Prospects for an influenza vaccine that induces cross-protective cytotoxic T lymphocytes

Comparison of PLA microparticles and alum as adjuvants for H5N1 influenza split vaccine: adjuvanticity evaluation and preliminary action mode analysis

PURPOSE

To compare the adjuvanticity of polymeric particles (new-generation adjuvant) and alum (the traditional and FDA-approved adjuvant) for H5N1 influenza split vaccine, and to investigate respective action mode.

METHODS

Vaccine formulations were prepared by incubating lyophilized poly(lactic acid) (PLA) microparticles or alum within antigen solution. Antigen-specific immune responses in mice were evaluated using ELISA, ELISpot, and flow cytometry assay. Adjuvants' action modes were investigated by determining antigen persistence at injection sites, local inflammation response, antigen transport into draining lymph node, and activation of DCs in secondary lymphoid organs (SLOs).

RESULTS

Alum promoted antigen-specific humoral immune response. PLA microparticles augmented both humoral immune response and cell-mediated-immunity which might enhance cross-protection of influenza vaccine. With regard to action mode, alum adjuvant functions by improving antigen persistence at injection sites, inducing severe local inflammation, slightly improving antigen transport into draining lymph nodes, and improving the expression of MHC II on DCs in SLOs. PLA microparticles function by slightly improving antigen transport into draining lymph nodes, and promoting the expression of both MHC molecules and co-stimulatory molecules on DCs in SLOs.

CONCLUSIONS

Considering the adjuvanticity and side effects (local inflammation) of both adjuvants, we conclude that PLA microparticles are promising alternative adjuvant for H5N1 influenza split vaccine.

Ex vivo restimulation of human PBMC expands a CD3+CD4-CD8- γδ+ T cell population that can confound the evaluation of CD4 and CD8 T cell responses to vaccination

The measurement of vaccine-induced humoral and CD4⁺ and CD8⁺ cellular immune responses represents an important correlate of vaccine efficacy. Accurate and reliable assays evaluating such responses are therefore critical during the clinical development phase of vaccines. T cells play a pivotal role both in coordinating the adaptive and innate immune responses and as effectors. During the assessment of cell-mediated immunity (CMI) in subjects participating in a large-scale influenza vaccine trial, we identified the expansion of an IFN-γ-producing CD3⁺CD4⁻CD8⁻γδ⁺ T cell population in the peripheral blood of 90/610 (15%) healthy subjects. The appearance of CD3⁺CD4⁻CD8⁻γδ⁺ T cells in the blood of subjects was transient and found to be independent of the study cohort, vaccine group, subject gender and ethnicity, and ex vivo restimulation conditions. Although the function of this population and relevance to vaccination are unclear, their inclusion in the total vaccine-specific T-cell response has the potential to confound data interpretation. It is thus recommended that when evaluating the induction of IFN-γ-producing CD4⁺ and CD8⁺ immune responses following vaccination, the CD3⁺CD4⁻CD8⁻γδ⁺ T cells are either excluded or separately enumerated from the overall frequency determination.

Protective CD8 T cell-mediated immunity against influenza A virus infection following influenza virus-like particle vaccination

The development of influenza A virus (IAV) vaccines capable of inducing cytotoxic CD8 T cell responses could potentially provide superior, long-term protection against multiple, heterologous strains of IAV. Although prior studies demonstrated the effectiveness of baculovirus-derived virus-like particle (VLP) vaccination in generating Ab-mediated protection, the role that CD8 T cell immunity plays in overall VLP-mediated protection is less-well understood. In this article, we demonstrate that intranasal vaccination of mice with a VLP containing the hemagglutinin and matrix 1 proteins of IAV/PR/8/34 leads to a significant increase in hemagglutinin 533-specific CD8 T cells in the lungs and protection following subsequent homologous challenge with IAV. VLP-mediated protection was significantly reduced by CD8 T cell depletion, indicating a critical role for CD8 T cells in protective immunity. Importantly, our results show that VLP vaccine-induced CD8 T cell-mediated protection is not limited to homologous IAV strains. VLP vaccination leads to an increase in protection following heterosubtypic challenge with a strain of IAV that avoids vaccine-induced neutralizing Abs but contains conserved, immunodominant CD8 T cell epitopes. Overall, our results demonstrate the ability of influenza protein-containing VLPs to prime IAV-specific CD8 T cell responses that contribute to protection from homo- and heterosubtypic IAV infections. These results further suggest that vaccination strategies focused on the development of cross-protective CD8 T cell responses may contribute to the development of "universal" IAV vaccines.

Influenza nucleoprotein delivered with aluminium salts protects mice from an influenza A virus that expresses an altered nucleoprotein sequence

Influenza virus poses a difficult challenge for protective immunity. This virus is adept at altering its surface proteins, the proteins that are the targets of neutralizing antibody. Consequently, each year a new vaccine must be developed to combat the current recirculating strains. A universal influenza vaccine that primes specific memory cells that recognise conserved parts of the virus could prove to be effective against both annual influenza variants and newly emergent potentially pandemic strains. Such a vaccine will have to contain a safe and effective adjuvant that can be used in individuals of all ages. We examine protection from viral challenge in mice vaccinated with the nucleoprotein from the PR8 strain of influenza A, a protein that is highly conserved across viral subtypes. Vaccination with nucleoprotein delivered with a universally used and safe adjuvant, composed of insoluble aluminium salts, provides protection against viruses that either express the same or an altered version of nucleoprotein. This protection correlated with the presence of nucleoprotein specific CD8 T cells in the lungs of infected animals at early time points after infection. In contrast, immunization with NP delivered with alum and the detoxified LPS adjuvant, monophosphoryl lipid A, provided some protection to the homologous viral strain but no protection against infection by influenza expressing a variant nucleoprotein. Together, these data point towards a vaccine solution for all influenza A subtypes.

Discovering naturally processed antigenic determinants that confer protective T cell immunity

CD8+ T cells (TCD8) confer protective immunity against many infectious diseases, suggesting that microbial TCD8 determinants are promising vaccine targets. Nevertheless, current T cell antigen identification approaches do not discern which epitopes drive protective immunity during active infection - information that is critical for the rational design of TCD8-targeted vaccines. We employed a proteomics-based approach for large-scale discovery of naturally processed determinants derived from a complex pathogen, vaccinia virus (VACV), that are presented by the most frequent representatives of four major HLA class I supertypes. Immunologic characterization revealed that many previously unidentified VACV determinants were recognized by smallpox-vaccinated human peripheral blood cells in a variegated manner. Many such determinants were recognized by HLA class I-transgenic mouse immune TCD8 too and elicited protective TCD8 immunity against lethal intranasal VACV infection. Notably, efficient processing and stable presentation of immune determinants as well as the availability of naive TCD8 precursors were sufficient to drive a multifunctional, protective TCD8 response. Our approach uses fundamental insights into T cell epitope processing and presentation to define targets of protective TCD8 immunity within human pathogens that have complex proteomes, suggesting that this approach has general applicability in vaccine sciences.

Complement mediated signaling on pulmonary CD103(+) dendritic cells is critical for their migratory function in response to influenza infection

Trafficking of lung dendritic cells (DCs) to the draining lymph node (dLN) is a crucial step for the initiation of T cell responses upon pathogen challenge. However, little is known about the factors that regulate lung DC migration to the dLN. In this study, using a model of influenza infection, we demonstrate that complement component C3 is critically required for efficient emigration of DCs from the lung to the dLN. C3 deficiency affect lung DC-mediated viral antigen transport to the dLN, resulting in severely compromised priming of virus-specific T cell responses. Consequently, C3-deficient mice lack effector T cell response in the lungs that affected viral clearance and survival. We further show that direct signaling by C3a and C5a through C3aR and C5aR respectively expressed on lung DCs is required for their efficient trafficking. However, among lung DCs, only CD103⁺ DCs make a significant contribution to lung C5a levels and exclusively produce high levels of C3 and C5 during influenza infection. Collectively, our findings show that complement has a profound impact on immune regulation by controlling tissue DC trafficking and highlights a potential utility for complement as an adjuvant in novel vaccine strategies.

Influenza is a global health problem frequented by epidemics and pandemics. Current vaccines against influenza offer limited protection hence the need for reformulation and repeated vaccination. There is a pressing need to develop newer vaccines that are able to generate T cell response. In order to develop such vaccines, there is a need to understand how T cell responses are generated during influenza infection. Influenza specific T cell responses are generated by the dendritic cells (DCs) in the lung. Upon influenza infection, DCs in the lung carry viral peptides to the draining lymph node (dLN) to initiate an immune response. Thus, migration of DCs from the lung to the dLN is an important step in the initiation of influenza specific T cell response. We now show that activation products of the complement system interact with their receptors on the DCs, which signals for the DCs to migrate from the lung to the dLN. Thus, our results reveal a previously unknown function for complement in mediating lung DC migration during influenza infection and highlight its potential as an adjuvant in novel vaccine strategies.

Neuraminidase-inhibiting antibody is a correlate of cross-protection against lethal H5N1 influenza virus in ferrets immunized with seasonal influenza vaccine

In preparing for the threat of a pandemic of avian H5N1 influenza virus, we need to consider the significant delay (4 to 6 months) necessary to produce a strain-matched vaccine. As some degree of cross-reactivity between seasonal influenza vaccines and H5N1 virus has been reported, this was further explored in the ferret model to determine the targets of protective immunity. Ferrets were vaccinated with two intramuscular inoculations of trivalent inactivated split influenza vaccine or subcomponent vaccines, with and without adjuvant, and later challenged with a lethal dose of A/Vietnam/1203/2004 (H5N1) influenza virus. We confirmed that vaccination with seasonal influenza vaccine afforded partial protection against lethal H5N1 challenge and showed that use of either AlPO(4) or Iscomatrix adjuvant with the vaccine resulted in complete protection against disease and death. The protection was due exclusively to the H1N1 vaccine component, and although the hemagglutinin contributed to protection, the dominant protective response was targeted toward the neuraminidase (NA) and correlated with sialic acid cleavage-inhibiting antibody titers. Purified heterologous NA formulated with Iscomatrix adjuvant was also protective. These results suggest that adjuvanted seasonal trivalent vaccine could be used as an interim measure to decrease morbidity and mortality from H5N1 prior to the availability of a specific vaccine. The data also highlight that an inducer of cross-protective immunity is the NA, a protein whose levels are not normally monitored in vaccines and whose capacity to induce immunity in recipients is not normally assessed.

Pseudotyped influenza A virus as a vaccine for the induction of heterotypic immunity

There is a need for vaccines that can protect broadly across all influenza A strains. We have produced a pseudotyped influenza virus based on suppression of the A/PR/8/34 hemagglutinin signal sequence (S-FLU) that can infect cells and express the viral core proteins and neuraminidase but cannot replicate. We show that when given by inhalation to mice, S-FLU is nonpathogenic but generates a vigorous T cell response in the lung associated with markedly reduced viral titers and weight loss after challenge with H1 and H3 influenza viruses. These properties of S-FLU suggest that it may have potential as a broadly protective A virus vaccine, particularly in the setting of a threatened pandemic before matched subunit vaccines become available.

Extracts of Larix Leptolepis effectively augments the generation of tumor antigen-specific cytotoxic T lymphocytes via activation of dendritic cells in TLR-2 and TLR-4-dependent manner

Type-1 immunity plays a crucial role in host defense against various tumors and infectious diseases. Here, we first demonstrated that extract of Larix Leptolepis (ELL), one of the most popular timbers at Hokkaido area in Japan, strongly activated Type-1 immunity. ELL induced production of Type-1 cytokines such as IL-12 and TNF-α from bone marrow-derived dendritic cells (BMDCs) in TLR2- and TLR4-dependent manner and remarkably up-regulated the expression of MHC and co-stimulatory molecules. In addition, antigen-specific CTLs were significantly augmented by the combined administration of ELL, antigen and BMDCs. Finally, we revealed that combination therapy using ELL, antigen and BMDCs significantly inhibited the growth of established tumor in mouse model. Thus, these findings suggested that ELL would be a novel adjuvant for inducing an activation of Type-1-dependent immunity including activation of BMDCs and induction of tumor-specific CTLs, which is applicable to the therapy of cancer and infectious diseases.

Critical role of perforin-dependent CD8+ T cell immunity for rapid protective vaccination in a murine model for human smallpox

Vaccination is highly effective in preventing various infectious diseases, whereas the constant threat of new emerging pathogens necessitates the development of innovative vaccination principles that also confer rapid protection in a case of emergency. Although increasing evidence points to T cell immunity playing a critical role in vaccination against viral diseases, vaccine efficacy is mostly associated with the induction of antibody responses. Here we analyze the immunological mechanism(s) of rapidly protective vaccinia virus immunization using mousepox as surrogate model for human smallpox. We found that fast protection against lethal systemic poxvirus disease solely depended on CD4 and CD8 T cell responses induced by vaccination with highly attenuated modified vaccinia virus Ankara (MVA) or conventional vaccinia virus. Of note, CD4 T cells were critically required to allow for MVA induced CD8 T cell expansion and perforin-mediated cytotoxicity was a key mechanism of MVA induced protection. In contrast, selected components of the innate immune system and B cell-mediated responses were fully dispensable for prevention of fatal disease by immunization given two days before challenge. In conclusion, our data clearly demonstrate that perforin-dependent CD8 T cell immunity plays a key role in MVA conferred short term protection against lethal mousepox. Rapid induction of T cell immunity might serve as a new paradigm for treatments that need to fit into a scenario of protective emergency vaccination.

Prophylactic use of vaccinia virus allowed eradication of human smallpox, one of the greatest successes in medicine. However there are concerns that variola virus, the infectious agent of smallpox, may be used as bioterroristic weapon and zoonotic monkeypox or cowpox remain threatening infections in humans. Thus, new developments of safe and rapidly protecting orthopoxvirus-specific vaccines have been initiated. The candidate vaccine modified vaccinia virus Ankara (MVA) was recently shown to protect against lethal systemic poxvirus disease even when applied shortly before or after infection of mice with ectromelia virus, the probably best animal model for human smallpox. Surprisingly, little is known about the protective mechanism of early immune responses elicited against orthopoxvirus infections. Here, we used the mousepox model to analyze the immunological basis of rapidly protective MVA vaccination. In contrast to common understanding of orthopoxvirus vaccine efficacy relying mainly on antibody mediated immunity, we observed unimpaired protection also in absence of B cells. Surprisingly, rapid protection by vaccination with MVA or conventional vaccinia virus was solely dependent on T cells, irrespective of the route of injection. Thus, our study suggests a key role for T cell immunity in rapidly protective immunization against orthopoxviruses and potentially other infectious agents.

Conservation analysis of dengue virus T-cell epitope-based vaccine candidates using Peptide block entropy

Broad coverage of the pathogen population is particularly important when designing CD8+ T-cell epitope vaccines against viral pathogens. Traditional approaches are based on combinations of highly conserved T-cell epitopes. Peptide block entropy analysis is a novel approach for assembling sets of broadly covering antigens. Since T-cell epitopes are recognized as peptides rather than individual residues, this method is based on calculating the information content of blocks of peptides from a multiple sequence alignment of homologous proteins rather than using the information content of individual residues. The block entropy analysis provides broad coverage of variant antigens. We applied the block entropy analysis method to the proteomes of the four serotypes of dengue virus (DENV) and found 1,551 blocks of 9-mer peptides, which cover 99% of available sequences with five or fewer unique peptides. In contrast, the benchmark study by Khan et al. (2008) resulted in 165 conserved 9-mer peptides. Many of the conserved blocks are located consecutively in the proteins. Connecting these blocks resulted in 78 conserved regions. Of the 1551 blocks of 9-mer peptides 110 comprised predicted HLA binder sets. In total, 457 subunit peptides that encompass the diversity of all sequenced DENV strains of which 333 are T-cell epitope candidates.

Cationic liposome-DNA complexes (CLDC) adjuvant enhances the immunogenicity and cross-protective efficacy of a pre-pandemic influenza A H5N1 vaccine in mice

The development of pre-pandemic influenza A H5N1 vaccines that confer both antigen-sparing and cross-clade protection are a high priority given the limited worldwide capacity for influenza vaccine production, and the antigenic and genetic heterogeneity of circulating H5N1 viruses. The inclusion of potent adjuvants in vaccine formulations may achieve both of these aims. Here we show that the addition of JVRS-100, an adjuvant consisting of cationic liposome-DNA complexes (CLDC) to a clade 1-derived H5N1 split vaccine induced significantly higher virus-specific antibody than unadjuvanted formulations, with a >30-fold dose-sparing effect and induction of increased antigen-specific CD4(+) T-cell responses in mice. All mice that received one dose of adjuvanted vaccine and subsequent H5N1 viral challenges exhibited mild illness, lower lung viral titers, undetectable spleen and brain viral titers, and 100% survival after either homologous clade 1 or heterologous clade 2 H5N1 viral challenges, whereas unadjuvanted vaccine recipients showed significantly increased weight loss, viral titers, and mortality. The protective immunity induced by JVRS-100 adjuvanted H5N1 vaccine was shown to last for over one year without significant waning. Thus, JVRS-100 adjuvanted H5N1 vaccine elicited enhanced humoral and T-cell responses, dose-sparing, and cross-clade protection in mice. CLDC holds promise as an adjuvant for human pre-pandemic inactivated H5N1 vaccines.

Lung CD103+ dendritic cells efficiently transport influenza virus to the lymph node and load viral antigen onto MHC class I for presentation to CD8 T cells

The uptake, transport, and presentation of Ags by lung dendritic cells (DCs) are central to the initiation of CD8 T cell responses against respiratory viruses. Although several studies have demonstrated a critical role of CD11b(low/neg)CD103(+) DCs for the initiation of cytotoxic T cell responses against the influenza virus, the underlying mechanisms for its potent ability to prime CD8 T cells remain poorly understood. Using a novel approach of fluorescent lipophilic dye-labeled influenza virus, we demonstrate that CD11b(low/neg)CD103(+) DCs are the dominant lung DC population transporting influenza virus to the posterior mediastinal lymph node as early as 20 h postinfection. By contrast, CD11b(high)CD103(neg) DCs, although more efficient for taking up the virus within the lung, migrate poorly to the lymph node and remain in the lung to produce proinflammatory cytokines instead. CD11b(low/neg)CD103(+) DCs efficiently load viral peptide onto MHC class I complexes and therefore uniquely possess the capacity to potently induce proliferation of naive CD8 T cells. In addition, the peptide transporters TAP1 and TAP2 are constitutively expressed at higher levels in CD11b(low/neg)CD103(+) DCs, providing, to our knowledge, the first evidence of a distinct regulation of the Ag-processing pathway in these cells. Collectively, these results show that CD11b(low/neg)CD103(+) DCs are functionally specialized for the transport of Ag from the lung to the lymph node and also for efficient processing and presentation of viral Ags to CD8 T cells.

Infection with seasonal influenza virus elicits CD4 T cells specific for genetically conserved epitopes that can be rapidly mobilized for protective immunity to pandemic H1N1 influenza virus

In recent years, influenza viruses with pandemic potential have been a major concern worldwide. One unresolved issue is how infection or vaccination with seasonal influenza virus strains influences the ability to mount a protective immune response to novel pandemic strains. In this study, we developed a mouse model of primary and secondary influenza infection by using a widely circulating seasonal H1N1 virus and the pandemic strain of H1N1 that emerged in Mexico in 2009, and we evaluated several key issues. First, using overlapping peptide libraries encompassing the entire translated sequences of 5 major influenza virus proteins, we assessed the specificity of CD4 T cell reactivity toward epitopes conserved among H1N1 viruses or unique to the seasonal or pandemic strain by enzyme-linked immunospot (ELISpot) assays. Our data show that CD4 T cells reactive to both virus-specific and genetically conserved epitopes are elicited, allowing separate tracking of these responses. Populations of cross-reactive CD4 T cells generated from seasonal influenza infection were found to expand earlier after secondary infection with the pandemic H1N1 virus than CD4 T cell populations specific for new epitopes. Coincident with this rapid CD4 T cell response was a potentiated neutralizing-antibody response to the pandemic strain and protection from the pathological effects of infection with the pandemic virus. This protection was not dependent on CD8 T cells. Together, our results indicate that exposure to seasonal vaccines and infection elicits CD4 T cells that promote the ability of the mammalian host to mount a protective immune response to pandemic strains of influenza virus.

Vaccinomics and a new paradigm for the development of preventive vaccines against viral infections

In this article we define vaccinomics as the integration of immunogenetics and immunogenomics with systems biology and immune profiling. Vaccinomics is based on the use of cutting edge, high-dimensional (so called "omics") assays and novel bioinformatics approaches to the development of next-generation vaccines and the expansion of our capabilities in individualized medicine. Vaccinomics will allow us to move beyond the empiric "isolate, inactivate, and inject" approach characterizing past vaccine development efforts, and toward a more detailed molecular and systemic understanding of the carefully choreographed series of biological processes involved in developing viral vaccine-induced "immunity." This enhanced understanding will then be applied to overcome the obstacles to the creation of effective vaccines to protect against pathogens, particularly hypervariable viruses, with the greatest current impact on public health. Here we provide an overview of how vaccinomics will inform vaccine science, the development of new vaccines and/or clinically relevant biomarkers or surrogates of protection, vaccine response heterogeneity, and our understanding of immunosenescence.

Influenza-specific T cells from older people are enriched in the late effector subset and their presence inversely correlates with vaccine response

T cells specific for persistent pathogens accumulate with age and express markers of immune senescence. In contrast, much less is known about the state of T cell memory for acutely infecting pathogens. Here we examined T cell responses to influenza in human peripheral blood mononuclear cells from older (>64) and younger (<40) donors using whole virus restimulation with influenza A (A/PR8/34) ex vivo. Although most donors had pre-existing influenza reactive T cells as measured by IFNγ production, older donors had smaller populations of influenza-responsive T cells than young controls and had lost a significant proportion of their CD45RA-negative functional memory population. Despite this apparent dysfunction in a proportion of the older T cells, both old and young donors' T cells from 2008 could respond to A/California/07/2009 ex vivo. For HLA-A2+ donors, MHC tetramer staining showed that a higher proportion of influenza-specific memory CD8 T cells from the 65+ group co-express the markers killer cell lectin-like receptor G1 (KLRG1) and CD57 compared to their younger counterparts. These markers have previously been associated with a late differentiation state or immune senescence. Thus, memory CD8 T cells to an acutely infecting pathogen show signs of advanced differentiation and functional deterioration with age. There was a significant negative correlation between the frequency of KLRG1(+)CD57(+) influenza M1-specific CD8 T cells pre-vaccination and the ability to make antibodies in response to vaccination with seasonal trivalent inactivated vaccine, whereas no such trend was observed when the total CD8(+)KLRG1(+)CD57(+) population was analyzed. These results suggest that the state of the influenza-specific memory CD8 T cells may be a predictive indicator of a vaccine responsive healthy immune system in old age.

Cold-adapted influenza and recombinant adenovirus vaccines induce cross-protective immunity against pH1N1 challenge in mice

Background

The rapid spread of the 2009 H1N1 pandemic influenza virus (pH1N1) highlighted problems associated with relying on strain-matched vaccines. A lengthy process of strain identification, manufacture, and testing is required for current strain-matched vaccines and delays vaccine availability. Vaccines inducing immunity to conserved viral proteins could be manufactured and tested in advance and provide cross-protection against novel influenza viruses until strain-matched vaccines became available. Here we test two prototype vaccines for cross-protection against the recent pandemic virus.

Methodology/Principal Findings

BALB/c and C57BL/6 mice were intranasally immunized with a single dose of cold-adapted (ca) influenza viruses from 1977 or recombinant adenoviruses (rAd) expressing 1934 nucleoprotein (NP) and consensus matrix 2 (M2) (NP+M2-rAd). Antibodies against the M2 ectodomain (M2e) were seen in NP+M2-rAd immunized BALB/c but not C57BL/6 mice, and cross-reacted with pH1N1 M2e. The ca-immunized mice did not develop antibodies against M2e. Despite sequence differences between vaccine and challenge virus NP and M2e epitopes, extensive cross-reactivity of lung T cells with pH1N1 peptides was detected following immunization. Both ca and NP+M2-rAd immunization protected BALB/c and C57BL/6 mice against challenge with a mouse-adapted pH1N1 virus.

Conclusion/Significance

Cross-protective vaccines such as NP+M2-rAd and ca virus are effective against pH1N1 challenge within 3 weeks of immunization. Protection was not dependent on recognition of the highly variable external viral proteins and could be achieved with a single vaccine dose. The rAd vaccine was superior to the ca vaccine by certain measures, justifying continued investigation of this experimental vaccine even though ca vaccine is already available. This study highlights the potential for cross-protective vaccines as a public health option early in an influenza pandemic.

Panvax(®): a monovalent inactivated unadjuvanted vaccine against pandemic influenza A (H1N1) 2009

Panvax(®) (CSL Biotherapies, Parkville, Australia) is one of a number of pandemic influenza A (H1N1) 2009 (pH1N1) vaccines fast-tracked for production, clinical trials and licensure in response to the emergence of the novel pH1N1 strain in early-mid-2009. Unexpectedly good immunogenicity following a single 15-µg dose was demonstrated in expedited clinical trials in adults and children. This facilitated early licensure and then rapid rollout for population immunization from October 2009. The vaccine's safety profile in the Australian population has been excellent.

A review of mathematical models of influenza A infections within a host or cell culture: lessons learned and challenges ahead

Most mathematical models used to study the dynamics of influenza A have thus far focused on the between-host population level, with the aim to inform public health decisions regarding issues such as drug and social distancing intervention strategies, antiviral stockpiling or vaccine distribution. Here, we investigate mathematical modeling of influenza infection spread at a different scale; namely that occurring within an individual host or a cell culture. We review the models that have been developed in the last decades and discuss their contributions to our understanding of the dynamics of influenza infections. We review kinetic parameters (e.g., viral clearance rate, lifespan of infected cells) and values obtained through fitting mathematical models, and contrast them with values obtained directly from experiments. We explore the symbiotic role of mathematical models and experimental assays in improving our quantitative understanding of influenza infection dynamics. We also discuss the challenges in developing better, more comprehensive models for the course of influenza infections within a host or cell culture. Finally, we explain the contributions of such modeling efforts to important public health issues, and suggest future modeling studies that can help to address additional questions relevant to public health.

Cross-protective immunity to influenza A viruses

Antigenic changes in influenza virus occur gradually, owing to mutations (antigenic drift), and abruptly, owing to reassortment among subtypes (antigenic shift). Availability of strain-matched vaccines often lags behind these changes, resulting in a shortfall in public health. In animal models, cross-protection by vaccines based on conserved antigens does not completely prevent infection, but greatly reduces morbidity, mortality, virus replication and, thus, viral shedding and spread. Such immunity is especially effective and long-lasting with mucosal administration. Cross-protective immunity in humans is controversial, but is suggested by some epidemiological findings. 'Universal' vaccines protective against all influenza A viruses might substantially reduce severity of infection and limit spread of disease during outbreaks. These vaccines could be used 'off the shelf' early in an outbreak or pandemic, before strain-matched vaccines are available.

The role of membrane fusion activity of a whole inactivated influenza virus vaccine in (re)activation of influenza-specific cytotoxic T lymphocytes

Induction of cytotoxic T lymphocyte (CTL) activity against conserved influenza antigens, e.g. nucleoprotein (NP) could be a step towards cross-protective influenza vaccine. The major challenge for non-replicating influenza vaccines aiming for activation of CTLs is targeting of antigen to the MHC class I processing and presentation pathway of professional antigen presenting cells, in particular dendritic cells (DCs). Intrinsic fusogenic properties of the vaccine particle itself can enable direct cytosolic delivery of the antigen by enhancing release of the antigen from the endosome to the cytosol. Alternatively, the vaccine particle would need to possess the capacity to activate DCs thereby triggering cell-intrinsic mechanisms of cross-presentation, processes that do not require fusion. Here, using fusion-active and fusion-inactive whole inactivated virus (WIV) as a vaccine model, we studied the relative contribution of these two pathways on priming and reactivation of influenza NP-specific CTLs in a murine model. We show that activation of bone marrow-derived DCs by WIV, as well as reactivation of NP-specific CTLs in vitro and in vivo were not affected by inactivation of membrane fusion of the WIV particles. However, in vivo priming of naive CTLs was optimal only upon vaccination with fusion-active WIV. Thus, DC-intrinsic mechanisms of cross-presentation are involved in the activation of CTLs upon vaccination with WIV. However, for optimal priming of naive CTLs these mechanisms should be complemented by delivery of antigen to the cytosol mediated by the membrane fusion capacity of the WIV particles.

Cationic lipid/DNA complex-adjuvanted influenza A virus vaccination induces robust cross-protective immunity

Influenza A virus is a negative-strand segmented RNA virus in which antigenically distinct viral subtypes are defined by the hemagglutinin (HA) and neuraminidase (NA) major viral surface proteins. An ideal inactivated vaccine for influenza A virus would induce not only highly robust strain-specific humoral and T-cell immune responses but also cross-protective immunity in which an immune response to antigens from a particular viral subtype (e.g., H3N2) would protect against other viral subtypes (e.g., H1N1). Cross-protective immunity would help limit outbreaks from newly emerging antigenically novel strains. Here, we show in mice that the addition of cationic lipid/noncoding DNA complexes (CLDC) as adjuvant to whole inactivated influenza A virus vaccine induces significantly more robust adaptive immune responses both in quantity and quality than aluminum hydroxide (alum), which is currently the most widely used adjuvant in clinical human vaccination. CLDC-adjuvanted vaccine induced higher total influenza virus-specific IgG, particularly for the IgG2a/c subclass. Higher levels of multicytokine-producing influenza virus-specific CD4 and CD8 T cells were induced by CLDC-adjuvanted vaccine than with alum-adjuvanted vaccine. Importantly, CLDC-adjuvanted vaccine provided significant cross-protection from either a sublethal or lethal influenza A viral challenge with a different subtype than that used for vaccination. This superior cross-protection afforded by the CLDC adjuvant required CD8 T-cell recognition of viral peptides presented by classical major histocompatibility complex class I proteins. Together, these results suggest that CLDC has particular promise for vaccine strategies in which T cells play an important role and may offer new opportunities for more effective control of human influenza epidemics and pandemics by inactivated influenza virus vaccine.

Single-dose mucosal immunization with a candidate universal influenza vaccine provides rapid protection from virulent H5N1, H3N2 and H1N1 viruses

BACKGROUND

The sudden emergence of novel influenza viruses is a global public health concern. Conventional influenza vaccines targeting the highly variable surface glycoproteins hemagglutinin and neuraminidase must antigenically match the emerging strain to be effective. In contrast, "universal" vaccines targeting conserved viral components could be used regardless of viral strain or subtype. Previous approaches to universal vaccination have required protracted multi-dose immunizations. Here we evaluate a single dose universal vaccine strategy using recombinant adenoviruses (rAd) expressing the conserved influenza virus antigens matrix 2 and nucleoprotein.

METHODOLOGY/PRINCIPAL FINDINGS

In BALB/c mice, administration of rAd via the intranasal route was superior to intramuscular immunization for induction of mucosal responses and for protection against highly virulent H1N1, H3N2, or H5N1 influenza virus challenge. Mucosally vaccinated mice not only survived, but had little morbidity and reduced lung virus titers. Protection was observed as early as 2 weeks post-immunization, and lasted at least 10 months, as did antibodies and lung T cells with activated phenotypes. Virus-specific IgA correlated with but was not essential for protection, as demonstrated in studies with IgA-deficient animals.

CONCLUSION/SIGNIFICANCE

Mucosal administration of NP and M2-expressing rAd vectors provided rapid and lasting protection from influenza viruses in a subtype-independent manner. Such vaccines could be used in the interval between emergence of a new virus strain and availability of strain-matched vaccines against it. This strikingly effective single-dose vaccination thus represents a candidate off-the-shelf vaccine for emergency use during an influenza pandemic.

Qualitatively different memory CD8+ T cells are generated after lymphocytic choriomeningitis virus and influenza virus infections

Viral infections often induce robust T cell responses that are long-lived and protective. However, it is unclear to what degree systemic versus mucosal infection influences the generation of effector and memory T cells. In this study, we characterized memory CD8(+) T cells generated after respiratory influenza virus infection and compared the phenotypic and functional qualities of these cells with memory T cells generated after systemic infection with lymphocytic choriomeningitis virus (LCMV). Using a recombinant influenza virus expressing the LCMV gp(33-41) epitope and TCR transgenic CD8(+) T cells with a fixed TCR, we compared responses to the same Ag delivered by mucosal or systemic viral infection. Memory cells generated postinfection with either virus showed only a few phenotypic differences. Yet, influenza memory T cells produced lower amounts of effector cytokines upon restimulation and displayed reduced proliferation compared with LCMV-induced memory cells. Strikingly, we observed reduced expansion of spleen- and, in particular, lung-derived influenza memory cells after recall in vivo, which correlated with reduced early protection from secondary infection. These findings suggest that qualitatively different memory CD8(+) T cells are generated after respiratory or systemic virus infections.

Cytotoxic T lymphocytes established by seasonal human influenza cross-react against 2009 pandemic H1N1 influenza virus

While few children and young adults have cross-protective antibodies to the pandemic H1N1 2009 (pdmH1N1) virus, the illness remains mild. The biological reasons for these epidemiological observations are unclear. In this study, we demonstrate that the bulk memory cytotoxic T lymphocytes (CTLs) established by seasonal influenza viruses from healthy individuals who have not been exposed to pdmH1N1 can directly lyse pdmH1N1-infected target cells and produce gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha). Using influenza A virus matrix protein 1 (M1(58-66)) epitope-specific CTLs isolated from healthy HLA-A2(+) individuals, we further found that M1(58-66) epitope-specific CTLs efficiently killed both M1(58-66) peptide-pulsed and pdmH1N1-infected target cells ex vivo. These M1(58-66)-specific CTLs showed an effector memory phenotype and expressed CXCR3 and CCR5 chemokine receptors. Of 94 influenza A virus CD8 T-cell epitopes obtained from the Immune Epitope Database (IEDB), 17 epitopes are conserved in pdmH1N1, and more than half of these conserved epitopes are derived from M1 protein. In addition, 65% (11/17) of these epitopes were 100% conserved in seasonal influenza vaccine H1N1 strains during the last 20 years. Importantly, seasonal influenza vaccination could expand the functional M1(58-66) epitope-specific CTLs in 20% (4/20) of HLA-A2(+) individuals. Our results indicated that memory CTLs established by seasonal influenza A viruses or vaccines had cross-reactivity against pdmH1N1. These might explain, at least in part, the unexpected mild pdmH1N1 illness in the community and also might provide some valuable insights for the future design of broadly protective vaccines to prevent influenza, especially pandemic influenza.

Exploiting cross-priming to generate protective CD8 T-cell immunity rapidly

The number of memory CD8 T cells generated by infection or vaccination correlates strongly with the degree of protection observed in infection and tumor models. Therefore, rapid induction of protective numbers of effector and memory CD8 T cells may be crucial in the case of malignancy, pandemic infection, or bioterrorism. Many studies have shown that amplifying T-cell numbers by prime-boost vaccination is most effective with a substantial time interval between immunizations. In contrast, immunization with peptide-coated mature dendritic cells (DCs) results in a CD8 T-cell response exhibiting accelerated acquisition of memory characteristics, including the ability to respond to booster immunization within days of initial priming. However, personalized DC immunization is too costly, labor intensive, and time-consuming for large-scale vaccination. Here, we demonstrate that in vivo cross-priming with cell-associated antigens or antigen-coated, biodegradable microspheres in the absence of adjuvant quickly generates CD8 T cells that display the phenotype and function of long-term memory populations. Importantly, cross-primed CD8 T cells can respond to booster immunization within days of the initial immunization to generate rapidly large numbers of effector and memory T cells that can protect against bacterial, viral, and parasitic infections, including lethal influenza and malaria-causing Plasmodium infection. Thus, accelerated CD8 T-cell memory after in vivo cross-priming in the absence of adjuvant is generalizable and can be exploited to generate protective immunity rapidly.

Preferential amplification of CD8 effector-T cells after transcutaneous application of an inactivated influenza vaccine: a randomized phase I trial

BACKGROUND

Current conventional vaccination approaches do not induce potent CD8 T-cell responses for fighting mostly variable viral diseases such as influenza, avian influenza viruses or HIV. Following our recent study on vaccine penetration by targeting of vaccine to human hair follicular ducts surrounded by Langerhans cells, we tested in the first randomized Phase-Ia trial based on hair follicle penetration (namely transcutaneous route) the induction of virus-specific CD8 T cell responses.

METHODS AND FINDINGS

We chose the inactivated influenza vaccine - a conventional licensed tetanus/influenza (TETAGRIP) vaccine - to compare the safety and immunogenicity of transcutaneous (TC) versus IM immunization in two randomized controlled, multi-center Phase I trials including 24 healthy-volunteers and 12 HIV-infected patients. Vaccination was performed by application of inactivated influenza vaccine according to a standard protocol allowing the opening of the hair duct for the TC route or needle-injection for the IM route. We demonstrated that the safety of the two routes was similar. We showed the superiority of TC application, but not the IM route, to induce a significant increase in influenza-specific CD8 cytokine-producing cells in healthy-volunteers and in HIV-infected patients. However, these routes did not differ significantly for the induction of influenza-specific CD4 responses, and neutralizing antibodies were induced only by the IM route. The CD8 cell response is thus the major immune response observed after TC vaccination.

CONCLUSIONS

This Phase Ia clinical trial (Manon05) testing an anti-influenza vaccine demonstrated that vaccines designed for antibody induction by the IM route, generate vaccine-specific CD8 T cells when administered transcutaneously. These results underline the necessity of adapting vaccination strategies to control complex infectious diseases when CD8 cellular responses are crucial. Our work opens up a key area for the development of preventive and therapeutic vaccines for diseases in which CD8 cells play a crucial role.

TRIAL REGISTRATION

Clinicaltrials.gov NCT00261001.

Shaping successful and unsuccessful CD8 T cell responses following infection

CD8 T cells play a vital role in the immunological protection against intracellular pathogens. Ideally, robust effector responses are induced, which eradicate the pathogen, and durable memory CD8 T cells are also established, which help confer protection against subsequent reinfection. The quality and magnitude of these responses is dictated by multiple factors, including their initial interactions with professional antigen-presenting cells, as well as the cytokine milieu and availability of CD4 T cell help. These factors set the transcriptional landscape of the responding T cells, which in turn influences their phenotypic and functional attributes as well as ultimate fate. Under certain conditions, such as during chronic infections, the development of these usually successful responses becomes subverted. Here we discuss advances in our understanding of the cellular and molecular determinants of T cell quality, and the formation of effector, memory, and exhausted CD8 T cells, during acute and chronic infections.

Memory CD4 T cells: generation, reactivation and re-assignment

Immunological memory is one of the features that define the adaptive immune response: by generating specific memory cells after infection or vaccination, the host provides itself with a set of cells and molecules that can prevent future infections and disease. Despite the obvious importance of memory cells, memory CD4 T cells are incompletely understood. Here we discuss recent progress in understanding which activated T cells surmount the barrier to enter into the memory pool and, once generated, what signals are important for memory cell survival. There is still, however, little understanding of how (or even whether) memory CD4 T cells are useful once they have been created; a surprising thought considering the critical role CD4 T cells play in all adaptive primary immune responses. In light of this, we will discuss how CD4 T memory T cells respond to reactivation in vivo and whether they are malleable to a re-assignment of their effector response.

Memory CD8+ T cell differentiation

In response to infection or effective vaccination, naive antigen-specific CD8+ T cells undergo a dramatic highly orchestrated activation process. Initial encounter with an appropriately activated antigen-presenting cell leads to blastogenesis and an exponential increase in antigen-specific CD8+ T cell numbers. Simultaneously, a dynamic differentiation process occurs, resulting in formation of both primary effector and long-lived memory cells. Current findings have emphasized the heterogeneity of effector and memory cell populations with the description of multiple cellular subsets based on phenotype, function, and anatomic location. Yet, only recently have we begun to dissect the underlying factors mediating the temporal control of the development of distinct effector and memory CD8+ T cell sublineages. In this review we will focus on the requirements for mounting an effective CD8+ T cell response and highlight the elements regulating the differentiation of effector and memory subsets.

A novel H1N1 virus causes the first pandemic of the 21st century

A novel H1N1 virus of swine origin (H1N1v ) is currently spreading in humans, giving rise to the first pandemic in 40 years. The disease is of moderate severity but has notable differences from seasonal influenza. In contrast to seasonal influenza, those over 60 years are relatively spared, a likely consequence of the presence of H1N1v cross-neutralizing antibody in this age group. Most patients appear to have mild influenza-like illness and many of the complications leading to hospitalization and mortality occur in those with underlying disease conditions or pregnancy. Studies in animal models suggest that the novel H1N1v pandemic virus causes a more severe illness and appears to have a greater predilection for the alveolar epithelium than seasonal influenza viruses. As there are as yet little data on the pathogenesis and immunology of H1N1v infection in humans, we have reviewed relevant data from past pandemics, from seasonal influenza and avian influenza H5N1 to highlight key issues pertaining to pathogenesis and immunology.

Immunization with live attenuated influenza viruses that express altered NS1 proteins results in potent and protective memory CD8+ T-cell responses

The generation of vaccines that induce long-lived protective immunity against influenza virus infections remains a challenging goal. Ideally, vaccines should elicit effective humoral and cellular immunity to protect an individual from infection or disease. Cross-reactive T- and B-cell responses that are elicited by live virus infections may provide such broad protection. Optimal induction of T-cell responses involves the action of type I interferons (IFN-I). Influenza virus expressed nonstructural protein 1 (NS1) functions as an inhibitor of IFN-I and promotes viral growth. We wanted to examine the priming of CD8(+) T-cell responses to influenza virus in the absence of this inhibition of IFN-I production. We generated recombinant mouse-adapted influenza A/PR/8/34 viruses with NS1 truncations and/or deletions that also express the gp33-41 epitope from lymphocytic choriomeningitis virus. Intranasal infection of mice with the attenuated viruses primed long-lived T- and B-cell responses despite significantly reduced viral replication in the lungs compared to wild-type virus. Antigen-specific CD8(+) T cells expanded upon rechallenge and generated increased protective memory T-cell populations after boosting. These results show that live attenuated influenza viruses expressing truncated NS1 proteins can prime protective immunity and may have implications for the design of novel modified live influenza virus vaccines.