title: PD-L1 Is Not Constitutively Expressed on Tasmanian Devil Facial Tumor Cells but Is Strongly Upregulated in Response to IFN-γ and Can Be Expressed in the Tumor Microenvironment.
abstract: The devil facial tumor disease (DFTD) is caused by clonal transmissible cancers that have led to a catastrophic decline in the wild Tasmanian devil (Sarcophilus harrisii) population. The first transmissible tumor, now termed devil facial tumor 1 (DFT1), was first discovered in 1996 and has been continually transmitted to new hosts for at least 20 years. In 2015, a second transmissible cancer [devil facial tumor 2 (DFT2)] was discovered in wild devils, and the DFT2 is genetically distinct and independent from the DFT1. Despite the estimated 136,559 base pair substitutions and 14,647 insertions/deletions in the DFT1 genome as compared to two normal devil reference genomes, the allograft tumors are not rejected by the host immune system. Additionally, genome sequencing of two sub-strains of DFT1 detected greater than 15,000 single-base substitutions that were found in only one of the DFT1 sub-strains, demonstrating the transmissible tumors are evolving and that generation of neoantigens is likely ongoing. Recent evidence in human clinical trials suggests that blocking PD-1:PD-L1 interactions promotes antitumor immune responses and is most effective in cancers with a high number of mutations. We hypothesized that DFTD cells could exploit the PD-1:PD-L1 inhibitory pathway to evade antitumor immune responses. We developed recombinant proteins and monoclonal antibodies (mAbs) to provide the first demonstration that PD-1 binds to both PD-L1 and PD-L2 in a non-placental mammal and show that PD-L1 is upregulated in DFTD cells in response to IFN-γ. Immunohistochemistry showed that PD-L1 is rarely expressed in primary tumor masses, but low numbers of PD-L1+non-tumor cells were detected in the microenvironment of several metastatic tumors. Importantly,in vitrotesting suggests that PD-1 binding to PD-L1 and PD-L2 can be blocked by mAbs, which could be critical to understanding how the DFT allografts evade the immune system.
authors.affiliation: Menzies Institute for Medical Research, University of Tasmania, Hobart, TAS, Australia; Experimental Therapeutics Laboratory, Hanson Institute, School of Pharmacy and Medical Science, University of South Australia, Adelaide, SA, Australia; Experimental Therapeutics Laboratory, Sansom Institute, School of Pharmacy and Medical Science, University of South Australia, Adelaide, SA, Australia.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Flies
authors.affiliation: School of Medicine, University of Tasmania , Hobart, TAS , Australia.
authors.forename: A Bruce
authors.initials: AB
authors.lastname: Lyons
authors.affiliation: Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, VIC, Australia.
authors.forename: Lynn M
authors.initials: LM
authors.lastname: Corcoran
authors.affiliation: Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, VIC, Australia; Computational Cancer Biology Program, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia.
authors.forename: Anthony T
authors.initials: AT
authors.lastname: Papenfuss
authors.affiliation: Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, VIC, Australia.
authors.forename: James M
authors.initials: JM
authors.lastname: Murphy
authors.affiliation: Mount Pleasant Laboratories, Tasmanian Department of Primary Industries, Parks, Water and the Environment , Prospect, TAS , Australia.
authors.forename: Graeme W
authors.initials: GW
authors.lastname: Knowles
authors.affiliation: Menzies Institute for Medical Research, University of Tasmania , Hobart, TAS , Australia.
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Woods
authors.affiliation: Experimental Therapeutics Laboratory, Hanson Institute, School of Pharmacy and Medical Science, University of South Australia, Adelaide, SA, Australia; Experimental Therapeutics Laboratory, Sansom Institute, School of Pharmacy and Medical Science, University of South Australia, Adelaide, SA, Australia; Discipline of Obstetrics and Gynaecology, School of Medicine, Robinson Research Institute, The University of Adelaide, Adelaide, SA, Australia.
authors.forename: John D
authors.initials: JD
authors.lastname: Hayball
keywords: DFTD; PD-1; PD-L1; allograft; inhibitory checkpoint molecule; marsupial; transmissible tumor; wild immunity