Stem cells: Types and use in medicine

In a nutshell

Stem cell research has grown and developed over recent years. Stem cells are unspecialised cells that can mature into any type of cell. This ability to differentiate has been manipulated for use in medicine. Stem cell therapy can be used to replace cells that have been damaged from disease or injury.

Stem cells

Definition

Stem cells are unspecialised cells that can differentiate into other cell types to become specialised.

Stem cell	Definition
Totipotent	Totipotent stem cells are only present in mammals during the first few cell divisions of an embryo. They can differentiate into any type of body cell, including placental cells.
Pluripotent	After the first few cell divisions, the embryonic stem cells become pluripotent. Pluripotent cells can differentiate into any type of body cell in an organism apart from placental cells.
Multipotent	Multipotent stem cells can differentiate into a few different types of cell.
Unipotent	Unipotent stem cells can only differentiate into one cell type.

Gene expression

Stem cells becomes specialised because of differential gene expression. This means that despite all stem cells containing the same genes, only a few are transcribed and translated. This is what allows them to become a certain cell type.

Example

A stem cell found in the bone marrow might express the genes that only white blood cells do. This means the stem cell will irreversibly differentiate into a white blood cell.

Cardiomyocytes

Cardiomyocytes are cells that make up muscle tissue in the heart. It was previously believed that our hearts could not regenerate and any damage was permanent. However, it is now believed that our hearts have their own supply of unipotent stem cells. This means old or damaged cardiomycytes can be replaced.

Stem cells in medicine

Existing stem cell therapies

Currently, stem cell therapies are used to treat some diseases. Stem cells are used to replaced diseased cells.

Example

Bone marrow transplants have been used to treat a type of blood cancer known as leukaemia. Transplanted bone marrow divides and differentiates into healthy blood cells.

Future stem cell therapies

There are many possible uses of stem cell therapies that are currently being explored by scientists.

Treatment	Use
Spinal cord injuries	Stem cells could replace damaged nerve tissue.
Heart damage	Stem cells could replace damaged heart tissue.
Bladder conditions	Whole bladders could be grown and implanted into patients.
Respiratory diseases	Windpipes that have been donated, can be stripped down to their simple collagen structure and then regenerated using tissue from stem cells. These can then be implanted into patients with respiratory diseases.
Organ transplants	Stem cells could be used to grow new organs that can be implanted into patients.

Benefits of stem cell therapies

Stem cell therapies could save many lives and do save many lives. People with leukaemia have a much better chance of survival after receiving a bone marrow transplant. Equally, stem cell therapies could improve the quality of life for many people.

Example

Future stem cell treatments may allow paralysed people to walk via the replacement of damaged tissues.

Stem cell sources

There are three main sources of human stem cells.

Source	Description
Adult stem cell	Adult stem cells are acquired from body tissues of an adult. They are relatively easy to obtain as they just require a simple surgical procedure. However, adult stem cells are multipotent so they cannot differentiate into many cell types.
Embryonic stem cell	Embryonic stem cells are derived from embryos that are $4$ - $5$ days old. They are acquired from the fertilisation of egg cells outside the uterus, this is known as in vitro fertilisation. Embryonic stem cells are pluripotent.
Induced pluripotent stem cell (iPS cells)	Induced pluripotent cells are derived from adult stem cells and are reprogrammed to behave like embryonic stem cells. They are made to express transcription factors that are typically expressed in pluripotent cells. This can be done using a specially modified virus that contains genes for these transcription factors. When the virus infects the cells, these genes are transcribed by the host.

Ethical issues

The use of embryonic stem cells has many ethical issues and this has led to many people disagreeing with their use. Obtaining stem cells from embryos leads to their destruction. Some people consider embryos life or potential life and therefore the destruction of them is seen as wrong.