Submitter Withdrawn 34th Lorne Cancer Conference 2022

Two distinct transcriptional responses to type II interferon treatment in Merkel cell carcinoma cell lines corresponds to immune infiltrate signatures found in clinical samples and patient overall survival (80058)

Alexander Caneborg 1 , Sara Roth 2 3 , Atara Posner 1 , Glen Guerra 2 3 , Robert Ramsay 2 3 , Shahneen Sandhu 2 3 4 , Rod Hicks 2 3 5 , Richard W Tothill 1
  1. Department of Clinical Pathology and Centre for Cancer Research, University Of Melbourne, Melbourne, VICTORIA, Australia
  2. Research Division, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
  3. Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, Victoria, Australia
  4. Medical Oncology Department, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
  5. Cancer Imaging Department, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia

Merkel cell carcinomas are highly immunogenic neuroendocrine skin cancers with two distinct aetiologies – one associated with the Merkel cell polyoma virus (MCPyV) and the other with UV-carcinogenesis. While multiple MCC cell lines have been previously described, most represent viral-positive MCC (VP-MCC). We established four MCC cell lines: three VN-MCC and one VP-MCC. Two cell lines were established from patient derived xenografts and two directly from tumour explants. All cell lines display a classical non-adherent growth pattern in culture and whole genome sequencing showed matching mutational profiles in cell lines and originating tumours. High tumour mutation burden, a UV-mutation signature, RB1 and TP53 mutations were all detected in VN-MCC, while the VP-MCC cell line had MCPyV genome integration and a UV signature with low mutation burden, which was a novel observation in VP-MCC. The cell lines differentially expressed neuroendocrine and epithelial to mesenchymal transition (EMT) marker genes.  Type II interferon (IFNg) treatment of the four cell lines revealed two distinct transcriptional responses (sig-A and sig-B). Gene-expression correlates of sig-A in a series of bulk tissue RNA analysed MCC tumours showed correlation to T cell markers, consistent with the sig-A expressing cell lines originating from tumours with brisk T cell (CD8+ and  gdT+) infiltrates and high PD-L1 expression. Sig-B correlated to myeloid cell gene markers and cell lines originated from tumours with low T cell infiltrates. Gene set enrichment analysis testing sig-A and sig-B combined with Cox-regression survival analysis in an expanded patient cohort (n=89) showed better overall survival for those patients with high sig-A enrichment scores (>75th percentile, p=0.003). We therefore demonstrated our MCC cell lines are representative models of VN and VP-MCC and that immune response and patient survival may be associated with an intrinsic cellular program linked to IFNg  response in tumour cells.