Abstract 590: A new standardized CD8 and PD-L1 dual assay

PD1/PD-L1 pathway blockade results in a durable clinical response in a fraction of the non-small cell lung cancer (NSCLC) patients. Today, the expression of PD-L1, detected by immunohistochemistry (IHC) at the surface of tumor or tumor-infiltrating immune cells, is used to select patients that may respond to immune checkpoint inhibitors (ICI). However the predictive value of that biomarker alone is questioned. In order to better stratify NSCLC patients, we have developed a new dual-staining IHC assay of PD-L1+ and CD8+ cells (TILs) present in the tumor microenvironment on a single slide prepared from FFPE tissue. The assay was optimized and fully automated on the Benchmark XT platform (Roche Ventana) with anti-PD-L1 (HDX3) and anti-CD8 (HDX2) monoclonal primary antibodies, respectively revealed with DAB and fast red substrates. Stained slides are analyzed by a pathologist like any other existing IVD test together with the TILs information. In addition, after digitization, the samples are analyzed to quantify brown and red cells with a newly developed digital Pathology (DP) tool. The following parameters are reported by the DP tool: (1) CD8+ cell density (cells/mm²) ; (2) PD-L1+ cell density (cells/mm²) ; proximity between CD8+ and PD-L1+ cells, either centered on CD8+ or on PD-L1+ cells and finally cluster indexes for CD8+ cells and PD-L1+ cells. HalioDx DP analysis tool can calculate these parameters on any Regions Of Interest (ROI) defined by the user. Accuracy of the automated numeration of CD8+ and PD-L1+ cells was validated by an expert pathologist. Cell-to-cell distances were validated with an independent DP tool. Variability was assessed for all parameters using adjacent dual-stained slides on complete tissue sections. The concordance with main IVD approved PD-L1 methods was established on a representative set of 55 NSCLC tumours. HalioDx has developed an innovative assay based on the dual staining of CD8+ and PD-L1+ cells associated to a DP tool to standardize the evaluation of the tumor microenvironment. This assay could have higher predictive performance than existing IVD tests used to identify ICI resistant NSCLC patients. Citation Format: Florence Monville, Emmanuel Prestat, Nadia Yessaad, Marine Villard, Luciana Batista, Jerome Galon, Julien Adam, Jacques Fieschi. A new standardized CD8 and PD-L1 dual assay [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 590. doi:10.1158/1538-7445.AM2017-590