NLRC5 regulates expression of MHC-I and provides a target for anti-tumor immunity in transmissible cancers

Abstract

Purpose Downregulation of MHC class I (MHC-I) is a common immune evasion strategy of many cancers. Similarly, two allogeneic clonal transmissible cancers have killed thousands of wild Tasmanian devils (Sarcophilus harrisii) and also modulate MHC-I expression to evade anti-cancer and allograft responses. IFNG treatment restores MHC-I expression on devil facial tumor (DFT) cells but is insufficient to control tumor growth. Transcriptional co-activator NLRC5 is a master regulator of MHC-I in humans and mice but its role in transmissible cancers remains unknown. In this study, we explored the regulation and role of MHC-I in these unique genetically mis-matched tumors. Methods We used transcriptome and flow cytometric analyses to determine how MHC-I shapes allogeneic and anti-tumor responses. Cell lines that overexpress NLRC5 to drive antigen presentation, and B2M-knockout cell lines incapable of presenting antigen on MHC-I were used to probe the role of MHC-I in rare cases of tumor regressions. Results Transcriptomic results suggest that NLRC5 plays a major role in MHC-I regulation in devils. NLRC5 was shown to drive the expression of many components of the antigen presentation pathway but did not upregulate PDL1. Serum from devils with tumor regressions showed strong binding to IFNG-treated and NLRC5 cell lines; antibody binding to IFNGtreated and NRLC5 transgenic tumor cells was diminished or absent following B2M knockout. Conclusion MHC-I could be identified as a target for anti-tumor and allogeneic immunity. Consequently, NLRC5 could be a promising target for immunotherapy and vaccines to protect devils from transmissible cancers and inform development of transplant and cancer therapies for humans.

CIITA induces expression of MHC-I and MHC-II in transmissible cancers

“…We have previously shown that MHC-I on DFT1 cells is the predominant antibody target in devils with natural and induced anti-DFT immune response including tumour regressions (Ong et al, 2021). Here we tested if expression of CIITA in DFT cells could also upregulate antibody targets on DFT cells.…”

“…Serum samples from four devils (My, TD4, TD5, and TD6), collected before (pre-immune) and after DFT1 clinical manifestations (immune), were used to assess antibody responses towards CIITA-expressing DFT cell lines (Supplementary Table 5). The serum samples were identified as immune from the presence of anti-DFT1 antibodies, which were found to be predominantly against MHC-I on DFT1 cells (Ong et al, 2021). 'My' was a devil that was immunised, challenged with DFT1 cells, and subsequently treated with an experimental immunotherapy that induced tumour regression (Tovar et al, 2017).…”

Class II transactivator induces expression of MHC-I and MHC-II in transmissible Tasmanian devil facial tumours

“…This occurs via epigenetic downregulation of several components of the MHC-I antigen processing pathway [5] and a hemizygous deletion of beta-2 microglobulin (B2M), which is necessary for stabilizing MHC-I complexes on the cell surface [6]. Natural and immunotherapyinduced tumour regressions have been observed in devils, along with antibody responses to DFT1 cells, albeit primarily in the context of MHC-I [7][8][9]. Conversely, the emerging DFT2 tumours do express MHC-I [10], suggesting that other immune evasion mechanisms are important.…”

Applied ecoimmunology: using immunological tools to improve conservation efforts in a changing world

“…Natural DFT1 regressions have also been observed in wild devils ( Pye et al , 2016 ; Margres et al , 2018 ). CRISPR/Cas9 was used to completely knockout MHC-I from DFT1 cells, and this cell line was used to show that MHC-I proteins are a major serum antibody target in devils that had immunotherapy-induced or natural DFT1 regressions ( Pye et al , 2016 ; Margres et al , 2018 ; Ong et al , 2021 ). Altogether these results suggest that low MHC-I diversity and reduced MHC-I expression are important for transmissible cancer cells, but additional mechanisms are likely employed to evade immune defences.…”