Signals Blog

The United Kingdom has begun its foray into using cells derived from human embryonic stem cells (ESCs) in clinical settings. I have to admit I was surprised that following coverage on the BBC and in The Guardian, there was virtually no anti-ESC protesting to be found, especially considering this was the first human ESC therapy to be attempted in the UK.

The BBC’s Fergus Walsh (once again!) does an excellent job at giving his audience the basics of the disease (macular degeneration) and the reason stem cells are being used to treat it.

One may ask why the therapy is using ESCs at all. It is true that while this particular set of procedures utilizes cells grown from an ESC source, it is possible that another non-embryonic source of cells could be made to produce the same number and quality of cells.

I think it’s important to emphasize why such therapies are currently tried using ESCs. They have the highest regenerative and proliferative potential, and the procedure has been shown to work in animal models using these cell sources. If the therapy works, I am certain that every effort will be made to find a non-ESC source to achieve the same result.

Where the Moorfields’ therapy gets somewhat tricky for me is in the ethical realm. I wonder how well the patients are being counseled about the source of the cells they are receiving?

At the basic level, it seems very simple: the patient has lost or damaged a very specific set of cells and the hospital will grow new cells to replace them. However, these cells come from ESCs grown in a laboratory – cells which, as our readers will have heard, have unlimited growth potential and can turn into the vast majority of cell types in the body. With such enormous potential, can we really be sure that these cells will only produce the required numbers of cells and then just stop there? With such conceivable risks, is compromised vision in one eye enough to warrant them? Both eyes? How will these risks be considered and assessed in the future?

This is what makes these first few patients so very important to observe closely. The question then becomes, “for how long will they be observed before the green light is given for an expanded trial?” Based on work in rodent models using embryonic stem cells, the abnormal cell growths that would be predicted to develop from these cells going awry would take a substantial amount of time to manifest themselves. What is that amount of time in humans? I wonder whether the patients have been made aware of what could potentially go wrong in such an experimental therapy.

Considering the public exposure and the fact that the groups involved in the Moorfields’ trial have been developing this therapy for 10 years, these questions have likely been addressed. Also, several centres across the world have already tried similar approaches (e.g., South Korea), which reduces, but does not eliminate, safety concerns. The eye is also an excellent first choice for such therapies because it is a site of immune privilege, meaning that tissue grafts have a much higher chance of surviving and, in the event that something goes wrong, miscreant cells are much less likely to cause trouble in other parts of the body.

So, as with most experimental therapies, we must wait and see what the products of this very public clinical test will be; either way, it will answer questions about the safety of using human ESCs as a source of cells for people with various ailments and, if successful, will increase the demand for such therapies.

If I were in the public policy world right now, I’d be doing some very serious thinking about two things: affordability of such a treatment – how much does it cost and how would a public system pay for it?; and, what does the increased demand of ESC-derived products mean for the supply chain of cells – where will they come from and how can they be responsibly supplied?

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David Kent

David Kent

Principal Investigator at University of Cambridge
Dr. David Kent is a Principal Investigator at the University of Cambridge in the Cambridge Stem Cell Institute ( His laboratory's research focuses on fate choice in single blood stem cells and how changes in their regulation lead to cancers. David is currently the Stem Cell Institute’s Public Engagement Champion and has a long history of public engagement and outreach including the creation of The Black Hole in 2009. He has been writing for Signals since 2010.