Antibodies and complement are key drivers of thrombosis.

Venous thromboembolism (VTE) is a common, deadly disease with an increasing incidence despite preventive efforts. Clinical observations have associated elevated antibody concentrations or antibody-based therapies with thrombotic events. However, how antibodies contribute to thrombosis is unknown. Here, we show that reduced blood flow enabled immunoglobulin M (IgM) to bind to FcµR and the polymeric immunoglobulin receptor (pIgR), initiating endothelial activation and platelet recruitment. Subsequently, the procoagulant surface of activated platelets accommodated antigen- and FcγR-independent IgG deposition. This leads to classical complement activation, setting in motion a prothrombotic vicious circle. Key elements of this mechanism were present in humans in the setting of venous stasis as well as in the dysregulated immunothrombosis of COVID-19. This antibody-driven thrombosis can be prevented by pharmacologically targeting complement. Hence, our results uncover antibodies as previously unrecognized central regulators of thrombosis. These findings carry relevance for therapeutic application of antibodies and open innovative avenues to target thrombosis without compromising hemostasis.

GPR126 is a specifier of blood-brain barrier formation in the mouse central nervous system.

The blood-brain barrier (BBB) acquires unique properties to regulate neuronal function during development. The formation of the BBB, which occurs in tandem with angiogenesis, is directed by the Wnt/ß-catenin signaling pathway. Yet the exact molecular interplay remains elusive. Our study reveals the G protein-coupled receptor GPR126 as a critical target of canonical Wnt signaling, essential for the development of the BBB's distinctive vascular characteristics and its functional integrity. Endothelial cell-specific deletion of the Gpr126 gene in mice induced aberrant vascular morphogenesis, resulting in disrupted BBB organization. Simultaneously, heightened transcytosis in vitro compromised barrier integrity, resulting in enhanced vascular permeability. Mechanistically, GPR126 enhanced endothelial cell migration, pivotal for angiogenesis, acting through an interaction between LRP1 and ß1 integrin, thereby balancing the levels of ß1 integrin activation and recycling. Overall, we identified GPR126 as a specifier of an organotypic vascular structure, which sustained angiogenesis and guaranteed the acquisition of the BBB properties during development.

LSD1 inhibition improves efficacy of adoptive T cell therapy by enhancing CD8+ T cell responsiveness.

The lysine-specific histone demethylase 1 A (LSD1) is involved in antitumor immunity; however, its role in shaping CD8 + T cell (CTL) differentiation and function remains largely unexplored. Here, we show that pharmacological inhibition of LSD1 (LSD1i) in CTL in the context of adoptive T cell therapy (ACT) elicits phenotypic and functional alterations, resulting in a robust antitumor immunity in preclinical models in female mice. In addition, the combination of anti-PDL1 treatment with LSD1i-based ACT eradicates the tumor and leads to long-lasting tumor-free survival in a melanoma model, complementing the limited efficacy of the immune or epigenetic therapy alone. Collectively, these results demonstrate that LSD1 modulation improves antitumoral responses generated by ACT and anti-PDL1 therapy, providing the foundation for their clinical evaluation.

Plasmacytoid dendritic cells control homeostasis of megakaryopoiesis.

Platelet homeostasis is essential for vascular integrity and immune defence1,2. Although the process of platelet formation by fragmenting megakaryocytes (MKs; thrombopoiesis) has been extensively studied, the cellular and molecular mechanisms required to constantly replenish the pool of MKs by their progenitor cells (megakaryopoiesis) remains unclear3,4. Here we use intravital imaging to track the cellular dynamics of megakaryopoiesis over days. We identify plasmacytoid dendritic cells (pDCs) as homeostatic sensors that monitor the bone marrow for apoptotic MKs and deliver IFNα to the MK niche triggering local on-demand proliferation and maturation of MK progenitors. This pDC-dependent feedback loop is crucial for MK and platelet homeostasis at steady state and under stress. pDCs are best known for their ability to function as vigilant detectors of viral infection5. We show that virus-induced activation of pDCs interferes with their function as homeostatic sensors of megakaryopoiesis. Consequently, activation of pDCs by SARS-CoV-2 leads to excessive megakaryopoiesis. Together, we identify a pDC-dependent homeostatic circuit that involves innate immune sensing and demand-adapted release of inflammatory mediators to maintain homeostasis of the megakaryocytic lineage.

Therapeutic potential of co-signaling receptor modulation in hepatitis B.

Reversing CD8+ T cell dysfunction is crucial in treating chronic hepatitis B virus (HBV) infection, yet specific molecular targets remain unclear. Our study analyzed co-signaling receptors during hepatocellular priming and traced the trajectory and fate of dysfunctional HBV-specific CD8+ T cells. Early on, these cells upregulate PD-1, CTLA-4, LAG-3, OX40, 4-1BB, and ICOS. While blocking co-inhibitory receptors had minimal effect, activating 4-1BB and OX40 converted them into antiviral effectors. Prolonged stimulation led to a self-renewing, long-lived, heterogeneous population with a unique transcriptional profile. This includes dysfunctional progenitor/stem-like (TSL) cells and two distinct dysfunctional tissue-resident memory (TRM) populations. While 4-1BB expression is ubiquitously maintained, OX40 expression is limited to TSL. In chronic settings, only 4-1BB stimulation conferred antiviral activity. In HBeAg+ chronic patients, 4-1BB activation showed the highest potential to rejuvenate dysfunctional CD8+ T cells. Targeting all dysfunctional T cells, rather than only stem-like precursors, holds promise for treating chronic HBV infection.

Highlights from the 2023 International Meeting on the Molecular Biology of Hepatitis B virus.

Since its discovery in 1965, our understanding of the hepatitis B virus (HBV) replication cycle and host immune responses has increased markedly. In contrast, our knowledge of the molecular biology of hepatitis delta virus (HDV), which is associated with more severe liver disease, is less well understood. Despite the progress made, critical gaps remain in our knowledge of HBV and HDV replication and the mechanisms underlying viral persistence and evasion of host immunity. The International HBV Meeting is the leading annual scientific meeting for presenting the latest advances in HBV and HDV molecular virology, immunology, and epidemiology. In 2023, the annual scientific meeting was held in Kobe, Japan and this review summarises some of the advances presented at the Meeting and lists gaps in our knowledge that may facilitate the development of new therapies.

Preclinical evaluation of therapeutic vaccines for chronic hepatitis B that stimulate antiviral activities of T cells and NKT cells.

Background & Aims: Liver diseases resulting from chronic HBV infection are a significant cause of morbidity and mortality. Vaccines that elicit T-cell responses capable of controlling the virus represent a treatment strategy with potential for long-term effects. Here, we evaluated vaccines that induce the activity of type I natural killer T (NKT) cells to limit viral replication and license stimulation of conventional antiviral T-cells. Methods: Vaccines were prepared by conjugating peptide epitopes to an NKT-cell agonist to promote co-delivery to antigen-presenting cells, encouraging NKT-cell licensing and stimulation of T cells. Activity of the conjugate vaccines was assessed in transgenic mice expressing the complete HBV genome, administered intravenously to maximise access to NKT cell-rich tissues. Results: The vaccines induced only limited antiviral activity in unmanipulated transgenic hosts, likely attributable to NKT-cell activation as T-cell tolerance to viral antigens is strong. However, in a model of chronic hepatitis B involving transfer of naive HBcAg-specific CD8+ T cells into the transgenic mice, which typically results in specific T-cell dysfunction without virus control, vaccines containing the targeted HBcAg epitope induced prolonged antiviral activity because of qualitatively improved T-cell stimulation. In a step towards a clinical product, vaccines were prepared using synthetic long peptides covering clusters of known HLA-binding epitopes and shown to be immunogenic in HLA transgenic mice. Predictions based on HLA distribution suggest a product containing three selected SLP-based vaccines could give >90 % worldwide coverage, with an average of 3.38 epitopes targeted per individual. Conclusions: The novel vaccines described show promise for further clinical development as a treatment for chronic hepatitis B. Impact and Implications: Although there are effective prophylactic vaccines for HBV infection, it is estimated that 350-400 million people worldwide have chronic hepatitis B, putting these individuals at significant risk of life-threatening liver diseases. Therapeutic vaccination aimed at activating or boosting HBV-specific T-cell responses holds potential as a strategy for treating chronic infection, but has so far met with limited success. Here, we show that a glycolipid-peptide conjugate vaccine designed to coordinate activity of type I NKT cells alongside conventional antiviral T cells has antiviral activity in a mouse model of chronic infection. It is anticipated that a product based on a combination of three such conjugates, each prepared using long peptides covering clusters of known HLA-binding epitopes, could be developed further as a treatment for chronic hepatitis B with broad global HLA coverage.

Antibody-independent protection against heterologous SARS-CoV-2 challenge conferred by prior infection or vaccination.

Vaccines have reduced severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) morbidity and mortality, yet emerging variants challenge their effectiveness. The prevailing approach to updating vaccines targets the antibody response, operating under the presumption that it is the primary defense mechanism following vaccination or infection. This perspective, however, can overlook the role of T cells, particularly when antibody levels are low or absent. Here we show, through studies in mouse models lacking antibodies but maintaining functional B cells and lymphoid organs, that immunity conferred by prior infection or mRNA vaccination can protect against SARS-CoV-2 challenge independently of antibodies. Our findings, using three distinct models inclusive of a novel human/mouse ACE2 hybrid, highlight that CD8+ T cells are essential for combating severe infections, whereas CD4+ T cells contribute to managing milder cases, with interferon-γ having an important function in this antibody-independent defense. These findings highlight the importance of T cell responses in vaccine development, urging a broader perspective on protective immunity beyond just antibodies.

Priming and Maintenance of Adaptive Immunity in the Liver.

The liver's unique characteristics have a profound impact on the priming and maintenance of adaptive immunity. This review delves into the cellular circuits that regulate adaptive immune responses in the liver, with a specific focus on hepatitis B virus infection as an illustrative example. A key aspect highlighted is the liver's specialized role in priming CD8+ T cells, leading to a distinct state of immune hyporesponsiveness. Additionally, the influence of the liver's hemodynamics and anatomical features, particularly during liver fibrosis and cirrhosis, on the differentiation and function of adaptive immune cells is discussed. While the primary emphasis is on CD8+ T cells, recent findings regarding the involvement of B cells and CD4+ T cells in hepatic immunity are also reviewed. Furthermore, we address the challenges ahead and propose integrating cutting-edge techniques, such as spatial biology, and combining mouse models with human sample analyses to gain comprehensive insights into the liver's adaptive immunity. This understanding could pave the way for novel therapeutic strategies targeting infectious diseases, malignancies, and inflammatory liver conditions like metabolic dysfunction-associated steatohepatitis and autoimmune hepatitis.

Deterministic reprogramming of neutrophils within tumors.

Neutrophils are increasingly recognized as key players in the tumor immune response and are associated with poor clinical outcomes. Despite recent advances characterizing the diversity of neutrophil states in cancer, common trajectories and mechanisms governing the ontogeny and relationship between these neutrophil states remain undefined. Here, we demonstrate that immature and mature neutrophils that enter tumors undergo irreversible epigenetic, transcriptional, and proteomic modifications to converge into a distinct, terminally differentiated dcTRAIL-R1+ state. Reprogrammed dcTRAIL-R1+ neutrophils predominantly localize to a glycolytic and hypoxic niche at the tumor core and exert pro-angiogenic function that favors tumor growth. We found similar trajectories in neutrophils across multiple tumor types and in humans, suggesting that targeting this program may provide a means of enhancing certain cancer immunotherapies.

CD8 cis-targeted IL-2 drives potent antiviral activity against hepatitis B virus.

CD8+ T cells are key antiviral effectors against hepatitis B virus (HBV), yet their number and function can be compromised in chronic infections. Preclinical HBV models displaying CD8+ T cell dysfunction showed that interleukin-2 (IL-2)-based treatment, unlike programmed cell death ligand 1 (PD-L1) checkpoint blockade, could reverse this defect, suggesting its therapeutic potential against HBV. However, IL-2's effectiveness is hindered by its pleiotropic nature, because its receptor is found on various immune cells, including regulatory T (Treg) cells and natural killer (NK) cells, which can counteract antiviral responses or contribute to toxicity, respectively. To address this, we developed a cis-targeted CD8-IL2 fusion protein, aiming to selectively stimulate dysfunctional CD8+ T cells in chronic HBV. In a mouse model, CD8-IL2 boosted the number of HBV-reactive CD8+ T cells in the liver without substantially altering Treg or NK cell counts. These expanded CD8+ T cells exhibited increased interferon-γ and granzyme B production, demonstrating enhanced functionality. CD8-IL2 treatment resulted in substantial antiviral effects, evidenced by marked reductions in viremia and antigenemia and HBV core antigen-positive hepatocytes. In contrast, an untargeted CTRL-IL2 led to predominant NK cell expansion, minimal CD8+ T cell expansion, negligible changes in effector molecules, and minimal antiviral activity. Human CD8-IL2 trials in cynomolgus monkeys mirrored these results, achieving a roughly 20-fold increase in peripheral blood CD8+ T cells without affecting NK or Treg cell numbers. These data support the development of CD8-IL2 as a therapy for chronic HBV infection.

Immunomodulatory leptin receptor+ sympathetic perineurial barrier cells protect against obesity by facilitating brown adipose tissue thermogenesis.

Adipose tissues (ATs) are innervated by sympathetic nerves, which drive reduction of fat mass via lipolysis and thermogenesis. Here, we report a population of immunomodulatory leptin receptor-positive (LepR+) sympathetic perineurial barrier cells (SPCs) present in mice and humans, which uniquely co-express Lepr and interleukin-33 (Il33) and ensheath AT sympathetic axon bundles. Brown ATs (BATs) of mice lacking IL-33 in SPCs (SPCΔIl33) had fewer regulatory T (Treg) cells and eosinophils, resulting in increased BAT inflammation. SPCΔIl33 mice were more susceptible to diet-induced obesity, independently of food intake. Furthermore, SPCΔIl33 mice had impaired adaptive thermogenesis and were unresponsive to leptin-induced rescue of metabolic adaptation. We therefore identify LepR+ SPCs as a source of IL-33, which orchestrate an anti-inflammatory BAT environment, preserving sympathetic-mediated thermogenesis and body weight homeostasis. LepR+IL-33+ SPCs provide a cellular link between leptin and immune regulation of body weight, unifying neuroendocrinology and immunometabolism as previously disconnected fields of obesity research.

The interplay of drug therapeutics and immune responses to SARS-CoV-2.

The SARS-CoV-2 pandemic has necessitated rapid therapeutic and preventative responses. While vaccines form the frontline of defense, antiviral treatments such as nirmatrelvir have emerged as vital adjunctive measures, particularly for those unable or unwilling to be vaccinated. This review delves into the potential influence of nirmatrelvir on enduring immunity. In parallel, the potential of drug repurposing is explored, with bisphosphonates being examined for their possible effects against COVID-19 due to their immunomodulatory properties. The importance of rigorous clinical trials and careful interpretation of preliminary data is emphasized.

Inhibition of the lysine demethylase LSD1 modulates the balance between inflammatory and antiviral responses against coronaviruses.

Innate immune responses to coronavirus infections are highly cell specific. Tissue-resident macrophages, which are infected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in patients but are inconsistently infected in vitro, exert critical but conflicting effects by secreting both antiviral type I interferons (IFNs) and tissue-damaging inflammatory cytokines. Steroids, the only class of host-targeting drugs approved for the treatment of coronavirus disease 2019 (COVID-19), indiscriminately suppress both responses, possibly impairing viral clearance. Here, we established in vitro cell culture systems that enabled us to separately investigate the cell-intrinsic and cell-extrinsic proinflammatory and antiviral activities of mouse macrophages infected with the prototypical murine coronavirus MHV-A59. We showed that the nuclear factor κB-dependent inflammatory response to viral infection was selectively inhibited by loss of the lysine demethylase LSD1, which was previously implicated in innate immune responses to cancer, with negligible effects on the antiviral IFN response. LSD1 ablation also enhanced an IFN-independent antiviral response, blocking viral egress through the lysosomal pathway. The macrophage-intrinsic antiviral and anti-inflammatory activity of Lsd1 inhibition was confirmed in vitro and in a humanized mouse model of SARS-CoV-2 infection. These results suggest that LSD1 controls innate immune responses against coronaviruses at multiple levels and provide a mechanistic rationale for potentially repurposing LSD1 inhibitors for COVID-19 treatment.

IL-1ß+ macrophages fuel pathogenic inflammation in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with high resistance to therapies1. Inflammatory and immunomodulatory signals co-exist in the pancreatic tumour microenvironment, leading to dysregulated repair and cytotoxic responses. Tumour-associated macrophages (TAMs) have key roles in PDAC2, but their diversity has prevented therapeutic exploitation. Here we combined single-cell and spatial genomics with functional experiments to unravel macrophage functions in pancreatic cancer. We uncovered an inflammatory loop between tumour cells and interleukin-1ß (IL-1ß)-expressing TAMs, a subset of macrophages elicited by a local synergy between prostaglandin E2 (PGE2) and tumour necrosis factor (TNF). Physical proximity with IL-1ß+ TAMs was associated with inflammatory reprogramming and acquisition of pathogenic properties by a subset of PDAC cells. This occurrence was an early event in pancreatic tumorigenesis and led to persistent transcriptional changes associated with disease progression and poor outcomes for patients. Blocking PGE2 or IL-1ß activity elicited TAM reprogramming and antagonized tumour cell-intrinsic and -extrinsic inflammation, leading to PDAC control in vivo. Targeting the PGE2-IL-1ß axis may enable preventive or therapeutic strategies for reprogramming of immune dynamics in pancreatic cancer.

Immunogenicity and Pre-Clinical Efficacy of an OMV-Based SARS-CoV-2 Vaccine.

The vaccination campaign against SARS-CoV-2 relies on the world-wide availability of effective vaccines, with a potential need of 20 billion vaccine doses to fully vaccinate the world population. To reach this goal, the manufacturing and logistic processes should be affordable to all countries, irrespective of economical and climatic conditions. Outer membrane vesicles (OMVs) are bacterial-derived vesicles that can be engineered to incorporate heterologous antigens. Given the inherent adjuvanticity, such modified OMVs can be used as vaccines to induce potent immune responses against the associated proteins. Here, we show that OMVs engineered to incorporate peptides derived from the receptor binding motif (RBM) of the spike protein from SARS-CoV-2 elicit an effective immune response in vaccinated mice, resulting in the production of neutralizing antibodies (nAbs) with a titre higher than 1:300. The immunity induced by the vaccine is sufficient to protect the animals from intranasal challenge with SARS-CoV-2, preventing both virus replication in the lungs and the pathology associated with virus infection. Furthermore, we show that OMVs can be effectively decorated with the RBM of the Omicron BA.1 variant and that such engineered OMVs induce nAbs against Omicron BA.1 and BA.5, as measured using the pseudovirus neutralization infectivity assay. Importantly, we show that the RBM438-509 ancestral-OMVs elicited antibodies which efficiently neutralize in vitro both the homologous ancestral strain, the Omicron BA.1 and BA.5 variants with a neutralization titre ranging from 1:100 to 1:1500, suggesting its potential use as a vaccine targeting diverse SARS-CoV-2 variants. Altogether, given the convenience associated with the ease of engineering, production and distribution, our results demonstrate that OMV-based SARS-CoV-2 vaccines can be a crucial addition to the vaccines currently available.

The guanine nucleotide exchange factor Rin-like controls Tfh cell differentiation via CD28 signaling.

T follicular helper (Tfh) cells are essential for the development of germinal center B cells and high-affinity antibody-producing B cells in humans and mice. Here, we identify the guanine nucleotide exchange factor (GEF) Rin-like (Rinl) as a negative regulator of Tfh generation. Loss of Rinl leads to an increase of Tfh in aging, upon in vivo immunization and acute LCMV Armstrong infection in mice, and in human CD4+ T cell in vitro cultures. Mechanistically, adoptive transfer experiments using WT and Rinl-KO naïve CD4+ T cells unraveled T cell-intrinsic GEF-dependent functions of Rinl. Further, Rinl regulates CD28 internalization and signaling, thereby shaping CD4+ T cell activation and differentiation. Thus, our results identify the GEF Rinl as a negative regulator of global Tfh differentiation in an immunological context and species-independent manner, and furthermore, connect Rinl with CD28 internalization and signaling pathways in CD4+ T cells, demonstrating for the first time the importance of endocytic processes for Tfh differentiation.