Optimization of Programmed Death Ligand-1 Immunohistochemical Protocol on Urothelial Carcinomas, Using an Automated Immunostainer (Leica, BOND-MAX)

Abstract

Background: In urothelial carcinomas, Programmed Death Ligand-1 (PD-L1) expression assessed by immunohistochemistry is essential in order to predict the response of patients to immunotherapy.

Objective: The aims of our study were (1) to optimise the automated immunohistochemistry staining technique for the PD-L1 antibody 73-10 clone (Leica Biosystems), using a control tissue, on the Leica BOND-MAX immunostaining platform at the Center for Advanced Medical and Pharmaceutical Research – Laboratory of Normal and Pathological Morphology (MORFO) and (2) to validate the technique by applying it on a series of 40 urothelial carcinomas.

Methods: The cases included in our study corresponded to muscle-invasive urothelial carcinomas diagnosed on radical cystectomy specimens. The cases were retrieved from the Pathology Department of Târgu-Mureș Emergency County Hospital database (between 2011-2018). The immunohistochemical staining was optimized according to the producer’s recommendation and adapted to our laboratory. Palatine tonsil specimen served as positive control tissue.  PD-L1 positivity was assessed in all urothelial carcinoma cases either by evaluating the tumor and immune cells, or by applying the Combined Positive Score.

Results: Our technique enabled us to obtain a well-optimized, high quality immunohistochemical PD-L1 staining on the control tissue, which was further successfully applied on the urothelial carcinoma cases. By assessing the PD-L1-positive tumor cells and/or immune cells percentages, 15 cases were considered PD-L1 positive. Using the Combined Positive Score, 16 cases were evaluated as positive.

Conclusion: The immunohistochemistry protocol optimization for any antibody is a crucial step that must be performed in each laboratory in order to obtain reliable and reproducible results, which enable further application into daily routine.