Effective construction of DNA vaccines against variable influenza genes by homologous recombination

Construction and identification of influenza plasmid pool imparting high yields to candidate vaccine viruses in Vero cell at low temperature

We generated plasmid pools for the rapid preparation of candidate vaccine strains, which could grow in the Vero cells at low temperature. Firstly, we cloned in the pHW2000 plasmid each of the eight gene segments (PB2, PB1, PA, hemagglutinin [HA], neuraminidase [NA], NS, NP, M) of two master donor strains (MDS), respectively, A/Yunnan/1/2005Vca(H3N2) and B/Yunnan/2/2005Vca(By), which had Vca phenotype (cold‐adapted phenotype in Vero cells). Secondly, the similar operation was implemented with each of the HA, NA and NP segments of circulating strains with epidemic potential (parental strains). The virus rescue techniques were employed in this study, according to the homology rate of HA segments between MDS and parental strains. Then, we harvested amount of new Vca virus strains. By transmission electron microscope, it could observe new viruses' diameter and length were from 100 to 120 nm. Importantly, these reassortant viruses could get high‐yield production in Vero cells at 25℃ from the beginning to the fourth generation, which was significantly differ from their original parental viruses. Additional, these production 16 new Vca strains could maintain enough antibody binding capacity and attenuation phenotype, which consisted with their MDS. So these plasmid pools constructed by mount of different influenza A and B virus gene fragments could present desired working performance and provide convenience and realization for more Vca reassortant virus as candidate vaccine strain if needing.

HIVIS-DNA or HIVISopt-DNA priming followed by CMDR vaccinia-based boosts induce both humoral and cellular murine immune responses to HIV

Background

In order to develop a more effective prophylactic HIV-1 vaccine it is important optimize the components, improve Envelope glycoprotein immunogenicity as well as to explore prime-boost immunization schedules. It is also valuable to include several HIV-1 subtype antigens representing the world-wide epidemic.

Methods

HIVIS-DNA plasmids which include Env genes of subtypes A, B and C together with Gag subtypes A and B and RTmut/Rev of subtype B were modified as follows: the Envelope sequences were shortened, codon optimized, provided with an FT4 sequence and an immunodominant region mutated. The reverse transcriptase (RT) gene was shortened to contain the most immunogenic N-terminal fragment and fused with an inactivated viral protease vPR gene. HIVISopt-DNA thus contains fewer plasmids but additional PR epitopes compared to the native HIVIS-DNA. DNA components were delivered intradermally to young Balb/c mice once, using a needle-free Biojector® immediately followed by dermal electroporation. Vaccinia-based MVA-CMDR boosts including Env gene E and Gag-RT genes A were delivered intramuscularly by needle, once or twice.

Results

Both HIVIS-DNA and HIVISopt-DNA primed humoral and cell mediated responses well. When boosted with heterologous MVA-CMDR (subtypes A and E) virus inhibitory neutralizing antibodies were obtained to HIV-1 subtypes A, B, C and AE. Both plasmid compositions boosted with MVA-CMDR generated HIV-1 specific cellular responses directed against HIV-1 Env, Gag and Pol, as measured by IFNγ ELISpot. It was shown that DNA priming augmented the vector MVA immunological boosting effects, the HIVISopt-DNA with a trend to improved (Env) neutralization, the HIVIS-DNA with a trend to better (Gag) cell mediated immune reponses.

Conclusions

HIVIS-DNA was modified to obtain HIVISopt-DNA that had fewer plasmids, and additional epitopes. Even with one DNA prime followed by two MVA-CMDR boosts, humoral and cell-mediated immune responses were readily induced by priming with either DNA construct composition. Priming by HIV-DNA augmented neutralizing antibody responses revealed by boosting with the vaccinia-based heterologous sequences. Cellular and antibody responses covered selected strains representing HIV-1 subtypes A, B, C and CRF01_AE. We assume this is related to the inclusion of heterologous full genes in the vaccine schedule.

Improved haemagglutinin antigen content in H5N1 candidate vaccine viruses with chimeric haemagglutinin molecules

The candidate vaccine virus NIBRG-14 was derived by reverse genetics and comprises the haemagglutinin (HA) and neuraminidase (NA) genes derived from the clade 1 virus A/Viet Nam/1194/2004 on an A/Puerto Rico/8/34 (PR8) backbone. The HA gene was modified to remove the multibasic cleavage site motif associated with high pathogenicity. Reports from manufacturers, confirmed by data generated in this laboratory, have shown that this virus yields a low amount of HA antigen. We have generated a panel of new viruses using reverse genetics in which each virus consists of the PR8 backbone, the NA gene from A/Viet Nam/1194/2004 and a chimeric HA gene with sequences from both PR8 and A/Viet Nam/1194/2004. Here we show that a number of these viruses have improved HA antigen content and yield and are therefore better candidate vaccine viruses for use in production of H5N1 vaccine.

Development of a vaccine against pandemic influenza viruses: current status and perspectives

The constant threat of a new influenza pandemic, which may be caused by a highly pathogenic avian influenza virus, necessitates the development of a vaccine capable of providing efficient, long-term, and cost-effective protection. Proven avenues for the development of vaccines against seasonal influenza as well as novel approaches have been explored over the past decade. Whereas significant insights are consistently being made, the generation of a highly efficient and cross-protective vaccine against the future pandemic influenza strain remains as the ultimate goal in the field. In this review, we re-examine these efforts and outline the scientific, political, and economic problems that befall this area of biotechnological research.

A single immunization with HA DNA vaccine by electroporation induces early protection against H5N1 avian influenza virus challenge in mice

Background

Developing vaccines for the prevention of human infection by H5N1 influenza viruses is an urgent task. DNA vaccines are a novel alternative to conventional vaccines and should contribute to the prophylaxis of emerging H5N1 virus. In this study, we assessed whether a single immunization with plasmid DNA expressing H5N1 hemagglutinin (HA) could provide early protection against lethal challenge in a mouse model.

Methods

Mice were immunized once with HA DNA at 3, 5, 7 days before a lethal challenge. The survival rate, virus titer in the lungs and change of body weight were assayed to evaluate the protective abilities of the vaccine. To test the humoral immune response induced by HA DNA, serum samples were collected through the eye canthus of mice on various days after immunization and examined for specific antibodies by ELISA and an HI assay. Splenocytes were isolated after the immunization to determine the antigen-specific T-cell response by the ELISPOT assay.

Results

Challenge experiments revealed that a single immunization of H5N1 virus HA DNA is effective in early protection against lethal homologous virus. Immunological analysis showed that an antigen-specific antibody and T-cell response could be elicited in mice shortly after the immunization. The protective abilities were correlated with the amount of injected DNA and the length of time after vaccination.

Conclusion

A single immunization of 100 μg H5 HA DNA vaccine combined with electroporation was able to provide early protection in mice against homologous virus infection.

Influenza virus-specific cytotoxic T lymphocytes: a correlate of protection and a basis for vaccine development

Since influenza A viruses of the H5N1 subtype continue to circulate in wild and domestic birds and cause an ever increasing number of human cases, it is feared that H5N1 viruses may cause the next influenza pandemic. Therefore, there is considerable interest in the development of vaccines that confer protection against infections with these viruses or ideally, protection against influenza viruses of different subtypes. For the development of broad-protective vaccines the induction of virus-specific cytotoxic T lymphocytes (CTL) may be an important target, since it has been demonstrated that CTL contribute to protective immunity and are largely directed to epitopes shared by influenza viruses of various subtypes. In the present paper, the possibility to develop (cross-reactive) CTL-inducing vaccines is discussed.

Protection against avian influenza H9N2 virus challenge by immunization with hemagglutinin- or neuraminidase-expressing DNA in BALB/c mice

Avian influenza viruses of H9N2 subtype are widely spread in avian species. The viruses have recently been transmitted to mammalian species, including humans, accelerating the efforts to devise protective strategies against them. In this study, an avian influenza H9N2 virus strain (A/Chicken/Jiangsu/7/2002), isolated in Jiangsu Province, China, was used to infect BALB/c mice for adaptation. After five lung-to-lung passages, the virus was stably proliferated in a large quantity in the murine lung and caused the deaths of mice. In addition, we explored the protection induced by H9N2 virus hemagglutinin (HA)- and neuraminidase (NA)-expressing DNAs in BALB/c mice. Female BALB/c mice aged 6-8 weeks were immunized once or twice at a 3-week interval with HA-DNA and NA-DNA by electroporation, respectively, each at a dose of 3, 10 or 30microg. The mice were challenged with a lethal dose (40x LD(50)) of influenza H9N2 virus four weeks after immunization once or one week after immunization twice. The protections of DNA vaccines were evaluated by the serum antibody titers, residual lung virus titers, and survival rates of the mice. The result showed that immunization once with not less than 10microg or twice with 3microg HA-DNA or NA-DNA provided effective protection against homologous avian influenza H9N2 virus.

Influenza vaccines: recent advances in production technologies

In spite of ongoing annual vaccination programs, the seasonal influenza epidemics remain a major cause of high morbidity and mortality. The currently used "inactivated" vaccines provide very short-term and highly specific humoral immunity due to the frequent antigenic variations in the influenza virion. These intra-muscularly administered vaccines also fail to induce protective mucosal immunity at the portal of viral entry and destruction of the virally infected cells by induction of cytotoxic T lymphocytes. Therefore, it is necessary to develop immunologically superior vaccines. This article highlights some of the recent developments in investigational influenza vaccines. The most notable recent developments of interest include the use of immunopotentiators, development of DNA vaccines, use of reverse genetics, and the feasibility of mammalian cell-based production processes. Presently, due to their safety and efficacy, the cold-adapted "live attenuated" vaccines are seen as viable alternatives to the "inactivated vaccines". The DNA vaccines are gaining importance due to the induction of broad-spectrum immunity. In addition, recent advances in recombinant technologies have shown the possibility of constructing pre-made libraries of vaccine strains, so that adequately preparations can be made for epidemics and pandemics.

Protective efficacy of a DNA influenza virus vaccine is markedly increased by the coadministration of a Schiff base-forming drug

Effective vaccination against heterologous influenza virus infection remains elusive. Immunization with plasmid DNA (pDNA) expressing conserved genes from influenza virus is a promising approach to achieve cross-variant protection. However, despite having been described for more than a decade, pDNA vaccination still requires further optimization to be applied clinically as a standard vaccination approach. We have recently described a simple and efficient approach to enhance pDNA immunization, based on the use of tucaresol, a Schiff base-forming drug. In this report we have tested the ability of this drug to increase the protection conferred by pDNA vaccination against influenza virus infection. Our results demonstrate that a significant protection was achieved in two strains of mice by using the combination of pDNA and tucaresol. This protection was associated with an elevated humoral and cellular response and a switch in the type of the T helper cell (Th) immune response from type 2 to type 1. This vaccine combination represents a promising strategy for designing a clinical study for the protection from influenza and similar infections.

Enhanced immune responses after DNA vaccination with combined envelope genes from different HIV-1 subtypes

In a multisubtype approach to HIV-1 vaccination, mice were immunized with HIV-1 envelope gp160 genes from subtypes A, B, and C. Subsequently the mice were challenged with syngeneic primary splenocytes infected with a HIV-1/MuLV pseudovirus carrying a subtype B genome. HIV-specific immune responses and protection were strongest in the group of animals immunized with a combination of subtype A, B, and C specific gp160 genes as compared to subtype B only. Immunization with the combination of the cross-reactive subtypes A and C envelope genes induced HIV-specific immune responses but did not result in significant protection to challenge with subtype B infected cells. From this we conclude that immunization with the envelope genes from several HIV-1 subtypes may indeed enhance immune responses. This study shows that by using a mix of subtype envelope genes, an enhanced protective immunity can be obtained experimentally, potentially also in humans.

DNA vaccination of ferrets with chimeric influenza A virus hemagglutinin (H3) genes

Recently a technology was established based on homologous recombination that allowed the rapid generation of chimeric HA genes of influenza viruses, containing the antigenic determinants obtained from various influenza virus A (H3N2) viruses. In the present report plasmids were generated using a H3 HA vector handle and the hypervariable regions of two genetically distinct influenza A H3N2 viruses, A/Stockholm/7/97 and A/Netherlands/18/94. In a ferret model it was shown that immunisation with plasmid DNA encoding chimeric HA indeed elicited antibody responses specific for the virus from which the hypervariable region with the antigenic determinants were obtained. After DNA-immunisation of the ferrets, protective immunity against infection with influenza virus A/Netherlands/18/94 was evaluated.

Enhanced immunogenicity of a human immunodeficiency virus type 1 env DNA vaccine by manipulating N-glycosylation signals. Effects of elimination of the V3 N306 glycan

DNA encoding HIV-1 env is a poorly efficient B-cell immunogen and one probable explanation is that the numerous gp120 N-linked glycans gp120 may interfere with B-cell epitope presentation. The N306 glycan in gp120 shields HIV-1 from neutralizing antibodies. A DNA immunogen lacking the N306 glycosylation signal (T308A) was constructed to determine whether this glycan affected the immune response. Mice were immunized intranasally twice with DNA containing either the wild type or the mutant env. Two additional groups were primed with wild type or mutant env and boosted with rgp160 protein, containing the complete set of N-linked glycans. Immunization with DNA alone resulted in priming of B-cell clones but was not sufficient to induce a complete antibody response. Animals primed with the N306 mutant and subsequently boosted with rgp160 protein displayed higher serum IgG-binding titers to gp120 than animals primed with wild type env DNA. The manipulation of the glycosylation sites of the env DNA strongly primes antibody responses (but non-neutralizing) as well as T-cell responses to the wild type strain gp160. However, priming with mutant plasmid did not result in higher neutralization titers to wild type or T308A-mutated virus than did the wild type plasmid. With the N306 mutant DNA we thus immunized a non-neutralization epitope, but obtained strong env-binding IgG after rgp160 boosting.

Update on influenza and other viral pneumonias

Major developments during the past 5 years concerning influenza prevention by vaccination and treatment with neuraminidase inhibitors are reviewed. These have been accompanied by increased media interest in related issues: pressures on hospital admissions, ethical concerns and controls on prescribing limiting professional autonomy. The new live attenuated influenza vaccines, adjuvanted vaccines and the emerging recombinant DNA vaccines are discussed. Recent information on neuraminidase inhibitor antivirals, surveillance for resistant viruses, the prospects for near patient tests (i.e. tests that can be used near the patient to improve immediate patient management or in the laboratory to give rapid feedback for physicians) and the clinical significance of other respiratory viruses are highlighted. The benefits of recent advances provide challenges for health care delivery and public acceptance as great as those involved in their scientific development.