TMIC-49. CHITINASE-3-LIKE 1 PROTEIN COMPLEXES REGULATE PD-1 SIGNALING-MEDIATED IMMUNOSUPPRESSION IN GLIOBLASTOMA

Abstract

Abstract Glioblastoma (GBM), the most common and lethal brain tumor with a median survival rate of only 15 months, remains largely incurable despite intensive multimodal treatment, including immunotherapeutic strategies being tested in clinical trials. GBM is highly immunosuppressive and resistant to immunotherapy because glioma cells escape from effective antitumor immunity through programing the tumor microenvironment (TME). Owing to the tremendous heterogeneity and plasticity of tumor cells and the surrounding TME, understanding the mechanisms of immune evasion by GBM remains elusive. We have recently discovered that the Chitinase-3-like-1 (CHI3L1)-Galectin-3 (Gal3) protein binding complex can selectively promote tumor-associated macrophage migration and infiltration with a protumor M2-like phenotype and T cell-mediated immunosuppression, which are governed by a transcriptional program of NF-κB/CEBPβ in the CHI3L1/Gal3-PI3K/AKT/mTOR axis. The immunoprecipitation coupled to liquid chromatography-mass spectrometry analysis revealed that galectin 3–binding protein (Gal3BP) competes with Gal3 to bind with CHI3L1 for negative regulation of the CHI3L1-Gal3 mediated processes. Interestingly, a newly-developed Gal3BP mimetic peptide can disrupt CHI3L1-Gal3 interaction, resulting in decreasing migration of M2-like bone marrow-derived macrophages (BMDMs), increasing CD8+ T cell infiltration, reversing immunosuppression, and inhibiting tumor progression in vitro and in vivo. Analyzing PD-1 signaling activation, we found that the Gal3BP mimetic peptide significantly decreased PD-L1 expression in tumor cells. Correlation analysis showed that CHI31L and Gal3 (encoded by LGALS3 gene) are significantly associated with both PD-L1 and PD-L2 in GBM patient samples. Furthermore, overexpression of CHI3L1 increased expression levels of PD-L1 and PD-L2, and CHI3L1 deletion decreased their expression in GBM patient-derived neurosphere lines. The treatment with recombinant CHI3L1 protein significantly increased PD-L1 and PD-L2 expression in M2-like BMDMs (with high levels of endogenous Gal3). Collectively, these data suggest that CHI3L1 protein complexes control the GBM immunosuppressive microenvironment by PD-1/PD-L1/PD-L2 signaling, providing new immunotherapeutic strategies for this brain cancer.