Macrophages reprogramming improves immunotherapy of IL-33 in peritoneal metastasis of gastric cancer

Peritoneal metastasis (PM) has a suppressive tumor immune microenvironment (TIME), which limits the effects of immunotherapy. This study aims to investigate the immunomodulatory effects of intraperitoneal administration of IL-33 on PM-associated TIME. Immunocompetent mice were used to investigate the role of IL-33 in development of abdominal dissemination and host outcome. Murine (m) and human (h) gastric cancer cells were tested for their response to IL-33 by qRT-PCR, flow cytometry, and immunofluorescence. Survival was significantly prolonged in patients with high Il-33 mRNA expression. Intraperitoneal administration of IL-33 could induce the celiac inflammatory environment, activate immunologic effector cells and reverse the immunosuppressive tumor microenvironment, which delayed tumor progression and peritoneal metastasis of gastric cancer. Mechanistically, IL-33 could induce M2 polarization by activating p38-GATA-binding protein 3 (GATA3) signaling pathway. IL-33 combined with anti-CSF1R or p38 inhibitor to regulate tumor-associated macrophages (TAMs) showed synergistic anti-tumor effect. Intraperitoneal administration of IL-33 inducing local inflammatory milieu provided a novel approach for the treatment of metastatic peritoneal malignancies, which combined with TAMs reprogramming to reshape TIME could achieve better treatment efficacy. To investigate the immunomodulatory effects of intraperitoneal administration of IL-33 on peritoneal metastasis-associated tumor immune microenvironment, we established abdominal dissemination tumor model by challenging 615-line mice with mouse forestomach carcinoma cells.