Tasmanian devil facial tumor disease

OK, I had to share with everyone one of the coolest things I've come across in a long time. Maybe you've heard about it on NPR, if you're in one of those labs that plays NPR all day (God knows I am).

The Tasmanian devil population has fallen by 90% across large parts of Tasmania. This is due to a recently evolved illness, Tasmanian devil tumor disease (DFTD). And holy cripes people, it looks painful. Just Google "Tasmanian devil cancer" and be horrified. It's a tumor of neuroendocrine origin that causes awful ulcerated lesions on the head and face of Tasmanian devils, usually starting in the mouth. If the tumors don't kill the devils by secreting hormones or impinging on essential organ function, then the devils typically starve to death or suffocate as the tumor mass in the face and throat increases. Once it's visible, it's 100% fatal within 4 months.

But here's the cool part: it's an infectious cancer! Seriously! Devils are really violent, especially when gettin' it on, and when they bite and scratch each other during sex, the cancer is transmitted by inoculation with the cancer cell line itself - basically an allograft. It's not a virus causing the cancer, which is what I totally thought it was gonna be when I heard this on the radio. (One of the articles I read called DFTD a "rogue cell line", which just sounds bad-ass.) The tumors do not have the same genotype as the affected animals - in fact, they all have identical chromosomal defects, indicating that the cancer is clonal throughout the population. It's basically a cancer that's somehow "learned" to be transmitted between immunologically different individuals of a species. As you may know, this is not how cancer usually works. If I got a big nasty facial tumor and made out with Scott, Scott would not get Cressida tumor popping up all over over his face. His immune system would be all like, WTF? And kill that shit. DFTD has found a way around that, which totally blows my mind.

I was really interested in this story, since I'm interested in anything infectious, especially eukaryotes. As it turns out, DFTD is the second example of a cell line that's become infectious, the first being the appetizing transmissible venereal sarcoma, a disease of doggy hoo-haa's and wee-wees. As it turns out, this disease is studied by my favorite evolutionary biologist, Armand Marie Leroi.

So in terms of organisms colonizing other organisms, we have:

1. proteins (prions)
   
2. viruses (HIV)
   
3. bacteria (tuberculosis)
   
4. traditional eukaryotic parasites (malaria)
   
5. helminths (tapeworms)
   
6. cell lines (DFTD)

What happens to the Tasmanian devils? From what I've read, biologists aren't too optimistic. The problem is that it's sexually transmitted, which means that even if very few individuals in a population have it, it will still be transmitted effectively (see HIV for an example of how that works). It's not clear yet how infectious it is, although it's thought to be poorly infectious as it's taken DFTD like 10 years to get half-way across Tasmania. If it were highly infectious, it would have moved more quickly, as devils travel great distances on a regular basis. Resistance has been slow coming; I saw one report that said that 3 female devils had been found that were partially resistant, but there are no reports confirming that. And the population's already been so decimated that other factors, like feral species or loss of habitat, become more able to drive devils to extinction. Several "insurance" colonies have been set up off shore, but you all know what that means: no more genetic diversity. This has been a problem in populations like cheetahs and ne ne geese that experienced severe bottlenecks in their evolution, leading to essentially clonal cheetahs. So one good infectious disease, and they're gone.

How can this happen, the evolution of a rogue cell line?? (Makes you look at those HeLa cells with a little more respect, eh?) It's obviously a very rare event, but what's going on immunologically to allow this? Cancer people, what gives?

Some cool resources for DFTD:
Save the Tasmanian Devil
FAQs from Tasmania's DNR equivalent
The Nature paper proving DFTD is a parasitic cancer
NPR story
Tasmanian devil movie