Whole influenza virus vaccine is more immunogenic than split influenza virus vaccine and induces primarily an IgG2a response in BALB/c mice

Inactivated influenza virus vaccines expressing COBRA hemagglutinin elicited broadly reactive, long-lived protective antibodies

The influenza viruses cause seasonal respiratory illness that affect millions of people globally every year. Prophylactic vaccines are the recommended method to prevent the breakout of influenza epidemics. One of the current commercial influenza vaccines consists of inactivated viruses that are selected months prior to the start of a new influenza season. In many seasons, the vaccine effectiveness (VE) of these vaccines can be relatively low. Therefore, there is an urgent need to develop an improved, more universal influenza vaccine (UIV) that can provide broad protection against various drifted strains in all age groups. To meet this need, the computationally optimized broadly reactive antigen (COBRA) methodology was developed to design a hemagglutinin (HA) molecule as a new influenza vaccine. In this study, COBRA HA-based inactivated influenza viruses (IIV) expressing the COBRA HA from H1 or H3 influenza viruses were developed and characterized for the elicitation of immediate and long-term protective immunity in both immunologically naïve or influenza pre-immune animal models. These results were compared to animals vaccinated with IIV vaccines expressing wild-type H1 or H3 HA proteins (WT-IIV). The COBRA-IIV elicited long-lasting broadly reactive antibodies that had hemagglutination-inhibition (HAI) activity against drifted influenza variants.

The molecular immune modulator adenosine deaminase-1 enhances HIV specific humoral and cellular responses to a native-like HIV envelope trimer DNA vaccine

There is currently no prophylactic vaccine available for human immunodeficiency virus (HIV). Research efforts have resulted in improved immunogens that mimic the native envelope (Env) glycoprotein structure. Recently, a novel triple tandem trimer (TTT) platform has been used to generate a plasmid encoding Env immunogen (pBG505-TTT) that expresses only as trimers, making it more suitable for nucleic acid vaccines. We have previously demonstrated that adenosine deaminase-1 (ADA-1) is critical to the T follicular helper (TFH) function and improves vaccine immune responses in vivo. In this study, we demonstrate that co-delivery of plasmid-encoded adenosine deaminase 1 (pADA) with pBG505-TTT enhances the magnitude, durability, isotype switching and functionality of HIV-specific antibodies in a dose-sparing manner. Co-delivery of the molecular immune modulator ADA-1 also enhances HIV-specific T cell polyfunctionality, activation, and degranulation as well as memory B cell responses. These data demonstrate that pADA enhances HIV-specific cellular and humoral immunity, making ADA-1 a promising immune modulator for HIV-targeting vaccines.

Lipid nanoparticle composition for adjuvant formulation modulates disease after influenza virus infection in quadrivalent influenza vaccine vaccinated mice

There are considerable avenues through which currently licensed influenza vaccines could be optimized. We tested influenza vaccination in a mouse model with two adjuvants: Sendai virus-derived defective interfering (SDI) RNA, a RIG-I agonist; and an amphiphilic imidazoquinoline (IMDQ-PEG-Chol), a TLR7/8 agonist. The negatively charged SDI RNA was formulated into lipid nanoparticles (LNPs) facilitating direct delivery of SDI RNA to the cytosol, where RIG-I sensing induces inflammatory and type I interferon responses. We previously tested SDI RNA and IMDQ-PEG-Chol as standalone and combination adjuvants for influenza and SARS-CoV-2 vaccines. Here, we tested two different ionizable lipids, K-Ac7-Dsa and S-Ac7-Dog, for LNP formulations. The LNPs were incorporated with SDI RNA to determine its potential as a combination adjuvant with IMDQ-PEG-Chol by evaluating the host immune response to vaccination and infection in immunized BALB/c mice. Adjuvanticity of IMDQ-PEG-Chol with and without empty or SDI-loaded LNPs was validated with quadrivalent inactivated influenza vaccine (QIV), showing robust induction of antibody titers and T-cell responses. Depending on the adjuvant combination and LNP formulation, humoral and cellular vaccine responses could be tailored towards type 1 or type 2 host responses with specific cytokine profiles that correlated with the protective responses to viral infection. The extent of protection conferred by different vaccine/LNP/adjuvant combinations was tested by challenging mice with a vaccine-matched strain of influenza A virus A/Singapore/gp1908/2015 IVR-180 (H1N1). Groups that received either LNP formulated with SDI or IMDQ-PEG-Chol, or both, showed very low levels of viral replication in their lungs at 5 days post-infection (DPI). These studies provide evidence that the combination of vaccines with LNPs and/or adjuvants promote antigen-specific cellular responses that can contribute to protection upon infection. Interestingly, we observed differences in humoral and cellular responses to vaccination between different groups receiving K-Ac7-Dsa or S-Ac7-Dog lipids in LNP formulations. The differences were also reflected in inflammatory responses in lungs of vaccinated animals to infection, depending on LNP formulations. Therefore, this study suggests that the composition of the LNPs, particularly the ionizable lipid, plays an important role in inducing inflammatory responses in vivo, which is important for vaccine safety and to prevent adverse effects upon viral exposure.

Influenza virus antibodies inhibit antigen-specific de novo B cell responses in mice

Antibody responses to influenza vaccines tend to be focused on epitopes encountered during prior influenza exposures, with little production of de novo responses to novel epitopes. To examine the contribution of circulating antibody to this phenomenon, we passively transferred a hemagglutinin (HA)-specific monoclonal antibody (mAb) into mice before immunizing with whole inactivated virions. The HA mAb inhibited de novo HA-specific antibodies, plasmablasts, germinal center B cells, and memory B cells, while responses to a second antigen in the vaccine, neuraminidase (NA), were uninhibited. The HA mAb potently inhibited de novo antibody responses against epitopes near the HA mAb binding site. The HA mAb also promoted IgG1 class switching, an effect that, unlike the inhibition of HA responses, relied on signaling through Fc-gamma receptors. These studies suggest that circulating antibodies inhibit de novo B cell responses in an antigen-specific manner, which likely contributes to differences in antibody specificities elicited during primary and secondary influenza virus exposures.

Assessment of the immune interference effects of multivalent vaccine for influenza epidemic strain in 2022-2023 and evaluation of its efficacy

The various strains of influenza virus cause respiratory symptoms in humans every year and annual vaccinations are recommended. Due to its RNA-type genes and segmented state, it belongs to a virus that mutates frequently with antigenic drift and shift, giving rise to various strains. Each year, the World Health Organization identifies the epidemic strains and operates a global surveillance system to suggest the viral composition for the influenza vaccine. Influenza viruses, which have multiple viral strains, are produced in the format of multivalent vaccine. However, the multivalent vaccine has a possibility of causing immune interference by introducing multiple strain-specific antigens in a single injection. Therefore, evaluating immune interference phenomena is essential when assessing multivalent vaccines. In this study, the protective ability and immunogenicity of multivalent and monovalent vaccines were evaluated in mice to assess immune interference in the multivalent vaccine. Monovalent and multivalent vaccines were manufactured using the latest strain of the 2022-2023 seasonal influenza virus selected by the World Health Organization. The protective abilities of both types of vaccines were tested through hemagglutination inhibition test. The immunogenicity of multivalent and monovalent vaccines were tested through enzyme-linked immunosorbent assay to measure the cellular and humoral immunity expression rates. As a result of the protective ability and immunogenicity test, higher level of virus neutralizing ability and greater amount of antibodies in both IgG1 and IgG2 were confirmed in the multivalent vaccine. No immune interference was found to affect the protective capacity and immune responses of the multivalent vaccines.

Lipid nanoparticle composition for adjuvant formulation modulates disease after influenza virus infection in QIV vaccinated mice

Adjuvants can enhance vaccine effectiveness of currently licensed influenza vaccines. We tested influenza vaccination in a mouse model with two adjuvants: Sendai virus derived defective interfering (SDI) RNA, a RIG-I agonist, and an amphiphilic imidazoquinoline (IMDQ-PEG-Chol), TLR7/8 adjuvant. The negatively charged SDI RNA was formulated into lipid nanoparticles (LNPs) facilitating the direct delivery of a RIG-I agonist to the cytosol. We have previously tested SDI and IMDQ-PEG-Chol as standalone and combination adjuvants for influenza and SARS-CoV-2 vaccines. Here we tested two different ionizable lipids, K-Ac7-Dsa and S-Ac7-Dog, for LNP formulations. The adjuvanticity of IMDQ-PEG-Chol with and without empty or SDI-loaded LNPs was validated in a licensed vaccine setting (quadrivalent influenza vaccine or QIV) against H1N1 influenza virus, showing robust induction of antibody titres and T cell responses. Depending on the adjuvant combination and LNP lipid composition (K-Ac7-Dsa or S-Ac7-Dog lipids), humoral and cellular vaccine responses could be tailored towards type 1 or type 2 host responses with specific cytokine profiles that correlated with protection during viral infection. The extent of protection conferred by different vaccine/LNP/adjuvant combinations was examined against challenge with the vaccine-matching strain of H1N1 influenza A virus. Groups that received either LNP formulated with SDI, IMDQ-PEG-Chol or both showed very low levels of viral replication in their lungs at five days post virus infection. LNP ionizable lipid composition as well as loading (empty versus SDI) also skewed host responses to infection, as reflected in the cytokine and chemokine levels in lungs of vaccinated animals upon infection. These studies show the potential of LNPs as adjuvant delivery vehicles for licensed vaccines and illustrate the importance of LNP composition for subsequent host responses to infection, an important point of consideration for vaccine safety.

Prolonging the delivery of influenza virus vaccine improves the quantity and quality of the induced immune responses in mice

Introduction

Influenza vaccines play a vital role in protecting individuals from influenza virus infection and severe illness. However, current influenza vaccines have suboptimal efficacy, which is further reduced in cases where the vaccine strains do not match the circulating strains. One strategy to enhance the efficacy of influenza vaccines is by extended antigen delivery, thereby mimicking the antigen kinetics of a natural infection. Prolonging antigen availability was shown to quantitatively enhance influenza virus-specific immune responses but how it affects the quality of the induced immune response is unknown. Therefore, the current study aimed to investigate whether prolongation of the delivery of influenza vaccine improves the quality of the induced immune responses over that induced by prime-boost immunization.

Methods

Mice were given daily doses of whole inactivated influenza virus vaccine for periods of 14, 21, or 28 days; the control group received prime-boost immunization with a 28 days interval.

Results

Our data show that the highest levels of cellular and humoral immune responses were induced by 28 days of extended antigen delivery, followed by 21, and 14 days of delivery, and prime-boost immunization. Moreover, prolonging vaccine delivery also improved the quality of the induced antibody response, as indicated by higher level of high avidity antibodies, a balanced IgG subclass profile, and a higher level of cross-reactive antibodies.

Conclusions

Our findings contribute to a better understanding of the immune response to influenza vaccination and have important implications for the design and development of future slow-release influenza vaccines.

RIG-I and TLR-7/8 agonists as combination adjuvant shapes unique antibody and cellular vaccine responses to seasonal influenza vaccine

Influenza vaccine effectiveness could be improved by combination with an adjuvant with the potential to enhance the host-vaccine response both quantitatively and qualitatively. The goal of this study was to explore a RIG-I agonist (SDI-nanogel) and a TLR7/8 agonist (Imidazoquinoline (IMDQ)-PEG-Chol) as adjuvants, when co-administered with a licensed quadrivalent inactivated influenza vaccine (QIV), and to determine the role of these adjuvants in directing helper T (Th) cell responses for their role in the immunoglobulin (Ig) class switching. Administration of QIV with the two adjuvants, individually or combined, resulted in enhanced HA-specific serum ELISA IgG titers, serum hemagglutination inhibition (HAI) titers and splenic T cell responses as examined by IFN-γ and IL-4 enzyme-linked immunosorbent spot (ELISPOT) assays, 4-weeks post-prime and post-boost vaccination in BALB/c mice. While QIV+SDI-nanogel largely induced antigen-specific IgG1 responses, QIV+IMDQ-PEG-Chol predominantly induced IgG2a antibody isotypes post-prime vaccination, suggesting efficient induction of Th2 (IL-4) and Th1 (IFN-γ) responses, respectively. Combination of the two adjuvants not only skewed the response completely towards IgG2a, but also resulted in induction of HAI titers that outperformed groups that received single adjuvant. Moreover, enhanced IgG2a titers correlate with antibody-mediated cellular cytotoxicity (ADCC) that targets both the highly conserved H1 hemagglutination (HA) stalk domain and N1 neuraminidase (NA). A booster vaccination with QIV+IMDQ-PEG-Chol resulted in a more balanced IgG1/IgG2a response in animals primed with QIV+IMDQ-PEG-Chol but increased only IgG2a titers in animals that received the combination adjuvant during prime vaccination, suggesting that class switching events in germinal centers during the prime vaccination contribute to the outcome of booster vaccination. Importantly, IMDQ-PEG-Chol, alone or in combination, always outperformed the oil-in-water control adjuvant Addavax. Vaccine-induced antibody and T cell responses correlated with protection against lethal influenza virus infection. This study details the benefit of adjuvants that target multiple innate immune receptors to shape the host vaccine response.

Characterization and Immunogenicity of Influenza H7N9 Vaccine Antigens Produced Using a Serum-Free Suspension MDCK Cell-Based Platform

Human infections with avian-origin H7N9 influenza A viruses were first reported in China, and an approximately 38% human mortality rate was described across six waves from February 2013 to September 2018. Vaccination is one of the most cost-effective ways to reduce morbidity and mortality during influenza epidemics and pandemics. Egg-based platforms for the production of influenza vaccines are labor-intensive and unable to meet the surging demand during pandemics. Therefore, cell culture-based technology is becoming the alternative strategy for producing influenza vaccines. The current influenza H7N9 vaccine virus (NIBRG-268), a reassortant virus from A/Anhui/1/2013 (H7N9) and egg-adapted A/PR/8/34 (H1N1) viruses, could grow efficiently in embryonated eggs but not mammalian cells. Moreover, a freezing-dry formulation of influenza H7N9 vaccines with long-term stability will be desirable for pandemic preparedness, as the occurrence of influenza H7N9 pandemics is not predictable. In this study, we adapted a serum-free anchorage-independent suspension Madin-Darby Canine Kidney (MDCK) cell line for producing influenza H7N9 vaccines and compared the biochemical characteristics and immunogenicity of three influenza H7N9 vaccine antigens produced using the suspension MDCK cell-based platform without freeze-drying (S-WO-H7N9), the suspension MDCK cell-based platform with freeze-drying (S-W-H7N9) or the egg-based platform with freeze-drying (E-W-H7N9). We demonstrated these three vaccine antigens have comparable biochemical characteristics. In addition, these three vaccine antigens induced robust and comparable neutralizing antibody (NT; geometric mean between 1016 and 4064) and hemagglutinin-inhibition antibody (HI; geometric mean between 640 and 1613) titers in mice. In conclusion, the serum-free suspension MDCK cell-derived freeze-dried influenza H7N9 vaccine is highly immunogenic in mice, and clinical development is warranted.

Magnitude and breadth of antibody cross-reactivity induced by recombinant influenza hemagglutinin trimer vaccine is enhanced by combination adjuvants

The effects of adjuvants for increasing the immunogenicity of influenza vaccines are well known. However, the effect of adjuvants on increasing the breadth of cross-reactivity is less well understood. In this study we have performed a systematic screen of different toll-like receptor (TLR) agonists, with and without a squalene-in-water emulsion on the immunogenicity of a recombinant trimerized hemagglutinin (HA) vaccine in mice after single-dose administration. Antibody (Ab) cross-reactivity for other variants within and outside the immunizing subtype (homosubtypic and heterosubtypic cross-reactivity, respectively) was assessed using a protein microarray approach. Most adjuvants induced broad IgG profiles, although the response to a combination of CpG, MPLA and AddaVax (termed 'IVAX-1') appeared more quickly and reached a greater magnitude than the other formulations tested. Antigen-specific plasma cell labeling experiments show the components of IVAX-1 are synergistic. This adjuvant preferentially stimulates CD4 T cells to produce Th1>Th2 type (IgG2c>IgG1) antibodies and cytokine responses. Moreover, IVAX-1 induces identical homo- and heterosubtypic IgG and IgA cross-reactivity profiles when administered intranasally. Consistent with these observations, a single-cell transcriptomics analysis demonstrated significant increases in expression of IgG1, IgG2b and IgG2c genes of B cells in H5/IVAX-1 immunized mice relative to naïve mice, as well as significant increases in expression of the IFNγ gene of both CD4 and CD8 T cells. These data support the use of adjuvants for enhancing the breath and durability of antibody responses of influenza virus vaccines.

A Glycolipid α-GalCer Derivative, 7DW8-5 as a Novel Mucosal Adjuvant for the Split Inactivated Influenza Vaccine

Influenza virus infects the host and transmits through the respiratory tract (i.e., the mouth and nose); therefore, the development of intranasal influenza vaccines that mimic the natural infection, coupled with an efficient mucosal adjuvant, is an attractive alternative to current parenteral vaccines. However, with the withdrawal of cholera toxin and Escherichia coli heat-labile endotoxin from clinical use due to side effects, there are no approved adjuvants for intranasal vaccines. Therefore, safe and effective mucosal adjuvants are urgently needed. Previously, we reported that one derivative of α-Galactosylceramide (α-GalCer), 7DW8-5, could enhance the protective efficacy of split influenza vaccine by injection administration. However, the mucosal adjuvanticity of 7DW8-5 is still unclear. In this study, we found that 7DW8-5 promotes the production of secret IgA antibodies and IgG antibodies and enhances the protective efficacy of the split influenza vaccine by intranasal administration. Furthermore, co-administration of 7DW8-5 with the split influenza vaccine significantly reduces the virus shedding in the upper and lower respiratory tract after lethal challenge. Our results demonstrate that 7DW8-5 is a novel mucosal adjuvant for the split influenza vaccine.

Immunogenicity Studies of Plant-Produced SARS-CoV-2 Receptor Binding Domain-Based Subunit Vaccine Candidate with Different Adjuvant Formulations

Due to the rapid transmission of the coronavirus disease 2019 (COVID-19) causing serious public health problems and economic burden, the development of effective vaccines is a high priority for controlling the virus spread. Our group has previously demonstrated that the plant-produced receptor-binding domain (RBD) of SARS-CoV-2 fused with Fc of human IgG was capable of eliciting potent neutralizing antibody and cellular immune responses in animal studies, and the immunogenicity could be improved by the addition of an alum adjuvant. Here, we performed a head-to-head comparison of different commercially available adjuvants, including aluminum hydroxide gel (alum), AddaVax (MF59), monophosphoryl lipid A from Salmonella minnesota R595 (mPLA-SM), and polyinosinic-polycytidylic acid (poly(I:C)), in mice by combining them with plant-produced RBD-Fc, and the differences in the immunogenicity of RBD-Fc with different adjuvants were evaluated. The specific antibody responses in terms of total IgG, IgG1, and IgG2a subtypes and neutralizing antibodies, as well as vaccine-specific T-lymphocyte responses, induced by the different tested adjuvants were compared. We observed that all adjuvants tested here induced a high level of total IgG and neutralizing antibodies, but mPLA-SM and poly (I:C) showed the induction of a balanced IgG1 and IgG2a (Th2/Th1) immune response. Further, poly (I:C) significantly increased the frequency of IFN-γ-expressing cells compared with control, whereas no significant difference was observed between the adjuvanted groups. This data revealed the adjuvants' role in enhancing the immune response of RBD-Fc vaccination and the immune profiles elicited by different adjuvants, which could prove helpful for the rational development of next-generation SARS-CoV-2 RBD-Fc subunit vaccines. However, additional research is essential to further investigate the efficacy and safety of this vaccine formulation before clinical trials.

Selecting and Using the Appropriate Influenza Vaccine for Each Individual

Despite seasonal influenza vaccines having been routinely used for many decades, influenza A virus continues to pose a global threat to humans, causing high morbidity and mortality each year. The effectiveness of the vaccine is largely dependent on how well matched the vaccine strains are with the circulating influenza virus strains. Furthermore, low vaccine efficacy in naïve populations such as young children, or in the elderly, who possess weakened immune systems, indicates that influenza vaccines need to be more personalized to provide broader community protection. Advances in both vaccine technologies and our understanding of influenza virus infection and immunity have led to the design of a variety of alternate vaccine strategies to extend population protection against influenza, some of which are now in use. In this review, we summarize the progress in the field of influenza vaccines, including the advantages and disadvantages of different strategies, and discuss future prospects. We also highlight some of the challenges to be faced in the ongoing effort to control influenza through vaccination.

Influence of adjuvants on the amount, specificity and functional activity of antibody response to human influenza vaccine in mice

It's been almost a century since immunologists started using adjuvants as tools to develop more effective vaccines. Despite the rising number of adjuvanted vaccines in the last decades, we still lack knowledge of the adjuvants' effects on antibody response. This study was aimed to test the effect of immunizing mice with the human Inactivated Influenza vaccine (IIV), either alone or combined with different widely used adjuvants on the specific antibody response induced. Differential levels of IgM and IgG subclasses were found with the different adjuvants tested. Higher levels of antibodies did not always correspond with a higher efficacy to interfere with the virus infectivity. Differences in neutralization properties are possibly mediated by the specificity of the repertoire of antibodies induced. The repertoire was studied using a phage display 7-mer peptide library to screen for epitopes/mimotopes recognized by serum pools from vaccinated mice. The selected phage clones included peptides that corresponded to conformational mimotopes since they have no homology with lineal sequences of the Influenza strains' proteins. Five peptides were identified as recognized by sera from mice immunized with the IIV vaccine alone, including peptides from the hemagglutinin stalk domain, and by sera from mice immunized with the vaccine plus the different adjuvants employed. Adjuvants elicited a more diverse repertoire of epitope-recognizing antibodies that recognized epitopes of the HA recombinant globular head. Mimotopes were theoretically located at the neutralizing antigenic sites of the globular head of Influenza A H1N1pdm09, Influenza A H3N2, and Influenza B hemagglutinin. This study illustrates how different adjuvants can modify the extent and quality of humoral immunity against the IIV vaccine and the effectiveness of vaccination.

Protective cellular and mucosal immune responses following nasal administration of a whole gamma-irradiated influenza A (subtype H1N1) vaccine adjuvanted with interleukin-28B in a mouse model

The use of gamma-irradiated influenza A virus (γ-Flu), retains most of the viral structural antigens, represent a promising option for vaccine development. However, despite the high effectiveness of γ-Flu vaccines, the need to incorporate an adjuvant to improve vaccine-mediated protection seems inevitable. Here, we examined the protective efficacy of an intranasal gamma-irradiated HIN1 vaccine co-administered with a plasmid encoding mouse interleukin-28B (mIL-28B) as a novel adjuvant in BALB/c mice. Animals were immunized intranasally three times at one-week intervals with γ-Flu, alone or in combination with the mIL-28B adjuvant, followed by viral challenge with a high lethal dose (10 LD₅₀) of A/PR/8/34 (H1N1) influenza virus. Virus-specific antibody, cellular and mucosal responses, and the balance of cytokines in the spleen IFN-γ, IL-12, and IL-4) and in lung homogenates (IL-6 and IL-10) were measured by ELISA. The lymphoproliferative activity of restimulated spleen cells was also determined by MTT assay. Furthermore, virus production in the lungs of infected mice was estimated using the Madin-Darby canine kidney (MDCK)/hemagglutination assay (HA). Our data showed that intranasal immunization with adjuvanted γ-Flu vaccine efficiently promoted humoral, cellular, and mucosal immune responses and efficiently decreased lung virus titers, all of which are associated with protection against challenge. This combination also reduced IL-6 and IL-10 levels in lung homogenates. The results suggest that IL-28B can enhance the ability of the vaccine to elicit virus-specific immune responses and could potentially be used as an effective adjuvant.

Comparative Immunological Study in Mice of Inactivated Influenza Vaccines Used in the Russian Immunization Program

A series of commercial inactivated influenza vaccines (IIVs) used in the Russian National Immunization Program were characterized to evaluate their protective properties on an animal model. Standard methods for quantifying immune response, such as hemagglutination inhibition (HAI) assay and virus neutralization (VN) assay, allowed us to distinguish the immunogenic effect of various IIVs from that of placebo. However, these standard approaches are not suitable to determine the role of various vaccine components in immune response maturation. The expanded methodological base including an enzyme-linked immunosorbent assay (ELISA) and a neuraminidase ELISA (NA-ELISA) helped us to get wider characteristics and identify the effectiveness of various commercial vaccines depending on the antigen content. Investigations conducted showed that among the IIVs tested, Ultrix^®, Ultrix^® Quadri and VAXIGRIP^® elicit the most balanced immune response, including a good NA response. For Ultrix^®, Ultrix^® Quadri, and SOVIGRIPP^® (FORT LLC), the whole-virus specific antibody subclass IgG1, measured in ELISA, seriously prevailed over IgG2a, while, for VAXIGRIP^® and SOVIGRIPP^® (NPO Microgen JSC) preparations, the calculated IgG1/IgG2a ratio was close to 1. So, the immune response varied drastically across different commercial IIVs injected in mice.

Immunogenicity and Toxicity of Different Adjuvants Can Be Characterized by Profiling Lung Biomarker Genes After Nasal Immunization

The efficacy of vaccine adjuvants depends on their ability to appropriately enhance the immunogenicity of vaccine antigens, which is often insufficient in non-adjuvanted vaccines. Genomic analyses of immune responses elicited by vaccine adjuvants provide information that is critical for the rational design of adjuvant vaccination strategies. In this study, biomarker genes from the genomic analyses of lungs after priming were used to predict the efficacy and toxicity of vaccine adjuvants. Based on the results, it was verified whether the efficacy and toxicity of the tested adjuvants could be predicted based on the biomarker gene profiles after priming. Various commercially available adjuvants were assessed by combining them with the split influenza vaccine and were subsequently administered in mice through nasal inoculation. The expression levels of lung biomarker genes within 24 h after priming were analyzed. Furthermore, we analyzed the antibody titer, cytotoxic T lymphocyte (CTL) induction, IgG1/IgG2a ratio, leukopenic toxicity, and cytotoxicity in mice vaccinated at similar doses. The association between the phenotypes and the changes in the expression levels of biomarker genes were analyzed. The ability of the adjuvants to induce the production of antigen-specific IgA could be assessed based on the levels of Timp1 expression. Furthermore, the expression of this gene partially correlated with the levels of other damage-associated molecular patterns in bronchoalveolar lavage fluid. Additionally, the changes in the expression of proteasome- and transporter-related genes involved in major histocompatibility complex class 1 antigen presentation could be monitored to effectively assess the expansion of CTL by adjuvants. The monitoring of certain genes is necessary for the assessment of leukopenic toxicity and cytotoxicity of the tested adjuvant. These results indicate that the efficacy and toxicity of various adjuvants can be characterized by profiling lung biomarker genes after the first instance of immunization. This approach could make a significant contribution to the development of optimal selection and exploratory screening strategies for novel adjuvants.

Safety and immunogenicity of an alum-adjuvanted whole-virion H7N9 influenza vaccine: a randomized, blinded, clinical trial

OBJECTIVES

A case of H7N9 influenza virus infection was first identified in China in 2013. This virus is considered to have high pandemic potential. Here we developed an H7N9 influenza vaccine containing an aluminium adjuvant and evaluated the safety and immunogenicity of the vaccine.

METHODS

From October 2017 through August 2018 we conducted a randomized, double-blinded, single-centre phase I clinical trial in China among 360 participants aged ≥12 years. All participants received two doses of the vaccine (7.5, 15 or 30 μg haemagglutinin antigen) or placebo at an interval of 21 days. Adverse event data were collected for 30 days after vaccination. Serum samples were collected on days 0, 21 and 42 for the haemagglutinin inhibition (HI) antibody assay.

RESULTS

A total of 347 participants (347/360, 96.4%) completed the study. The proportions of vaccine-related adverse events after one injection were 56.7% (34/60) in the 7.5-μg group, 86.7% (52/60) in the 15-μg group and 86.7% (52/60) in the 30-μg group. The proportions of adverse events after two injections were less than those reported after the first dose. None of the serious adverse events were related to the vaccine. After receiving two doses of the 7.5-μg vaccine, the proportion of participants achieving an HI titre of ≥40 was 98.2% (55/56, 95%CI 72.3~100.0%), with a geometric mean titre (GMT) of 192.6 (95%CI 162.9~227.8).

CONCLUSIONS

The alum-adjuvanted H7N9 whole-virion inactivated vaccine was safe and strongly immunogenic in a population aged ≥12 years.

Metformin-induced suppression of IFN-α via mTORC1 signalling following seasonal vaccination is associated with impaired antibody responses in type 2 diabetes

Diabetes mellitus (DM) patients are at an increased risk of complications following influenza-virus infection, seasonal vaccination (SV) is recommended. However, SV with trivalent influenza vaccine (TIV) can induce antibody and type-I interferon (IFN) responses, and the effect of anti-DM treatment on these responses is incompletely understood. We evaluated the antibody response and IFN-α expression in individuals with and without type 2 DM (T2DM) following SV, and examined the effects on anti-DM treatment. TIV elicited sero-protection in all groups, but antibody persistency was <8 months, except for the antibody response to B-antigens in non-DM. T2DM impaired the IgG avidity index, and T2DM showed a significantly decreased response against H1N1 and H3N2, in addition to delaying and reducing haemagglutination-inhibition persistency against influenza B-antigens in DM groups treated with metformin (Met-DM) or glibenclamide (GB-DM). Following TIV, the Met-DM and GB-DM groups exhibited reduced IFN-α expression upon stimulation with whole- and split-virion influenza vaccines. Suppression of IFN-α expression in the Met-DM group was associated with a reduction in the mechanistic target of rapamycin complex-1 pathway and impaired IgG avidity index. Thus, single-dose TIV each year might not be suitable for T2DM. Our data could aid the development of an efficacious influenza vaccine for T2DM.

Outer membrane vesicle increases the efficacy of an influenza vaccine in a diet-induced obese mouse model

Obesity has been associated with increased symptoms and mortality in influenza patients and impaired immune responses to the influenza vaccine. To date, however, there is no effective adjuvant to improve vaccine efficacy for the obese population. To address this issue, we generated a modified outer membrane vesicle with attenuated endotoxicity (fmOMV) and tested its adjuvant effect on the influenza vaccine in comparison with a squalene-based oil-in-water adjuvant (AddaVax) using a diet-induced obese (DIO) mouse model. Although coadministration of fmOMV did not affect neutralizing antibody (Ab) response, it preferentially induced IgG2c antibody response and significantly increased the vaccine-induced T cell response. More importantly, fmOMV conferred significant protection against homologous and heterologous influenza virus challenge, whereas AddaVax showed marginal protection irrespective of the strongest Ab and T cell responses in DIO mice. These results indicate that fmOMV improves the antigen-specific T cell response and the efficacy of an influenza vaccine, suggesting a potential influenza vaccine adjuvant for the obese population.

Cross-Protective Potential and Protection-Relevant Immune Mechanisms of Whole Inactivated Influenza Virus Vaccines Are Determined by Adjuvants and Route of Immunization

Adjuvanted whole inactivated virus (WIV) influenza vaccines show promise as broadly protective influenza vaccine candidates. Using WIV as basis we assessed the relative efficacy of different adjuvants by carrying out a head-to-head comparison of the liposome-based adjuvants CAF01 and CAF09 and the protein-based adjuvants CTA1-DD and CTA1-3M2e-DD and evaluated whether one or more of the adjuvants could induce broadly protective immunity. Mice were immunized with WIV prepared from A/Puerto Rico/8/34 (H1N1) virus intramuscularly with or without CAF01 or intranasally with or without CAF09, CTA1-DD, or CTA1-3M2e-DD, followed by challenge with homologous, heterologous or heterosubtypic virus. In general, intranasal immunizations were significantly more effective than intramuscular immunizations in inducing virus-specific serum-IgG, mucosal-IgA, and splenic IFNγ-producing CD4 T cells. Intranasal immunizations with adjuvanted vaccines afforded strong cross-protection with milder clinical symptoms and better control of virus load in lungs. Mechanistic studies indicated that non-neutralizing IgG antibodies and CD4 T cells were responsible for the improved cross-protection while IgA antibodies were dispensable. The role of CD4 T cells was particularly pronounced for CTA1-3M2e-DD adjuvanted vaccine as evidenced by CD4 T cell-dependent reduction of lung virus titers and clinical symptoms. Thus, intranasally administered WIV in combination with effective mucosal adjuvants appears to be a promising broadly protective influenza vaccine candidate.

Inactivated or damaged? Comparing the effect of inactivation methods on influenza virions to optimize vaccine production

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β-propiolactone (BPL) and formaldehyde (FA) were used to inactivate several influenza virus strains.

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BPL abolished the infectivity, FA was unable to completely inactivate the virus.

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All methods damaged the binding and fusion capacity; BPL caused greater loss than FA.

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FA treatments caused the highest reduction in TLR-7 stimulation.

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All the observed effects were strain-dependent.

The vast majority of commercially available inactivated influenza vaccines are produced from egg-grown or cell-grown live influenza virus. The first step in the production process is virus inactivation with β-propiolactone (BPL) or formaldehyde (FA). Recommendations for production of inactivated vaccines merely define the maximal concentration for both reagents, leaving the optimization of the process to the manufacturers. We assessed the effect of inactivation with BPL and FA on 5 different influenza virus strains. The properties of the viral formulation, such as successful inactivation, preservation of hemagglutinin (HA) binding ability, fusion capacity and the potential to stimulate a Toll-like receptor 7 (TLR7) reporter cell line were then assessed and compared to the properties of the untreated virus. Inactivation with BPL resulted in undetectable infectivity levels, while FA-treated virus retained very low infectious titers. Hemagglutination and fusion ability were highly affected by those treatments that conferred higher inactivation, with BPL-treated virus binding and fusing at a lower degree compared to FA-inactivated samples. On the other hand, BPL-inactivated virus induced higher levels of activation of TLR7 than FA-inactivated virus. The alterations caused by BPL or FA treatments were virus strain dependent. This data shows that the inactivation procedures should be tailored on the virus strain, and that many other elements beside the concentration of the inactivating agent, such as incubation time and temperature, buffer and virus concentration, have to be defined to achieve a functional product.

Development of a novel oil-in-water emulsion and evaluation of its potential adjuvant function in a swine influenza vaccine in mice

Background

Vaccination is the principal strategy for prevention and control of diseases, and adjuvant use is an effective strategy to enhance vaccine efficacy. Traditional mineral oil-based adjuvants have been reported with post-immunization reactions. Developing new adjuvant formulations with improved potency and safety will be of great value.

Results

In the study reported herein, a novel oil-in-water (O/W) Emulsion Adjuvant containing Squalane (termed EAS) was developed, characterized and investigated for swine influenza virus immunization. The data show that EAS is a homogeneous nanoemulsion with small particle size (~ 105 nm), low viscosity (2.04 ± 0.24 cP at 20 °C), excellent stability (at least 24 months at 4 °C) and low toxicity. EAS-adjuvanted H3N2 swine influenza vaccine was administrated in mice subcutaneously to assess the adjuvant potency of EAS. The results demonstrated that in mice EAS-adjuvanted vaccine induced significantly higher titers of hemagglutination inhibition (HI) and IgG antibodies than water-in-oil (W/O) vaccines or antigen alone, respectively, at day 42 post vaccination (dpv) (P < 0.05). EAS-adjuvanted vaccine elicited significantly stronger IgG1 and IgG2a antibodies and higher concentrations of Th1 (IFN-γ and IL-2) cytokines compared to the W/O vaccine or antigen alone. Mice immunized with EAS-adjuvanted influenza vaccine conferred potent protection after homologous challenge.

Conclusion

The O/W emulsion EAS developed in the present work induced potent humoral and cellular immune responses against inactivated swine influenza virus, conferred effective protection after homologous virus challenge and showed low toxicity in mice, indicating that EAS is as good as the commercial adjuvant MF59. The superiority of EAS to the conventional W/O formulation in adjuvant activity, safety and stability will make it a potential veterinary adjuvant.

Co-stimulation With TLR7 Agonist Imiquimod and Inactivated Influenza Virus Particles Promotes Mouse B Cell Activation, Differentiation, and Accelerated Antigen Specific Antibody Production

Current influenza vaccines have relatively low effectiveness, especially against antigenically drifted strains, the effectiveness is even lower in the elderly and immunosuppressed individuals. We have previously shown in a randomized clinical trial that the topical application of a toll-like receptor 7 agonist, imiquimod, just before intradermal influenza vaccine could expedite and augment antibody response, including to antigenically-drifted strains. However, the mechanism of this vaccine and imiquimod combination approach is poorly understood. Here, we demonstrated that imiquimod alone directly activated purified mouse peritoneal B cells. When combined with inactivated H1N1/415742Md influenza virus particle (VP) as vaccine, co-stimulation of mouse peritoneal B cells in vitro induced stronger activation, proliferation, and production of virus-antigen specific IgM and IgG. Intraperitoneal injection of a combination of VP and imiquimod (VCI) was associated with an increased number of activated B cells with enhanced expression of CD86 in the mesenteric draining lymph nodes (mesLN) and the spleen at 18 h after injection. Three days after immunization with VCI, mouse spleen showed significantly more IgM and IgG secreting cells upon in vitro re-stimulation with inactivated virus, mouse sera were detected with viral neutralizing antibody. Transfer of these spleen B cells to naïve mice improved survival after lethal dose of H1N1/415742Md challenge. More importantly, the functional response of VCI-induced B cell activation was demonstrated by early challenge with a lethal dose of H1N1/415742Md influenza virus at 3 days after immunization. The spleen and mediastinal lymph nodes (mdLN) in mice immunized with VCI had germinal center formation, and significantly higher number of plasmablasts, plasma cells, and virus-antigen specific IgM and IgG secreting cells at only 3–4 days post virus challenge, compared with those of mice that have received imiquimod, inactivated virus alone or PBS. Serum virus-specific IgG2a, IgG2b, and IgG1 and bronchoalveolar lavage fluid (BALF) virus-specific IgA at 3 or 4 days post challenge were significantly higher in mice immunized with VCI, which had significantly reduced lung viral load and 100% survival. These findings suggested that imiquimod accelerates the vaccine-induced antibody production via inducing rapid differentiation of naïve B cells into antigen-specific antibody producing cells.

Sex bias in mouse humoral immune response to influenza vaccine depends on the vaccine type

The study explored influence of biological sex on development of humoral immune response to seasonal trivalent whole inactivated virus (WIV) and split virus (SV) influenza vaccines in outbred Swiss mouse model. To this end, mice of both sexes were immunized with WIV (WIV mice) and SV vaccines (SV mice) and examined for specific antibody response. Irrespective of sex, total IgG and neutralizing antibody responses to distinct virus strains were weaker in SV than in WIV mice. In WIV mice of both sexes, irrespective of strain specificity, IgG isotype response was dominated by IgG2a antibodies, while in SV mice nearly equal representation of IgG2a and IgG1 antibodies was found. The analyses of sex differences showed higher titers of H1N1-specific and both H1N1- and H3N2-specific total IgG and neutralizing antibodies in female WIV and SV mice, respectively. Additionally, sexual dimorphism in IgG subclass profile depended on vaccine type. Specifically, compared with males, in females WIV shifted IgG2a/IgG1 antibody ratio towards IgG2a isotype on the account of weaker IgG1 response, whereas in SV mice, irrespective of virus strain, IgG2a and IgG1 isotypes were equally represented in both sexes. These findings indicate the vaccine type-dependent sex bias in antibody response to inactivated influenza vaccines.

Opinion: Making Inactivated and Subunit-Based Vaccines Work

Empirically derived vaccines have in the past relied on the isolation and growth of disease-causing microorganisms that are then inactivated or attenuated before being administered. This is often done without prior knowledge of the mechanisms involved in conferring protective immunity. Recent advances in scientific technologies and in our knowledge of how protective immune responses are induced enable us to rationally design novel and safer vaccination strategies. Such advances have accelerated the development of inactivated whole-organism- and subunit-based vaccines. In this review, we discuss ideal attributes and criteria that need to be considered for the development of vaccines and some existing vaccine platforms. We focus on inactivated vaccines against influenza virus and ways by which vaccine efficacy can be improved with the use of adjuvants and Toll-like receptor-2 signaling.

Calcium phosphate nanoparticle (CaPNP) for dose-sparing of inactivated whole virus pandemic influenza A (H1N1) 2009 vaccine in mice

The emergence of pandemic influenza strains, particularly the reemergence of the swine-derived influenza A (H1N1) in 2009, is reaffirmation that influenza viruses are very adaptable and influenza remains as a significant global public health treat. As recommended by the World Health Organization (WHO), the use of adjuvants is an attractive approach to improve vaccine efficacy and allow dose-sparing during an influenza emergency. In this study, we utilized CaPtivate Pharmaceutical's proprietary calcium phosphate nanoparticles (CaPNP) vaccine adjuvant and delivery platform to formulate an inactivated whole virus influenza A/CA/04/2009 (H1N1pdm) vaccine as a potential dose-sparing strategy. We evaluated the relative immunogenicity and the efficacy of the formulation in BALB/c mice following single intramuscularly administration of three different doses (0.3, 1, or 3µg based on HA content) of the vaccine in comparison to non-adjuvanted or alum-adjuvant vaccines. We showed that, addition of CaPNP in vaccine elicited significantly higher hemagglutination inhibition (HAI), virus neutralization (VN), and IgG antibody titers, at all dose levels, relative to the non-adjuvanted vaccine. In addition, the vaccine containing CaPNP provided equal protection with 1/3rd of the antigen dose as compared to the non-adjuvanted or alum-adjuvanted vaccines. Our data provided support to earlier studies indicating that CaPNP is an attractive vaccine adjuvant and delivery system and should play an important role in the development of safe and efficacious dose-sparing vaccines. Our findings also warrant further investigation to validate CaPNP's capacity as an alternative adjuvant to the ones currently licensed for influenza/pandemic influenza vaccination.

Inactivated influenza virus vaccines: the future of TIV and QIV

Influenza viruses continue to be a major public health concern, despite the availability of vaccines. Currently licensed influenza vaccines aim at the induction of antibodies that target hemagglutinin, the major antigenic determinant on the surface of influenza virions that is responsible for attachment of the virus to the host cell that is to be infected. Currently licensed influenza vaccines come as inactivated or live attenuated influenza vaccines and are trivalent or quadrivalent as they contain antigens of two influenza A and one or two influenza B strains that circulate in the human population, respectively. In this review we briefly compare trivalent and quadrivalent inactivated influenza vaccines (TIV and QIV) with live attenuated influenza vaccines (LAIV). The use of the latter vaccine type in children age 2-8 has been disrecommended recently by the American Centers for Disease Control and Prevention due to inferior vaccine effectiveness in this age group in recent seasons. This recommendation will favor the use of TIV and QIV over LAIV in the near future. However, there is much evidence from studies in humans that illustrate the benefit of LAIV and we discuss some of the mechanisms that contribute to broader protection against influenza viruses of different subtypes induced by natural infection and LAIV. The future challenge will be to apply these insights to allow induction of broader and long-lasting protection provided by TIV and QIV vaccines, for example, by the use of adjuvants or combining LAIV with TIV and QIV. Other immune factors than serum hemagglutination inhibiting antibodies have shown to correlate with protection provided by TIV and QIV, which illustrates the need for other correlates of protection than hemagglutination inhibition by serum antibodies and justifies more focus on influenza antigens in the TIV and QIV other than hemagglutinin.

Potency of whole virus particle and split virion vaccines using dissolving microneedle against challenges of H1N1 and H5N1 influenza viruses in mice

Transdermal vaccination using a microneedle (MN) confers enhanced immunity compared with subcutaneous (SC) vaccination. Here we developed a novel dissolving MN patch for the influenza vaccine. The potencies of split virion and whole virus particle (WVP) vaccines prepared from A/Puerto Rico/8/1934 (H1N1) and A/duck/Hokkaido/Vac-3/2007 (H5N1), respectively, were evaluated. MN vaccination induced higher neutralizing antibody responses than SC vaccination in mice. Moreover, MN vaccination with a lower dose of antigens conferred protective immunity against lethal challenges of influenza viruses than SC vaccination in mice. These results suggest that the WVP vaccines administered using MN are an effective combination for influenza vaccine to be further validated in humans.

A Rapid-Response Humoral Vaccine Platform Exploiting Pre-Existing Non-Cognate Populations of Anti-Vaccine or Anti-Viral CD4+ T Helper Cells to Confirm B Cell Activation

The need for CD4+ T cell responses to arise de novo following vaccination can limit the speed of B cell responses. Populations of pre-existing vaccine-induced or anti-viral CD4+ T cells recognising distinct antigens could be exploited to overcome this limitation. We hypothesise that liposomal vaccine particles encapsulating epitopes that are recognised, after processing and B cell MHCII presentation, by pre-existing CD4+ T cells will exploit this pre-existing T cell help and result in improved antibody responses to distinct target antigens displayed on the particle surface. Liposomal vaccine particles were engineered to display the malaria circumsporozoite (CSP) antigen on their surface, with helper CD4+ epitopes from distinct vaccine or viral antigens contained within the particle core, ensuring the B cell response is raised but focused against CSP. In vivo vaccination studies were then conducted in C57Bl/6 mice as models of either vaccine-induced pre-existing CD4+ T cell immunity (using ovalbumin-OVA) or virus-induced pre-existing CD4+ T cell immunity (murine cytomegalovirus-MCMV). Following the establishment of pre-existing by vaccination (OVA in the adjuvant TiterMax® Gold) or infection with MCMV, mice were administered CSP-coated liposomal vaccines containing the relevant OVA or MCMV core CD4+ T cell epitopes. In mice with pre-existing anti-OVA CD4+ T cell immunity, these vaccine particles elicited rapid, high-titre, isotype-switched CSP-specific antibody responses-consistent with the involvement of anti-OVA T helper cells in confirming activation of anti-CSP B cells. Responses were further improved by entrapping TLR9 agonists, combining humoral vaccination signals 'one', 'two' and 'three' within one particle. Herpes viruses can establish chronic infection and elicit significant, persistent cellular immune responses. We then demonstrate that this principle can be extended to re-purpose pre-existing anti-MCMV immunity to enhance anti-CSP vaccine responses-the first description of a strategy to specifically exploit anti-cytomegalovirus immunity to augment vaccination against a target antigen.

Editor's Highlight: Subvisible Aggregates of Immunogenic Proteins Promote a Th1-Type Response

Protein aggregation is associated with enhanced immunogenicity of biotherapeutics. As a result, regulatory guidelines recommend screening for aggregation during bioprocessing. However, the mechanisms underlying the enhanced immunogenicity of aggregates are poorly understood. In the investigations described herein, the immunogenicity in mice of a humanized single chain variable antibody fragment (scFv) purified after expression in Escherichia coli has been examined. Reproducible scFv aggregates were obtained within the subvisible particle size range (mean diameter 2 µm) using thermal and mechanical stresses. Intraperitoneal immunization of BALB/c strain mice with 1 mg/ml of aggregated or monomeric scFv induced similar IgG and IgG1 antibody responses. In contrast, aggregate preparations stimulated significantly higher levels of anti-scFv IgG2a antibody than did the monomer. In comparative studies, aggregates of ovalbumin (OVA) within the subvisible particle size range were prepared by stir stress, and their immunogenicity compared with that of monomeric OVA in mice. Aggregated and monomeric OVA induced similar anti-OVA IgG and IgG1 antibody responses, whereas IgG2a antibody levels were significantly higher in aggregate-immunized mice. Furthermore, cytokine profiles in supernatants taken from splenocyte-dendritic cell co-cultures were consistent with aggregated preparations inducing a T helper (Th) 1-type response. Aggregated proteins within the subvisible range were therefore shown to induce a preferential Th1 type response, whereas monomeric proteins elicited a selective Th2 response. These data indicate that protein aggregation can impact on both the vigor and quality of immune responses.

Masking of antigenic epitopes by antibodies shapes the humoral immune response to influenza

The immune responses to influenza, a virus that exhibits strain variation, show complex dynamics where prior immunity shapes the response to the subsequent infecting strains. Original antigenic sin (OAS) describes the observation that antibodies to the first encountered influenza strain, specifically antibodies to the epitopes on the head of influenza's main surface glycoprotein, haemagglutinin (HA), dominate following infection with new drifted strains. OAS suggests that responses to the original strain are preferentially boosted. Recent studies also show limited boosting of the antibodies to conserved epitopes on the stem of HA, which are attractive targets for a 'universal vaccine'. We develop multi-epitope models to explore how pre-existing immunity modulates the immune response to new strains following immunization. Our models suggest that the masking of antigenic epitopes by antibodies may play an important role in describing the complex dynamics of OAS and limited boosting of antibodies to the stem of HA. Analysis of recently published data confirms model predictions for how pre-existing antibodies to an epitope on HA decrease the magnitude of boosting of the antibody response to this epitope following immunization. We explore strategies for boosting of antibodies to conserved epitopes and generating broadly protective immunity to multiple strains.

Whole-Virion Influenza Vaccine Recalls an Early Burst of High-Affinity Memory B Cell Response through TLR Signaling

Inactivated influenza vaccines have two formulations, whole- and split-virion types; however, how differential formulations impact their booster effects remain unknown. In this study, we demonstrate that whole-virion vaccines recall two waves of Ab responses, early T cell-independent (TI) and late T cell-dependent responses, whereas split-virion vaccines elicit the late T cell-dependent response only. Notably, higher-affinity Abs with improved neutralizing activity are provided from the early TI response, which emphasizes the important contribution of the formulation-dependent response in the protective immunity. Moreover, we show that the early TI response completely requires B cell-intrinsic TLR7 signaling, which can be delivered through viral RNAs within whole-virion vaccine. Thus, our results indicate that TLR agonists in whole-virion type improve recall Ab responses by directly targeting memory B cells, a finding with important implications for vaccine strategies aimed at the prompt recall of high-affinity neutralizing Abs.

Orally Administered Salacia reticulata Extract Reduces H1N1 Influenza Clinical Symptoms in Murine Lung Tissues Putatively Due to Enhanced Natural Killer Cell Activity

Influenza is a major cause of respiratory tract infection. Although most cases do not require further hospitalization, influenza periodically causes epidemics in humans that can potentially infect and kill millions of people. To countermeasure this threat, new vaccines need to be developed annually to match emerging influenza viral strains with increased resistance to existing vaccines. Thus, there is a need for finding and developing new anti-influenza viral agents as alternatives to current treatments. Here, we tested the antiviral effects of an extract from the stems and roots of Salacia reticulata (SSRE), a plant rich in phytochemicals, such as salacinol, kotalanol, and catechins, on H1N1 influenza virus-infected mice. Following oral administration of 0.6 mg/day of SSRE, the incidence of coughing decreased in 80% of mice, and only one case of severe pulmonary inflammation was detected. Moreover, when compared with mice given Lactobacillus casei JCM1134, a strain previously shown to help increase in vitro natural killer (NK) cell activity, SSRE-administered mice showed greater and equal NK cell activity in splenocytes and pulmonary cells, respectively, at high effector cell:target cell ratios. Next, to test whether or not SSRE would exert protective effects against influenza in the absence of gut microbiota, mice were given antibiotics before being inoculated influenza virus and subsequently administered SSRE. SSRE administration induced an increase in NK cell activity in splenocytes and pulmonary cells at levels similar to those detected in mice not treated with antibiotics. Based on our results, it can be concluded that phytochemicals in the SSRE exerted protective effects against influenza infection putatively via modulation of the immune response, including enhancement of NK cell activity, although some protective effects were not necessarily through modulation of gut microbiota. Further investigation is necessary to elucidate the molecular mechanisms underlying the protective effects of SSRE against influenza infection.

Intranasal vaccination with a plant-derived H5 HA vaccine protects mice and ferrets against highly pathogenic avian influenza virus challenge

Highly pathogenic avian influenza H5N1 infection remains a public health threat and vaccination is the best measure of limiting the impact of a potential pandemic. Mucosal vaccines have the advantage of eliciting immune responses at the site of viral entry, thereby preventing infection as well as further viral transmission. In this study, we assessed the protective efficacy of hemagglutinin (HA) from the A/Indonesia/05/05 (H5N1) strain of influenza virus that was produced by transient expression in plants. The plant-derived vaccine, in combination with the mucosal adjuvant (3′,5′)-cyclic dimeric guanylic acid (c-di-GMP) was used for intranasal immunization of mice and ferrets, before challenge with a lethal dose of the A/Indonesia/05/05 (H5N1) virus. Mice vaccinated with 15 μg or 5 μg of adjuvanted HA survived the viral challenge, while all control mice died within 10 d of challenge. Vaccinated animals elicited serum hemagglutination inhibition, IgG and IgA antibody titers. In the ferret challenge study, all animals vaccinated with the adjuvanted plant vaccine survived the lethal viral challenge, while 50% of the control animals died. In both the mouse and ferret models, the vaccinated animals were better protected from weight loss and body temperature changes associated with H5N1 infection compared with the non-vaccinated controls. Furthermore, the systemic spread of the virus was lower in the vaccinated animals compared with the controls. Results presented here suggest that the plant-produced HA-based influenza vaccine adjuvanted with c-di-GMP is a promising vaccine/adjuvant combination for the development of new mucosal influenza vaccines.

Administration of Poly[di(sodium carboxylatoethylphenoxy)phosphazene] (PCEP) and Avian Beta Defensin as Adjuvants in Inactivated Inclusion Body Hepatitis Virus and its Hexon Protein-Based Experimental Vaccine Formulations in Chickens

Inclusion body hepatitis (IBH) is one of the major infectious diseases adversely affecting the poultry industry of the United States and Canada. Currently, no effective and safe vaccine is available for the control of IBH virus (IBHV) infection in chickens. However, based on the excellent safety and immunogenic profiles of experimental veterinary vaccines developed with the use of new generation adjuvants, we hypothesized that characterization of vaccine formulations containing inactivated IBHV or its capsid protein hexon as antigens, along with poly[di(sodium carboxylatoethylphenoxy)phosphazene] (PCEP) and avian beta defensin 2 (ABD2) as vaccine adjuvants, will be helpful in development of an effective and safe vaccine formulation for IBH. Our data demonstrated that experimental administration of vaccine formulations containing inactivated IBHV and a mixture of PCEP with or without ABD2 as an adjuvant induced significantly higher antibody responses compared with other vaccine formulations, while hexon protein-based vaccine formulations showed relatively lower levels of antibody responses. Thus, a vaccine formulation containing inactivated IBHV with PCEP or a mixture of PCEP and ABD2 (with a reduced dosage of PCEP) as an adjuvant may serve as a potential vaccine candidate. However, in order to overcome the risks associated with whole virus inactivated vaccines, characterization of additional viral capsid proteins, including fiber protein and penton of IBHV along with hexon protein in combination with more new generation adjuvants, will be helpful in further improvements of vaccines against IBHV infection.

Safety and immunogenicity of influenza whole inactivated virus vaccines: A phase I randomized clinical trial

BACKGROUND

Influenza vaccine production capacity is still insufficient to meet global demand in case of a pandemic. To expand worldwide influenza vaccine production capacity, a solid and transferable egg-based influenza vaccine production process was established that is suitable for upscaling and technology transfer to vaccine manufacturers in low- and middle-income countries. As a proof-of-concept, the safety and immunogenicity of a pandemic whole inactivated virus (WIV) vaccine (H5N1) and a monovalent seasonal WIV vaccine (H3N2) were evaluated in a phase I clinical trial in adults.

METHODS

Subjects were vaccinated with 2 doses of pandemic WIV vaccine (pWIV), or one dose of either seasonal WIV vaccine (sWIV) or a commercially available trivalent comparator vaccine followed by a placebo dose. Haemagglutination inhibiting antibody titres against the influenza strains were determined before and 21 d after each vaccination.

RESULTS

The frequency and severity of adverse reactions were comparable between groups. No serious adverse events were reported. After a single dose of sWIV the seroconversion rate was 91% (Committee for Proprietary Medicinal Products (CPMP) criterion >40%), the seroprotection rate was 100% (CPMP criterion >70%), and the mean geometric mean titre (GMT) increase was 24.9 (CPMP criterion >2.5). After two doses of pWIV, seroconversion rate and seroprotection rate were both 71%, and the mean GMT increase was 7.8.

CONCLUSIONS

Both pWIV and sWIV were equally well-tolerated as the comparator vaccine, and both vaccines complied with all 3 CPMP criteria. EudraCT 2011-000159-17. Netherlands National Trial Register 2695.

Induction of Local Secretory IgA and Multifunctional CD4⁺ T-helper Cells Following Intranasal Immunization with a H5N1 Whole Inactivated Influenza Virus Vaccine in BALB/c Mice

Avian influenza subunit vaccines have been shown to be poorly immunogenic, leading to the re-evaluation of the immunogenic and dose-sparing potential of whole virus vaccines. In this study, we investigated the immune responses after one or two doses of intramuscular or intranasal whole inactivated influenza H5N1 virus vaccine in BALB/c mice. Serum samples and nasal washings were collected weekly post-vaccination and analysed using enzyme-linked immunosorbent assay (ELISA). Sera were also analysed by the haemagglutination inhibition (HI) assay. Antibody-secreting cells were measured in lymphocytes from spleen and bone marrow via enzyme-linked immunospot (ELISPOT). Splenocytes were stimulated in vitro, and T-helper profiles were measured through multiplex bead assay in the supernatants, or intracellularly by multiparametric flow cytometry. Both vaccine routes induced high HI titres following the second immunization (intramuscular = 370, intranasal = 230). Moreover, the intramuscular group showed significantly higher levels of serum IgG (P < 0.01), IgG1 (P < 0.01) and IgG2a (P < 0.01) following the second vaccine dose, while the intranasal group exhibited significantly higher levels of serum IgA (P < 0.05) and local IgA (P < 0.01) in the nasal washings. Also, IgA antibody-secreting cells were found in significantly higher numbers in the intranasal group in both the spleen (P < 0.01) and the bone marrow (P < 0.01). Moreover, Th1 (TNF-α, IL-2, IFN-γ) and Th2 (IL-4, IL-5, IL-10) cytokines were expressed by both groups, yet only the intranasal group expressed the Th17 marker IL-17. As the intranasal vaccines induce local IgA and are easily administered, we suggest the intranasally administered whole virus vaccine as a promising candidate for a pandemic H5N1 vaccine.

Matrix M H5N1 Vaccine Induces Cross-H5 Clade Humoral Immune Responses in a Randomized Clinical Trial and Provides Protection from Highly Pathogenic Influenza Challenge in Ferrets

BACKGROUND AND METHODS

Highly pathogenic avian influenza (HPAI) viruses constitute a pandemic threat and the development of effective vaccines is a global priority. Sixty adults were recruited into a randomized clinical trial and were intramuscularly immunized with two virosomal vaccine H5N1 (NIBRG-14) doses (21 days apart) of 30 μg HA alone or 1.5, 7.5 or 30 μg HA adjuvanted with Matrix M. The kinetics and longevity of the serological responses against NIBRG-14 were determined by haemagglutination inhibition (HI), single radial haemolysis (SRH), microneutralization (MN) and ELISA assays. The cross-H5 clade responses in sera were determined by HI and the antibody-secreting (ASC) cell ELISPOT assays. The protective efficacy of the vaccine against homologous HPAI challenge was evaluated in ferrets.

RESULTS

The serological responses against the homologous and cross-reactive strains generally peaked one week after the second dose, and formulation with Matrix M augmented the responses. The NIBRG-14-specific seroprotection rates fell significantly by six months and were low against cross-reactive strains although the adjuvant appeared to prolong the longevity of the protective responses in some subjects. By 12 months post-vaccination, nearly all vaccinees had NIBRG-14-specific antibody titres below the protective thresholds. The Matrix M adjuvant was shown to greatly improve ASC and serum IgG responses following vaccination. In a HPAI ferret challenge model, the vaccine protected the animals from febrile responses, severe weight loss and local and systemic spread of the virus.

CONCLUSION

Our findings show that the Matrix M-adjuvanted virosomal H5N1 vaccine is a promising pre-pandemic vaccine candidate.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00868218.

The avian influenza vaccine Emerflu. Why did it fail?

Emerflu is an inactivated, split-virion pandemic preparedness vaccine, containing 30 μg of hemagglutinin (HA) and 600 μg of aluminum hydroxide adjuvant. It is administered in two doses, 3 weeks apart. Only moderate immunogenicity was evident from clinical studies with the vaccine in adults, and HA antibody responses were below the criteria established by the EMA and US FDA for licensure. With the exception of Australia, the vaccine remains unlicensed. Further clinical development appears to have been suspended, and newer adjuvants such as MF59 and AS03 have since demonstrated safety and superior immunogenicity with lower HA doses. Emerflu is symbolic of the failure of aluminum salts as an adjuvant for influenza vaccines. Reasons for this failure are unclear, and may reflect problems with the adjuvant-antigen complex or interference in the immune response by heterosubtypic immunity.

Innate responses induced by whole inactivated virus or subunit influenza vaccines in cultured dendritic cells correlate with immune responses in vivo

Vaccine development involves time-consuming and expensive evaluation of candidate vaccines in animal models. As mediators of both innate and adaptive immune responses dendritic cells (DCs) are considered to be highly important for vaccine performance. Here we evaluated how far the response of DCs to a vaccine in vitro is in line with the immune response the vaccine evokes in vivo. To this end, we investigated the response of murine bone marrow-derived DCs to whole inactivated virus (WIV) and subunit (SU) influenza vaccine preparations. These vaccine preparations were chosen because they differ in the immune response they evoke in mice with WIV being superior to SU vaccine through induction of higher virus-neutralizing antibody titers and a more favorable Th1-skewed response phenotype. Stimulation of DCs with WIV, but not SU vaccine, resulted in a cytokine response that was comparable to that of DCs stimulated with live virus. Similarly, the gene expression profiles of DCs treated with WIV or live virus were similar and differed from that of SU vaccine-treated DCs. More specifically, exposure of DCs to WIV resulted in differential expression of genes in known antiviral pathways, whereas SU vaccine did not. The stronger antiviral and more Th1-related response of DCs to WIV as compared to SU vaccine correlates well with the superior immune response found in mice. These results indicate that in vitro stimulation of DCs with novel vaccine candidates combined with the assessment of multiple parameters, including gene signatures, may be a valuable tool for the selection of vaccine candidates.

Development of a bio-analytical strategy for characterization of vaccine particles combining SEC and nanoES GEMMA

Commonly used methods for size and shape analysis of bionanoparticles found in vaccines like X-ray crystallography and cryo-electron microscopy are very time-consuming and cost-intensive. The nano-electrospray (nanoES) gas-phase electrophoretic mobility macromolecular analyzer (GEMMA), belonging to the group of ion mobility spectrometers, was used for size determination of vaccine virus particles because it requires less analysis time and investment (no vacuum system). Size exclusion chromatography (SEC) of viral vaccines and production intermediates turned out to be a good purification/isolation method prior to GEMMA, TEM (transmission electron microscopy) and AFM (atomic force microscopy) investigations, as well as providing a GEMMA analysis-compatible buffer. Column materials and different elution buffers were tested for optimal vaccine particle yield. We used a Superdex 200 column with a 50 mM ammonium acetate buffer. In addition, SEC allowed the removal of process-related impurities from the virions of interest. A sample concentrating step or a detergent addition step was also investigated. As a final step of our strategy SEC-purified or untreated vaccine-nanoparticles were further analyzed: (a) by immunological detection with a specific polyclonal antibody (dot blot) to verify the biological functionality, (b) by GEMMA to provide the size of the particles at atmospheric pressure and (c) by AFM and (d) TEM to obtain both size and shape information. The mean diameter of inactivated tick-borne encephalitis virions (i.e. vaccine particles) determined by GEMMA measurement was 46.6 ± 0.5 nm, in contrast to AFM and TEM images providing diameters of about 58 ± 4 and 52 ± 5 nm, respectively.

Influenza vaccines: a moving interdisciplinary field

Vaccination is by far the most effective way of preventing morbidity and mortality due to infection of the upper respiratory tract by influenza virus. Current vaccines require yearly vaccine updates as the influenza virus can escape vaccine-induced humoral immunity due to the antigenic variability of its surface antigens. In case of a pandemic, new vaccines become available too late with current vaccine practices. New technologies that allow faster production of vaccine seed strains in combination with alternative production platforms and vaccine formulations may shorten the time gap between emergence of a new influenza virus and a vaccine becoming available. Adjuvants may allow antigen-sparing, allowing more people to be vaccinated with current vaccine production capacity. Adjuvants and universal vaccines can target immune responses to more conserved influenza epitopes, which eventually will result in broader protection for a longer time. In addition, further immunological studies are needed to gain insights in the immune features that contribute to protection from influenza-related disease and mortality, allowing redefinition of correlates of protection beyond virus neutralization in vitro.

Modified vaccinia virus Ankara encoding influenza virus hemagglutinin induces heterosubtypic immunity in macaques

Current influenza virus vaccines primarily aim to induce neutralizing antibodies (NAbs). Modified vaccinia virus Ankara (MVA) is a safe and well-characterized vector for inducing both antibody and cellular immunity. We evaluated the immunogenicity and protective efficacy of MVA encoding influenza virus hemagglutinin (HA) and/or nucleoprotein (NP) in cynomolgus macaques. Animals were given 2 doses of MVA-based vaccines 4 weeks apart and were challenged with a 2009 pandemic H1N1 isolate (H1N1pdm) 8 weeks after the last vaccination. MVA-based vaccines encoding HA induced potent serum antibody responses against homologous H1 or H5 HAs but did not stimulate strong T cell responses prior to challenge. However, animals that received MVA encoding influenza virus HA and/or NP had high frequencies of virus-specific CD4(+) and CD8(+) T cell responses within the first 7 days of H1N1pdm infection, while animals vaccinated with MVA encoding irrelevant antigens did not. We detected little or no H1N1pdm replication in animals that received vaccines encoding H1 (homologous) HA, while a vaccine encoding NP from an H5N1 isolate afforded no protection. Surprisingly, H1N1pdm viral shedding was reduced in animals vaccinated with MVA encoding HA and NP from an H5N1 isolate. This reduced shedding was associated with cross-reactive antibodies capable of mediating antibody-dependent cellular cytotoxicity (ADCC) effector functions. Our results suggest that ADCC plays a role in cross-protective immunity against influenza. Vaccines optimized to stimulate cross-reactive antibodies with ADCC function may provide an important measure of protection against emerging influenza viruses when NAbs are ineffective.

IMPORTANCE

Current influenza vaccines are designed to elicit neutralizing antibodies (NAbs). Vaccine-induced NAbs typically are effective but highly specific for particular virus strains. Consequently, current vaccines are poorly suited for preventing the spread of newly emerging pandemic viruses. Therefore, we evaluated a vaccine strategy designed to induce both antibody and T cell responses, which may provide more broadly cross-protective immunity against influenza. Here, we show in a translational primate model that vaccination with a modified vaccinia virus Ankara encoding hemagglutinin from a heterosubtypic H5N1 virus was associated with reduced shedding of a pandemic H1N1 virus challenge, while vaccination with MVA encoding nucleoprotein, an internal viral protein, was not. Unexpectedly, this reduced shedding was associated with nonneutralizing antibodies that bound H1 hemagglutinin and activated natural killer cells. Therefore, antibody-dependent cellular cytotoxicity (ADCC) may play a role in cross-protective immunity to influenza virus. Vaccines that stimulate ADCC antibodies may enhance protection against pandemic influenza virus.

Modulation of innate immune responses by influenza-specific ovine polyclonal antibodies used for prophylaxis

In the event of a novel influenza A virus pandemic, prophylaxis mediated by antibodies provides an adjunct control option to vaccines and antivirals. This strategy is particularly pertinent to unvaccinated populations at risk during the lag time to produce and distribute an effective vaccine. Therefore, development of effective prophylactic therapies is of high importance. Although previous approaches have used systemic delivery of monoclonal antibodies or convalescent sera, available supply is a serious limitation. Here, we have investigated intranasal delivery of influenza-specific ovine polyclonal IgG antibodies for their efficacy against homologous influenza virus challenge in a mouse model. Both influenza-specific IgG and F(ab')2 reduced clinical scores, body weight loss and lung viral loads in mice treated 1 hour before virus exposure. Full protection from disease was also observed when antibody was delivered up to 3 days prior to virus infection. Furthermore, effective prophylaxis was independent of a strong innate immune response. This strategy presents a further option for prophylactic intervention against influenza A virus using ruminants to generate a bulk supply that could potentially be used in a pandemic setting, to slow virus transmission and reduce morbidity associated with a high cytokine phenotype.

Near-infrared laser adjuvant for influenza vaccine

Safe and effective immunologic adjuvants are often essential for vaccines. However, the choice of adjuvant for licensed vaccines is limited, especially for those that are administered intradermally. We show that non-tissue damaging, near-infrared (NIR) laser light given in short exposures to small areas of skin, without the use of additional chemical or biological agents, significantly increases immune responses to intradermal influenza vaccination without augmenting IgE. The NIR laser-adjuvanted vaccine confers increased protection in a murine influenza lethal challenge model as compared to unadjuvanted vaccine. We show that NIR laser treatment induces the expression of specific chemokines in the skin resulting in recruitment and activation of dendritic cells and is safe to use in both mice and humans. The NIR laser adjuvant technology provides a novel, safe, low-cost, simple-to-use, potentially broadly applicable and clinically feasible approach to enhancing vaccine efficacy as an alternative to chemical and biological adjuvants.