What Can We Learn from the (Tasmanian) Devil?
Why might stem cell scientists care about a small marsupial unique to Tasmania, a small island off the coast of Australia? Good question. Tasmanian devils are afflicted with a unique type of cancer that is transmitted from animal to animal – a disease that is threatening existence of the species. Scientists are studying stem cells from these animals in the hopes that they can learn how the cancer spreads and develop life-saving treatments to save this marsupial from extinction.
Studying stem cells to learn about disease is integral to the work of stem cell scientists, who will soon be gathering across the Bass Straight from Tasmania in Melbourne, Australia for the International Society for Stem Cell Research (ISSCR) 2018 Annual Meeting. Nearly 3500 researchers from around the world will be on hand to report and discuss the latest findings in stem cell research. The meeting highlights the diverse ways that stem cells are being studied and applied, with an eye toward insights that can improve human health.
While the meeting location is coincidental, it is does highlight the importance of studying stem cells in a wide variety of living organisms. About 70% of living marsupial species reside on the Australian continent. They are a type of mammal named for their distinctive pouch that some use to carry and protect their developing young, and many species face extinction. Notably, Tasmanian devils have experienced an 80% decline in population over the last 20 years, decimated by devil facial tumor disease (DFTD), a form of transmissible cancer passed between animals, with no known cure.
Transmissible tumors are extremely rare. In order to infect another animal with cancer the tumor cells need the ability to do two things: pass between individuals and evade the new host’s immune system. To date, the only other types of transmissible cancer that have been identified are canine transmissible venereal tumors and a recently described cancer in soft-shell crabs.
Tasmanian devils spread DFTD when they bite each other during feeding or mating, passing along the tumor cells. In most mammals the infected cells would be rejected because the recipient’s immune system would recognize them as foreign and eliminate them. In Tasmanian devils, however, it appears that the tumor cells use escape mechanisms to evade immune attack. The cells suppress expression of some key genes that would normally identify the tumor cells as foreign invaders to be destroyed. In the absence of these signals, the tumor cells multiply and continue to spread between animals. While transmissible cancers have not been detected in humans, tumor cells from cancers such as melanoma and breast carcinoma can escape immune response using these and other mechanisms.
In order to understand this disease and to try to develop treatments to help Tasmanian devils survive, scientists are using induced pluripotent stem (iPS) cells. These cells are created in the lab, using cells that normally cannot become another type of cell, such as skin cells, and engineering them to acquire “stemness,” the ability to become any type of cell. These iPS cells have been generated from a number of non-marsupial mammals, but it was unknown whether they could be made from marsupials until recently when a group of scientists at the University of Queensland, Australia, successfully generated marsupial iPS cells for the first time (see this EurekAlert! article for more).
As researchers uncover how the DFTD tumors form and escape detection, they hope to develop iPS cell-derived treatments that could target the tumors and stop them from growing and being transmitted. This same research may one day lead scientists to identify novel cancer therapeutics for use in humans.The study of different animal species, such as the Tasmanian devil, is an essential aspect of scientific discovery; stem cells from one species can often shed light on the developmental biology and disease in another type of living organism. A focus on animals at risk of extinction, such as the Tasmanian devil, is also not new. iPS cells have been generated from endangered species such as the orangutan, snow leopard, and northern white rhinoceros, of which there are only 3 left in existence. Scientists hope that studying these iPS cells will illuminate the biology that makes each of these species unique and will enable regenerative medicine efforts that might help dwindling populations recover from genetic or metabolic diseases. By understanding more about these distinctive animals, and looking for similarities with aspects of human biology, researchers can also gain insights into how to address human disease.