A CD138+ tumor-associated macrophage-Siglec-F+ neutrophil feedforward loop promotes immune evasion in pancreatic cancer

Immune evasion is a major obstacle ahead of pancreatic cancer therapy. Recent data implicate pro-inflammatory macrophages in the progression of pancreatic ductal adenocarcinoma (PDAC) and its therapeutic response. However, whether or which of the pro-inflammatory macrophage subtypes play a crucial role in the immune escape of PDAC remains unclear. Here we identify a population of CD138+ tumor-associated macrophages (TAMs), characterized by their pro-inflammatory and neutrophil-chemotactic activity, which undergo significant expansion in both PDAC patients and mouse models. These cells are elicited by a local synergy between IL-34-syndecan-1 and PGE2-EP2 signaling and are associated with immune evasion and poor clinical outcomes in patients, while also promoting immune escape and disease progression in mouse models. Mechanistically, CD138+ TAMs establish a feedforward loop with immunosuppressive Siglec-F+ neutrophils, which exhibit elevated PGE2 expression, via the secretion of Saa3 and Cxcl1. Targeting CD138+ TAMs by disrupting IL-34-syndecan-1 signaling with anti-IL-34 neutralizing antibodies significantly suppresses PDAC progression, especially when combined with anti-PD-1 antibodies. Together, our study elucidates a CD138+ TAM-Siglec-F+ neutrophil axis that drives immune escape in PDAC and proposes a therapeutic strategy that integrates IL-34-syndecan-1 signaling blockade with anti-PD-1 immunotherapy for the treatment of PDAC.