Updated by: Jan Barfoot

It is not the news most people want to hear, but there are still only a few approved clinical uses of stem cell research. Some other applications of stem cells, for a range of conditions, are being investigated in clinical trials. A very large amount of research is ongoing globally.

    The most well-established and widely used stem cell treatment is the transplantation of blood stem cells to treat diseases and conditions of the blood and immune system, or to restore the blood system after treatments for specific cancers.

    Further, since the 1980s, skin stem cells have been used to grow skin grafts for patients with severe burns on very large areas of the body.

    A new stem-cell-based treatment to repair damage to the cornea (the surface of the eye) after an injury like a chemical burn has recently received marketing approval in Europe.

    Currently, these are the only stem cell therapies that have been thoroughly established as safe and effective treatments.

    Some other applications of stem cells, for a range of conditions, are being investigated in clinical trials. It is still too early to know whether any of these applications will work. We need the evidence gathered through a clinical trial process to determine whether a proposed treatment is safe, effective AND better than existing treatments.

    There are several ongoing or completed clinical trials involving pluripotent stem cells. The main areas of progress are highlighted below:

    The following list highlights progress in new, ongoing or completed clinical trials involving tissue stem cells.

    It is worth noting that there are numerous other clinical trials (not listed here) aimed at

    • testing specific drugs to stimulate stem cells in the patient’s own body
    • deriving cells or cell lines to be used in research and clinical trials

    Despite an enormous amount of research being undertaken there are still disappointingly few new safe and effective treatments available to patients. There is high expectation on stem cell research but not yet high delivery of stem cell treatments. Partly this is because complex diseases which are currently incurable require complex treatments (often with a personalised aspect).

    As with any breakthrough technology, all treatments should be considered experimental until they have successfully passed the stages of clinical trials required to demonstrate safety and clinical benefit. Only then can a treatment be approved for widespread use.

    Stem cell treatments are all specialist procedures. They should be performed only in specialized centres authorized by national health authorities. Some advertise so-called stem cell products that have not been through rigorous national and european regulatory approval and are not based on sound scientific rationale. Extreme caution is advised when paying for treatments in Europe or beyond.

    The most well-established and widely used stem cell treatment is the transplantation of blood stem cells to treat diseases and conditions of the blood and immune system, or to restore the blood system after treatments for specific cancers. The US National Marrow Donor Program has a full list of diseases treatable by blood stem cell transplant.  More than 26,000 patients are treated with blood stem cells in Europe each year.

    Since the 1980s, skin stem cells have been used to grow skin grafts for patients with severe burns on very large areas of the body. Only a few clinical centres are able to carry out this treatment and it is usually reserved for patients with life-threatening burns.

    A new stem-cell-based treatment to repair damage to the cornea (the surface of the eye) after an injury like a chemical burn, has received conditional marketing approval in Europe.

    Stem cell therapy using tissue stem cells has been in routine use since the 1970s! Bone marrow transplants are able to replace a patient’s diseased blood system for life, thanks to the properties of blood stem cells. Many thousands of patients benefit from this kind of treatment every year, although some do suffer from complications as with other organ transplants: the donor’s immune cells sometimes attack the patient’s tissues (graft-versus-host disease or GVHD) and there is a risk of infection during the treatment because the patient’s own bone marrow cells, and with them the patient’s immune system, have to be killed with chemotherapy before the transplant can take place.

    Skin stem cells have been used since the 1980s to grow sheets of new skin in the lab for severe burn patients. However, the new skin has no hair follicles, sweat glands or sebaceous (oil) glands, so the technique is far from perfect and further research is needed to improve it. Currently, the technique is mainly used to save the lives of patients who have third degree burns over very large areas of their bodies and is only carried out in a few clinical centres.

    Cord blood stem cells can be harvested from the umbilical cord of a baby after birth. The cells can be frozen (‘cryopreserved’) in cell banks and are currently used to treat children with cancerous blood disorders such as leukaemia, as well as genetic blood diseases like Fanconi anaemia. Treatment of adults has been more challenging, due to the low cell number obtained from one umbilical cord. As such adult treatment requires a double unit cord blood transplantation (i.e. cord blood stem cells from two umbilical cords). And although one advantage of cord blood transplants is that they appear to be less likely to be rejected by the immune system than conventional bone marrow transplants, cord blood must still be matched to the patient to be successful. And even then an increased immune response in adult recipients might cause problems.

    So far, only blood diseases can be treated with cord blood stem cells. Although some studies have suggested cord blood may contain stem cells that can produce other types of specialised cells not related to the blood, none of this research has been confirmed.

    Mesenchymal stem cells (MSCs) are found in the bone marrow and are responsible for bone and cartilage repair. On top of that, they can also produce fat cells. Early research suggesting that MSCs could differentiate into many other cell types and that they could also be obtained from a wide variety of tissues other than bone marrow have not been confirmed. There is still considerable scientific debate surrounding the exact nature of the cells (which are also termed Mesenchymal stem cells) obtained from these other tissues.

    As of now, no treatments using mesenchymal stem cells are proven to be effective. There are, however, some clinical trials investigating the safety and effectiveness of MSC treatments for repairing bone or cartilage. Other trials are investigating whether MSCs might help repair blood vessel damage linked to heart attacks or diseases such as critical limb ischaemia, but it is not yet clear whether these treatments will be effective.

    Several other features of MSCs, such as their potential effect on immune responses in the body to reduce inflammation to help treat transplant rejection or autoimmune diseases are still under thorough investigation. It will take numerous studies to evaluate their therapeutic value in the future.

    Clinical studies in patients have shown that tissue stem cells taken from an area of the eye called the limbus can be used to repair damage to the cornea – the transparent layer at the front of the eye. If the cornea is severely damaged, for example by a chemical burn, limbal stem cells can be taken from the patient, multiplied in the lab and transplanted back onto the patient’s damaged eye(s) to restore sight. However, this can only help patients who have some undamaged limbal stem cells remaining in one of their eyes. The treatment has been shown to be safe and effective in clinical trials and has now been approved by regulatory authorities for widespread use in Europe. Limbal stem cells are one of only three stem cell therapies (treatments utilising blood stem cells and skin stem cells being the other two) that are available through healthcare providers in Europe.

    Recently, human ESCs (embryonic stem cells) that meet the strict quality requirements for use in patients have been produced. These ‘clinical grade’ human ESCs have been approved for use in a very small number of early clinical trials. One example is a clinical trial carried out by The London Project to Cure Blindness, using ESCs to produce a particular type of eye cell for treatment of patients with age-related macular degeneration (AMD).  The biotechnology company  AIRM is also using human ESCs to make cells for patients with AMD and another eye disease: Stargardt’s macular dystrophy. Early clinical trials for both conditions are now completed. Before these therapies can be offered to a wide range of patients, currently ongoing long term studies need to test them for their safety, security and efficiency. If the initial clinical trials are successful in terms of safety and clinical benefit, ESC research may soon begin to deliver its first clinical applications.

    However, therapies for any other disease than AMD or Stargardt’s using ESCs will have to undergo the same thorough testing for safety and efficacy in clinical trials. The road to success will be a long and winding one as described in our graphic short story. 

    In 2014, the only clinical trial so far using iPSCs (induced pluripotent stem cells) was started. However, the study to treat a degenerative eye condition, was soon put on hold due to safety concerns.  iPSC therapies still have a long way to go until the safety of the cells and clinical effectiveness can ultimately be proven.

    Disease modelling using cells is an established method.

    In recent years stem cells were used as a powerful tool for establishing patient-derived disease models both to understand the molecular basis for disorders and to use them for drug development (in a dish). Genetic disorders don’t always arise from a mutation in a single gene (so called monogenic disorders) or in a bigger building block of the genome, a chromosome (so called chromosomal disorders). A lot of diseases are more complex and are caused by mutations in a number of genes at the same time. These are difficult to model, even with modern genome engineering techniques. iPSCs, however, can help in these situations.

    iPSCs have huge implications for disease research and drug development. For example, researchers have generated brain cells from iPSCs made from skin samples of patients with neurological disorders such as Down’s syndrome or Parkinson’s disease. These lab-grown brain cells show signs of the patients’ diseases. This has implications for understanding how the diseases actually happen – researchers can watch the process in a dish – and for searching and testing new drugs.

    Here are a few more examples of diseases, which have been modelled using ESCs or iPSCs or where drug development using pluripotent stem cells is under way (further information is given via the links and in the reference list below):

     

    References:

    1. Simsek, S. et al. Modeling Cystic Fibrosis Using Pluripotent Stem Cell-Derived Human Pancreatic Ductal Epithelial Cells. Stem Cells Translational Medicine 5, 572–579 (2016). (No access without subscription.)
    2. Luo, Y. et al. Uniparental disomy of the entire X chromosome in Turner syndrome patient-specific induced pluripotent stem cells. Nature Cell Discovery 1–11 (2015). doi:10.1038/celldisc.2015.22 (This article is available  to readers for free)

    3. DeRosa, B. A. et al. Derivation of autism spectrum disorder-specific induced pluripotent stem cells from peripheral blood mononuclear cells. Neuroscience Letters 516, 9–14 (2012). (This article is available to readers for free)
    4. Ardhanareeswaran, K., Coppola, G., & Vaccarino, F. The Use of Stem Cells to Study Autism Spectrum Disorder. The Yale Journal of Biology and Medicine, 88(1), 5–16 (2015). (This article is available to readers for free )
    5. Ko, H. C. & Gelb, B. D. Concise Review: Drug Discovery in the Age of the Induced Pluripotent Stem Cell. Stem Cells Translational Medicine 3, 500–509 (2014). (This article is available to readers for free)
    6. Bellin, M., Marchetto, M. C., Gage, F. H. & Mummery, C. L. Induced pluripotent stem cells: the new patient? Nature Reviews Molecular Cell Biology 13, 713–726 (2012). (No access without subscription.)
    7. Avior, Y., Sagi, I. & Benvenisty, N. Pluripotent stem cells in disease modelling and drug discovery. Nature Reviews Molecular Cell Biology 170–182 (2016). doi:10.1038/nrm.2015.27 (This article is available to readers for free)

    This factsheet was created by Claire Cox and reviewed by Austin Smith, with expert input from Paolo Bianco, Ian Chambers, Allen Eaves, Tariq Enver and Thomas Graf. It was later researched and updated by Sabine Gogolok.

    Lead image © iStock/Les Cunliffe. Embryonic stem cell images by Aoife O’Shaughnessy. Skin images by Claire Cox. Dendrite and neural stem cell images by Peter Kirwan.