The Effects And Mechanism Of Eosinophils On Anti-CTLA4 Therapy

Background: Tumor-infiltrating eosinophils have been observed in a range of solid tumors,such as breast cancer,but their roles in antitumor immunity remain controversial.Recent clinical trials indicate that elevated levels of circulating eosinophils after immune checkpoint blockade therapy are correlated with better survival benefit.Objective: To investigate the effects and mechanism of eosinophils on anti-CTLA4 treatments in breast cancer.Methods: By establishing EO771 and MCaP0008 breast tumor models,we compared the sensitivity of the two tumor models to anti-CTLA4 therapy.We then analyzed the effects of anti-CTLA4 therapy on tumor-infiltrating eosinophils and its relationship with the efficacy of anti-CTLA4 therapy.By using an anti-siglecF monoclonal antibody,we depleted eosinophils in vivo and deter mined the roles of eosinophils in the imapcts of anti-CTLA4 therapy on tumor growth and tumor blood vessels.Moreover,we developed a CCL24-overexpressing EO771 cell line(EO771-CCL24)as well as a mock EO771 cell line(EO771-PCDH),and analyzed the impacts of CCL24 overexpression on the tumor infiltration of eosinophils,the tumor vasculature,and the transcription of genes related to immune response and angiogenesis.We then investigated the influences of CCL24 overexpression on immune cell tumor infiltration and the tumor vasculature upon anti-CTLA4 therapy.In addition,we performed in vitro experiments to analyze the effects of CCL24 on tumor cell proliferation and apoptosis,as well as its impact on HUVEC tube formation.Results: Anti-CTLA4 therapy inhibited tumor growth,induced tumor vascular normalization,and increased tumor-infiltrating eosinophils in EO771,but not MCaP0008,breast tumor model.In vivo depletion of eosinophils partially reversed tumor growth inhibition and abrogated vascular normalization induced by anti-CTLA4 therapy.Overexpressing CCL24 promoted eosinophil tumor infiltration,while compromised the antitumor effects of anti-CTLA4 therapy in EO771 breast tumor.Overexpressing CCL24 reduced tumor-infiltrating CD8+ T cells,decreased the levels of IFN-? and CXCL9,increased tumor blood vessel density,and reduced vascular function in EO771 breast tumor.In addition,overexpressing CCL24 promoted EO771 tumor cell proliferation while decreased its apoptosis.In vitro experiments showed that CCL24 did not affect tube formation of HUVEC.Conclusion: The elevated levels of eosinophils upon anti-CTLA4 therapy were associated with the therapeutic efficacy in breast tumor models.Anti-CTLA4 therapy promoted the normalization of tumor blood vessels in an eosinophil dependent manner.Overexpressing CCL24 increased tumor-infiltrating eosinophils,decreased the transcription levels of IFN-? and CXCL9,promoted tumor vascular abnormlaization,and compromised the antitumor effect of anti-CTLA4 therapy.These findings indicated that eosinophils under different tumor microenvironment could promote tumor vascular normalization or abnormalization,and thus might exert different effects on immune checkpoint therapy.