Anti-influenza Antibody Responses Research Articles

Expression of the SARS-CoV-2 receptor-binding domain by live attenuated influenza vaccine virus as a strategy for designing a bivalent vaccine against COVID-19 and influenza

Influenza and SARS-CoV-2 are two major respiratory pathogens that cocirculate in humans and cause serious illness with the potential to exacerbate disease in the event of co-infection. To develop a bivalent vaccine, capable of protecting against both infections, we inserted the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein into hemagglutinin (HA) molecule or into the open reading frame of the truncated nonstructural protein 1 (NS1) of live attenuated influenza vaccine (LAIV) virus and assessed phenotypic characteristics of the rescued LAIV-RBD viruses, as well as their immunogenicity in mouse and Syrian hamster animal models. A panel of 9 recombinant LAIV-RBD viruses was rescued using the A/Leningrad/17 backbone. Notably, only two variants with RBD insertions into the HA molecule could express sufficient quantities of RBD protein in infected MDCK cells. Intranasal immunization of mice induced high levels of anti-influenza antibody responses in all chimeric LAIV-RBD viruses, which was comparable to the LAIV virus vector. The RBD-specific antibody responses were most pronounced in the variant expressing RBD194 fragment as a chimeric HA protein. This candidate was further tested in Syrian hamsters and was shown to be immunogenic and capable of protecting animals against both infections.

Formulation Approach that Enables the Coating of a Stable Influenza Vaccine on a Transdermal Microneedle Patch.

A trivalent influenza split vaccine was formulated at high concentration for coating on the transdermal microneedle system. Monovalent vaccine bulks of three influenza strains, two influenza A strains, and one B strain were diafiltrated, concentrated, and lyophilized. The lyophilized powder of each vaccine strain was separately reconstituted and subsequently combined into a coating formulation of high concentration trivalent vaccine. The formulation process converted the monovalent vaccine bulks with low hemagglutinin (HA) concentrations 0.1 mg/mL into a viscous, emulsion containing HA at ~50 mg/mL. This physically stable emulsion demonstrated viscosity 1 poise and 30° contact angle for effective, homogeneous coating on each microneedle. Evaluation of the vaccine antigen HA by SRID and SDS-PAGE/Western blot showed that HA remained stable throughout the vaccine transdermal microneedle system manufacturing process and 1-year ambient storage (25°C). Anti-influenza antibody responses were evaluated by ELISA and hemagglutination inhibition (HAI) assay after primary and booster immunization with the vaccine-coated transdermal microneedle systems at either 25-μg or 40-μg total HA. The results showed the induction of serum anti-influenza IgG and anti-HA neutralizing antibodies after primary immunization and significant titer rises after booster immunization for both doses, indicating the dry-coated trivalent vaccine delivered by transdermal microneedle system elicited both primary and recall antibody responses against all three antigen strains. The study demonstrates that the transdermal microneedle system provides an attractive alternative for influenza vaccine delivery with key advantages such as preservative-free and room-temperature storage.

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

SummaryPolyreactivity 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.

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 comprehensively analyzing more than 500 monoclonal antibodies (mAbs) derived from B cells induced by numerous influenza virus vaccines and infections, we find mAbs targeting conserved neutralizing influenza virus hemagglutinin epitopes are polyreactive. Polyreactive mAbs are preferentially induced by novel viral exposures due to their broad viral binding breadth. Polyreactivity augments 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 polyreactivity is a beneficial feature of antibodies targeting conserved epitopes.

Application of volumetric absorptive microsampling (VAMS) to measure multidimensional anti-influenza IgG antibodies by the mPlex-Flu assay.

Introduction: Recently, volumetric absorptive microsampling (VAMS) has been used for accurate sampling of a fixed peripheral blood volume (10 µL) on a volumetric swab, and long-term sample storage. The mPlex-Flu assay is a novel, high-throughput assay that simultaneously measures the concentration of antibodies against the hemagglutinin (HA) proteins from multiple influenza virus strains with ≤5 µL of serum. Here we describe combining these two methods to measure multidimensional anti-influenza IgG activity in whole blood samples collected by a finger stick and VAMS, with correction for serum volume based on simultaneous hemoglobin measurement. Methods: We compared capillary blood samples obtained from a finger stick using a VAMS device with serum samples collected by traditional phlebotomy from 20 subjects, with the influenza antibody profiles measured by the mPlex-Flu assay. Results: We found that results with the two sampling methods were highly correlated within subjects and across all influenza strains (mean R 2 = 0.9470). Adjustment for serum volume, based on hemaglobin measurement, was used to estimate serum volume of samples and improved the accuracy. IgG measurements were stable over 3 weeks when VAMS samples were stored at room temperature or transported using a variety of shipping methods. Additionally, when volunteers performed finger-stick VAMS at-home by themselves, the comparison results of anti-HA antibody concentrations were highly consistent with sampling performed by study personnel on-site (R 2 = 0.9496). Conclusions: This novel approach can provide a simple, accurate, and low-cost means for monitoring the IgG anti-influenza HA antibody responses in large population studies and clinical trials.

English

Inactivated oil based avian influenza vaccines are being used to confront viral outbreaks but seem to be ineffective due to the shorter life span of broiler birds. In such situations immunostimulating agents may play a vital role to overcome the problem. The current study was designed to investigate the co-stimulatory effect of levamisole on humoral response of chicken against inactivated oil based influenza vaccines in broiler birds. The efficacy of levamisole (LMS) hydrochloride, a standard immune modulator was evaluated on one hundred broilers in association with inactivated adjuvanted avian influenza vaccines. Avian influenza susceptible broilers were divided into nine groups, each having ten birds. The birds in groups G1, G2, G3, G5, G6 and G7 were offered 30 , 20 and 15mg kg-1 bwt levamisole for four consecutive days after being vaccinated with oil and gel based inactivated influenza vaccines respectively; birds in group G9 were kept as control. Whereas, birds in Group G4 were kept as oil base vaccinated control and Group G8 were kept as gel base vaccinated control without levamisole medication. Blood samples were obtained from wing vein on 14th, 28th and 36th days post vaccination. Anti-influenza antibody response was measured using haemagglutination inhibition (HI) technique.  Data analyzed by one way ANOVA and DMR test showed that levamisole in both regimens had appreciable effect on antibody titers (p<0.05). In conclusion, LMS can stimulate immune system which causes better response to vaccination. Further studies are needed to evaluate other effective factors for each of the best results of LMS. Key words: Levamisole, AIV H7N3, Immunomodulation. &nbsp

Declining responsiveness to influenza vaccination with progression of human pregnancy

BackgroundInfluenza immunization is universally recommended during pregnancy to protect mothers and their offspring. However, pregnancy-induced shifts in vaccine responsiveness remain poorly defined. MethodsQuantitative and qualitative shifts in the serological response to influenza vaccination were evaluated in healthy women throughout the course of pregnancy. Serum was obtained before and after vaccination among 71 pregnant and 67 non-pregnant women during the 2011–12 and 2012–13 influenza seasons. Serum hemagglutination inhibition (HAI) assay was used to investigate anti-influenza antibody responses by comparing pre-vaccine and post-vaccine geometric mean titers (GMTs) between groups for each antigen. IgG1, IgG2, IgG3, and IgG4 anti-influenza titers were also evaluated by enzyme-linked immunosorbent assay (ELISA). Pregnancy induced shifts in HAI titers and levels of each anti-influenza antibody isotype were evaluated using linear regression models. ResultsPost-vaccine GMTs at day 28 were significantly reduced for women vaccinated during pregnancy for A/California (H1N1) in 2011 (p = 0.027), A/Perth (H3N2) in 2011 (p = 0.037), and B/Wisconsin in 2012 (p = 0.039). Vaccine responses progressively declined with the initiation of vaccination later in pregnancy. Anti-H1N1 IgG1, IgG2, and IgG3 titers were reduced in pregnant women compared to non-pregnant controls, and these titers declined with pregnancy progression. The most striking differences were found for anti-H1N1 IgG1, where titers decreased by approximately 7% each week throughout pregnancy. ConclusionsHAI responses elicited by immunization were significantly reduced during pregnancy for three different influenza vaccine antigens. Anti-H1N1 IgG1 was significantly lower in pregnant women and decreased throughout the course of pregnancy. Waning serological responsiveness to influenza vaccination with the progression of human pregnancy has important translational implications for when immunization should be optimally administered during pregnancy.

Activation and Induction of Antigen-Specific T Follicular Helper Cells Play a Critical Role in Live-Attenuated Influenza Vaccine-Induced Human Mucosal Anti-influenza Antibody Response.

ABSTRACTThere is increasing interest recently in developing intranasal vaccines against respiratory tract infections. The antibody response is critical for vaccine-induced protection, and T follicular helper cells (TFH) are considered important for mediating the antibody response. Most data supporting the role for TFH in the antibody response are from animal studies, and direct evidence from humans is limited, apart from the presence of TFH-like cells in blood. We studied the activation and induction of TFH and their role in the anti-influenza antibody response induced by a live-attenuated influenza vaccine (LAIV) in human nasopharynx-associated lymphoid tissue (NALT). TFH activation in adenotonsillar tissues was analyzed by flow cytometry, and anti-hemagglutinin (anti-HA) antibodies were examined following LAIV stimulation of tonsillar mononuclear cells (MNC). Induction of antigen-specific TFH by LAIV was studied by flow cytometry analysis of induced TFH and CD154 expression. LAIV induced TFH proliferation, which correlated with anti-HA antibody production, and TFH were shown to be critical for the antibody response. Induction of TFH from naive T cells by LAIV was shown in newly induced TFH expressing BCL6 and CD21, followed by the detection of anti-HA antibodies. Antigen specificity of LAIV-induced TFH was demonstrated by expression of the antigen-specific T cell activation marker CD154 upon challenge by H1N1 virus antigen or HA. LAIV-induced TFH differentiation was inhibited by BCL6, interleukin-21 (IL-21), ICOS, and CD40 signaling blocking, and that diminished anti-HA antibody production. In conclusion, we demonstrated the induction by LAIV of antigen-specific TFH in human NALT that provide critical support for the anti-influenza antibody response. Promoting antigen-specific TFH in NALT by use of intranasal vaccines may provide an effective vaccination strategy against respiratory infections in humans.IMPORTANCE Airway infections, such as influenza, are common in humans. Intranasal vaccination has been considered a biologically relevant and effective way of immunization against airway infection. The vaccine-induced antibody response is crucial for protection against infection. Recent data from animal studies suggest that one type of T cells, TFH, are important for the antibody response. However, data on whether TFH-mediated help for antibody production operates in humans are limited due to the lack of access to human immune tissue containing TFH. In this study, we demonstrate the induction of TFH in human immune tissue, providing critical support for the anti-influenza antibody response, by use of an intranasal influenza vaccine. Our findings provide direct evidence that TFH play a critical role in vaccine-induced immunity in humans and suggest a novel strategy for promoting such cells by use of intranasal vaccines against respiratory infections.

The anti-influenza M2e antibody response is promoted by XCR1 targeting in pig skin

XCR1 is selectively expressed on a conventional dendritic cell subset, the cDC1 subset, through phylogenetically distant species. The outcome of antigen-targeting to XCR1 may therefore be similar across species, permitting the translation of results from experimental models to human and veterinary applications. Here we evaluated in pigs the immunogenicity of bivalent protein structures made of XCL1 fused to the external portion of the influenza virus M2 proton pump, which is conserved through strains and a candidate for universal influenza vaccines. Pigs represent a relevant target of such universal vaccines as pigs can be infected by swine, human and avian strains. We found that cDC1 were the only cell type labeled by XCR1-targeted mCherry upon intradermal injection in pig skin. XCR1-targeted M2e induced higher IgG responses in seronegative and seropositive pigs as compared to non-targeted M2e. The IgG response was less significantly enhanced by CpG than by XCR1 targeting, and CpG did not further increase the response elicited by XCR1 targeting. Monophosphoryl lipid A with neutral liposomes did not have significant effect. Thus altogether M2e-targeting to XCR1 shows promises for a trans-species universal influenza vaccine strategy, possibly avoiding the use of classical adjuvants.

Age and testosterone mediate influenza pathogenesis in male mice.

Influenza severity increases with age, with hospitalization and mortality rates during seasonal influenza epidemics being higher in older men than age-matched women. As it is known that with age, circulating testosterone levels decline in males, we hypothesized that reduced testosterone contributes to age-associated increases in influenza severity. A murine model was used to test this hypothesis. As in men, testosterone concentrations were lower in aged (18 mo) than young (2 mo) male C57BL/6 mice. Following inoculation with influenza A virus (IAV), aged males experienced greater morbidity, clinical disease, and pulmonary inflammation than young males, and had lower neutralizing and total anti-influenza IgG antibody responses. Peak titers of virus in the lungs did not differ between aged and young males, but virus clearance was delayed in aged males. In young males, removal of the gonads increased-whereas treatment of gonadectomized males with testosterone reduced-morbidity, clinical illness, and pulmonary pathology, but viral replication was not altered by hormone manipulation in young males. Treatment of aged males with testosterone improved survival following infection but did not alter either virus replication or pulmonary pathology. These results indicate that low concentrations of testosterone, whether induced surgically in young males or naturally occurring in aged males, negatively impact the outcome of influenza.

A critical role of T follicular helper cells in human mucosal anti-influenza response that can be enhanced by immunological adjuvant CpG-DNA

T Follicular helper cells (TFH) are considered critical for B cell antibody response, and recent efforts have focused on promoting TFH in order to enhance vaccine efficacy. We studied the frequency and function of TFH in nasopharynx-associated lymphoid tissues (NALT) from children and adults, and its role in anti-influenza antibody response following stimulation by a live-attenuated influenza vaccine (LAIV) or an inactivated seasonal virus antigen (sH1N1). We further studied whether CpG-DNA promotes TFH and by which enhances anti-influenza response. We showed NALT from children aged 1.5–10 years contained abundant TFH, suggesting efficient priming of TFH during early childhood. Stimulation by LAIV induced a marked increase in TFH that correlated with a strong production of anti-hemagglutinin (HA) IgA/IgG/IgM antibodies in tonsillar cells. Stimulation by the inactivated sH1N1 antigen induced a small increase in TFH which was markedly enhanced by CpG-DNA, accompanied by enhanced anti-HA antibody responses. In B cell co-culture experiment, anti-HA responses were only seen in the presence of TFH, and addition of plasmacytoid dendritic cell to TFH-B cell co-culture enhanced the TFH-mediated antibody production following CpG-DNA and sH1N1 antigen stimulation. Induction of TFH differentiation from naïve T cells was also shown following the stimulation. Our results support a critical role of TFH in human mucosal anti-influenza antibody response. Use of an adjuvant such as CpG-DNA that has the capacity to promote TFH by which to enhance antigen-induced antibody responses in NALT tissue may have important implications for future vaccination strategies against respiratory pathogens.

8. Stress, insomnia and influenza vaccine response

The current analyses were part of a larger two-year study examining the relationship between perceived stress and influenza vaccine antibody responses in a healthy young adult population by comparing people with insomnia to people without insomnia. Self-reported stress levels were assessed in all individuals using the Perceived Stress Scale (PSS). Influenza strains included H1N1, H3N2 and B. Participants gave a blood sample for antibody assessment both before and four weeks after the vaccine. Anti-influenza IgG antibody amounts were measured via ELISA. Correlations were examined between PSS scores (assessed prior to vaccination) and antibody amounts among the various influenza strains both pre- and post-vaccine. Overall, self-reported stress was negatively correlated with antibody levels pre-vaccine for the H1N1 (−.214, p = .009) and H3N2 (−.243, p = .003) strains and post-vaccine for H3N2 (−.244, p = .004) and B (−.186, p = .028) strains. Results indicated that overall, PSS scores were negatively correlated with anti-influenza antibody (IgG) responses both pre- and post-vaccine for some strains/years, a result that is consistent with a number of studies examining stress and vaccine responses. Interestingly, while people with insomnia self-reported more stress than those without (p = .000), covariate analyses examining stress as a predictor of antibody responses pre- to post-vaccine was not significant (p > .05).

Pregnancy increases the IgG4 and decreases the IgG1 response to influenza vaccine (VAC2P.935)

Abstract Although the increased morbidity and mortality of influenza during pregnancy provide a compelling reason to vaccinate pregnant women, pregnancy is associated with a decreased hemagglutination inhibition (HAI) response to influenza vaccine. We hypothesized that in addition to this quantitative reduction, pregnancy-associated increases in IL-4, IL-10 and IL-13 secretion might promote production of IgG4 over the better complement- and Fc receptor-activating isotypes, IgG1 and IgG3; such a change might decrease antibody-dependent killing of virus. To begin to evaluate this hypothesis, we compared IgG1, IgG3 and IgG4 anti-H1N1 titers by ELISA in sera obtained from 50 pregnant and non-pregnant 18-39 year old women 24-31 days after vaccination. The IgG1:IgG4 ratio was significantly decreased in pregnant vs. non-pregnant women (29.0±35.0 vs. 69.3±94.1 (mean ± SD), p=0.04). Both HAI (p=0.017) and IgG1 (p=0.047) titers were decreased in trimesters 2 and 3 vs. trimester 1. These changes could be quite marked: 28% of women immunized during trimesters 2 and 3 had a combination of high IgG4/low IgG1 titers that was not seen in any non-pregnant or first trimester vaccinated women. Our results suggest that cytokine-mediated qualitative and quantitative changes in the anti-influenza antibody response may decrease protection in a considerable percentage of women vaccinated during the last 2/3 of pregnancy, which, in turn, suggests a need to consider changes in vaccination for this population.

The regulatory T cells in anti-influenza antibody response post influenza vaccination

The efficacy and effectiveness of influenza vaccines depend primarily on the vaccine recipient and the virus similarity to the endemic virus. Regulatory T cells (Tregs) and cytokines are known to restrict immune responses against viral infections. We conducted this study to explore the role of Tregs, cytokines, and antibody production after influenza vaccination. The whole blood was collected from healthy subjects (n = 36) before and two weeks after influenza vaccine immunization for two or three consecutive years. The cell surface markers, intracellular staining of Foxp3+ Tregs, and Th1/Th2 cytokines were determined. The antibody titer was detected using the hemagglutination inhibition test. The CD3+, CD127+, CD4+CD25+ and CD4+Foxp3+cells were increased significantly post vaccination. The plasma level of the transforming growth factor (TGF-β), but not interleukin (IL)-2, IL-4, IL-5, IL-10, IFN-γ, TNF-α, was also found to increase significantly after vaccination. We further correlated the cytokine fold-increases with the anti-influenza antibody titer for individual post vaccination. It was found that the IL-10 level after vaccination correlated with the fold-increases of anti-H1N1, anti-H3N2, anti-B/Yamagata, and anti-B/Victoria antibodies. But, a negative relationship occurs between the TGF-β level and fold-increases of anti-H1N1, anti-H3N2, anti-B/Yamagata, and anti-B/Victoria antibodies post vaccination. Treg cells and TGF-β seem to participate in the downregulation of the anti-influenza antibody response post influenza vaccination. Alteration of Treg activity might enhance influenza vaccine antibody responses and efficacy.

Influenza vaccination can induce new-onset anticardiolipins but not β2-glycoprotein-I antibodies among patients with systemic lupus erythematosus.

Antiphospholipid syndrome is characterized by autoantibodies against cardiolipins (aCL), lupus anticoagulant, and independent β2-glycoprotein (β2GPI). Controversy exists as to whether vaccination triggers the development of antiphospholipid antibodies (aPL) in patients with systemic lupus erythematosus (SLE). Patients with SLE (101) and matched controls (101) were enrolled from 2005-2009 and received seasonal influenza vaccinations. Sera were tested by ELISA for aCL at baseline, 2, 6, and 12 weeks after vaccination. Vaccine responses were ranked according to an overall anti-influenza antibody response index. Individuals with positive aCL were further tested for β2GPI antibodies. Patients with SLE and healthy controls can develop new-onset aCL post vaccination, although at rates which do not differ between patients and controls (12/101 cases and 7/101 controls, OR 1.81, p = 0.34). New-onset moderate aCL are slightly enriched in African American SLE patients (5/36 cases; p = 0.094). The optical density measurements for aCL reactivity in patients were significantly higher than baseline at 2 weeks (p < 0.05), 6 weeks (p < 0.05), and 12 weeks (p < 0.05) post vaccination. No new β2GPI antibodies were detected among patients with new aCL reactivity. Vaccine response was not different between patients with and without new-onset aCL reactivity (p = 0.43). This study shows transient increases in aCL, but not anti-β2GPI responses, after influenza vaccination.

Patients with humoral primary immunodeficiency do not develop protective anti-influenza antibody titers after vaccination with trivalent subunit influenza vaccine

Yearly influenza vaccination is recommended for patients with humoral primary immunodeficiency (hPID). However, humoral responses following vaccination can be expected to be reduced in these patients. The efficacy of influenza vaccination in patients with hPID, anti-influenza antibody responses was assessed in 26 patients with hPID and 26 matched healthy controls (HC) using hemagglutination inhibition assay. Following vaccination, geometric mean titers (GMT) significantly increased for all influenza strains in the HC group, but only for A/H1N1 in the patient group. Fold increase in anti-influenza titer and seroprotection rates were lower for patients than for HC for A/H3N2 and A/H1N1, leading to postvaccination titer > or =40 in only 29% and 83% vs. 77% and 100%, respectively. Previous vaccination in patients and treatment with IVIg did not result in a higher rate of postvaccination titer > or =40. In conclusion, patients with hPID show hardly any humoral response following influenza vaccination.

Impact of clinical and demographic features in influenza vaccination responses in human systemic lupus erythematosus (99.38)

Abstract The goal of this study is to understand intrinsic and extrinsic defects in influenza vaccination responses in systemic lupus erythematosus (SLE) patients. SLE is a prototypic autoimmune disease characterized by high titers of autoantibodies. We enrolled 72 patients to evaluate anti-influenza antibody responses, autoantibody titers and disease activity after vaccination. In addition, detailed clinical and demographic information was collected. Individuals received the current influenza vaccine and sera were collected at baseline, 2, 6, and 12 weeks post vaccination. Based upon post-vaccination antibody responses, relative antibody affinities and hemaglutination inhibition levels, patients were grouped into "high" and "low" responders. Surprisingly, the high responder group was enriched in older subjects and African Americans. Patients with high anti-influenza antibodies had an increased frequency of discoid rash and anti-nRNP autoantibodies, while patients with low antibody responses had an increase in hematological criteria and anti-aPL autoantibodies. Interestingly, several patients had increased autoantibody titers following vaccination, but there were no significant associated increases in disease flare. In summary, specific demographic, clinical, and autoantibody features were associated with poor antibody responses to influenza vaccination in SLE patients. NIH: NO1-AI-50026

Hydrophobic Inactivation of Influenza Viruses Confers Preservation of Viral Structure with Enhanced Immunogenicity

The use of inactivated influenza virus for the development of vaccines with broad heterosubtypic protection requires selective inactivation techniques that eliminate viral infectivity while preserving structural integrity. Here we tested if a hydrophobic inactivation approach reported for retroviruses could be applied to the influenza virus. By this approach, the transmembrane domains of viral envelope proteins are selectively targeted by the hydrophobic photoactivatable compound 1,5-iodonaphthyl-azide (INA). This probe partitions into the lipid bilayer of the viral envelope and upon far UV irradiation reacts selectively with membrane-embedded domains of proteins and lipids while the protein domains that localize outside the bilayer remain unaffected. INA treatment of influenza virus blocked infection in a dose-dependent manner without disrupting the virion or affecting neuraminidase activity. Moreover, the virus maintained the full activity in inducing pH-dependent lipid mixing, but pH-dependent redistribution of viral envelope proteins into the target cell membrane was completely blocked. These results indicate that INA selectively blocks fusion of the virus with the target cell membrane at the pore formation and expansion step. Using a murine model of influenza virus infection, INA-inactivated influenza virus induced potent anti-influenza virus serum antibody and T-cell responses, similar to live virus immunization, and protected against heterosubtypic challenge. INA treatment of influenza A virus produced a virus that is noninfectious, intact, and fully maintains the functional activity associated with the ectodomains of its two major envelope proteins, neuraminidase and hemagglutinin. When used as a vaccine given intranasally (i.n.), INA-inactivated influenza virus induced immune responses similar to live virus infection.

Value of immunological markers in predicting responsiveness to influenza vaccination in elderly individuals.

Elderly individuals are at high risk for morbidity and mortality when infected with influenza virus. Vaccinations with inactivated virus are less effective in the elderly due to the declining competency of the aging immune system. We have explored whether immunological parameters predict poor anti-influenza virus vaccine responses and can be used as biological markers of immunosenescence. One hundred fifty-three residents of community-based retirement facilities aged 65 to 98 years received a trivalent influenza vaccine. Vaccine-induced antibody responses were determined by comparing hemagglutination inhibition titers before and 28 days after immunization. The composition of the T-cell compartment was analyzed by flow cytometry and the sizes of three T-cell subsets, CD4(+) CD45RO(+) cells, CD4(+) CD28(null) cells, and CD8(+) CD28(null) cells, were determined. Only 17% of the vaccine recipients were able to generate an increase in titers of antibody to all three vaccine components, and 46% of the immunized individuals failed to respond to any of the three hemagglutinins. The likelihood of successful vaccination declined with age and was independently correlated with the expansion of a particular T-cell subset, CD8(+) CD28(null) T cells. The sizes of the CD4(+) CD45RO(+) memory T-cell and CD4(+) CD28(null) T-cell subsets had no effect on the ability to mount anti-influenza virus antibody responses. Frequencies of CD8(+) CD28(null) T cells are useful biological markers of compromised immunocompetence, identifying individuals at risk for insufficient antibody responses.

Associations between human leukocyte antigens and nonresponsiveness to influenza vaccine.

Influenza remains a major cause of morbidity and mortality, particularly in at-risk groups where vaccination reduces complications of infection but is not universally protective. In order to determine whether human leukocyte antigen (HLA) class II polymorphisms modulate anti-influenza antibody responses to vaccination, a cohort of HLA-typed at-risk donors was investigated. The subjects were recruited from a single urban family practice. Hemagglutination-inhibition (HAI) titers were measured immediately before and 28 days after subunit vaccination. Nonresponsiveness was defined as failure to mount an HAI response to any component of the trivalent influenza vaccine. When the nonresponders and responders with HLA class II were compared, the nonresponder group had more HLA-DRB1*07-positive donors (13/32 vs. 6/41 responders; P=.016, Fisher's exact test) and fewer HLA-DQB1*0603-9/14-positive donors (2/32 vs. 14/41 responders; P=.0045). Thus, polymorphisms in HLA class II molecules appear to modulate antibody responses to influenza vaccination.