Moelker, Eliese

Abstract Introduction Bone marrow (BM) is the primary immune organ responsible for stem cell maintenance. Neurotropic infections elicit sequestration of T cells within the BM. Changes of the BM niche during brain viral infections are unknown. Intracranial infection with the neurotropic Theiler’s Murine Encephalomyelitis Virus (TMEV) in C57BL/6 mouse is cleared by 30 days due to generation of an antigen-specific CD8 T cell response. Methods We used brain viral infection and injury models to test T cell responses against brain antigens in the bone marrow. Results We determined that 1-10% of CD8 T cells present in the sternal, femoral, and cranial BM were virus antigen-specific 7 days post intracranial infection. Over 70% of these CD8 T cells were tissue resident. We determined antigen-specific CD8 T cells were generated in the BM within 4 days of infection. Continuous treatment with FTY720, which sequesters T cells outside of the blood, did not eliminate antigen-specific CD8 T cells in any BM compartment. CD8 T cells in the BM established durable memory populations and were reactivated upon antigen reencounter. In the memory phase (200 days post brain TMEV infection), bone marrow resident CD8 T cell could be reactivated upon cognate peptide delivery. Such reactivation of antigen specific memory CD8 T cells caused an increase in lineage-, Sca-1+, ckit + (LSK) cells in the BM in a CD8 dependent manner. Similarly, injection of the model antigen AF488-conjugated OVA mixed with Poly IC into the brain recapitulated antigen specific CD8 T cell generation within the bone marrow and further demonstrated the antigen presenting cell involved in the response to be a CD103 expressing myeloid DC. We conclude that viral infections and inflammatory stimulation in the brain induce in situ effector and memory T cell responses within the BM which is associated with significant stem cell dysregulation. Conclusion Our data paves the way for crucial studies of BM resident antigen-specific CD8 T cells in health and disease. Funding Source NIH K99/R00 Topic Categories Viral Immunology (VIR)

Abstract Introduction Peripheral nervous system innervation of various organs has been associated with the development and maintenance of the immune system. Yet, the intricate details of thymic innervation remain less well-studied. Interestingly, various neurological insults including brain tumors, and neurotropic infections have been shown to have profound impacts on thymic size and cellularity and T cell development. Methods We used flow cytometry, confocal microscopy, neuro tracers, and genetic knockout mice to evaluate developing T cell-neuron interactions within the thymus. Results We have identified neuronal cell bodies within the thymus. These cells express neuronal markers such as NeuN and tyrosine hydroxylase and lack TEC identifiers, such as EpCAM, UEA-1, and Ly51. Thymic neurons can be infected with a neurotropic rabies vector, further cementing their neuronal identity. Considering the thymus consists mostly of T cells, we next investigated a potential interaction between T cells and thymic neurons. Interestingly, loss of T cell development results in a lack of thymic neuron development indicating T cell-neuron coregulation during development. However, thymic neurons can be recovered following a bone marrow transplant, suggesting the provision of a differentiation and/or survival signal for neurons provided by the developing T cells. Using knockout mice lacking the T cell lineage at various stages of development, we determined that TCR beta selection is required for the development of thymic neurons. Finally, we determined that a lack of transition from DN4 to DP severely diminishes the development of thymic neurons. Analysis of the publicly available bulk RNA-sequencing data comparing thymic DP to DN cell populations indicates the potential involvement of IL34 in neuronal development in the thymus. Conclusion We describe a novel population of neuronal cells within the thymus that interact with developing thymocytes to establish optimal thymic architecture. Funding Source NIH K99/R00 Topic Categories Neuroimmunology (NEUR)

Abstract Introduction Glioblastoma is an aggressive brain cancer with poor prognosis for which immunotherapies have fared poorly. In part, the failure in immunotherapies is attributed to the existence of severe local and systemic immunosuppression in GBM. We determined that majority of hallmark features of systemic immunosuppression were linked to immunosuppressive factors in serum. Our data indicate that serum of glioma-bearing mice harbors heightened levels of cell-free DNA (CF-DNA). Methods We evaluated the extent to which CF-DNA contributes to systemic T cell dysfunction in mouse models of GBM and GBM patient plasma samples. Results We determined that majority of hallmark features of systemic immunosuppression were linked to immunosuppressive factors in serum. Our data indicate that serum of glioma-bearing mice harbors heightened levels of cell-free DNA (CF-DNA). Removing CF-DNA from serum improves T cell responses while adding CF-DNA derived from serum of glioma-bearing subjects to healthy T cells directly inhibits their functions. We have also verified that CF-DNA is detectible in sera isolated from patients with GBM. When compared to healthy controls, GBM patients have higher quantities of CF-DNA is their plasma. Interestingly, our preliminary data implicates neutrophil NETosis as the likely source of CF-DNA in sera of GBM patients. Moreover, we stained GBM tumor sections with citrullinated histone 3 (cit-H3) to evaluate the extent of NETosis in GBM patients. We determined evidence of significant NETosis within patient brain tumors. Systemic immunosuppression is detrimental to the success of immune-modulating therapies and patient survival. By identifying and removing the source of systemic immunosuppression, we will enhance immune responses against the tumor likely improving patient survival. Conclusion Glioblastoma causes immune suppression outside of the brain via the released CF-DNA. Our studies in GBM patients and mouse models help develop strategies to reverse immune dysfunction and improve outcomes. Funding Source NIH K99/R00 Topic Categories Immune Mechanisms of Human Disease (HUM)

Abstract Bone marrow is the primary immune organ responsible for stem cell maintenance and hematopoiesis. However, the contribution of the bone marrow niche for the generation of adaptive immune responses is less well-understood. We therefore assessed the capacity of virus antigen-specific CD8 T cells to be generated and expanded in bone marrow following acute neurotropic virus infection. Intracranial infection with the neurotropic Theiler’s Murine Encephalomyelitis Virus (TMEV) results in an acute infection in the C57BL/6 mouse which is cleared within 4 weeks post infection due to the generation of an antigen-specific CD8 T cell response against the immunodominant epitope VP2 121-130 . We determined that 1-10% of CD8 T cells present in the femoral, and sternal bone marrow were virus antigen-specific 5-7 days after intracranial TMEV infection. We determined that antigen-specific CD8 T cells were generated in the bone marrow with similar kinetics to that of conventional responses in the secondary lymphoid organs. Importantly, continuous treatment with FTY720, which sequesters T cells outside of the blood, did not eliminate antigen-specific CD8 T cells in the bone marrow compartment indicating generation within the bone marrow niche. Similarly, injection of Poly I:C admixed with fluorescently labeled ovalbumin into the brain generated a similar antigen-specific CD8 T cell response in the bone marrow indicating these responses occur following various brain insults. This model also identified the likely antigen presenting cell (APC) responsible for scavenging antigens from the brain and trafficking into the bone marrow as a migratory myeloid-derived APC. Moreover, following clearance of TMEV infection, CD8 T cells in the bone marrow established durable memory. Antigen-specific memory CD8 T cells in the bone marrow reactivated and expanded upon cognate antigen reencounter. Antigen-specific reactivation of memory CD8 T cells within the bone marrow caused a concurrent increase in Lineage-, Sca-1+, c-Kit+ (LSK) and CD11b+ MHCII+ myeloid cells. This increase in the LSKs and myeloid cells in the bone marrow niche was abrogated with CD8 T cell depletion. We conclude that brain viral infections induce in situ effector and memory T cell responses within the bone marrow compartment. Memory recall CD8 T cell responses induce niche dysregulation by expanding LSK cells and lead to an influx of MHCII+ myeloid cells. Our data pave the way for crucial studies of bone marrow resident antigen-specific CD8 T cells in health and diseases.

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 Description Glioblastoma (GBM) is an aggressive brain cancer with poor survival. GBM patients have severe peripheral immunosuppression, including defective T cell responses. We showed that serum-derived factors were sufficient to inhibit T cell proliferation. This factor was nonsteroidal and larger than 100kDa. Mass-spectrometry and pathway analysis of suppressive serum implicated proteins involved in DNA response elements. We hypothesized that the suppressive factor is cell-free DNA (cfDNA). In support of this, serum levels of cfDNA are increased in glioma-bearing mice. Exposure to cfDNA from serum of glioma-bearing mice was sufficient to directly and potently inhibit T cell proliferation. 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 was sufficient to partially restore proliferation capacity. We determined that the T cell proliferation defects were independent of AIM2 DNA sensing mechanisms, implicating a novel pathway of DNA sensing in T cells. Finally, to determine the origin of the cfDNA, we used methylation-seq and found that the majority of cfDNA originated from neutrophils, implicating NETosis. Together, we contend that cfDNA from neutrophils induces immunosuppressive effects in GBM. Our work highlights a potential role for targeting cfDNA, neutrophils, and/or NETs in order to reverse T cell dysfunction and improve patient outcomes in GBM. Funding Sources R00NS117799 Topic Categories Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)

Abstract Description Bone marrow (BM) is the primary immune organ responsible for stem cell maintenance. Neurotropic infections elicit sequestration of T cells within the BM. Changes of the BM niche during brain viral infections are unknown. Intracranial infection with the neurotropic Theiler’s Murine Encephalomyelitis Virus (TMEV) in C57BL/6 mouse is cleared by 30 days due to generation of an antigen-specific CD8 T cell response. We determined that 1-10% of CD8 T cells present in the sternal, femoral, and cranial BM were virus antigen-specific 7 days post intracranial infection. Over 70% of these CD8 T cells were tissue resident. We determined antigen-specific CD8 T cells were generated in the BM within 4 days of infection, a timeline similar to lymph nodes. Continuous treatment with FTY720, which sequesters T cells outside of the blood, did not eliminate antigen-specific CD8 T cells in any BM compartment. CD8 T cells in the BM established durable memory populations and were reactivated upon antigen reencounter. Both acute infection and reactivation caused an increase in lineage-, Sca-1+, ckit + (LSK) cells in the BM. This LSK dysregulation was abrogated upon CD8 T cell depletion and was limited to the intracranial routes of infection. We conclude that brain viral infections induce in situ effector and memory T cell responses within the BM and cause stem cell dysregulation. Our data paves the way for crucial studies of BM resident antigen-specific CD8 T cells in health and disease. Topic Categories Viral Immunology (VIR)

Abstract Description Neutrophils heavily infiltrate the brain following acute and chronic brain insults. Neutrophils infiltrating brain tumors display a prolonged lifespan compared to blood neutrophils. We investigated presence and potential function of neutrophils in the brain following infection with Theiler’s Murine Encephalomyelitis (TMEV) and kainic acid-induced seizures. Both total myeloid cells and neutrophils started infiltrating the brain as early as day 1, peaked at day 3, and remained elevated at least 7 days post-infection. Further characterization of the neutrophils revealed upregulation of MHC-II, indicating a potential role in antigen presentation. We detected similar accumulation of total myeloid cells and neutrophils in the brain of mice following seizures. MHC-II expression was upregulated on infiltrating neutrophils. Given the sustained and unusual accumulation of neutrophils in the brain past innate time points, we evaluated the bone marrow niche for evidence of myelopoiesis. Frequencies of Lin-Sca-1+c-Kit + (LSK) were significantly higher in all bone marrow compartments in mice infected intracranially with TMEV. This increase in LSK cells concurred with an increase in frequencies of total myeloid cells. These changes were not observed when mice were infected with TMEV systemically. Our data highlights dysregulation of bone marrow hematopoiesis and a potential novel role of neutrophils in response to neuroinflammation following intracranial pathologies. Topic Categories Neuroimmunology (NEUR)