Comparative analysis of antibody induction and protection against influenza virus infection by DNA immunization with HA, HAe, and HA1 in mice

Immunomodulatory effects of probiotic Lactobacillus casei on GM-CSF-adjuvanted influenza DNA vaccine

Aim: This study investigates the protective efficacy of influenza DNA vaccine combined with a granulocyte macrophage-colony stimulating factor (GM-CSF) adjuvant, and probiotic Lactobacillus casei, an oral immunomodulator, in a BALB/c mice. Materials & methods: The mice were immunized with HA1 DNA vaccine along with GM-CSF and probiotic twice within a one-week interval. Results: The results showed that both adjuvants exert a synergistic effect in enhancing the humoral and cellular immune responses of the DNA vaccine. This combination also deceased IL-6 and IL-17A levels in the lung homogenates. The protection patterns were closely associated with influenza virus-specific splenocyte proliferative and serum IgG antibody (Ab) responses. Conclusion: The Findings demonstrate L. casei modulate balanced Th1/Th2 immune responses toward HA1 DNA vaccine adjuvanted by GM-CSF.

Vaccination with Consensus H7 Elicits Broadly Reactive and Protective Antibodies against Eurasian and North American Lineage H7 Viruses

H7 subtype avian influenza viruses have caused outbreaks in poultry, and even human infection, for decades in both Eurasia and North America. Although effective vaccines offer the best protection against avian influenza viruses, antigenically distinct Eurasian and North American lineage subtype H7 viruses require the development of cross-protective vaccine candidates. In this study, a methodology called computationally optimized broadly reactive antigen (COBRA) was used to develop four consensus H7 antigens (CH7-22, CH7-24, CH7-26, and CH7-28). In vitro experiments confirmed the binding of monoclonal antibodies to the head and stem domains of cell surface-expressed consensus HAs, indicating display of their antigenicity. Immunization with DNA vaccines encoding the four antigens was evaluated in a mouse model. Broadly reactive antibodies against H7 viruses from Eurasian and North American lineages were elicited and detected by binding, inhibition, and neutralizing analyses. Further infection with Eurasian H7N9 and North American H7N3 virus strains confirmed that CH7-22 and CH7-24 conferred the most effective protection against hetero-lethal challenge. Our data showed that the consensus H7 vaccines elicit a broadly reactive, protective response against Eurasian and North American lineage H7 viruses, which are suitable for development against other zoonotic influenza viruses.

Comparison of the Protective Efficacy of Neutralizing Epitopes of 2009 Pandemic H1N1 Influenza Hemagglutinin

The 2009 H1N1 influenza (Pdm09) pandemic has been referred to as the first influenza pandemic of the twenty-first century. There is a marked difference in antigenicity between the pandemic H1N1 virus and past seasonal H1N1 viruses, which allowed the pandemic virus to spread rapidly in humans. Antibodies (Abs) against hemagglutinin (HA), especially neutralizing Abs against epitopes in the head of HA, play critical roles in defending the host against the virus. Some preexisting neutralizing Abs that recognize neutralizing epitopes of Pdm09 HA, thereby affording cross-protection, have been reported. To better understand the protective effects of epitopes in Pdm09 HA, we constructed a series of plasmid DNAs (DNA vaccines) by cloning various combinations of Pdm09 neutralizing epitopes into the HA backbone derived from A/PR/8/1934 (H1N1). We subsequently compared the protective immune responses induced by these various forms of HA in a mouse model. We found that the plasmid DNAs with epitope substitutions provided better protection against lethal virus challenge and induced higher strain-specific antibody titers, with epitope Sa being the most effective. Moreover, the combination of epitopes Sa and Sb provided almost complete protection in mice. These findings provide new insights into the protective efficacy of neutralizing epitopes of influenza HA.

Linear DNA vaccine prepared by large-scale PCR provides protective immunity against H1N1 influenza virus infection in mice

Linear DNA vaccines provide effective vaccination. However, their application is limited by high cost and small scale of the conventional polymerase chain reaction (PCR) generally used to obtain sufficient amounts of DNA effective against epidemic diseases. In this study, a two-step, large-scale PCR was established using a low-cost DNA polymerase, RKOD, expressed in Pichia pastoris. Two linear DNA vaccines encoding influenza H1N1 hemagglutinin (HA) 1, LEC-HA, and PTO-LEC-HA (with phosphorothioate-modified primers), were produced by the two-step PCR. Protective effects of the vaccines were evaluated in a mouse model. BALB/c mice were immunized three times with the vaccines or a control DNA fragment. All immunized animals were challenged by intranasal administration of a lethal dose of influenza H1N1 virus 2 weeks after the last immunization. Sera of the immunized animals were tested for the presence of HA-specific antibodies, and the total IFN-γ responses induced by linear DNA vaccines were measured. The results showed that the DNA vaccines but not the control DNA induced strong antibody and IFN-γ responses. Additionally, the PTO-LEC-HA vaccine effectively protected the mice against the lethal homologous mouse-adapted virus, with a survival rate of 100% versus 70% in the LEC-HA-vaccinated group, showing that the PTO-LEC-HA vaccine was more effective than LEC-HA. In conclusion, the results indicated that the linear H1N1 HA-coding DNA vaccines induced significant immune responses and protected mice against a lethal virus challenge. Thus, the low-cost, two-step, large-scale PCR can be considered a potential tool for rapid manufacturing of linear DNA vaccines against emerging infectious diseases.

A DNA Aptamer Against Influenza A Virus: An Effective Inhibitor to the Hemagglutinin-Glycan Interactions

Most therapeutical nucleic acid aptamers tend to inhibit protein-protein interactions and thereby function as antagonists. Attachment of the influenza virus surface glycoprotein hemagglutinin (HA) to sialic acid-containing host cell receptors (glycan) facilitates the initial stage of viral infection. Inhibition of the attachment may result in an antiviral effect on the proliferation of the influenza virus. To develop therapeutically interesting agents, we selected two single-stranded DNA (ssDNA) aptamers specific to the HA protein of H1N1 influenza virus (A/Puerto Rico/8/1934) through a procedure of systematic evolution of ligands by exponential enrichment. As it showed a higher binding affinity for HA protein (Kd = 78 ± 1 nM), aptamer 1 was tested for its ability to interfere with HA-glycan interactions using chicken red blood cell hemagglutination and microneutralization assays, which demonstrated that it significantly suppressed the viral infection in host cells. These results indicate that the isolated ssDNA aptamer may be developed as an antiviral agent against influenza through appropriate therapeutic formulation.

Long-term immunogenicity of an inactivated split-virion 2009 pandemic influenza A H1N1 virus vaccine with or without aluminum adjuvant in mice

In 2009, a global epidemic of influenza A(H1N1) virus caused the death of tens of thousands of people. Vaccination is the most effective means of controlling an epidemic of influenza and reducing the mortality rate. In this study, the long-term immunogenicity of influenza A/California/7/2009 (H1N1) split vaccine was observed as long as 15 months (450 days) after immunization in a mouse model. Female BALB/c mice were immunized intraperitoneally with different doses of aluminum-adjuvanted vaccine. The mice were challenged with a lethal dose (10× 50% lethal dose [LD(50)]) of homologous virus 450 days after immunization. The results showed that the supplemented aluminum adjuvant not only effectively enhanced the protective effect of the vaccine but also reduced the immunizing dose of the vaccine. In addition, the aluminum adjuvant enhanced the IgG antibody level of mice immunized with the H1N1 split vaccine. The IgG level was correlated to the survival rate of the mice. Aluminum-adjuvanted inactivated split-virion 2009 pandemic influenza A H1N1 vaccine has good immunogenicity and provided long-term protection against lethal influenza virus challenge in mice.

Advancements in the development of subunit influenza vaccines

The ongoing threat of influenza epidemics and pandemics has emphasized the importance of developing safe and effective vaccines against infections from divergent influenza viruses. In this review, we first introduce the structure and life cycle of influenza A viruses, describing major influenza A virus-caused pandemics. We then compare different types of influenza vaccines and discuss current advancements in the development of subunit influenza vaccines, particularly those based on nucleoprotein (NP), extracellular domain of matrix protein 2 (M2e) and hemagglutinin (HA) proteins. We also illustrate potential strategies for improving the efficacy of subunit influenza vaccines.

Novel vaccine approaches for protection against intracellular pathogens

Vaccination against intracellular pathogens requires generation of a pool of memory T cells able to respond upon infection and mediate either killing of the infected cell or induce killing mechanisms in the infected cell. T cell-inducing vaccines must aim to target the antigen to antigen-presenting cells (APCs) so that it can be presented on MHC molecules on the cell surface. Methods to do this include making use of vectors such as plasmid DNA or viruses, live attenuated pathogens or subunit vaccines targeted and enhanced using adjuvants. The choice of approach should be guided by the phenotype and localization of the desired T cell response. This review will discuss current approaches in the pipeline for the development of T cell-inducing vaccines, including vectored, live attenuated, and subunit vaccines.