Comprehensive immunohistochemical analysis of PD-L1 shows scarce expression in castration-resistant prostate cancer
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Christian D. Fankhauser1, Peter J. Schüffler2,3, Silke Gillessen4, Aurelius Omlin4, Niels J. Rupp5, Jan H. Rueschoff5, Thomas Hermanns1, Cedric Poyet1, Tullio Sulser1, Holger Moch5 and Peter J. Wild5
1Department of Urology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
2Department of Computer Science, ETH Zurich, Zurich, Switzerland
3Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, USA
4Department of Medical Oncology and Hematology, Cantonal Hospital, St. Gallen, Switzerland
5Department of Pathology and Molecular Pathology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
Peter J. Wild, email: [email protected]
Keywords: prostate cancer, PD-L1, immunotherapy, immune response
Received: September 30, 2016 Accepted: November 15, 2017 Published: December 04, 2017
Background: We aimed to analyze the frequency and distribution of PD-L1 expression in specimens from prostate cancer (PC) patients using two different anti-PD-L1 antibodies (E1L3N, SP263).
Materials and Methods: PD-L1 immunohistochemistry was performed in a tissue microarray consisting of 82 castration-resistant prostate cancer (CRPC) specimens, 70 benign prostate hyperplasia (BPH) specimens, 96 localized PC cases, and 3 PC cell lines, using two different antibodies (clones E1L3N, and SP263). Staining images for CD4, CD8, PD-L1, and PanCK of a single PD-L1 positive case were compared, using a newly developed dot-wise correlation method for digital images to objectively test for co-expression.
Results: Depending on the antibody used, in tumor cells (TC) only five (E1L3N: 6%) and three (SP263: 3.7%) samples were positive. In infiltrating immune cells (IC) 12 (SP263: 14.6%) and 8 (E1L3N: 9.9%) specimens showed PD-L1 expression. Two PC cell lines (PC3, LnCaP) also displayed membranous immunoreactivity. All localized PCs or BPH samples tested were negative. Dot-wise digital correlation of expression patterns revealed a moderate positive correlation between PD-L1 and PanCK expression, whereas both PanCK and PD-L1 showed a weak negative Pearson correlation coefficient between CD4 and CD8.
Conclusions: PD-L1 was not expressed in localized PC or BPH, and was only found in a minority of CRPC tumors and infiltrating immune cells. Protein expression maps and systematic dot-wise comparison could be a useful objective way to describe the relationship between immuno- and tumor-related proteins in the future, without the need to develop multiplex staining methods.
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