Generation and evaluation of an H9N1 influenza vaccine derived by reverse genetics that allows utilization of a DIVA strategy for control of H9N2 avian influenza

Quantitative regulation of the thermal stability of enveloped virus vaccines by surface charge engineering to prevent the self-aggregation of attachment glycoproteins

The development of thermostable vaccines can relieve the bottleneck of existing vaccines caused by thermal instability and subsequent poor efficacy, which is one of the predominant reasons for the millions of deaths caused by vaccine-preventable diseases. Research into the mechanism of viral thermostability may provide strategies for developing thermostable vaccines. Using Newcastle disease virus (NDV) as model, we identified the negative surface charge of attachment glycoprotein as a novel determinant of viral thermostability. It prevented the temperature-induced aggregation of glycoprotein and subsequent detachment from virion surface. Then structural stability of virion surface was improved and virus could bind to and infect cells efficiently after heat-treatment. Employing the approach of surface charge engineering, thermal stability of NDV and influenza A virus (IAV) vaccines was successfully improved. The increase in the level of vaccine thermal stability was determined by the value-added in the negative surface charge of the attachment glycoprotein. The engineered live and inactivated vaccines could be used efficiently after storage at 37°C for at least 10 and 60 days, respectively. Thus, our results revealed a novel surface-charge-mediated link between HN protein and NDV thermostability, which could be used to design thermal stable NDV and IAV vaccines rationally.

Transcriptional response to a prime/boost vaccination of chickens with three vaccine variants based on HA DNA and Pichia-produced HA protein

Highly pathogenic avian influenza causes severe economic losses and is a potential threat to public health. Better knowledge of the mechanisms of chicken response to the novel types of vaccines against avian influenza might be helpful in their successful implementation into poultry vaccination programs in different countries. This work presents a comprehensive analysis of gene expression response elicited in chicken spleens by a combined DNA/recombinant protein prime/boost vaccination compared to DNA/DNA and protein/protein regimens. All groups of vaccinated chickens displayed changes in spleen transcriptomes in comparison to the control group with 423, 375 and 212 identified differentially expressed genes in protein/protein, DNA/DNA and DNA/protein group, respectively. Genes with most significantly changed expression belong to immune-related categories. Depending on a group, a fraction of 15-34% of up-regulated and a fraction of 15-42% of down-regulated immune-related genes are shared by all groups. Interestingly, the most upregulated genes encode β-defensins, short peptides with antimicrobial activity and immunomodulatory functions. Microarray results were validated with RT-qPCR method, which confirmed differential regulation of the selected immune-related genes. Immune-related differentially expressed genes and metabolic pathways identified in this work are compared to the available literature data on gene expression changes in vaccinated and non-vaccinated chickens after influenza infection.

Recombinant Newcastle disease virus expressing H9 HA protects chickens against heterologous avian influenza H9N2 virus challenge

In order to produce an efficient poultry H9 avian influenza vaccine that provides cross-protection against multiple H9 lineages, two Newcastle disease virus (NDV) LaSota vaccine strain recombinant viruses were generated using reverse genetics. The recombinant NDV-H9Con virus expresses a consensus-H9 hemagglutinin (HA) that is designed based on available H9N2 sequences from Chinese and Middle Eastern isolates. The recombinant NDV-H9Chi virus expresses a chimeric-H9 HA in which the H9 ectodomain of A/Guinea Fowl/Hong Kong/WF10/99 was fused with the cytoplasmic and transmembrane domain of the fusion protein (F) of NDV. Both recombinant viruses expressed the inserted HA stably and grew to high titers. An efficacy study in chickens showed that both recombinant viruses were able to provide protection against challenge with a heterologous H9N2 virus. In contrast to the NDV-H9Chi virus, the NDV-H9Con virus induced a higher hemagglutination inhibition titer against both NDV and H9 viruses in immunized birds, and efficiently inhibited virus shedding through the respiratory route. Moreover, sera collected from birds immunized with either NDV-H9Con or NDV-H9Chi were able to cross-neutralize two different lineages of H9N2 viruses, indicating that NDV-H9Con and NDV-H9Chi are promising vaccine candidates that could provide cross-protection among different H9N2 lineage viruses.

Avian Influenza Virus and DIVA Strategies

Vaccination is becoming a more acceptable option in the effort to eradicate avian influenza viruses (AIV) from commercial poultry, especially in countries where AIV is endemic. The main concern surrounding this option has been the inability of the conventional serological tests to differentiate antibodies produced due to vaccination from antibodies produced in response to virus infection. In attempts to address this issue, at least six strategies have been formulated, aiming to differentiate infected from vaccinated animals (DIVA), namely (i) sentinel birds, (ii) subunit vaccine, (iii) heterologous neuraminidase (NA), (iv) nonstructural 1 (NS1) protein, (v) matrix 2 ectodomain (M2e) protein, and (vi) haemagglutinin subunit 2 (HA2) glycoprotein. This short review briefly discusses the strengths and limitations of these DIVA strategies, together with the feasibility and practicality of the options as a part of the surveillance program directed toward the eventual eradication of AIV from poultry in countries where highly pathogenic avian influenza is endemic.

DIVA vaccination strategies for avian influenza virus

Vaccination for both low pathogenicity avian influenza and highly pathogenic avian influenza is commonly used by countries that have become endemic for avian influenza virus, but stamping-out policies are still common for countries with recently introduced disease. Stamping-out policies of euthanatizing infected and at-risk flocks has been an effective control tool, but it comes at a high social and economic cost. Efforts to identify alternative ways to respond to outbreaks without widespread stamping out has become a goal for organizations like the World Organisation for Animal Health. A major issue with vaccination for avian influenza is trade considerations because countries that vaccinate are often considered to be endemic for the disease and they typically lose their export markets. Primarily as a tool to promote trade, the concept of DIVA (differentiate infected from vaccinated animals) has been considered for avian influenza, but the goal for trade is to differentiate vaccinated and not-infected from vaccinated and infected animals because trading partners are unwilling to accept infected birds. Several different strategies have been investigated for a DIVA strategy, but each has advantages and disadvantages. A review of current knowledge on the research and implementation of the DIVA strategy will be discussed with possible ways to implement this strategy in the field. The increased desire for a workable DIVA strategy may lead to one of these ideas moving from the experimental to the practical.

Characterization of influenza A virus with nine segments: effect gene segment on virus property

The influenza A virus genome consists of eight segments of negative-strand RNA. In previous study, we generated a recombinant influenza virus with nine segments by reverse genetics. In present study, we evaluated characteristics of the recombinant influenza virus. The recombinant virus exhibited similar property to wild-type virus on virion morphology, virion composition, plaque phenotype and other aspects. Whereas, the recombinant virus propagated to lower titers than did wild-type virus in cells and mice, and there was decreased protein level and vRNA incorporation in the recombinant virions compared to wild-type H9N2 virions. Our results indicated that influenza A virus with eight segments exhibits more advantages than the virus with nine segments.

Strategies for differentiating infection in vaccinated animals (DIVA) for foot-and-mouth disease, classical swine fever and avian influenza

The prophylactic use of vaccines against exotic viral infections in production animals is undertaken exclusively in regions where the disease concerned is endemic. In such areas, the infection pressure is very high and so, to assure optimal protection, the most efficient vaccines are used. However, in areas considered to be free from these diseases and in which there is the possibility of only limited outbreaks, the use of Differentiation of Infected from Vaccinated Animals (DIVA) or marker vaccines allows for vaccination while still retaining the possibility of serological surveillance for the presence of infection. This literature review describes the current knowledge on the use of DIVA diagnostic strategies for three important transboundary animal diseases: foot-and-mouth disease in cloven-hoofed animals, classical swine fever in pigs and avian influenza in poultry.

A Closer Look at the NS1 of Influenza Virus

The Non-Structural 1 (NS1) protein is a multifactorial protein of type A influenza viruses that plays an important role in the virulence of the virus. A large amount of what we know about this protein has been obtained from studies using human influenza isolates and, consequently, the human NS1 protein. The current global interest in avian influenza, however, has highlighted a number of sequence and functional differences between the human and avian NS1. This review discusses these differences in addition to describing potential uses of NS1 in the management and control of avian influenza outbreaks.