Tasmanian devils are caught in a battle against a deadly facial tumor. The cancer has wiped out 77% of most devil populations in Tasmania since it was first recorded in 1996. Tasmanian devils are now categorised as endangered on the IUCN Red List.
Unlike most cancers, Devil Facial Tumour Disease is not only transmissible but is able to dodge immune defences as it is passed from one animal to another.
The disease is spread through bites, a common occurrence during reproduction and fighting. Once transmitted, the cancer causes large tumours on the face and neck of infected animals and results in mortality in almost all cases.
Conservationist see a vaccine as the key to protecting the species outside of carefully monitored cancer-free populations, most of which are held in captive breeding programs.
In 2016, 33 Tasmanian devils from a cancer-free insurance population were released at Stony Head in northern Tasmania. The devils had been given an experimental vaccine intended to target the cancer’s ability to mask itself from the immune system. The research, published in 2018, states all of the animals showed an immune response from the vaccine upon release.
But when eight of the individuals were recaptured during trapping trips in 2019, six had facial tumours.
Another study in 2017 saw the same trend in a group of captive devils given a similar experimental vaccine. Both vaccinated and unvaccinated devils contracted facial tumours. But, subsequent analysis found the tumours in vaccinated devils differed from those in unvaccinated devils. Their immune systems had higher infiltration into the tumours and, after researchers put them through immunotherapy, the animals displayed complete tumour regression.
Samples of the devils in this experiment were preserved and used in a new study published in Immunology & Cell Biology this month. The authors sought to determine how the cancer still produced facial tumours after vaccination.
They found the tumours can react to the immune system of their host animal by changing their gene expression. Facial tumours in unvaccinated devils express genes that make them appear like the cells that form myelin sheaths around neurons in the nervous system. These are the same cells the cancer originates from.
In vaccinated devils, the facial tumours reduce the expression of these genes and boost the expression of genes associated with other cells including immune genes. This allows the tumour to sidestep the vaccine by changing its gene expression to avoid detection by the devils’ immune systems since the vaccine trains it to identify the original gene expression.
Now the researchers have discovered the mechanism used by the facial tumour disease, they hope future vaccines can be modified to account for this adaptable gene expression. They say the finding could also go on to inform us about how cancers avoid immune systems in other animals and may play a part in the development of human cancer therapeutics.