Defining the antibody cross-reactome directed against the influenza virus surface glycoproteins.

Infection with influenza virus induces antibodies to the viral surface glycoproteins hemagglutinin and neuraminidase, and these responses can be broadly protective. To assess the breadth and magnitude of antibody responses, we sequentially infected mice, guinea pigs and ferrets with divergent H1N1 or H3N2 subtypes of influenza virus. We measured antibody responses by ELISA of an extensive panel of recombinant glycoproteins representing the viral diversity in nature. Guinea pigs developed high titers of broadly cross-reactive antibodies; mice and ferrets exhibited narrower humoral responses. Then, we compared antibody responses after infection of humans with influenza virus H1N1 or H3N2 and found markedly broad responses and cogent evidence for 'original antigenic sin'. This work will inform the design of universal vaccines against influenza virus and can guide pandemic-preparedness efforts directed against emerging influenza viruses.

Polyreactive Broadly Neutralizing B cells Are Selected to Provide Defense against Pandemic Threat Influenza Viruses.

Polyreactivity is the ability of a single antibody to bind to multiple molecularly distinct antigens and is a common feature of antibodies induced upon pathogen exposure. However, little is known about the role of polyreactivity during anti-influenza virus antibody responses. By analyzing more than 500 monoclonal antibodies (mAbs) derived from B cells induced by numerous influenza virus vaccines and infections, we found mAbs targeting conserved neutralizing influenza virus hemagglutinin epitopes were polyreactive. Polyreactive mAbs were preferentially induced by novel viral exposures due to their broad viral binding breadth. Polyreactivity augmented mAb viral binding strength by increasing antibody flexibility, allowing for adaption to imperfectly conserved epitopes. Lastly, we found affinity-matured polyreactive B cells were typically derived from germline polyreactive B cells that were preferentially selected to participate in B cell responses over time. Together, our data reveal that polyreactivity is a beneficial feature of antibodies targeting conserved epitopes.

A Single Immunization with Nucleoside-Modified mRNA Vaccines Elicits Strong Cellular and Humoral Immune Responses against SARS-CoV-2 in Mice.

SARS-CoV-2 infection has emerged as a serious global pandemic. Because of the high transmissibility of the virus and the high rate of morbidity and mortality associated with COVID-19, developing effective and safe vaccines is a top research priority. Here, we provide a detailed evaluation of the immunogenicity of lipid nanoparticle-encapsulated, nucleoside-modified mRNA (mRNA-LNP) vaccines encoding the full-length SARS-CoV-2 spike protein or the spike receptor binding domain in mice. We demonstrate that a single dose of these vaccines induces strong type 1 CD4+ and CD8+ T cell responses, as well as long-lived plasma and memory B cell responses. Additionally, we detect robust and sustained neutralizing antibody responses and the antibodies elicited by nucleoside-modified mRNA vaccines do not show antibody-dependent enhancement of infection in vitro. Our findings suggest that the nucleoside-modified mRNA-LNP vaccine platform can induce robust immune responses and is a promising candidate to combat COVID-19.

SARS-CoV-2 Omicron boosting induces de novo B cell response in humans.

The primary two-dose SARS-CoV-2 mRNA vaccine series are strongly immunogenic in humans, but the emergence of highly infectious variants necessitated additional doses and the development of vaccines aimed at the new variants1-4. SARS-CoV-2 booster immunizations in humans primarily recruit pre-existing memory B cells5-9. However, it remains unclear whether the additional doses induce germinal centre reactions whereby re-engaged B cells can further mature, and whether variant-derived vaccines can elicit responses to variant-specific epitopes. Here we show that boosting with an mRNA vaccine against the original monovalent SARS-CoV-2 mRNA vaccine or the bivalent B.1.351 and B.1.617.2 (Beta/Delta) mRNA vaccine induced robust spike-specific germinal centre B cell responses in humans. The germinal centre response persisted for at least eight weeks, leading to significantly more mutated antigen-specific bone marrow plasma cell and memory B cell compartments. Spike-binding monoclonal antibodies derived from memory B cells isolated from individuals boosted with either the original SARS-CoV-2 spike protein, bivalent Beta/Delta vaccine or a monovalent Omicron BA.1-based vaccine predominantly recognized the original SARS-CoV-2 spike protein. Nonetheless, using a more targeted sorting approach, we isolated monoclonal antibodies that recognized the BA.1 spike protein but not the original SARS-CoV-2 spike protein from individuals who received the mRNA-1273.529 booster; these antibodies were less mutated and recognized novel epitopes within the spike protein, suggesting that they originated from naive B cells. Thus, SARS-CoV-2 booster immunizations in humans induce robust germinal centre B cell responses and can generate de novo B cell responses targeting variant-specific epitopes.

Broadly neutralizing antibodies target a haemagglutinin anchor epitope.

Broadly neutralizing antibodies that target epitopes of haemagglutinin on the influenza virus have the potential to provide near universal protection against influenza virus infection1. However, viral mutants that escape broadly neutralizing antibodies have been reported2,3. The identification of broadly neutralizing antibody classes that can neutralize viral escape mutants is critical for universal influenza virus vaccine design. Here we report a distinct class of broadly neutralizing antibodies that target a discrete membrane-proximal anchor epitope of the haemagglutinin stalk domain. Anchor epitope-targeting antibodies are broadly neutralizing across H1 viruses and can cross-react with H2 and H5 viruses that are a pandemic threat. Antibodies that target this anchor epitope utilize a highly restricted repertoire, which encodes two public binding motifs that make extensive contacts with conserved residues in the fusion peptide. Moreover, anchor epitope-targeting B cells are common in the human memory B cell repertoire and were recalled in humans by an oil-in-water adjuvanted chimeric haemagglutinin vaccine4,5, which is a potential universal influenza virus vaccine. To maximize protection against seasonal and pandemic influenza viruses, vaccines should aim to boost this previously untapped source of broadly neutralizing antibodies that are widespread in the human memory B cell pool.

Safety and Immunogenicity of mRNA-1010, an Investigational Seasonal Influenza Vaccine, in Healthy Adults: Final Results From a Phase 1/2 Randomized Trial.

BACKGROUND: Seasonal influenza remains a global public health concern. A messenger RNA (mRNA)-based quadrivalent seasonal influenza vaccine, mRNA-1010, was investigated in a 3-part, first-in-human, phase 1/2 clinical trial. METHODS: In Parts 1-3 of this stratified, observer-blind study, adults aged ≥18 years old were randomly assigned to receive a single dose (6.25 µg to 200 µg) of mRNA-1010 or placebo (Part 1) or an active comparator (Afluria; Parts 2-3). Primary study objectives were assessment of safety, reactogenicity, and humoral immunogenicity of mRNA-1010, placebo (Part 1), or active comparator (Parts 2-3). Exploratory endpoints included assessment of cellular immunogenicity (Part 1) and antigenic breadth against vaccine heterologous (A/H3N2) strains (Parts 1-2). RESULTS: In all study parts, solicited adverse reactions were reported more frequently for mRNA-1010 than placebo or Afluria and most were grade 1 or 2 in severity. No vaccine-related serious adverse events or deaths were reported. In Parts 1-2, a single dose of mRNA-1010 (25 µg to 200 µg) elicited robust Day 29 hemagglutination inhibition (HAI) titers that persisted through 6 months. In Part 3, lower doses of mRNA-1010 (6.25 µg to 25 µg) elicited Day 29 HAI titers that were higher or comparable to Afluria for influenza A strains. Compared with Afluria, mRNA-1010 (50 µg) elicited broader A/H3N2 antibody responses (Part 2). mRNA-1010 induced greater T-cell responses than placebo at Day 8 that were sustained or stronger at Day 29 (Part 1). CONCLUSIONS: Data support the continued development of mRNA-1010 as a seasonal influenza vaccine. CLINICALTRIALS.GOV IDENTIFIER: NCT04956575 (https://clinicaltrials.gov/study/NCT04956575).

Influenza hemagglutinin-specific IgA Fc-effector functionality is restricted to stalk epitopes.

In this study, we utilized a panel of human immunoglobulin (Ig) IgA monoclonal antibodies isolated from the plasmablasts of eight donors after 2014/2015 influenza virus vaccination (Fluarix) to study the binding and functional specificities of this isotype. In this cohort, isolated IgA monoclonal antibodies were primarily elicited against the hemagglutinin protein of the H1N1 component of the vaccine. To compare effector functionalities, an H1-specific subset of antibodies targeting distinct epitopes were expressed as monomeric, dimeric, or secretory IgA, as well as in an IgG1 backbone. When expressed with an IgG Fc domain, all antibodies elicited Fc-effector activity in a primary polymorphonuclear cell-based assay which differs from previous observations that found only stalk-specific antibodies activate the low-affinity FcγRIIIa. However, when expressed with IgA Fc domains, only antibodies targeting the stalk domain showed Fc-effector activity in line with these previous findings. To identify the cause of this discrepancy, we then confirmed that IgG signaling through the high-affinity FcγI receptor was not restricted to stalk epitopes. Since no corresponding high-affinity Fcα receptor exists, the IgA repertoire may therefore be limited to stalk-specific epitopes in the context of Fc receptor signaling.

A single-shot adenoviral vaccine provides hemagglutinin stalk-mediated protection against heterosubtypic influenza challenge in mice.

Conventional influenza vaccines fail to confer broad protection against diverse influenza A viruses with pandemic potential. Efforts to develop a universal influenza virus vaccine include refocusing immunity towards the highly conserved stalk domain of the influenza virus surface glycoprotein, hemagglutinin (HA). We constructed a non-replicating adenoviral (Ad) vector, encoding a secreted form of H1 HA, to evaluate HA stalk-focused immunity. The Ad5_H1 vaccine was tested in mice for its ability to elicit broad, cross-reactive protection against homologous, heterologous, and heterosubtypic lethal challenge in a single-shot immunization regimen. Ad5_H1 elicited hemagglutination inhibition (HI+) active antibodies (Abs), which conferred 100% sterilizing protection from homologous H1N1 challenge. Furthermore, Ad5_H1 rapidly induced H1-stalk-specific Abs with Fc-mediated effector function activity, in addition to stimulating both CD4+ and CD8+ stalk-specific T cell responses. This phenotype of immunity provided 100% protection from lethal challenge with a head-mismatched, reassortant influenza virus bearing a chimeric HA, cH6/1, in a stalk-mediated manner. Most importantly, 100% protection from mortality following lethal challenge with a heterosubtypic avian influenza virus, H5N1, was observed following a single immunization with Ad5_H1. In conclusion, Ad-based influenza vaccines can elicit significant breadth of protection in naive animals and could be considered for pandemic preparedness and stockpiling.

Adjuvanted H5N1 influenza vaccine enhances both cross-reactive memory B cell and strain-specific naive B cell responses in humans.

There is a need for improved influenza vaccines. In this study we compared the antibody responses in humans after vaccination with an AS03-adjuvanted versus nonadjuvanted H5N1 avian influenza virus inactivated vaccine. Healthy young adults received two doses of either formulation 3 wk apart. We found that AS03 significantly enhanced H5 hemagglutinin (HA)-specific plasmablast and antibody responses compared to the nonadjuvanted vaccine. Plasmablast response after the first immunization was exclusively directed to the conserved HA stem region and came from memory B cells. Monoclonal antibodies (mAbs) derived from these plasmablasts had high levels of somatic hypermutation (SHM) and recognized the HA stem region of multiple influenza virus subtypes. Second immunization induced a plasmablast response to the highly variable HA head region. mAbs derived from these plasmablasts exhibited minimal SHM (naive B cell origin) and largely recognized the HA head region of the immunizing H5N1 strain. Interestingly, the antibody response to H5 HA stem region was much lower after the second immunization, and this suppression was most likely due to blocking of these epitopes by stem-specific antibodies induced by the first immunization. Taken together, these findings show that an adjuvanted influenza vaccine can substantially increase antibody responses in humans by effectively recruiting preexisting memory B cells as well as naive B cells into the response. In addition, we show that high levels of preexisting antibody can have a negative effect on boosting. These findings have implications toward the development of a universal influenza vaccine.

Is a Universal Influenza Virus Vaccine Possible?

Influenza viruses remain a severe burden to human health because of their contribution to overall morbidity and mortality. Current seasonal influenza virus vaccines do not provide sufficient protection to alleviate the annual impact of influenza and cannot confer protection against potentially pandemic influenza viruses. The lack of protection is due to rapid changes of the viral epitopes targeted by the vaccine and the often suboptimal immunogenicity of current immunization strategies. Major efforts to improve vaccination approaches are under way. The development of a universal influenza virus vaccine may be possible by combining the lessons learned from redirecting the immune response toward conserved viral epitopes, as well as the use of adjuvants and novel vaccination platforms.

Enhancing Neuraminidase Immunogenicity of Influenza A Viruses by Rewiring RNA Packaging Signals.

Humoral immune protection against influenza virus infection is mediated largely by antibodies against hemagglutinin (HA) and neuraminidase (NA), the two major glycoproteins on the virus surface. While influenza virus vaccination efforts have focused mainly on HA, NA-based immunity has been shown to reduce disease severity and provide heterologous protection. Current seasonal vaccines do not elicit strong anti-NA responses-in part due to the immunodominance of the HA protein. Here, we demonstrate that by swapping the 5' and 3' terminal packaging signals of the HA and NA genomic segments, which contain the RNA promoters, we are able to rescue influenza viruses that express more NA and less HA. Vaccination with formalin-inactivated "rewired" viruses significantly enhances the anti-NA antibody response compared to vaccination with unmodified viruses. Passive transfer of sera from mice immunized with rewired virus vaccines shows better protection against influenza virus challenge. Our results provide evidence that the immunodominance of HA stems in part from its abundance on the viral surface, and that rewiring viral packaging signals-thereby increasing the NA content on viral particles-is a viable strategy for improving the immunogenicity of NA in an influenza virus vaccine.IMPORTANCE Influenza virus infections are a major source of morbidity and mortality worldwide. Increasing evidence highlights neuraminidase as a potential vaccination target. This report demonstrates the efficacy of rewiring influenza virus packaging signals for creating vaccines with more neuraminidase content which provide better neuraminidase (NA)-based protection.

A Multi-Targeting, Nucleoside-Modified mRNA Influenza Virus Vaccine Provides Broad Protection in Mice.

Influenza viruses are respiratory pathogens of public health concern worldwide with up to 650,000 deaths occurring each year. Seasonal influenza virus vaccines are employed to prevent disease, but with limited effectiveness. Development of a universal influenza virus vaccine with the potential to elicit long-lasting, broadly cross-reactive immune responses is necessary for reducing influenza virus prevalence. In this study, we have utilized lipid nanoparticle-encapsulated, nucleoside-modified mRNA vaccines to intradermally deliver a combination of conserved influenza virus antigens (hemagglutinin stalk, neuraminidase, matrix-2 ion channel, and nucleoprotein) and induce strong immune responses with substantial breadth and potency in a murine model. The immunity conferred by nucleoside-modified mRNA-lipid nanoparticle vaccines provided protection from challenge with pandemic H1N1 virus at 500 times the median lethal dose after administration of a single immunization, and the combination vaccine protected from morbidity at a dose of 50 ng per antigen. The broad protective potential of a single dose of combination vaccine was confirmed by challenge with a panel of group 1 influenza A viruses. These findings support the advancement of nucleoside-modified mRNA-lipid nanoparticle vaccines expressing multiple conserved antigens as universal influenza virus vaccine candidates.

Hemagglutinin Stalk Antibody Responses Following Trivalent Inactivated Influenza Vaccine Immunization of Pregnant Women and Association With Protection From Influenza Virus Illness.

BACKGROUND: The conserved, immuno-subdominant influenza virus hemagglutinin (HA) stalk region is a potential universal group-specific influenza virus vaccine epitope. We analyzed antibody responses to H1 hemagglutinin stalk domain (H1/stalk) following trivalent influenza inactivated vaccine (IIV3) immunization in pregnant women, and association with protection against influenza virus illness. METHODS: One hundred forty-five human immunodeficiency virus (HIV)-uninfected pregnant women (68 IIV3 and 77 placebo recipients) and 140 pregnant women with HIV infection (72 IIV3 and 68 placebo recipients) were independently randomized in placebo-controlled efficacy trials of IIV3. Plasma samples were tested for H1/stalk immunoglobulin G (IgG) and hemagglutination inhibition (HAI) antibodies prevaccination and 1 month postvaccination. Women had weekly surveillance for influenza illness, confirmed by polymerase chain reaction. RESULTS: Increases in H1/stalk IgG (and HAI) antibody levels were elicited post-IIV3, with responses being higher in HIV-uninfected women than in women living with HIV. Among HIV-uninfected vaccinees, there was no correlation (postvaccination) between H1/stalk and HAI antibody responses, whereas a strong correlation was observed in vaccinees with HIV. The H1/stalk IgG concentration was lower among women developing A/H1N1 illness (85.3 arbitrary units [AU]/mL) than those without A/H1N1 illness (219.6 AU/mL; P = .001). H1/stalk IgG concentration ≥215 AU/mL was associated with 90% lower odds (odds ratio, 0.09; P = .005) of A/H1N1 illness. Also, H1/stalk IgG was significantly lower among women with influenza B illness (93.9 AU/mL) than among their counterparts (215.5 AU/mL) (P = .04); however, no association was observed after adjusting for HAI titers. CONCLUSIONS: H1/stalk IgG concentration was associated with lower odds for A/H1N1 influenza virus illness, indicating its potential as an epitope for a universal vaccine against group 1 influenza virus.

Pre-existing Antineuraminidase Antibodies Are Associated With Shortened Duration of Influenza A(H1N1)pdm Virus Shedding and Illness in Naturally Infected Adults.

BACKGROUND: Influenza causes a substantial burden worldwide, and current seasonal influenza vaccine has suboptimal effectiveness. To develop better, more broadly protective vaccines, a more thorough understanding is needed of how antibodies that target the influenza virus surface antigens, hemagglutinin (HA) (including head and stalk regions) and neuraminidase (NA), impact influenza illness and virus transmission. METHODS: We used a case-ascertained, community-based study of household influenza virus transmission set in Managua, Nicaragua. Using data from 170 reverse transcriptase-polymerase chain reaction (RT-PCR)-confirmed influenza virus A(H1N1)pdm infections and 45 household members with serologically confirmed infection, we examined the association of pre-existing NA, hemagglutination inhibiting, and HA stalk antibody levels and influenza viral shedding and disease duration using accelerated failure time models. RESULTS: Among RT-PCR-confirmed infections in adults, pre-existing anti-NA antibody levels ≥40 were associated with a 69% (95% confidence interval [CI], 34-85%) shortened shedding duration (mean, 1.0 vs 3.2 days). Neuraminidase antibody levels ≥80 were associated with further shortened shedding and significantly shortened symptom duration (influenza-like illness, 82%; 95% CI, 39-95%). Among RT-PCR-confirmed infections in children, hemagglutination inhibition titers ≥1:20 were associated with a 32% (95% CI, 13-47%) shortened shedding duration (mean, 3.9 vs 6.0 days). CONCLUSIONS: Our results suggest that anti-NA antibodies play a large role in reducing influenza illness duration in adults and may impact transmission, most clearly among adults. Neuraminidase should be considered as an additional target in next-generation influenza virus vaccine development.We found that antibodies against neuraminidase were associated with significantly shortened viral shedding, and among adults they were also associated with shortened symptom duration. These results support neuraminidase as a potential target of next-generation influenza virus vaccines.

Development of Influenza B Universal Vaccine Candidates Using the "Mosaic" Hemagglutinin Approach.

Influenza B viruses cause seasonal epidemics and are a considerable burden to public health. However, protection by current seasonal vaccines is suboptimal due to the antigenic changes of the circulating strains. In this study, we report a novel universal influenza B virus vaccination strategy based on "mosaic" hemagglutinins. We generated mosaic B hemagglutinins by replacing the major antigenic sites of the type B hemagglutinin with corresponding sequences from exotic influenza A hemagglutinins and expressed them as soluble trimeric proteins. Sequential vaccination with recombinant mosaic B hemagglutinin proteins conferred cross-protection against both homologous and heterologous influenza B virus strains in the mouse model. Of note, we rescued recombinant influenza B viruses expressing mosaic B hemagglutinins, which could serve as the basis for a universal influenza B virus vaccine.IMPORTANCE This work reports a universal influenza B virus vaccination strategy based on focusing antibody responses to conserved head and stalk epitopes of the hemagglutinin. Recombinant mosaic influenza B hemagglutinin proteins and recombinant viruses have been generated as novel vaccine candidates. This vaccine strategy provided broad cross-protection in the mouse model. Our findings will inform and drive development toward a more effective influenza B virus vaccine.

Synthetic Rhamnose Glycopolymer Cell-Surface Receptor for Endogenous Antibody Recruitment.

Synthetic materials capable of engineering the immune system are of great relevance in the fight against cancer to replace or complement the current monoclonal antibody and cell therapy-based immunotherapeutics. Here, we report on antibody recruiting glycopolymers (ARGPs). ARGPs consist of polymeric copies of a rhamnose motif, which can bind endogenous antirhamnose antibodies present in human serum. As a proof-of-concept, we have designed ARGPs with a lipophilic end group that efficiently inserts into cell-surface membranes. We validate the specificity of rhamnose to attract antibodies from human serum to the target cell surface and demonstrate that ARGPs outperform an analogous small-molecule compound containing only one single rhamnose motif. The ARGP concept opens new avenues for the design of potent immunotherapeutics that mark target cells for destruction by the immune system through antibody-mediated effector functions.

Broadly Reactive Human Monoclonal Antibodies Elicited following Pandemic H1N1 Influenza Virus Exposure Protect Mice against Highly Pathogenic H5N1 Challenge.

Broadly cross-reactive antibodies (Abs) that recognize conserved epitopes within the influenza virus hemagglutinin (HA) stalk domain are of particular interest for their potential use as therapeutic and prophylactic agents against multiple influenza virus subtypes, including zoonotic virus strains. Here, we characterized four human HA stalk-reactive monoclonal antibodies (MAbs) for their binding breadth and affinity, in vitro neutralization capacity, and in vivo protective potential against an highly pathogenic avian influenza virus. The monoclonal antibodies were isolated from individuals shortly following infection with (70-1F02 and 1009-3B05) or vaccination against (05-2G02 and 09-3A01) A(H1N1)pdm09. Three of the MAbs bound HAs from multiple strains of group 1 viruses, and one MAb, 05-2G02, bound to both group 1 and group 2 influenza A virus HAs. All four antibodies prophylactically protected mice against a lethal challenge with the highly pathogenic A/Vietnam/1203/04 (H5N1) strain. Two MAbs, 70-1F02 and 09-3A01, were further tested for their therapeutic efficacy against the same strain and showed good efficacy in this setting as well. One MAb, 70-1F02, cocrystallized with H5 HA and showed heavy-chain-only interactions similar to those seen with the previously described CR6261 anti-stalk antibody. Finally, we show that antibodies that compete with these MAbs are prevalent in serum from an individual recently infected with the A(H1N1)pdm09 virus. The antibodies described here can be developed into broad-spectrum antiviral therapeutics that could be used to combat infections by zoonotic or emerging pandemic influenza viruses.IMPORTANCE The rise in zoonotic infections of humans by emerging influenza viruses is a worldwide public health concern. The majority of recent zoonotic human influenza cases were caused by H7N9 and H5Nx viruses and were associated with high morbidity and mortality. In addition, seasonal influenza viruses are estimated to cause up to 650,000 deaths annually worldwide. Currently available antiviral treatment options include only neuraminidase inhibitors, but some influenza viruses are naturally resistant to these drugs, and others quickly develop resistance-conferring mutations. Alternative therapeutics are urgently needed. Broadly protective antibodies that target the conserved "stalk" domain of the hemagglutinin represent potential potent antiviral prophylactic and therapeutic agents that can assist pandemic preparedness. Here, we describe four human monoclonal antibodies that target conserved regions of influenza HA and characterize their binding spectrum as well as their protective capacity in prophylactic and therapeutic settings against a lethal challenge with a zoonotic influenza virus.

Progesterone-Based Contraceptives Reduce Adaptive Immune Responses and Protection against Sequential Influenza A Virus Infections.

In addition to their intended use, progesterone (P4)-based contraceptives promote anti-inflammatory immune responses, yet their effects on the outcome of infectious diseases, including influenza A virus (IAV) infection, are rarely evaluated. To evaluate their impact on immune responses to sequential IAV infections, adult female mice were treated with placebo or one of two progestins, P4 or levonorgestrel (LNG), and infected with a mouse-adapted H1N1 (maH1N1) virus. Treatment with P4 or LNG reduced morbidity but had no effect on pulmonary virus titers during primary H1N1 infection compared to placebo treatment. In serum and bronchoalveolar lavage fluid, total anti-IAV IgG and IgA titers and virus-neutralizing antibody titers but not hemagglutinin stalk antibody titers were lower in progestin-treated mice than placebo-treated mice. Females were challenged 6 weeks later with either an maH1N1 drift variant (maH1N1dv) or maH3N2 IAV. The level of protection following infection with the maH1N1dv was similar among all groups. In contrast, following challenge with maH3N2, progestin treatment reduced survival as well as the numbers and activity of H1N1- and H3N2-specific memory CD8+ T cells, including tissue-resident cells, compared with placebo treatment. In contrast to primary IAV infection, progestin treatment increased the titers of neutralizing and IgG antibodies against both challenge viruses compared with those achieved with placebo treatment. While the immunomodulatory properties of progestins protected immunologically naive female mice from the severe outcomes from IAV infection, it made them more susceptible to secondary challenge with a heterologous IAV, despite improving their antibody responses against a secondary IAV infection. Taken together, the immunomodulatory effects of progestins differentially regulate the outcome of infection depending on exposure history.IMPORTANCE The impact of hormone-based contraceptives on the outcome of infectious diseases outside the reproductive tract is rarely considered. Using a mouse model, we have made the novel observation that treatment with either progesterone or a synthetic analog found in hormonal contraceptives, levonorgestrel, impacts sequential influenza A virus infection by modulating antibody responses and decreasing the numbers and activity of memory CD8+ T cells. Progestins reduced the antibody responses during primary H1N1 virus infection but increased antibody titers following a sequential infection with either an H1N1 drift variant or an H3N2 virus. Following challenge with an H3N2 virus, female mice treated with progestins experienced greater mortality with increased pulmonary inflammation and reduced numbers and activity of CD8+ T cells. This study suggests that progestins significantly affect adaptive immune responses to influenza A virus infection, with their effect on the outcome of infection depending on exposure history.

Cross-Reactive and Cross-Neutralizing Activity of Human Mumps Antibodies Against a Novel Mumps Virus From Bats.

To evaluate the antigenic relationship between bat mumps virus (BMV) and the JL5 vaccine strain of mumps virus (MuVJL5), we rescued a chimeric virus bearing the F and HN glycoproteins of BMV in the background of a recombinant JL5 genome (rMuVJL5). Cross-reactivity and cross-neutralization between this chimeric recombinant MuV bearing the F and HN glycoproteins of BMV (rMuVJL5-F/HNBMV) virus and rMuVJL5 were demonstrated using hyperimmune mouse serum samples and a curated panel of human serum. All mouse and human serum samples that were able to neutralize rMuVJL5 infection had cross-neutralizing activity against rMuVJL5-F/HNBMV. Our data suggest that persons who have neutralizing antibodies against MuV might be protected from infection by BMV.

Induction of Broadly Cross-Reactive Stalk-Specific Antibody Responses to Influenza Group 1 and Group 2 Hemagglutinins by Natural H7N9 Virus Infection in Humans.

Background: The outbreak of novel avian H7N9 influenza virus infections in China in 2013 has demonstrated the continuing threat posed by zoonotic pathogens. Deciphering the immune response during natural infection will guide future vaccine development. Methods: We assessed the induction of heterosubtypic cross-reactive antibodies induced by H7N9 infection against a large panel of recombinant hemagglutinins and neuraminidases by quantitative enzyme-linked immunosorbent assay, and novel chimeric hemagglutinin constructs were used to dissect the anti-stalk or -head humoral immune response. Results: H7N9 infection induced strong antibody responses against divergent H7 hemagglutinins. Interestingly, we also found induction of antibodies against heterosubtypic hemagglutinins from both group 1 and group 2 and a boost in heterosubtypic neutralizing activity in the absence of hemagglutination inhibitory activity. Kinetic monitoring revealed that heterosubtypic binding/neutralizing antibody responses typically appeared and peaked earlier than intrasubtypic responses, likely mediated by memory recall responses. Conclusions: Our results indicate that cross-group binding and neutralizing antibody responses primarily targeting the stalk region can be elicited after natural influenza virus infection. These data support our understanding of the breadth of the postinfection immune response that could inform the design of future, broadly protective influenza virus vaccines.