Merkel polyomavirus-specific T cells fluctuate with merkel cell carcinoma burden and express therapeutically targetable PD-1 and Tim-3 exhaustion markers.
OBJECTIVE
The persistent expression of Merkel cell polyomavirus (MCPyV) oncoproteins in Merkel cell carcinoma (MCC) provides a unique opportunity to characterize immune evasion mechanisms in human cancer. We isolated MCPyV-specific T cells and determined their frequency and functional status.


METHODS
Multiparameter flow cytometry panels and HLA/peptide tetramers were used to identify and characterize T cells from tumors (n = 7) and blood (n = 18) of patients with MCC and control subjects (n = 10). PD-1 ligand (PD-L1) and CD8 expression within tumors were determined using mRNA profiling (n = 35) and immunohistochemistry (n = 13).


RESULTS
MCPyV-specific CD8 T cells were detected directly ex vivo from the blood samples of 7 out of 11 (64%) patients with MCPyV-positive tumors. In contrast, 0 of 10 control subjects had detectable levels of these cells in their blood (P < 0.01). MCPyV-specific T cells in serial blood specimens increased with MCC disease progression and decreased with effective therapy. MCPyV-specific CD8 T cells and MCC-infiltrating lymphocytes expressed higher levels of therapeutically targetable PD-1 and Tim-3 inhibitory receptors compared with T cells specific to other human viruses (P < 0.01). PD-L1 was present in 9 of 13 (69%) MCCs and its expression was correlated with CD8-lymphocyte infiltration.


CONCLUSIONS
MCC-targeting T cells expand with tumor burden and express high levels of immune checkpoint receptors PD-1 and Tim-3. Reversal of these inhibitory pathways is therefore a promising therapeutic approach for this virus-driven cancer.
Authors' Affiliations: Departments of Medicine/Dermatology, Pathology, Medicine, Laboratory Medicine, Global Health, University of Washington; Fred Hutchinson Cancer Research Center; Benaroya Research Institute, Seattle, Washington; and Department of Medicine/Dermatology, Saga University, Nabeshima, Japan.
Olga K
OK
Afanasiev
Lola
L
Yelistratova
Natalie
N
Miller
Kotaro
K
Nagase
Kelly
K
Paulson
Jayasri G
JG
Iyer
Dafina
D
Ibrani
David M
DM
Koelle
Paul
P
Nghiem
D000914:Antibodies, Viral / Q000276:immunology; D000956:Antigens, Viral / Q000276:immunology / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D015266:Carcinoma, Merkel Cell / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology / Q000821:virology; D016022:Case-Control Studies; D000072597:Hepatitis A Virus Cellular Receptor 2; D007150:Immunohistochemistry; D016130:Immunophenotyping; D016246:Lymphocytes, Tumor-Infiltrating / Q000276:immunology / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D059965:Merkel cell polyomavirus / Q000276:immunology*; D009856:Oncogene Proteins, Viral / Q000276:immunology / Q000378:metabolism; D061026:Programmed Cell Death 1 Receptor / Q000378:metabolism*; D016176:T-Lymphocyte Subsets / Q000276:immunology* / Q000378:metabolism; D047368:Tumor Burden / Q000276:immunology
D000914:Antibodies, Viral; D000956:Antigens, Viral; D015415:Biomarkers; C448908:HAVCR2 protein, human; D000072597:Hepatitis A Virus Cellular Receptor 2; D008565:Membrane Proteins; D009856:Oncogene Proteins, Viral; D061026:Programmed Cell Death 1 Receptor