Use of the Microparticle Nanoscale Silicon Dioxide as an Adjuvant To Boost Vaccine Immune Responses against Influenza Virus in Neonatal Mice

Promotion of Th17 Polarized Immunity via Co-Delivery of Mincle Agonist and Tuberculosis Antigen Using Silica Nanoparticles

Adjuvants and immunomodulators that effectively drive a Th17-skewed immune response are not part of the standard vaccine toolkit. Vaccine adjuvants and delivery technologies that can induce Th17 or Th1/17 immunity and protection against bacterial pathogens, such as tuberculosis (TB), are urgently needed. Th17-polarized immune response can be induced using agonists that bind and activate C-type lectin receptors (CLRs) such as macrophage inducible C-type lectin (Mincle). A simple but effective strategy was developed for codelivering Mincle agonists with the recombinant Mycobacterium tuberculosis fusion antigen, M72, using tunable silica nanoparticles (SNP). Anionic bare SNP, hydrophobic phenyl-functionalized SNP (P-SNP), and cationic amine-functionalized SNP (A-SNP) of different sizes were coated with three synthetic Mincle agonists, UM-1024, UM-1052, and UM-1098, and evaluated for adjuvant activity in vitro and in vivo. The antigen and adjuvant were coadsorbed onto SNP via electrostatic and hydrophobic interactions, facilitating multivalent display and delivery to antigen presenting cells. The cationic A-SNP showed the highest coloading efficiency for the antigen and adjuvant. In addition, the UM-1098-adsorbed A-SNP formulation demonstrated slow-release kinetics in vitro, excellent stability over 12 months of storage, and strong IL-6 induction from human peripheral blood mononuclear cells. Co-adsorption of UM-1098 and M72 on A-SNP significantly improved antigen-specific humoral and Th17-polarized immune responses in vivo in BALB/c mice relative to the controls. Taken together, A-SNP is a promising platform for codelivery and proper presentation of adjuvants and antigens and provides the basis for their further development as a vaccine delivery platform for immunization against TB or other diseases for which Th17 immunity contributes to protection.

Co-Delivery of a Novel Lipidated TLR7/8 Agonist and Hemagglutinin-Based Influenza Antigen Using Silica Nanoparticles Promotes Enhanced Immune Responses

Co-delivery of antigens and adjuvants to the same antigen-presenting cells (APCs) can significantly improve the efficacy and safety profiles of vaccines. Here, we report amine-grafted silica nanoparticles (A-SNP) as a tunable vaccine co-delivery platform for TLR7/8 agonists along with the recombinant influenza antigen hemagglutinin H7 (H7) to APCs. A-SNP of two different sizes (50 and 200 nm) were prepared and coated with INI-4001 at different coating densities, followed by co-adsorption of H7. Both INI-4001 and H7 showed >90% adsorption to the tested A-SNP formulations. TNF-α and IFN-α cytokine release by human peripheral blood mononuclear cells as well as TNF-α, IL-6, and IL-12 release by mouse bone marrow-derived dendritic cells revealed that the potency of the INI-4001-adsorbed A-SNP (INI-4001/A-SNP) formulations was improved relative to aqueous formulation control. This improved potency was dependent on particle size and ligand coating density. In addition, slow-release profiles of INI-4001 were measured from INI-4001/A-SNP formulations in plasma with 30-50% INI-4001 released after 7 days. In vivo murine immunization studies demonstrated significantly improved H7-specific humoral and Th1/Th17-polarized T cell immune responses with no observed adverse reactions. Low-density 50 nm INI-4001/A-SNP elicited significantly higher IFN-γ and IL-17 induction over that of the H7 antigen-only group and INI-4001 aqueous formulation controls. In summary, this work introduces an effective and biocompatible SNP-based co-delivery platform that enhances the immunogenicity of TLR7/8 agonist-adjuvanted subunit influenza vaccines.

Polymer formulated self-amplifying RNA vaccine is partially protective against influenza virus infection in ferrets

COVID-19 has demonstrated the power of RNA vaccines as part of a pandemic response toolkit. Another virus with pandemic potential is influenza. Further development of RNA vaccines in advance of a future influenza pandemic will save time and lives. As RNA vaccines require formulation to enter cells and induce antigen expression, the aim of this study was to investigate the impact of a recently developed bioreducible cationic polymer, pABOL for the delivery of a self-amplifying RNA (saRNA) vaccine for seasonal influenza virus in mice and ferrets. Mice and ferrets were immunized with pABOL formulated saRNA vaccines expressing either haemagglutinin (HA) from H1N1 or H3N2 influenza virus in a prime boost regime. Antibody responses, both binding and functional were measured in serum after immunization. Animals were then challenged with a matched influenza virus either directly by intranasal inoculation or in a contact transmission model. While highly immunogenic in mice, pABOL-formulated saRNA led to variable responses in ferrets. Animals that responded to the vaccine with higher levels of influenza virus-specific neutralizing antibodies were more protected against influenza virus infection. pABOL-formulated saRNA is immunogenic in ferrets, but further optimization of RNA vaccine formulation and constructs is required to increase the quality and quantity of the antibody response to the vaccine.

Engineered Nanoparticle Applications for Recombinant Influenza Vaccines

Influenza viruses cause seasonal epidemics and represent a pandemic risk. With current vaccine methods struggling to protect populations against emerging strains, there is a demand for a next-generation flu vaccine capable of providing broad protection. Recombinant biotechnology, combined with nanomedicine techniques, could address this demand by increasing immunogenicity and directing immune responses toward conserved antigenic targets on the virus. Various nanoparticle candidates have been tested for use in vaccines, including virus-like particles, protein and carbohydrate nanoconstructs, antigen-carrying lipid particles, and synthetic and inorganic particles modified for antigen presentation. These methods have yielded some promising results, including protection in animal models against antigenically distinct influenza strains, production of antibodies with broad reactivity, and activation of potent T cell responses. Based on the evidence of current research, it is feasible that the next generation of influenza vaccines will combine recombinant antigens with nanoparticle carriers.

Self-Assembled Nanoparticles: Exciting Platforms for Vaccination

Vaccination is successfully advanced to control several fatal diseases and improve human life expectancy. However, additional innovations are required in this field because there are no effective vaccines to prevent some infectious diseases. The shift from the attenuated or inactivated pathogens to safer but less immunogenic protein or peptide antigens has led to a search for effective antigen delivery carriers that can function as both antigen vehicles and intrinsic adjuvants. Among these carriers, self-assembled nanoparticles (SANPs) have shown great potential to be the best representative. For the nanoscale and multiple presentation of antigens, with accurate control over size, geometry, and functionality, these nanoparticles are assembled spontaneously and mimic pathogens, resulting in enhanced antigen presentation and increased cellular and humoral immunity responses. In addition, they may be applied through needle-free routes due to their adhesive ability, which gives them a great future in vaccination applications. This review provides an overview of various SANPs and their applications in prophylactic vaccines.

Influence of zinc nanoaquacitrate on the immuno-physiological reactivity and productivity of the organism of rabbits

Zinc is necessary for maintaining the immune status, and its deficiency in the organisms of animals is usually accompanied by the condition of immune deficiency. The objective of the study was determining the effect of different amounts of zinc on the immune-biological reactivity and productivity of the organism of rabbits after their weaning on the 50th and 86th days of life. For the study, rabbits with the weight of 1.2–1.4 kg were selected and divided into four groups (control and three experimental). The rabbits of the control group were fed with unlimited balanced granulated compound feed, and had free access to water. The animals of the I, II and III experimental groups were watered with zinc nanoaquacitrate in the amounts of 0.25, 0.50 and 0.75 mg of Zn/kg of body weight. Compared with the control group, watering of the animals of the experimental groups with zinc nanoaquacitrate to a greater extent affected the content of phagocytic activity, lysozymic and bactericidal activities of the blood serum as integral factors of non-specific cellular and humoral resistance of the organism, which manifested in the increase in their content in blood on the 12th, 24th and 36th days of the experiment. Use of organic supplement in the diet of rabbits had a stimula­ting effect on the functioning of the immune system of their organism, which was seen in the higher content of total immunoglobulins, sialic acids and ceruloplasmin in the blood of animals watered with zinc nanoaquacitrate in the quantities of 0.50 and 0.75 mg of Zn/kg of body weight on the 24th and 36th days of the experiment. Use of organic compound of zinc in the diet caused high parameters of growth of the organism of rabbits during the period of 36 days, which manifested in the highest parameters of average-day increments and body weight on the 86th day of the life of the rabbits from the III experimental group, which received zinc nanoaquacitrate in the amounts of 0.75 mg of Zn/kg of body weight compared with the control group. Watering rabbits with zinc nanoaquacitrate during the study was accompanied by probable changes in the number of erythrocytes, concentration of hemoglobin and erythrocyte indices, which could indicate a positive effect of the employed additives on the hematopoietic function of the rabbits’ organism. The data of the performed experiment suggest that watering with larger amounts of organic compound of zinc has a positive effect on the processes of formation of immuno-physiological reactivity of the rabbits’ organism and increase in their productivity. The practical purpose is the study of the impact of watering with zinc nanoaquacitrate on the immuno-biological reactivity of the organism of rabbit dams during the period of lactation.

Conjugation of a Small-Molecule TLR7 Agonist to Silica Nanoshells Enhances Adjuvant Activity

Stimulation of Toll-like receptors (TLRs) and/or NOD-like receptors on immune cells initiates and directs immune responses that are essential for vaccine adjuvants. The small-molecule TLR7 agonist, imiquimod, has been approved by the FDA as an immune response modifier but is limited to topical application due to its poor pharmacokinetics that causes undesired adverse effects. Nanoparticles are increasingly used with innate immune stimulators to mitigate side effects and enhance adjuvant efficacy. In this study, a potent small-molecule TLR7 agonist, 2-methoxyethoxy-8-oxo-9-(4-carboxybenzyl)adenine (1V209), was conjugated to hollow silica nanoshells (NS). Proinflammatory cytokine (IL-6, IL-12) release by mouse bone-marrow-derived dendritic cells and human peripheral blood mononuclear cells revealed that the potency of silica nanoshells-TLR7 conjugates (NS-TLR) depends on nanoshell size and ligand coating density. Silica nanoshells of 100 nm diameter coated with a minimum of ∼6000 1V209 ligands/particle displayed 3-fold higher potency with no observed cytotoxicity when compared to an unconjugated TLR7 agonist. NS-TLR activated the TLR7-signaling pathway, triggered caspase activity, and stimulated IL-1β release, while neither unconjugated TLR7 ligands nor silica shells alone produced IL-1β. An in vivo murine immunization study, using the model antigen ovalbumin, demonstrated that NS-TLR increased antigen-specific IgG antibody induction by 1000× with a Th1-biased immune response, compared to unconjugated TLR7 agonists. The results show that the TLR7 ligand conjugated to silica nanoshells is capable of activating an inflammasome pathway to enhance both innate immune-stimulatory and adjuvant potencies of the TLR7 agonist, thereby broadening applications of innate immune stimulators.

Silica nanoparticles as an enhancer in the IL-1β-induced inflammation cycle of A549 cells

Objective: The industrial production and combustion of coal can produce silica nanoparticles (nano-SiO₂). It enters the human body mainly through the respiratory tract and exerts a toxic effect. However, whether nano-SiO₂ can increase the IL-1β-induced inflammatory expression in A549 cells has not been tested. Therefore, the synergistic toxicity of nano-SiO₂ and IL-1β to A549 was observed in our study. Materials and methods: We exposed A549 cells to nano-SiO₂ (0, 100, 500, and 1000 μg/ml) for 12 and 24 h. The effect of nano-SiO₂ on the viability of A549 cells was observed by the CCK-8 method. The A549 cells were exposed to nano-SiO₂ (1 mg/mL) and cytokine IL-1β (10 ng/mL) for 4 h, and we detected the expression of IL-1β and IL-6 cytokines by real time quantitative polymerase chain (RT-qPCR) and enzyme linked immunosorbent assay (ELISA). The expression of β-Actin, I-κB, phospho-ERK_1/2 (P-ERK_1/2), total-ERK_1/2 (T-ERK_1/2), phospho-JNK (P-JNK), total-JNK (T-JNK), phospho-P38 (P-P38), and total-P38 (T-P38) in A549 cells was detected by the Western Blot method. Results: The nano-SiO₂ treatment resulted in a time-dependent decrease in the viability of A549 cells. The synergistic effect of nano-SiO₂ and IL-1β was observed on the new production of IL-1β and IL-6 in A549 cells. The Western blot results showed that nano-SiO₂ can increase the expression of IL-1β and IL-6 by promoting the phosphorylation of ERK_1/2 and elevating the phosphorylation of I-κB by IL-1β. IL-1β and IL-6 were induced by nano-SiO₂, and the IL-1β treatment with 20 μM of I-κBα phosphorylation inhibitor (PD98059) and 20 μM of ERK_1/2 inhibitor (BAY11-7082) for 1 h was significantly lower than that of the control group in A549 cells. Discussion and conclusion: These results indicated that nano-SiO₂ had a toxic effect on A549 cells, and this effect could increase IL-1β on the A549 cell-induced inflammatory response. The results suggested that the release of IL-1β and IL-6 in A549 was enhanced by the synergistic IL-1β-induced phosphorylation of ERK_1/2 and I-κB. This process is similar to a snowball, and it is possible that IL-1β is continuously produced and repeatedly superimposed in A549 cells to produce an inflammatory effect; then, a vicious circle occurs, and an inflammatory storm is accelerated.

A nano silicon adjuvant enhances inactivated transmissible gastroenteritis vaccine through activation the Toll-like receptors and promotes humoral and cellular immune responses

Inactivated transmissible gastroenteritis virus (TGEV) vaccines are widely used in swine herds in China. These are limited, however, by the need to elicit both humoral and cellular immunity, as well as the efficiency of adjuvants. In this study, a 70-nm nano silicon particle was applied with inactivated TGEV vaccine in mice, and its immune-enhancing effects and mechanism of action investigated. We found that nano silicon applied with inactivated TGEV vaccine induced high antibody titers, increase IL-6, TNF-α and IFN-γ expression, and stimulate CD3+ T cell proliferation with a high CD4+/CD8+ T lymphocyte ratio. Nano silicon could quickly activate innate and adaptive immunity by stimulating Toll-like receptor signaling pathways, indicating that the nano silicon adjuvant enhanced long-term humoral and early cellular immune responses when combined with inactivated TGEV vaccine. Nano silicon could be considered for use as an antigen- carrier and adjuvant for veterinary vaccines.

Mouse Models of Influenza Infection with Circulating Strains to Test Seasonal Vaccine Efficacy

Influenza virus infection is a significant cause of morbidity and mortality worldwide. The surface antigens of influenza virus change over time blunting both naturally acquired and vaccine induced adaptive immune protection. Viral antigenic drift is a major contributing factor to both the spread and disease burden of influenza. The aim of this study was to develop better infection models using clinically relevant, influenza strains to test vaccine induced protection. CB6F1 mice were infected with a range of influenza viruses and disease, inflammation, cell influx, and viral load were characterized after infection. Infection with circulating H1N1 and representative influenza B viruses induced a dose-dependent disease response; however, a recent seasonal H3N2 virus did not cause any disease in mice, even at high titers. Viral infection led to recoverable virus, detectable both by plaque assay and RNA quantification after infection, and increased upper airway inflammation on day 7 after infection comprised largely of CD8 T cells. Having established seasonal infection models, mice were immunized with seasonal inactivated vaccine and responses were compared to matched and mismatched challenge strains. While the H1N1 subtype strain recommended for vaccine use has remained constant in the seven seasons between 2010 and 2016, the circulating strain of H1N1 influenza (2009 pandemic subtype) has drifted both genetically and antigenically since 2009. To investigate the effect of this observed drift on vaccine induced protection, mice were immunized with antigens from A/California/7/2009 (H1N1) and challenged with H1N1 subtype viruses recovered from 2009, 2010, or 2015. Vaccination with A/California/7/2009 antigens protected against infection with either the 2009 or 2010 strains, but was less effective against the 2015 strain. This observed reduction in protection suggests that mouse models of influenza virus vaccination and infection can be used as an additional tool to predict vaccine efficacy against drift strains.

Re-evaluation of silicon dioxide (E 551) as a food additive

The EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) provides a scientific opinion re-evaluating the safety of silicon dioxide (E 551) when used as a food additive. The forms of synthetic amorphous silica (SAS) used as E 551 include fumed silica and hydrated silica (precipitated silica, silica gel and hydrous silica). The Scientific Committee on Food (SCF) established a group acceptable daily intake (ADI) 'not specified' for silicon dioxide and silicates. SAS materials used in the available biological and toxicological studies were different in their physicochemical properties; their characteristics were not always described in sufficient detail. Silicon dioxide appears to be poorly absorbed. However, silicon-containing material (in some cases presumed to be silicon dioxide) was found in some tissues. Despite the limitations in the subchronic, reproductive and developmental toxicological studies, including studies with nano silicon dioxide, there was no indication of adverse effects. E 551 does not raise a concern with respect to genotoxicity. In the absence of a long-term study with nano silicon dioxide, the Panel could not extrapolate the results from the available chronic study with a material, which does not cover the full-size range of the nanoparticles that could be present in the food additive E 551, to a material complying with the current specifications for E 551. These specifications do not exclude the presence of nanoparticles. The highest exposure estimates were at least one order of magnitude lower than the no observed adverse effect levels (NOAELs) identified (the highest doses tested). The Panel concluded that the EU specifications are insufficient to adequately characterise the food additive E 551. Clear characterisation of particle size distribution is required. Based on the available database, there was no indication for toxicity of E 551 at the reported uses and use levels. Because of the limitations in the available database, the Panel was unable to confirm the current ADI 'not specified'. The Panel recommended some modifications of the EU specifications for E 551.

The role of the NLRP3 inflammasome in regulation of antiviral responses to influenza A virus infection

The innate immune system provides the host with both a dynamic barrier to prevent infection and a means to which rapid anti-microbial responses can be mounted. The inflammasome pathway is a critical host early response mechanism that enables detection of pathogens and initiates production of inflammatory cytokines, inducing recruitment of effector cells to the site of infection. The complete mechanism of inflammasome activation requires two signals: an initial priming step upon detection of pathogen, followed by activation of intracellular pattern recognition receptors critical to the formation of the inflammasome complex. The inflammasome complex is made of intracellular multiprotein oligomers which includes a sensor protein such as the nucleotide-binding oligomerization domain (NOD) like receptor proteins (NLRP), and an adapter protein, ASC, which critically activates pro-caspase-1. The mature caspase-1 then proteolytically cleaves cytosolic pro-IL-1β and pro-IL-18, which are then secreted as inflammatory cytokines that activate the inflammatory arm of the immune response to infection. Active caspase-1 also results in pyroptosis, which is a form of cell death triggered by inflammation. The induction and activation of IL-1β and IL-18 are considered critical signatures for inflammasome activation. With focus upon influenza A virus infection, this review will address present knowledge on the mechanisms of inflammasome complex activation, particularly how the viral components modulate activation of the cytosolic NOD-like receptor protein-3 (NLRP3)-dependent inflammasome complex. We also discuss potential therapeutic strategies that target the inflammasome to ameliorate illness, as well as novel methods of vaccination that target inflammasome stimulation with the aim to increase efficacy.

Nasal IgA Provides Protection against Human Influenza Challenge in Volunteers with Low Serum Influenza Antibody Titre

In spite of there being a number of vaccines, influenza remains a significant global cause of morbidity and mortality. Understanding more about natural and vaccine induced immune protection against influenza infection would help to develop better vaccines. Virus specific IgG is a known correlate of protection, but other factors may help to reduce viral load or disease severity, for example IgA. In the current study we measured influenza specific responses in a controlled human infection model using influenza A/California/2009 (H1N1) as the challenge agent. Volunteers were pre-selected with low haemagglutination inhibition (HAI) titres in order to ensure a higher proportion of infection; this allowed us to explore the role of other immune correlates. In spite of HAI being uniformly low, there were variable levels of H1N1 specific IgG and IgA prior to infection. There was also a range of disease severity in volunteers allowing us to compare whether differences in systemic and local H1N1 specific IgG and IgA prior to infection affected disease outcome. H1N1 specific IgG level before challenge did not correlate with protection, probably due to the pre-screening for individuals with low HAI. However, the length of time infectious virus was recovered from the nose was reduced in patients with higher pre-existing H1N1 influenza specific nasal IgA or serum IgA. Therefore, IgA contributes to protection against influenza and should be targeted in vaccines.

Inflammatory responses to influenza vaccination at the extremes of age

Age affects the immune response to vaccination, with individuals at the extremes of age responding poorly. The initial inflammatory response to antigenic materials shapes the subsequent adaptive response and so understanding is required about the effect of age on the profile of acute inflammatory mediators. In this study we measured the local and systemic inflammatory response after influenza vaccination or infection in neonatal, young adult and aged mice. Mice were immunized intramuscularly with inactivated influenza vaccine with and without the adjuvant MF59 and then challenged with H1N1 influenza. Age was the major factor affecting the inflammatory profile after vaccination: neonatal mice had more interleukin-1α (IL-1α), C-reactive protein (CRP) and granulocyte-macrophage colony-stimulating factor (GMCSF), young adults more tumour necrosis factor-α (TNF), and elderly mice more interleukin-1 receptor antagonist (IL-1RA), IL-2RA and interferon-γ-induced protein 10 (IP10). Notably the addition of MF59 induced IL-5, granulocyte colony-stimulating factor (G-CSF), Keratinocyte Chemotractant (KC) and monocyte chemoattractant protein 1 (MCP1) in all ages of animals and levels of these cytokines correlated with antibody responses. Age also had an impact on the efficacy of vaccination: neonatal and young adult mice were protected against challenge, but aged mice were not. There were striking differences in the localization of the cytokine response depending on the route of exposure: vaccination led to a high serum response whereas intranasal infection led to a low serum response but a high lung response. In conclusion, we demonstrate that age affects the inflammatory response to both influenza vaccination and infection. These age-induced differences need to be considered when developing vaccination strategies for different age groups.

Nanomaterials in the Context of Type 2 Immune Responses-Fears and Potentials

The type 2 immune response is an adaptive immune program involved in defense against parasites, detoxification, and wound healing, but is predominantly known for its pathophysiological effects, manifesting as allergic disease. Engineered nanoparticles (NPs) are non-self entities that, to our knowledge, do not stimulate detrimental type 2 responses directly, but have the potential to modulate ongoing reactions in various ways, including the delivery of substances aiming at providing a therapeutic benefit. We review, here, the state of knowledge concerning the interaction of NPs with type 2 immune responses and highlight their potential as a multifunctional platform for therapeutic intervention.

Evaluation of different chemical adjuvants on an avian influenza H6 DNA vaccine in chickens

This study assessed the ability of three adjuvants (aluminium hydroxide, Essai (microparticle) and Phema (nanoparticle)) to enhance the immune response of chickens to an H6N2 avian influenza DNA vaccine. No haemagglutination inhibition antibody was detected following two intramuscular immunizations with the adjuvanted and non-adjuvanted pCAG-HAk vaccine, which has previously been shown to induce moderate H6 haemagglutinin antibody response in SPF chickens. Following virus challenge, neither the vaccinated group without adjuvant nor the Essai-adjuvanted group showed a statistically significant reduction in virus shedding in oropharyngeal and cloacal swabs compared with the naive control group. However, the aluminium hydroxide and Phema-adjuvanted groups significantly reduced the frequency of virus shedding in oropharyngeal swabs, indicating that these adjuvants appeared to further enhance the vaccine potency. Aluminium hydroxide holds promise as an adjuvant for enhancing DNA-induced immune response in chickens owing to its low price and safety record.

DNA Vaccines Encoding Antigen Targeted to MHC Class II Induce Influenza-Specific CD8(+) T Cell Responses, Enabling Faster Resolution of Influenza Disease

Current influenza vaccines are effective but imperfect, failing to cover against emerging strains of virus and requiring seasonal administration to protect against new strains. A key step to improving influenza vaccines is to improve our understanding of vaccine-induced protection. While it is clear that antibodies play a protective role, vaccine-induced CD8⁺ T cells can improve protection. To further explore the role of CD8⁺ T cells, we used a DNA vaccine that encodes antigen dimerized to an immune cell targeting module. Immunizing CB6F1 mice with the DNA vaccine in a heterologous prime-boost regime with the seasonal protein vaccine improved the resolution of influenza disease compared with protein alone. This improved disease resolution was dependent on CD8⁺ T cells. However, DNA vaccine regimes that induced CD8⁺ T cells alone were not protective and did not boost the protection provided by protein. The MHC-targeting module used was an anti-I-E^d single chain antibody specific to the BALB/c strain of mice. To test the role of MHC targeting, we compared the response between BALB/c, C57BL/6 mice, and an F1 cross of the two strains (CB6F1). BALB/c mice were protected, C57BL/6 were not, and the F1 had an intermediate phenotype; showing that the targeting of antigen is important in the response. Based on these findings, and in agreement with other studies using different vaccines, we conclude that, in addition to antibody, inducing a protective CD8 response is important in future influenza vaccines.