Abstract 5625: Identification and validation of a PD-L1 specific peptide for determination of PD-L1 expression in tumors

In recent years, immunotherapy has seen a resurgence as a promising method of treating cancers. The interaction between Programmed Death Ligand 1 (PD-L1) and its receptor, Programmed Death 1 receptor (PD-1) has been of particular interest. Many different types of tumors have been shown to overexpress PD-L1, which causes host immune cells that express the PD-1 receptor and bind PD-L1 to cease killing the tumor. Patients who have tumors exhibiting high levels of PD-L1 show poor prognosis compared to those who do not. Inhibition of the PD-L1 PD-1 binding axis has been shown to restore host immunity to the tumor, and recently many new drugs such as atezolizumab and pembrolizumab have been developed to target this interaction. Current methods of PD-L1 diagnosis have shown to vary based on the antibody, detection kit brand, antigen retrieval method, and clinically strict defined methods for use by the FDA for assessment. To refine detection of PD-L1, we have identified a PD-L1 specific peptide which can be used to detect PD-L1 expressing tumors using either conventional immunohistochemistry or flow cytometry. Immunohistochemistry using this peptide was tested against the FDA-approved PD-L1 (SP263) Rabbit monoclonal primary antibody on biopsied patient tissues. Flow cytometry was performed on both cultured cell lines and patient tissues. We have shown that our PD-L1 peptide shows specific staining in the tumor regions of FFPE tissues where the SP263 kit does not stain, and we can also detect PD-L1 expression in both cell samples and patient tissues using flow cytometry. Citation Format: Charles Caldwell, Cory Johnson, Richard Hammer, Raghuraman Kannan. Identification and validation of a PD-L1 specific peptide for determination of PD-L1 expression in tumors [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 5625. doi:10.1158/1538-7445.AM2017-5625