Unlocking the Immunobiology of Conventional Dendritic Cells to Augment T Cell Activation in Glioblastoma - PROJECT SUMMARY This proposal centers on the study of endogenous dendritic cell (DC) function in glioblastoma (GBM). GBM remains an extremely challenging cancer to treat, and clinical outcomes remain poor. However, despite the seismic influence of immunotherapy in cancer, there remain no FDA approved immunotherapies for GBM. There are several reasons that underlie the difficulty in extending immune-based treatments to the central nervous system (CNS). GBM harbors few T cells and is considered “non-inflamed”, a myriad of immunosuppressive features has been identified in patients, there is a paucity of DC in the brain parenchyma, and the CNS is also immunologically specialized due to the presence of site-specific elements not seen elsewhere—e.g., lack of lymph nodes, presence of dural lymphatics, and the blood-brain barrier, among others. In this context, how and where endogenous DC drive T cell activation and expansion remains a huge gap in our understanding of how immune responses to GBM can develop and, ultimately, be accelerated therapeutically. As compelling as exogenously administered DC therapies have been in our field, here we focus on understanding how the endogenous DC-driven immune response to GBM develops. We have assembled a team with Dr. Petti that brings diverse expertise to this work. We have previously shown that conventional dendritic cell type 1 (cDC1) are required for endogenous neoantigen specific responses to the murine GL261 GBM model and are necessary for anti-PD-L1 mediated treatment of GL261-bearing mice. Moreover, cDC1 are able to acquire antigen and traffic to the cervical lymphatics and are also present in the dural layer of the meninges. Finally, we observed that cDC infiltrate human glioblastoma and acquire metabolites from 5-ALA fluorescence guided surgery. In Aim 1, we will deepen our mechanistic understanding of cDC1-mediated T cell priming by exploring the CCR7 and STING dependence in T cell responses to GBM. We will also examine the relative contributions of cDC1 and cDC2 in brain tumor immunity using cDC-selective mouse models and, finally, investigate the basis of cDC1- dependence in anti-PD-L1 mediated GBM immunotherapy. In Aim 2, we will study when and where cDC1 acquire tumor-derived antigen and investigate where antigen-carrying cDC1 can be found in specialized dural structures and present antigen. We will extend these observations by testing the exciting possibility that accelerating antigen flux through dural lymphangiogenesis can augment anti-GBM T cell responses. Finally, in Aim 3, we will translate our observations to patients by creating a cell atlas from enriched GBM infiltrating DC and testing whether DC carrying metabolites from 5-ALA exhibit enhanced antigen presenting capacity. We will then study DC in situ using cutting edge spatial transcriptomics in tumors, dura, choroid plexus, and cervical lymph nodes in patients recently deceased from GBM through the unique rapid autopsy program at MGH. Together, these Aims will reveal novel mechanistic insights into how cDC drive T cell responses to GBM in preclinical models and patients that may illuminate compelling new avenues for immunotherapeutic strategies.
