Abstract 5529: PD-L1 and CD8 IHC dual assessment in NSCLC using the Halioseek® assay: A multicentric study
Authors: Batista Luciana , Brandone Nicolas , Garcia Stéphane , Boumber Yanis , Dulaimi Essel , Tanière Philippe , Hofman Paul , Ilié Marius , Adam Julien , Galon Jérôme , Gerbon Catherine , Fieschi Jacques 
Published: August 2018

Abstract
Background
Immune checkpoint inhibitors (ICI) have revolutionized the treatment of NSCLC, but only a small proportion of treated patients exhibit a long term response. Improved selection of the patients that will respond to ICI is a major unmet need. Despite its relatively limited predictive value, the percentage of PD-L1+ tumor cells supports their application. It is proposed that NSCLC patient stratification might be improved by additional biomarkers, in particular, the presence of tumor infiltrating lymphocytes (TILs) which play a crucial role in tumor immune response. Halioseek® PD-L1 staining allows accurate detection of positive tumor cells in NSCLC, is comparable to other IVD assays, and is CE-IVD marked (In Vitro Diagnostic Medical Device compliant with European Directive 98/79). This standardized assay also provides complementary characterization of the tumor micro-environment without requiring additional precious tumor samples. The dual staining of Halioseek® allows simultaneous evaluation of PD-L1+ and CD8+ cells on the same tissue section. The assay also includes a Digital Pathology (DP) analysis module to determine CD8+ cell density and a proximity index between CD8+ and PD-L1+ cells.
Material and methods
A multi-centric study including 5 laboratories was performed in order to 1) Further demonstrate the inter-laboratory reproducibility of the Halioseek® assay; 2) Compare Halioseek® results to routine PD-L1 laboratory tests; 3) Explore Halioseek® Analyzer DP tools to further characterize NSCLC samples. 10 NSCLC FFPE samples (50 slides) were stained using Halioseek® by 5 independent laboratories and 66 NSCLC FFPE samples were assessed using both Halioseek® and the laboratory's routinely used PD-L1 assay by 4 independent centers. The Halioseek® assay staining was performed according to manufacturer's instructions. Percentage of PD-L1+ tumor cells was estimated by pathologists; DP analysis was performed using Halioseek® Analyzer.
Results
For the 50 slides stained using Halioseek® and evaluated independently by 5 different laboratories, a concordance of 94% and 90% was observed using the 1% and 50% cut-offs of PD-L1 positive tumor cells, respectively. When analyzed by the same pathologist, concordance increased to 100% and 94%, respectively. For the 66 samples analyzed using both Halioseek® and laboratory PD-L1 routine test, concordances were 92% and 97%. Digital pathology tools allowed further characterization of patient samples in terms of CD8+ cells density and proximity indexes.
Conclusion
Halioseek® is a new robust assay leveraging the advantages of DP to combine TILs and PD-L1 quantification within the tumor and its microenvironment. Halioseek® gives reproducible and accurate results in independent routine laboratories and its DP solution allows better sample characterization. The predictive performance of Halioseek® for the response to ICI needs to be further investigated.
Citation Format: Luciana Batista, Nicolas Brandone, Stéphane Garcia, Yanis Boumber, Essel Dulaimi, Philippe Tanière, Paul Hofman, Marius Ilié, Julien Adam, Jérôme Galon, Catherine Gerbon, Jacques Fieschi. PD-L1 and CD8 IHC dual assessment in NSCLC using the Halioseek® assay: A multicentric study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5529.