IMMU-08. EOSINOPHILS ARE IMPORTANT MODULATORS OF AN IMMUNE-RESPONSIVE TUMOR-MICROENVIRONMENT IN GLIOBLASTOMA

Abstract

Abstract Eosinophils, bone marrow-derived granulocytes involved in allergic asthma and autoimmunity, have attracted increasing attention due to their assumed role in effective responses to immune checkpoint blockade in some extracranial tumors. However, the role of this rare type of immune cells in immunologically cold tumors such as glioblastoma (GBM) has not been studied so far. When quantifying immune infiltrates and levels of 30 immune-relevant cytokines in 60 matched pairs of human primary and recurrent GBM, strongest correlations (r= 0.71-0.93) were observed for the eosinophil-associated cytokines Eotaxin and Il-5 as well as for TNFa, IFNg and Il2 which are important cytokines for cytotoxic T cell responses. A combined score of these cytokines (Eo score) turned out to be an independent prognostic marker for improved overall survival of GBM patients. Furthermore, multicolor immunofluorescent staining revealed that Eo score high GBM are significantly higher infiltrated by effector T cells and show a significantly lower infiltration with anti-inflammatory M2-like tumor-associated macrophages / microglia cells (M2-TAM) in recurrent GBM. Flowcytometry analysis of GBM-derived single cell suspensions confirmed a positive correlation of higher eosinophil numbers with higher numbers of tumor-infiltrating T cells, while an inverse relation between eosinophils and monocytes could be demonstrated in the TCGA data set. Spatial transcriptomic data of human GBM confirmed that areas with a higher eosinophil infiltration showed higher numbers of T cells and pro-inflammatory M1-TAM, lower numbers of M2-TAM and a remarkable vessel normalization. Finally, in a newly developed patient-derived GBM organoid model we could corroborate the functional impact of eosinophils on the tumor-microenvironment. An increase of eosinophil numbers in these patient avatars resulted in a significantly decreased number of M2-TAM. Altogether, tumor-infiltrating eosinophils seem to be a novel type of immune-modulator in GBM and may enhance immune responses by shaping the tumor niche from an immunosuppressive to an immunepermissive microenvironment.