Hoyt-Miggelbrink, Alexandra

Abstract Description Peripheral nervous system innervation of various organs has been associated with the development and maintenance of the immune system. Various neurological insults including brain tumors induce thymic involution. Using flow cytometry and confocal microscopy, we identified a population of cells within the thymus that contained neuronal markers and morphology. Subsets expressed tyrosine hydroxylase, BIII tubulin and/or NeuN, distinguishing them from thymic epithelial cells. These cells do not express AIRE. Neuronal cell bodies and/or axonal processes were identified within the thymus. Using retrograde rabies vector neurotracers, we confirmed axonal connections and the identity of thymic neurons. To determine developmental T cell stages that support neuronal development, we evaluated RAG1/2 KO, TCRβ KO, TCRα KO, TCRγδ KO, CD4 KO, CD8 KO and OT-I and -II transgenics. RAG1/2 and TCRβ deficiency resulted in complete loss of thymic neurons. This is while TCRα KO, TCRγδ KO, CD4/8 KO and OT-II transgenics had normal thymic neuron development. Importantly, OT-I transgenics had a significant loss of neuron-like cells, indicating developing CD8 T cells pre-alpha arrangement control thymic innervation. Finally, introduction of healthy bone marrow into irradiated RAG KO mice can restore neuron development. To summarize, we describe a novel population of neuronal cells within the thymus that interact with developing thymocytes to establish optimal thymic innervation. Funding Sources R00NS117799 Topic Categories Neuroimmunology (NEUR)

Abstract Glioblastoma (GBM) is an aggressive form of brain cancer with poor survival despite standard of care. Checkpoint inhibitors aimed to revive dysfunctional T cells have significantly improved outcomes in other cancers, but have failed GBM. GBM patients have severe peripheral immunosuppression, including severe lymphopenia, immune organ atrophy, and defective T cell responses. This immunosuppression is a critical barrier to patient survival and the success of immunotherapies. Using parabiosis, we demonstrated that serum-derived factors were sufficient to drive hallmark features of immunosuppression, including inhibition of ex vivo T cell proliferation. This factor was nonsteroidal in nature and had molecular weights greater than 100kDa. Mass-spectrometry and pathway analysis of the suppressive serum implicated proteins involved in DNA response elements, cell death, and DNA-histone complexes. We hypothesized that the factor is cell-free DNA (cfDNA). Confirming this, serum levels of cfDNA are increased in glioma-bearing mice. Moreover, exposure to cfDNA from serum of glioma-bearing mice was sufficient to directly and potently inhibit T cell proliferation ex vivo. Interestingly, exposure to genomic DNA was not sufficient to induce proliferation defects in T cells, highlighting the unique features of cfDNA. Importantly, reducing cfDNA content using DNaseI partially restored proliferation capacity. We determined that the T cell proliferation defects were independent of DNA sensing mechanisms through AIM2, implicating a novel pathway of DNA sensing in T cells. Finally, to determine the origin of the cfDNA, we employed methyl-seq. The chromatin signature most closely represented neutrophils. This highlights a potential role for neutrophils-derived cfDNA as a targetable strategy in GBM. Together, we contend that cfDNA induces immunosuppressive effects in GBM and devising strategies to reduce circulating cfDNA could be a therapeutic approach to improve T cell functions and outcomes in GBM patients.

AbstractBackgroundThe nervous and immune systems interact in a reciprocal manner, both under physiologic and pathologic conditions. Literature spanning various CNS pathologies including brain tumors, stroke, traumatic brain injury and de-myelinating diseases describes a number of associated systemic immunologic changes, particularly in the T-cell compartment. These immunologic changes include severe T-cell lymphopenia, lymphoid organ contraction, and T-cell sequestration within the bone marrow.MethodsWe performed an in-depth systematic review of the literature and discussed pathologies that involve brain insults and systemic immune derangements.ConclusionsIn this review, we propose that the same immunologic changes hereafter termed ‘systemic immune derangements’, are present across CNS pathologies and may represent a novel, systemic mechanism of immune privilege for the CNS. We further demonstrate that systemic immune derangements are transient when associated with isolated insults such as stroke and TBI but persist in the setting of chronic CNS insults such as brain tumors. Systemic immune derangements have vast implications for informed treatment modalities and outcomes of various neurologic pathologies.