Tertiary lymphoid structures in glioblastoma : Discovery, Characterization and Therapeutic Induction

Sammanfattning: Glioblastoma (GBM) is an incurable brain cancer with a median survival of less than two years from diagnosis. The tumor microenvironment plays a major role in GBM progression through sustaining immunosuppression and poor lymphocytic infiltration. Tertiary lymphoid structures (TLS) are ectopic lymphoid aggregates that form in inflamed tissues and are associated with positive prognosis in numerous cancers outside the central nervous system. Prior to this work, TLS had not been reported or studied in GBM. In this thesis, we aimed to characterize TLS in glioma patients, and to investigate immunotherapeutic approaches that could reprogram the GBM microenvironment to induce these structures, promote anti-tumor responses and prolong survival.In Paper I, we discovered the presence of TLS in low grade and high grade glioma tissues, and found that they correlated with increased T cell infiltration inside the tumor. Moreover, we demonstrated that agonistic CD40 therapy (αCD40) induced the formation of TLS with a follicle-like organization in murine glioma models. αCD40 also promoted a population of CD11b+ regulatory B cells, which inhibited T cell activation. These cells were not present within the TLS, indicating that TLS formation and the induction of CD11b+ B cells were likely two independent processes.In Paper II, we employed murine glioma models to study the therapeutic effect of cytokines involved in lymphoid tissue development, and selected LIGHT as the most promising candidate. To therapeutically deliver LIGHT to the tumor microenvironment, we engineered an AAV vector targeted to the brain endothelial cells to express LIGHT (AAV-LIGHT). AAV-LIGHT promoted the formation of TLS and functional high endothelial venules. Moreover, AAV-LIGHT strengthened effector and memory CD8+ T cell responses, and boosted a population of TCF1+CD8+ stem-like T cells. This was associated with a prolonged survival, indicating that AAV-LIGHT is a promising therapeutic candidate for the treatment of GBM. In Paper III, we coupled advanced spatial transcriptomics of human GBM tissue and time point experiments in murine glioma models to investigate the stages of TLS assembly. We found that TLS formation is a step-wise process, where each stage is characterized by specific cell components and pathways. Understanding the steps underlying TLS assembly will be critical to develop efficient TLS-inducing immunotherapies.