The dengue-specific immune response and antibody identification with machine learning

Dengue virus poses a serious threat to global health and there is no specific therapeutic for it. Broadly neutralizing antibodies recognizing all serotypes may be an effective treatment. High-throughput adaptive immune receptor repertoire sequencing (AIRR-seq) and bioinformatic analysis enable in-depth understanding of the B-cell immune response. Here, we investigate the dengue antibody response with these technologies and apply machine learning to identify rare and underrepresented broadly neutralizing antibody sequences. Dengue immunization elicited the following signatures on the antibody repertoire: (i) an increase of CDR3 and germline gene diversity; (ii) a change in the antibody repertoire architecture by eliciting power-law network distributions and CDR3 enrichment in polar amino acids; (iii) an increase in the expression of JNK/Fos transcription factors and ribosomal proteins. Furthermore, we demonstrate the applicability of computational methods and machine learning to AIRR-seq datasets for neutralizing antibody candidate sequence identification. Antibody expression and functional assays have validated the obtained results.

In-depth analysis of human virus-specific CD8+ T cells delineates unique phenotypic signatures for T cell specificity prediction

Following viral infection, the human immune system generates CD8+ T cell responses to virus antigens that differ in specificity, abundance, and phenotype. A characterization of virus-specific T cell responses allows one to assess infection history and to understand its contribution to protective immunity. Here, we perform in-depth profiling of CD8+ T cells binding to CMV-, EBV-, influenza-, and SARS-CoV-2-derived antigens in peripheral blood samples from 114 healthy donors and 55 cancer patients using high-dimensional mass cytometry and single-cell RNA sequencing. We analyze over 500 antigen-specific T cell responses across six different HLA alleles and observed unique phenotypes of T cells specific for antigens from different virus categories. Using machine learning, we extract phenotypic signatures of antigen-specific T cells, predict virus specificity for bulk CD8+ T cells, and validate these predictions, suggesting that machine learning can be used to accurately predict antigen specificity from T cell phenotypes.

Complement Activation by an Anti-Dengue/Zika Antibody with Impaired Fcγ Receptor Binding Provides Strong Efficacy and Abrogates Risk of Antibody-Dependent Enhancement

To combat infectious diseases, vaccines are considered the best prophylactic strategy for a wide range of the population, but even when vaccines are effective, the administration of therapeutic antibodies against viruses could provide further treatment options, particularly for vulnerable groups whose immunity against the viruses is compromised. Therapeutic antibodies against dengue are ideally engineered to abrogate binding to Fcγ receptors (FcγRs), which can induce antibody-dependent enhancement (ADE). However, the Fc effector functions of neutralizing antibodies against SARS-CoV-2 have recently been reported to improve post-exposure therapy, while they are dispensable when administered as prophylaxis. Hence, in this report, we investigated the influence of Fc engineering on anti-virus efficacy using the anti-dengue/Zika human antibody SIgN-3C and found it affected the viremia clearance efficacy against dengue in a mouse model. Furthermore, we demonstrated that complement activation through antibody binding to C1q could play a role in anti-dengue efficacy. We also generated a novel Fc variant, which displayed the ability for complement activation but showed very low FcγR binding and an undetectable level of the risk of ADE in a cell-based assay. This Fc engineering approach could make effective and safe anti-virus antibodies against dengue, Zika and other viruses.

Ketamine Reduces the Surface Density of the Astroglial Kir4.1 Channel and Inhibits Voltage-Activated Currents in a Manner Similar to the Action of Ba2+ on K+ Currents

A single sub-anesthetic dose of ketamine evokes rapid and long-lasting beneficial effects in patients with a major depressive disorder. However, the mechanisms underlying this effect are unknown. It has been proposed that astrocyte dysregulation of extracellular K⁺ concentration ([K⁺]_o) alters neuronal excitability, thus contributing to depression. We examined how ketamine affects inwardly rectifying K⁺ channel Kir4.1, the principal regulator of K⁺ buffering and neuronal excitability in the brain. Cultured rat cortical astrocytes were transfected with plasmid-encoding fluorescently tagged Kir4.1 (Kir4.1-EGFP) to monitor the mobility of Kir4.1-EGFP vesicles at rest and after ketamine treatment (2.5 or 25 µM). Short-term (30 min) ketamine treatment reduced the mobility of Kir4.1-EGFP vesicles compared with the vehicle-treated controls (p < 0.05). Astrocyte treatment (24 h) with dbcAMP (dibutyryl cyclic adenosine 5'-monophosphate, 1 mM) or [K⁺]_o (15 mM), which increases intracellular cAMP, mimicked the ketamine-evoked reduction of mobility. Live cell immunolabelling and patch-clamp measurements in cultured mouse astrocytes revealed that short-term ketamine treatment reduced the surface density of Kir4.1 and inhibited voltage-activated currents similar to Ba²⁺ (300 µM), a Kir4.1 blocker. Thus, ketamine attenuates Kir4.1 vesicle mobility, likely via a cAMP-dependent mechanism, reduces Kir4.1 surface density, and inhibits voltage-activated currents similar to Ba²⁺, known to block Kir4.1 channels.

A nonstructural protein 1 capture enzyme-linked immunosorbent assay specific for dengue viruses

Dengue non-structural protein (NS1) is an important diagnostic marker during the acute phase of infection. Because NS1 is partially conserved across the flaviviruses, a highly specific DENV NS-1 diagnostic test is needed to differentiate dengue infection from Zika virus (ZIKV) infection. In this study, we characterized three newly isolated antibodies against NS1 (A2, D6 and D8) from a dengue-infected patient and a previously published human anti-NS1 antibody (Den3). All four antibodies recognized multimeric forms of NS1 from different serotypes. A2 bound to NS1 from DENV-1, -2, and -3, D6 bound to NS1 from DENV-1, -2, and -4, and D8 and Den3 interacted with NS1 from all four dengue serotypes. Using a competition ELISA, we found that A2 and D6 bound to overlapping epitopes on NS1 whereas D8 recognized an epitope distinct from A2 and D6. In addition, we developed a capture ELISA that specifically detected NS1 from dengue viruses, but not ZIKV, using Den3 as the capture antibody and D8 as the detecting antibody. This assay detected NS1 from all the tested dengue virus strains and dengue-infected patients. In conclusion, we established a dengue-specific capture ELISA using human antibodies against NS1. This assay has the potential to be developed as a point-of-care diagnostic tool.

Intranasal Delivery of RIG-I Agonist Drives Pulmonary Myeloid Cell Activation in Mice

Viral respiratory infections cause substantial health and economic burden. There is a pressing demand for efficacious vaccination strategies and, therefore, a need for a better understanding of the mechanisms of action of novel potential adjuvants. Here we investigated the effect of a synthetic RIG-I agonist, the dsRNA hairpin 3p10LA9, on the activation of pulmonary myeloid cells. Analysis of early innate immune responses revealed that a single intranasal 3p10LA9 dose induces a transient pulmonary interferon-stimulated gene (ISG) and pro-inflammatory cytokine/chemokine response, which leads to the maturation of three distinct dendritic cell subpopulations in the lungs. While lung resident dendritic cell decrease shortly after 3p10LA9 delivery, their numbers increase in the draining mediastinal lymph node, where they have migrated, maintaining their activated phenotype. At the same time, dsRNA hairpin-induced chemokines attract transiently infiltrating monocytes into the lungs, which causes a short temporary pulmonary inflammation. However, these monocytes are dispensable in controlling influenza infection since in CCR2 deficient mice, lacking these infiltrating cells, the virus load was similar to the wild type mice when infected with the influenza virus at a sublethal dose. In summary, our data suggest that intranasal delivery of dsRNA hairpins, used as a RIG-I targeting adjuvant, represents an attractive strategy to boost type I inteferon-mediated lung dendritic cell maturation, which supports viral reduction in the lungs during infection.

Immune cell phenotypes associated with disease severity and long-term neutralizing antibody titers after natural dengue virus infection

Prior immunological exposure to dengue virus can be both protective and disease-enhancing during subsequent infections with different dengue virus serotypes. We provide here a systematic, longitudinal analysis of B cell, T cell, and antibody responses in the same patients. Antibody responses as well as T and B cell activation differentiate primary from secondary responses. Hospitalization is associated with lower frequencies of activated, terminally differentiated T cells and higher percentages of effector memory CD4 T cells. Patients with more severe disease tend to have higher percentages of plasmablasts. This does not translate into long-term antibody titers, since neutralizing titers after 6 months correlate with percentages of specific memory B cells, but not with acute plasmablast activation. Overall, our unbiased analysis reveals associations between cellular profiles and disease severity, opening opportunities to study immunopathology in dengue disease and the potential predictive value of these parameters.

A Human Antibody Neutralizes Different Flaviviruses by Using Different Mechanisms

Human antibody SIgN-3C neutralizes dengue virus (DENV) and Zika virus (ZIKV) differently. DENV:SIgN-3C Fab and ZIKV:SIgN-3C Fab cryoelectron microscopy (cryo-EM) complex structures show Fabs crosslink E protein dimers at extracellular pH 8.0 condition and also when further incubated at acidic endosomal conditions (pH 8.0-6.5). We observe Fab binding to DENV (pH 8.0-5.0) prevents virus fusion, and the number of bound Fabs increase (from 120 to 180). For ZIKV, although there are already 180 copies of Fab at pH 8.0, virus structural changes at pH 5.0 are not inhibited. The immunoglobulin G (IgG):DENV structure at pH 8.0 shows both Fab arms bind to epitopes around the 2-fold vertex. On ZIKV, an additional Fab around the 5-fold vertex at pH 8.0 suggests one IgG arm would engage with an epitope, although the other may bind to other viruses, causing aggregation. For DENV2 at pH 5.0, a similar scenario would occur, suggesting DENV2:IgG complex would aggregate in the endosome. Hence, a single antibody employs different neutralization mechanisms against different flaviviruses.

Inhibiting glycolysis rescues memory impairment in an intellectual disability Gdi1-null mouse

OBJECTIVES

GDI1 gene encodes for αGDI, a protein controlling the cycling of small GTPases, reputed to orchestrate vesicle trafficking. Mutations in human GDI1 are responsible for intellectual disability (ID). In mice with ablated Gdi1, a model of ID, impaired working and associative short-term memory was recorded. This cognitive phenotype worsens if the deletion of αGDI expression is restricted to neurons. However, whether astrocytes, key homeostasis providing neuroglial cells, supporting neurons via aerobic glycolysis, contribute to this cognitive impairment is unclear.

METHODS

We carried out proteomic analysis and monitored [¹⁸F]-fluoro-2-deoxy-d-glucose uptake into brain slices of Gdi1 knockout and wild type control mice. d-Glucose utilization at single astrocyte level was measured by the Förster Resonance Energy Transfer (FRET)-based measurements of cytosolic cyclic AMP, d-glucose and L-lactate, evoked by agonists selective for noradrenaline and L-lactate receptors. To test the role of astrocyte-resident processes in disease phenotype, we generated an inducible Gdi1 knockout mouse carrying the Gdi1 deletion only in adult astrocytes and conducted behavioural tests.

RESULTS

Proteomic analysis revealed significant changes in astrocyte-resident glycolytic enzymes. Imaging [¹⁸F]-fluoro-2-deoxy-d-glucose revealed an increased d-glucose uptake in Gdi1 knockout tissue versus wild type control mice, consistent with the facilitated d-glucose uptake determined by FRET measurements. In mice with Gdi1 deletion restricted to astrocytes, a selective and significant impairment in working memory was recorded, which was rescued by inhibiting glycolysis by 2-deoxy-d-glucose injection.

CONCLUSIONS

These results reveal a new astrocyte-based mechanism in neurodevelopmental disorders and open a novel therapeutic opportunity of targeting aerobic glycolysis, advocating a change in clinical practice.

Noradrenaline-induced l-lactate production requires d-glucose entry and transit through the glycogen shunt in single-cultured rat astrocytes

During cognitive efforts mediated by local neuronal networks, approximately 20% of additional energy is required; this is mediated by chemical messengers such as noradrenaline (NA). NA targets astroglial aerobic glycolysis, the hallmark of which is the end product l-lactate, a fuel for neurons. Biochemical studies have revealed that astrocytes exhibit a prominent glycogen shunt, in which a portion of d-glucose molecules entering the cytoplasm is transiently incorporated into glycogen, a buffer and source of d-glucose during increased energy demand. Here, we studied single astrocytes by measuring cytosolic L-lactate ([lac]_i ) with the FRET nanosensor Laconic. We examined whether NA-induced increase in [lac]_i is influenced by: (a) 2-deoxy-d-glucose (2-DG, 3 mM), a molecule that enters the cytosol and inhibits the glycolytic pathway; (b) 1,4-dideoxy-1,4-imino-d-arabinitol (DAB, 300 µM), a potent inhibitor of glycogen phosphorylase and glycogen degradation; and (c) 3-nitropropionic acid (3-NPA, 1 mM), an inhibitor of the Krebs cycle. The results of these pharmacological experiments revealed that d-glucose uptake is essential for the NA-induced increase in [lac]_i , and that this exclusively arises from glycogen degradation, indicating that most, if not all, d-glucose molecules in NA-stimulated cells transit the glycogen shunt during glycolysis. Moreover, under the defined transmembrane d-glucose gradient, the glycolytic intermediates were not only used to produce l-lactate, but also to significantly support oxidative phosphorylation, as demonstrated by an elevation in [lac]_i when Krebs cycle was inhibited. We conclude that l-lactate production via aerobic glycolysis is an essential energy pathway in NA-stimulated astrocytes; however, oxidative metabolism is important at rest.

Ultrapotent human antibodies protect against SARS-CoV-2 challenge via multiple mechanisms

Efficient therapeutic options are needed to control the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that has caused more than 922,000 fatalities as of 13 September 2020. We report the isolation and characterization of two ultrapotent SARS-CoV-2 human neutralizing antibodies (S2E12 and S2M11) that protect hamsters against SARS-CoV-2 challenge. Cryo-electron microscopy structures show that S2E12 and S2M11 competitively block angiotensin-converting enzyme 2 (ACE2) attachment and that S2M11 also locks the spike in a closed conformation by recognition of a quaternary epitope spanning two adjacent receptor-binding domains. Antibody cocktails that include S2M11, S2E12, or the previously identified S309 antibody broadly neutralize a panel of circulating SARS-CoV-2 isolates and activate effector functions. Our results pave the way to implement antibody cocktails for prophylaxis or therapy, circumventing or limiting the emergence of viral escape mutants.

Single molecule, near full-length genome sequencing of dengue virus

Current methods for dengue virus (DENV) genome amplification, amplify parts of the genome in at least 5 overlapping segments and then combine the output to characterize a full genome. This process is laborious, costly and requires at least 10 primers per serotype, thus increasing the likelihood of PCR bias. We introduce an assay to amplify near full-length dengue virus genomes as intact molecules, sequence these amplicons with third generation “nanopore” technology without fragmenting and use the sequence data to differentiate within-host viral variants with a bioinformatics tool (Nano-Q). The new assay successfully generated near full-length amplicons from DENV serotypes 1, 2 and 3 samples which were sequenced with nanopore technology. Consensus DENV sequences generated by nanopore sequencing had over 99.5% pairwise sequence similarity to Illumina generated counterparts provided the coverage was > 100 with both platforms. Maximum likelihood phylogenetic trees generated from nanopore consensus sequences were able to reproduce the exact trees made from Illumina sequencing with a conservative 99% bootstrapping threshold (after 1000 replicates and 10% burn-in). Pairwise genetic distances of within host variants identified from the Nano-Q tool were less than that of between host variants, thus enabling the phylogenetic segregation of variants from the same host.

Mapping Neutralizing and Immunodominant Sites on the SARS-CoV-2 Spike Receptor-Binding Domain by Structure-Guided High-Resolution Serology

Analysis of the specificity and kinetics of neutralizing antibodies (nAbs) elicited by SARS-CoV-2 infection is crucial for understanding immune protection and identifying targets for vaccine design. In a cohort of 647 SARS-CoV-2-infected subjects, we found that both the magnitude of Ab responses to SARS-CoV-2 spike (S) and nucleoprotein and nAb titers correlate with clinical scores. The receptor-binding domain (RBD) is immunodominant and the target of 90% of the neutralizing activity present in SARS-CoV-2 immune sera. Whereas overall RBD-specific serum IgG titers waned with a half-life of 49 days, nAb titers and avidity increased over time for some individuals, consistent with affinity maturation. We structurally defined an RBD antigenic map and serologically quantified serum Abs specific for distinct RBD epitopes leading to the identification of two major receptor-binding motif antigenic sites. Our results explain the immunodominance of the receptor-binding motif and will guide the design of COVID-19 vaccines and therapeutics.

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SARS-CoV-2 RBD is immunodominant and accounts for 90% of serum neutralizing activity

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RBD antibodies decline with a half-life of ∼50 days, but their avidity increases

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Structural definition of a SARS-CoV-2 RBD antigenic map using monoclonal antibodies

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ACE2-binding site dominates SARS-CoV-2 polyclonal neutralizing antibody responses

Using recombination-dependent lethal mutations to stabilize reporter flaviviruses for rapid serodiagnosis and drug discovery

Background

Many flaviviruses are significant human pathogens that cause global public health threats. Developing research tools for studying and diagnosing these pathogens is a top priority. Reporter flaviviruses are useful tools for studying viral pathogenesis, diagnosing disease, and screening antiviral compounds. However, the stability of reporter flaviviruses has been challenged by viral RNA recombination, leading to deletion of the engineered reporter gene during viral replication. The instability of reporter viruses has limited their application to research and countermeasure development. Thus, new approaches to overcome the instability of reporter flaviviruses are critically needed to advance the flavivirus field.

Methods

To create a stable flavivirus bearing a reporter gene, we engineered mutations in the viral capsid gene that are rendered virus-lethal upon recombination. Thus, only non-recombined reporter virus propagates. We tested this strategy using Zika virus (ZIKV) bearing a nano-luciferase (NanoLuc) gene and passaged both virus with capsid mutations and virus without mutations.

Findings

The recombination-dependent lethal mutations succeeded in stabilizing the NanoLuc ZIKV through ten passages, while WT reporter virus showed instability as early as five passages. The stability of NanoLuc ZIKV was supported by RT-PCR, sequencing, focus forming assay, and luciferase assay. The success of this method was reconfirmed by also establishing a stable NanoLuc Yellow Fever 17D virus, indicating that the recombination-dependent lethal approach can be applied to other flaviviruses. To demonstrate the utility of the stable reporter viruses, we showed that NanoLuc ZIKV and YFV17D could be used to measure neutralizing antibody titers with a turnaround time as short as four hours. Importantly, the neutralizing antibody titers derived from the reporter virus assay were equivalent to those derived from the conventional plaque assay, indicating the new assay maintains the gold standard of serology testing. Furthermore, using a known inhibitor, we showed that the reporter viruses could be reliably used for antiviral evaluation.

Interpretation

The study has developed a recombination-dependent lethal approach to produce stable reporter flaviviruses that may be used for rapid serodiagnosis, trans-gene delivery, vaccine evaluation, and antiviral discovery.

Funding

National Institute of Health, Robert J. Kleberg, Jr. and Helen C. Kleberg Foundation; John S. Dunn Foundation; Amon G. Carter Foundation; Gillson Longenbaugh Foundation; Summerfield G. Roberts Foundation.

Cross-neutralization of SARS-CoV-2 by a human monoclonal SARS-CoV antibody

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a newly emerged coronavirus that is responsible for the current pandemic of coronavirus disease 2019 (COVID-19), which has resulted in more than 3.7 million infections and 260,000 deaths as of 6 May 2020^1,2. Vaccine and therapeutic discovery efforts are paramount to curb the pandemic spread of this zoonotic virus. The SARS-CoV-2 spike (S) glycoprotein promotes entry into host cells and is the main target of neutralizing antibodies. Here we describe several monoclonal antibodies that target the S glycoprotein of SARS-CoV-2, which we identified from memory B cells of an individual who was infected with severe acute respiratory syndrome coronavirus (SARS-CoV) in 2003. One antibody (named S309) potently neutralizes SARS-CoV-2 and SARS-CoV pseudoviruses as well as authentic SARS-CoV-2, by engaging the receptor-binding domain of the S glycoprotein. Using cryo-electron microscopy and binding assays, we show that S309 recognizes an epitope containing a glycan that is conserved within the Sarbecovirus subgenus, without competing with receptor attachment. Antibody cocktails that include S309 in combination with other antibodies that we identified further enhanced SARS-CoV-2 neutralization, and may limit the emergence of neutralization-escape mutants. These results pave the way for using S309 and antibody cocktails containing S309 for prophylaxis in individuals at a high risk of exposure or as a post-exposure therapy to limit or treat severe disease.

Structural and functional analysis of a potent sarbecovirus neutralizing antibody

SARS-CoV-2 is a newly emerged coronavirus responsible for the current COVID-19 pandemic that has resulted in more than one million infections and 73,000 deaths ^1,2 . Vaccine and therapeutic discovery efforts are paramount to curb the pandemic spread of this zoonotic virus. The SARS-CoV-2 spike (S) glycoprotein promotes entry into host cells and is the main target of neutralizing antibodies. Here we describe multiple monoclonal antibodies targeting SARS-CoV-2 S identified from memory B cells of a SARS survivor infected in 2003. One antibody, named S309, potently neutralizes SARS-CoV-2 and SARS-CoV pseudoviruses as well as authentic SARS-CoV-2 by engaging the S receptor-binding domain. Using cryo-electron microscopy and binding assays, we show that S309 recognizes a glycan-containing epitope that is conserved within the sarbecovirus subgenus, without competing with receptor attachment. Antibody cocktails including S309 along with other antibodies identified here further enhanced SARS-CoV-2 neutralization and may limit the emergence of neutralization-escape mutants. These results pave the way for using S309 and S309-containing antibody cocktails for prophylaxis in individuals at high risk of exposure or as a post-exposure therapy to limit or treat severe disease.

Temporal release of a three-component protein subunit vaccine from polymer multilayers

Sustained antigen and adjuvant availability have been shown to improve antiviral immune responses following vaccination. Transcutaneous delivery of vaccines using microneedles has also shown promise and may be particularly relevant for mosquito-borne viruses. We aim to combine these traits to create a three-component Protein Subunit vaccine on Microneedle Arrays (PSMNs) for transcutaneous delivery using layer-by-layer (LbL) assembly. Polymer multilayer thin films were generated to co-deliver a model combination of three chemically distinct vaccine components, a dengue virus Envelope protein Domain III (EDIII) subunit antigen and two adjuvants, a double-stranded RNA (Poly (inosinic:cytidylic acid) (PolyI:C)) and an amphiphilic hexapeptide, Pam3CSK4. Following application of PSMNs to the skin, implanted thin films facilitated sustained and temporal release of individual vaccine components from polymer multilayers. By modulating LbL composition and architecture, component release profiles in the skin could be independently tuned to allow release of adjuvants and antigen from days up to two weeks. Uptake of antigen and adjuvant from implanted vaccine films by antigen-presenting cells was demonstrated using in vivo mouse and ex vivo human skin models. Overall, we believe that such modular vaccine strategies offer design principles for enhancing the immunogenicity of protein subunit vaccines.

Large-Scale HLA Tetramer Tracking of T Cells during Dengue Infection Reveals Broad Acute Activation and Differentiation into Two Memory Cell Fates

T cells play important multifaceted roles during dengue infection, and understanding their responses is important for defining correlates of protective immunity and identifying effective vaccine antigens. Using mass cytometry and a highly multiplexed peptide-HLA (human leukocyte antigen) tetramer staining strategy, we probed T cells from dengue patients-a total of 430 dengue and control candidate epitopes-together with key markers of activation, trafficking, and differentiation. During acute disease, dengue-specific CD8⁺ T cells expressed a distinct profile of activation and trafficking receptors that distinguished them from non-dengue-specific T cells. During convalescence, dengue-specific T cells differentiated into two major cell fates, CD57⁺ CD127^--resembling terminally differentiated senescent memory cells and CD127⁺ CD57^--resembling proliferation-capable memory cells. Validation in an independent cohort showed that these subsets remained at elevated frequencies up to one year after infection. These analyses aid our understanding of the generation of T cell memory in dengue infection or vaccination.

Structure-guided design of immunomodulatory RNAs specifically targeting the cytoplasmic viral RNA sensor RIG-I

The cytoplasmic immune sensor RIG-I detects viral RNA and initiates an antiviral immune response upon activation. It has become a potential target for vaccination and immunotherapies. To develop the smallest but potent immunomodulatory RNA (immRNAs) species, we performed structure-guided RNA design and used biochemical, structural, and cell-based methods to select and characterize the immRNAs. We demonstrated that inserting guanosine at position 9 to the 10mer RNA hairpin (3p10LG9) activates RIG-I more robustly than the parental RNA. 3p10LG9 interacts strongly with the RIG-I helicase-CTD RNA sensing module and disrupts the auto-inhibitory interaction between the HEL2i and CARDs domains. We further showed that 3p10LA9 has a stronger cellular activity than 3p10LG9. Collectively, purine insertion at position 9 of the immRNA species triggered more robust activation of RIG-1.

Altered monocyte response to the dengue virus in those with varying severity of past dengue infection

OBJECTIVE

We sought to investigate the differences in monocyte immune responses to the dengue virus (DENV) in those who previously had either severe disease (past SD) or non-severe dengue (past NSD) following a secondary dengue infection.

METHOD

Monocytes from healthy individuals who had either past SD (n = 6) or past NSD (n = 6) were infected at MOI one with all four DENV serotypes following incubation with autologous serum. 36-hours post infection, levels of inflammatory cytokines and viral loads were measured in the supernatant and expression of genes involved in viral sensing and interferon signaling was determined.

RESULTS

Monocytes of individuals with past SD produced significantly higher viral loads (p = 0.0426 and cytokines (IL-10 p = 0.008, IL-1β p = 0.008 and IL-6 p = 0.0411) when infected with DENV serotypes they were not immune to, compared to those who has past NSD. Monocytes of individuals with past SD also produced significantly higher viral loads (p = 0.022) and cytokines (IL-10 p < 0.0001, IL-1β < 0.0001 and IL-6 p < 0.0001) when infected with DENV serotypes they were previously exposed to, despite the monocytes being infected in the presence of autologous serum. A significant upregulation of NLRP3 (p = 0.005), RIG-I (0.0004) and IFNB-1 (0.01) genes were observed in those who had past SD compared to past NSD when infected with non-immune DENV serotypes.

CONCLUSION

Monocytes from those with past SD appear to show marked differences in viral loads, viral sensing and production of inflammatory mediators in response to the DENV, when compared to those who experienced past NSD, suggesting that initial innate immune responses may influence the disease outcome.

[Freiburg Cardiac Arrest Receiving Team (CART) : Interdisciplinary solution for the acute management of non-traumatic out-of-hospital cardiac arrest]

Standard procedures and guidelines provide specific instructions for basic and advanced cardiac life support. Recommendations for the admission of patients from preclinical into clinical structures after successful cardiopulmonary resuscitation (CPR) are available, but only a few are detailed. In the presence of ST-elevation myocardial infarction after return of spontaneous circulation (ROSC), coronary angiography must be performed as soon as possible. However, acute management and consecutive diagnostic procedures after hospital admission are up to the doctor on duty, who can rely on standard internal hospital procedures at best. Despite the enormous progress and new findings in intensive care and emergency medicine, intra-hospital mortality, as well as long-term survival, after CPR remains low and depends on a wide variety of influencing factors. To optimize in-hospital acute care of successfully resuscitated patients, an interdisciplinary admission team, a so-called cardiac arrest receiving team (CART), has been implemented at the University Hospital of Freiburg, Germany. The aim of the CART is to provide primary care to resuscitated patients as quickly and in as standardized a manner as possible with predefined diagnostic and therapeutic pathways by a team with special expertise in the field of CPR and post-resuscitation management. Accordingly, clear criteria for procedures and the location of primary care (e.g. emergency room vs. cardiac catheter laboratory), the composition of the CART and concrete treatment measures were defined.

A Novel, Five-Marker Alternative to CD16-CD14 Gating to Identify the Three Human Monocyte Subsets

Human primary monocytes are heterogeneous in terms of phenotype and function, but are sub-divided only based on CD16 and CD14 expression. CD16 expression distinguishes a subset of monocytes with highly pro-inflammatory properties from non-CD16 expressing “classical” monocytes. CD14 expression further subdivides the CD16⁺ monocytes into non-classical CD14^low and intermediate CD14^high subsets. This long-standing CD16–CD14 classification system, however, has limitations as CD14 is expressed in a continuum, leading to subjectivity in delineating the non-classical and intermediate subsets; in addition, CD16 expression is unstable, making identification of the subsets impossible after in vitro culture or during inflammatory conditions in vivo. Hence, we aimed to identify the three monocyte subsets using an alternative combination of markers. Additionally, we wanted to address whether the monocyte subset perturbations observed during infection is real or an artifact of differential CD16 and/or CD14 regulation. Using cytometry by time-of-flight (CyTOF), we studied the simultaneous expression of 34 monocyte markers on total monocytes, and derived a combination of five markers (CD33, CD86, CD64, HLA-DR, and CCR2), that could objectively delineate the three subsets. Using these markers, we could also distinguish CD16⁺ monocytes from CD16⁻ monocytes after in vitro stimulation. Finally, we found that the observed expansion of intermediate (CD14^high) monocytes in dengue virus-infected patients was due to up-regulated CD16 expression on classical monocytes. With our new combination of markers, we can now identify monocyte subsets without CD16 and CD14, and accurately re-examine monocyte subset perturbations in diseases.

RIG-I Activation by a Designer Short RNA Ligand Protects Human Immune Cells against Dengue Virus Infection without Causing Cytotoxicity

Virus-derived double-stranded RNA (dsRNA) molecules containing a triphosphate group at the 5' end are natural ligands of retinoic acid-inducible gene I (RIG-I). The cellular pathways and proteins induced by RIG-I are an essential part of the innate immune response against viral infections. Starting from a previously published RNA scaffold (3p10L), we characterized an optimized small dsRNA hairpin (called 3p10LG9, 25 nucleotides [nt] in length) as a highly efficient RIG-I activator. Dengue virus (DENV) infection in cell lines and primary human skin cells could be prevented and restricted through 3p10LG9-mediated activation of RIG-I. This antiviral effect was RIG-I and interferon signal dependent. The effect was temporary and was reversed above a saturating concentration of RIG-I ligand. This finding revealed an effective feedback loop that controls potentially damaging inflammatory effects of the RIG-I response, at least in immune cells. Our results show that the small RIG-I activator 3p10LG9 can confer short-term protection against DENV and can be further explored as an antiviral treatment in humans.IMPORTANCE Short hairpin RNA ligands that activate RIG-I induce antiviral responses in infected cells and prevent or control viral infections. Here, we characterized a new short hairpin RNA molecule with high efficacy in antiviral gene activation and showed that this molecule is able to control dengue virus infection. We demonstrate how structural modifications of minimal RNA ligands can lead to increased potency and a wider window of RIG-I-activating concentrations before regulatory mechanisms kick in at high concentrations. We also show that minimal RNA ligands induce an effective antiviral response in human skin dendritic cells and macrophages, which are the target cells of initial infection after the mosquito releases virus into the skin. Using short hairpin RNA as RIG-I ligands could therefore be explored as antiviral therapy.

Dengue Mosaic Vaccines Enhance Cellular Immunity and Expand the Breadth of Neutralizing Antibody Against All Four Serotypes of Dengue Viruses in Mice

An estimated 400 million people in the world are infected with any of the four types of dengue virus (DENV) annually. The only licensed dengue vaccine cannot effectively prevent infection with all of the four DENVs, especially in those immunologically naïve at baseline. In this study, we explored a mosaic vaccine approach, which utilizes an artificial recombinant sequence for each serotype to achieve maximum coverage of variant epitopes in the four DENVs. We determined the immunogenicity and cross-reactivity of DNA plasmids encoding individual mosaic sequences or the natural sequences in mice. We show that the mosaic vaccines, particularly those targeting DENV serotype 1 and 2, improved vaccine immunogenicity by increasing the percentage of antigen-specific IFNγ- or TNFα-secreting CD4 and CD8 T cells, and titers of neutralizing antibodies. The mosaic vaccine diversified and broadened anti-dengue T cell responses and cross-reactive neutralizing antibodies against all four serotypes. The mosaic vaccines also induced higher level of antigen-specific B cell responses. These results suggest that mosaic vaccines comprising of DENV serotype 1 and 2 variant epitopes could stimulate strong and broad immune responses against all four serotypes.

[Postcardiac arrest treatment guide]

BACKGROUND

Treatment after cardiac arrest has become more complex and interdisciplinary over the last few years. Thus, the clinically active intensive and emergency care physician not only has to carry out the immediate care and acute diagnostics, but also has to prognosticate the neurological outcome.

AIM

The different, most important steps are presented by leading experts in the area, taking into account the interdisciplinarity and the currently valid guidelines.

MATERIALS AND METHODS

Attention was paid to a concise, practice-oriented presentation.

RESULTS AND DISCUSSION

The practical guide contains all important steps from the acute care to the neurological prognosis generation that are relevant for the clinically active intensive care physician.

Studies on B Cells in the Fruit-Eating Black Flying Fox (Pteropus alecto)

The ability of bats to act as reservoir for viruses that are highly pathogenic to humans suggests unique properties and functional characteristics of their immune system. However, the lack of bat specific reagents, in particular antibodies, has limited our knowledge of bat's immunity. Here, we report a panel of cross-reactive antibodies against MHC-II, NK1.1, CD3, CD21, CD27, and immunoglobulin (Ig), that allows flow cytometry analysis of B, T and NK cell populations in two different fruit-eating bat species namely, Pteropus alecto and E. spelaea. Results confirmed predominance of T cells in the spleen and blood of bats, as previously reported by us. However, the percentages of B cells in bone marrow and NK cells in spleen varied greatly between wild caught P. alecto bats and E. spelaea colony bats, which may reflect inherent differences of their immune system or different immune status. Other features of bat B cells were investigated. A significant increase in sIg⁺ B cell population was observed in the spleen and blood from LPS-injected bats but not from poly I:C-injected bats, supporting T-independent polyclonal B cell activation by LPS. Furthermore, using an in vitro calcium release assay, P. alecto B cells exhibited significant calcium release upon cross-linking of their B cell receptor. Together, this work contributes to improve our knowledge of bat adaptive immunity in particular B cells.

Can We Improve Vaccine Efficacy by Targeting T and B Cell Repertoire Convergence?

Traditional vaccine development builds on the assumption that healthy individuals have virtually unlimited antigen recognition repertoires of receptors in B cells and T cells [the B cell receptor (BCR) and TCR respectively]. However, there are indications that there are "holes" in the breadth of repertoire diversity, where no or few B or T cell are able to bind to a given antigen. Repertoire diversity may in these cases be a limiting factor for vaccine efficacy. Assuming that it is possible to predict which B and T cell receptors will respond to a given immunogen, vaccine strategies could be optimized and personalized. In addition, vaccine testing could be simplified if we could predict responses through sequencing BCR and TCRs. Bulk sequencing has shown putatively specific converging sequences after infection or vaccination. However, only single cell technologies have made it possible to capture the sequence of both heavy and light chains of a BCR or the alpha and beta chains the TCR. This has enabled the cloning of receptors and the functional validation of a predicted specificity. This review summarizes recent evidence of converging sequences in infectious diseases. Current and potential future applications of single cell technology in immune repertoire analysis are then discussed. Finally, possible short- and long- term implications for vaccine research are highlighted.

Position Paper on Road Map for RNA Virus Research in India

The Indian subcontinent with its population density, climatic conditions, means of subsistence, socioeconomic factors as well as travel and tourism presents a fertile ground for thriving of RNA viruses. Despite being pathogens of huge significance, there is very little focus on research into the biology and pathogenesis of RNA viruses in India. Studies on epidemiology and disease burden, risk factors, the immune response to RNA viruses, circulating virus strains and virus evolution, animal models of disease, antivirals and vaccines are strikingly absent. Emerging RNA viruses such as Zika virus, Nipah virus and Crimean-Congo haemorrhagic fever virus are a matter of grave concern to India. Here we summarize the outcome of the India|EMBO symposium on “RNA viruses: immunology, pathogenesis and translational opportunities” organized at Faridabad, National Capital Region, India, on March 28–30, 2018. The meeting focused on RNA viruses (non-HIV), and both national and international experts on RNA viruses covered topics ranging from epidemiology, immune response, virus evolution and vaccine trials concerning RNA viruses. The aim of the symposium was to create a road map for RNA virus research in India. Both concrete and tentative ideas pointing towards short-term and long-term goals were presented with recommendations for follow-up at government level.

Stripping off hydrogens in imidazole triggered by the attachment of a single electron

Imidazole [C₃H₄N₂] is ubiquitous in nature as an important biological building block of amino acids, purine nucleobases or antibiotics. In the present study, dissociative electron attachment to imidazole shows low energy shape resonances at 1.52 and 2.29 eV leading to the most abundant dehydrogenated anion [imidazole - H]^- through dehydrogenation at the N1 position. All the other anions formed exhibit core excited resonances observed dominantly at similar electron energies of ∼7 and 11 eV, suggesting an initial formation through two temporary negative ion states. Among these anions, multiple dehydrogenation reactions are observed resulting in the loss of 2 up to 4 hydrogens, thus, leading to a complete dehydrogenation of the imidazole molecule, an interesting prototype of complex unimolecular decay induced by the attachment of a single electron. Additionally, the quantum chemical calculations reveal that these multiple dehydrogenation reactions are responsible for the remarkable one electron-induced gas-phase chemistry leading to the opening of the ring. The formation of the observed anions is likely driven by the high positive electron affinity of cyanocarbon molecules supported by quantum chemical calculations. The formation of H^- showed additional resonance at about 5 eV and dipolar dissociation above ∼14 eV.

Characterization of a candidate tetravalent vaccine based on 2'-O-methyltransferase mutants

Dengue virus (DENV) is one of the most widespread arboviruses. The four DENV serotypes infect about 400 million people every year, causing 96 million clinical dengue cases, of which approximately 500’000 are severe and potentially life-threatening. The only licensed vaccine has a limited efficacy and is only recommended in regions with high endemicity. We previously reported that 2’-O-methyltransferase mutations in DENV-1 and DENV-2 block their capacity to inhibit type I IFNs and render the viruses attenuated in vivo, making them amenable as vaccine strains; here we apply this strategy to all four DENV serotypes to generate a tetravalent, non-chimeric live-attenuated dengue vaccine. 2’-O-methyltransferase mutants of all four serotypes are highly sensitive to type I IFN inhibition in human cells. The tetravalent formulation is attenuated and immunogenic in mice and cynomolgus macaques and elicits a response that protects from virus challenge. These results show the potential of 2’-O-methyltransferase mutant viruses as a safe, tetravalent, non-chimeric dengue vaccine.

Skin dendritic cell and T cell activation associated with dengue shock syndrome

The pathogenesis of severe dengue remains unclear, particularly the mechanisms underlying the plasma leakage that results in hypovolaemic shock in a small proportion of individuals. Maximal leakage occurs several days after peak viraemia implicating immunological pathways. Skin is a highly vascular organ and also an important site of immune reactions with a high density of dendritic cells (DCs), macrophages and T cells. We obtained skin biopsies and contemporaneous blood samples from patients within 24 hours of onset of dengue shock syndrome (DSS), and from healthy controls. We analyzed cell subsets by flow cytometry, and soluble mediators and antibodies by ELISA; the percentage of migratory CD1a⁺ dermal DCs was significantly decreased in the DSS patients, and skin CD8⁺ T cells were activated, but there was no accumulation of dengue-specific antibodies. Inflammatory monocytic cells were not observed infiltrating the skin of DSS cases on whole-mount histology, although CD14^dim cells disappeared from blood.

Deep Sequencing in Infectious Diseases: Immune and Pathogen Repertoires for the Improvement of Patient Outcomes

The inaugural workshop “Deep Sequencing in Infectious Diseases: Immune and Pathogen Repertoires for the Improvement of Patient Outcomes” was held in Singapore on 13–14 October 2016. The aim of the workshop was to discuss the latest trends in using high-throughput sequencing, bioinformatics, and allied technologies to analyze immune and pathogen repertoires and their interplay within the host, bringing together key international players in the field and Singapore-based researchers and clinician-scientists. The focus was in particular on the application of these technologies for the improvement of patient diagnosis, prognosis and treatment, and for other broad public health outcomes. The presentations by scientists and clinicians showed the potential of deep sequencing technology to capture the coevolution of adaptive immunity and pathogens. For clinical applications, some key challenges remain, such as the long turnaround time and relatively high cost of deep sequencing for pathogen identification and characterization and the lack of international standardization in immune repertoire analysis.

Cross-reactive dengue human monoclonal antibody prevents severe pathologies and death from Zika virus infections

Zika virus (ZIKV) infections have been linked with neurological complications and congenital Zika syndrome. Given the high level of homology between ZIKV and the related flavivirus dengue virus (DENV), we investigated the level of cross-reactivity with ZIKV using a panel of DENV human mAbs. A majority of the mAbs showed binding to ZIKV virions, with several exhibiting neutralizing capacities against ZIKV in vitro. Three of the best ZIKV-neutralizing mAbs were found to recognize diverse epitopes on the envelope (E) glycoprotein: the highly conserved fusion-loop peptide, a conformation-specific epitope on the E monomer, and a quaternary epitope on the virion surface. The most potent ZIKV-neutralizing mAb (SIgN-3C) was assessed in 2 type I interferon receptor–deficient (IFNAR^–/–) mouse models of ZIKV infection. Treatment of adult nonpregnant mice with SIgN-3C rescued mice from virus-induced weight loss and mortality. The SIgN-3C variant with Leu-to-Ala mutations in the Fc region (SIgN-3C-LALA) did not induce antibody-dependent enhancement (ADE) in vitro but provided similar levels of protection in vivo. In pregnant ZIKV-infected IFNAR^–/– mice, treatment with SIgN-3C or SIgN-3C-LALA significantly reduced viral load in the fetal organs and placenta and abrogated virus-induced fetal growth retardation. Therefore, SIgN-3C-LALA holds promise as a ZIKV prophylactic and therapeutic agent.

The immunogenetics of narcolepsy associated with A(H1N1)pdm09 vaccination (Pandemrix) supports a potent gene-environment interaction

The influenza A(H1N1)pdm09 vaccination campaign from 2009 to 2010 was associated with a sudden increase in the incidence of narcolepsy in several countries. Narcolepsy with cataplexy is strongly associated with the human leukocyte antigen (HLA) class II DQB1*06:02 allele, and protective associations with the DQB1*06:03 allele have been reported. Several non-HLA gene loci are also associated, such as common variants of the T-cell receptor-α (TRA), the purinergic receptor P2RY11, cathepsin H (CTSH) and TNFSF4/OX40L/CD252. In this retrospective multicenter study, we investigated if these predisposing gene loci were also involved in vaccination-associated narcolepsy. We compared HLA- along with single-nucleotide polymorphism genotypes for non-HLA regions between 42 Pandemrix-vaccinated narcolepsy cases and 1990 population-based controls. The class II gene loci associations supported previous findings. Nominal association (P-value<0.05) with TRA as well as suggestive (P-value<0.1) associations with P2RY11 and CTSH were found. These associations suggest a very strong gene-environment interaction, in which the influenza A(H1N1)pdm09 strain or Pandemrix vaccine can act as potent environmental triggers.

A potent neutralizing antibody with therapeutic potential against all four serotypes of dengue virus

A therapy for dengue is still elusive. We describe the neutralizing and protective capacity of a dengue serotype-cross-reactive antibody isolated from the plasmablasts of a patient. Antibody SIgN-3C neutralized all four dengue virus serotypes at nano to picomolar concentrations and significantly decreased viremia of all serotypes in adult mice when given 2 days after infection. Moreover, mice were protected from pathology and death from a lethal dengue virus-2 infection. To avoid potential Fc-mediated uptake of immune complexes and ensuing enhanced infection, we introduced a LALA mutation in the Fc part. SIgN-3C-LALA was as efficient as the non-modified antibody in neutralizing dengue virus and in protecting mice while antibody-dependent enhancement was completely abrogated. The epitope of the antibody includes conserved amino acids in all three domains of the glycoprotein, which can explain its cross-reactivity. SIgN-3C-LALA neutralizes dengue virus both pre and post-attachment to host cells. These attributes likely contribute to the remarkable protective capacity of SIgN-3C.

Interaction of Pubertal Development and Metabolic Control in Adolescents with Type 1 Diabetes Mellitus

BACKGROUND

In T1DM, delayed pubertal development and reduced final height are associated with inadequate metabolic control.

OBJECTIVE

To assess whether T1DM affects pubertal growth spurt and whether metabolic control during puberty is gender-related.

METHODS

Using a large multicentre database, longitudinal data from 1294 patients were analysed. Inclusion criteria: complete records of height and HbA1c from the age of seven to 16 years. Exclusion criteria: other significant chronic diseases and medications, T1DM duration less than three months, and initial BMI < 3rd or >97th percentile.

RESULTS

Growth velocity (GV) was impaired with a significant reduction of peak GV by 1.2 cm in boys. HbA1c increase during male puberty was lower except for a period of 1.5 years. The highest HbA1c increase in boys coincided with maximum growth spurt. In girls, the highest HbA1c increase was observed during late puberty. Even though there is impaired GV, both sexes reach a height at 16 years of age which corresponds to the background population height.

CONCLUSION

Worsening of metabolic control is sex-discordant and associated with gender-specific alterations of GV. However, the vast majority of boys and girls with T1DM seems to reach normal height at the age of 16 years.

The effect of sazetidine-A and other nicotinic ligands on nicotine controlled goal-tracking in female and male rats

Nicotine is the primary addictive component of tobacco products and its complex stimulus effects are readily discriminated by human and non-human animals. Previous research with rodents directly investigating the nature of the nicotine stimulus has been limited to males. The current study began to address this significant gap in the literature by training female and male rats to discriminate 0.4 mg/kg nicotine from saline in the discriminated goal-tracking task. In this task, access to sucrose was intermittently available on nicotine session. On interspersed saline session, sucrose was not available. Both sexes acquired the discrimination as evidenced by increased head entries into sucrose receptacle (goal-tracking) evoked by nicotine; the nicotine generalization curves were also similar between females and males. The pharmacological profile of the nicotine stimulus was assessed using substitution and targeted combination tests with the following ligands: sazetidine-A, PHA-543613, PNU-120596, bupropion, nornicotine, and cytisine. For females and males, nornicotine fully substituted for the nicotine stimulus, whereas sazetidine-A, bupropion, and cytisine all evoked partial substitution. Female and male rats responded in a similar manner to interaction tests where a combination of 1 mg/kg of sazetidine-A plus nicotine or nornicotine shifted the nicotine dose-effect curve to the left. The combination of sazetidine-A plus bupropion or cytisine failed to do so. These findings begin to fill a significant gap the in scientific literature by studying the nature of the nicotine stimulus and response to therapeutically interesting combinations using a model that includes both sexes.

Severity of Plasma Leakage Is Associated With High Levels of Interferon γ-Inducible Protein 10, Hepatocyte Growth Factor, Matrix Metalloproteinase 2 (MMP-2), and MMP-9 During Dengue Virus Infection

BACKGROUND

 Dengue virus infection typically causes mild dengue fever, but, in severe cases, life-threatening dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) occur. The pathophysiological hallmark of DHF and DSS is plasma leakage that leads to enhanced vascular permeability, likely due to a cytokine storm.

METHODS

 Ninety patients with dengue during 2010-2012 in Singapore were prospectively recruited and stratified according to their disease phase, primary and secondary infection status, and disease severity, measured by plasma leakage. Clinical parameters were recorded throughout the disease progression. The levels of various immune mediators were quantified using comprehensive multiplex microbead-based immunoassays for 46 immune mediators.

RESULTS

 Associations between clinical parameters and immune mediators were analyzed using various statistical methods. Potential immune markers, including interleukin 1 receptor antagonist, interferon γ-inducible protein 10, hepatocyte growth factor, soluble p75 tumor necrosis factor α receptor, vascular cell adhesion molecule 1, and matrix metalloproteinase 2, were significantly associated with significant plasma leakage. Secondary dengue virus infections were also shown to influence disease outcome in terms of disease severity.

CONCLUSIONS

 This study identified several key markers for exacerbated dengue pathogenesis, notably plasma leakage. This will allow a better understanding of the molecular mechanisms of DHF and DSS in patients with dengue.

Plasmablasts During Acute Dengue Infection Represent a Small Subset of a Broader Virus-specific Memory B Cell Pool

Dengue is endemic in tropical countries worldwide and the four dengue virus serotypes often co-circulate. Infection with one serotype results in high titers of cross-reactive antibodies produced by plasmablasts, protecting temporarily against all serotypes, but impairing protective immunity in subsequent infections. To understand the development of these plasmablasts, we analyzed virus-specific B cell properties in patients during acute disease and at convalescence. Plasmablasts were unrelated to classical memory cells expanding in the blood during early recovery. We propose that only a small subset of memory B cells is activated as plasmablasts during repeat infection and that plasmablast responses are not representative of the memory B cell repertoire after dengue infection.

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Antibody sequences and functions were analyzed in longitudinal acute and convalescent samples from dengue patients

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Plasmablast antibodies were virus glycoprotein-specific whereas memory B cell-derived antibodies bound to more viral proteins

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plasmablasts seem to be activated from only a small subset of memory B cells

Antibody-mediated immune memory is orchestrated by various B cell types that are relevant during different phases after an infection. Antibody-secreting cells or so-called plasmablasts are generated from activated specific memory B cell a few days after re-infection. However, little in known whether the antibodies produced by these plasmablasts are relevant for protection in humans and whether the parent memory B cells are further maintained in the memory pool, possibly as affinity-matured versions of the original clones. This is important in the context of vaccination since the repertoires of individual B cell subsets could represent biomarkers to assess efficacy and long-term protection. In addition, the generation of “protective” B cell subsets could potentially be influenced by vaccine design and by the use of adjuvants.

We studied the relationship of plasmablasts and memory B cells in longitudinal blood samples from dengue patients. Dengue virus (DENV) has four serotypes and pre-existing antibodies can be cross-protective or can enhance disease after a heterologous infection via Fc-gamma-receptor-mediated uptake of virus-antibody complexes. B cell memory can therefore be both beneficial and detrimental. Here we studied plasmablasts and DENV-specific memory B cells and their relationship and protective potential by assessing antibody sequences and monoclonal antibodies. We found that both populations produced largely serotype cross-neutralizing antibodies, whereas more plasmablast antibodies were neutralizing. Few plasmablast clones could be found in the memory pool, suggesting that only a subset of memory B cells is activated during acute disease and that a separate repertoire of cells is retained as longer-term memory. In this study we started to dissect the complexity of B cell immune memory to dengue infection and the finding can inform further investigations into which immune cell subsets are disease-enhancing after a heterologous infection.

Low antibody titers 5 years after vaccination with the CYD-TDV dengue vaccine in both pre-immune and naïve vaccinees

Globally, dengue virus (DENV) is one of the most widespread vector-borne viruses. Dengue disease affects populations in endemic areas and, increasingly, tourists who travel to these countries, but there is currently no approved vaccine for dengue. A phase 3 efficacy trial with Sanofi-Pasteur's recombinant, live-attenuated, tetravalent dengue vaccine (CYD-TDV) conducted in South East Asia showed an overall efficacy of 56% against virologically confirmed dengue infections of any severity and any of the 4 serotypes, but the long-term protection of the vaccine has yet to be demonstrated. To address longevity of antibody titers and B cell memory, we recalled study participants from an earlier CYD immunogenicity study (Phase 2) conducted in Singapore that enrolled healthy volunteers in the year 2009. Depending on the age group, 57-84% of the participants initially generated a neutralizing antibody titer ≥ 10 to all 4 DENV serotypes 28 d after the third and final dose. We observed very low antibody titers in blood samples collected from 23 vaccinees 5 y after the first dose, particularly titers of antibodies binding to virus particles compared with those binding to recombinant E protein. The in vivo efficacy of plasma antibodies against DENV-2 challenge was also tested in a mouse model, which found that only 2 out of 23 samples were able to reduce viremia. Although the sample size is too small for general conclusions, dengue immune memory after vaccination with CYD-TDV appears relatively low.