Abstract C045: Multiplex fluorescent immunohistochemistry reveals immune microenvironment alterations in COMPASS-like complex gene mutated pancreatic cancer
Authors: Zhang Shungang , McGue Jake , Daniels Elaina , Kim Hong Sun , Thomas Dafydd , Shi Jiaqi 
Published: January 2024

Abstract
Background: Pancreatic ductal adenocarcinoma (PDAC) is highly resistant to chemoradiation and immune therapies. There is limited biomarker to identify subsets of PDAC that responds to immunotherapy or targeted therapy. We have identified a subset of PDACs (approximately 25%) carrying COMPASS-like complex (CLC) gene mutations. Analysis of the clinicopathologic and molecular features of this PDAC subset revealed that these tumors are an aggressive group of PDACs with poor or squamous histologic differentiation, increased rates of TP53 mutations, and poor patient survival compared to control PDACs. Our preliminary data showed that PDACs carrying mutations in two members of the CLC genes (KDM6A and KMT2D) have immunosuppressive tumor microenvironment (TME), suggesting that CLC genes are candidate biomarkers for immunotherapy. However, a comprehensive analysis of the immune composition, immune checkpoint expression, and the relationship between tumor cells and immune cells in CLC gene mutated PDACs compared to controls has not been performed. In this study, we characterized the immune composition in CLC gene mutated PDACs compared to paired control PDACs using tyramide signal amplification multiplex fluorescent immunohistochemistry (mfIHC). Methods: Human PDAC tissue slides were stained with 7 markers using mfIHC and allowed for phenotyping of 7 cell types: PD-L1- epithelial cells (ECs) (pancytokeratin+PD-L1-), PD-L1+ ECs (pancytokeratin+PD-L1+), cytotoxic T lymphocytes (CTLs) (CD3+CD8+), helper T cells (CD3+CD8-FoxP3-), Tregs (CD3+CD8-FoxP3+), PD-L1- antigen presenting cells (APCs) (CD163+PD-L1-), and PD-L1+ APCs (CD163+PD-L1+). Random image sections were selected in each sample (5~8 sections per sample) and divided into wild-type (WT) group (n=49) and mutant group (n=49) and analyzed using inForm Cell Analysis software. Tissue segmentation training was performed to separate stromal and epithelial elements. Cell percentage, cell density, and nearest neighbor distance of each cell type were calculated using R program. Results: There is an increased infiltration of T cells, Tregs, and helper T cells in the epithelial component of the mutant group compared with WT group. The epithelial cells are more frequent to express PD-L1. Interestingly, we also observed more Treg infiltration in the stromal component and total tissue in the mutant group compared with WT group. The CTLs are more engaged with the epithelial cells, regardless of their PD-L1 status, in the mutant group compared with WT group. Conclusions: Our results provide insight into the effects of CLC gene mutations on shaping the immune microenvironment of PDAC and suggest that CLC gene mutated PDACs have a different immune microenvironment than other PDACs and may respond differently to immunotherapy.
Citation Format: Shungang Zhang, Jake McGue, Elaina Daniels, Hong Sun Kim, Dafydd Thomas, Jiaqi Shi. Multiplex fluorescent immunohistochemistry reveals immune microenvironment alterations in COMPASS-like complex gene mutated pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C045.