Interferon Gamma Induces Higher Neutrophil Extracellular Traps Leading to Tumor-Killing Activity in Microsatellite Stable Colorectal Cancer

Many colorectal cancer (CRC) patients do not respond to immune checkpoint blockade (ICB) therapy, highlighting the urgent need to understand tumor resistance mechanisms. Recently, the link between the IFNγ signaling pathway integrity and ICB resistance in the CRC tumor microenvironment has been revealed. The immunosuppressive microenvironment poses a significant challenge to antitumor immunity in CRC development. Tumor-associated neutrophils (TANs) found in tumor tissues exhibit an immunosuppressive phenotype and are associated with CRC patient prognosis. Neutrophil extracellular traps (NETs), DNA meshes containing cytotoxic enzymes released into the extracellular space, may be promising therapeutic targets in cancer. This study showed increased NETs in tumor tissues and peripheral neutrophils of high levels of microsatellite instability (MSI-H) CRC patients compared to microsatellite stable (MSS) CRC patients. IFNγ response genes were enriched in MSI-H CRC patients compared to MSS CRC patients. Co-culturing neutrophils with MSI-H CRC cell lines induced more NET formation and higher cellular apoptosis than MSS CRC cell lines. IFNγ treatment induced more NET formation and apoptosis in MSS CRC cell lines. Using subcutaneous or orthotopic CT-26 (MSS)-tumor-bearing mice models, IFNγ reduced tumor size and enhanced PD-1 antibody-induced tumor-killing activity, accompanied by upregulated NETs and cellular apoptosis. These findings suggest IFNγ could be a therapeutic strategy for MSS CRC.