In the 16 years since Devil Facial Tumor Disease emerged among the devils of Tasmania, DFTD has devastated the island’s population of these carnivorous marsupials. The infection spreads easily among the violent animals — they bite each other, passing tumor cells from one devil to the next — and DFTD always ends in death.
A devil’s immune system should be able to put up some sort of fight against the cancer cells, but it doesn’t. And a group of scientists led by the University of Cambridge in England now say they know why; they report their findings today in the Proceedings of the National Academy of Sciences.
DFTD cells, they found, don’t express major histocompatability complex (MHC) molecules on their surface. These molecules alert the T cells of the immune system that a foreign cell is foreign. Without the molecules, the immune system doesn’t know it should fight back.
There are two types of MHC molecules — class I and class II. The DFTD cells likely don’t have class II molecules because the cells got their start as Schwann cells, a type of nervous system cell. In humans and rodents, Schwann cells are known to not express class II MHC molecules; it may be the same in devils.
The class I MHC molecules, though, were probably lost later, the researchers say, but not because of a mutation. Instead, these molecules are not expressed because of epigenetic changes that likely occurred years ago when a devil’s Schwann cells transformed into DFTD cells. It’s one of the changes that turned DFTD into such a horrible, dangerous disease.
But the discovery of how DFTD evades the immune system gave the researchers an idea on how they could prime a devil’s immune system to fight the disease: They suggest that modifying DFTD cells to express MHC molecules could work as a vaccine.
Time is running out, though. Already 84 percent of the devil population is gone. And a vaccine may not prove a savior. “Even if we had a perfect vaccine, we’d probably have to vaccinate every animal more than once,” Alexandre Kreiss, a research fellow at the Menzies Research Institute in Tasmania told the New York Times in January. “I don’t see us doing that for the whole population.”
Image courtesy of flickr user quollism