A biomaterial-based platform of pancreatic cancer reveals kallikrein-related peptidase 6 (KLK6) as a mediator of neutrophil recruitment and immunosuppression

In pancreatic cancer, response to treatment is impaired by the tumor microenvironment (TME), forming a desmoplastic barrier. However, experimental 3D models that adequately model the pancreatic TME are still missing. Here, we employ a matrix metalloproteinase (MMP)-degradable star-shaped poly(ethylene glycol) (star-PEG)-heparin hydrogel matrix to replicate pathophysiological features of the pancreatic environment and investigate the role of the tumor-associated protease kallikrein-related peptidase 6 (KLK6) in 3D. Coupled with CRISPR/Cas9, we found that KLK6 promotes cancer growth. RNA sequencing revealed that KLK6 impairs genes associated with antigen presentation and neutrophil recruitment, all major immune suppressors in pancreatic cancer. In patients, KLK6 expression correlated with neutrophil-recruiting chemokines. Neutrophil recruitment was recapitulated in vitro, which was lower in the absence of KLK6. Treatment of neutrophils with cell-conditioned KLK6 knockout medium reduced the immunosuppressive phenotype, indicated by decreased arginase 1 (Arg1) expression. KLK6 also impacted genes associated with immune checkpoint inhibition and decreased cell responses to anti-PD-1 checkpoint blockade in vitro. Our study identified KLK6 as a drug target as it regulates neutrophil recruitment, immunosuppression, and cell responses to anti-PD-1 therapy in a biomaterial-based disease model.