The Future of Cell Therapy
Chris - Now we've just heard about how gene therapy can help to correct health issues caused by genetic mutations, but another approach looks at using whole cells instead. And now, I'm joined by three pioneers in this field. Dr. Robin Ali is a molecular biologist at the Institute of Ophthalmology at University College London. He's looking at ways to repair the damaged and diseased retina. Dr. Ludwig Vallier is a Stem Cell Biologist at Cambridge University and at the Sanger Institute, Professor Giulio Cossu is a Stem Cell Biologist also at University College London and he has an interest in muscular dystrophies. If each of you could first give us a quick overview in just one line on what you're work is. We'll start with you, Robin...
Robin - Well, the aim of my work is to develop a new treatment for blindness that is caused by the loss of photo receptor cells which are the light sensitive cells and the retina. And we aim to be able to replace these cells in order to restore vision.
Chris - Giulio, you're trying to do for muscles what Robin is trying to do for the eye.
Giulio - Pretty much. With that difference that for the eye, you need very few cells whereas if you want to treat a disease like a muscular dystrophy that affects 40% of that mass of our body, you're going to need a lot of cell, and that is right now, our major problem.
Chris - And Ludwig, one way to tackle both problems might be to make cells that are the individual's own cells, rather than going and getting cells from someone else that will be incompatible genetically with the individual. Wouldn't it be nice if we can make cells that are from the individuals themselves?
Ludwig - So, I guess now we have a technology to reprogram the identity of other cells into or stem cells which are capable to grow indefinitely and differentiate into a diversity of other cell types including cells for the eyes, muscle cells. And so, that - I mean, that we can generate even quantity of those cells which will be extremely useful for the cell therapy that Robin and Giulio have just described.
Chris - So Robin, when you do your work, can you just talk us through the story so far, what you've achieved, and how you've done it?
Ludwig - So, some years ago, we wanted to tell whether it might be at all possible to transplant a photoreceptor cell.
Chris - The rods and cones.
Ludwig - Rods and cone cells. They're one of the most specialised cells in the body and they make very specific connections. We hypothesise that it may be possible to transplant these cells and have the appropriate connections. We carried out to see those experiments in which we looked on what stage of development is necessary for successful transplantation. We determined that it was a very specific stage which was between a fully mature cell and one, not quite fully mature. And provided we transplant photoreceptor cells at this stage, they're able to integrate into the retina and make appropriate connections.
Chris - How do they know where to go in the retina because you're literally taking a retina from say, let's call it a 'donor animal' which is at the right stage of development? You're taking the cells out of that retina and injecting them into an animal with a lack of those photoreceptors. How do they know? How do you know you are taking photoreceptors where they will go in the retina?
Ludwig - They are already almost fully mature photoreceptors. We discovered that injection of stem cells doesn't result in maturing into photoreceptors and connections. They are almost fully mature photoreceptors. They're then migrating within the retina and they're just recapitulating that normal development. We're transplanting them very close to the site that they finally end up. So, they're probably just following their normal processes of development.
Chris - And the mice, because you're doing this in mice at the moment aren't you, that the mice that get these cells, can they see again afterwards?
Ludwig - So, we carried out experiments last year in which we could show in mice that lack night vision. They have no functional rods, if we transplant new rods into these animals that we can restore cognitive vision. So, not only do the cells integrates into the retina, but they're making functional connections to the brain and the mice were able to see in dim light.
Chris - How does this work with a muscular dystrophy study there because Robin is saying, "Well, I'm just able to put the cells roughly where they needed to go. They don't have far to go and they're almost the sorts of cells that they need to be." Is that the same with your approach?
Ludwig - It is quite similar indeed. If you transplant stem cells, they still do not know what they will become. The chance that they will learn how to make a functional muscle cell are very small and if you transplant a mature contracting muscle fibre, most likely, it will not survive. So, also in this case, you have to transplant cells that are already committed, they have decided that they will become muscle, but they're not yet muscle. And in terms of knowing where to go, obviously, you have to inject them in the right place that don't have a map so that you can put them in the brain and they travel to the muscle.
Chris - Well, if you look at say, what a haematologist does with a bone marrow stem cell when we have a bone marrow transplant, actually, we do just inject stem cells into a vein and they do know where to go. They go back to the bone marrow and they repopulate new bone marrow and turn into new blood.
Ludwig - That's correct, but this is the exception. It's not the rule. For the very simple reason, the blood is the only tissue that is liquid and the cells circulate and by circulating, they have to learn how to find the right signal how to move and how to go home. All the other tissue do not have this evaluative pressure to find their way home so you have to put them close to the place where you want them to be.
Chris - So, in your example of muscular dystrophy, does this mean that a person who was going to have this sort of therapy would face a total body injection for want of a better word? You've got to inject everywhere or is there a way of doing for muscles what a haematologist does for bone marrow.
Ludwig - There is a weight in between. But 20 years ago, there were trials where the cells were injected directly into skeletal muscles. But because we have so many muscle and the cell don't move much from the point of injection, this would turn out to be non-practical. What we found that another kind of muscle progenitor that can be delivered through the arterial circulation can inject in the artery will come out of the arteries if there is inflammation like there is in muscular dystrophy. And so, with a single injection, you can colonise all the muscle downstream of the artery that you are injecting. This is not 100% efficient, but it's a way to bring the cells where you want to be.
Chris - What is that cell that's able to do that?
Ludwig - The cells, we call mesoangioblast and is a name like mesenchymal stem cell or embryonic stem cell. These are not real cells. Our cells we have adopted to grow in culture starting from a specific cell type. In our case, a cell called pericyte that is around the very small blood vessel.
Chris - So these cells, when you put them into the arterial circulation and they find themselves going through a muscle, is it the environment in the muscle that says to the cell, "You should now become a mature skeletal muscle cell"?
Ludwig - Yes, obviously, these cells, once you've taken them and isolated from a skeletal muscle will never be able to turn into neuron or into hepatocyte, but they have a few developmental options. They can decide to become a skeletal muscle or a smooth muscle that will form the layer around the blood vessel and will decide what to do depending on where they find physically associated. So, if they get close to a regenerating muscle fibre and will get into the fibre and will be incorporated in the newly fibre. As they remain close to the vessel wall, they most likely will become part of the vessel wall.
Chris - In (a dish in) muscular dystrophy, patients with this don't just manifest problems in their skeletal muscles. They have other muscles in the body including cardiac muscle. Will these mesoangioblasts also find their way into the heart and repopulate the heart with healthy cardiomyocytes there?
Ludwig - Not the one that we isolated from skeletal muscle. There are other strategies to treat the heart and right now, pharmacological help seem to be the easiest way to go.
Chris - So, you're doing this in dogs which have a form of muscular dystrophy similar to a human. Is therefore the capacity if it works in a dog to translate this to a human? Do you think it'll work?
Ludwig - Well, we did it. We have a trial running in my previous institution at in Milan and we are accumulating results to see whether first of all, there are damage for the patient, what is called a phase 1 trial is designed to test safety and then to see whether we get some efficacy.
Chris - And the cells you are using, are they the patients' own or are they from somewhere else?
Ludwig - No. In this case, they come from an agely identical donor, a brother. Pretty much, like it happens for bone marrow transplantation.
Chris - So, the obviously more solution in both these cases would be Ludwig, if we could get some cells that were from the individual themselves. Practically speaking, is that possible now with the science we have? Can we derive new cells for mature tissues?
Ludwig - So we can. Yeah, definitely now, stem cells can form tissue by reprogramming them, by overexpressing protein that by actually bringing them back to a more foetal stage directly.
Chris - So, you take skin cells.
Ludwig - Skin cells, blood cells...
Chris - And put the factors into it.
Ludwig - Yes.
Chris - How do you get those factors?
Ludwig - So, the most common method right now is still, using in fact gene therapy approach using your viruses and retroviruses.
Chris - So, you put these four factors in.
Ludwig - Yes.
Chris - And what does that physically do to the skin cell to make it into a stem cell again?
Ludwig - Any cell type in the body will have a very strong mark on the DNA. And what we do is that we just erase this identity and then pose a new one with those factors and these identities are stem cell identity which give them this capacity to grow and to differentiate. That is very interesting for genetic medicine.
Chris - And one thing you can obviously do with those cells, you can turn them into other cells which means presumably, if Robin says, "Well, I want to model why some of my patients get a certain type of eye degeneration." You could take cells from their skin, turn them into the sorts of cells that become diseased in that patient group and then study the disease in the dish rather than having to go and find loads of different patients and study them all individually.
Ludwig - Yeah, that is what we are doing already now in the past 3 or 4 years. We take sample from patient with genetic disorder, or many, and then differentiate the stem cell generated from this patient into cell type that's affected by the disease and that's how we can model a disease in the dish and do studies, studies that will now be possible to do from a biopsy or primary tissue from those patients. And that new individual model to skin drug and other agent...
Chris - Are these cells safe?
Ludwig - So clearly, those cells are like any other cells gone In Vitro. They accumulate genetic modification over time when you grow them. But that's a natural process. That occur in any cells In Vivo and In Vitro. But now, what is really important to say is that, now, we have in fact the quality control that enable us to design different cells, is too much damaged, or is safe to be used In Vivo because we can't directly sequence all genome in less than a week for a cost that is not effective for therapies. So, it doesn't mean that we can't really quality control cells and we can now have some level of safety for transplantation of these cells.
Chris - So Robin, why are you fiddling around with embryonic cells? You've got Ludwig here, you could use some cells from an adult!
Robin - Our approach is to always take the low-hanging fruits and we start our studies with cell transplantation donor retinas, just on sound transplantation. We subsequently started to work with embryonic stem cells in order to see whether we can derive the appropriate cells for transplantation and that's a huge challenge because we've been able to make photoreceptors from embryonic stem cells for some time. What we've not been able to do until very recently is to obtain sufficient numbers of embryonic stem cell derived photoreceptors for transplantation. That's taken a huge amount of time and effort to do with embryonic stem cells. IPS cells have tremendous potential, but there are still further challenges remaining with IPS also. I think that maybe ultimately the most effective way of avoiding rejection to have a personalised medicine, but I think it's going to be some time before we're able to really implement that technology clinically.
Kate - Thanks to Dr. Robin Ali, Dr. Ludwig Vallier, and Professor Giulio Cossu. This is the Naked Scientists with Chris Smith and with me, Kate Lamble. If you'd like to get in touch with any questions or comments about these therapies we've been discussing today, do email us to firstname.lastname@example.org, you can tweet @nakedscientists or find us on Facebook.