Abstract 624: Characterization of PD-L1 expression and the immune cell microenvironment in hepatocellular carcinoma (HCC) and non-cirrhotic liver tissue adjacent to HCC

Abstract

Still-emerging evidence suggests that HCC is at least moderately responsive to therapeutic agents that target tumor immune suppression pathways, specifically the programmed death 1/programmed death ligand 1 (PD-L1) pathway. Prior studies raise the possibility that PD-L1 is a prognostic biomarker in HCC, where its expression levels have been reported to correlate with tumor aggressiveness and recurrence following surgical resection. The purpose of this study was to evaluate the expression of PD-L1 in non-cirrhotic liver tissue adjacent to HCC and HCC itself in 68 procured tissue samples, as well as elucidate the immune cell composition of the HCC tumor microenvironment. All cases showed the typical morphology of HCC and were classified as low- to high-grade trabecular, pseudoglandular, or solid with the common cytoplasmic features. Immunohistochemical (IHC) staining for PD-L1 in tumor-free liver (TFL) revealed PD-L1 staining in sinusoidal lining cells (macrophages [Mϕ] and endothelial cells [EC], as confirmed by double labeling for CD68 and CD31), although there was considerable heterogeneity in the extent of PD-L1 staining. More specifically, in TFL, some but not all CD68+ Mϕ were also PD-L1+, whereas most CD31+ EC were also PD-L1+. Furthermore, we evaluated PD-L1 staining qualitatively and semiquantitatively in HCC. Only few tumor cells displayed membranous PD-L1 staining, and 62/68 of the cases (91.2%) were categorized as PD-L1- vs 6/68 (8.8%) PD-L1+ (≥1% and <25% = PD-L1+); instead, PD-L1 expression within the tumor microenvironment predominantly emanated from immune cell infiltrates (as confirmed by PD-L1/pan-cytokeratin double labeling). Then we assessed the immune milieu in HCC tissue specimens using quantitative IHC. We found considerable interspecimen variation in the number of CD68+ Mϕ, CD8+ cytotoxic T lymphocytes, and FoxP3+ regulatory T lymphocytes. Comparing the number of immune cells in different tumor compartments showed that the prevalence of CD68+ cells (p=.0005), CD8+ cells (p=.0004), and FoxP3+ cells (p=.05) was significantly higher within the invasive margin vs the center of the tumor. Quantitative analysis of the immune cell content also showed that there was no correlation between T lymphocyte infiltration (CD8+/FoxP3+) and Mϕ infiltration in any compartment. Taken together, our findings confirm the intertumoral heterogeneity of the immune cell microenvironment in HCC; however, future studies are needed to correlate these findings to the clinical setting with immunooncologic treatments. Citation Format: Christian Ihling, Sienna Yoast, Yue Zhang, Bartholomew Naughton, Miriam Urban, P. Alexander Rolfe, Eveline Frick-Krieger, Isabelle Dussault. Characterization of PD-L1 expression and the immune cell microenvironment in hepatocellular carcinoma (HCC) and non-cirrhotic liver tissue adjacent to HCC [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 624. doi:10.1158/1538-7445.AM2017-624