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. 2018 Nov 27;6(1):131.
doi: 10.1186/s40425-018-0450-7.

Merkel cell polyomavirus-specific immune responses in patients with Merkel cell carcinoma receiving anti-PD-1 therapy

Natalie J Miller  1 , Candice D Church  1 , Steven P Fling  2 , Rima Kulikauskas  1 , Nirasha Ramchurren  2 , Michi M Shinohara  1 , Harriet M Kluger  3 , Shailender Bhatia  1 , Lisa Lundgren  2 , Martin A Cheever  2   4 , Suzanne L Topalian  5 , Paul Nghiem  6
Affiliations

Merkel cell polyomavirus-specific immune responses in patients with Merkel cell carcinoma receiving anti-PD-1 therapy

Natalie J Miller et al. J Immunother Cancer. .

Abstract

Background: Merkel cell carcinoma (MCC) is an aggressive skin cancer that frequently responds to anti-PD-1 therapy. MCC is associated with sun exposure and, in 80% of cases, Merkel cell polyomavirus (MCPyV). MCPyV-specific T and B cell responses provide a unique opportunity to study cancer-specific immunity throughout PD-1 blockade therapy.

Methods: Immune responses were assessed in patients (n = 26) with advanced MCC receiving pembrolizumab. Peripheral blood mononuclear cells (PBMC) were collected at baseline and throughout treatment. MCPyV-oncoprotein antibodies were quantified and T cells were assessed for MCPyV-specificity via tetramer staining and/or cytokine secretion. Pre-treatment tumor biopsies were analyzed for T cell receptor clonality.

Results: MCPyV oncoprotein antibodies were detectable in 15 of 17 (88%) of virus-positive MCC (VP-MCC) patients. Antibodies decreased in 10 of 11 (91%) patients with responding tumors. Virus-specific T cells decreased over time in patients who had a complete response, and increased in patients who had persistent disease. Tumors that were MCPyV(+) had a strikingly more clonal (less diverse) intratumoral TCR repertoire than virus-negative tumors (p = 0.0001).

Conclusions: Cancer-specific T and B cell responses generally track with disease burden during PD-1 blockade, in proportion to presence of antigen. Intratumoral TCR clonality was significantly greater in VP-MCC than VN-MCC tumors, suggesting expansion of a limited number of dominant clones in response to fewer immunogenic MCPyV antigens. In contrast, VN-MCC tumors had lower clonality, suggesting a diverse T cell response to numerous neoantigens. These findings reveal differences in tumor-specific immunity for VP-MCC and VN-MCC, both of which often respond to anti-PD-1 therapy.

Keywords: Anti-PD-1; Immunotherapy; Merkel cell carcinoma; Merkel cell polyomavirus; Pembrolizumab; T cell; Viral cancer antigen.

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Conflict of interest statement

Ethics approval and consent to participate

The protocol was approved by the institutional review board at each participating center, and the study was conducted in accordance with the Declaration of Helsinki and the International Conference on Harmonisation Good Clinical Practice guidelines. All the patients provided written informed consent before study entry.

Consent for publication

Patients provided informed consent for publication of de-identified data. The consent is held by the Cancer Immunotherapy Trials Network and is available for review.

Competing interests

PN serves as a paid consultant for EMD Serono. Bristol Myers Squibb has provided research support to PN’s institution. SLT has research grants from Bristol-Myers Squibb, and receives consulting fees and stock from Five Prime Therapeutics; her spouse receives consulting fees from Amgen, Compugen, MedImmune, Merck, Pfizer, and Potenza Therapeutics, and receives stock options from Compugen, Jounce Therapeutics, and Potenza.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1
Fig. 1
MCPyV-oncoprotein antibody titers over the course of anti-PD-1 therapy. 15 of 17 (88%) patients with VP-MCC tumors produced antibodies specific for MCPyV small T oncoprotein while no VN-MCC patients produced antibodies. MCPyV-oncoprotein antibody titer was tracked over time in seropositive individuals with available post-treatment serum samples (n = 13). Titers are plotted as percent change from baseline (100%). a) Patients with a complete response experienced a decrease in titer (n = 3). b) Among partial responders (n = 8), titer initially decreased over time in 7 of 8 patients. Two patients subsequently recurred (denoted by *); clinical detection of recurrence was preceded by a rise in titer in both cases
Fig. 2
Fig. 2
Frequency of MCPyV-specific CD8 T cells over the course of anti-PD-1 therapy. MCPyV-specific HLA class I tetramer-positive T cells were detected in pre-treatment PBMC in 6 of 9 (66%) of patients with VP-MCC tumors and appropriate HLA-I types, and in 0 of 8 patients with VN-MCC tumors with appropriate HLA class I types. a) Representative gating strategy for detection of MCPyV-specific T cells as indicated by tetramer binding. b) The frequency of tetramer-positive T cells increased after therapy in patients with a partial response (dashed, n = 3), yet remained similar to baseline or decreased in patients with a complete response (black, n = 2). Two patients subsequently recurred (denoted by * for recurrence on treatment and ** for recurrence after end of treatment)
Fig. 3
Fig. 3
T cell reactivity to MCPyV-specific peptides increased after therapy in a patient who had a robust partial response to pembrolizumab. a) There was a significant reduction in burden of liver metastases (white arrow heads) as visualized by CT scans obtained at baseline and 12 weeks after initiating therapy. b) IFN-γ and IL-2 production by CD8+ cells from circulating PBMC to pools of MCPyV-specific peptides from samples obtained immediately pre-treatment and after 12 weeks of pembrolizumab therapy show a ~15x increase in anti-MCPyV-reactivity to peptide pools 1 and 2 after subtraction of background stimulation by DMSO. c) The frequency of tetramer+ CD8 cells restricted to HLA-B*07:02 ‘APNCYGNIPL’ (an epitope in Pool 1) increased significantly (~7x) after therapy
Fig. 4
Fig. 4
Comparison of T cell receptor clonality by viral status and response to anti-PD-1. a) TCR clonality is significantly higher in patients with VP-MCCs compared to those with VN-MCCs (p = 0.0001 by Mann-Whitney test). b) TCR clonality is not associated with response to pembrolizumab (p = 0.2636 by Mann-Whitney test). This observation remains true when comparing clonality among responding versus non-responding patients whose tumors are virus-positive (virus(+) = open circles; virus(−) = black squares)
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