Influenza vaccines: T-cell responses deserve more attention

Co-Delivery of Multiple Toll-Like Receptor Agonists and Avian Influenza Hemagglutinin on Protein Nanoparticles Enhances Vaccine Immunogenicity and Efficacy

Most seasonal and pandemic influenza vaccines are derived from inactivated or attenuated virus propagated in chicken eggs, while more advanced delivery technologies, such as the use of recombinant proteins and adjuvants, are under-utilized. In this study, the E2 protein nanoparticle (NP) platform is engineered to synthesize vaccines that simultaneously co-deliver influenza hemagglutinin (H5) antigen, TLR5 agonist flagellin (FliCc), and TLR9 agonist CpG 1826 (CpG) all on one particle (termed H5-FliCc-CpG-E2), with uniform molecular orientation significant for immunomodulation. Antigen-bound NP formulations elicit higher IgG antibody responses and broader homosubtypic cross-reactivity against different H5 variants than unconjugated antigen alone. IgG1/IgG2c skewing is modulated by adjuvant type and NP attachment. Conjugation of flagellin to the NP causes significant IgG1 (Th2) skewing while attachment of CpG yields significant IgG2c (Th1) skewing, and simultaneous conjugation of both flagellin and CpG results in a balanced IgG1/IgG2c (Th2/Th1) response. Animals immunized with E2-based NP vaccines and subsequently challenged with H5N1 influenza show 100% survival, and only animals that receive adjuvanted NP formulations are also protected against morbidity. This investigation highlights that NP-based delivery of antigen and multiple adjuvants can be designed to effectively modulate the strength, breadth toward variants, and bias of an immune response against influenza viruses.

Design and evaluation of a poly-epitope based vaccine for the induction of influenza A virus cross-reactive CD8 + T cell responses

The availability of influenza vaccines that can induce broadly protective immune responses is highly desirable and could also mitigate the impact of future influenza pandemics. Ideally, these vaccines also induce virus-specific CD8 + T cells, which have been identified as an independent correlate of protection. In the present study, we explored the use of an artificial immunogen that comprises of twenty highly conserved influenza virus CD8 + T cell epitopes with an HLA coverage of 99.5% of the world population. The highly attenuated viral vector Modified Vaccinia virus Ankara (MVA) was used to deliver the artificial poly-epitope sequence (rMVA-PE) and by using T cell lines raised against individual epitopes, we confirmed that the epitopes are liberated from the artificial immunogen. For efficient antigen processing and presentation, the epitopes were separated by spacer sequences. Stimulation of peripheral blood mononuclear cells of HLA-typed blood donors with rMVA-PE resulted in the activation of influenza virus-specific T cell responses. Furthermore, immunization of humanized HLA-A2.1-/HLA-DR1-transgenic H-2 class I-/class II-knockout mice (HLA-A*02:01) with rMVA-PE induced influenza virus-specific CD8 + T cell responses. Thus, rMVA-PE proved to be immunogenic both in vitro and in vivo and constitutes a promising vaccine candidate for the induction of cross-reactive CD8 + T cell responses that could afford protection against antigenically distinct influenza A viruses (IAV) of various subtypes and species, and is currently considered for further clinical testing.

Lovastatin enhances humoral and cellular immune responses to H1N1 influenza vaccine

The Swine Influenza Virus (SIV) is a major respiratory pathogen in swine, causing acute, febrile, and highly transmissible infections. This virus is widespread globally and poses significant risks to human health and social development. Traditional prevention strategies for SIV rely on the use of inactivated vaccines combined with Alum adjuvants. However, this method is limited by insufficient protection due to the lack of cellular immunity provided by Alum adjuvants. In this study, we investigated the effect of lovastatin, a specific inhibitor of the mevalonate pathway, on the immune response in mice vaccinated with the H1N1 vaccine. We focused on its impact on antibody production, as well as T-cell and B-cell development. Our findings reveal that the combination of lovastatin and H1N1 vaccine (Lov/H1N1) significantly enhances the production of H1N1-specific serum IgG and hemagglutination inhibition (HI) antibodies. Additionally, it promotes T-cell activation in both draining lymph nodes (dLNs) and the spleen. Analysis of cytokines produced after antigenic restimulation of splenic lymphocytes from immunized mice showed that the Lov/H1N1 combination induces both Th1-type (IFNγ, TNFα) and Th2-type (IL4, IL6) responses. Moreover, Lov/H1N1 facilitates the formation of germinal centers (GCs), which are crucial for the generation of memory B cells and long-lived plasma cells. These results indicate that lovastatin is a promising adjuvant candidate, capable of inducing robust cellular and humoral immune responses, thereby overcoming the limitations of Alum adjuvants. Our study provides a foundation for future research on combined vaccine strategies, highlighting Lovastatin's potential to enhance vaccine efficacy through improved immune responses.

Protein Nanoparticle-Mediated Delivery of Recombinant Influenza Hemagglutinin Enhances Immunogenicity and Breadth of the Antibody Response

The vast majority of seasonal influenza vaccines administered each year are derived from virus propagated in eggs using technology that has changed little since the 1930s. The immunogenicity, durability, and breadth of response would likely benefit from a recombinant nanoparticle-based approach. Although the E2 protein nanoparticle (NP) platform has been previously shown to promote effective cell-mediated responses to peptide epitopes, it has not yet been reported to deliver whole protein antigens. In this study, we synthesized a novel maleimido tris-nitrilotriacetic acid (NTA) linker to couple protein hemagglutinin (HA) from H1N1 influenza virus to the E2 NP, and we evaluated the HA-specific antibody responses using protein microarrays. We found that recombinant H1 protein alone is immunogenic in mice but requires two boosts for IgG to be detected and is strongly IgG1 (Th2) polarized. When conjugated to E2 NPs, IgG2c is produced leading to a more balanced Th1/Th2 response. Inclusion of the Toll-like receptor 4 agonist monophosphoryl lipid A (MPLA) significantly enhances the immunogenicity of H1-E2 NPs while retaining the Th1/Th2 balance. Interestingly, broader homo- and heterosubtypic cross-reactivity is also observed for conjugated H1-E2 with MPLA, compared to unconjugated H1 with or without MPLA. These results highlight the potential of an NP-based delivery of HA for tuning the immunogenicity, breadth, and Th1/Th2 balance generated by recombinant HA-based vaccination. Furthermore, the modularity of this protein-protein conjugation strategy may have utility for future vaccine development against other human pathogens.

Narrative review on century of respiratory pandemics from Spanish flu to COVID-19 and impact of nanotechnology on COVID-19 diagnosis and immune system boosting

The rise of the highly lethal severe acute respiratory syndrome-2 (SARS-2) as corona virus 2019 (COVID-19) reminded us of the history of other pandemics that happened in the last century (Spanish flu) and stayed in the current century, which include Severe-Acute-Respiratory-Syndrome (SARS), Middle-East-Respiratory-Syndrome (MERS), Corona Virus 2019 (COVID-19). We review in this report the newest findings and data on the origin of pandemic respiratory viral diseases, reservoirs, and transmission modes. We analyzed viral adaption needed for host switch and determinants of pathogenicity, causative factors of pandemic viruses, and symptoms and clinical manifestations. After that, we concluded the host factors associated with pandemics morbidity and mortality (immune responses and immunopathology, ages, and effect of pandemics on pregnancy). Additionally, we focused on the burdens of COVID-19, non-pharmaceutical interventions (quarantine, mass gatherings, facemasks, and hygiene), and medical interventions (antiviral therapies and vaccines). Finally, we investigated the nanotechnology between COVID-19 analysis and immune system boosting (Nanoparticles (NPs), antimicrobial NPs as antivirals and immune cytokines). This review presents insights about using nanomaterials to treat COVID-19, improve the bioavailability of the abused drugs, diminish their toxicity, and improve their performance.

The role of cell-mediated immunity against influenza and its implications for vaccine evaluation

Influenza vaccines remain the most effective tools to prevent flu and its complications. Trivalent or quadrivalent inactivated influenza vaccines primarily elicit antibodies towards haemagglutinin and neuraminidase. These vaccines fail to induce high protective efficacy, in particular in older adults and immunocompromised individuals and require annual updates to keep up with evolving influenza strains (antigenic drift). Vaccine efficacy declines when there is a mismatch between its content and circulating strains. Current correlates of protection are merely based on serological parameters determined by haemagglutination inhibition or single radial haemolysis assays. However, there is ample evidence showing that these serological correlates of protection can both over- or underestimate the protective efficacy of influenza vaccines. Next-generation universal influenza vaccines that induce cross-reactive cellular immune responses (CD4+ and/or CD8+ T-cell responses) against conserved epitopes may overcome some of the shortcomings of the current inactivated vaccines by eliciting broader protection that lasts for several influenza seasons and potentially enhances pandemic preparedness. Assessment of cellular immune responses in clinical trials that evaluate the immunogenicity of these new generation vaccines is thus of utmost importance. Moreover, studies are needed to examine whether these cross-reactive cellular immune responses can be considered as new or complementary correlates of protection in the evaluation of traditional and next-generation influenza vaccines. An overview of the assays that can be applied to measure cell-mediated immune responses to influenza with their strengths and weaknesses is provided here.

Randomized, Double-Blind, Reference-Controlled, Phase 2a Study Evaluating the Immunogenicity and Safety of OVX836, A Nucleoprotein-Based Influenza Vaccine

OVX836 is a recombinant protein-based vaccine targeting the highly conserved influenza nucleoprotein (NP), which aims to confer a broad-spectrum protection against influenza. In a Phase 1 study, OVX836, administered intramuscularly, has been found safe and immunogenic. The 90µg and 180µg dose levels were selected to be further evaluated in this randomized, monocenter, reference-controlled (Influvac Tetra™: quadrivalent seasonal influenza subunit vaccine), parallel group, double-blind, Phase 2a study in 300 healthy volunteers, aged 18-65 years, during the 2019/2020 flu season. Safety, influenza-like illness episodes (ILI; based on the Flu-PRO^® questionnaire) and immunogenicity were assessed up to 180 days post-vaccination. OVX836 was safe and presented a reactogenicity profile similar to Influvac Tetra. It induced a significant increase in terms of NP-specific interferon-gamma (IFNγ) spot forming cells (SFCs), NP-specific CD4+ T-cells (essentially polyfunctional cells) and anti-NP IgG responses. OVX836 was superior to Influvac Tetra for all immunological parameters related to NP, and the 180µg dose was significantly superior to the 90µg dose for SFCs and CD4+ T-cells expressing IFNγ. Both the CD4+ T-cell and the anti-NP IgG responses persisted up to Day 180. An efficacy signal was observed with OVX836 at 180µg through reduction of ILI episodes occurring during the flu season as of 14 days post-vaccination. In conclusion, these results encourage further clinical evaluation of OVX836 in order to confirm the signal of efficacy on ILIs and/or laboratory-confirmed influenza cases. NCT04192500 (https://clinicaltrials.gov/ct2/show/study/NCT04192500).

Selective dependence on IL-7 for antigen-specific CD8 T cell responses during airway influenza infection

Interleukin-7 (IL-7) is a cytokine known for its importance in T cell development and survival. How IL-7 shapes CD8 T cell responses during an acute viral infection is less understood. We had previously shown that IL-7 signaling deficient mice have reduced accumulation of influenza-specific CD8 T cells following influenza infection. We sought to determine whether IL-7 affects early CD8 T cell expansion in the mediastinal lymph node and effector function in the lungs. Using IL-7Rα signaling deficient mice, we show that IL-7 is required for a normal sized mediastinal lymph node and the early clonal expansion of influenza-specific CD8 T cells therein. We show that IL-7 plays a cell-intrinsic role in the accumulation of NP366-374 and PA224-233-specific CD8 T cells in the lymph node. We also found that IL-7 shapes terminal differentiation, degranulation and cytokine production to a greater extent in PA224-233-specific than NP366-374-specific CD8 T cells. We further demonstrate that IL-7 is induced in the lung tissue by viral infection and we characterize multiple cellular sources that contribute to IL-7 production. Our findings on IL-7 and its effects on lower respiratory diseases will be important for expanding the utility of therapeutics that are currently available.

Protein transduction domain-mediated influenza NP subunit vaccine generates a potent immune response and protection against influenza virus in mice

The nucleoprotein (NP) is a highly conserved internal protein of the influenza virus, a major target for universal influenza vaccine. Our previous studies have proven NP-based subunit vaccine can provide partial protection in mice. It is reported that the protein transduction domain (PTD) TAT protein from human immunodeficiency virus-1 (HIV-1) is able to penetrate cells when added exogenous protein and could effectively enhance the immune response induced by the exogenous protein. In present study, the recombinant protein TAT-NP, a fusion of TAT and NP was effectively expressed in Escherichia coli and purified as a candidate component for an influenza vaccine. We evaluated the immunogenicity and protective efficacy of recombinant influenza TAT-NP vaccine by intranasal immunization. In vitro experiments showed that TAT-NP could efficiently penetrate into cells. Animal results showed that mice vaccinated with TAT-NP could not only induce higher levels of IgG and mucosal IgA, but also elicit a robust cellular immune response. Moreover, the TAT-NP fusion protein could significantly increase the protection of mice against lethal doses of homologous influenza virus PR8 and could also provide mice protection against a lethal dose challenge against heterosubtypic H9N2 and H3N2 influenza virus. In conclusion, the recombinant TAT-NP might be a universal vaccine candidate against influenza virus.

Structural basis of Blastomyces Endoglucanase-2 adjuvancy in anti-fungal and -viral immunity

The development of safe subunit vaccines requires adjuvants that augment immunogenicity of non-replicating protein-based antigens. Current vaccines against infectious diseases preferentially induce protective antibodies driven by adjuvants such as alum. However, the contribution of antibody to host defense is limited for certain classes of infectious diseases such as fungi, whereas animal studies and clinical observations implicate cellular immunity as an essential component of the resolution of fungal pathogens. Here, we decipher the structural bases of a newly identified glycoprotein ligand of Dectin-2 with potent adjuvancy, Blastomyces endoglucanase-2 (Bl-Eng2). We also pinpoint the developmental steps of antigen-specific CD4⁺ and CD8⁺ T responses augmented by Bl-Eng2 including expansion, differentiation and tissue residency. Dectin-2 ligation led to successful systemic and mucosal vaccination against invasive fungal infection and Influenza A infection, respectively. O-linked glycans on Bl-Eng2 applied at the skin and respiratory mucosa greatly augment vaccine subunit- induced protective immunity against lethal influenza and fungal pulmonary challenge.

Fungal disease remains a challenging clinical and public health problem in part because there is no commercial vaccine available. The lack of suitable adjuvants is a critical barrier to developing safe and effective vaccines against fungal pathogens. Current adjuvants such as alum preferentially induce antibody responses which may be limited in mediating protection against fungi. Clinical observations and animal studies implicate cellular immunity as the essential component for the resolution of fungal infections. We have recently discovered an adjuvant that augments cell mediated immune responses and vaccine induced protection against fungi. Here, we identified the structural and mechanistic requirements by which this newly discovered adjuvant induces cell mediated immunity against fungi. As a proof of principle we also demonstrate that the adjuvant drives cellular immune responses against viruses such as influenza. We anticipate that our adjuvant can be used for vaccination with safe subunit vaccines against many microbial pathogens including viruses, intracellular bacteria, fungi and parasites that require cell mediated immune responses.

Vaccine-Induced CD8+ T Cell Responses in Children: A Review of Age-Specific Molecular Determinants Contributing to Antigen Cross-Presentation

Infections are most common and most severe at the extremes of age, the young and the elderly. Vaccination can be a key approach to enhance immunogenicity and protection against pathogens in these vulnerable populations, who have a functionally distinct immune system compared to other age groups. More than 50% of the vaccine market is for pediatric use, yet to date vaccine development is often empiric and not tailored to molecular distinctions in innate and adaptive immune activation in early life. With modern vaccine development shifting from whole-cell based vaccines to subunit vaccines also comes the need for formulations that can elicit a CD8+ T cell response when needed, for example, by promoting antigen cross-presentation. While our group and others have identified many cellular and molecular determinants of successful activation of antigen-presenting cells, B cells and CD4+ T cells in early life, much less is known about the ontogeny of CD8+ T cell induction. In this review, we summarize the literature pertaining to the frequency and phenotype of newborn and infant CD8+ T cells, and any evidence of induction of CD8+ T cells by currently licensed pediatric vaccine formulations. In addition, we review the molecular determinants of antigen cross-presentation on MHC I and successful CD8+ T cell induction and discuss potential distinctions that can be made in children. Finally, we discuss recent advances in development of novel adjuvants and provide future directions for basic and translational research in this area.

Vaccination of aged mice with adjuvanted recombinant influenza nucleoprotein enhances protective immunity

Elderly individuals are highly susceptible to influenza virus (IAV) infection and respond poorly to influenza vaccines. Although the generally accepted correlate of protection following influenza vaccination is neutralizing antibody titers, cytotoxic T cell activity has been found to be a better correlate in the elderly. This suggests that vaccines designed to protect against influenza in the elderly should induce both humoral and cellular immunity. The co-induction of T cell immunity is additionally advantageous, as virus-specific T cells are frequently cross-reactive against different strains of IAV. Here, we tested the capacity of a synthetic TLR-4 adjuvant, SLA-SE (second-generation lipid adjuvant formulated in a squalene-based oil-in-water emulsion) to elicit T cell immunity to a recombinant influenza nucleoprotein (rNP), in both young and aged mice. IAV challenge of vaccinated mice resulted in a modest increase in the numbers of NP-specific CD4 and CD8 effector T cells in the spleen, but did not increase numbers of memory phenotype CD8 T cells generated following viral clearance (compared to control vaccinated mice). Cytotoxic activity of CD8, but not CD4 T cells was increased. In addition, SLA-SE adjuvanted vaccination specifically enhanced the production of NP-specific IgG2c antibodies in both young and aged mice. Although NP-specific antibodies are not neutralizing, they can cooperate with CD8 T cells and antigen-presenting cells to enhance protective immunity. Importantly, SLA-SE adjuvanted rNP-vaccination of aged mice resulted in significantly enhanced viral clearance. In addition, vaccination of aged mice resulted in enhanced survival after lethal challenge compared to control vaccination, that approached statistical significance. These data demonstrate the potential of SLA-SE adjuvanted rNP vaccines to (i) generate both cellular and humoral immunity to relatively conserved IAV proteins and (ii) elicit protective immunity to IAV in aged mice.

A Phase 1 Randomized Placebo-Controlled Study to Assess the Safety, Immunogenicity and Genetic Stability of a New Potential Pandemic H7N9 Live Attenuated Influenza Vaccine in Healthy Adults

This study describes a double-blind randomized placebo-controlled phase I clinical trial in healthy adults of a new potential pandemic H7N9 live attenuated influenza vaccine (LAIV) based on the human influenza virus of Yangtze River Delta hemagglutinin lineage (ClinicalTrials.gov Identifier: NCT03739229). Two doses of H7N9 LAIV or placebo were administered intranasally to 30 and 10 subjects, respectively. The vaccine was well-tolerated and not associated with increased rates of adverse events or with any serious adverse events. Vaccine virus was detected in nasal swabs during the 6 days after vaccination or revaccination. A lower frequency of shedding was observed after the second vaccination. Twenty-five clinical viral isolates obtained after the first and second doses of vaccine retained the temperature-sensitive and cold-adapted phenotypic characteristics of LAIV. There was no confirmed transmission of the vaccine strain from vaccinees to placebo recipients. After the two H7N9 LAIV doses, an immune response was observed in 96.6% of subjects in at least one of the assays conducted.

Induction of Human T-cell and Cytokine Responses Following Vaccination with a Novel Influenza Vaccine

Cell mediated immunity plays a vital role in defense against influenza infection in humans. Less is known about the role of vaccine-induced cell mediated immunity and the cytokine responses elicited. We measured CD4⁺ and CD8⁺ T-cell reactivity in human subjects following vaccination with licensed trivalent influenza vaccine and a novel virus-like particle based vaccine. We detected influenza-specific CD4⁺ T-cell responses following vaccination with the licensed trivalent influenza vaccine and found that these correlated with antibody measurements. Administration of the novel virus-like particle based vaccine elicited influenza-specific CD4⁺ and CD8⁺ T-cell responses and the induction of the cytokines IFN-γ, IL-17A, IL17F, IL-5, IL-13, IL-9, IL-10 and IL-21. Pre-existing cytokine responses influenced the profile of the cytokine response elicited by vaccination. In a subset of individuals the VLP vaccine changed pre-vaccination production of type 2 cytokines such as IL-5 and IL-13 to a post-vaccination type 1 cytokine signature characterized by IFN-γ. A transcriptional signature to vaccination was found to correlate with antibody titer, IFN-γ production by T-cells and expression of a putative RNA helicase, DDX17, on the surface of immune cells.

Virus-like particle vaccines: immunology and formulation for clinical translation

INTRODUCTION

Virus-like particle (VLP) vaccines face significant challenges in their translation from laboratory models, to routine clinical administration. While some VLP vaccines thrive and are readily adopted into the vaccination schedule, others are restrained by regulatory obstacles, proprietary limitations, or finding their niche amongst the crowded vaccine market. Often the necessity to supplant an existing vaccination regimen possesses an immediate obstacle for the development of a VLP vaccine, despite any preclinical advantages identified over the competition. Novelty, adaptability and formulation compatibility may prove invaluable in helping place VLP vaccines at the forefront of vaccination technology.

AREAS COVERED

The purpose of this review is to outline the diversity of VLP vaccines, VLP-specific immune responses, and to explore how modern formulation and delivery techniques can enhance the clinical relevance and overall success of VLP vaccines.

EXPERT COMMENTARY

The role of formation science, with an emphasis on the diversity of immune responses induced by VLP, is underrepresented amongst clinical trials for VLP vaccines. Harnessing such diversity, particularly through the use of combinations of select excipients and adjuvants, will be paramount in the development of VLP vaccines.

Humoral and cell-mediated immune responses to H5N1 plant-made virus-like particle vaccine are differentially impacted by alum and GLA-SE adjuvants in a Phase 2 clinical trial

The hemagglutinination inhibition (HI) response remains the gold standard used for the licensure of influenza vaccines. However, cell-mediated immunity (CMI) deserves more attention, especially when evaluating H5N1 influenza vaccines that tend to induce poor HI response. In this study, we measured the humoral response (HI) and CMI (flow cytometry) during a Phase II dose-ranging clinical trial (NCT01991561). Subjects received two intramuscular doses, 21 days apart, of plant-derived virus-like particles (VLP) presenting the A/Indonesia/05/2005 H5N1 influenza hemagglutinin protein (H5) at the surface of the VLP (H5VLP). The vaccine was co-administrated with Alhydrogel^® or with a glucopyranosyl lipid adjuvant-stable emulsion (GLA-SE). We demonstrated that low doses (3.75 or 7.5 μg H5VLP) of GLA-SE-adjuvanted vaccines induced HI responses that met criteria for licensure at both antigen doses tested. Alhydrogel adjuvanted vaccines induced readily detectable HI response that however failed to meet licensure criteria at any of three doses (10, 15 and 20 μg) tested. The H5VLP also induced a sustained (up to 6 months) polyfunctional and cross-reactive HA-specific CD4⁺ T cell response in all vaccinated groups. Interestingly, the frequency of central memory Th1-primed precursor cells before the boost significantly correlated with HI titers 21 days after the boost. The ability of the low dose GLA-SE-adjuvanted H5VLP to elicit both humoral response and a sustained cross-reactive CMI in healthy adults is very attractive and could result in significant dose-sparing in a pandemic situation.

Hemagglutinin-specific CD4+ T-cell responses following 2009-pH1N1 inactivated split-vaccine inoculation in humans

Influenza A virus remains a major threat to public health, and the inactivated split-virus vaccine is the most prevalent vaccine used worldwide. However, our knowledge about cellular immune responses to the inactivated influenza virus vaccine and its correlation with humoral responses are yet limited, which has restricted our understanding of the vaccine's protective mechanisms. Herein, in two clinical trials, T-cell responses specific for both previously identified human leucocyte antigen (HLA)-I-restricted epitopes from influenza virus and hemagglutinin (HA) protein were longitudinally investigated before, during, and after a two-dose vaccination with the inactivated 2009 pandemic H1N1 (2009-pH1N1) vaccine. A robust antibody response in all of the donors after vaccination was observed. Though no CD8⁺ T-cell responses to known epitopes were detected, HA-specific T-cell responses were primed following vaccination, and the responses were found to be mainly CD4⁺ T-cell dependent. However, HA-specific T-cells circulating in peripheral blood dropped to baseline levels 6weeks after vaccination, but humoral immune responses maintained a high level for 4months post-vaccination. Significant correlations between the magnitude of the HA-specific T-cell responses and hemagglutination inhibition antibody titers were demonstrated, indicating a priming role of HA-specific T-cells for humoral immune responses. In conclusion, our study indicates that HA-specific CD4⁺ T-cell responses can be primed by the inactivated 2009-pH1N1 vaccine, which may coordinate with the elicitation of antibody protection. These findings would benefit a better understanding of the immune protective mechanisms of the widely used inactivated 2009-pH1N1 vaccine.

Frequencies of peripheral immune cells in older adults following seasonal influenza vaccination with an adjuvanted vaccine

As age increases, immune responses and consequently protection following vaccination to seasonal influenza is commonly believed to decrease. Possible drivers of this immune dysfunction include immunosenescence, repeated exposure to the same seasonal influenza antigens, and prior infection with cytomegalovirus (CMV). Here, to determine immune parameters distinguishing vaccine humoral responders (R) from non-responders (NR) following vaccination, we surveyed broad peripheral blood "cellular immune correlates" of older adults vaccinated with Fluad® (an adjuvanted subunit influenza vaccine containing strains H1N1, H3N2 and B). Phenotyping included αβ-T-cells, γδ-T-cells, B-cells and myeloid cells. The frequencies of most of these lymphocyte phenotypes were found to be similar in R and NR, although perhaps counterintuitively, one of the few differences seen between the two groups was higher frequencies of regulatory T-cells in R. These differences were more prominent for responses to the vaccine strains H1N1 and H3N2 than to the B strain, and in CMV-seropositive than CMV-seronegative elderly. Further, frequencies of early-differentiated CD4+ T-cells tended to be higher and frequencies of memory CD4+ T-cells tended to be lower in R than NR. There were also differences in B-cells, with higher frequencies in R compared to NR. To the best of our knowledge, these results are the first to report such differences in elderly people responding or failing to respond to adjuvanted seasonal influenza vaccination.

Effective Respiratory CD8 T-Cell Immunity to Influenza Virus Induced by Intranasal Carbomer-Lecithin-Adjuvanted Non-replicating Vaccines

CD8⁺ cytotoxic T lymphocytes (CTLs) are critical for clearing many viral infections, and protective CTL memory can be induced by vaccination with attenuated viruses and vectors. Non-replicating vaccines are typically potentiated by the addition of adjuvants that enhance humoral responses, however few are capable of generating CTL responses. Adjuplex is a carbomer-lecithin-based adjuvant demonstrated to elicit robust humoral immunity to non-replicating antigens. We report that mice immunized with non-replicating Adjuplex-adjuvanted vaccines generated robust antigen-specific CTL responses. Vaccination by the subcutaneous or the intranasal route stimulated systemic and mucosal CTL memory respectively. However, only CTL memory induced by intranasal vaccination was protective against influenza viral challenge, and correlated with an enhancement of memory CTLs in the airways and CD103⁺ CD69⁺ CXCR3⁺ resident memory-like CTLs in the lungs. Mechanistically, Myd88-deficient mice mounted primary CTL responses to Adjuplex vaccines that were similar in magnitude to wild-type mice, but exhibited altered differentiation of effector cell subsets. Immune potentiating effects of Adjuplex entailed alterations in the frequency of antigen-presenting-cell subsets in vaccine draining lymph nodes, and in the lungs and airways following intranasal vaccination. Further, Adjuplex enhanced the ability of dendritic cells to promote antigen-induced proliferation of naïve CD8 T cells by modulating antigen uptake, its intracellular localization, and rate of processing. Taken together, we have identified an adjuvant that elicits both systemic and mucosal CTL memory to non-replicating antigens, and engenders protective CTL-based heterosubtypic immunity to influenza A virus in the respiratory tract. Further, findings presented in this manuscript have provided key insights into the mechanisms and factors that govern the induction and programming of systemic and protective memory CTLs in the respiratory tract.

Current respiratory-virus vaccines typically employ non-replicating antigens and rely solely on the generation of humoral responses for protection. Viruses such as influenza can mutate and escape these responses, thereby limiting immunity and necessitating revaccination. Cell-mediated immunity (CMI) could provide broader protection by targeting viral components that infrequently mutate, however non-replicating vaccines capable of inducing CMI are not available. Impediments to vaccine development include an incomplete understanding of the nature of protective respiratory CMI and a lack of vaccine adjuvants capable of eliciting CMI to non-replicating antigens. Using a mouse model, we characterized the protective immunity afforded by CMI responses to non-replicating vaccines formulated with the adjuvant Adjuplex. We found that vaccination via either the subcutaneous or intranasal route was capable of inducing potent CMI responses. However, only intranasal vaccination protected against challenge with heterosubtypic influenza viruses. This protection correlated with enhancement of T cells with a resident-memory phenotype in the lungs. Additionally, mechanistic studies showed that Adjuplex affects antigen-presenting cells via activation and alteration of antigen uptake, processing, and presentation. The current studies: (1) identified an adjuvant that elicits protective CMI to respiratory viral pathogens; (2) suggested that stimulation of protective CMI in the respiratory tract requires intranasal vaccine delivery.

Universal or Specific? A Modeling-Based Comparison of Broad-Spectrum Influenza Vaccines against Conventional, Strain-Matched Vaccines

Despite the availability of vaccines, influenza remains a major public health challenge. A key reason is the virus capacity for immune escape: ongoing evolution allows the continual circulation of seasonal influenza, while novel influenza viruses invade the human population to cause a pandemic every few decades. Current vaccines have to be updated continually to keep up to date with this antigenic change, but emerging ‘universal’ vaccines—targeting more conserved components of the influenza virus—offer the potential to act across all influenza A strains and subtypes. Influenza vaccination programmes around the world are steadily increasing in their population coverage. In future, how might intensive, routine immunization with novel vaccines compare against similar mass programmes utilizing conventional vaccines? Specifically, how might novel and conventional vaccines compare, in terms of cumulative incidence and rates of antigenic evolution of seasonal influenza? What are their potential implications for the impact of pandemic emergence? Here we present a new mathematical model, capturing both transmission dynamics and antigenic evolution of influenza in a simple framework, to explore these questions. We find that, even when matched by per-dose efficacy, universal vaccines could dampen population-level transmission over several seasons to a greater extent than conventional vaccines. Moreover, by lowering opportunities for cross-protective immunity in the population, conventional vaccines could allow the increased spread of a novel pandemic strain. Conversely, universal vaccines could mitigate both seasonal and pandemic spread. However, where it is not possible to maintain annual, intensive vaccination coverage, the duration and breadth of immunity raised by universal vaccines are critical determinants of their performance relative to conventional vaccines. In future, conventional and novel vaccines are likely to play complementary roles in vaccination strategies against influenza: in this context, our results suggest important characteristics to monitor during the clinical development of emerging vaccine technologies.

Influenza vaccines used today offer good protection, but have limitations: they have to be updated regularly, to remain effective in the face of ongoing virus evolution, and they cannot be used in advance of an influenza pandemic. In this study we considered how such ‘conventional’ vaccines might compare on the population level against new ‘universal’ vaccines currently being developed, that may protect against a broad spectrum of influenza viruses. We developed a mathematical model to capture the interactions between vaccination, influenza transmission, and viral evolution. The model suggests that annual vaccination with universal vaccines could control annual influenza epidemics more efficiently than conventional vaccines. In doing so they could slow viral evolution, rather than promoting it, while maintaining the broadly protective immunity that could mitigate against the emergence of a pandemic. These effects depend sensitively on the duration of protection that universal vaccines can afford, an important quantity to monitor in their development. In future, it is likely that conventional and universal vaccines would be deployed in tandem: we suggest that they could fulfill distinct roles, with universal vaccines being prioritised for managing transmission and evolution, and conventional vaccines being focused on protecting specific risk groups.

A plant-derived quadrivalent virus like particle influenza vaccine induces cross-reactive antibody and T cell response in healthy adults

Recent issues regarding efficacy of influenza vaccines have re-emphasized the need of new approaches to face this major public health issue. In a phase 1-2 clinical trial, healthy adults received one intramuscular dose of a seasonal influenza plant-based quadrivalent virus-like particle (QVLP) vaccine or placebo. The hemagglutination inhibition (HI) titers met all the European licensure criteria for the type A influenza strains at the 3μg/strain dose and for all four strains at the higher dosages 21days after immunization. High HI titers were maintained for most of the strains 6months after vaccination. QVLP vaccine induced a substantial and sustained increase of hemagglutinin-specific polyfunctional CD4 T cells, mainly transitional memory and TEMRA effector IFN-γ(+) CD4 T cells. A T cells cross-reactive response was also observed against A/Hong-Kong/1/1968 H3N2 and B/Massachusetts/2/2012. Plant-based QVLP offers an attractive alternative manufacturing method for producing effective and HA-strain matching seasonal influenza vaccines.

Plant-derived H7 VLP vaccine elicits protective immune response against H7N9 influenza virus in mice and ferrets

In March 2013, the Chinese Centre for Disease Control and Prevention confirmed the first reported case of human infection with an avian influenza A H7N9 virus. Infection with this virus often caused severe pneumonia and acute respiratory distress syndrome resulting in a case fatality rate >35%. The risk of pandemic highlighted, once again, the need for a more rapid and scalable vaccine response capability. Here, we describe the rapid (19 days) development of a plant-derived VLP vaccine based on the hemagglutinin sequence of influenza H7N9 A/Hangzhou/1/2013. The immunogenicity of the H7 VLP vaccine was assessed in mice and ferrets after one or two intramuscular dose(s) with and without adjuvant (alum or GLA-SE™). In ferrets, we also measured H7-specific cell-mediated immunity. The mice and ferrets were then challenged with H7N9 A/Anhui/1/2013 influenza virus. A single immunization with the adjuvanted vaccine elicited a strong humoral response and protected mice against an otherwise lethal challenge. Two doses of unadjuvanted vaccine significantly increased humoral response and resulted in 100% protection with significant reduction of clinical signs leading to nearly asymptomatic infections. In ferrets, a single immunization with the alum-adjuvanted H7 VLP vaccine induced strong humoral and CMI responses with antigen-specific activation of CD3(+) T cells. Compared to animals injected with placebo, ferrets vaccinated with alum-adjuvanted vaccine displayed no weight loss during the challenge. Moreover, the vaccination significantly reduced the viral load in lungs and nasal washes 3 days after the infection. This candidate plant-made H7 vaccine therefore induced protective responses after either one adjuvanted or two unadjuvanted doses. Studies are currently ongoing to better characterize the immune response elicited by the plant-derived VLP vaccines. Regardless, these data are very promising for the rapid production of an immunogenic and protective vaccine against this potentially pandemic virus.

Immunopotentiator-Loaded Polymeric Microparticles as Robust Adjuvant to Improve Vaccine Efficacy

PURPOSE

Adjuvants are required to ensure the efficacy of subunit vaccines. Incorporating molecular immunopotentiators within particles could overcome drawbacks of molecular adjuvants (such as solubility and toxicity), and improve adjuvanticity of particles, achieving stronger adjuvant activity. Aim of this study is to evaluate the adjuvanticity of immunopotentiator-loaded polymeric particles for subunit vaccine.

METHODS

PLGA microparticles (PMPs) and imiquimod (TLR-7 ligand)-loaded PLGA microparticles (IPMPs) were prepared by SPG premix membrane emulsification. In vitro and in vivo studies were performed to their adjuvant activity, using ovalbumin and H5N1 influenza split vaccine as antigens.

RESULTS

Incorporating imiquimod into microparticles significantly improved the efficacy of PLGA microparticles in activating BMDCs and pMΦs, and antigen uptake by pMΦs was also promoted. IPMPs showed stronger adjuvanticity to augment OVA-specific immune responses than PMPs. IgG subclass profiles and cytokine secretion levels by splenocytes indicated that IPMPs elicited more Th1-polarized immune response, compared to PMPs. In vivo study using H5N1 influenza split vaccine as antigen also confirmed the effects of IPMPs on antigen-specific cellular immunity.

CONCLUSIONS

Considering adjuvanticity and safety profiles (PLGA and IMQ, both approved by FDA), we conclude that IMQ-loaded PLGA microparticles are promising robust adjuvant for subunit vaccines.

Boosted Influenza-Specific T Cell Responses after H5N1 Pandemic Live Attenuated Influenza Virus Vaccination

Background

In a phase I clinical trial, a H5N1 pandemic live attenuated influenza virus (pLAIV) VN2004 vaccine bearing avian influenza H5N1 hemagglutinin (HA) and NA genes on the A/Ann Arbor cold-adapted vaccine backbone displayed very restricted replication. We evaluated T cell responses to H5N1 pLAIV vaccination and assessed pre-existing T cell responses to determine whether they were associated with restricted replication of the H5N1 pLAIV.

Method

ELISPOT assays were performed using pools of overlapping peptides spanning the entire H5N1 proteome and the HA proteins of relevant seasonal H1N1 and H3N2 viruses. We tested stored peripheral blood mononuclear cells (PBMCs) from 21 study subjects who received two doses of the H5N1 pLAIV. The PBMCs were collected 1 day before and 7 days after the first and second pLAIV vaccine doses, respectively.

Result

T cell responses to conserved internal proteins M and NP were significantly boosted by vaccination (p = 0.036). In addition, H5N1 pLAIV appeared to preferentially stimulate and boost pre-existing seasonal influenza virus HA-specific T cell responses that showed low cross-reactivity with the H5 HA. We confirmed this observation by T cell cloning and identified a novel HA-specific epitope. However, we did not find any evidence that pre-existing T cells prevented pLAIV replication and take.

Conclusion

We found that cross-reactive T cell responses could be boosted by pLAIV regardless of the induction of antibody. The impact of the “original antigenic sin” phenomenon in a subset of volunteers, with preferential expansion of seasonal influenza-specific but not H5N1-specific T cell responses merits further investigation.

A truncated C-terminal fragment of Mycobacterium tuberculosis HSP70 enhances cell-mediated immune response and longevity of the total IgG to influenza A virus M2e protein in mice

As the importance of virus-specific IgG2a and strong induction of Th1 type immune response for virus clearance was reported, conventional influenza vaccines induce a highly humoral immune response and fail to induce cytotoxic T-lymphocyte (CTL) immunity. Hence, in agreement with heat shock protein 70 (HSP70) acting as Th1 cytokine-like adjuvant, an Escherichia coli-expressed r4M2e.HSP70c fusion protein comprising C-terminus of Mycobacterium tuberculosis HSP70 genetically fused to four tandem repeats of influenza A virus M2e was constructed. Then, the case-control study was carried out to evaluate the humoral and cellular responses elicited against M2e in Balb/C mice by intramuscular immunization with r4M2e.HSP70c alone. Our results showed that r4M2e.HSP70c rather than control groups, r4M2e, r4M2e+Alum, or rHSP70c, significantly elevated both longevity and serum level of the total M2e-specific IgG antibody, induced a Th1 skewed humoral and cellular immune responses, increased the level of IFN-γ in BALF, and promoted the proliferation of peripheral blood lymphocytes. Furthermore, a virus challenge experiment revealed that mice vaccinated with r4M2e.HSP70c limited the severity of influenza A disease by 100% survival rate, less sever body weight loss and delaying the onset of morbidity in mice for 2days rather than other control groups. Here, we used r4M2e.HSP70c to stimulate M2e-specific antibody and cellular immune responses in Balb/C mice. The mHSP70c in the fusion form induced a long lasting Th1 skewed humoral and cellular immune responses against its associated protein. It seems anti-M2e antibodies limit viral replication and ameliorate influenza infection that allows the immune system to induce sterilizing HA-antibody against whole virion that leads to full protection against virulent influenza infection.

Chemical-free inactivated whole influenza virus vaccine prepared by ultrashort pulsed laser treatment

There is an urgent need for rapid methods to develop vaccines in response to emerging viral pathogens. Whole inactivated virus (WIV) vaccines represent an ideal strategy for this purpose; however, a universal method for producing safe and immunogenic inactivated vaccines is lacking. Conventional pathogen inactivation methods such as formalin, heat, ultraviolet light, and gamma rays cause structural alterations in vaccines that lead to reduced neutralizing antibody specificity, and in some cases, disastrous T helper type 2-mediated immune pathology. We have evaluated the potential of a visible ultrashort pulsed (USP) laser method to generate safe and immunogenic WIV vaccines without adjuvants. Specifically, we demonstrate that vaccination of mice with laser-inactivated H1N1 influenza virus at about a 10-fold lower dose than that required using conventional formalin-inactivated influenza vaccines results in protection against lethal H1N1 challenge in mice. The virus, inactivated by the USP laser irradiation, has been shown to retain its surface protein structure through hemagglutination assay. Unlike conventional inactivation methods, laser treatment did not generate carbonyl groups in protein, thereby reducing the risk of adverse vaccine-elicited T helper type 2 responses. Therefore, USP laser treatment is an attractive potential strategy to generate WIV vaccines with greater potency and safety than vaccines produced by current inactivation techniques.

Influenza T-cell epitope-loaded virosomes adjuvanted with CpG as a potential influenza vaccine

Purpose

Influenza CD8⁺ T-cell epitopes are conserved amongst influenza strains and can be recognized by influenza-specific cytotoxic T-cells (CTLs), which can rapidly clear infected cells. An influenza peptide vaccine that elicits these CTLs would therefore be an alternative to current influenza vaccines, which are not cross-reactive. However, peptide antigens are poorly immunogenic due to lack of delivery to antigen presenting cells, and therefore need additional formulation with a suitable delivery system. In this study, the potential of virosomes as a delivery system for an influenza T-cell peptide was investigated.

Methods

The conserved human HLA-A2.1 influenza T-cell epitope M1_58–66 was formulated with virosomes. The immunogenicity and protective effect of the peptide-loaded virosomes was assessed in HLA-A2 transgenic mice. Delivery properties of the virosomes were studied in mice and in in vitro dendritic cell cultures.

Results

Immunization of HLA-A2.1 transgenic C57BL/6 mice with peptide-loaded virosomes in the presence of the adjuvant CpG-ODN 1826 increased the number of peptide-specific CTLs. Vaccination with adjuvanted peptide-loaded virosomes reduced weight loss in mice after heterologous influenza infection. Association with fusion-active virosomes was found to be crucial for antigen uptake by dendritic cells, and subsequent induction of CTLs in mice.

Conclusions

These results show that influenza virosomes loaded with conserved influenza epitopes could be the basis of a novel cross-protective influenza vaccine.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-014-1556-3) contains supplementary material, which is available to authorized users.

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.

Influenza virus-like particle vaccines made in Nicotiana benthamiana elicit durable, poly-functional and cross-reactive T cell responses to influenza HA antigens

Cell-mediated immunity plays a major role in long-lived, cross-reactive protection against influenza virus. We measured long-term poly-functional and cross-reactive T cell responses to influenza hemagglutinin (HA) elicited by a new plant-made Virus-Like Particle (VLP) vaccine targeting either H1N1 A/California/7/09 (H1) or H5N1 A/Indonesia/5/05 (H5). In two independent clinical trials, we characterized the CD4(+) and CD8(+) T cell homotypic and heterotypic responses 6 months after different vaccination regimens. Responses of VLP-vaccinated subjects were compared with placebo and/or a commercial trivalent inactivated vaccine (TIV:Fluzone™) recipients. Both H1 and H5 VLP vaccines elicited significantly greater poly-functional CD4(+) T cell responses than placebo and TIV. Poly-functional CD8(+) T cell responses were also observed after H1 VLP vaccination. Our results show that plant-made HA VLP vaccines elicit both strong antibody responses and poly-functional, cross-reactive memory T cells that persist for at least 6 months after vaccination.

Intranasal delivery of influenza rNP adjuvanted with c-di-AMP induces strong humoral and cellular immune responses and provides protection against virus challenge

There is a critical need for new influenza vaccines able to protect against constantly emerging divergent virus strains. This will be sustained by the induction of vigorous cellular responses and humoral immunity capable of acting at the portal of entry of this pathogen. In this study we evaluate the protective efficacy of intranasal vaccination with recombinant influenza nucleoprotein (rNP) co-administrated with bis-(3′,5′)-cyclic dimeric adenosine monophosphate (c-di-AMP) as adjuvant. Immunization of BALB/c mice with two doses of the formulation stimulates high titers of NP-specific IgG in serum and secretory IgA at mucosal sites. This formulation also promotes a strong Th1 response characterized by high secretion of INF-γ and IL-2. The immune response elicited promotes efficient protection against virus challenge. These results suggest that c-di-AMP is a potent mucosal adjuvant which may significantly contribute towards the development of innovative mucosal vaccines against influenza.

A novel peptide-based pan-influenza A vaccine: a double blind, randomised clinical trial of immunogenicity and safety

BACKGROUND

FP-01.1 is a novel synthetic influenza A vaccine consisting of six fluorocarbon-modified 35-mer peptides that encapsulate multiple CD4+ and CD8+ T-cell epitopes and is designed to induce an immune response across a broad population.

METHODS

FP-01.1 was evaluated for safety and immunogenicity in a randomised, double-blind, placebo-controlled, dose-escalation, phase I clinical study in healthy adult volunteers (n=49). IFNγ ELISpot assays and multicolour flow cytometry were used to characterise the immune response.

RESULTS

FP-01.1 was safe and well tolerated at all doses tested with a similar adverse event profile in actively vaccinated subjects compared with controls. Maximum immunogenicity was in the 150 μg/peptide dose group where a robust response (243 spots/million PBMC) was demonstrated in 75% subjects compared with 0% in placebo controls. All six peptides were immunogenic. FP-01.1 induced dual CD4+ and CD8+ T cell responses and vaccine-specific T cells cross-recognise divergent influenza strains.

CONCLUSIONS

This first-in-human study showed that FP-01.1 has an acceptable safety and tolerability profile and generated robust anti-viral T cell responses in a high proportion of subjects tested. The results support the further clinical testing of FP-01.1 prior to clinical, proof-of-concept, live viral challenge studies.

Immunological assessment of influenza vaccines and immune correlates of protection

Influenza vaccines remain the primary public health tool in reducing the ever-present burden of influenza and its complications. In seeking more immunogenic, more effective and more broadly cross-protective influenza vaccines, the landscape of influenza vaccines is rapidly expanding, both in near-term advances and next-generation vaccine design. Although the first influenza vaccines were licensed over 60 years ago, the hemagglutination-inhibition antibody titer is currently the only universally accepted immune correlate of protection against influenza. However, hemagglutination-inhibition titers appear to be less effective at predicting protection in populations at high risk for severe influenza disease; older adults, young children and those with certain medical conditions. The lack of knowledge and validated methods to measure alternate immune markers of protection against influenza remain a substantial barrier to the development of more immunogenic, broadly cross-reactive and effective influenza vaccines. Here, the authors review the knowledge of immune effectors of protection against influenza and discuss assessment methods for a broader range of immunological parameters that could be considered in the evaluation of traditional or new-generation influenza vaccines.

Evaluation of a novel immunogenic vaccine platform based on a genome replication-deficient Sendai vector

We developed a novel vaccine platform based on a paramyxoviral, genome replication-deficient Sendai virus vector that can express heterologous genes inserted into the genome. To validate the novel approach in vivo, we generated a combined vaccine candidate against human respiratory syncytial virus (RSV) and human parainfluenza virus type 3 (PIV3). The present study compares two different methods of displaying heterologous antigens: (i) the RSV fusion (F) protein, encoded as a secretable version in an additional transcription unit, serves as an antigen only after being expressed in infected cells; (ii) PIV3 fusion (F) and hemagglutinin-neuraminidase (HN) genes, replacing Sendai counterparts in the vector genome, are also expressed as structural components on the surface of vaccine particles. The efficacy of this prototype vaccine was assessed in a mouse model after mucosal administration. The vaccine candidate was able to elicit specific mucosal, humoral and T cell-mediated immune responses against RSV and PIV3. However, PIV3 antigen display on the vaccine particles' surface induced higher antibody titers than the RSV antigen, being expressed only after cell infection. Consequently, this construct induced an adequate neutralizing antibody response only to PIV3. Finally, replicating virus particles were not detected in the lungs of immunized mice, confirming the genome stability and replication deficiency of this vaccine vector in vivo. Both factors can contribute substantially to the safety profile of vaccine candidates. In conclusion, this replication-deficient Sendai vector represents an efficient platform that can be used for vaccine developments against various viral pathogens.

To dream the impossible dream: universal influenza vaccination

Year in and year out, influenza viruses exact a deadly and expensive toll on humanity. Current vaccines simply do not keep pace with viral immune evasion, providing partial protection, at best, among various age groups. A quantum leap in understanding the basic principles of the adaptive and innate immune responses to influenza viruses offers the opportunity to develop vaccines that forestall, and potentially ultimately defeat, influenza virus antigenic variation.

Memory CD4 T cell-mediated immunity against influenza A virus: more than a little helpful

Recent observations have uncovered multiple pathways whereby CD4 T cells can contribute to protective immune responses against microbial threats. Incorporating the generation of memory CD4 T cells into vaccine strategies thus presents an attractive approach toward improving immunity against several important human pathogens, especially those against which antibody responses alone are inadequate to confer long-term immunity. Here, we review how memory CD4 T cells provide protection against influenza viruses. We discuss the complexities of protective memory CD4 T cell responses observed in animal models and the potential challenges of translating these observations into the clinic. Specifically, we concentrate on how better understanding of organ-specific heterogeneity of responding cells and defining multiple correlates of protection might improve vaccine-generated memory CD4 T cells to better protect against seasonal, and more importantly, pandemic influenza.

Immunity against heterosubtypic influenza virus induced by adenovirus and MVA expressing nucleoprotein and matrix protein-1

Alternate prime/boost vaccination regimens employing recombinant replication-deficient adenovirus or MVA, expressing Influenza A virus nucleoprotein and matrix protein 1, induced antigen-specific T cell responses in intradermally (ID) vaccinated mice; with the strongest responses resulting from Ad/MVA immunization. In BALB/C mice the immunodominant response was shifted from the previously identified immunodominant epitope to a novel epitope when the antigen was derived from A/Panama/2007/1999 rather than A/PR/8. Alternate immunization routes did not affect the magnitude of antigen-specific systemic IFN-γ response, but higher CD8(+) T-cell IFN-γ immune responses were seen in the bronchoalveolar lavage following intransal (IN) boosting after intramuscular (IM) priming, whilst higher splenic antigen-specific CD8(+) T cell IFN-γ was seen following IM boosting. Partial protection against heterologous influenza virus challenge was achieved following either IM/IM or IM/IN but not ID/ID immunization. These data may be of relevance for the design of optimal immunization regimens for human influenza vaccines, especially for influenza-naïve infants.