Australasian Science: Australia's authority on science since 1938

Tumour Is Devilishly Complex

By Stephen Luntz

Devil facial tumour disease, which is threatening the survival of the largest carnivorous marsupial, the Tasmanian devil, is proving more complex than originally recognised.

The secret of this transmissible cancer was thought to lie in the lack of genetic diversity among Tasmanian devils, so that the immune system of one devil could not recognise cancer cells from another individual as foreign.

“The unique ability of DFTD to hide from the devil’s immune system is intriguing and baffling,” says A/Prof Greg Woods of the Menzies Research Institute Tasmania. “We know that a lack of genetic diversity is part of the reason, but we were keen to test the severity of this limited diversity.”

Skin grafts from genetically similar individuals survive, while those from animals with a different immune system are rejected. Mr Frank Kimble, a plastic surgeon from Royal Hobart Hospital, was recruited to graft samples from both healthy and diseased devils to others but all of the grafts were rejected, suggesting that the devils are less similar genetically than had been thought.

“That result brings us back to the tumour,” Woods says. “What is special about the tumour cells that they can avoid rejection by the host devil? A lack of genetic diversity is still part of the answer, but there must be something else.”

Woods says that “we have ideas” about what this might be, “but we still have to test”. One possibility to explore is that the tumour produces something that turns the devil’s immune system off. Another is that the tumour is missing something that would enable the immune system to detect and fight it.

While the answer is unknown, Woods denies that researchers are back to square one. “Sometimes you float a theory you don’t think will be the final answer but is the best you have at the time. Given the lack of diversity in the devil population, it was logical to think this was a factor. It’s definitely part of the answer, but doesn’t account for the disease on its own.”

Woods is unconcerned that the tumour might infect other animals. Mice have proven immune, and closer relatives such as the quoll do not engage in the biting behaviour that allows the tumour to spread among devils.