The hype around stem cells therapies is to be expected, after all they have the potential to cure diseases in a completely new way - by replacing damaged parts of the human body. Diseases which would particularly benefit from such a treatment could include diabetes, blood cancers and heart conditions, where vital organs become damaged and require replacement. We often hear about all this exciting potential, but how do stem cells actually work and how are they actually being used today?
Stem cells are defined as cells that are undifferentiated - they don't have any particular function or structure. They can, however differentiate into multiple different cell types. If you think about how all animals develop from one fertilised egg, it's clear that the first few cells in a tiny embryo must be stem cells, as they have to divide and give rise to all the different cells in your body. In fact, cells from early human embryos (4-5 days old) can be used to harvest embryonic stem cells (ESCs), which are pluripotent, meaning they can differentiate into any type of cell in the body. ESCs have limitations - they are harvested from embryos donated by consenting parents undergoing IVF, so are limited in number and come with ethical issues.
As we grow into adults, our ESCs differentiate into all the cell types of our body. Some cell types, however, maintain some of the abilities of ESCs. These specialised adult stem cells are multipotent, meaning they can differentiate into a limited set of different cell types. These cell types exist to replace cells in the body, for example hematopoietic stem cells (HSCs) in your bone marrow can turn into any type of blood cell, or intestinal stem cells continuously replace the lining of your gut. They can also contribute to changes such as during puberty or pregnancy. Adult stem cells avoid ethical issues and can be used from the patient him/herself, so another donor isn't needed.
In 2007, Yamanaka and his lab group completely changed the field of stem cell biology. Using a cocktail of chemicals, they were able to convert normal adult skin cells into cells that looked and acted like ESCs - they called these cells induced pluripotent stem cells (iPSCs). iPSCs have the pluripotency of ESCs, but the ethical considerations and ease of use of adult stem cells (actually even better if you only need a skin sample rather than some bone marrow cells!). Many labs now almost exclusively use iPSCs for research in a huge variety of areas (post coming soon).
So there are 3 types of stem cells, but what are they currently being used for?
Stem cell therapies that have undergone regulatory checks and been approved for medical use are actually very limited compared to their vast potential.
The most established stem cell therapy is haematopoietic stem cell transplantation (HSCT). Blood cancer patients undergoing chemotherapy often lose many of their healthy blood cells along with the cancerous ones. HSCs can differentiate into all types of blood cells and divide enough to replace all the healthy cells in the patient's blood. These cells come from various sources: the patient's own bone marrow or circulating blood before the chemotherapy, someone else's bone marrow or blood, or umbilical cord blood (which can be collected non-invasively after childbirth). In all cases the HSCs are similar in their ability to differentiate into all blood cell types.
Other stem cell therapies are beginning to be approved in various countries, but often they focus on adult stem cells. What about the other stem cell types, that can turn into any type of cell?
Due to the exciting potential of stem cell research being hyped by the media, it is common to assume that these therapies are already routinely being use for a whole variety of conditions. Going back to the screenshot of the stem cell therapy google search: apart from cancer, none of the top searched conditions are approved for use in Europe or the USA. Reading and being interested in the, often exciting, research of stem cells for these conditions is essential to maintain a dialogue between scientists and patients or the public. What is concerning is when the line is blurred between the phases of 'research' and 'approved by regulatory authorities'.
Many people are not just googling 'cell therapy for autism', but paying thousands of pounds to private institutes such as the Autism Regenerative Centre in London to treat their children, with the promise to show "evident improvements" in "80% of cases". They offer a research section of their website, in which you can see that their optimism is based on trials with small numbers of patients or data from other experiments they have re-purposed, but no large-scale clinical trials with hundreds of patients - which is what is required for any medicine to prove that it is safe and it works. Unfortunately, there are many private clinics carrying out these practices, taking advantage of legal loop-holes to avoid having to undergo the same rigorous testing that all medicines we take have to go through. Various governments and institutions are warning of the potential dangers of using these clinics, and the rise of crowd-funding to pay for treatments.
As with any medication or therapy, we need time to properly understand if there are any potentially harmful side-effects and whether these treatments are really effective at treating the diseases they claim they to. This requires certain steps of clinical trials and checks (look out for the next post to learn about therapies undergoing clinical trials!). Dodging these crucial regulations only takes us backwards - creating confusion and delivering potentially untested therapies. If these private clinics really cared about curing autism, diabetes or arthritis, they would first test them in a controlled way rather than charging thousands for a 'golden-bullet' injection of questionable stem cells. As usual, medicine is not that simple.
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This post is part of a series 'The World of Stem Cells' - watch this space for more stem cell-related posts!
References to find out more: