Johnson, Aaron J.

Abstract Aging is considered to be a major risk factor for host morbidity and mortality upon acute respiratory virus infections. To better elucidate the immune determinants of viral pathogenesis during aging, we chronological characterized lung cellular and molecular profiles following influenza virus (PR8) infection in young or aged mice till 60 days post infection. Time-course scRNAseq coupled with high dimensional flow cytometry enabled the description of changes in both immune and stromal compartment between young and aged hosts. We further zoomed into the myeloid compartment and focused on the dynamic responses of lung macrophages given their complex roles in viral pathogenesis, tissue repair and lung fibrosis. Enlarged Monocyte-derived Macrophage (MoM) population as well as decreased resident-Alveolar Macrophage (AM) population were observed in the aged mice when compared to those of the young mice. Despite the self-sustain nature of AMs during homeostasis, it has been reported that Ly6Chi monocytes can gain AM identity following severe lung damage like influenza virus infection. We found that the gain of AM identity from monocytes was abrogated in the aged hosts, which likely contributed to the age-associated impairment in lung recovery after influenzas virus infection. Additionally, trajectory analysis with scRNAseq allowed us to identify IFNα/γ signaling to be potential pathways contributing to such defect. This notion is also supported by elevated IFNγ level in BAL from the aged host during lung recovery. Our results thus have improved our understanding on the cellular and molecular mechanisms by which aged hosts exhibit severe diseases and delayed recovery after respiratory viral infection.

Abstract Brain atrophy is a common feature of many neurological diseases as diverse as Alzheimer’s disease, cerebral palsy, Huntington’s disease, multiple sclerosis, epilepsy, encephalitis, neurosyphilis, neuroAIDS, and Covid-19 infection. We have developed a murine model of brain atrophy using the Theiler’s murine encephalomyelitis virus (TMEV) infection mouse model of multiple sclerosis. In this study, we investigated the contribution of the MHC class I molecule, H-2Db, in generating an immune response associated with the onset of brain atrophy using mice with a C57BL/6 background. The H-2DbClass I molecule not only contributed to significantly more ventricular enlargement in a T2-weighted MRI at 45 d.p.i., but this ventricular enlargement correlated to CD8 T cell infiltration. To further define the cellular and molecular mechanisms of MHC class I molecules in TMEV induced brain atrophy we investigated the cell specific contribution of brain resident antigen presenting cells (APCs) in ventricular atrophy. We developed novel bi-transgenic mouse lines with tamoxifen induced conditional ablation of the H-2Db class I molecule in Cx3CR1+ brain resident myeloid cells. Cx3CR1cre+/Db Lox P mice presented with significantly less ventricular atrophy at 45 d.p.i., compared to cre- littermates along with a decrease in CD8 T cell infiltration. These results strongly imply that antigen presentation by H-2Db on myeloid cells, at least in part is responsible for the development of brain atrophy and provided insight into the molecular mechanism of this poorly understood neuropathology. NS103212, NS122174

Abstract Intracranial infection with neurotropic Theiler’s Murine Encephalomyelitis Virus induces robust generation of brain TRMs against the immunodominant antigen, VP2121–130, following viral clearance in C57BL/6 mice. While the presence of TRMs in the brain is documented, neurological consequences of TRM reactivation and their causal role in neuropathology remain understudied. We disabled peripheral CD8 T cells via anti CD8 depleting strategies and FTY720 treatment to determine the causal link between brain TRM reactivation and neuropathology. We depleted peripheral T cells and then administrated VP2 peptide IV to reactivate TRMs 60–200 days post infection as this elegant technique isolates responses of brain TRMs away from other branches of memory. We used state-of-the-art flow cytometry and MRI analysis to evaluate neurological consequences of TRM reactivation. TRM reactivation induced severe neuroinflammation in the brain as evident by infiltration of myeloid cells and blasting of T cells. MRI detected gadolinium leakage marking severe blood-brain-barrier (BBB) disruption when brain TRMs were reactivated. Depletion of peripheral CD8 T cells with low-dose anti CD8 antibodies or their sequestration via FTY720 did not alter neuroinflammation indicating brain TRM reactivation causally initiates neuropathology. Confirming this, tissue depletion of all TRMs in the brain using high-dose anti CD8 antibodies prevented both neuroinflammation and neuropathology. Hence, TRM reactivation causes severe neuroinflammation and BBB disruption from within the brain independently of peripheral T cells. Targeting brain TRM reactivation is a novel potential therapeutic for patients with many acute and chronic neurological diseases. Supported by grants from NIH (K99NS117799-01A1 (KA), R01NS103212 (AJJ), and RF1NS122174(AJJ)

Abstract Background Glioblastoma (GBM) is the most common malignant brain tumor and has a poor prognosis. Imaging findings at diagnosis and in response to treatment are nonspecific. Developing noninvasive assays to augment imaging would be helpful. Plasma extracellular vesicles (EVs) are a promising biomarker source for this. Here, we develop spectral flow cytometry techniques that demonstrate differences in bulk plasma EV phenotype between GBM patients and normal donors that could serve as the basis of a liquid biopsy. Methods Plasma EVs were stained for EV-associated tetraspanins (CD9/CD63/CD81), markers indicating cell of origin (CD11b/CD31/CD41a/CD45), and actin/phalloidin (to exclude cell debris). EVs were analyzed using spectral flow cytometry. Multiparametric analysis using t-distributed stochastic neighbor embedding (t-SNE) and self-organizing maps on flow cytometry data (FlowSOM) was performed comparing GBM and normal donor (ND) plasma EVs. Results Size exclusion chromatography plus spectral-based flow cytometer threshold settings enriched plasma EVs while minimizing background noise. GBM patients had increased CD9+, CD63+, CD81+, and myeloid-derived (CD11b+) EVs. Multiparametric analysis demonstrated distinct surface marker expression profiles in GBM plasma EVs compared to ND EVs. Fifteen plasma EV sub-populations differing in size and surface marker expression were identified, six enriched in GBM patients and two in normal donors. Conclusions Multiparametric analysis demonstrates that GBM patients have a distinct nonneoplastic plasma EV phenotype compared to ND. This simple rapid analysis can be performed without purifying tumor EVs and may serve as the basis of a liquid biopsy.

Our understanding of tissue-resident memory T (T RM ) cell biology has been largely developed from acute infection models in which antigen is cleared and sterilizing immunity is achieved. Less is known about T RM cells in the context of chronic antigen persistence and inflammation. We investigated factors that underlie T RM maintenance in a kidney transplantation model in which T RM cells drive rejection. In contrast to acute infection, we found that T RM cells declined markedly in the absence of cognate antigen, antigen presentation, or antigen sensing by the T cells. Depletion of graft-infiltrating dendritic cells or interruption of antigen presentation after T RM cells were established was sufficient to disrupt T RM maintenance and reduce allograft pathology. Likewise, removal of IL-15 transpresentation or of the IL-15 receptor on T cells during T RM maintenance led to a decline in T RM cells, and IL-15 receptor blockade prevented chronic rejection. Therefore, antigen and IL-15 presented by dendritic cells play nonredundant key roles in CD8 T RM cell maintenance in settings of antigen persistence and inflammation. These findings provide insights that could lead to improved treatment of chronic transplant rejection and autoimmunity.

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.

Abstract Glioblastoma (GBM) is the most common malignant brain tumor in adults, responsible for approximately 225,000 deaths per year. Despite preclinical successes, most interventions have failed to extend patient survival by more than a few months. Treatment with anti—programmed cell death protein 1 (anti–PD-1) immune checkpoint blockade (ICB) monotherapy has been beneficial for malignant tumors such as melanoma and lung cancers but has yet to be effectively employed in GBM. This study aimed to determine whether supplementing anti–PD-1 ICB with engineered extended half-life IL2, a potent lymphoproliferative cytokine, could improve outcomes. This combination therapy, subsequently referred to as enhanced checkpoint blockade (ECB), delivered intraperitoneally, reliably cures approximately 50% of C57BL/6 mice bearing orthotopic GL261 gliomas and extends median survival of the treated cohort. In the CT2A model, characterized as being resistant to CBI, ECB caused a decrease in CT2A tumor volume in half of measured animals similar to what was observed in GL261-bearing mice, promoting a trending survival increase. ECB generates robust immunologic responses, features of which include secondary lymphoid organ enlargement and increased activation status of both CD4 and CD8 T cells. This immunity is durable, with long-term ECB survivors able to resist GL261 rechallenge. Through employment of depletion strategies, ECB's efficacy was shown to be independent of host MHC class I–restricted antigen presentation but reliant on CD4 T cells. These results demonstrate ECB is efficacious against the GL261 glioma model through an MHC class I–independent mechanism and supporting further investigation into IL2-supplemented ICB therapies for tumors of the central nervous system.

Abstract Immune organ innervation by the peripheral nervous system enables autonomic function in the development and maintenance of immunity. Specifically, the role of thymic innervation in health and following neurological insults is unknown. An in depth identification of the connectome within the thymus and the extent to which nervous impulses delivered to the thymus affect T cell development and other biological processes within the thymus is needed. We sought to determine the exact nature of innervation within the thymus. Using both flow cytometry and confocal microscopy, we determined that the thymus contains both extrinsic neuronal processes (cell bodies outside of the thymus), and surprisingly, intrinsic neurons (cells bodies within the thymus). We further verified that subsets of neurons within the thymus express tyrosine hydroxylase, BIII tubulin, and/or NeuN, and are distinct from epithelial cells (EPCAM+, UEA1+, Ly51+) and tuft cells (DLCK1+). Furthermore, neuronal cell bodies found within the thymus did not express AIRE, consistent with their identity as neurons. Subsets of intrinsic neurons within the thymus express MHCII implying a potential role in T cell development. Importantly, using rabies virus retrograde and anterograde neurotracers, we mapped a novel, previously undescribed, connectome of neurons within the thymus. Finally, we determined that both epithelial cells and neurons are significantly reduced in RAG deficient mice, indicating a possible co-regulation between thymic neurons and epithelial cells. In summary, we describe a novel network of neurons within the thymus and put forward implications of the thymic connectome’s role in T cell development and establishment of thymic architecture.

Abstract Immune-mediated blood brain barrier (BBB) disruption is a prominent feature of various neurological conditions for which an emerging role of CD8 T cells is being realized. Our group has developed a unique model of CD8 T cell-mediated BBB disruption which employs Theiler’s murine encephalomyelitis virus (TMEV) infection. Upon intravenous administration of VP2121–130 viral peptide during the peak antiviral adaptive response, Db:VP2121–130 epitope specific CD8 T cells induce BBB disruption in a perforin dependent manner. In this model, we addressed the role of microglia in relation to antigen specific CD8+ T cells and permeable cerebral vessels. Using real time two-photon in vivo imaging, we demonstrate that microglia adopt distinct morphological features, including enlarged cell body and fewer ramified processes as early as 6 hours post administration of VP2 peptide. Notably, microglial population exhibit robust down-regulation of homeostatic markers including CX3CR1 during BBB disruption. This study demonstrates CD8 T cells can promote microglia activation in a perforin-dependent manner during BBB disruption. Importantly, microglial activation occurs concurrently with the onset of vascular permeability and could serve as a critical cell type in this process.

Abstract CD8 T cell responses are essential for clearance of infections in the CNS but contribute to neuropathology. T cell interaction with antigen presenting cells (APCs) at CNS barriers is thought to allow activated antigen-specific T cells to infiltrate the CNS during neuroinflammation. However, the role of CNS-resident APCs during CD8 T cell infiltration of the CNS is unclear. To address this, we utilized Theiler’s murine encephalomyelitis virus (TMEV) and Plasmodium berghei ANKA (PbA) to assess the role of APCs during CD8 T cell responses to CNS infection in mice. During infection, we observed robust upregulation of MHC class I on microglia and brain associated macrophages (BAM). Microglia and BAMs were located in close proximity to inflamed vasculature where antigen presentation to T cells could occur. Thus, we hypothesized that microglia and BAMs are critical APCs for CNS infiltration of antigen specific CD8 T cells. To test this, we generated mice with inducible deletion of MHC class I on microglia and BAMs by crossing CX3CR1creERT2 mice with H-2Db or H-2Kb floxed mice (Db cKO or Kb cKO). We found that brain infiltrating virus-specific CD8 T cells were reduced in Db cKO mice compared to controls during TMEV infection, while peripheral priming of T cells was unaffected. Conversely, antigen-specific CD8 T cell infiltration was not impacted in Kb cKO mice infected with TMEV-OVA257–264. In Db cKO mice, brain-infiltrating CD8 T cells were increased during PbA induced experimental cerebral malaria (ECM), indicating a potential inhibitory role for CNS APCs. These results demonstrate that local antigen presentation by microglia/BAMs can both positively and negatively regulate CD8 T cell infiltration of the brain in discrete neurologic disease models.