A bizarre facial cancer threatening to wipe out the Tasmanian devil probably evolved from a single female about 16 years ago, new scans of the cancer reveal. The scans are also helping to identify gene mutations found in the cancer but not healthy tissue, which might provide targets for a vaccine to rescue the endangered species.
Devil facial tumour disease is unusual in that the cancer cells themselves act as infectious agents. The cells spread between animals through biting during fights or mating. A vaccine could prime uninfected animals against the cancer if they are subsequently bitten.
鈥淣ow we know which genes are mutated, we can begin assessing which ones might be good antigens for a vaccine,鈥� says of the Wellcome Trust Sanger Institute in Hinxton, UK, who led the team.
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The immortal devil
After analysing DNA from 104 tumours in 69 devils, Murchison found that all of them trace back to a single female 鈥� dubbed the 鈥渋mmortal devil鈥�. This animal must have been the first to develop the cancer, around 16 years ago.
She passed it on by biting other devils, and the cancer then spread through the entire population, which has seen declines of 80 per cent in affected areas.
鈥淚t鈥檚 one cancer, in one devil, and has now spread through the population, like it has metastasised,鈥� says Murchison. 鈥淭hat devil lived on the east coast of Tasmania, and although she鈥檚 dead, her cancer lives on in thousands of devils in Tasmania today, which is why I call her the immortal devil.鈥�
Evolution of a cancer
As well as revealing possible leads for vaccines, the study revealed how the original cancer has evolved. In the Forestier peninsula in the south-east of Tasmania, for example, there鈥檚 evidence that one variety of the cancer disappeared and another became dominant in its place.
Tracing how the cancer is evolving might help predict how it will spread when it reaches unaffected areas, says Murchison.
Murchison and her colleagues also found evidence of mutations in immunity genes within the cancer, which could help explain why the immune systems of newly infected animals don鈥檛 recognise tumours as 鈥渇oreign鈥� and kill them off.
Other researchers have suggested that extensive inbreeding might explain how the cancers evade destruction, because they are mistaken for part of the animal鈥檚 normal tissue. However, Murchison said that a study by researchers at the University of Tasmania appeared to rule out the inbreeding hypothesis by showing that skin grafts between devils were rapidly attacked and eliminated.
Cancer-causing genes
鈥淗aving the genome should also allow us to identify cancer-causing genes, and hopefully find drugs that may help to control the disease,鈥� says , an authority on Tasmanian devils at the University of Sydney, who was not involved in the study.
鈥淭here is some early evidence that the disease is behaving differently in devils in north-west Tasmanian populations,鈥� says Belov. 鈥淭he disease there is affecting fewer devils and taking longer to kill them off, and at this stage we don鈥檛 know whether that鈥檚 because the devils there are more resistant, or the tumour strains are different, or both,鈥� she says. 鈥淕enomics will help us to solve this.鈥�
Murchison says that although the research is focused on the devils, the knowledge gained may be valuable if a similar disease ever emerges in humans. The only other known cancer infectious in this way is a venereal disease in dogs.
Journal reference: Cell, DOI: 10.1016/j.cell.2011.11.065
