Seasonal influenza vaccine provides priming for A/H1N1 immunization

Mass vaccination against the 2009 A/H1N1 influenza virus, with different vaccine formulations, is being implemented globally. Because of the urgency with which the vaccine has been prepared, little information has been gathered on variables that influence the effectiveness of the vaccine. Specifically, it is not clear whether priming by previous infection with or vaccination against seasonal influenza affects the response to the vaccine. Similarly, the role of vaccine adjuvants in vaccine response is not known. To address these questions, we injected ferrets with seasonal influenza vaccine and then vaccinated with 2009 A/H1N1 vaccine with or without the oil-in-water adjuvant MF59. The results show that the seasonal flu vaccine, although it did not induce functional antibodies against the 2009 A/H1N1 virus, provided immunological priming and allowed production of protective antibodies to 2009 A/H1N1 after one dose of 2009 A/H1N1 vaccine. The vaccine given without adjuvant significantly reduced viral load in the lungs but did not protect from infection. Only the vaccine with adjuvant completely prevented both pulmonary and nasal infection.

Ultra-fast analysis of plasma and intracellular levels of HIV protease inhibitors in children: a clinical application of MALDI mass spectrometry

HIV protease inhibitors must penetrate into cells to exert their action. Differences in the intracellular pharmacokinetics of these drugs may explain why some patients fail on therapy or suffer from drug toxicity. Yet, there is no information available on the intracellular levels of HIV protease inhibitors in HIV infected children, which is in part due to the large amount of sample that is normally required to measure the intracellular concentrations of these drugs. Therefore, we developed an ultra-fast and sensitive assay to measure the intracellular concentrations of HIV protease inhibitors in small amounts of peripheral blood mononuclear cells (PBMCs), and determined the intracellular concentrations of lopinavir and ritonavir in HIV infected children. An assay based on matrix-assisted laser desorption/ionization (MALDI) - triple quadrupole mass spectrometry was developed to determine the concentrations of HIV protease inhibitors in 10 µL plasma and 1×10⁶ PBMCs. Precisions and accuracies were within the values set by the FDA for bioanalytical method validation. Lopinavir and ritonavir did not accumulate in PBMCs of HIV infected children. In addition, the intracellular concentrations of lopinavir and ritonavir correlated poorly to the plasma concentrations of these drugs. MALDI-triple quadrupole mass spectrometry is a new tool for ultra-fast and sensitive determination of drug concentrations which can be used, for example, to assess the intracellular pharmacokinetics of HIV protease inhibitors in HIV infected children.

Plasma concentrations of oseltamivir and oseltamivir carboxylate in critically ill children on extracorporeal membrane oxygenation support

INTRODUCTION

To evaluate the effect of extracorporeal membrane oxygenation (ECMO) support on pharmacokinetics of oseltamivir and oseltamivir carboxylate (OC) in children.

METHODOLOGY

Steady state 0-12 hour pharmacokinetic sampling was performed in new influenza A (H1N1) infected children treated with oseltamivir while on ECMO support. Cmax, Cmin and AUC(0-12 h) were calculated. The age-specific oseltamivir dosage was doubled to counter expected decreased plasma drug concentrations due to increased volume of distribution on ECMO support.

PRINCIPAL FINDINGS

Three patients were enrolled aged 15, 6 and 14 years in this pharmacokinetic case series. For two children the OC plasma concentrations were higher than those found in children and adults not on ECMO. These increased plasma concentrations related to the increased oseltamivir dosage and decreased kidney function. In one patient suboptimal plasma concentrations coincided with a decreased gastric motility.

CONCLUSION

Oseltamivir pharmacokinetics do not appear to be significantly influenced by ECMO support. Caution is required in case of nasogastric administration and decreased gastric motility. Due to the limited number of (paediatric) patients available further multicenter studies are warranted.

Cross-clade immunity in cats vaccinated with a canarypox-vectored avian influenza vaccine

Several felid species have been shown to be susceptible to infection with highly pathogenic avian influenza (HPAI) viruses of the H5N1 subtype. Infection of felids by H5N1 HPAI virus is often fatal, and cat-to-cat transmission has been documented. Domestic cats may then be involved in the transmission of infection to other animals but also to humans. A particular concern is the hypothetical role of the cat in the adaptation of the virus to mammalian species, thus increasing the pandemic risk. Therefore, the development of a HPAI vaccine for domestic cats should be considered a veterinary and also a public health priority. Here we show that vaccination of cats with a recombinant canarypox (ALVAC)(1)) virus, expressing the hemagglutinin (HA) of influenza virus A/chicken/Indonesia/03 (H5N1) confers protection against challenge infection with two antigenically distinct H5N1 virus isolates from humans. Despite low hemagglutination inhibiting (HI) antibody titers at the time of challenge, all vaccinated cats were protected against mortality and had reduced histopathological changes in the lungs. Importantly, viral shedding was reduced in vaccinated cats as compared to controls, suggesting that vaccination of cats could reduce the risk of viral transmission. In conclusion this study showed that the recombinant canarypox virus protected cats against homologous and heterologous H5N1 HPAI virus challenges.

Severity of pneumonia due to new H1N1 influenza virus in ferrets is intermediate between that due to seasonal H1N1 virus and highly pathogenic avian influenza H5N1 virus

Background. The newly emerged influenza A(H1N1) virus (new H1N1 virus) is causing the first influenza pandemic of this century. Three influenza pandemics of the previous century caused variable mortality, which largely depended on the development of severe pneumonia. However, the ability of the new H1N1 virus to cause pneumonia is poorly understood.

Methods. The new H1N1 virus was inoculated intratracheally into ferrets. Its ability to cause pneumonia was compared with that of seasonal influenza H1N1 virus and highly pathogenic avian influenza (HPAI) H5N1 virus by using clinical, virological, and pathological analyses.

Results. Our results showed that the new H1N1 virus causes pneumonia in ferrets intermediate in severity between that caused by seasonal H1N1 virus and by HPAI H5N1 virus. The new H1N1 virus replicated well throughout the lower respiratory tract and more extensively than did both seasonal H1N1 virus (which replicated mainly in the bronchi) and HPAI H5N1 virus (which replicated mainly in the alveoli). High loads of new H1N1 virus in lung tissue were associated with diffuse alveolar damage and mortality.

Conclusions. The new H1N1 virus may be intrinsically more pathogenic for humans than is seasonal H1N1 virus.

Plasma levels of inter-alpha inhibitor proteins in children with acute Dengue virus infection

Background

Inter-α inhibitor proteins (IaIp) belong to a family of protease inhibitors that are involved in the haemostatic and the vascular system. Dengue viruses (DENV) infections are characterized by coagulopathy and increased vascular permeability. In this study we measured the concentration of IaIp during DENV infections and evaluated its potential as a biomarker.

Methods and Findings

Concentrations of IaIp were measured in patients with acute DENV infections using a quantitative, competitive enzyme linked immunoassay. Concentrations of IaIp measured in pediatric patients suffering from severe DENV infections were significantly lower than in healthy controls.

Conclusions

This is the first report to demonstrate changes in concentration of IaIp during viral infections. The data also highlight the potential of IaIp as a biological marker for severity of DENV infections.

Vaccination with whole inactivated virus vaccine affects the induction of heterosubtypic immunity against influenza virus A/H5N1 and immunodominance of virus-specific CD8+ T-cell responses in mice

It was recently shown that the use of an experimental subunit vaccine protected mice against infection with a human A/H3N2 influenza virus, but consequently affected the induction of heterosubtypic immunity to a highly pathogenic A/H5N1 influenza virus, which was otherwise induced by the A/H3N2 infection. As whole inactivated virus (WIV) vaccines are widely used to protect against seasonal influenza and also contain inner viral proteins such as the nucleoprotein (NP), the potential of a WIV vaccine to induce protective immunity against infection was tested with a homologous A/H3N2 (A/Hong Kong/2/68) and a heterosubtypic A/H5N1 influenza virus (A/Indonesia/5/05). As expected, the vaccine afforded protection against infection with the A/H3N2 virus only. In addition, it was demonstrated that the use of WIV vaccine for protection against A/H3N2 infection affected the induction of heterosubtypic immunity that was otherwise afforded by A/H3N2 influenza virus infection. The reduction in protective immunity correlated with changes in the immunodominance patterns of the CD8(+) T-cell responses directed to the epitopes located in the acid polymerase subunit of the viral RNA polymerase (PA(224-233)) and the NP (NP(366-374)). In unvaccinated mice that experienced infection with the A/H3N2 influenza virus, the magnitude of the CD8(+) T-cell response to both peptides was similar on secondary infection with A/H5N1 influenza virus. In contrast, prior vaccination with WIV affected the immunodominance pattern and skewed the response after infection with influenza virus A/Indonesia/5/05 towards a dominant NP(366-374)-specific response. These findings may have implications for vaccination strategies aimed at the induction of protective immunity to seasonal and/or pandemic influenza.

"Filoviruses": a real pandemic threat?

Filoviruses are zoonotic and among the deadliest viruses known to mankind, with mortality rates in outbreaks reaching up to 90%. Despite numerous efforts to identify the host reservoir(s), the transmission cycle of filoviruses between the animal host(s) and humans remains unclear. The last decade has witnessed an increase in filovirus outbreaks with a changing epidemiology. The high mortality rates and lack of effective antiviral drugs or preventive vaccines has propagated the fear that filoviruses may become a real pandemic threat. This article discusses the factors that could influence the possible pandemic potential of filoviruses and elaborates on the prerequisites for the containment of future outbreaks, which would help prevent the evolution of filovirus into more virulent and more transmissible viruses.

Specific CD8(+) T-lymphocytes control dissemination of measles virus

Measles continues to be an important cause of childhood mortality in developing countries. Measles virus (MV) is lymphotropic and infects high percentages of B- and T-lymphocytes in lymphoid tissues. Cellular immunity is considered crucial for viral clearance; however, MV-specific T-lymphocytes generated during primary infection also constitute a potential target for MV infection. We therefore aimed to identify T-lymphocyte subsets that can clear MV infection without becoming infected. To this end, we infected human EBV transformed B-lymphoblastic cell lines (B-LCL) with a recombinant MV strain expressing enhanced GFP, and co-cultured these with non-infected B-LCL resulting in rapid viral spread. MV-specific CD8(+) T-cell clones efficiently suppressed MV dissemination in autologous and HLA-matched, but not in HLA-mismatched B-LCL. In contrast, CD4(+) T-cell clones could not control MV dissemination but became a target for MV infection themselves. Furthermore, PBMC collected 6-9 months after acute measles and stimulated with autologous MV-infected B-LCL also efficiently suppressed MV dissemination; this was mediated by the fraction containing CD8(+) T-lymphocytes. In conclusion, we have developed a powerful tool to study cellular immunity against measles, and demonstrate that control of MV dissemination is mediated by virus-specific CD8(+) rather than by CD4(+) T-lymphocytes.

Animal models for the preclinical evaluation of candidate influenza vaccines

At present, new influenza A (H1N1)2009 viruses of swine origin are responsible for the first influenza pandemic of the 21st Century. In addition, highly pathogenic avian influenza A/H5N1 viruses continue to cause outbreaks in poultry and, after zoonotic transmission, cause an ever-increasing number of human cases, of which 59% have a fatal clinical outcome. It is also feared that these viruses adapt to replication in humans and become transmissible from human to human. The development of effective vaccines against epidemic and (potentially) pandemic viruses is therefore considered a priority. In this review, we discuss animal models that are used for the preclinical evaluation of novel candidate influenza vaccines. In most cases, a tier of multiple animal models is used before the evaluation of vaccine candidates in clinical trials is considered. Commonly, vaccines are tested for safety and efficacy in mice, ferrets and/or macaques. The use of each of these species has its advantages and limitations, which are addressed here.

Seasonal and pandemic human influenza viruses attach better to human upper respiratory tract epithelium than avian influenza viruses

Influenza viruses vary markedly in their efficiency of human-to-human transmission. This variation has been speculated to be determined in part by the tropism of influenza virus for the human upper respiratory tract. To study this tropism, we determined the pattern of virus attachment by virus histochemistry of three human and three avian influenza viruses in human nasal septum, conchae, nasopharynx, paranasal sinuses, and larynx. We found that the human influenza viruses-two seasonal influenza viruses and pandemic H1N1 virus-attached abundantly to ciliated epithelial cells and goblet cells throughout the upper respiratory tract. In contrast, the avian influenza viruses, including the highly pathogenic H5N1 virus, attached only rarely to epithelial cells or goblet cells. Both human and avian viruses attached occasionally to cells of the submucosal glands. The pattern of virus attachment was similar among the different sites of the human upper respiratory tract for each virus tested. We conclude that influenza viruses that are transmitted efficiently among humans attach abundantly to human upper respiratory tract, whereas inefficiently transmitted influenza viruses attach rarely. These results suggest that the ability of an influenza virus to attach to human upper respiratory tract is a critical factor for efficient transmission in the human population.

New class of monoclonal antibodies against severe influenza: prophylactic and therapeutic efficacy in ferrets

BACKGROUND

The urgent medical need for innovative approaches to control influenza is emphasized by the widespread resistance of circulating subtype H1N1 viruses to the leading antiviral drug oseltamivir, the pandemic threat posed by the occurrences of human infections with highly pathogenic avian H5N1 viruses, and indeed the evolving swine-origin H1N1 influenza pandemic. A recently discovered class of human monoclonal antibodies with the ability to neutralize a broad spectrum of influenza viruses (including H1, H2, H5, H6 and H9 subtypes) has the potential to prevent and treat influenza in humans. Here we report the latest efficacy data for a representative antibody of this novel class.

METHODOLOGY/PRINCIPAL FINDINGS

We evaluated the prophylactic and therapeutic efficacy of the human monoclonal antibody CR6261 against lethal challenge with the highly pathogenic avian H5N1 virus in ferrets, the optimal model of human influenza infection. Survival rates, clinically relevant disease signs such as changes in body weight and temperature, virus replication in lungs and upper respiratory tract, as well as macro- and microscopic pathology were investigated. Prophylactic administration of 30 and 10 mg/kg CR6261 prior to viral challenge completely prevented mortality, weight loss and reduced the amount of infectious virus in the lungs by more than 99.9%, abolished shedding of virus in pharyngeal secretions and largely prevented H5N1-induced lung pathology. When administered therapeutically 1 day after challenge, 30 mg/kg CR6261 prevented death in all animals and blunted disease, as evidenced by decreased weight loss and temperature rise, reduced lung viral loads and shedding, and less lung damage.

CONCLUSIONS/SIGNIFICANCE

These data demonstrate the prophylactic and therapeutic efficacy of this new class of human monoclonal antibodies in a highly stringent and clinically relevant animal model of influenza and justify clinical development of this approach as intervention for both seasonal and pandemic influenza.

West Nile Virus: is a vaccine needed?

West Nile virus (WNV) is a neurotropic Flavivirus that was associated with sporadic outbreaks of meningoencephalitis in Africa and the Middle East until 1999, when a more virulent strain emerged in the US that caused thousands of infections among humans and horses, with reported fatality rates between 10 and 50%. Although the epidemiology of WNV is changing into a more endemic pattern in the US, and the incidence of neuroinvasive disease is decreasing, the long-term effects of resolved WNV infections in humans, characterized as persistent movement disorders and various functional disabilities, are a significant cause of morbidity. In addition, the horse industry is also negatively impacted by WNV infections, resulting in significant economic losses. Together with the fact that WNV is a potential bioterrorism agent, these factors suggest that there is a need for the development of a safe and effective vaccine against WNV. The increased understanding of WNV pathogenesis and correlates of protection enables the rational design of such a vaccine. Several experimental vaccines have been tested in preclinical models and some have undergone clinical trials. The challenges related to the development of cheaper, safer and more effective vaccines for use in both humans and horses are likely to be overcome by new technological developments in the field of vaccinology.

Response to imported case of Marburg hemorrhagic fever, the Netherland

Adventure tourism may bring this disease to Western countries.

On July 10, 2008, Marburg hemorrhagic fever was confirmed in a Dutch patient who had vacationed recently in Uganda. Exposure most likely occurred in the Python Cave (Maramagambo Forest), which harbors bat species that elsewhere in Africa have been found positive for Marburg virus. A multidisciplinary response team was convened to perform a structured risk assessment, perform risk classification of contacts, issue guidelines for follow-up, provide information, and monitor the crisis response. In total, 130 contacts were identified (66 classified as high risk and 64 as low risk) and monitored for 21 days after their last possible exposure. The case raised questions specific to international travel, postexposure prophylaxis for Marburg virus, and laboratory testing of contacts with fever. We present lessons learned and results of the follow-up serosurvey of contacts and focus on factors that prevented overreaction during an event with a high public health impact.

Influenza virus CTL epitopes, remarkably conserved and remarkably variable

Virus-specific cytotoxic T lymphocytes (CTL) contribute to the control of virus infections including those caused by influenza viruses. Especially under circumstances when antibodies induced by previous infection or vaccination fail to recognize and neutralize the virus adequately, CTL are important and contribute to protective immunity. During epidemic outbreaks caused by antigenic drift variants and during pandemic outbreaks of influenza, humoral immunity against influenza viruses is inadequate. Under these circumstances, pre-existing CTL directed to the relatively conserved internal proteins of the virus may provide cross-protective immunity. Indeed, most of the known human influenza virus CTL epitopes are conserved. However, during the evolution of influenza A/H3N2 viruses, the most important cause of seasonal influenza outbreaks, variation in CTL epitopes has been observed. The observed amino acid substitutions affected recognition by virus-specific CTL and the human virus-specific CTL response in vitro. Examples of variable epitopes and their HLA restrictions are: NP(383-391)/HLA-B*2705, NP(380-388)/HLA-B*0801, NP(418-426)/HLA-B*3501, NP(251-259)/HLA-B*4002, NP(103-111)/HLA-B*1503. In some cases amino acid substitutions occurred at anchor residues and in other cases at T cell receptor contact residues. It is of special interest that the R384G substitution in the NP(383-391) epitope was detrimental to virus fitness and was only tolerated in the presence of multiple functionally compensating co-mutations. In contrast, other epitopes, like the HLA-A*0201 restricted epitope from the matrix protein, M1(58-66), are highly conserved despite their immunodominant nature and the high prevalence of HLA-A*0201 in the population. A mutational analysis of this epitope indicated that it is under functional constraints. Also in influenza A viruses of other subtypes, including H5N1, the M1(58-66) is highly conserved.

Acyclovir susceptibility and genetic characteristics of sequential herpes simplex virus type 1 corneal isolates from patients with recurrent herpetic keratitis

PURPOSE

The incidence and clinical significance of herpes simplex virus type 1 (HSV-1) acyclovir resistance were determined in patients with recurrent herpetic keratitis (RHK).

METHODS

Sequential corneal isolates (n = 39) from 15 immunocompetent patients with RHK were assayed for acyclovir susceptibility and genotyped by analyzing the hypervariable regions of the HSV-1 genes US1 and US12. The thymidine kinase (TK) gene of each isolate was sequenced, and the proportion of acyclovir-resistant viruses within isolates was determined.

RESULTS

Uniform acyclovir-resistant or acyclovir-sensitive sequential isolates were identified in 4 and 2 patients, respectively. Notably, the acyclovir susceptibility of sequential isolates changed from acyclovir sensitive to acyclovir resistant (5 patients) or from acyclovir resistant to acyclovir sensitive (3 patients). The acyclovir-resistant phenotype of the isolates correlated with the patient's unresponsiveness to acyclovir therapy. Combined analyses of the TK gene and genotype of sequential isolates showed that acyclovir-sensitive isolates contained multiple acyclovir-resistant variants of the same virus and that an identical acyclovir-resistant HSV-1 strain reappeared in the patient's cornea during RHK episodes.

CONCLUSIONS

Corneal HSV-1 isolates are mixtures of acyclovir-sensitive and acyclovir-resistant viruses that share the same genotype but have different TK sequences. Recovery of the same acyclovir-resistant virus during consecutive herpetic keratitis episodes suggests that acyclovir-resistant HSV-1 establishes latency and reactivates intermittently to cause acyclovir-refractory RHK.

MVA-based H5N1 vaccine affords cross-clade protection in mice against influenza A/H5N1 viruses at low doses and after single immunization

Human infections with highly pathogenic avian influenza viruses of the H5N1 subtype, frequently reported since 2003, result in high morbidity and mortality. It is feared that these viruses become pandemic, therefore the development of safe and effective vaccines is desirable. MVA-based H5N1 vaccines already proved to be effective when two immunizations with high doses were used. Dose-sparing strategies would increase the number of people that can be vaccinated when the amount of vaccine preparations that can be produced is limited. Furthermore, protective immunity is induced ideally after a single immunization. Therefore the minimal requirements for induction of protective immunity with a MVA-based H5N1 vaccine were assessed in mice. To this end, mice were vaccinated once or twice with descending doses of a recombinant MVA expressing the HA gene of influenza virus A/Vietnam/1194/04. The protective efficacy was determined after challenge infection with the homologous clade 1 virus and a heterologous virus derived from clade 2.1, A/Indonesia/5/05 by assessing weight loss, virus replication and histopathological changes. It was concluded that MVA-based vaccines allowed significant dose-sparing and afford cross-clade protection, also after a single immunization, which are favorable properties for an H5N1 vaccine candidate.

The application of genomics to emerging zoonotic viral diseases

Interspecies transmission of pathogens may result in the emergence of new infectious diseases in humans as well as in domestic and wild animals. Genomics tools such as high-throughput sequencing, mRNA expression profiling, and microarray-based analysis of single nucleotide polymorphisms are providing unprecedented ways to analyze the diversity of the genomes of emerging pathogens as well as the molecular basis of the host response to them. By comparing and contrasting the outcomes of an emerging infection with those of closely related pathogens in different but related host species, we can further delineate the various host pathways determining the outcome of zoonotic transmission and adaptation to the newly invaded species. The ultimate challenge is to link pathogen and host genomics data with biological outcomes of zoonotic transmission and to translate the integrated data into novel intervention strategies that eventually will allow the effective control of newly emerging infectious diseases.

Evaluation of a rapid molecular algorithm for detection of pandemic influenza A (H1N1) 2009 virus and screening for a key oseltamivir resistance (H275Y) substitution in neuraminidase

BACKGROUND

Rapid and specific molecular tests for identification of the recently identified pandemic influenza A/H1N1 2009 virus as well as rapid molecular tests to identify antiviral resistant strains are urgently needed.

OBJECTIVES

We have evaluated the performance of two novel reverse transcriptase polymerase chain reactions (RT-PCRs) targeting specifically hemagglutinin and neuraminidase of pandemic influenza A/H1N1 virus in combination with a conserved matrix PCR. In addition, we investigated the performance of a novel discrimination RT-PCR for detection of the H275Y resistance mutation in the neuraminidase gene.

STUDY DESIGN

Clinical performance of both subtype specific RT-PCR assays was evaluated through analysis of 684 throat swaps collected from individuals meeting the WHO case definition for the novel pandemic influenza virus. Analytical performance was analyzed through testing of 10-fold serial dilutions of RNA derived from the first Dutch sequenced and cultured confirmed case of novel pandemic influenza infection. Specificity and discriminative capacities of the H275Y discrimination assay were performed by testing wild type and recombinant H275Y pandemic influenza.

RESULTS

121 throat swaps collected from April 2009 to July 2009 were positive by at least two out of three RT-PCRs, and negative for the seasonal H3/H1 subtype specific RT-PCR assays. 117 of these were tested positive for all three (Ct-values from 15.1 to 36.8). No oseltamivir resistance was detected.

CONCLUSIONS

We present a sensitive and specific approach for detection of pandemic influenza A/H1N1 2009 and a rapid RT-PCR assay detecting a primary oseltamivir resistance mutation which can be incorporated easily into clinical virology algorithms.

Dendritic cells are crucial for maintenance of tertiary lymphoid structures in the lung of influenza virus-infected mice

Tertiary lymphoid organs (TLOs) are organized aggregates of B and T cells formed in postembryonic life in response to chronic immune responses to infectious agents or self-antigens. Although CD11c⁺ dendritic cells (DCs) are consistently found in regions of TLO, their contribution to TLO organization has not been studied in detail. We found that CD11c^hi DCs are essential for the maintenance of inducible bronchus-associated lymphoid tissue (iBALT), a form of TLO induced in the lungs after influenza virus infection. Elimination of DCs after the virus had been cleared from the lung resulted in iBALT disintegration and reduction in germinal center (GC) reactions, which led to significantly reduced numbers of class-switched plasma cells in the lung and bone marrow and reduction in protective antiviral serum immunoglobulins. Mechanistically, DCs isolated from the lungs of mice with iBALT no longer presented viral antigens to T cells but were a source of lymphotoxin (LT) β and homeostatic chemokines (CXCL-12 and -13 and CCL-19 and -21) known to contribute to TLO organization. Like depletion of DCs, blockade of LTβ receptor signaling after virus clearance led to disintegration of iBALT and GC reactions. Together, our data reveal a previously unappreciated function of lung DCs in iBALT homeostasis and humoral immunity to influenza virus.

Both conventional and interferon killer dendritic cells have antigen-presenting capacity during influenza virus infection

Natural killer cells are innate effector cells known for their potential to produce interferon-gamma and kill tumour and virus-infected cells. Recently, B220(+)CD11c(int)NK1.1(+) NK cells were found to also have antigen-presenting capacity like dendritic cells (DC), hence their name interferon-producing killer DC (IKDC). Shortly after discovery, it has already been questioned if IKDC really represent a separate subset of NK cells or merely represent a state of activation. Despite similarities with DCs, in vivo evidence that they behave as bona fide APCs is lacking. Here, using a model of influenza infection, we found recruitment of both conventional B220(-) NK cells and IKDCs to the lung. To study antigen-presenting capacity of NK cell subsets and compare it to cDCs, all cell subsets were sorted from lungs of infected mice and co-cultured ex vivo with antigen specific T cells. Both IKDCs and conventional NK cells as well as cDCs presented virus-encoded antigen to CD8 T cells, whereas only cDCs presented to CD4 T cells. The absence of CD4 responses was predominantly due to a deficiency in MHCII processing, as preprocessed peptide antigen was presented equally well by cDCs and IKDCs. In vivo, the depletion of NK1.1-positive NK cells and IKDCs reduced the expansion of viral nucleoprotein-specific CD8 T cells in the lung and spleen, but did finally not affect viral clearance from the lung. In conclusion, we found evidence for APC function of lung NK cells during influenza infection, but this is a feature not exclusive to the IKDC subset.

The novel adjuvant CoVaccineHT increases the immunogenicity of cell-culture derived influenza A/H5N1 vaccine and induces the maturation of murine and human dendritic cells in vitro

A candidate influenza H5N1 vaccine based on cell-culture-derived whole inactivated virus and the novel adjuvant CoVaccineHT was evaluated in vitro and in vivo. To this end, mice were vaccinated with the whole inactivated influenza A/H5N1 virus vaccine with and without CoVaccineHT and virus-specific antibody and cellular immune responses were assessed. The addition of CoVaccineHT increased virus specific primary and secondary antibody responses against the homologous and an antigenically distinct heterologous influenza A/H5N1 strain. The superior antibody responses induced with the CoVaccineHT-adjuvanted vaccine correlated with the magnitude of the virus-specific CD4+ T helper cell responses. CoVaccineHT did not have an effect on the magnitude of the CD8+ T cell response. In vitro, CoVaccineHT upregulated the expression of co-stimulatory molecules both on mouse and human dendritic cells and induced the secretion of pro-inflammatory cytokines TNF-alpha, IL-6, IL-1beta and IL-12p70 in mouse- and IL-6 in human dendritic cells. Inhibition experiments indicated that the effect of CoVaccineHT is mediated through TLR4 signaling. These data suggest that CoVaccineHT also will increase the immunogenicity of an influenza A/H5N1 vaccine in humans.