur or why certain cells develop into cancer cells
- test new drugs for safety and effectiveness- Researchers are also using differentiated stem cells to test the safety and effectiveness of new medications. Testing drugs on human stem cells eliminates the need to test them on animals.
If researchers can find a reliable way to direct the differentiation of embryonic stem cells, they may be able to use the cells to treat certain diseases. For example, by directing the embryonic stem cells to turn into insulin-producing cells, they may be able to transplant the cells into people with type 1 diabetes. The medical conditions that may potentially be treated with embryonic stem cells include:
- Traumatic spinal cord injury
- Severe burns and skin disorders
- Rheumatoid arthritis
- Osteonecrosis of femoral hip
- Tendon rupture
- Heart disease
- Hearing loss
- Retinal disease
- Huntington’s disease
- Parkinson’s disease
- Alzheimer’s disease
A detailed list of the disease programs and clinical trials currently underway in stem cell research. Examples of such projects include:
- injecting modified stem cells directly into the brain after a stroke
- using stem cells to replace damaged cells in the inner ear that detect sound, helping to restore hearing
- altering the genes of stem cells to make them resistant to diseases, such as AIDS, and then inserting them into people with the disease
- cultivating stem cells to repair the fragile bones of people with osteoporosis
Mechanism of Action:
Stem cell therapy, also known as regenerative medicine, promotes the repair response of diseased, dysfunctional or injured tissue using stem cells or their derivatives. It is the next chapter in organ transplantation and uses cells instead of donor organs, which are limited in supply.
Researchers grow stem cells in a lab. These stem cells are manipulated to specialize into specific types of cells, such as heart muscle cells, blood cells or nerve cells. The specialized cells can then be implanted into a person. For example, if the person has heart disease, the cells could be injected into the heart muscle. The healthy transplanted heart muscle cells could then contribute to repairing defective heart muscle.
Researchers have already shown that adult bone marrow cells guided to become heart-like cells can repair heart tissue in people, and more research is ongoing.
Stem Cell Controversy:
Adult stem cells don’t present any ethical problems. However, in recent years, there has been controversy surrounding the way human embryonic stem cells are obtained. During the process of harvesting embryotic stem cells, the embryo is destroyed. This raises ethical concerns for people who believe that the destruction of a fertilized embryo is morally wrong.
Opponents believe that an embryo is a living human being. They don’t think the fertilized eggs should be used for research. They argue that the embryo should have the same rights as every other human and that these rights should be protected.
Supporters of stem cell research, on the other hand, believe that the embryos are not yet humans. They note that researchers receive consent from the donor couple whose eggs and sperm were used to create the embryo. Supporters also argue that the fertilized eggs created during in-vitro fertilization would be discarded anyway, so they might be put to better use for scientific research.
With the breakthrough discovery of induced pluripotent stem cell (iPSCs), there may be less of a need for human embryos in research. This may help ease the concerns of those who are against using embryos for medical research. However, if iPSCs have the potential to develop into a human embryo, researchers could theoretically create a clone of the donor. This presents another ethical issue to take into consideration. Many countries already have legislation in place that effectively bans human cloning.
Stem cells have great potential to become one of the most important aspects of medicine. In addition to the fact that they play a large role in developing restorative (regenerative) medicine, their study reveals much information about the complex events that happen during human development. Stem cell research can further help in better understanding stem cell physiology. This may result in finding new ways of treating currently incurable diseases.