What if I tell you there is a way to regrow or replace your body organs? What if you could regrow an amputated limb or generate damaged nerve cells? How about if I tell you there are treatments that would possibly cure cancer, diabetes, cardiovascular disease, spinal cord injuries, and many other disorders? Sounds like science fiction. How can we regrow an organ back if we lost one? But you have probably heard there are animals which can regrow parts of their body such as starfish, salamanders or cockroaches. Axolotl (Ambystoma mexicanum) known as the Mexican walking fish is an amphibian that can regenerate their eyes, limbs, spinal cord, skin, tail, and jaw. They use stem cells to regenerate those damaged organs.
Figure 01: Axolotl, species of salamander (Ambistoma mexicanum)Figure 02: Starfish, class of echinoderms (Fromia monilis)
What are Stem Cells?
One can say stem cells are the beginning of all life on Earth. Stem cells are found in all of us. We can identify different types of stem cells that are used for research. These are unique among other cells because of the following two reasons.
Self-renewing ability:The ability to produce more stem cells that are identical to the parent cell.
Differentiation:Stem cells have the ability to differentiate into any type of cell in the three germ layers which are endoderm, mesoderm, and ectoderm. Simply meaning that the stem cells can become any kind of cell in your body according to their cell potency.
Figure 03: Characteristics of Stem Cells
These two main properties of stem cells have given the way for scientists to find medical treatments to cure disorders regarding damaged, dead, or lost cells.
Types of Stem Cells we can Identify
01. Human Embryonic Stem cells (hESCs): They are derived from the inner cell mass of the blastocyst (human embryo reaches the blastocyst stage 4-5 days after fertilization). These cells are pluripotent cells as they have the ability to differentiate into any kind of cell type in the body.
Figure 04: Embryonic stem cells under a microscope
02. Cord blood stem cells: Cord blood stem cells can be obtained from the umbilical cord at birth. They can also make several cell types but not all the cell types of the body. They can be specialized into cell types found in blood and the cells in the immune system. These cells are been used to treat children with blood cancers like leukemia, sickle cell anemia, and genetic blood disorders.
Figure 05: Dylan Perkins was diagnosed with Acute Lymphocytic Leukemia at 8 weeks old. He received a cord blood transplant at 6 months old. Now his cancer is in remission.
03. Adult stem cells: Also known as somatic stem cells. These are undifferentiated stem cells that are found in the body’s mature tissues. They can make only the cells in the tissue in which they reside.
04. iPS cells: Induced Pluripotent Stem Cells are those that are artificially produced by reprogramming the skin or blood cells of the body into an embryonic cell state. This groundbreaking discovery was regenerated by Professor Shinya Yamanaka and his team in 2006. In 2012 Shinya Yamanaka and another researcher John B. Gurdon have been awarded the Nobel Prize in ‘Physiology or Medicine’ for this marvelous discovery.
Figure 06: Japanese stem cell researcher, Prof. Shinya YamanakaFigure 07: Shinya Yamanaka receiving the Nobel Prize, 10th December, 2012
Figure 08: Human iPS cell colonies
05. SCNT stem cells (Somatic Cell Nuclear Transferstem cells): SCNT is a method used to generate embryonic stem cells. SCNT stem cells are generated by removing the nucleus of an egg cell and replacing it with a nucleus of an adult cell. These are used for stem cell research purposes.
Cell Potency
The ability of cells to differentiate into other types of cells is known as cell potency. Stem cells can be divided into more areas according to the cell potency.
Totipotent: This type of cell has the highest potency as the prefix “Toti” defines wholly or entirely. They have the capacity to differentiate into any cell type of the body and capable of generating an entire organism. E.g. zygote is considered totipotent.
Pluripotent: These are also undifferentiated stem cells (pluri- prefix meaning many, several) that have the ability to differentiate into any cell type of the body. E.g. Human embryonic stem cells, iPS cells
Multipotent: Potency is relatively low than the above two units. These are considered partially differentiated stem cells. They can make a limited number of cell types within a particular cell lineage. E.g. Adult stem cells, cord blood cells
Unipotent: Prefix “uni-” meaning one, this type can differentiate into only one cell type.
Figure 09: Lineage restriction of human developmental potency
Applications of Stem Cells in Medicine
They can be used to understand the development of organisms. If we could understand how stem cells differentiate and specialize in various other cells, we may able to treat fatal medical conditions such as cancers and birth defects. Scientists are still researching this field. We can consider this as a goal in stem cell research.
Being used to replace damaged cells and treat various diseases is of importance here. We can already see this in medicine. As mentioned earlier, patients with Leukemia are treated using cord blood stem cells. In the situations like extensive burns as well, we can replace damaged cells.
They can be used to study diseases. It is not always possible to study some diseases for various reasons. Stem cells can be used as models to study diseases in laboratories and possibly find cures.
They are also used in testing treatments for diseases. Scientists are using animal drug testing to find medicine for diseases. But that does not give 100% assurance about the capability of that drug. And in this process animals are harmed. We cannot use humans for drug testing either. But we can use stem cells to test new drugs or treatments in laboratories.
However, this area of science is still under research and there are controversies regarding the usage of stem cells for research because of ethical and political issues.
