What are stem cells?
Stem cells are unspecialised cells in the body that have two distinct properties:
- the ability to ‘self-renew’, or make more copies of themselves;
- to ‘differentiate’ or grow into different specialised cell types.
While all stem cells have these attributes, they can also be classified as either tissuestem cell or pluripotent stem cells.
Tissue stem cells
Tissue stem cells, sometimes also referred to as adult stem cells, reside in organs of the body and can usually only mature into a limited number of cell types usually found within the tissues of that organ. These stem cells are required for the normal function of that tissue. For example, blood stem cells that reside in bone marrow, will differentiate into blood cells, including red blood cells, white blood cells and platelet cells. Stem cells present in the lining of the gut, make replacement cells that keep the gut intact. Tissue stem cells are present in most organs of our body.
Pluripotent stem cells
Pluripotent stem cells have the ability to develop into any cell type in the body. Embryonic stem cells, obtained from donated IVF embryos, are pluripotent and were first type of isolated in the late 1990s. When given the right signals in the laboratory, these stem cells can give rise to large numbers of specific types of mature cells. For example, researchers can make beating heart muscle or red blood cells from embryonic stem cells. More recently, researchers have worked out how to make a similar type of pluripotent stem cell from a donated body cell. By changing the pattern of genes being expressed, researchers can induce a mature body cell to change back to a more primitive, pluripotent stem cells. This type of stem cell is called induced pluripotent stem cell (iPSC) and can be coaxed to form specific types of mature cells in the laboratory. Importantly, by taking a cell from a patient with a particular disease, such as motor neuron disease, and making iPSCs, researchers can now study how the disease develops in the laboratory and even test possible new drugs.
Using stem cells in research and in the clinic
Human stem cells are used extensively by researchers to understand how we develop, what goes awry during disease and ageing, and as a source of cells to treat patients. Researchers are also starting to evaluate whether stem cells, or cells made from stem cells, can help patients suffering from certain conditions. Different sources of stem cells are used depending on the question the researchers are trying to answer.
For example, pluripotent stem cells are being used in laboratory research to grow organoids (mini-organs) that mimic how organs develop and can be used to test potential drugs to see if they work or even harm the cells. Other researchers are interested in understanding more about how tissue stem cells work (so called endogenous stem cells) with a view to seeing if they could be employed to replace those cells damaged in an organ as result of illness or disease. Others are looking to see if they can develop more sophisticated structures on which to grow stem cells. Researchers are also exploring whether we can use stem cells, and the knowledge we have gained from studying them, to design cells to act as living instruments that could give real-time read outs on our health or deliver much needed drugs on demand.
Although doctors do already use blood stem cells from the bone marrow or cord blood to treat conditions that affect the blood and immune system – like leukaemia – there are at present few other proven stem cell treatments. Skin and corneal grafting (which rely on stem cells within the graft to heal the patient) are other examples of where stem cells contribute to medical care. However, all other applications remain at the research stage of their development and the subject of clinical trials to test if they are safe and effective. Media reports and marketing claims posted on websites may give a false impression on how close we are to delivering new stem cell-based treatments.
Clinical trials are used to test new interventions in humans. While the interventions offered to patients in approved clinical trials are experimental, they have undergone extensive safety and efficacy tests, usually in animal models, as well as a full review by an independent ethics committee. Patients in properly conducted clinical trials are informed about the possible outcomes and risks involved in participation, are not usually asked to pay to participate, and must give informed consent prior to becoming part of the trial.
Visit Australian Clinical Trials website to find out more.
Stem cell therapies
Treatments that use stem cells, or cells derived from stem cells, are called stem cell therapies. Stem cell therapies work by replacing or repairing damaged cells or tissues in the body through either injecting the cells into the bloodstream, or directly transplanting them into the damaged tissues. Stem cells can also be recruited from the patient’s own cells for self-repair.
Stem cell science holds great potential for treatments for injury or disease. While media reports often suggest that stem cell therapies are already available for a wide range of conditions, the reality is that further research is required to develop safe and effective treatments. Currently, the only proven stem cell therapies use blood stem cells for blood and certain immune disorders. The majority of therapies are still in early stages of research and development.