Well, the more they are studied the more they tell us about how our body functions in normal and diseased states, showing amazing potential in a therapeutic sense. In the US, 2009 and 2010 saw the first use of human embryonic stem cells in clinical trials, but they were turned into neural support cells before they were implanted in spinal cord injury patients. This research was performed on animal models first to ensure its safety, and stands as a landmark in stem cell therapy. Currently, this is largely how such therapies are developing; taking an embryonic stem cell and turning it into a more committed cell type that can then be implanted.
Other notions of directly injecting embryonic stem cells into patients to treat disease and degeneration are a premature and scary thought, putting patients at high risk of cancer, and thankfully are not allowed in most countries. As stem cell scientists, we don’t want to promise miracle cures, but we are very much aware of how they can help current strategies against many illnesses. For example, embryonic stem cells can divide forever and create two new cells each time. These divisions are tightly controlled, but cancer shows the same ability without the control. So, as you may see, learning what controls and restricts division improves our understanding of what goes wrong in a normal cell that allows it to switch to a cancerous state, and how we may set about stopping this. Some respected theories even suggest that cancer occurs when an adult stem cell loses control of its ability to replicate. Indeed, it appears that cancer is a natural part of life.
Of course, adult stem cells have been used for decades without being isolated, for example in bone marrow transplants for patients with leukeamia. Because the patient has reduced ability to make white blood cells, they cannot fight infection, so donor bone marrow replaces their own. In the new bone marrow exist adult stem cells – hematopoietic stem cells – that can make all the blood cells necessary to repopulate the body. In recent years, more and more funding has gone into studies on adult stem cells. The main reasons for this are because it does not require taking the early embryo, and bypasses a biological problem that embryonic stem cells have. If we were to take such a cell, and then inject it into another person – either as itself or a more restricted cell type – the human body would mount an immune reaction because it has molecules from a source that it cannot recognize. By manipulating the stem cells that are already within us, the body doesn’t have to cope with an immune reaction at the same time. Many of these studies, despite relatively early, provide a convincing approach towards new therapies, improve our understanding of how our bodies maintain themselves, what can go wrong, and possibly identify stem cell populations as new drug targets.
Mesenchymal stem cells are another type of adult stem cell taken from bone marrow, but another good source is fat tissue. It was found that they could be easily grown in culture, and have the ability to become a wide variety of cells. Due to their lack of ethical controversy, and ease in sourcing, they have become an integral part of tissue engineering and current regenerative therapies, for example there are clinical trials on patients with MS (multiple sclerosis) and coronary heart disease, and have been proved successful in many other diseases and injuries. This fact could mean that mesenchymal stem cells could soon be widely used, for a host of reasons, and in many places. Perhaps you will one day rely on a mesenchymal stem cell based therapy.
Induced pluripotent stem cells are also a new hope for regenerative therapy. These cells would be derived from the individual patient, and then directed into whatever cell types were necessary. Unfortunately, this process is still very inefficient and has a very long way to go before you see any science fiction like organs being transplanted back into us to replace our old ones! However, they do provide a way to generate tissues and systems that can be used as a model for an organ. With this, it is possible to use them to test new drugs and are potentially an alternative therapeutic strategy to embryonic stem cells. They do not stimulate the same intensity of ethical debate, and are currently being used by many labs to see whether they can aid in regeneration of different parts of the body and to understand more about cell fate decisions. Again, these studies can be thought of as preliminary, as scientists are still learning about their differences and problems that are encountered when using cells that have been forced to become stem cells.
This description has barely touched the surface of the research that is out there, but even so, it is obvious and amazing to see just how much power these cells hold and how our fate is inextricably linked with stem cells, both embryonic and adult. They are an essential part of our biological development, and hold key responsibilities in maintaining life. Understanding their influence on our biological world is the next step towards improving it, but Nature does not give up its secrets easily, and has a unique way of dangling the truth behind the smoke and mirrors.
Simple Steps to a Neuron – I.S.
Adult neural stem cell; must give rise to a neural progenitor before being committed to a neuron
Embryonic stem cell; must give rise to a neural progenitor before being committed to a neuron
Induced pluripotent stem cell; fibroblast must be turned into a pluripotent cell, which then needs to gives rise to a neural progenitor before being committed to a neuron
Immature neurons, or support cells, could be targeted (Adult NSC) or transplanted (ESC, IPS) to required regions of the central nervous system
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