Lissa Heron, Roslin Institute
Kat - While there was much talk at the symposium of mammals, the Roslin Instituteís Lissa Heron is working with a different type of agricultural animal - chickens. Although chickens canít be cloned in the same way that mammals can, they can be genetically modified, meaning that their eggs might provide us with a lot more than a tasty breakfast in the future.
Lissa - Well, chickens are a really useful system. Theyíve been used historically for studying developmental biology, development of the embryo. But they're also compared to large animals like sheep or cows. They're much easier to keep and you can keep a lot more chickens in the same kind of space that you would keep sheep. They're a lot cheaper to feed as well. They have a shorter life cycle, faster breeding cycle, and they're really easy to scale up. In terms of pharmaceutical production, the egg is a really great system because it produces a lot of protein. You donít need to disturb the hen really because you just take the eggs and thatís it. and there's an easy way of now making the genetically modified chicken so that you produce a lot of whatever protein you want in the eggs. The other benefits of chickens are that they can make proteins that behave more like human proteins compared to some cells and some other mammals. And so, when you give these proteins to humans as a therapeutic, they are less likely to cause an immune response Ė a negative immune response and they're also more likely to be active compared to proteins made in other systems.
Kat - So, what sort of drugs, what sort of molecules are we talking about here that you could make in chickens?
Lissa - So, a lot of the classic drugs that people are familiar with like aspirin or paracetamol, these are small molecules that can be synthesised in a chemistry lab. But a lot of the newer drugs that are having a lot more success in treating cancers and chronic illnesses are actually proteins. The very first drug that was actually made this way on the pharmaceutical market was insulin. So insulin is a protein made by cells in your body and people who were diabetic can't produce this. And so, they used to have to purify it from animals. Obviously, a lot of potential for infections and other problems and also itís cruelty, you have to kill the animals to get the insulin. So, they started looking to see whether we can make this in bacteria. and fortunately with insulin, you can. Itís a relatively simply protein. So they started making it in a bacteria and that way, you can have much greater control over the cleanliness of the protein and how safe it is. You can make little tweaks, the sequence, to make it more active or last longer in the body, all these sorts of things. So, once you got insulin successfully used in human patients, we started thinking, ďWhat else could we make for patients?Ē more and more of these sorts of things have been coming up. So you have what are called monoclonal antibodies that target cancer cells. An example of that is Herceptin, and then you also have things like interferon alpha which is used to treat hepatitis and also various cancers. So you have all these sorts of proteins but a protein can't be synthesised. It has to be made in a cell system because itís a very complex biological process and itís a very large molecule. So, it needs to be expressed and it needs to be folded properly and some of them have to have sugars added to them and various modifications like that. So you need a more complex biological system to make them.
Kat - So, if that complex biological system is the chickenís egg, how do you get the genes that make the proteins into the chickens?
Lissa - We use a system called a lentivirus. This is a type of virus that is actually related to the HIV virus. These viruses are really useful because they're able to integrate into the genome of your target animal. They are not silenced like a lot of other genetic modifications that are made because the lentivirus needs it to replicate eventually. But we remove the ability of the virus to replicate. So, weíre only using the bit of the virus that inserts into the genome and expresses and thatís it. So, once you put the virus into the chicken, there's no more virus made. There's not any infectious agents or anything. But that puts the gene into the chicken and that gene is also attached to a promoter which is a bit of DNA that tells the cells to make a protein in a particular place. In this case, itís the promoter that is used for ovalbumin which is the protein that is most abundant in eggs, in egg white. And that then drives the expression of whatever gene that weíve put in for expressing another protein.
Kat - And then presumably, when the eggs are laid, you just get the egg white and get the protein out the other end of it.
Lissa - Yes, thatís exactly it. we just dilute the egg white down and remove one of the proteins from it which is called ovamucin and thatís the protein that creates the kind of jelly-like structure of egg white. So we have to get rid of that so that we can access the rest of it and then we can run it down a standard chromatography column. So this is how all proteins are separated whether for research or for pharmaceuticals. Because the egg only has about 12 proteins in it, itís actually really easy to separate out compared to maybe trying to purify something out of a cell that has hundreds and thousands of proteins.
Kat - How do you know that this works? Are there any drugs that are already made in chickenís eggs and what are the kind of drugs are you working on?
Lissa - So there are actually three drugs on the market that are made from transgenic animals. The very first one was approved in 2009 and thatís from the milk of a transgenic goat. There's another a couple of years later which was from the milk of rabbits. I donít know how they milk rabbits so donít ask.
Kat - Carefully. With very small hands!
Lissa - Yes. I just picture there are some very tiny little milkers. And then just in the last year and a half or so, there was another drug that was approved and that is made in transgenic chickens which use pretty much the same methods that we do.
Kat - Given that this seems like an incredible system for making drugs, molecules, that are really active in humans and could be really useful in medicine, is it then feasible? I mean, near where my mom lives, there's a nice free range chicken farm. There are some chickens running around. Presumably, you're going to need more chickens than that.
Lissa - It depends entirely on the drugs you're looking at. So some drugs actually only require a very small dose. And so, you would only maybe need a few hundred chickens and that would do you for your market. There are others where you would probably need farms of hundreds of thousands of chickens. In terms of the feasibility of that and obviously, you have environmental regulations and about having livestock animals, the chickens would have to be indoors. You can't have free range chickens because they might be exposed to outside infections and things eaten by foxes and that sort of thing. You donít want that. But the likelihood of using chickens to replace every single pharmaceutical protein production is very unlikely. It wouldnít be suitable for every single kind. So I think that the thing where you're really going to be targeting these is where you need to make a biologic in very large quantities for a low amount of money but where the dose doesnít need to be that big. So one of the things that weíre targeting is actually the animal health market because at the moment, animals are priced out of the biologicís market because itís too expensive to make and people can't afford to pay lots and lots of money for an antibiotic for their dog or treatment for livestock animals. So, these sorts of things where you can't afford to pay a hundred pounds for a dose for each pig you have or each cow you have. But if you can bring that price down by producing it in chickens, then youíve suddenly got a big market open to you where you can treat a lot of animals, you can treat companion animals, you can treat livestock without having to overuse antibiotics or without having to just let these animals die because there was no treatment available before.
Kat - The Roslin Instituteís Lissa Heron. And if you want to find out more about the legacy of Dolly, take a look at the Roslin Instituteís special website - thatís dolly.roslin.ac.uk or you can follow @Dollyat20 on Twitter.