Neutrophil extracellular traps promote pre-metastatic niche formation in the omentum by expanding innate-like B cells that express IL-10.

Disseminated cancer cells in the peritoneal fluid often colonize omental fat-associated lymphoid clusters but the mechanisms are unclear. Here, we identify that innate-like B cells accumulate in the omentum of mice and women with early-stage ovarian cancer concomitantly with the extrusion of chromatin fibers by neutrophils called neutrophil extracellular traps (NETs). Studies using genetically modified NET-deficient mice, pharmacologic inhibition of NETs, and adoptive B cell transfer show that NETs induce expression of the chemoattractant CXCL13 in the pre-metastatic omentum, stimulating recruitment of peritoneal innate-like B cells that in turn promote expansion of regulatory T cells and omental metastasis through producing interleukin (IL)-10. Ex vivo studies show that NETs elicit IL-10 production in innate-like B cells by inactivating SHP-1, a phosphatase that inhibits B cell activation pathways, and by generating reactive oxygen species. These findings reveal that NETs alter immune cell dynamics in the pre-metastatic omentum, rendering this niche conducive for colonization.