Acute and persistent responses after H5N1 vaccination in humans.

To gain insight into how an adjuvant impacts vaccination responses, we use systems immunology to study human H5N1 influenza vaccination with or without the adjuvant AS03, longitudinally assessing 14 time points including multiple time points within the first day after prime and boost. We develop an unsupervised computational framework to discover high-dimensional response patterns, which uncover adjuvant- and immunogenicity-associated early response dynamics, including some that differ post prime versus boost. With or without adjuvant, some vaccine-induced transcriptional patterns persist to at least 100 days after initial vaccination. Single-cell profiling of surface proteins, transcriptomes, and chromatin accessibility implicates transcription factors in the erythroblast-transformation-specific (ETS) family as shaping these long-lasting signatures, primarily in classical monocytes but also in CD8+ naive-like T cells. These cell-type-specific signatures are elevated at baseline in high-antibody responders in an independent vaccination cohort, suggesting that antigen-agnostic baseline immune states can be modulated by vaccine antigens alone to enhance future responses.

Licensed H5N1 vaccines generate cross-neutralizing antibodies against highly pathogenic H5N1 clade 2.3.4.4b influenza virus.

The emergence of highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b viruses and their transmission to dairy cattle and animals, including humans, poses a major global public health threat. Therefore, the development of effective vaccines and therapeutics against H5N1 clade 2.3.4.4b virus is considered a public health priority. In the United States, three H5N1 vaccines derived from earlier strains of HPAI H5N1 (A/Vietnam, clade 1, and A/Indonesia, clade 2.1) virus, with (MF59 or AS03) or without adjuvants, are licensed and stockpiled for pre-pandemic preparedness, but whether they can elicit neutralizing antibodies against circulating H5N1 clade 2.3.4.4b viruses is unknown. In this study, we evaluated the binding, hemagglutination inhibition and neutralizing antibody response generated after vaccination of adults with the three licensed vaccines. Individuals vaccinated with the two adjuvanted licensed H5N1 vaccines generated cross-reactive binding and cross-neutralizing antibodies against the HPAI clade 2.3.4.4b A/Astrakhan/3212/2020 virus. Seroconversion rates of 60-95% against H5 clade 2.3.4.4b were observed after two doses of AS03-adjuvanted-A/Indonesia or three doses of MF59-adjuvanted-A/Vietnam vaccine. These findings suggest that the stockpiled US-licensed adjuvanted H5N1 vaccines generate cross-neutralizing antibodies against circulating HPAI H5N1 clade 2.3.4.4b in humans and may be useful as bridging vaccines until updated H5N1 vaccines become available.

Influenza vaccination reveals sex dimorphic imprints of prior mild COVID-19.

Acute viral infections can have durable functional impacts on the immune system long after recovery, but how they affect homeostatic immune states and responses to future perturbations remain poorly understood1-4. Here we use systems immunology approaches, including longitudinal multimodal single-cell analysis (surface proteins, transcriptome and V(D)J sequences) to comparatively assess baseline immune statuses and responses to influenza vaccination in 33 healthy individuals after recovery from mild, non-hospitalized COVID-19 (mean, 151 days after diagnosis) and 40 age- and sex-matched control individuals who had never had COVID-19. At the baseline and independent of time after COVID-19, recoverees had elevated T cell activation signatures and lower expression of innate immune genes including Toll-like receptors in monocytes. Male individuals who had recovered from COVID-19 had coordinately higher innate, influenza-specific plasmablast, and antibody responses after vaccination compared with healthy male individuals and female individuals who had recovered from COVID-19, in part because male recoverees had monocytes with higher IL-15 responses early after vaccination coupled with elevated prevaccination frequencies of 'virtual memory'-like CD8+ T cells poised to produce more IFNγ after IL-15 stimulation. Moreover, the expression of the repressed innate immune genes in monocytes increased by day 1 to day 28 after vaccination in recoverees, therefore moving towards the prevaccination baseline of the healthy control individuals. By contrast, these genes decreased on day 1 and returned to the baseline by day 28 in the control individuals. Our study reveals sex-dimorphic effects of previous mild COVID-19 and suggests that viral infections in humans can establish new immunological set-points that affect future immune responses in an antigen-agnostic manner.

Influenza vaccination and single cell multiomics reveal sex dimorphic immune imprints of prior mild COVID-19.

Viral infections can have profound and durable functional impacts on the immune system. There is an urgent need to characterize the long-term immune effects of SARS-CoV-2 infection given the persistence of symptoms in some individuals and the continued threat of novel variants. Here we use systems immunology, including longitudinal multimodal single cell analysis (surface proteins, transcriptome, and V(D)J sequences) from 33 previously healthy individuals after recovery from mild, non-hospitalized COVID-19 and 40 age- and sex-matched healthy controls with no history of COVID-19 to comparatively assess the post-infection immune status (mean: 151 days after diagnosis) and subsequent innate and adaptive responses to seasonal influenza vaccination. Identification of both sex-specific and -independent temporally stable changes, including signatures of T-cell activation and repression of innate defense/immune receptor genes (e.g., Toll-like receptors) in monocytes, suggest that mild COVID-19 can establish new post-recovery immunological set-points. COVID-19-recovered males had higher innate, influenza-specific plasmablast, and antibody responses after vaccination compared to healthy males and COVID-19-recovered females, partly attributable to elevated pre-vaccination frequencies of a GPR56 expressing CD8+ T-cell subset in male recoverees that are "poised" to produce higher levels of IFNγ upon inflammatory stimulation. Intriguingly, by day 1 post-vaccination in COVID-19-recovered subjects, the expression of the repressed genes in monocytes increased and moved towards the pre-vaccination baseline of healthy controls, suggesting that the acute inflammation induced by vaccination could partly reset the immune states established by mild COVID-19. Our study reveals sex-dimorphic immune imprints and in vivo functional impacts of mild COVID-19 in humans, suggesting that prior COVID-19, and possibly respiratory viral infections in general, could change future responses to vaccination and in turn, vaccines could help reset the immune system after COVID-19, both in an antigen-agnostic manner.

Antibody-dependent enhancement of influenza disease promoted by increase in hemagglutinin stem flexibility and virus fusion kinetics.

Several next-generation (universal) influenza vaccines and broadly neutralizing antibodies (bNAbs) are in clinical development. Some of these mediate inhibitions of virus replication at the postentry stage or use Fc-dependent mechanisms. Nonneutralizing antibodies have the potential to mediate enhancement of viral infection or disease. In the current study, two monoclonal antibodies (MAbs) 72/8 and 69/1, enhanced respiratory disease (ERD) in mice following H3N2 virus challenge by demonstrating increased lung pathology and changes in lung cytokine/chemokine levels. MAb 78/2 caused changes in the lung viral loads in a dose-dependent manner. Both MAbs increased HA sensitivity to trypsin cleavage at a higher pH range, suggesting MAb-induced conformational changes. pHrodo-labeled virus particles' entry and residence time in the endocytic compartment were tracked during infection of Madin-Darby canine kidney (MDCK) cells. Both MAbs reduced H3N2 virus residence time in the endocytic pathway, suggesting faster virus fusion kinetics. Structurally, 78/2 and 69/1 Fabs bound the globular head or base of the head domain of influenza hemagglutinin (HA), respectively, and induced destabilization of the HA stem domain. Together, this study describes Mab-induced destabilization of the influenza HA stem domain, faster kinetics of influenza virus fusion, and ERD in vivo. The in vivo animal model and in vitro assays described could augment preclinical safety evaluation of antibodies and next-generation influenza vaccines that generate antibodies which do not block influenza virus-receptor interaction.

AS03-adjuvanted H5N1 vaccine promotes antibody diversity and affinity maturation, NAI titers, cross-clade H5N1 neutralization, but not H1N1 cross-subtype neutralization.

Immune responses to inactivated vaccines against avian influenza are poor due in part to lack of immune memory. Adjuvants significantly increased virus neutralizing titers. We performed comprehensive analyses of polyclonal antibody responses following FDA-approved adjuvanted H5N1-A/Indonesia vaccine, administered in presence or absence of AS03. Using Whole Genome Fragment Phage Display Libraries, we observed that AS03 induced antibody epitope diversity to viral hemagglutinin (HA) and neuraminidase compared with unadjuvanted vaccine. Furthermore, AS03 promoted significant antibody affinity maturation to properly folded H5-HA1 (but not to HA2) domain, which correlated with neutralization titers against both vaccine and heterologous H5N1 strains. However, no increase in heterosubtypic cross-neutralization of Group1-H1N1 seasonal strains was observed. AS03-H5N1 vaccine also induced higher neuraminidase inhibition antibody titers. This study provides insight into the differential impacts of AS03 adjuvant on H5N1 vaccine-induced antibody responses that may help optimize vaccine platforms for future vaccines with improved protection against seasonal and pandemic influenza strains.

A Potent Germline-like Human Monoclonal Antibody Targets a pH-Sensitive Epitope on H7N9 Influenza Hemagglutinin.

The H7N9 influenza virus causes high-mortality disease in humans but no effective therapeutics are available. Here we report a human monoclonal antibody, m826, that binds to H7 hemagglutinin (HA) and protects against H7N9 infection. m826 binds to H7N9 HA with subnanomolar affinity at acidic pH and 10-fold lower affinity at neutral pH. The high-resolution (1.9 Å) crystal structure of m826 complexed with H7N9 HA indicates that m826 binds an epitope that may be fully exposed upon pH-induced conformational changes in HA. m826 fully protects mice against lethal challenge with H7N9 virus through mechanisms likely involving antibody-dependent cell-mediated cytotoxicity. Interestingly, immunogenetic analysis indicates that m826 is a germline antibody, and m826-like sequences can be identified in H7N9-infected patients, healthy adults, and newborn babies. These m826 properties offer a template for H7N9 vaccine immunogens, a promising candidate therapeutic, and a tool for exploring mechanisms of virus infection inhibition by antibodies.

Impaired B cell immunity in acute myeloid leukemia patients after chemotherapy.

BACKGROUND: Changes in adaptive immune cells after chemotherapy in adult acute myeloid leukemia (AML) may have implications for the success of immunotherapy. This study was designed to determine the functional capacity of the immune system in adult patients with AML who have completed chemotherapy and are potential candidates for immunotherapy. METHODS: We used the response to seasonal influenza vaccination as a surrogate for the robustness of the immune system in 10 AML patients in a complete remission post-chemotherapy and performed genetic, phenotypic, and functional characterization of adaptive immune cell subsets. RESULTS: Only 2 patients generated protective titers in response to vaccination, and a majority of patients had abnormal frequencies of transitional and memory B-cells. B-cell receptor sequencing showed a B-cell repertoire with little evidence of somatic hypermutation in most patients. Conversely, frequencies of T-cell populations were similar to those seen in healthy controls, and cytotoxic T-cells demonstrated antigen-specific activity after vaccination. Effector T-cells had increased PD-1 expression in AML patients least removed from chemotherapy. CONCLUSION: Our results suggest that while some aspects of cellular immunity recover quickly, humoral immunity is incompletely reconstituted in the year following intensive cytotoxic chemotherapy for AML. The observed B-cell abnormalities may explain the poor response to vaccination often seen in AML patients after chemotherapy. Furthermore, the uncoupled recovery of B-cell and T-cell immunity and increased PD-1 expression shortly after chemotherapy might have implications for the success of several modalities of immunotherapy.

Patients with MS under daclizumab therapy mount normal immune responses to influenza vaccination.

OBJECTIVE: The purpose of this study was to assess the potential immunosuppressive role of daclizumab, a humanized monoclonal antibody against the α chain of the interleukin 2 receptor, in vivo, by comparing immune responses to the 2013 seasonal influenza vaccination between patients with multiple sclerosis (MS) on long-term daclizumab therapy and controls. METHODS: Previously defined subpopulations of adaptive immune cells known to correlate with the immune response to the influenza vaccination were evaluated by 12-color flow cytometry in 23 daclizumab-treated patients with MS and 14 MS or healthy controls before (D0) and 1 day (D1) and 7 days (D7) after administration of the 2013 Afluria vaccine. Neutralizing antibody titers and CD4(+), CD8(+) T cell, B cell, and natural killer cell proliferation to 3 strains of virus contained in the Afluria vaccine were assessed at D0, D7, and 180 days postvaccination. RESULTS: Daclizumab-treated patients and controls demonstrated comparable, statistically significant expansions of previously defined subpopulations of activated CD8(+) T cells and B cells that characterize the development of effective immune responses to the influenza vaccine, while proliferation of T cells to influenza and control antigens was diminished in the daclizumab cohort. All participants fulfilled FDA criteria for seroconversion or seroprotection in antibody assays. CONCLUSION: Despite the mild immunosuppressive effects of daclizumab in vivo demonstrated by an increased incidence of infectious complications in clinical trials, patients with MS under daclizumab therapy mount normal antibody responses to influenza vaccinations.

Oral priming with replicating adenovirus serotype 4 followed by subunit H5N1 vaccine boost promotes antibody affinity maturation and expands H5N1 cross-clade neutralization.

A Phase I trial conducted in 2009-2010 demonstrated that oral vaccination with a replication competent Ad4-H5 (A/Vietnam) vector with dosages ranging from 107-1011 viral particles was well tolerated. HA-specific T-cell responses were efficiently induced, but very limited hemagglutination-inhibiting (HI) humoral responses were measured. However, a single boost of Ad4-H5-Vtn vaccinated individuals with a unadjuvanted licensed H5N1 (A/Vietnam) subunit vaccine resulted in superior HI titers compared with unprimed subjects. In the current study, the impact of Ad4-H5 priming on the quality of the polyclonal humoral immune response was evaluated using a real-time kinetics assay by surface plasmon resonance (SPR). Total binding of serum polyclonal antibodies from the Ad4-H5-Vtn primed groups against both homologous H5N1-A/Vietnam/1194/2004 (clade 1) and heterologous A/Indonesia-5/2005 (clade 2.1) HA1 head domain was significantly higher compared with sera from individuals that received subunit H5N1 vaccination alone. SPR measurements also demonstrated that the antigen-antibody complex dissociation rates (a surrogate for antibody affinity) of serum antibodies against the HA1 of H5N1-A/Vietnam were significantly higher in the Ad4-H5 primed groups compared with those from the unprimed group. Furthermore, strong correlations were observed between the antibody affinities for HA1 (but not HA2) and the virus neutralization titers against the homologous strain and a panel of heterologous clade 2 H5N1 strains. These findings support the concept of oral prime-boost vaccine approaches against pandemic influenza to elicit long-term memory B cells with high affinity capable of rapid response to variant pandemic viruses likely to emerge and adapt to human transmissions.

H5 N-terminal ß sheet promotes oligomerization of H7-HA1 that induces better antibody affinity maturation and enhanced protection against H7N7 and H7N9 viruses compared to inactivated influenza vaccine.

Initiation of mass vaccination is critical in response to influenza pandemic. There is an urgent need of a simple, rapid method for production of influenza vaccine that is more effective than current traditional influenza vaccines. Recent H7N9 transmissions to humans in China with high morbidity/mortality initiated extensive vaccine evaluation. We produced the HA1 domains (amino acids 1-320) from H7N9 and H7N7 strains in E. coli. Both were found to contain primarily monomers/trimers with low oligomeric content. However, when residues from the N-terminal ß sheet (first 8 amino acid) of H7 HA1 domains were swapped with the corresponding amino acids from H5N1, functional oligomeric H7 HA1 were produced (HA1-DS), demonstrating strong receptor binding and hemagglutination. In rabbits, the HA1-DS from either H7N9 or H7N7 generated high neutralization titers against both homologous and heterologous H7 strains, superior to the unmodified H7 HA1 proteins. In ferrets, HA1-DS from H7N7 elicited higher (and faster) HI titers, better protected ferrets from lethality, weight loss, and reduced viral loads following challenge with wild-type highly pathogenic H7N7 virus compared with inactivated H7N7 subunit vaccine. HA1-DS vaccinated ferrets were also better protected from weight loss after challenge with the heterologous H7N9 virus compared with inactivated H7N7 subunit vaccine. Importantly, the H7N7 HA1-DS vaccine induced antibody affinity maturation far superior to the inactivated H7N7 subunit vaccine, which strongly correlated with control of viral loads in the nasal washes after challenge with either H7N7 or H7N9 strains. We conclude that N-terminus ß sheet domain-swap can be used to produce stable functional oligomeric forms of better recombinant HA1 vaccines in simple, inexpensive bacterial system for rapid response to emerging pandemic threat for the global population.

Novel antibody-independent receptor-binding SPR-based assay for rapid measurement of influenza vaccine potency.

A WHO workshop organized following the 2009 H1N1 pandemic recommended development of alternative influenza vaccine potency assays as high priority that could expedite the release of vaccine lots in the face of future influenza pandemics. We have developed an antibody independent, simple, high throughput receptor-binding SPR-based potency assay, which does not require any reference antisera and could be used for rapid HA quantitation and vaccine release in pandemic scenarios. The assay utilizes synthetic glycans with sialic acid (SA) of either α-2,6 or α-2,3 linkage to galactose. Only functionally active forms of HA (trimers and oligomers) recognize the SA-glycans and are quantified in this receptor-binding SPR assay. The SA-glycan SPR assay demonstrated broad dynamic range for quantitation of HA content in influenza vaccines from different manufacturers for both seasonal (A/H1N1, A/H3N2, B lineages) and pandemic influenza (A/H5N1, A/H7N9) strains with high reproducibility and low variability across multiple assays. In addition, the SA-glycan SPR assay is indicative of active HA stability, and can accurately quantify HA content in alum and oil-in-water adjuvanted influenza vaccines. Importantly, there was a good agreement between HA content determined by the SPR-based potency assay and the traditional SRID assay.

A live attenuated influenza A(H5N1) vaccine induces long-term immunity in the absence of a primary antibody response.

BACKGROUND: Highly pathogenic avian influenza A(H5N1) causes severe infections in humans. We generated 2 influenza A(H5N1) live attenuated influenza vaccines for pandemic use (pLAIVs), but they failed to elicit a primary immune response. Our objective was to determine whether the vaccines primed or established long-lasting immunity that could be detected by administration of inactivated subvirion influenza A(H5N1) vaccine (ISIV). METHODS: The following groups were invited to participate in the study: persons who previously received influenza A(H5N1) pLAIV; persons who previously received an irrelevant influenza A(H7N3) pLAIV; and community members who were naive to influenza A(H5N1) and LAIV. LAIV-experienced subjects received a single 45-µg dose of influenza A(H5N1) ISIV. Influenza A(H5N1)- and LAIV-naive subjects received either 1 or 2 doses of ISIV. RESULTS: In subjects who had previously received antigenically matched influenza A(H5N1) pLAIV followed by 1 dose of ISIV compared with those who were naive to influenza A(H5N1) and LAIV and received 2 doses of ISIV, we observed an increased frequency of antibody response (82% vs 50%, by the hemagglutination inhibition assay) and a significantly higher antibody titer (112 vs 76; P = .04). The affinity of antibody and breadth of cross-clade neutralization was also enhanced in influenza A(H5N1) pLAIV-primed subjects. CONCLUSIONS: ISIV administration unmasked long-lasting immunity in influenza A(H5N1) pLAIV recipients, with a rapid, high-titer, high-quality antibody response that was broadly cross-reactive across several influenza A(H5N1) clades. CLINICAL TRIALS REGISTRATION: NCT01109329.

Vaccine-induced anti-HA2 antibodies promote virus fusion and enhance influenza virus respiratory disease.

Vaccine-induced disease enhancement has been described in connection with several viral vaccines in animal models and in humans. We investigated a swine model to evaluate mismatched influenza vaccine-associated enhanced respiratory disease (VAERD) after pH1N1 infection. Vaccinating pigs with whole inactivated H1N2 (human-like) virus vaccine (WIV-H1N2) resulted in enhanced pneumonia and disease after pH1N1 infection. WIV-H1N2 immune sera contained high titers of cross-reactive anti-pH1N1 hemagglutinin (HA) antibodies that bound exclusively to the HA2 domain but not to the HA1 globular head. No hemagglutination inhibition titers against pH1N1 (challenge virus) were measured. Epitope mapping using phage display library identified the immunodominant epitope recognized by WIV-H1N2 immune sera as amino acids 32 to 77 of pH1N1-HA2 domain, close to the fusion peptide. These cross-reactive anti-HA2 antibodies enhanced pH1N1 infection of Madin-Darby canine kidney cells by promoting virus membrane fusion activity. The enhanced fusion activity correlated with lung pathology in pigs. This study suggests a role for fusion-enhancing anti-HA2 antibodies in VAERD, in the absence of receptor-blocking virus-neutralizing antibodies. These findings should be considered during the evaluation of universal influenza vaccines designed to elicit HA2 stem-targeting antibodies.

DNA priming prior to inactivated influenza A(H5N1) vaccination expands the antibody epitope repertoire and increases affinity maturation in a boost-interval-dependent manner in adults.

DNA priming improves the response to inactivated influenza A(H5N1) vaccination. We compared the immunogenicity of an H5 DNA prime (using strain A/Indonesia/5/2005) followed by an H5N1 monovalent inactivated vaccine boost at 4, 8, 12, 16, or 24 weeks to that of 2 doses of H5N1 monovalent inactivated vaccine in adults. Antibody epitope repertoires were elucidated by genome-fragment phage-display library analysis, and antibody avidities for HA1 and HA2 domains were measured by surface plasmon resonance. H5 DNA priming expanded the H5-specific antibody epitope repertoire and enhanced antibody avidity to the HA1 (but not the HA2) domain in an interval-dependent manner. Enhanced HA1 binding and avidity after an interval of ≥12 weeks between prime and boost correlated with improved neutralization of homologous and heterologous H5N1 strains. Clinical trials registration NCT01086657.

Effects of postchallenge administration of ST-246 on dissemination of IHD-J-Luc vaccinia virus in normal mice and in immune-deficient mice reconstituted with T cells.

Whole-body bioimaging was used to study dissemination of vaccinia virus (VACV) in normal and in immune deficient (nu(-)/nu(-)) mice protected from lethality by postchallenge administration of ST-246. Total fluxes were recorded in the liver, spleen, lungs, and nasal cavities of live mice after intranasal infection with a recombinant IHD-J-Luc VACV expressing luciferase. Areas under the flux curve were calculated for individual mice to assess viral loads. Treatment for 2 to 5 days of normal BALB/c mice with ST-246 at 100 mg/kg starting 24 h postchallenge conferred 100% protection and reduced viral loads in four organs compared to control mice. Mice also survived after 5 days of treatment with ST-246 at 30 mg/kg, and yet the viral loads and poxes were higher in these mice compared to 100-mg/kg treatment group. Nude mice were not protected by ST-246 alone or by 10 million adoptively transferred T cells. In contrast, nude mice that received T cells and 7-day treatment with ST-246 survived infection and exhibited reduced viral loads compared to nonreconstituted and ST-246-treated mice after ST-246 was stopped. Similar protection of nude mice was achieved using adoptively transferred 1.0 and 0.1 million, but not 0.01 million, purified T cells or CD4(+) or CD8(+) T cells in conjunction with ST-246 treatment. These data suggest that ST-246 protects immunocompetent mice from lethality and reduces viral dissemination in internal organs and poxvirus lesions. Furthermore, immune-deficient animals with partial T cell reconstitution can control virus replication after a course of ST-246 and survive lethal vaccinia virus challenge.

Preconfiguration of the antigen-binding site during affinity maturation of a broadly neutralizing influenza virus antibody.

Affinity maturation refines a naive B-cell response by selecting mutations in antibody variable domains that enhance antigen binding. We describe a B-cell lineage expressing broadly neutralizing influenza virus antibodies derived from a subject immunized with the 2007 trivalent vaccine. The lineage comprises three mature antibodies, the unmutated common ancestor, and a common intermediate. Their heavy-chain complementarity determining region inserts into the conserved receptor-binding pocket of influenza HA. We show by analysis of structures, binding kinetics and long time-scale molecular dynamics simulations that antibody evolution in this lineage has rigidified the initially flexible heavy-chain complementarity determining region by two nearly independent pathways and that this preconfiguration accounts for most of the affinity gain. The results advance our understanding of strategies for developing more broadly effective influenza vaccines.

Humans with chronic granulomatous disease maintain humoral immunologic memory despite low frequencies of circulating memory B cells.

CD27(+) memory B cells are reduced in the blood of patients with chronic granulomatous disease (CGD) for reasons and consequences that remain unclear. Here we confirm not only decreased CD27(+) but also IgG(+) B cells in the blood of CGD patients compared with healthy donors (HDs). However, among IgG(+) B cells, the ratio of CD27(-) to CD27(+) was significantly higher in CGD patients compared with HDs. Similar to conventional memory B cells, CD27(-)IgG(+) B cells of CGD patients expressed activation markers and had undergone somatic hypermutation, albeit at levels lower than their CD27(+) counterparts. Functional analyses revealed slight reductions in frequencies of total IgG but not influenza-specific memory B-cell responses, as measured by Elispot in CGD patients compared with HDs. Serum IgG levels and influenza-specific antibodies were also normal in these CGD patients. Finally, we provide evidence that influenza-specific memory B cells can be present within the CD27(-)IgG(+) B-cell compartment. Together, these findings show that, despite reduced circulating CD27(+) memory B cells, CGD patients maintain an intact humoral immunologic memory, with potential contribution from CD27(-) B cells.

H5N1 virus-like particle vaccine elicits cross-reactive neutralizing antibodies that preferentially bind to the oligomeric form of influenza virus hemagglutinin in humans.

Transmission of pathogenic avian influenza viruses (AIV) from wild birds to domestic poultry and humans is continuing in multiple countries around the world. In preparation for a potential AIV pandemic, multiple vaccine candidates are under development. In the case of H5N1 AIV, a clear shift in transmission from clade 1 to clade 2 viruses occurred in recent years. The virus-like particle (VLP) represents an economical approach to pandemic vaccine development. In the current study, we evaluated the humoral immune response in humans vaccinated with H5N1 A/Indonesia/05/2005 (clade 2.1) VLP vaccine manufactured in Sf9 insect cells. The VLPs were comprised of the influenza virus hemagglutinin (HA), neuraminidase (NA), and matrix 1 (M1) proteins. In an FDA-approved phase I/II human clinical study, two doses of H5N1 VLPs at 15, 45, or 90 µg HA/dose resulted in seroconversion and production of functional antibodies. Moreover, cross-reactivity against other clade 2 subtypes was demonstrated using virus neutralization assays. H5N1 whole-genome fragment phage display libraries (GFPDL) were used to elucidate the antibody epitope repertoire in postvaccination human sera. Diverse epitopes in HA1/HA2 and NA were recognized by postvaccination sera from the two high-dose groups, including large segments spanning the HA1 receptor binding domain. Importantly, the vaccine elicited sera that preferentially bound to an oligomeric form of recombinant HA1 compared with monomeric HA1. The oligomeric/monomeric HA1 binding ratios of the sera correlated with the virus neutralizing titers. Additionally, the two high-dose VLP vaccine groups generated NA-inhibiting antibodies that were associated with binding to a C-terminal epitope close to the sialic acid binding site. These findings represent the first report describing the quality of the antibody responses in humans following AIV VLP immunization and support further development of such vaccines against emerging influenza virus strains.

Broadly neutralizing human antibody that recognizes the receptor-binding pocket of influenza virus hemagglutinin.

Seasonal antigenic drift of circulating influenza virus leads to a requirement for frequent changes in vaccine composition, because exposure or vaccination elicits human antibodies with limited cross-neutralization of drifted strains. We describe a human monoclonal antibody, CH65, obtained by isolating rearranged heavy- and light-chain genes from sorted single plasma cells, coming from a subject immunized with the 2007 trivalent influenza vaccine. The crystal structure of a complex of the hemagglutinin (HA) from H1N1 strain A/Solomon Islands/3/2006 with the Fab of CH65 shows that the tip of the CH65 heavy-chain complementarity determining region 3 (CDR3) inserts into the receptor binding pocket on HA1, mimicking in many respects the interaction of the physiological receptor, sialic acid. CH65 neutralizes infectivity of 30 out of 36 H1N1 strains tested. The resistant strains have a single-residue insertion near the rim of the sialic-acid pocket. We conclude that broad neutralization of influenza virus can be achieved by antibodies with contacts that mimic those of the receptor.