Stem Cells
What are stem cells?
Stem cells are the foundational cells of the human body, giving rise to all other cell types, such as blood cells, nerve cells, and more. They serve as the “originators” of new human cells and coordinate the various cell populations within the human body.
During early human development, a fertilised egg undergoes division, yielding embryonic stem cells, which subsequently specialise into various cell types to construct a fully developed human being. Furthermore, these versatile stem cells migrate to different regions of the body to facilitate tissue repair and regeneration, particularly in response to trauma or injury. Nevertheless, as humans age, the quantity of stem cells in the body gradually diminishes, contributing to the ageing process.
Properties of Stem Cells
- Self-renewal – The capacity to undergo numerous rounds of cell division while retaining an undifferentiated state.
- Multipotency – The capability to generate various types of cells.
Classification of Stem Cells
- Stem cells are categorised based on their differentiation potential into four types:
- Totipotent stem cells
These stem cells have the remarkable ability to give rise to all the cell types found in a complete organism.
- Pluripotent stem cells
Pluripotent stem cells, such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), possess the potential to differentiate into a wide range of cell types and tissues.
- Multipotent stem cells
Multipotent stem cells, including hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs), are capable of both proliferating and differentiating into multiple tissue types.
- Unipotent stem cells
Unipotent stem cells are more specialised, as they can only differentiate into one or a few closely related cell types, such as epithelial tissue cells.
- Totipotent stem cells
These classifications are based on the extent of the stem cells’ differentiation capabilities.
- Stem cells can also be classified based on their developmental stage into two categories:
- Embryonic Stem Cells
These stem cells are derived from the inner cells of a blastocyst, and they are highly undifferentiated. They have the remarkable potential to differentiate into various types of cells, tissues, and even organs within the human body. Their applications in regenerative medicine hold significant promise for developing therapies and treating diseases. However, research involving human embryonic stem cells often gives rise to ethical, religious, and legal debates, leading many countries and regions to impose restrictions or prohibit such research.
- Adult Stem Cells
Adult stem cells, including neural stem cells, hematopoietic stem cells, mesenchymal stem cells, and epidermal stem cells, are undifferentiated cells found throughout the body. These cells possess the capacity to repair and regenerate damaged or ageing tissues. They are crucial in maintaining and repairing the body’s various cell types and tissues.
- Embryonic Stem Cells
Adult stem cells can be categorised into two primary groups:
- Hematopoietic Stem Cells (HSCs)
These versatile cells can be sourced from bone marrow, umbilical cord blood, and adult peripheral blood. HSCs have the remarkable ability to differentiate into red blood cells, white blood cells, and platelets. They find valuable applications in cellular therapy for blood-related disorders, including blood cancers (marrow and umbilical cord blood transplantation) and conditions like thalassemia.
- Mesenchymal Stem Cells (MSCs)
MSCs are present in various tissues, including the umbilical cord, bone marrow, fat, and dental pulp. They play a crucial role in regenerating and repairing cells and tissues in the nervous system, heart, liver, lungs, kidneys, bones, and other organs. MSCs have shown effectiveness in treating conditions such as spinal cord injuries, cirrhosis, strokes, arthritis, dementia, and more. Furthermore, they are widely utilised in anti-ageing and health-related treatments.