Identification of cold tumor induction–related markers in pancreatic cancer and the clinical implication of PCDH7. Identification of cold tumor induction–related markers in pancreatic cancer and the clinical implication of PCDH7

Purpose: Pancreatic ductal adenocarcinoma (PDAC) is considered a “cold” tumor because the tumor immune microenviron- ment (TIME) exhibits poor intratumoral T-cell infiltration. This study aimed to identify the marker genes associated with induction of cold TIME in PDAC cells. Methods: We orthotopically transplanted 10 primary cultures of PDAC derived from KrasG12D/+; Trp53R172H/+; Pdx-1- Cre (KPC) mice into immunocompetent mice and evaluated TIME by immunohistochemistry (IHC) staining of CD8. We divided primary cultures into two groups: cold TIME group with low CD8+ T-cell infiltration and a hot TIME group with high infiltration. RNA sequencing was performed to identify specific genes in the cold TIME group, and single-cell RNA sequencing (scRNA-seq) data was used for validation. IHC was performed to evaluate expressions in human PDAC samples. Results: We identified six genes specific in PDAC cells to the cold TIME group by RNA sequencing; these were defined as “cold tumor induction–related genes”. Human PDAC scRNA-seq data revealed that cold tumor induction–related genes were significantly and negatively correlated with the number of CD8+ T-cells (p = 0.0341). These genes included protocad- herin 7 (PCDH7). High expression of PCDH7 significantly and negatively correlated with the number of CD8+ T-cells in scRNA-seq (p = 0.0474) and IHC (p = 0.0110) data using human PDAC samples. PCDH7 was an independent factor for poor prognosis in PDAC (overall survival: hazard ratio = 2.07, p = 0.0367). Conclusion: PCDH7 is a prognostic marker associated with CD8+ T-cell infiltration for PDAC patients. Overall design: RNA sequencing of murine PDAC cell lines inducing low or high infiltration of CD8+ T cells