Types of Stem Cells | What are Stem Cells, Properties, and Cell Therapy

In this article, we will read about What are stem cells, the different types of stem cells, their properties, and Cell Therapy. So let’s get started…

What are Stem Cells?

Stem cells can be defined as the cells in multicellular organisms, that are undifferentiated or partially differentiated. They can differentiate and form different types of cells. These are the earliest cell of cell lineage.

Properties of Stem Cells

The stem cells possess two properties that are described below:-

• Self-renewal

• Potency

SELF-RENEWAL STEM CELLS

It can be described as the ability of a cell to undergo multiple cycles of cell division and cell growth. During the cell division and growth, it maintains its undifferentiated state. Two mechanisms have been involved that help in maintaining the population of the stem cells.

The mechanisms are described below:-

• ASYMMETRIC CELL DIVISION:  During cell division the stem cell produces two types of cells. One cell is exactly like the original stem cell and is known as the mother cell. The mother cell will again undergo division same as the stem cell. The other cell that is formed is daughter cell and it undergoes differentiation.

• STOCHASTIC DIFFERENTIATION: The two cells that are formed during the asymmetric division have different fate. When one stem grows and differentiate further and form two different daughter cells, the other stem cells divide by mitosis and form two stem cells that are identical to the original. For extending the limit of cell division the stem cells uses telomerase enzyme that is responsible for restoring telomeres and protecting DNA from degradation. This lead to extension in the limit of cell division.

POTENCY OF STEM CELLS

It can be defined as the capacity of a cell to differentiate into specialized cell types. In simple terms, it can be explained as the ability of a cell to form different types of cells. Cells have different potentials for generating different cells. Stem cells need to be either totipotent or pluripotent. But few cells that are multipotent and unipotent are also considered stem cells.

On the basis of potency, the stem cells can be of different types that are mentioned under:-

• TOTIPOTENT: The totipotent cells can produce embryonic as well as extra-embryonic cell types. These are also known as the omnipotent stem cells because they have potential to form all type of cells and are capable of forming the whole viable organism. The totipotent cell is produced by the fusion of sperm and egg. After initial stage of cell division in fertilized egg, the cells are totipotent.

• PLEURIPOTENT: The totipotent cells are the descendants of the totipotent cells. The can produce all type of cells except the extra-embryonic cells. E.g. Inner cell mass (ICM) of embryo

• MULTIPOTENT: These cells can produce number of cells but these cells need to be of close and related families. E.g. Hematopoietic stem cells (HSCs) that form the different types of blood cells.

• UNIPOTENT:These cells can produce only one cell type, their own. They are responsible for their self-renewal.

Different types of Stem Cells (reference: Novus biologicals)

EMBRYONIC STEM CELLS(ESCs)

• These are the stem cells that are derived from the inner cell mass of the blastocyst which is formed at an early stage of development after 4-5 days of fertilization.

• These cells are pluripotent.

• They have the ability to self-renew themselves.

• They divide frequently as they have shortened the G1 phase in their cell cycle.

• Currently, the studies are focusing on the ability of these cells for therapeutic purpose.

• They can be used in tissue engineering, cell replacement therapies, drug discovery, etc.

FETAL STEM CELLS

These are the stem cells that are located in the organs of foetuses.

There are two types of fetal stem cells:-

Proper fetal stem cells: These are the cells that come from the organs of foetus proper and are obtained after the abortion of a foetus. They are multipotent, immortal, and have a high level of division.

Extra embryonic fetal stem cells: These are obtained from the extraembryonic membranes and cannot be differentiated from the adult stem cells. They are acquired after the birth of a fully developed foetus. They are not immortal but they show a high level of cell division.

MESENCHYMAL STEM CELLS (MSC)

• MSC are the multipotent cells that are found in adult tissues such as muscle, liver, and bone marrow.

• They provide structural support to various organs such as muscle, liver, bone marrow.

• Mesenchymal stem cells are also responsible for controlling the movement of substances.

• They can differentiate into numerous cells that are derived from mesodermal layer.

• It plays important role in regenerative medicine.

• They can be easily isolated and have high yield and plasticity ( can develop into different tissues).

• MSC are heterogeneous, and they express a high level of pluripotent markers when compared to other types of stem cells, such as embryonic stem cells.

ADULT STEM CELLS

• Adult stem cells are also known as somatic stem cells.

• They are responsible for maintaining and repairing the tissue in which they are found.

• They are found in all individuals.

• There are three sources of adult stem cells: Bone marrow (found in pelvic bones), adipose tissue (fat cells), and blood.

•  They can also be taken from the umbilical cord just after the birth of a child.

• Bone marrow is the richest source of adult stem cells. These are used in treating many medical conditions such as liver cirrhosis, chronic limb ischemia, and heart failure.

• Bone marrow stem cells decline with increasing age and their number is greater in males as compared to females during reproductive years.

• Most of the stem cells are lineage-restricted i.e. they are multipotent.

• Adult stem cells are named on the basis of their tissue origin such as mesenchymal stem cell, adipose-derived stem cell, endothelial stem cell, a dental pulp stem cell.

• Muse cells (multi-lineage differentiating stress enduring cells) are a recently discovered pluripotent stem cell type found in multiple adult tissues, including adipose, dermal fibroblasts, and bone marrow.

• Adult stem cells are used for treating leukemia and related bone or blood cancer through bone marrow transplants process. They are also used for treating tendon and ligament injuries in horses.

• There is no risk of rejection while using adult cells.

AMNIOTIC STEM CELLS

• These cells are also known as perinatal stem cells.

• They are found in amniotic fluid and blood of the umbilical cord.

• These cells are very active and expand in high numbers.

• These cells are not tumorigenic.

• They have a multipotent nature.

• They can differentiate in cells of different lineage such as adipogenic, osteogenic, myogenic, endothelial, hepatic, and neuronal.

INDUCED PLURIPOTENT STEM CELLS

• These cells are fully differentiated cells that are reprogrammed back into an embryonic- like pleuripotent state.

• They are derived from skin or blood cells.

• It allow for the development of an unlimited source of any type of human cells that are needed for the therapeutic purposes.

• They can be used for treating diabetes by differentiating into beta islet cells or blood cells to create new blood that is free from cancer cells or neurons for treating a neurological disorder.

• The first induced pluripotent cell was created by a BSCRC team in 2007. The team members were Kathrin Plath, William Lowry, Amander Clark and April Pyle.

• These cells have become foundation for a new regenerative medicine.

WHAT IS STEM CELL THERAPY?

Stem cell therapy can be described as a medical treatment in which the stem cells are used for treating or preventing a disease or condition.

Bone marrow transplant is a type of stem cell therapy that is effective in clinical trials and is being used for many years.

As all therapies have some advantages and disadvantages the stem cell therapy also has its advantages and disadvantages which are mentioned under:

Advantages of Stem Cell Therapy

• Treatment with stem cells can lower the symptoms of disease or condition that is being treated.

• As the symptoms are lowered it allows patients to reduce the intake of drugs for the disease.

• The treatment can also provide knowledge and understanding of stem cells for future treatment.

• It is an autologous treatment as the stem cells that are used for treatment come from the body of the patient and there is less or no risk of rejection.

 

Disadvantages of Stem Cell Therapy

• The treatment of stem cells may require immunosuppression because there is a requirement of radiation before the transplant to remove previous cells of the patient or because the immune system of the patient may target the stem cells. To avoid the risk of rejected stem cells are used from the patient that is being treated.

• With some stem cells, it becomes difficult to obtain a specific cell type as the cells are pluripotent. It becomes difficult to obtain the desired cell type.

• Some stem cells can also form tumors after transplantation.

• The use of embryonic stem cells for research and medical purpose has been under ethical concerns. When the cells are harvested from the blastocyst it results in the death of the blastocyst. The debate is ongoing whether the blastocyst should be considered as human life or not.

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