Within just a handful of generations, Tasmanian devils appear to have evolved resistance to an unusual contagious cancer that was widely expected to make the ill-tempered carnivorous marsupials extinct in the wild.
The remarkable finding gives hope that the unique animals could survive the disease, which has already wiped out 80% of the animals in just a few decades. It could also give scientists an insight into human cancer.
First detected in 1996, devil facial tumour disease is one of just three transmissible cancers seen outside the laboratory. It kills virtually every animal it infects and has spread across 95% of Tasmania, affecting almost every known devil population.
Despite models suggesting some long-infected populations of the devils should have been extinct by now, most were clinging on. That led Andrew Storfer from Washington State University and his colleagues to suspect that those populations might have evolved some degree of resistance to the disease.
Unusually for research of this kind, the scientists had access to tissue samples collected from Tasmanian devils from several points in time, including before the devil populations were infected.
Menna Jones, a co-author on the study from the University of Tasmania, had collected nearly 10,000 tissue samples since 1999, allowing the team to compare the DNA of populations before, during and after disease arrival.
The researchers examined the genomes of almost 300 individuals from three different populations, looking for genes that changed in frequency over that time.
“Our hope was that we would find some genes that were perhaps associated with cancer or resistance to cancer or immune function,” said Storfer. “And in fact we did find seven different genes in two small regions of the genome that seem to have implications for cancers in other animals, including humans.”
Storfer said some of those genes thought to be involved in directing immune cells to attack dysfunctional cells or pathogens were particularly promising. If they do help confer resistance to the cancer, it meant the immune system might be evolving to recognise and attack the tumour cells.
Since the same changes were seen in three independent populations, the researchers said it was very unlikely that they were a result of a more random process.
Storfer said the next step was to try to figure out exactly what those genes do in Tasmanian devils. He said the team was growing the tumour cells in the lab and were editing their genome to examine the influence of the genes on their growth.
The researchers said it was unlikely these genes made animals completely resistant, but they might allow the devils to survive long enough to reproduce.
They said the finding of such fast resistance – occurring between four and six generations – to highly lethal disease in wild populations was unique. The only other example was rabbit resistance to myxomatosis in Australia, but that occurred over many more generations.
“First and foremost … this gives us hope for the survival of the Tasmanian devil, which was predicted to be extinct but isn’t,” said Storfer.
Other researchers in Australia, including Greg Woods from the University of Tasmania, have been trialling a promising vaccine against the devil facial tumour disease.
“This research provides support for vaccine research as devils appear to respond to the tumours,” Woods said. “This will require functional data to confirm.”
Devil facial tumour disease is one of just three known contagious cancers that exist in the wild.
About 11,000 years ago, dogs developed canine transmissible venereal tumours, which is usually not lethal, suggesting they might have developed resistance to it. And just this year, it was discovered that mussels, clams and other bivalves have a contagious cancer that is similar to leukaemia, which can even spread between species.
Storfer said contagious cancers in animals, and resistance to them, could help understand the causes of different responses to human cancer. Since the same cancer line is spread from one animal to the next, it is like studying a very long-lived cancer in a single patient.
“So this may give us some insights into cancer remission and recurrence in humans,” Storfer said.
The results were published in the journal Nature Communications.
This article was first published by The Guardian on 30 Aug 2016.