Generation of recombinant pandemic H1N1 influenza virus with the HA cleavable by bromelain and identification of the residues influencing HA bromelain cleavage

Development of an Inactivated H7N9 Subtype Avian Influenza Serological DIVA Vaccine Using the Chimeric HA Epitope Approach

H7N9 avian influenza virus (AIV) is an emerging zoonotic pathogen, and it is necessary to develop a differentiating infected from vaccinated animals (DIVA) vaccine for the purpose of eradication. H7N9 subtype AIV hemagglutinin subunit 2 glycoprotein (HA2) peptide chips and antisera of different AIV subtypes were used to screen H7N9 AIV-specific epitopes. A selected specific epitope in the HA2 protein of H7N9 AIV strain A/Chicken/Huadong/JD/17 (JD/17) was replaced with an epitope from an H3N2 subtype AIV strain by reverse genetics. The protection and serological DIVA characteristics of the recombinant H7N9 AIV strain were evaluated. The results showed that a specific epitope on the HA2 protein of H7N9 AIV, named the H7-12 peptide, was successfully screened. The recombinant H7N9 AIV with a modified epitope in the HA2 protein was rescued and named A/Chicken/Huadong/JD-cHA/17 (JD-cHA/17). The HA titer of JD-cHA/17 was 10 log₂, and the 50% egg infective dose (EID₅₀) titer was 9.67 log₁₀ EID₅₀/ml. Inactivated JD-cHA/17 induced a hemagglutination inhibition (HI) antibody titer similar that of the parent strain and provided 100% protection against high-pathogenicity or low-pathogenicity H7N9 AIV challenge. A peptide chip coated with H7-12 peptide was successfully applied to detect the seroconversion of chickens infected or vaccinated with JD/17, while there was no reactivity with antisera of chickens vaccinated with JD-cHA/17. Therefore, the marked vaccine candidate JD-cHA/17 can be used as a DIVA vaccine against H7N9 avian influenza when combined with an H7-12 peptide chip, making it a useful tool for stamping out the H7N9 AIV.

IMPORTANCE DIVA vaccine is a useful tool for eradicating avian influenza, especially for highly pathogenic avian influenza. Several different DIVA strategies have been proposed for avian influenza inactivated whole-virus vaccine, involving the neuraminidase (NA), nonstructural protein 1 (NS1), matrix protein 2 ectodomain (M2e), or HA2 gene. However, virus reassortment, residual protein in a vaccine component, or reduced vaccine protection may limit the application of these DIVA strategies. Here, we constructed a novel chimeric H7N9 AIV, JD-cHA/17, that expressed the entire HA protein with substitution of an H3 AIV epitope in HA2. The chimeric H7N9 recombinant vaccine provides full clinical protection against high-pathogenicity or low-pathogenicity H7N9 AIV challenge. Combined with a short-peptide-based microarray chip containing the H7N9 AIV epitope in HA2, our finding is expected to be useful as a marker vaccine designed for avian influenza.

Effect of Plant-Derived Proteases on Infectivity of Tulane Virus, Murine Norovirus, and Hepatitis A Virus

ABSTRACT

Plant-derived proteases, bromelain, papain, and ficin, are broad-acting enzymes with generally recognized as safe status for foods and have current application in several food industries. These proteases have also been reported to have antimicrobial properties. This study investigated the efficacy of commercially prepared bromelain, papain, and ficin, individually and combined (2,500 ppm of crude extract), for inactivation of hepatitis A virus (HAV) and human norovirus surrogates, Tulane virus (TV), and murine norovirus (MNV). Various treatment temperatures (45, 50, or 55°C), times (10 or 60 min), and pH values (5.5 or 7.0) in the presence of cysteine (2 mM) were evaluated. Inactivation was assessed by infectivity in plaque assay for TV and MNV and by median tissue culture infective dose for HAV. No reduction in infectious TV or HAV was attributed to the plant-derived proteases at any of the conditions tested. Infectious MNV was reduced by 1 to 3 log PFU/mL; the most effective treatment was bromelain at pH 7 and 50°C for 10 min. A time course study with MNV in bromelain at 50°C indicated that a 2-log PFU/mL reduction could be achieved within 6 min, but extended treatment of 15 min was still insufficient to eliminate infectious MNV. The lack of or limited efficacy of bromelain, papain, and ficin on HAV, TV, and MNV, even at elevated temperatures and exposure times, suggests the plant-derived proteases are not commercially applicable for inactivation of virus on commodities or materials that could not also withstand mild heat treatment. The variable susceptibilities observed between TV and MNV illustrate limitations in utilization of surrogates for predicting pathogen behavior for a structure-specific treatment.

HIGHLIGHTS

Development and characterization of standard reagents for cell-based prepandemic influenza vaccine products

Outbreaks of infection by novel avian influenza virus strains in humans cause public health issues worldwide, and the development of vaccines against such novel strains is the most effective method for the prevention of these virus outbreaks. All types of vaccines must be tested for potency before use; thus, quantitative potency assays are needed for influenza vaccines. The single radial immunodiffusion (SRID) assay is considered the gold standard for quantification of influenza virus antigens, and the SRID reference reagents are essential for the determination of vaccine potency. However, it remains debatable whether reference reagents derived from egg-based vaccine platforms can be used to precisely quantify non-egg-derived vaccines; thus, influenza vaccine production using cell-based platforms has attracted increasing attention. To evaluate the utility of reference reagents derived from a cell-based influenza vaccine platform, we prepared cell-based reference reagents from MDCK cell-grown viruses and compared them with egg-derived reference reagents. A primary liquid standard (PLS) was purified from cell-derived candidate influenza vaccine viruses, and hemagglutinin (HA) antigen content was determined by a densitometric method. The produced PLS could be stored at 4°C for more than 10 months. We also established a simple HA protein purification method for goat antiserum preparation, and the performance of the resulting antiserum was compared to that of standard reagents obtained using different production platforms. The results of this study indicate that these reference reagents can be used for both cell-based and egg-based production platforms and that the differences between these two types of platforms are negligible.

Molecular features of influenza A (H1N1)pdm09 prevalent in Mexico during winter seasons 2012-2014

Since the emergence of the pandemic H1N1pdm09 virus in Mexico and California, biannual increases in the number of cases have been detected in Mexico. As observed in previous seasons, pandemic A/H1N1 09 virus was detected in severe cases during the 2011-2012 winter season and finally, during the 2013-2014 winter season it became the most prevalent influenza virus. Molecular and phylogenetic analyses of the whole viral genome are necessary to determine the antigenic and pathogenic characteristics of influenza viruses that cause severe outcomes of the disease. In this paper, we analyzed the evolution, antigenic and genetic drift of Mexican isolates from 2009, at the beginning of the pandemic, to 2014. We found a clear variation of the virus in Mexico from the 2011-2014 season due to different markers and in accordance with previous reports. In this study, we identified 13 novel substitutions with important biological effects, including virulence, T cell epitope presented by MHC and host specificity shift and some others substitutions might have more than one biological function. The systematic monitoring of mutations on whole genome of influenza A pH1N1 (2009) virus circulating at INER in Mexico City might provide valuable information to predict the emergence of new pathogenic influenza virus.

Vaccine Efficacy of Inactivated, Chimeric Hemagglutinin H9/H5N2 Avian Influenza Virus and Its Suitability for the Marker Vaccine Strategy

In order to produce a dually effective vaccine against H9 and H5 avian influenza viruses that aligns with the DIVA (differentiating infected from vaccinated animals) strategy, we generated a chimeric H9/H5N2 recombinant vaccine that expressed the whole HA1 region of A/CK/Korea/04163/04 (H9N2) and the HA2 region of recent highly pathogenic avian influenza (HPAI) A/MD/Korea/W452/14 (H5N8) viruses. The chimeric H9/H5N2 virus showed in vitro and in vivo growth properties and virulence that were similar to those of the low-pathogenic avian influenza (LPAI) H9 virus. An inactivated vaccine based on this chimeric virus induced serum neutralizing (SN) antibodies against both H9 and H5 viruses but induced cross-reactive hemagglutination inhibition (HI) antibody only against H9 viruses. Thus, this suggests its compatibility for use in the DIVA strategy against H5 strains. Furthermore, the chimeric H9/H5N2 recombinant vaccine protected immunized chickens against lethal challenge by HPAI H5N8 viruses and significantly attenuated virus shedding after infection by both H9N2 and HPAI H5N8 viruses. In mice, serological analyses confirmed that HA1- and HA2 stalk-specific antibody responses were induced by vaccination and that the DIVA principle could be employed through the use of an HI assay against H5 viruses. Furthermore, each HA1- and HA2 stalk-specific antibody response was sufficient to inhibit viral replication and protect the chimeric virus-immunized mice from lethal challenge with both mouse-adapted H9N2 and wild-type HPAI H5N1 viruses, although differences in vaccine efficacy against a homologous H9 virus (HA1 head domain immune-mediated protection) and a heterosubtypic H5 virus (HA2 stalk domain immune-mediated protection) were observed. Taken together, these results demonstrate that the novel chimeric H9/H5N2 recombinant virus is a low-pathogenic virus, and this chimeric vaccine is suitable for a DIVA vaccine with broad-spectrum neutralizing antibody against H5 avian influenza viruses.IMPORTANCE Current influenza virus killed vaccines predominantly induce antihemagglutinin (anti-HA) antibodies that are commonly strain specific in that the antibodies have potent neutralizing activity against homologous strains but do not cross-react with HAs of other influenza virus subtypes. In contrast, the HA2 stalk domain is relatively well conserved among subtypes, and recently, broadly neutralizing antibodies against this domain have been isolated. Therefore, in light of the need for a vaccine strain that applies the DIVA strategy utilizing an HI assay and induces broad cross-protection against H5N1 and H9N2 viruses, we generated a novel chimeric H9/H5N1 virus that expresses the entire HA1 portion from the H9N2 virus and the HA2 region of the heterosubtypic H5N8 virus. The chimeric H9/H5N2 recombinant vaccine protected immunized hosts against lethal challenge with H9N2 and HPAI H5N1 viruses with significantly attenuated virus shedding in immunized hosts. Therefore, this chimeric vaccine is suitable as a DIVA vaccine against H5 avian influenza viruses.

The biochemical characterization, stabilization studies and the antiproliferative effect of bromelain against B16F10 murine melanoma cells

The current study aims to extract bromelain from different parts (stem, crown, peels, pulp and leaves) of Ananas comosus var. comosus AGB 772; to determine of optimum pH and temperature; to test bromelain stability in disodium EDTA and sodium benzoate, and to investigate its pharmacological activity on B16F10 murine melanoma cells in vitro. The highest enzymatic activity was found in bromelain extracted from the pulp and peel. The optimum bromelain pH among all studied pineapple parts was 6.0. The optimum temperature was above 50 °C in all bromelain extracts. The fluorescence analysis confirmed the stability of bromelain in the presence of EDTA and sodium benzoate. Bromelain was pharmacologically active against B16F10 melanoma cells and it was possible verifying approximately 100% inhibition of tumor cell proliferation in vitro. Since bromelain activity was found in different parts of pineapple plants, pineapple residues from the food industry may be used for bromelain extraction.

Influenza hemagglutinin (HA) stem region mutations that stabilize or destabilize the structure of multiple HA subtypes

Influenza A viruses enter host cells through endosomes, where acidification induces irreversible conformational changes of the viral hemagglutinin (HA) that drive the membrane fusion process. The prefusion conformation of the HA is metastable, and the pH of fusion can vary significantly among HA strains and subtypes. Furthermore, an accumulating body of evidence implicates HA stability properties as partial determinants of influenza host range, transmission phenotype, and pathogenic potential. Although previous studies have identified HA mutations that can affect HA stability, these have been limited to a small selection of HA strains and subtypes. Here we report a mutational analysis of HA stability utilizing a panel of expressed HAs representing a broad range of HA subtypes and strains, including avian representatives across the phylogenetic spectrum and several human strains. We focused on two highly conserved residues in the HA stem region: HA2 position 58, located at the membrane distal tip of the short helix of the hairpin loop structure, and HA2 position 112, located in the long helix in proximity to the fusion peptide. We demonstrate that a K58I mutation confers an acid-stable phenotype for nearly all HAs examined, whereas a D112G mutation consistently leads to elevated fusion pH. The results enhance our understanding of HA stability across multiple subtypes and provide an additional tool for risk assessment for circulating strains that may have other hallmarks of human adaptation. Furthermore, the K58I mutants, in particular, may be of interest for potential use in the development of vaccines with improved stability profiles.

IMPORTANCE

The influenza A hemagglutinin glycoprotein (HA) mediates the receptor binding and membrane fusion functions that are essential for virus entry into host cells. While receptor binding has long been recognized for its role in host species specificity and transmission, membrane fusion and associated properties of HA stability have only recently been appreciated as potential determinants. We show here that mutations can be introduced at highly conserved positions to stabilize or destabilize the HA structure of multiple HA subtypes, expanding our knowledge base for this important phenotype. The practical implications of these findings extend to the field of vaccine design, since the HA mutations characterized here could potentially be utilized across a broad spectrum of influenza virus subtypes to improve the stability of vaccine strains or components.

Production of live attenuated influenza vaccines against seasonal and potential pandemic influenza viruses

Vaccination remains the most effective means to prevent morbidity and mortality caused by influenza epidemics and pandemics. Live attenuated influenza vaccine (LAIV) has been proven to be effective in preventing influenza with broad cross reactivity to drifted strains. Owing to the sophisticated nature of the influenza vaccine production process, the time needed to develop high yield LAIV strains for vaccine production and product release remains a constant challenge. This review summarizes LAIV production process with highlights on the experiences gained during the past decade generating seasonal and pandemic LAIV seeds by reverse genetics strategy.

A single amino acid in the stalk region of the H1N1pdm influenza virus HA protein affects viral fusion, stability and infectivity

The 2009 H1N1 pandemic (H1N1pdm) viruses have evolved to contain an E47K substitution in the HA2 subunit of the stalk region of the hemagglutinin (HA) protein. The biological significance of this single amino acid change was investigated by comparing A/California/7/2009 (HA2-E47) with a later strain, A/Brisbane/10/2010 (HA2-K47). The E47K change was found to reduce the threshold pH for membrane fusion from 5.4 to 5.0. An inter-monomer salt bridge between K47 in HA2 and E21 in HA1, a neighboring highly conserved residue, which stabilized the trimer structure, was found to be responsible for the reduced threshold pH for fusion. The higher structural and acid stability of the HA trimer caused by the E47K change also conferred higher viral thermal stability and infectivity in ferrets, suggesting a fitness advantage for the E47K evolutionary change in humans. Our study indicated that the pH of HA fusion activation is an important factor for influenza virus replication and host adaptation. The identification of this genetic signature in the HA stalk region that influences vaccine virus thermal stability also has significant implications for influenza vaccine production.

Assessment of viral replication in eggs and HA protein yield of pre-pandemic H5N1 candidate vaccine viruses

H5N1 infection and the potential for spread from human to human continue to pose a severe public health concern. Since vaccination remains the most effective way to prevent a potential H5N1 pandemic, the World Health Organization (WHO) Collaborating Centers (CCs) and Essential Regulatory Laboratories (ERLs) engineered and developed a panel of H5N1 pre-pandemic vaccine viruses for pandemic vaccine preparedness as well as production of antigen potency testing reagents (reference antigen and reference anti-serum) for vaccine standardization. To develop a strategy utilizing a number of biochemical methods for the characterization of the viral growth properties and protein yield in eggs, we have selected eight H5N1 pre-pandemic viruses and determined the viral Egg Infectious Dose 50 (EID50), total protein yield, hemagglutinin (HA) to nucleoprotein (NP) ratios (HA:NP), and HA1 content of each virus. Our results showed that all the tested H5N1 vaccine viruses grew to high titers in eggs. The total viral protein yield varies within a narrow range, whereas there were greater differences in the HA:NP protein ratios among the eight viruses. The RP-HPLC based HA1 content analysis demonstrated that the viruses A/Anhui/1/2010, A/Hubei/1/2005, and A/goose/Guiyang/337/2006 contained higher HA contents than other five viruses including A/Vietnam/1203/2003. Our approach for analyzing virus growth and protein yield will allow us identify optimal vaccine virus in a timely manner. In addition, we successfully purified the HA proteins of H5N1 vaccine viruses by optimizing bromelain cleavage conditions. Our studies on the HA protein purification may improve the quality control of the production of influenza vaccine test reagent.

Effect of natural and chimeric haemagglutinin genes on influenza A virus replication in baby hamster kidney cells

Baby hamster kidney (BHK21) cells are used to produce vaccines against various viral veterinary diseases, including rabies and foot-and-mouth-disease. Although particular influenza virus strains replicate efficiently in BHK21 cells the general use of these cells for influenza vaccine production is prohibited by the poor replication of most strains, including model strain A/PR/8/34 [H1N1] (PR8). We now show that in contrast to PR8, the related strain A/WSN/33 [H1N1] (WSN) replicates efficiently in BHK21 cells. This difference is determined by the haemagglutinin (HA) protein since reciprocal reassortant viruses with swapped HAs behave similarly with respect to growth on BHK21 cells as the parental virus from which their HA gene is derived. The ability or inability of six other influenza virus strains to grow on BHK21 cells appears to be similarly dependent on the nature of the HA gene since reassortant PR8 viruses containing the HA of these strains grow to similar titres as the parental virus from which the HA gene was derived. However, the growth to low titres of a seventh influenza strain was not due to the nature of the HA gene since a reassortant PR8 virus containing this HA grew efficiently on BHK21 cells. Taken together, these results suggest that the HA gene often primarily determines influenza replication efficiency on BHK21 cells but that in some strains other genes are also involved. High virus titres could be obtained with reassortant PR8 strains that contained a chimeric HA consisting of the HA1 domain of PR8 and the HA2 domain of WSN. HA1 contains most antigenic sites and is therefore important for vaccine efficacy. This method of producing the HA1 domain as fusion to a heterologous HA2 domain could possibly also be used for the production of HA1 domains of other viruses to enable the use of BHK21 cells as a generic platform for veterinary influenza vaccine production.

Influenza viruses expressing chimeric hemagglutinins: globular head and stalk domains derived from different subtypes

The influenza virus hemagglutinin molecule possesses a globular head domain that mediates receptor binding and a stalk domain at the membrane-proximal region. We generated functional influenza viruses expressing chimeric hemagglutinins encompassing a variety of globular head and stalk combinations, not only from different hemagglutinin subtypes but also from different hemagglutinin phylogenetic groups. These chimeric recombinant viruses possess growth properties similar to those of wild-type influenza viruses and can be used as reagents to measure domain-specific antibodies in virological and immunological assays.