title: Transmission of a fatal clonal tumor by biting occurs due to depleted MHC diversity in a threatened carnivorous marsupial.
abstract: A fatal transmissible tumor spread between individuals by biting has emerged in the Tasmanian devil (Sarcophilus harrisii), a carnivorous marsupial. Here we provide genetic evidence establishing that the tumor is clonal and therefore foreign to host devils. Thus, the disease is highly unusual because it is not just a tumor but also a tissue graft, passed between individuals without invoking an immune response. The MHC plays a key role in immune responses to both tumors and grafts. The most common mechanism of immune evasion by tumors is down-regulation of classical cell surface MHC molecules. Here we show that this mode of immune escape does not occur. However, because the tumor is a graft, it should still be recognized and rejected by the host's immune system due to foreign cell surface antigens. Mixed lymphocyte responses showed a lack of alloreactivity between lymphocytes of different individuals in the affected population, indicating a paucity of MHC diversity. This result was verified by genotyping, providing a conclusive link between a loss of MHC diversity and spread of a disease through a wild population. This novel disease arose as a direct result of loss of genetic diversity and the aggressive behavior of the host species. The neoplastic clone continues to spread although the population, and, without active disease control by removal of affected animals and the isolation of disease-free animals, the Tasmanian devil faces extinction.
authors.affiliation: Faculty of Veterinary Science, University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: Hannah V
authors.initials: HV
authors.lastname: Siddle
authors.forename: Alexandre
authors.initials: A
authors.lastname: Kreiss
authors.forename: Mark D B
authors.initials: MD
authors.lastname: Eldridge
authors.forename: Erin
authors.initials: E
authors.lastname: Noonan
authors.forename: Candice J
authors.initials: CJ
authors.lastname: Clarke
authors.forename: Stephen
authors.initials: S
authors.lastname: Pyecroft
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Woods
authors.forename: Katherine
authors.initials: K
authors.lastname: Belov
mesh_terms: D000595:Amino Acid Sequence; D000820:Animal Diseases / Q000235:genetics / Q000276:immunology / Q000635:transmission; D000818:Animals; D001733:Bites and Stings; D004247:DNA / Q000235:genetics; D053476:Extinction, Biological; D005805:Genes, MHC Class I; D005802:Genes, MHC Class II; D014644:Genetic Variation; D007959:Lymphocyte Culture Test, Mixed; D008285:Major Histocompatibility Complex; D008394:Marsupialia / Q000235:genetics* / Q000276:immunology*; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D009369:Neoplasms / Q000235:genetics* / Q000276:immunology / Q000662:veterinary*; D018807:Polymorphism, Single-Stranded Conformational; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
chemical_list: D004247:DNA