Introduction: Pancreatic ductal adenocarcinomas (PDACs) are poorly responsive to both chemo- and immunotherapies, mainly because of the presence of highly dense fibrotic stroma and extensive myeloid-derived immune cells, which are known major drivers for an immunosuppressive tumor microenvironment (TME). Another feature of PDACs that may suppress the immune microenvironment is the small ‘fibrin clots’ that are chiefly found in tumor vasculature and interstitial space. PDACs exhibit high levels of fibrinogen and fibrin clots throughout the tumor stroma surrounding the tumor cells. Fibrinogen, a coagulation factor that polymerizes into fibrin, is overrepresented in the stroma from early-to-late stage PDA, suggesting an early activation of coagulation cascade in PDAC. Taken together, we hypothesize that cross-linked fibrin-stroma may suppress the immune microenvironment of PDAC. Methods: Analyzing transcriptome of PDAC patients, we observed the clinical correlation between fibrin-clot relevant genes (FGA, FGB, and FGG) with various immune genes’ expressions and overall survival. We performed multiplex analysis of tumor tissues from PDAC patients (N = 25) with higher and lower fibrin expression, and correlated the abundance of tumor fibrin-clot with plethora of immune cells in the tumor stroma. Using a microfluidic tissue-on-a-chip PDAC model, we determined the role of fibrin in TME immune landscape focusing on macrophage differentiation. Knocking out of FGB in KPC689 cells (KPC689FGB-/-), derived from KPC mice, we determined the role of targeting tumor fibrin in attenuating immunosuppressive TME. Results: Patients with higher expression of FGA, FGB, and FGG (> median) showed significantly lower survival rate in PDAC (p < 0.002) compared to those with lower expression (< median). Markedly, the expression levels of FGB positively correlated with various immune-related genes in PDAC patients, including PD1-L1, PD1-L2, PD-1, FOXP3, macrophage-1 antigen (ITGAM), and CD8β+. Multiplex analysis revealed that Fibrinlow PDAC tissues had higher abundance of CD8+ T-cells but higher number of M2 (CD163+/MCHII-) versus M1 (CD68+/MHCII+/CD163-) macrophages than in Fibrinhigh PDAC tissues. In PDAC-on-a-chip model, human monocytes, when cultured in collagen gels into one compartment along with PDAC in Peak 2 Fibrin (P2F) gels into the side compartment, induced M2 phenotype, infiltrated into the PDAC/P2F compartment, and increased the survival of PDAC cells. Both KPC689FGB+/+ and KPC689FGB-/- cells grew at the same rate, when inoculated into the pancrease of mice, but the abundance of fibrin-laden stroma decreased in KPC689FGB-/- tumors. FACS analysis from explanted tumors showed higher number of activated IFNγ+CD8β+ T cells but lower number of CD11b+Gr1+ MDSCs in KPC689FGB-/- than KPC689FGB+/+ tumors. Conclusion: Our data suggest that in-situ fibrin-formation controls immune microenvironment in PDAC and targeting intratumoral fibrin formation can ‘heat up’ the TME by mitigating the immunosuppression in PDAC.

Citation Format: Riajul Wahab, Mazharul Karim, Md Mahedi Hassan, Paul Grippo, Faraz Bisheshari, Taslim Al-Hilal. Intratumoral fibrin as a novel immunomodulatory factor in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C008.