Poster Presentation 32nd Lorne Cancer 2020

Exploring Gamma Delta T Cells in Merkel Cell Carcinoma (#129)

Alexander Caneborg 1 , Nicholas Gherardin 2 , Kelly Waldeck 3 , Martelotto Luciano 1 , Balachander Shiva 1 , Zethoven Magnus 3 , Pasquale Petrone 3 , Andrew Pattison 1 , James S Wilmott 4 , Fernando Rossello 1 , Atara Posner 1 , Jeanette Raleigh 3 , Athena Hatzimihalis 3 , Shahneen Sandhu 5 , Paul Neeson 3 , Sergio Q Para 2 , Jürgen C Becker 6 , Paolo De leso 7 , Meredith Johnston 8 9 , Margaret Chua 7 , Grant McArthur 5 , Anthony J Gill 10 , Richard A Scolyer 4 11 , Rodney Hicks 12 , Dale J Godfrey 2 , Richard W Tothill 1
  1. Department of Clinical Pathology and Centre for Cancer Research, University Of Melbourne, Melbourne, VICTORIA, Australia
  2. Peter Doherty Institute, University Of Melbourne, Melbourne, Victoria, Australia
  3. Research Division, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
  4. Melanoma Institute of Australia, University of Sydney, Sydney, NSW, Australia
  5. Medical Oncology Department, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
  6. German Cancer Consortium (DKTK), University Hospital of Essen and DKFZ, Heidelberg, Germany
  7. Skin and Melanoma Radiation Oncology Unit, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
  8. Liverpool Hospital, Sydney, NSW, Australia
  9. Radiation Oncology Research, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
  10. Cancer Diagnosis and Pathology Group, Kolling Institute of Medical Research and the University of Sydney, Sydney, NSW, Australia
  11. Tissue Pathology and Diagnostic Oncology, Royal Prince Alfred Hospital, Sydney, NSW, Australia
  12. Cancer Imaging Department, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia

Background

Merkel Cell Carcinoma (MCC) is a rare but aggressive skin malignancy associated with Merkel cell polyoma virus (MCPyV) infection and UV-carcinogenesis. MCC tumours can elicit a strong T cell response and approximately 50% of MCC patients benefit from anti-PD1/PD-L1 immune checkpoint therapy. Past research has focussed on characterising canonical ab T cell populations (CD4+ and CD8+) in MCC. Non-conventional T cells, including gamma-delta (gd) T cells, have not been reported in MCC.

Methods & Results

Multiplex-IHC was performed on 53 tumours from 35 patients targeting CD3, CD4, CD8, FOXP3, PD-L1 and synaptophysin to stain tumour cells.  Predominant (>50%) infiltration of either CD4+ or CD8+ T cells was observed in most tumours; however, 8/53 (15%) had predominant CD4-CD8- double negative (DN) T cell infiltrates, while 24/53 (45%) tumours had >20% DN T cells. No statistically significant associations were observed between T cell subsets and MCPyV-status. Flow cytometry showed that most MCC infiltrating DN T cells were gd T cells, they expressed high levels of immune checkpoint molecules PD-1 and LAG-3, consistent with immune suppression, and co-expressed CD69 and CD103, consistent with a tissue resident phenotype. T cell receptor (TCR) repertoire analysis in one patient indicated a predominance of clonally expanded Vd1 T cells, consistent with antigen-driven expansion. scRNA-seq identified a transcriptional profile of gdT cells, which was used in conjunction with Gene Set Variance Analysis (GSVA) to predict gd T cell enrichment in bulk RNA-seq tumour data. gd T cell GSVA scores were positively correlated with DN-T cells measured by m-IHC in matching tumour samples. GSVA analysis in an independent MCC cohort treated with anti-PD1/PD-L1 showed high gd T cell enrichment scores in four patients of which three had a complete response. 

Conclusion

gd T cells are abundant in some MCC. These cells express cell surface PD1 and are likely targets of immunotherapy. Further validation of our gd T cell gene-expression signature in MCC and other cancer types is underway.