Relationship between podoplanin-expressing cancer-associated fibroblasts and the immune microenvironment of early lung squamous cell carcinoma

Aim: Cancer-associated fibroblasts (CAFs) expressing podoplanin (PDPN) harbor a fibrous tumor microenvironment that promotes cancer progression in lung adenocarcinoma. In this study, we investigated whether tumor-promoting PDPN+ CAFs contribute to the immunosuppressive microenvironment in lung squamous cell carcinoma (SqCC). M&M: The gene expression profiles of immunosuppressive cytokines were compared using The Cancer Genome Atlas (TCGA) microarray lung SqCC data (n = 484) between a PDPN-high group and a PDPN-low group. Further, using patient-derived CAFs from surgically resected lung SqCC, the PDPN+ fraction was sorted and gene and protein expressions were analyzed. Finally, immunohistochemical staining was conducted on 131 surgically resected lung SqCC; CD8(+) and FOXP3(+) tumor infiltrating lymphocytes (TILs), and CD204(+) tumor-associated macrophages (TAMs) were evaluated in cases with PDPN+ and PDPN- CAFs. Results: Analysis of TCGA database revealed that the PDPN-high group exhibited significantly higher expression of interleukin (IL)-1A, IL-1B, IL-6, IL-10, monocyte chemoattractant protein-1 (CCL2), colony stimulating factor 1 (CSFI), fibroblast growth factor 2 (FGF2), galectin 1 (LGALSI), platelet derived growth factor subunit A (PDGFA), PDGFB, and transforming growth factor-beta 1 (TGFBI) than those in the PDPN-low group. Among them, it was found that TGFBI expression was higher in patient-derived PDPN+ CAFs. Immunohistochemical analyses revealed that more CD204(+) TAMs infiltrated the tumor tissues in cases with PDPN+ CAFs than in cases with PDPN- CAFs (P < 0.03), while CD8(+) and FOXP3(+) TILs did not. Furthermore, in the same tumor, CD204(+) TAMs infiltrated more in PDPN+ CAF-rich areas (P = 0.005). Conclusion: PDPN+ CAFs showed higher expression of TGFB1 and were associated with CD204(+) TAM infiltration in stage-I lung SqCC, suggesting that PDPN+ CAFs were associated with the immunosuppressive tumor microenvironment.