Eosinophils exhibit a unique transcriptional signature and increased sensitivity to IL-3-induced activation in response to colorectal cancer cells.

Eosinophils have been mainly studied in allergic diseases and parasitic infections. Nonetheless, eosinophils accumulate in a variety of solid tumors, including colorectal cancer, where their presence is associated with improved prognosis. Eosinophils can promote antitumor immunity through various mechanisms, including direct cytotoxicity toward tumor cells and promoting T-cell activation. However, the mechanisms by which tumor cells regulate eosinophil activities are largely unknown. Herein, we characterized the potential interactions between eosinophils and colorectal cancer cells using an unbiased transcriptomic and proteomic analyses approach. Human eosinophils were stimulated with colorectal cancer cell conditioned media, containing tumor cell secreted factors from multiple cancer cell lines. RNA sequencing analysis identified a "core" signature consisting of 101 genes that characterize a baseline transcriptional program for the response of human eosinophils to colorectal cancer cells. Among these, the increased expression of IL-3Rα and its βc chain was identified and validated at the protein level. Secreted factors from tumor cells potentiated IL-3-induced expression of the adhesion molecule CD11a in eosinophils. Combining proteomics analysis of tumor cell secreted factors with RNA sequencing revealed potential ligand-receptor pairs between tumor cells and eosinophils and the potential involvement of the adhesion molecule CD18 and F2RL3/PAR4. Subsequent functional analyses demonstrated that F2RL3/PAR4 suppresses eosinophil migration in response tumor cell secreted factors. These findings add to the growing body of evidence that eosinophils are conditioned by their local microenvironment. Identifying mechanisms by which eosinophils interact with tumor cells could lead to the development of new immunotherapies for colorectal cancer and other solid tumors.