Tasmanian Devils Threatened by an Infectious Cancer

In the mid-1990s zoologists in Tasmania noticed something grotesque. Growing from the maws of one of the world's most tenacious carnivores were masses of malignant tumors. The Tasmanian Devil Sarcophilus harrisii is famed for its high prey drive, aggressive social behaviors, and its loud vocalizations. These tumors quickly popped up on Tasmanian Devils throughout the island, an epidemic of cancer. Most cancers are isolated to the individual afflicted by the cancer, meaning that the cancer starts its cycle and ends its cycle (usually this means death) within the body of the infected. The cancer afflicting Tasmanian Devils was quickly recognized as transmissible via contact with body fluids, and named "Devil Facial Tumor Disease" (DFTD for short). As previously mentioned, DFTD spreads from contact with bodily fluids, Tasmanian Devils have the unfortunate habit of communicating with one another through bites and open mouth displays meant to intimidate rival devils. This pattern of behavior makes it very likely that an infected individual will spread DFTD to an uninfected individual via saliva or any open wounds on the face caused by previous squabbles. 

A pair of Tasmanian Devils biting one another, a common transmission vector for DFTD

DFTD has decimated 80% of the Tasmanian Devil wild populations and is a serious concern amongst conservationists as it could very well mean extinction for the Tasmanian Devil. DFTD cells exhibit tetraploidy, meaning that they have four sets of chromosomes instead of the typical diploid condition. DFTD cells also release Major Histocompatibility Complexes (MCH) which trick the Devil's immune system into thinking that the tumor cells are normal diploid somatic cells.

A Tasmanian Devil with advanced DFTD

 This bizarre distinction between the chromosome counts and the release of specific MCH molecules aids scientists in saving the species through vaccines. Previous efforts to create and implement vaccines using dead DFTD cells have had some success in the past, however, these vaccines were only effective in about 20% of the population with the remaining 80% still at risk of dying. Earlier this year an mRNA Adenovirus Vaccine was approved to be tested on captive populations. Much like the Covid-19 Vaccines, this new DFTD vaccine uses a modified adenovirus to break into cells and insert proteins similar to the MCH into the Tasmanian Devil's body.

 This, in theory, should train the Tasmanian Devil's immune system to recognize MCH molecules in the body as a foreign threat. By mounting an immune response to the MCH proteins, DFTD cells that also produce those proteins will be unable to trick the Devil's immune system into allowing the tumors to enter and proliferate within the body. This will hopefully create a more effective preventative for the spread of DFTD and give these charismatic devils a leg up against the looming threat of extinction.

See Nature Article on DFTD here

Tasmanian Devils and Cancer

           When you first see Tasmanian Devil, you probably start to think about Taz from the Looney Toons. Just like the fictional character, the Tasmanian Devils are very aggressive and are known to attack one another. A carnivorous marsupial from the island of Tasmania off the coast of Australia, the Tasmanian devil has seen a major decline and is considered endangered mainly due to the infectious disease known as the Devil Facial Tumor Disease or DFTD. In less than 20 years, the population of the Tasmanian Devils declined more than 80% due to DFTD.

            Interestingly enough, some populations of the Tasmanian Devil that were thought to have been extinct by now are actually still alive. Researchers then decided to look at the genome of these animals and determined that these genes were actually protecting the Tasmanian Devils. These researchers also discovered that these genes were helping the immune system to identify DFTD and fight back. Over the past two decades, the Tasmanian Devils seem to have been evolving a resistance to DFTD. Researchers went to the island of Tasmania and sectioned two candidate populations of the animals to view genes related to cancer or immune function. The two likely genes that have been selected for are the CD146 and the THY1 genes. Both of which are involved in immune system regulation as well as cell to cell communication and cell adhesion. Researchers thus believe that these genes are adapting to recognize the tumors formed from DFTD.

          With the strong selection due to the high fatality chance of DFTD, the evolutionary response of the Tasmanian Devil to such a selective pressure is astonishing. Although this is exciting news for the Tasmanian Devil, many of its species still succumb to DFTD. The next step in this process is to determine a way in which the gene can be used to save more of the Tasmanian Devils. A proposition would be the selective breeding of unaffected individuals with favorable genotypes for detection of the DFTD in hopes of the continued survival of the Tasmanian Devil. I personally think that researchers are on the right track for helping to protect this endangered species. I also believe that they are on their way to making a great breakthrough in terms of hopefully being able to apply the way these Tasmanian Devils are able to counteract the DFTD.

(http://www.sciencemag.org/news/2016/08/tasmanian-devils-are-rapidly-evolving-resistance-contagious-cancer)