Citations

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 Environmental exposure to food allergens (e.g. peanut antigens) through the skin or airways increases the risk of developing food allergy (e.g. peanut allergy). In contrast, oral antigen exposure (e.g., consumption of peanut products) early in life reduces the risk. The objective of this study was to investigate the immunologic mechanisms by which oral antigen exposure provides systemic immunotolerance and protection from food allergy development using murine models. Methods Naive mice were administered ovalbumin (OVA) through their drinking water to promote oral immunotolerance. Mice were subsequently exposed intranasally (i.n.) to OVA plus peanut flour, as an allergic adjuvant. CD4+ T cells from lung draining lymph nodes (dLNs) were assessed by single-cell RNA sequencing, MHC-II tetramer staining, and flow cytometry. Results Following i.n. exposure to OVA plus peanut flour, mice developed OVA-specific IgE (OVA-IgE) and showed symptoms of acute anaphylaxis upon intraperitoneal OVA challenge. Oral OVA feeding prior to i.n. OVA exposure reduced OVA-IgE and protected mice from anaphylaxis. Protection was associated with suppression of OVA-specific T follicular helper (Tfh) and germinal center B cells in dLNs. Tolerance was reversed by administration of anti-CTLA-4 blocking antibody but was not affected by deletion of Foxp3+Bcl6+ T follicular regulatory (Tfr) cells. Accordingly, conventional Foxp3+T regulatory (Treg) cells were not increased in dLNs of OVA-fed mice. Rather, protection was associated with the emergence of OVA-specific Foxp3-CTLA4+ cells expressing markers of stemness. Conclusion Oral antigen exposure suppresses the development of antigen-specific Tfh cells in remote dLNs thereby preventing systemic allergic sensitization. Systemic oral tolerance is dependent on CTLA-4 and unlikely requires conventional Foxp3+ Treg cells. Funding Source Supported by NIH F31 AI86242, R37 AI71106, and Mayo Clinic Graduate School of Biomedical Sciences. Topic Categories Immediate Hypersensitivity, Asthma, and Allergic Responses (HYP)

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 Introduction Mucosal immunization and respiratory IgA offer significant promise in protecting against airborne pathogens, including SARS-CoV-2. However, the conditions and mechanisms that lead to the robust induction of respiratory IgA responses following mucosal vaccination remain poorly understood. Methods In this project, we established SARS-CoV-2 breakthrough infection and mucosal adenovirus-based booster vaccination models. Using genetic mouse models and various in vivo and in vitro blockade or depletion approaches, we further investigated the mechanisms regulating respiratory IgA responses. Results Here we found that a mucosal adenovirus-based booster vaccination in mouse models revealed that respiratory booster immunization elicited markedly stronger and more durable respiratory IgA, T cell response, and protective immunity against SARS-CoV-2, supporting the promise of respiratory mucosal vaccination. Mechanistically, we identified that local CD4+ T cells support respiratory IgA production by promoting IgA+ B cell class switching, proliferation, and survival in situ. This T cell help depended on interactions between local Blimp-1+ T-bet+ Th1 cells and B cells, mediated through ICOS/CD40L/MHC-II engagement and IL-21 signaling. Furthermore, lung macrophages contributed to the mucosal IgA response via TGF-β production. Consequently, mucosal administration of SARS-CoV-2 Spike-encoding mRNA encapsulated in pulmonary surfactant (PS)- incorporated lipid nanoparticles designed to target lung macrophages elicited a stronger mucosal IgA response. Conclusion Our results uncover a local cellular network supporting enhanced mucosal IgA responses, with implications for the development of optimal mucosal immunization strategies against SARS-CoV-2 and other respiratory pathogens such as H5N1 influenza. Funding Source AI147394, AG069264, AI112844, HL170961, AI154598, AI176171 to J.S., AI67986, AI177467 to Hui.H; U54CA260582 to S.L.L; R01AI168684 to G. Z.; S.L.L was also supported by a fund provided by an anonymous private donor to The Ohio State University. Topic Categories Mucosal and Regional Immunology (MUC)

Abstract Introduction The lifetime risk for colorectal cancer (CRC) in the United States is approximately 4%. Individuals with Inflammatory Bowel Disease, including Ulcerative Colitis and Crohn’s Disease, have a substantially increased risk of developing colorectal cancer. Siglecs (sialic acid immunoglobulin lectin-like proteins) are a family of receptors that regulates the immune response. Siglec-E is a mouse inhibitory receptor that is primarily expressed by innate cells. While others have demonstrated that Siglec-E KO mice reject tumors faster in multiple tumor models, we have found that colorectal cancer is accelerated in Siglec-E KO mice. Here we aim to investigate the role of Siglec-E in immune homeostasis, inflammation and colorectal cancer development. Methods We used two models of colorectal cancer to assess the role of Siglec-E in tumorigenesis: TS4-cre LSL KRASG12D APClox468/wt (TAR mice) and the DSS/AOM model of colitis-associated cancer. Colons were prepared by separating lamina propria (LP) and epithelial (EP) fractions for flow cytometry. 2cm sections were taken from the middle of colons to generate lysates for ELISA. DSS was administered to WT and Siglec-E KO mice to assess the susceptibility to intestinal inflammation. H&E and IHC for PCNA were performed on colonic tissue from experiments. Results We have found that in both the spontaneous and DSS induced models of CRC, Siglec-E KO mice grow more tumors than WT mice. Siglec-E KO mice have an exquisite susceptibility to DSS induced inflammation and reduced number and proportion of neutrophils after treatment. Lastly, we have found that Siglec-E KO mice at baseline have increased VEGF-A in the colon. Conclusion Siglec-E has a critical role in regulating immune homeostasis in the colon. Siglec-E functions as a brake for intestinal inflammation which protects from the development of colorectal cancer. Funding Source This research was funded by NIH grant CA243545-01A1 (VSS), NIH T32 AI170478 (VSS/BM), and and grant R25 GM055252-26 Deans fellowship: Initiative for maximizing student development (IMSD). Topic Categories Cellular Adhesion, Migration, and Inflammation (CAM)

Abstract Introduction Checkpoint blockade revolutionized cancer therapy. However, only a small proportion of cancers respond to checkpoint blockade. B7-H3 is a member of the B7 superfamily, which includes both co-inhibitory and co-stimulatory receptors. B7-H3 is upregulated by many tumors which is generally associated with a worse prognosis. However, the exact mechanism by which B7-H3 suppresses the immune response remains elusive. Methods We transfected human HEK293T cells and assessed the binding to recombinant Siglecs via flow cytometry. We generated monoclonal antibody F7 against human B7-H3 and tested its blocking function using B7-H3 transfected HEK293T cells. We examined the extent of degranulation and NK cell-mediated killing on B7-H3 expressing HEK293T cells in vitro, as well as the CART19 cells mediated killing in relapse model of B7-H3 expressing CD19+ leukemia Nalm6 cells NSG mice. Results We demonstrated that sialylated B7-H3 binds to the inhibitory receptor Siglec-9 on immune cells but not to the related protein Siglec-7. A high affinity monoclonal antibody (mAb) F7 against B7-H3 blocks Siglec-9 binding. Functionally, F7 enhances NK cell killing of B7-H3 expressing target cells in vitro. F7 also dramatically enhances CART19 mediated killing of B7-H3 expressing Nalm6 cells in a relapse model in NSG mice in vivo. Conclusion We have now shown for the first time that B7-H3 binds to the inhibitory receptor Siglec-9 and generated a novel monoclonal antibody F7 that target a unique sequence in B7-H3 as compared to other monoclonal antibodies being examined for clinical efficacy. F7 can promote NK cell killing of B7-H3 expressing target cells in vitro and synergize with CART19 to enhance killing of B7-H3 expressing tumor cells in vivo. As B7-H3 is overexpressed in many human cancers, this work is critical toward understanding how B7-H3 mediates immune evasion through Siglec-9 for enhancing anti-tumor immunity. Funding Source R01CA243545-01A1 Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)

Abstract Introduction Generation of T cells requires dynamic epigenetic alteration of histones to control gene expression at each developmental stage. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) facilitate addition or removal of various acyl groups from lysine residues, including acetylation (KAc) and crotonylation (KCr). The Class I deacetylases HDAC1, HDAC2, and HDAC3 have been shown to have 3 functions: adaptor, decrotonylase, and deacetylase activity. The relative importance of each function in T cells is not known. Genetic knockout of HDAC3 in mice using CD2icre results in a severe block in T cell development and spontaneous development of severe colitis. Our lab determined that HDAC3 is required for three different aspects of this process: CD4+CD8 + (DP) cell survival, positive selection, and CD4+ lineage commitment. We generated a novel mouse model with CD2icre-mediated deletion of endogenous HDAC3 and linked re-expression of HDAC3 “VRPP” mutant mice, which maintained adaptor function but lacks enzymatic activity. Strikingly, these mice do not develop spontaneous colitis even up to one year of age. Methods We used flow cytometry to assess T cell development and maturation in the thymus, spleen, mLN, and colon of HDAC3 cKO vs. HDAC3 VRPP mice. CUT&RUN was utilized to determine differences in H3K9Ac, H3K27Ac, and H3K18Cr across CD8 and CD4 lineage genes. H&E was utilized to assess structural changes in thymus and colon. Results Similar to CD2icre HDAC3 cKO mice, HDAC3 VRPP mice have a block in positive selection due to failure to down regulate RORγt and decreased DP cell survival due to increased expression of P2RX7. Although fewer T cells are produced in HDAC3 VRPP mice, CD4+ lineage commitment is restored, likely mitigating the development of spontaneous colitis. Conclusion Our results demonstrate that HDAC3 enzymatic activity is necessary for several aspects of T cell development, while HDAC3 adaptor function is sufficient to restore CD4+ lineage commitment. Funding Source NIAID RO1 AI150100, T32 AI170478 Topic Categories Hematopoiesis and Immune System Development (HEM)

Abstract Introduction The immune environment of the brain plays a major role in neurodegenerative conditions such as Alzheimer’s disease. The abnormally clean facilities in which laboratory mice are kept limit immune experience and cause major concerns regarding the translatability of research to humans. These facilities, although not germ-free, lack the normal exposures to diverse commensal and environmental microorganisms experienced by mice in the wild or diverse environments such as a pet store. By breeding inbred lab mice that have previously experienced exposure to the dirty bedding of pet store mice, we can generate “bred dirty” mice with immune systems that mirror those of adult humans more closely. It is unclear whether these immune changes extend to the brain and whether this plays a role in neurodegenerative disease. Methods We used the P301s transgenic mouse model of Alzheimer’s disease that accumulates age-dependent tau pathology. We exposed these mice to dirty bedding obtained from pet store mice, and bred them to establish a line of “bred dirty” tau-P301S mice and appropriate controls. At endpoint, we collected brain and spleen for flow cytometry, immunofluorescence, and bulk RNAseq. Results The proportions of CD3+ T cells, monocytes, and macrophages were significantly increased in the brains of the dirty tau-P301S mice compared to their clean tau-P301S counterparts. The brains of the dirty tau-P301S mice also showed an increase in the proportion of CD8+ T cells, specifically effector differentiated (CD62L-CD44+) CD8+ T cells. The proportion of activated (CD11c+) microglia was increased in tau-P301S mice but unaffected by dirty status. Conclusion Disease-associated infiltration of adaptive immune cells into the brain is amplified by dirty status without grossly affecting microglial activation. Given the increasingly recognized role of T cells in Alzheimer’s disease pathogenesis, our results suggest that more immune educated models might better represent the role of T cells in neurodegenerative disease. Funding Source Mayo Clinic and The Translational Genomics Research Institute Topic Categories Neuroimmunology (NEUR)

Abstract Introduction The mitochondrial transporter ABCB7 is essential for exporting iron-sulfur (Fe-S) clusters, a function known to be critical in B cells. This study was conducted to investigate the broader, previously unknown roles of ABCB7 in regulating the overall lymphocyte development and homeostasis. Methods The study utilized conditional knockout (cKO) mouse models (CD2-iCre and Mb1-Cre) to create a specific deficiency of ABCB7 in certain immune populations. To determine if the observed effects were due to ABCB7 deletion in myeloid cells, two further models (CD2i-Cre ABCB7 cKO/C/EBPα and CD2-iCre LSL TMT ABCB7 cKO) were developed. The effects of blocking the cytokine G-CSF were also examined to understand its role in the observed myelopoiesis. Results ABCB7 deficiency was found to dramatically impair erythropoiesis while simultaneously driving emergency myelopoiesis. We confirmed that the myeloid expansion was not a direct result of ABCB7 loss in myeloid cells. A significant autoimmune phenotype also developed, characterized by hyperactivated T cells and a sharp decrease in peripheral regulatory T cells (Tregs). This Treg instability was linked to decreased thymic expression of key stability genes (like CD28 and PD-1) and reduced O-GlcNAc modification in T cells, a process crucial for maintaining Treg lineage. Conclusion The findings establish ABCB7 as a pivotal regulator of hematopoietic balance, linking mitochondrial function to both myeloid expansion and Treg stability. Funding Source T32AI170478 Topic Categories Hematopoiesis and Immune System Development (HEM)

Abstract Introduction The H-2Db class I restricted CD8 T cell response is critical for clearance of neurotropic Theiler’s virus encephalomyelitis virus (TMEV) infection. However, the key central nervous system cell types required to present H-2Db for CD8 T cell trafficking and expansion in the brain are not known. Mural cells are a critical cellular component of the neurovascular unit for maintaining vascular integrity which also express MHC class I molecules. However, the importance of mural cell antigen-restricted engagement by CD8 T cells has not been investigated. Methods To determine the function of mural cell MHC Class I antigen presentation, we crossed the Pdgfrβ-creERT2 mouse to our novel H-2Db LoxP mouse developed by our laboratory. This transgenic mouse approach enabled us to target mural cells during neuroinflammation. Results We observed robust knockdown of H-2Db on mural cells during acute TMEV infection. Conditional H-2Db knockdown in mural cells resulted in increased brain infiltration of CD8 T cells specific to the immunodominant Db:VP2 121-130 epitope of TMEV, demonstrating an important role of mural cells for immune cell recruitment. Conclusion To our knowledge, this is the first study demonstrating MHC class I antigen presentation by mural cells impacts CD8 T cell recruitment during neuroinflammation. Funding Source R01-NS103212, T32-AI170478 Topic Categories Neuroimmunology (NEUR)