Studying Devil Facial Tumour Disease
Chris - A very unusual type of cancer is currently hitting Tasmanian devils called Devil Facial Tumour disease. As the name suggests, it leads to tumours on these devils' faces which makes it, amongst other things, very hard for them to eat which means they don't tend to live very long once they actually begin to show the symptoms. But what's really unusual about this tumour is that it's directly passed between the animals probably when they bite each other and Elizabeth Murchison is from the from the Wellcome Trust Sanger Institute. She's with us today and she's been looking to the genetic basis of the disease. Hello, Elizabeth. Thank you for coming in and joining us.
Elizabeth - Hello.
Chris - First of all, for people that are not acquainted or ill-acquainted with what Tasmanian devils are, just describe one for us.
Elizabeth - Tasmanian devils are a small dog-sized black creature. They have a black coat with a white stripe under their chest and they're very well-known for their piercing nocturnal scream which is I think where they got their name from and they have very, very strong powerful jaws which they use for crunching bones.
Chris - They sound like wonderful creatures. What's the background to the emergence of this problem? When did it first become apparent that there was an issue with them?
Elizabeth - The story really started back in 1996 when a wildlife photographer took a picture of a devil with a strange mass on its face and he was a bit concerned at the time and he took this photograph to the local authorities and people just thought that this was just one particular devil with one strange cancer and didn't really think too much more about that. But then over subsequent years, more and more devils started to show up with these unusual facial tumours all up and down the east coast of Tasmania, and around 2000-2001, it became very, very apparent that this was a new type of infectious disease affecting devils.
Chris - And from a conservation point of view, people were presumably worried because they don't exactly go far across anywhere. They're just stuck in Tasmania, aren't they now?
Elizabeth - That's right. So devils used to be found all over Australia but they went extinct about a thousand years ago in the mainland of Australia. They've been isolated now on the island of Tasmania for about 14,000 years and they're very unique. They're not found anywhere else and they're really an icon for Tasmania.
Chris - Indeed. Well the name says it all, doesn't it? But what have researchers done then to try and work out what these tumours are and get to the bottom of how they're spreading amongst the animals?
Elizabeth - Well obviously, it was a very, very strange thing to find a cancer which was being transmitted as an infectious disease. So the first thought that people thought of was that it was probably a virus. And so, experiments were directed at trying to find viral particles in these cells and really didn't get anywhere and at the same time, researchers in Tasmania were looking at the chromosomes of the tumour, and they found surprisingly that all the Tasmanian devil tumours that they looked at had remarkably similar chromosomal rearrangement. So cancers tend to have very rearranged chromosomes but each cancer is different and has a different set of rearrangements. But the striking thing about this cancer was that all the tumours had the same, almost identical rearrangements which really couldn't occur in any other way other than them actually being the same cancer.
Chris - So somehow physically, cells from one tumour were going from one animal to the other and seeding a fresh tumour in the recipient animal.
Elizabeth - That was the only conclusion that could kind of be consistent with this data - that the same actual physical cancer cell was being transmitted between individuals probably by biting, and that the same cancer which arose once in a single individual that probably lived back in the mid-1990s has actually spread through the Tasmanian devil population and is now affecting thousands of devils around Tasmania.
Chris - So some poor devil - excuse the pun, originally had a cancer because its chromosomes were rearranged, it had some genetic changes that made it develop a tumour and it then spawned this disease which began to pass on to other individuals.
Elizabeth - Exactly and we really don't know very much about those early events but we think that one individual devil that probably lived up in the northeast of Tasmania got some normal type of cancer which then acquired the capability of being transmitted between individuals.
Chris - So what's special about it so it can do that because is it that the animals, because they're a restricted population, they're very, very alike and therefore, putting a cell from one animal into another, the immune system doesn't view it as necessarily that hostile so it kind of tolerates it?
Elizabeth - That's right. So there's something very, very odd about this cancer because normally if you take any tissue from one individual and put it into another individual, it gets rejected because our immune systems are able to tell self from non-self. In this case, this tumour is not being recognised as non-self and is not being rejected. And we don't really understand how that works, but one possibility is that devils are very restricted in in-bred population that don't tend to recognise self from non-self because they're too closely related. The other possibility is that perhaps the tumour is secreting substances or somehow actively tricking the immune system not to see it as a foreign tissue.
Chris - That's interesting. So devils can do this. Does that mean that other animals can or is this an isolated thing? Is this the only example of a cancer we're seeing spreading like this?
Elizabeth - No. There's another case of a naturally occurring transmittable cancer which is spread by living cancer cells in dogs actually and it's a very, very interesting cancer. It's venereal and it's transmitted by sexual contact. And it's actually a very, very old cancer that probably is at least 2,000 years old if not older than that which is spread through the entire world population of dogs and is found everywhere, but it's all derived from single cancer which arose in a dog some thousands of years ago. So the devil is not the only case.
Chris - So can you get clues from what's going on in the dogs to ask how this is happening in devils then? Does it give you clues?
Elizabeth - Exactly. That's what we're hoping to do. I'm actually studying this dog cancer quite intensively as well because I'm a geneticist and we don't have a lot of genetics tools for devils at least at the moment and so, we have a dog genome sequence that we can use to study this dog cancer and study the genetic mutations that have happened to allow this dog cancer to evade the immune system and we're hoping to perhaps transfer that to the devil.
Chris - Because if those cancers, both the dog's and the devil's are secreting something interesting, which puts the immune system off the scent, that could be really helpful medically, couldn't it? If you can work out how it's doing that because we've got a big problem with organ transplants where we have to immunosupress people very heavily to tolerate donor organs. If we had a way of making the immune system tolerate specific tissues, that could be a massive breakthrough.
Elizabeth - Absolutely and I think it's going to be very, very interesting when we start to learn how these cancers are evading the immune system and to see whether or not we could use similar strategies to trick immune systems to not recognising foreign grafts as really being foreign.
Chris - Any progress yet?
Elizabeth - It's still early days. We are finding mutations in the devil cancer which is allowing us to start to track how the devils cancer is spread through Tasmania and in the case of the dog, we're finding interesting different pockets of cancer mutations that have arisen in different continents. But it's still early days and we're hoping to eventually develop something that will be able to help the devils in the wild.
Chris - Well we wish you luck. Thank you very much. Elizabeth Murchison from the Wellcome Trust Sanger Institute.
Kat - It's also important to point out that so far, the only cancers you can catch are these devil cancer and the dog cancer and there's no worry that you can catch cancer from another person with cancer as I should point this out. I get asked that a lot. "Can you catch cancer from someone?"
Chris - Well having said that Kat, what about organ transplants because obviously, if there is a cancer that we don't know about lurking inside the donor organ, there's a possibility you could transmit that, couldn't you?
Kat - There is a possibility and also, interestingly, in patients who have had organ transplants, they're often on immunosuppressive drugs to stop their immune system attacking the cancer, and in fact, this can lead to an increase in certain types of cancer in a patient. But you shouldn't be worried if one of your relatives is affected by cancer. You can't catch it off them so that's important to point out.