Protein-level profiling of TIGIT axis components in human PDAC reveals immune-suppressive expression patterns.

[PURPOSE] In pancreatic ductal adenocarcinoma (PDAC), immune checkpoint inhibitors have shown limited efficacy, and the role of the TIGIT axis remains underexplored. This study aimed to characterize TIGIT axis components on protein level and their relationship to PD-1/PD-L1 expression in matched blood and tumor samples from PDAC patients to identify immunosuppressive mechanisms and fuel future strategies for immune checkpoint co-targeting in PDAC patients.

[EXPERIMENTAL DESIGN] Fresh tumor and peripheral blood samples were collected from PDAC patients undergoing surgical resection. Flow cytometry was performed on tumor-infiltrating lymphocytes and PBMCs to assess expression of TIGIT, DNAM-1, TACTILE, and PD-1. Ligands CD111, CD112, CD113, and CD155 were analyzed using immunohistochemistry. Additional RNA expression analysis (TCGA/GTEx) was used to evaluate ligand distribution and gene expression profiles.

[RESULTS] TIGIT was highly upregulated on intratumoral CD8⁺ T cells and regulatory T cells, frequently co-expressed with PD-1. DNAM-1 expression was significantly reduced in tumors. However, contrasting pattern emerges with Tregs, which uniquely upregulate DNAM-1 in the PDAC TME. In addition, CD112 and CD155 were broadly expressed, including novel stromal CD112 localization. NK cells were nearly absent intratumorally, correlating with DNAM-1 downregulation.

[CONCLUSIONS] Our findings identify TIGIT as a promising immunotherapeutic target in PDAC and suggest that dual checkpoint blockade (TIGIT/PD-1), alongside restoration of DNAM-1 signaling, may overcome immune suppression. These results provide mechanistic rationale to inform future clinical trials in PDAC.