[Show abstract][Hide abstract] ABSTRACT: Recently, A/H5N1 influenza viruses were shown to acquire airborne transmissibility between ferrets upon targeted mutagenesis and virus passage. The critical genetic changes in airborne A/Indonesia/5/05 were not yet identified. Here, five substitutions proved to be sufficient to determine this airborne transmission phenotype. Substitutions in PB1 and PB2 collectively caused enhanced transcription and virus replication. One substitution increased HA thermostability and lowered the pH of membrane fusion. Two substitutions independently changed HA binding preference from α2,3-linked to α2,6-linked sialic acid receptors. The loss of a glycosylation site in HA enhanced overall binding to receptors. The acquired substitutions emerged early during ferret passage as minor variants and became dominant rapidly. Identification of substitutions that are essential for airborne transmission of avian influenza viruses between ferrets and their associated phenotypes advances our fundamental understanding of virus transmission and will increase the value of future surveillance programs and public health risk assessments.
[Show abstract][Hide abstract] ABSTRACT: To assess the efficacy of novel antiviral drugs against influenza in clinical trials it is necessary to quantify infectious virus titers in patients' respiratory tract samples. Typically, this is achieved by inoculating virus-susceptible cells with serial dilutions of clinical specimens, and detecting the production of progeny virus by hemagglutination since influenza viruses generally have the capacity to bind and agglutinate erythrocytes of various species through their hemagglutinin (HA). This readout method is no longer adequate, since an increasing number of currently circulating A(H3) influenza viruses display reduced capacity to agglutinate erythrocytes.Here, we report the magnitude of this problem by analyzing the frequency of HA deficient A(H3) viruses detected in the Netherlands from 1999-2012. Furthermore, we report development and validation of an alternative method to monitor the production of progeny influenza virus in quantitative virus cultures, which is independent of the capacity to agglutinate erythrocytes. This method is based on detection of viral nucleoprotein (NP) in virus culture plates by ELISA, and it produced similar results compared to the hemagglutination assay using strains with good HA activity, including A/Brisbane/059/07 (H1N1), A/Victoria/210/09 (H3N2) and other seasonal A(H1N1), A(H1N1)pdm09 and the majority of A(H3) virus strains isolated in 2009. In contrast, many A(H3) viruses that circulate since 2010 failed to display HA activity and infectious virus titers could only be determined by detecting NP. The virus culture ELISA described here will enable efficacy testing of new antiviral compounds in clinical trials during seasons in which non-hemagglutinating influenza A viruses circulate.
Journal of clinical microbiology 03/2014; · 4.16 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Influenza A virus-specific T cells are highly cross-reactive and contribute to heterosubtypic immunity, which may afford protection against novel pandemic strains of influenza virus. However, the magnitude and nature of virus-specific T-cell responses induced by natural infections and/or vaccination in young children is poorly understood. Host factors, such as the development of the immune system during childhood and environmental factors such as exposure rates to influenza viruses and interference by vaccination contribute to shaping the magnitude and specificity of the T-cell response. Here, the authors review several of these factors, including the differences between T-cell responses of young children and adults, the age-dependent frequency of virus-specific T cells and the impact of annual childhood influenza vaccination. In addition, the authors summarize all currently available studies in which influenza vaccine-induced T-cell responses were evaluated. The authors discuss these findings in the light of developing vaccines and vaccination strategies aiming at the induction of protective immunity to seasonal and pandemic influenza viruses of antigenically distinct subtypes.
Expert Review of Vaccines 01/2014; 11(8). · 4.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Influenza virus infections yearly cause high morbidity and mortality burdens in humans, and the development of a new influenza pandemic continues to threaten mankind as a Damoclean sword. Influenza vaccines have been produced by using egg-based virus growth and passaging techniques that were developed more than 60 years ago, following the identification of influenza A virus as an etiological agent of seasonal influenza. These vaccines aimed mainly at eliciting neutralizing antibodies targeting antigenically variable regions of the hemagglutinin (HA) protein, which requires regular updates to match circulating seasonal influenza A and B virus strains. Given the relatively limited protection induced by current seasonal influenza vaccines, a more universal influenza vaccine that would protect against more-if not all-influenza viruses is among the largest unmet medical needs of the 21st century. New insights into correlates of protection from influenza and into broad B- and T-cell protective anti-influenza immune responses offer promising avenues for innovative vaccine development as well as manufacturing strategies or platforms, leading to the development of a new generation of vaccines. These aim at the rapid and massive production of influenza vaccines that provide broad protective and long-lasting immunity. Recent advances in influenza vaccine research demonstrate the feasibility of a wide range of approaches and call for the initiation of preclinical proof-of-principle studies followed by clinical trials in humans.
[Show abstract][Hide abstract] ABSTRACT: Highly pathogenic avian influenza (HPAI) viruses of the H5N1 subtype are genetically highly variable and have diversified into multiple phylogenetic clades over the past decade. Antigenic drift is a well-studied phenomenon for seasonal human influenza viruses, but much less is known about the antigenic evolution of HPAI H5N1 viruses that circulate in poultry. In this study, we focused on HPAI H5N1 viruses that are enzootic to Indonesia. We selected representative viruses from genetically distinct lineages that are currently circulating and determined their antigenic properties by hemagglutination inhibition assays. At least six antigenic variants have circulated between 2003, when H5N1 clade 2.1 viruses were first detected in Indonesia, and 2011. During this period, multiple antigenic variants cocirculated in the same geographic regions. Mutant viruses were constructed by site-directed mutagenesis to represent each of the circulating antigenic variants, revealing that antigenic differences between clade 2.1 viruses were due to only one or very few amino acid substitutions immediately adjacent to the receptor binding site. Antigenic variants of H5N1 virus evaded recognition by both ferret and chicken antibodies. The molecular basis for antigenic change in clade 2.1 viruses closely resembled that of seasonal human influenza viruses, indicating that the hemagglutinin of influenza viruses from different hosts and subtypes may be similarly restricted to evade antibody recognition.
[Show abstract][Hide abstract] ABSTRACT: Respiratory viruses infections caused by influenza viruses, human parainfluenza virus (hPIV), respiratory syncytial virus (RSV) and coronaviruses are an eminent threat for public health. Currently, there are no licensed vaccines available for hPIV, RSV and coronaviruses, and the available seasonal influenza vaccines have considerable limitations. With regard to pandemic preparedness, it is important that procedures are in place to respond rapidly and produce tailor made vaccines against these respiratory viruses on short notice. Moreover, especially for influenza there is great need for the development of a universal vaccine that induces broad protective immunity against influenza viruses of various subtypes. Modified Vaccinia Virus Ankara (MVA) is a replication-deficient viral vector that holds great promise as a vaccine platform. MVA can encode one or more foreign antigens and thus functions as a multivalent vaccine. The vector can be used at biosafety level 1, has intrinsic adjuvant capacities and induces humoral and cellular immune responses. However, there are some practical and regulatory issues that need to be addressed in order to develop MVA-based vaccines on short notice at the verge of a pandemic. In this review, we discuss promising novel influenza virus vaccine targets and the use of MVA for vaccine development against various respiratory viruses.
[Show abstract][Hide abstract] ABSTRACT: Influenza is a major burden to public health. Due to high mutation rates and selection pressure, mutant viruses emerge which are resistant to currently used antiviral drugs. Therefore, there is a need for the development of novel classes of antiviral drugs that suffer less from the emergence of resistant viruses. Antiviral drugs based on collectin-like surfactant protein D (SP-D) may fulfil these requirements. Especially porcine SP-D displays strong antiviral activity to influenza A viruses. In the present study the antiviral activity of recombinant porcine SP-D was investigated in ex vivo cultures of respiratory tract tissue infected with human influenza A virus of the H3N2 subtype. Porcine SP-D has antiviral activity in these test systems. It is suggested that porcine SP-D may be used as a venue to develop a novel class of antiviral drugs.
[Show abstract][Hide abstract] ABSTRACT: Influenza A(H3N2) viruses became widespread in humans during the 1968 H3N2 virus pandemic and have been a major cause of influenza epidemics ever since. The viruses evolve continuously by reassortment and genomic evolution. Antigenic drift is the cause for the need to update the influenza vaccine frequently. Using two datasets that span the entire period of circulation of human influenza A(H3N2) viruses, it was shown that the influenza A(H3N2) virus evolution could be mapped into thirteen antigenic clusters. Here, we have analyzed the full genome of 286 influenza A(H3N2) viruses from these two datasets to investigate the genomic evolution and reassortment patterns. Numerous reassortment events, scattered over the entire period of virus circulation, were found, but most prominently in viruses circulating between 1991 and 1998. Some of these reassortment events persisted over time, and one of these coincided with an antigenic cluster transition. Further, selection pressures and nucleotide and amino acid substitution rates of all proteins were studied, including the recently discovered PB1-N40, PA-X, PA-N155, and PA-N182 proteins. Rates of nucleotide and amino acid substitution were most pronounced for hemagglutinin, neuraminidase, and PB1-F2 proteins. Selection pressures were highest in hemagglutinin, neuraminidase, matrix 1 and non-structural protein 1. This study of genotype in relation to the antigenic phenotype throughout the entire period of circulation of human influenza A(H3N2) viruses leads to a better understanding of its evolution.
[Show abstract][Hide abstract] ABSTRACT: The molecular basis of antigenic drift was determined for the hemagglutinin (HA) of human influenza A/H3N2 virus. From 1968 to 2003, antigenic change was caused mainly by single amino acid substitutions, which occurred at only seven positions in HA immediately adjacent to the receptor binding site. Most of these substitutions were involved in antigenic change more than once. Equivalent positions were responsible for the recent antigenic changes of influenza B and A/H1N1 viruses. Substitution of a single amino acid at one of these positions substantially changed the virus-specific antibody response in infected ferrets. These findings have potentially far-reaching consequences for understanding the evolutionary mechanisms that govern influenza viruses.
[Show abstract][Hide abstract] ABSTRACT: In February 2013 zoonotic transmission of a novel influenza A virus of the H7N9 subtype was reported in China. Although at present no sustained human-to-human transmission has been reported, a pandemic outbreak of this H7N9 virus is feared. Since neutralizing antibodies to the hemagglutinin (HA) globular head domain of this virus are virtually absent in the human population, there is interest in identifying other correlates of protection, such as cross-reactive CD8(+) T cells (cytotoxic T lymphocytes (CTLs)) elicited during seasonal influenza A virus infections. These virus-specific CD8(+) T cells are known to recognize conserved internal proteins of influenza A viruses predominantly, but it is unknown to what extent they cross-react with the newly emerging H7N9 virus. Here, we assessed the cross-reactivity of seasonal H3N2, H1N1 and pandemic H1N1 influenza A virus-specific polyclonal CD8(+) T cells, obtained from HLA-typed study subjects, with the novel H7N9 virus. The cross-reactivity of CD8(+) T cells to H7N9 variants of known influenza A epitopes and H7N9 virus infected cells was determined by their IFN-γ response and lytic activity. It was concluded that, apart from recognition of individual H7N9 variant epitopes, CD8(+) T cells to seasonal influenza viruses display considerable cross-reactivity with the novel H7N9 virus. The presence of these cross-reactive CD8(+) T cells may afford some protection against infection with this new virus.
[Show abstract][Hide abstract] ABSTRACT: Higher rates of hospitalization and mortality are described in oncology patients with influenza virus infection compared to the general population. Yearly influenza vaccination is recommended for patients treated with chemotherapy. The optimal moment to administer the vaccine during a treatment cycle has not been studied extensively.
During the influenza season 2011-2012 we conducted a multicenter randomized controlled trial (OFLUVAC, NTR2858, no sponsoring) in the Netherlands. Patients receiving adjuvant chemotherapy for breast or colorectal cancer were randomized between early (day 5 after chemotherapy) and late (day 16 after chemotherapy) vaccination with the influenza virus vaccine (Influvac(®) 2011/2012-Vaxigrip(®) 2011/2012). Influenza virus-specific antibody titres were determined before, 3 and 12 weeks after vaccination by haemagglutination inhibition.
Thirty-eight breast cancer patients (early=21; late=17) and 18 colorectal cancer patients (early=8; late=10) were analyzed. In breast cancer patients overall serologic responses were adequate. A statistically significant higher response in patients who received early compared to late vaccination in the chemotherapy cycle was observed. Geometric mean titres post vaccination on day 5 versus day 16 were 69.3 versus 27.4 (H3N2), 76.4 versus 17.5 (H1N1) and 34.4 versus 26.0 (B/Brisbane), respectively. In colorectal cancer patients overall serologic responses were adequate, no significant difference was found between early and late vaccination. Geometric mean titres post vaccination on day 5 versus day 16 were 170.1 versus 192.4 (H3N2), 233.0 versus 280.8 (H1N1) and 62.6 versus 75.9 (B/Brisbane), respectively.
Overall antibody response to the influenza virus vaccine in patients treated with chemotherapy for breast or colorectal cancer patients is adequate. Breast cancer patients seem to mount the best antibody response when vaccinated early after a chemotherapy cycle (≤day 5). No difference was found between early and late vaccination in colorectal cancer patients.
[Show abstract][Hide abstract] ABSTRACT: Influenza A viruses cause yearly seasonal epidemics and occasional global pandemics in humans. In the last century, four human influenza A virus pandemics have occurred. Occasionally, influenza A viruses that circulate in other species cross the species barrier and infect humans. Virus reassortment (i.e. mixing of gene segments of multiple viruses) and the accumulation of mutations contribute to the emergence of new influenza A virus variants. Fortunately, most of these variants do not have the ability to spread among humans and subsequently cause a pandemic. In this review, we focus on the threat of animal influenza A viruses which have shown the ability to infect humans. In addition, genetic factors which could alter the virulence of influenza A viruses are discussed. The identification and characterisation of these factors may provide insights into genetic traits which change virulence and help us to understand which genetic determinants are of importance for the pandemic potential of animal influenza A viruses.
European Journal of Clinical Microbiology 09/2013; · 3.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Wild waterfowl form the main reservoir of influenza A viruses, from which transmission occurs directly or indirectly to various secondary hosts, including humans. Direct avian-to-human transmission has been observed for viruses of subtypes A(H5N1), A(H7N2), A(H7N3), A(H7N7), A(H9N2) and A(H10N7) upon human exposure to poultry, but a lack of sustained human-to-human transmission has prevented these viruses from causing new pandemics. Recently, avian A(H7N9) viruses were transmitted to humans, causing severe respiratory disease and deaths in China. Because transmission via respiratory droplets and aerosols (hereafter referred to as airborne transmission) is the main route for efficient transmission between humans, it is important to gain an insight into airborne transmission of the A(H7N9) virus. Here we show that although the A/Anhui/1/2013 A(H7N9) virus harbours determinants associated with human adaptation and transmissibility between mammals, its airborne transmissibility in ferrets is limited, and it is intermediate between that of typical human and avian influenza viruses. Multiple A(H7N9) virus genetic variants were transmitted. Upon ferret passage, variants with higher avian receptor binding, higher pH of fusion, and lower thermostability were selected, potentially resulting in reduced transmissibility. This A(H7N9) virus outbreak highlights the need for increased understanding of the determinants of efficient airborne transmission of avian influenza viruses between mammals.
[Show abstract][Hide abstract] ABSTRACT: Infections with low pathogenic avian influenza (LPAI) A(H7N9) viruses have caused more than 100 hospitalized human cases of severe influenza in China since February 2013 with a case fatality rate exceeding 25%. Most of these human infections presented with severe viral pneumonia, while limited information is available currently on the occurrence of mild and subclinical cases. In the present study, a ferret model for this virus infection in humans is presented to evaluate the pathogenesis of the infection in a mammalian host, as ferrets have been shown to mimic the pathogenesis of human infection with influenza viruses most closely. Ferrets were inoculated intratracheally with increasing doses (>10 e5 TCID50) of H7N9 influenza virus A/Anhui/1/2013 and were monitored for clinical and virological parameters up to four days post infection. Virus replication was detected in the upper and lower respiratory tracts while animals developed fatal viral pneumonia. This study illustrates the high pathogenicity of LPAI-H7N9 virus for mammals. Furthermore, the intratracheal inoculation route in ferrets proofs to offer a solid model for LPAI-H7N9 virus induced pneumonia in humans. This model will facilitate the development and assessment of clinical intervention strategies for LPAI-H7N9 virus infection in humans, such as preventive vaccination and the use of antivirals.
[Show abstract][Hide abstract] ABSTRACT: Influenza A viruses cause annual epidemics and occasionally pandemics. Antibodies directed to the conserved viral nucleoprotein (NP) may play a role in immunity against various influenza A virus subtypes. Here we assessed the immunological significance of a human monoclonal antibody directed to NP in vitro. This antibody bound to virus-infected cells, but did not display virus-neutralizing activity, complement-dependent cell-cytotoxicity or opsonization of viral antigen for improved antigen presentation to CD8+ T cells by dendritic cells.
Clinical and vaccine Immunology: CVI 06/2013; · 2.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Influenza A H5N1 viruses remain a substantial threat to global public health. In particular, the expanding genetic diversity of H5N1 viruses and the associated risk for human adaptation underscore the importance of better understanding host immune responses that may protect against disease or infection. Although much emphasis has been placed on investigating early virus-host interactions and the induction of innate immune responses, little is known of the consequent adaptive immune response to H5N1 virus infection. In this review, we describe the H5N1 virus-specific and cross-reactive antibody and T cell responses in humans and animal models. Data from limited studies suggest that although initially robust, there is substantial waning of the serum antibody responses in survivors of H5N1 virus infection. Characterization of monoclonal antibodies generated from memory B cells of survivors of H5N1 virus infection has provided an understanding of the fine specificity of the human antibody response to H5N1 virus infection and identified strategies for immunotherapy. Human T cell responses induced by infection with seasonal influenza viruses are directed to relatively conserved internal proteins and cross-react with the H5N1 subtype. A role for T cell-based heterosubtypic immunity against H5N1 viruses is suggested in animal studies. Further studies on adaptive immune responses to H5N1 virus infection in both humans and animals are needed to inform the design of optimal immunological treatment and prevention modalities.