Skou, Rikke Birgitte Lyngaa3; Pedersen, Natasja Wulff1; Schrama, David4; Thrue, Charlotte Albæk1; Ibrani, Dafina4; Met, Ozcan1; thor Straten, Per1; Nghiem, Paul4; Becker, Jürgen C4; Hadrup, Sine Reker1
1 Department of Haematology, Herlev and Gentofte Hospital, The Capital Region of Denmark2 Oncology, Herlev and Gentofte Hospital, The Capital Region of Denmark3 Clinical Research Centre, Amager and Hvidovre Hospital, The Capital Region of Denmark4 unknown
PURPOSE: Merkel cell carcinoma (MCC) is a highly aggressive skin cancer with strong evidence of viral carcinogenesis. The association of MCC with the Merkel cell polyomavirus (MCPyV) may explain the explicit immunogenicity of MCC. Indeed, MCPyV-encoded proteins are likely targets for cytotoxic immune responses to MCC as they are both foreign to the host and necessary to maintain the oncogenic phenotype. However, to date only a single MCPyV-derived CD8 T-cell epitope has been described, thus impeding specific monitoring of T-cell responses to MCC. Method: To overcome this limitation, we scanned the MCPyV oncoprotein large T and small T antigens and the virus capsid protein VP1 for potential T-cell epitopes, and tested for MHC class I affinity. We confirmed the relevance of these epitopes using a high-throughput platform for T-cell enrichment and combinatorial encoding of MHC class I multimers. RESULTS: In peripheral blood from 38 patients with MCC and 30 healthy donors, we identified 53 MCPyV-directed CD8 T-cell responses against 35 different peptide sequences. Strikingly, T-cell responses against oncoproteins were exclusively present in patients with MCC, but not in healthy donors. We further demonstrate both the processing and presentation of the oncoprotein-derived epitopes, as well as the lytic activity of oncoprotein-specific T cells toward MHC-matched MCC cells. Demonstrating the presence of oncoprotein-specific T cells among tumor-infiltrating lymphocytes further substantiated the relevance of the identified epitopes. CONCLUSION: These T-cell epitopes represent ideal targets for antigen-specific immune therapy of MCC, and enable tracking and characterization of MCPyV-specific immune responses.
Clinical Cancer Research, 2014, Vol 20, Issue 7, p. 1768-78