Citations

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)

Abstract Introduction Glioblastoma (GBM), the most aggressive primary brain tumor in adults, is marked by profound immune suppression. Tumor-derived extracellular vesicles (TEVs) are increasingly recognized as key mediators of this immunosuppressive environment. Methods In this study, we examined the tumor-immune microenvironment using ultrasonic aspirate samples from GBM patients (n = 14). Results Several immune checkpoint molecules, including PDL1, B7-H3, and VISTA, were notably elevated. TIGIT, a receptor typically associated with T cells, was widely expressed across multiple myeloid subsets, including monocytic myeloid-derived suppressor cells (mMDSCs; 64.27±7.99%) and non-classical monocytes (NCM; 39.8±4.37%). Co-culture of healthy donor CD11b+ cells (n = 10) with TEVs replicated similar effects (mMDSCs; control 11.691.87 vs EV treated 23.322.0). We found CD155, a primary TIGIT ligand, to be heavily enriched in TEVs and co-localized with TIGIT in co-culture, suggesting the TIGIT/CD155 axis may be involved in promoting immune suppression. induced MDSCs markedly suppressed T cell proliferation (30.65 ± 5.97% vs. control 86.47 ± 2.94, p = 0.0001), accompanied by elevated Th2 cytokine production and increased NLRP3 and IL-1β expression. Interestingly, TIGIT knockdown did not affect NLRP3 expression, but did restore T cell proliferation (64.13±1.33%; p = 0.02) and pro-inflammatory cytokine production. However, this effect was lost upon NLRP3 knockdown, indicating its essential role in mediating immune rescue. Furthermore, IL-13 (a Th2 cytokine) blockade, in this model, enhanced pro-inflammatory response by suppressing phosphorylation of STAT-6 protein. Conclusion Overall, our findings highlight a crucial role for the TIGIT/CD155 axis in driving myeloid-mediated immune suppression in GBM. Furthermore, TIGIT inhibition may unmask NLRP3 function, potentially contributing to immune rescue. Funding Source Neurosurgery Research & Education Foundation through the B*CURED & NREF Young Clinician Investigator Award, as well as intramural K12 funding through the Institute for Clinical and Translational Research and the NCI Paul Calabresi Career Development Award (1K12CA279871). Topic Categories Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)

Abstract Introduction T cell activation is a dynamic process governed by the strength and duration of antigen recognition via the T cell receptor (TCR). The timing of in vivo TCR signaling— when and how strongly memory CD8+ T cells become reactivated in the inflamed brain following antigen exposure— is a fundamental mechanism that remains unclear. The Nr4a3-Tocky reporter (Tocky) mouse employs a fluorescent timer that shifts from blue to red after TCR-driven Nr4a3 activation, which allows researchers to track activation kinetics through two parameters: the Timer Angle (recency of T cell activation), and the Timer Intensity (strength of signaling). Methods To understand CD8+ T cell activation during this neuroinflammation, we generated memory CD8+ T cells by intracranial Theiler’s murine encephalomyelitis virus infection of these Tocky mice. After viral clearance, we reactivated memory CD8+ T cells by intravenously injecting their cognate antigen. Tissues were collected 0-72 hours post-injection and profiled by flow cytometry. An R pipeline was constructed to transform event-level flow data to quantify the TCR activation. Data were analyzed with a Metropolis—Hastings MCMC algorithm to model activation dynamics and estimate probabilistic transitions between biologically defined states (newly activated, persistent, arrested states). Results These empirical transition probabilities enabled Bayesian comparison of antigen-specific versus nonspecific CD8+ T cells. It was revealed that antigen-specific CD8+ T cells rapidly transition to a high-intensity activation state within 24 hours and maintain persistent signaling compared to nonspecific populations. Conclusion This establishes a biologically grounded, in vivo framework for modeling and comparing TCR signaling during neuroinflammation. Funding Source R01 - NS103212 Topic Categories Neuroimmunology (NEUR)

Abstract Introduction We have shown that combining CAR T cells with oncolytic viruses (OVs) generates a subpopulation of highly cytotoxic CAR T cells that can mediate long-term solid tumor therapy. Methods To profile these CAR T cells, we used C57BL/6 mice bearing B16F10 tumors expressing EGFRviii, treated with anti-EGFRviii CAR T cells and the OV vesicular stomatitis virus (VSV). TCR signaling in CAR T cells was investigated using the novel Tocky transgenic mouse model, which reports T cell activation over time using an unstable fluorescent protein reporter of Nr4a3. We further investigated CAR T phenotypes using CyTOF and scRNA-Seq. Results Using an MHC I tetramer for the dominant VSV epitope VSV N52-59, we found that 20-50% of transfused CAR T adopted TCR specificity against VSV N (referred to as TCR-primed), indicating significant in vivo expansion. Ex vivo, these TCR-primed CAR T produced increased levels of granzyme B and IFNγ over tetramer-negative CAR T against either TCR or CAR targets. However, TCR-primed CAR T cells were notably less activated via Nr4a3 as compared to non-TCR-primed CAR T. CyTOF and scRNA-Seq analyses demonstrated a hypereffector phenotype among TCR-primed CAR, with increased expression of T-bet, CD44, granzyme B, IFNγ, and perforin. TCR sequencing revealed hyperexpansion of VSV N-specific CAR T cells and little overlap in clonotypes between CAR T co-treated with PBS versus VSV. These TCR-primed CAR T cells exhibited a CD4-helped phenotype with increased expression of chemotactic and migratory transcripts. When CAR T and OV were administered with antibody-mediated CD4 depletion, the TCR-primed CAR population was significantly diminished, emphasizing the importance of the immune triad for CAR T expansion. Conclusion Overall, CAR T cells that undergo endogenous anti-viral TCR priming and signaling adopt a unique phenotype that promotes their expansion and cytotoxic function. Interactions with CD4 T cells appear to be integral for the generation of this subpopulation of CD8 CAR T cells. Funding Source NIH Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)

Abstract Introduction Colorectal cancer (CRC) is the second leading cause of cancer death in the U.S., with stage IV patients showing poor five-year survival. Immune checkpoint blockade shows limited efficacy in CRC, highlighting the need to better understand how CD8+ T cells are regulated by the tumor microenvironment (TME). In the TME, CD8+ T cells often become exhausted and lose cytotoxic function. Terminally exhausted cells express high inhibitory receptors, PD-1, Tim-3, and low proliferative capacity; whereas stem-like exhausted cells can self-renew and respond well to checkpoint blockade. Metabolic regulation is critical for CD8+ T cells, including membrane channels that export metabolites. Our lab studies Pannexin-1 (PANX1), a channel that exports ATP and promotes memory CD8+ T cell survival via AMPK signaling. Methods We found that PANX1 is crucial for effective antitumor CD8+ T cell responses in CRC. High PANX1 expression correlates with increased CD8+ T cell infiltration and better prognosis in stage IV CRC patients. Using CRC mouse models, CD8-specific Panx1 knockout males, but not females, fail to control MC38 tumors, with tumor-infiltrating CD8+ T cells showing higher exhaustion, fewer stem-like cells in lymph nodes, and lower AMPK activity. Results Single-cell RNAseq and InfinityFlow confirm enhanced exhaustion signatures in PANX1-KO tumor-infiltrating stem-like exhausted cells, while wild-type tumors accumulate more effector-like (Zeb2+) CD8+T cells. Preliminary data suggests that AMPK overactivation (AICAR) significantly restores PANX1-KO exhausted CD8+ T cells. Finally, the gender-specific discrepancies may involve androgen receptor signaling, elevated in PANX1-KO exhausted cells. Ongoing studies examine whether PANX1-mediated AMPK activity regulates androgen receptor expression. Conclusion Together, these findings suggest PANX1 promotes CD8+T cell-driven anti-tumor immunity in CRC in a gender-dependent manner, potentially explaining sex-based differences. Funding Source n/a Topic Categories Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)

Abstract Introduction Ovarian cancer (OvCa) remains the most lethal gynecologic malignancy, with older women experiencing the poorest outcomes. Aging profoundly remodels the ovarian tumor immune microenvironment (TME), promoting regulatory T cell (Treg) mediated immune evasion; however, the underlying metabolic mechanisms remain unclear. Methods Using young (3-month) and aged (22-month) female mice injected intraperitoneally with ID8p53⁻/⁻ OvCa cells, we investigated how age associated metabolic reprogramming influences tumor immunity Results Aged OvCa bearing mice exhibited accelerated tumor progression, reduced survival (median 54 vs. 72 days), decreased CD4+ and CD8+ T cells, and an expanded Treg population. Metabolomic profiling revealed increased succinate accumulation in ascites, tumor tissue, and serum of aged mice and elderly OvCa patients. Exogenous succinate enhanced CCR4+FOXP3+ Treg frequency and upregulated IL-10 and TGF-β secretion. Elevated levels of CCL22, a CCR4 ligand, were also detected in ascites from aged mice and patients, suggesting a chemokine-driven reinforcement of Treg recruitment. PBMCs from aged patients displayed an OXPHOS-reprogrammed CCR4+FOXP3+ Treg subset with heightened suppressive capacity, markedly inhibiting CD4+ and CD8+ effector cytotoxicity. Treatment with AA6, an α-ketoglutarate dehydrogenase inhibitor that blocks succinate synthesis, reduced CCR4+FOXP3+ Treg accumulation, restored effector T-cell function, and significantly prolonged survival in aged OvCa-bearing mice. Conclusion Together, these findings reveal a novel succinate—CCR4 metabolic—chemokine axis that drives Treg mediated immunosuppression in aged OvCa. Targeting this pathway offers a promising strategy to restore anti-tumor immunity and overcome age-related immunotherapy resistance in ovarian cancer. Funding Source N/A Topic Categories Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)

Abstract Introduction Glioblastoma (GBM) is the most aggressive primary brain tumor in adults with an incident rate of 12,000 cases in the United States every year. Current treatment options for these patients include surgical resection, radiation, and chemotherapy. Despite these conventional treatments, patients have a dismal prognosis mostly due to the inability to deliver therapeutic agents across the blood-brain barrier. In recent years, the use of oncolytic picornavirus has been employed as a novel virotherapy for GBM. We hypothesized that we could enhance antibody delivery to the brain through harnessing the immune response associated with this oncolytic virus. Prior work from our lab has shown that CD8 T cell engagement with MHC class I on brain endothelium induces CNS vascular permeability which is dependent on perforin. We therefore asked if picornavirus antigen specific CD8 T cells could enhance antibody delivery to the brain. Methods To test this, we evaluated the potential of activating MHC class I restricted CD8 T cells in vivo through intravenous administration of their cognate picornavirus antigens. Results We determined that this approach enhanced delivery of antibody to brain parenchyma. Importantly, antibody delivery to the brain was still enhanced when CD8 T cells lacked perforin expression which significantly reduced the toxicity of this combination approach. Conclusion These findings demonstrate that theCD8 T cell response towards virotherapy can be harnessed to promote delivery of therapeutic antibody to the brain. Funding Source NCI — R01 CA 94953 NINDS — R01 NS122174 NINDS —R01 NS103212 Mayo Clinic Graduate School of Biomedical sciences Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)

Abstract Introduction CD8 T cells are key immune cells in viral clearance, targeting infected cells following recognition of MHC class I restricted antigen presentation. Previous work has determined that microglia and perivascular macrophages are essential for normal CD8 T cell responses against neurotropic viral infection, indicating that cells at the neurovascular unit can act as antigen-presenting cells. However, the specific importance of microglia MHC class I restricted antigen presentation to brain-infiltrating CD8 T cells has been difficult to define. Methods To address this question, our laboratory generated novel single MHC Class I conditional knockout mice in which H-2Kb or H-2Db can be deactivated specifically in Tmem119+ microglia with tamoxifen administration. Recombinant Theiler’s murine encephalomyelitis virus (TMEV) encoding the model OVA antigen enabled analysis of virus antigen-specific CD8 T cells restricted to H-2Kb class I molecules while Daniel’s strain TMEV H-2Db class I molecules enabled analysis of Db:VP2 specific CD8 T cells. Results Our results revealed profound differences in the response of CD8 T cells upon deletion of MHC class I molecules on microglia. Conditional knockout of H-2Kb in Tmem119+ microglia reduced Kb:OVA epitope specific CD8 T cells in the brain compared to Cre negative littermate controls, and BrdU staining revealed differences in T cell proliferation. Meanwhile, mice with deletion of Db in Tmem119+ microglia had reduced levels of perforin in Db:VP2 CD8 T cells. Furthermore, in a model of CNS vascular disease, the deletion of H-2Db of Tmem119+ microglia reduced CD8 T cell numbers in the brain, as well as the blood-brain barrier (BBB) breakdown observed by a FITC albumin assay. Conclusion These findings demonstrate discrete roles for specific MHC Class I molecules on microglia during CNS viral infection. This data will further our understanding of brain infiltrating CD8 T cell responses in neurologic diseases as well as the regulation of BBB by microglia. Funding Source R01 NS 103212 R01 NS122174 Topic Categories Neuroimmunology (NEUR)