Lipofection-Based Delivery of DNA Vaccines

The preventive and therapeutic potential of DNA vaccines combined with benefits of lipid-based delivery (lipofection) allow efficient nucleic acid transfer and immunization applicable in treatment of infections, cancer or autoimmune disorders. Lipofecting compositions consisting of cationic and neutral lipids can be used for both in vitro and in vivo applications and may also play the role of adjuvants. Here we describe a simple protocol of DNA vaccine carrier preparation based on cationic polyprenyl derivatives (PTAI-trimethylpolyprenylammonium iodides) and commonly used helper lipids with use of basic laboratory equipment. Such formulas have proven effective for immunization of animals as well as for cell transfection.

Differences in gene expression profiles at the early stage of Solanum lycopersicum infection with mild and severe variants of potato spindle tuber viroid

Viroids with small, non-coding circular RNA genome can induce diseases in many plant species. The extend of infection symptoms depends on environmental conditions, viroid strain, and host plant species and cultivar. Pathogen recognition leads to massive transcriptional reprogramming to favor defense responses over normal cellular functions. To better understand the interaction between plant host and potato spindle tuber viroid (PSTVd) variants that differ in their virulence, comparative transcriptomic analysis was performed by an RNA-seq approach. The changes of gene expression were analyzed at the time point when subtle symptoms became visible in plants infected with the severe PSTVd-S23 variant, while those infected with the mild PSTVd-M variant looked like non-infected healthy plants. Over 3000 differentially expressed genes (DEGs) were recognized in both infections, but the majority of them were specific for infection with the severe variant. In both infections recognized DEGs were mainly related to biotic stress, hormone metabolism and signaling, transcription regulation, protein degradation, and transport. The DEGs related to cell cycle and microtubule were uniquely down-regulated only in the PSTVd-S23-infected plants. Similarly, expression of transcription factors from C2C2-GATA and growth-regulating factor (GRF) families was only altered upon infection with the severe variant. Both PSTVd variants triggered plant immune response; however expression of genes encoding crucial factors of this process was markedly more changed in the plants infected with the severe variant than in those with the mild one.

Response to a DNA vaccine against the H5N1 virus depending on the chicken line and number of doses

Background

Avian influenza virus infections cause significant economic losses on poultry farms and pose the threat of a possible pandemic outbreak. Routine vaccination of poultry against avian influenza is not recommended in Europe, however it has been ordered in some other countries, and more countries are considering use of the avian influenza vaccine as a component of their control strategy. Although a variety of such vaccines have been tested, most research has concentrated on specific antibodies and challenge experiments.

Methods

We monitored the transcriptomic response to a DNA vaccine encoding hemagglutinin from the highly pathogenic H5N1 avian influenza virus in the spleens of broiler and layer chickens. Moreover, in layer chickens the response to one and two doses of the vaccine was compared.

Results

All groups of birds immunized with two doses of the vaccine responded at the humoral level by producing specific anti-hemagglutinin antibodies. A response to the vaccine was also detected in the spleen transcriptomes. Differential expression of many genes encoding noncoding RNA and proteins functionally connected to the neuroendocrine-immune system was observed in different immunized groups.

Conclusion

Broiler chickens showed a higher number and wider range of fold-changes in the transcriptional response than laying hens.

Root Transcriptomic Analysis Reveals Global Changes Induced by Systemic Infection of Solanum lycopersicum with Mild and Severe Variants of Potato Spindle Tuber Viroid

Potato spindle tuber viroid (PSTVd) causes systemic infection in plant hosts. There are many studies on viroid-host plant interactions, but they have predominantly focused on the aboveground part of the plant. Here, we investigated transcriptomic profile changes in tomato roots systemically infected with mild or severe PSTVd variants using a combined microarray/RNA-seq approach. Analysis indicated differential expression of genes related to various Gene Ontology categories depending on the stage of infection and PSTVd variant. A majority of cell-wall-related genes were down-regulated at early infection stages, but at the late stage, the number of up-regulated genes increased significantly. Along with observed alterations of many lignin-related genes, performed lignin quantification indicated their disrupted level in PSTVd-infected roots. Altered expression of genes related to biosynthesis and signaling of auxin and cytokinin, which are crucial for lateral root development, was also identified. Comparison of both PSTVd infections showed that transcriptional changes induced by the severe variant were stronger than those caused by the mild variant, especially at the late infection stage. Taken together, we showed that similarly to aboveground plant parts, PSTVd infection in the underground tissues activates the plant immune response.

Sequential DNA immunization of chickens with bivalent heterologous vaccines induce highly reactive and cross-specific antibodies against influenza hemagglutinin

Vaccines against avian influenza are mostly based on hemagglutinin (HA), which is the main antigen of this virus and a target for neutralizing antibodies. Traditional vaccines are known to be poorly efficient against newly emerging strains, which is an increasing worldwide problem for human health and for the poultry industry. As demonstrated by research and clinical data, sequential exposure to divergent influenza HAs can boost induction of universal antibodies which recognize conserved epitopes. In this work, we have performed sequential immunization of laying hens using monovalent or bivalent compositions of DNA vaccines encoding HAs from distant groups 1 and 2 (H5, H1, and H3 subtypes, respectively). This strategy gave promising results, as it led to induction of polyclonal antibodies against HAs from both groups. These polyclonal antibodies showed cross-reactivity between different HA strains in ELISA, especially when bivalent formulations were used for immunization of birds. However, cross-reactivity of antibodies induced against H3 and H5 HA subtypes was rather limited against each other after homologous immunization. Using a cocktail of HA sequences and/or sequential DNA vaccination with different strains presents a good strategy to overcome the limited effectiveness of vaccines and induce broader immunity against avian influenza. Such a strategy could be adapted for vaccinating laying hens or parental flocks of different groups of poultry.

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.

The varied ability of grains to synthesize and catabolize ABA is one of the factors affecting dormancy and its release by after-ripening in imbibed triticale grains of cultivars with different pre-harvest sprouting susceptibilities

Abscisic acid (ABA) is a phytohormone involved in the acquisition of primary dormancy during seeds maturation as well as dormancy maintenance in imbibed seeds. After imbibition, the ABA content decreased to a much lower level in embryos of freshly harvested triticale grains of the Leontino cultivar, which is more susceptible to pre-harvest sprouting (PHS) than embryos of the Fredro cultivar. Lower ABA content in the Leontino cultivar resulted from increased expression of TsABA8'OH1 and TsABA8'OH2, which encode ABA 8'-hydroxylase and are involved in ABA catabolism. Higher ABA content and maintenance of dormancy in Fredro grains were correlated with intensified ABA biosynthesis, which resulted from higher expression of TsNCED1, which encodes 9-cis-epoxycarotenoid dioxygenase. These results suggest that grains of triticale cultivars with different resistance to PHS vary in their ability to metabolize ABA after imbibition. After-ripening did not affect the ABA content in embryos of dry grains of either triticale cultivar. However, after-ripening caused dormancy release in Fredro grains and significantly affected the ABA content and the rate of its metabolism after imbibition. A more rapid decline in ABA content in imbibed Fredro grains was accompanied by decreased transcript levels of TsNCED1 as well as increased expression of TsABA8'OH1 and TsABA8'OH2. Thus, after-ripening may affect dormancy of grains through reduction of the ABA biosynthesis rate and intensified ABA catabolism. Overexpression of TsNCED1 in tobacco increases ABA content and delays germination, while overexpression of TsABA8'OH2 decreases ABA content, accelerates germination, and reduces the sensitivity to ABA of transgenic seeds compared to seeds of wild-type plants. Therefore, these genes might play an important role in the regulation of triticale grain dormancy, thus affecting susceptibility to PHS.

Time-Course Microarray Analysis Reveals Differences between Transcriptional Changes in Tomato Leaves Triggered by Mild and Severe Variants of Potato Spindle Tuber Viroid

Viroids are small non-capsidated non-coding RNA replicons that utilize host factors for efficient propagation and spread through the entire plant. They can incite specific disease symptoms in susceptible plants. To better understand viroid-plant interactions, we employed microarray analysis to observe the changes of gene expression in “Rutgers” tomato leaves in response to the mild (M) and severe (S23) variants of potato spindle tuber viroid (PSTVd). The changes were analyzed over a time course of viroid infection development: (i) the pre-symptomatic stage; (ii) early symptoms; (iii) full spectrum of symptoms and (iv) the so-called ‘recovery’ stage, when stem regrowth was observed in severely affected plants. Gene expression profiles differed depending on stage of infection and variant. In S23-infected plants, the expression of over 3000 genes was affected, while M-infected plants showed 3-fold fewer differentially expressed genes, only 20% of which were specific to the M variant. The differentially expressed genes included many genes related to stress; defense; hormone metabolism and signaling; photosynthesis and chloroplasts; cell wall; RNA regulation, processing and binding; protein metabolism and modification and others. The expression levels of several genes were confirmed by nCounter analysis.

Β-defensins - Underestimated peptides in influenza combat

Defensins are a family of host defense peptides present in vertebrates, invertebrates and plants. They display broad antimicrobial activity and immunomodulatory functions. Herein, the natural anti-influenzal role of β-defensins, as well as their potential usage as anti-influenza vaccine adjuvants and therapeutic agents, is reviewed. This article summarizes previously published information on β-defensin modes of action, expression changes after influenza infection and vaccination, biotechnological usage and possible boosting of their production by dietary supplementation.

Immunogenicity of DNA Vaccine against H5N1 Containing Extended Kappa B Site: In Vivo Study in Mice and Chickens

Influenza is one of the most important illnesses in the modern world, causing great public health losses each year due to the lack of medication and broadly protective, long-lasting vaccines. The development of highly immunogenic and safe vaccines is currently one of the major problems encountered in efficient influenza prevention. DNA vaccines represent a novel and powerful alternative to the conventional vaccine approaches. To improve the efficacy of the DNA vaccine against influenza H5N1, we inserted three repeated kappa B (κB) motifs, separated by a 5-bp nucleotide spacer, upstream of the cytomegalovirus promoter and downstream of the SV40 late polyadenylation signal. The κB motif is a specific DNA element (10pb-long) recognized by one of the most important transcription factors NFκB. NFκB is present in almost all animal cell types and upon cell stimulation under a variety of pathogenic conditions. NFκB is released from IκB and translocates to the nucleus and binds to κB sites, thereby leading to enhanced transcription and expression of downstream genes. We tested the variants of DNA vaccine with κB sites flanking the antigen expression cassette and without such sites in two animal models: chickens (broilers and layers) and mice (BALB/c). In chickens, the variant with κB sites stimulated stronger humoral response against the target antigen. In mice, the differences in humoral response were less apparent. Instead, it was possible to spot several gene expression differences in the spleens isolated from mice immunized with both variants. The results of our study indicate that modification of the sequence outside of the sequence encoding the antigen might enhance the immune response to the target but understanding the mechanisms responsible for this process requires further analysis.

Effective usage of cationic derivatives of polyprenols as carriers of DNA vaccines against influenza virus

Background

Cationic derivatives of polyprenols (trimethylpolyprenylammonium iodides – PTAI) with variable chain length between 6 and 15 isoprene units prepared from naturally occurring poly-cis-prenols were tested as DNA vaccine carriers in chickens and mice. This study aimed to investigate if PTAI could be used as an efficient carrier of a DNA vaccine.

Methods

Several vaccine mixtures were prepared by combining different proportions of the vaccine plasmid (carrying cDNA encoding a vaccine antigen, hemagglutinin from H5N1 influenza virus) and various compositions of PTAI. The vaccines were delivered by intramuscular injection to either chickens or mice. The presence of specific antibodies in sera collected from the immunized animals was analyzed by enzyme-linked immunosorbent assay (ELISA) and hemagglutination inhibition (HI) test.

Results

The mixtures of PTAI with helper lipids, such as DOPE (1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine), DC-cholesterol [{3ß-[N-(N′,N′-dimethylaminoethane)-carbamoyl] cholesterol} hydrochloride] or DOPC (1,2-dioleoyl-sn-glycero-3-phosphatidylcholine) induced strong humoral response to the antigen encoded by the DNA vaccine plasmid.

Conclusion

The animal immunization results confirmed that PTAI compositions, especially mixtures of PTAI with DOPE and DC-cholesterol, do work as effective carriers of DNA vaccines, comparable to the commercially available lipid transfection reagent.

A prime/boost vaccination with HA DNA and Pichia-produced HA protein elicits a strong humoral response in chickens against H5N1

Highly pathogenic avian influenza viruses cause severe disease and huge economic losses in domestic poultry and might pose a serious threat to people because of the high mortality rates in case of an accidental transmission to humans. The main goal of this work was to evaluate the immune responses and hemagglutination inhibition potential elicited by a combined DNA/recombinant protein prime/boost vaccination compared to DNA/DNA and protein/protein regimens in chickens. A plasmid encoding hemagglutinin (HA) from the A/swan/Poland/305-135V08/2006 (H5N1) virus, or the recombinant HA protein produced in Pichia pastoris system, both induced H5 HA-specific humoral immune responses in chickens. In two independent experiments, anti-HA antibodies were detected in sera collected two weeks after the first dose and the response was enhanced by the second dose of a vaccine, regardless of the type of subunit vaccine (DNA or recombinant protein) administered. The serum collected from chickens two weeks after the second dose was characterized by three types of assays: indirect ELISA, hemagglutination inhibition (HI) and a diagnostic test based on H5 antibody competition. Although the indirect ELISA failed to detect superiority of any of the three vaccine regimens, the other two tests clearly indicated that priming of chickens with the DNA vaccine significantly enhanced the protective potential of the recombinant protein vaccine produced in P. pastoris.

Characterization of mAb6-9-1 monoclonal antibody against hemagglutinin of avian influenza virus H5N1 and its engineered derivative, single-chain variable fragment antibody

Hemagglutinin (HA), as a major surface antigen of influenza virus, is widely used as a target for production of neutralizing antibodies. Monoclonal antibody, mAb6-9-1, directed against HA of highly pathogenic avian influenza virus A/swan/Poland/305-135V08/2006(H5N1) was purified from mouse hybridoma cells culture and characterized. The antigenic specificity of mAb6-9-1 was verified by testing its cross-reactivity with several variants of HA. The mimotopes recognized by mAb6-9-1 were selected from two types of phage display peptide libraries. The comparative structural model of the HA variant used for antibody generation was developed to further facilitate epitope mapping. Based on the sequences of the affinity- selected polypeptides and the structural model of HA the epitope was located to the region near the receptor binding site (RBS). Such localization of the epitope recognized by mAb6-9-1 is in concordance with its moderate hemagglutination inhibiting activity and its antigenic specificity. Additionally, total RNA isolated from the hybridoma cell line secreting mAb6-9-1 was used for obtaining two variants of cDNA encoding recombinant single-chain variable fragment (scFv) antibody. To ensure high production level and solubility in bacterial expression system, the scFv fragments were produced as chimeric proteins in fusion with thioredoxin or displayed on a phage surface after cloning into the phagemid vector. Specificity and affinity of the recombinant soluble and phage-bound scFv were assayed by suitable variants of ELISA test. The observed differences in specificity were discussed.

Codon optimization of antigen coding sequences improves the immune potential of DNA vaccines against avian influenza virus H5N1 in mice and chickens

Background

Highly pathogenic avian influenza viruses are a serious threat to domestic poultry and can be a source of new human pandemic and annual influenza strains. Vaccination is the main strategy of protection against influenza, thus new generation vaccines, including DNA vaccines, are needed. One promising approach for enhancing the immunogenicity of a DNA vaccine is to maximize its expression in the immunized host.

Methods

The immunogenicity of three variants of a DNA vaccine encoding hemagglutinin (HA) from the avian influenza virus A/swan/Poland/305-135V08/2006 (H5N1) was compared in two animal models, mice (BALB/c) and chickens (broilers and layers). One variant encoded the wild type HA while the other two encoded HA without proteolytic site between HA1 and HA2 subunits and differed in usage of synonymous codons. One of them was enriched for codons preferentially used in chicken genes, while in the other modified variant the third position of codons was occupied in almost 100 % by G or C nucleotides.

Results

The variant of the DNA vaccine containing almost 100 % of the GC content in the third position of codons stimulated strongest immune response in two animal models, mice and chickens. These results indicate that such modification can improve not only gene expression but also immunogenicity of DNA vaccine.

Conclusion

Enhancement of the GC content in the third position of the codon might be a good strategy for development of a variant of a DNA vaccine against influenza that could be highly effective in distant hosts, such as birds and mammals, including humans.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-016-0599-y) contains supplementary material, which is available to authorized users.

A biosensor based on electroactive dipyrromethene-Cu(II) layer deposited onto gold electrodes for the detection of antibodies against avian influenza virus type H5N1 in hen sera

This paper describes the development of a biosensor for the detection of anti-hemagglutinin antibodies against the influenza virus hemagglutinin. The steps of biosensor fabrications are as follows: (i) creation of a mixed layer containing the thiol derivative of dipyrromethene and 4-mercapto-1-butanol, (ii) complexation of Cu(II) ions, (iii) oriented immobilization of the recombinant histidine-tagged hemagglutinin, and (iv) filling free spaces with bovine serum albumin. The interactions between recombinants hemagglutinin from the highly pathogenic avian influenza virus type H5N1 and anti-hemagglutinin H5 monoclonal antibodies were explored with Osteryoung square-wave voltammetry. The biosensor displayed a good detection limit of 2.4 pg/mL, quantification limit of 7.2 pg/mL, and dynamic range from 4.0 to 100.0 pg/mL in buffer. In addition, this analytical device was applied for the detection of antibodies in hen sera from individuals vaccinated and non-vaccinated against the avian influenza virus type H5N1. The limit of detection for the assay was the dilution of sera 1: 7 × 10(6), which is about 200 times better than the enzyme-linked immunosorbent assay.

Influenza prevention and treatment by passive immunization

Passive immunity is defined as a particular antigen resistance provided by external antibodies. It can be either naturally or artificially acquired. Natural passive immunization occurs during pregnancy and breast-feeding in mammals and during hatching in birds. Maternal antibodies are passed through the placenta and milk in mammals and through the egg yolk in birds. Artificial passive immunity is acquired by injection of either serum from immunized (or infected) individuals or antibody preparations. Many independent research groups worked on selection, verification and detailed characterization of polyclonal and monoclonal antibodies against the influenza virus. Numerous antibody preparations were tested in a variety of in vitro and in vivo experiments for their efficacy to neutralize the virus. Here, we describe types of antibodies tested in such experiments and their viral targets, review approaches resulting in identification of broadly neutralizing antibodies and discuss methods used to demonstrate their protective effects. Finally, we shortly discuss the phenomenon of maternal antibody transfer as a way of effective care for young individuals and as an interfering factor in early vaccination.

DNA vaccines against influenza

Genetic vaccine technology has been considerably developed within the last two decades. This cost effective and promising strategy can be applied for therapy of cancers and for curing allergy, chronic and infectious diseases, such as a seasonal and pandemic influenza. Despite numerous advantages, several limitations of this technology reduce its performance and can retard its commercial exploitation in humans and its veterinary applications. Inefficient delivery of the DNA vaccine into cells of immunized individuals results in low intracellular supply of suitable expression cassettes encoding an antigen, in its low expression level and, in turn, in reduced immune responses against the antigen. Improvement of DNA delivery into the host cells might significantly increase effectiveness of the DNA vaccine. A vast array of innovative methods and various experimental strategies have been applied in order to enhance the effectiveness of DNA vaccines. They include various strategies improving DNA delivery as well as expression and immunogenic potential of the proteins encoded by the DNA vaccines. Researchers focusing on DNA vaccines against influenza have applied many of these strategies. Recent examples of the most successful modern approaches are discussed in this review.

Influenza prevention and treatment by passive immunization

Passive immunity is defined as a particular antigen resistance provided by external antibodies. It can be either naturally or artificially acquired. Natural passive immunization occurs during pregnancy and breast-feeding in mammals and during hatching in birds. Maternal antibodies are passed through the placenta and milk in mammals and through the egg yolk in birds. Artificial passive immunity is acquired by injection of either serum from immunized (or infected) individuals or antibody preparations. Many independent research groups worked on selection, verification and detailed characterization of polyclonal and monoclonal antibodies against the influenza virus. Numerous antibody preparations were tested in a variety of in vitro and in vivo experiments for their efficacy to neutralize the virus. Here, we describe types of antibodies tested in such experiments and their viral targets, review approaches resulting in identification of broadly neutralizing antibodies and discuss methods used to demonstrate their protective effects. Finally, we shortly discuss the phenomenon of maternal antibody transfer as a way of effective care for young individuals and as an interfering factor in early vaccination.

DNA vaccines against influenza

Genetic vaccine technology has been considerably developed within the last two decades. This cost effective and promising strategy can be applied for therapy of cancers and for curing allergy, chronic and infectious diseases, such as a seasonal and pandemic influenza. Despite numerous advantages, several limitations of this technology reduce its performance and can retard its commercial exploitation in humans and its veterinary applications. Inefficient delivery of the DNA vaccine into cells of immunized individuals results in low intracellular supply of suitable expression cassettes encoding an antigen, in its low expression level and, in turn, in reduced immune responses against the antigen. Improvement of DNA delivery into the host cells might significantly increase effectiveness of the DNA vaccine. A vast array of innovative methods and various experimental strategies have been applied in order to enhance the effectiveness of DNA vaccines. They include various strategies improving DNA delivery as well as expression and immunogenic potential of the proteins encoded by the DNA vaccines. Researchers focusing on DNA vaccines against influenza have applied many of these strategies. Recent examples of the most successful modern approaches are discussed in this review.

Plant expression systems for production of hemagglutinin as a vaccine against influenza virus

Many examples of a successful application of plant-based expression systems for production of biologically active recombinant proteins exist in the literature. These systems can function as inexpensive platforms for the large scale production of recombinant pharmaceuticals or subunit vaccines. Hemagglutinin (HA) is a major surface antigen of the influenza virus, thus it is in the centre of interests of various subunit vaccine engineering programs. Large scale production of recombinant HA in traditional expression systems, such as mammalian or insect cells, besides other limitations, is expensive and time-consuming. These difficulties stimulate an ever-increasing interest in plant-based production of this recombinant protein. Over the last few years many successful cases of HA production in plants, using both transient and stable expression systems have been reported. Various forms of recombinant HA, including monomers, trimers, virus like particles (VLPs) or chimeric proteins containing its fusion with other polypeptides were obtained and shown to maintain a proper antigenicity. Immunizations of animals (mice, ferrets, rabbits or chickens) with some of these plant-derived hemagglutinin variants were performed, and their effectiveness in induction of immunological response and protection against lethal challenge with influenza virus demonstrated. Plant-produced recombinant subunit vaccines and plant-made VLPs were successfully tested in clinical trials (Phase I and II) that confirmed their tolerance and immunogenicity.

Plant expression systems for production of hemagglutinin as a vaccine against influenza virus

Many examples of a successful application of plant-based expression systems for production of biologically active recombinant proteins exist in the literature. These systems can function as inexpensive platforms for the large scale production of recombinant pharmaceuticals or subunit vaccines. Hemagglutinin (HA) is a major surface antigen of the influenza virus, thus it is in the centre of interests of various subunit vaccine engineering programs. Large scale production of recombinant HA in traditional expression systems, such as mammalian or insect cells, besides other limitations, is expensive and time-consuming. These difficulties stimulate an ever-increasing interest in plant-based production of this recombinant protein. Over the last few years many successful cases of HA production in plants, using both transient and stable expression systems have been reported. Various forms of recombinant HA, including monomers, trimers, virus like particles (VLPs) or chimeric proteins containing its fusion with other polypeptides were obtained and shown to maintain a proper antigenicity. Immunizations of animals (mice, ferrets, rabbits or chickens) with some of these plant-derived hemagglutinin variants were performed, and their effectiveness in induction of immunological response and protection against lethal challenge with influenza virus demonstrated. Plant-produced recombinant subunit vaccines and plant-made VLPs were successfully tested in clinical trials (Phase I and II) that confirmed their tolerance and immunogenicity.

Antibody response to DNA vaccine against H5N1 avian influenza virus in broilers immunized according to three schedules

Broiler type chickens were immunized intramuscularly with a DNA vaccine encoding hemagglutinin (HA) from H5N1 avian influenza virus. The chickens were divided into four groups: control group which was not immunized, a group which obtained only one dose, and two groups which were immunized twice, one group with a boost two weeks after the priming and the other four weeks. Blood samples were collected at several time points and the dynamics of the humoral response to the vaccine was studied. High level of anti-HA antibodies was detected only in the last two groups, that is in chickens immunized according to the prime-boost strategy, regardless of the schedule. An additional interesting observation of this study was detection of the cross-reactivity of an anti-H5 HA positive serum with H5N2 and H1N1 viruses, suggesting that the DNA vaccine tested can induce antibodies of a broad specificity.

Antibody response to DNA vaccine against H5N1 avian influenza virus in broilers immunized according to three schedules

Broiler type chickens were immunized intramuscularly with a DNA vaccine encoding hemagglutinin (HA) from H5N1 avian influenza virus. The chickens were divided into four groups: control group which was not immunized, a group which obtained only one dose, and two groups which were immunized twice, one group with a boost two weeks after the priming and the other four weeks. Blood samples were collected at several time points and the dynamics of the humoral response to the vaccine was studied. High level of anti-HA antibodies was detected only in the last two groups, that is in chickens immunized according to the prime-boost strategy, regardless of the schedule. An additional interesting observation of this study was detection of the cross-reactivity of an anti-H5 HA positive serum with H5N2 and H1N1 viruses, suggesting that the DNA vaccine tested can induce antibodies of a broad specificity.

An immunosensor based on antibody binding fragments attached to gold nanoparticles for the detection of peptides derived from avian influenza hemagglutinin H5

This paper concerns the development of an immunosensor for detection of peptides derived from avian influenza hemagglutinin H5. Its preparation consists of successive gold electrode modification steps: (i) modification with 1,6-hexanedithiol and gold colloidal nanoparticles; (ii) immobilization of antibody-binding fragments (Fab') of anti-hemagglutinin H5 monoclonal antibodies Mab 6-9-1 via S-Au covalent bonds; and (iii) covering the remaining free space on the electrode surfaces with bovine serum albumin. The interactions between Fab' fragments and hemagglutinin (HA) variants have been explored with electrochemical impedance spectroscopy (EIS) in the presence of [Fe(CN)6](3-/4-) as an electroactive marker. The immunosensor was able to recognize three different His-tagged variants of recombinant hemagglutinin from H5N1 viruses: H1 subunit (17-340 residues) of A/swan/Poland/305-135V08/2006, the long HA (17-530 residues) A/Bar-headed Goose/Qinghai/12/2005 and H1 subunit (1-345 residues) of A/Vietnam/1194/2004. The strongest response has been observed for the long variant with detection limit of 2.2 pg/mL and dynamic range from 4.0 to 20.0 pg/mL.

A highly sensitive electrochemical genosensor based on Co-porphyrin-labelled DNA

Cobalt-porphyrin-modified DNA was used to design an electrochemical genosensor which is able to detect a minimum of 1000 DNA molecules.

Electrochemical immunosensor for detection of antibodies against influenza A virus H5N1 in hen serum

This paper describes the development of an immunosensor for detection of anti-hemagglutinin antibodies. Its preparation consists of successive modification steps of glassy carbon electrodes: (i) creation of COOH groups, (ii) covalent immobilization of protein A with EDC/NHS coupling reaction, (iii) covering with anti-His IgG monoclonal antibody, (iv) immobilization of the recombinant His-tagged hemagglutinin (His6-H5 HA), (v) filling free space with BSA. The interactions between two variants of recombinant HA (short and long) from highly pathogenic avian influenza virus H5N1 and the anti-H5 HA monoclonal antibody (Mab 6-9-1) have been explored with electrochemical impedance spectroscopy (EIS). The impedimetric immunosensor displayed a very good detection limit (LOD) of 2.1 pg/mL, the quantification limit (LOQ) of 6.3 pg/mL and a dynamic range from 4 pg/mL to 20 pg/mL. In addition, this analytical device was applied for detection of antibodies against His6-H5 HA in serum of vaccinated hen using serial 10-fold dilutions of serum. The immunosensor proposed was able to detect antibody in hen serum diluted up to 7 × 10(7)-fold. The sensitivity of immunosensor was about four orders of magnitude much better than ELISA.

Transgenic tobacco plants as production platform for biologically active human interleukin 2 and its fusion with proteinase inhibitors

Transgenic plants offer a low-cost approach for the production of pharmaceutically important and commercially valuable recombinant proteins. Our studies were focused on the plant-based production of human interleukin 2 (hIL-2) and its fusion with proteinase inhibitors, either SPI2 from Galleria mellonella or CMTI from Cucurbita maxima. Finally, five plant expression cassettes were obtained. Three of them contained the single cDNA encoding CMTI I, SPI2 and hIL-2, respectively, while two of them contained the translational fusion, SPI2::hIL-2 and CMTI::hIL-2. In all cases, the transgenes were controlled by the RbcS1 promoter and terminator and the recombinant proteins were targeted to the endoplasmic reticulum. After tobacco transformation, five groups of transgenic plants were obtained and analysed. The level of recombinant proteins was estimated either by Western blot or by ELISA. The biological activity of plant-produced hIL-2 alone or in a fusion with SPI2 or CMTI was confirmed using the mammalian cells proliferation assay. The activities of proteinase inhibitors were confirmed in proteolysis assay using azocoll as a substrate. The usefulness of using proteinase inhibitor CMTI I in a fusion with hIL-2 as a protective agent against trypsin digestion was demonstrated.

Recombinant mouse granulocyte-macrophage colony-stimulating factor is glycosylated in transgenic tobacco and maintains its biological activity

The granulocyte-macrophage colony-stimulating factor (GM-CSF) is a cytokine with many important applications and, due to its immunostimulatory properties, could also be used as a vaccine adjuvant. A simple strategy to produce recombinant mouse GM-CSF (mGM-CSF) in transgenic Nicotiana tabacum plants was used in this study. The mGM-CSF cDNA followed by the sequence encoding endoplasmic reticulum retention signal (KDEL) was cloned into the ImpactVector under the control of the strong promoter from the gene encoding a small subunit of Rubisco. In transgenic plants the accumulation level of recombinant mGM-CSF varied in the individual transformants from 8 to 19 microg/g of fresh leaf tissue, which makes up to 0.22% of total soluble protein. In most analyzed plants, the apparent molecular weight of the recombinant protein was larger than predicted due to its N-glycosylation, presumably in 2 sites. The recombinant plant-produced murine GM-CSF retained its biological activity as confirmed in vitro in proliferation assay using a mouse cell line, which is growth-dependent on GM-CSF.

[Plant-based production of recombinant cytokines]

Modern biotechnology has led to increase of interest in producing pharmaceutically important and commercially valuable proteins in plants. Plants can efficiently produce recombinant proteins in large quantities and plant-derived proteins are free of human disease factors. In general, plant systems can now be used to produce a variety of proteins, including antibodies, cytokines, blood substitutes, vaccines and others. Cytokines are small proteins secreted by animal cells. They mediate and regulate immunity, inflammation, and hematopoiesis. Due to their properties many cytokines have medical application, mostly in treatment of virus infections, cancer symptoms and diseases affecting the immune system. However clinical deployment of cytokines is limited by the high production costs. Recently, several research groups reported using various plant-based expression systems for the production of biologically active mammalian cytokines.

Co-inoculation with two non-infectious cDNA copies of potato spindle tuber viroid (PSTVd) leads to the appearance of novel fully infectious variants

Potato spindle tuber viroid (PSTVd) is one of the smallest (about 360 nt) infectious plant agents. It is composed of a single-stranded circular non-coding RNA molecule. In the course of previous passage experiments with two intermediate PSTVd variants I2 and I4, three non-infectious clones (I2-50, I4-37 and I4 VI-17) were found. When inoculated separately as cDNAs on tomato "Rutgers" test plants these variants did not induce any visible disease symptoms and did not produce progeny. The presence of such non-infectious variants raises several questions about their origin and biology and to answer them, mixed co-infections with cDNA copies of two non-infectious variants (I2-50, I4-37) were performed. PSTVd infection was observed in seven out of 30 inoculated plants. The progeny isolated from three separate plants contained novel variants, together with the parental I2 and I4 sequences. It is conceivable that the appearance of repaired PSTVd molecules, clearly capable of cell-to-cell movement leading to the systemic infection, results from recombination events. An analysis of the recombinant molecules and comparison with databases identified the specific sites responsible for the restricted infectivity of the I2-50 and I4-37 PSTVd variants. In parallel experiments in which (+) strand PSTVd infectious transcripts were used, no recombinants were observed, and the original I2-50 and I4-37 non-infectious sequences were not detected in the progeny.

Co-inoculation with two non-infectious cDNA copies of potato spindle tuber viroid (PSTVd) leads to the appearance of novel fully infectious variants

Potato spindle tuber viroid (PSTVd) is one of the smallest (about 360 nt) infectious plant agents. It is composed of a single-stranded circular non-coding RNA molecule. In the course of previous passage experiments with two intermediate PSTVd variants I2 and I4, three non-infectious clones (I2-50, I4-37 and I4 VI-17) were found. When inoculated separately as cDNAs on tomato "Rutgers" test plants these variants did not induce any visible disease symptoms and did not produce progeny. The presence of such non-infectious variants raises several questions about their origin and biology and to answer them, mixed co-infections with cDNA copies of two non-infectious variants (I2-50, I4-37) were performed. PSTVd infection was observed in seven out of 30 inoculated plants. The progeny isolated from three separate plants contained novel variants, together with the parental I2 and I4 sequences. It is conceivable that the appearance of repaired PSTVd molecules, clearly capable of cell-to-cell movement leading to the systemic infection, results from recombination events. An analysis of the recombinant molecules and comparison with databases identified the specific sites responsible for the restricted infectivity of the I2-50 and I4-37 PSTVd variants. In parallel experiments in which (+) strand PSTVd infectious transcripts were used, no recombinants were observed, and the original I2-50 and I4-37 non-infectious sequences were not detected in the progeny.

Viroids: unusual small pathogenic RNAs

Viroids are small (about 300 nucleotides), single-stranded, circular, non-encapsidated pathogenic RNA molecules. They do not code for proteins and thus depend on plant host enzymes for their replication and other functions. They induce plant diseases by direct interaction with host factors but the mechanism of pathogenicity is still unknown. They can alter the expression of selected plant genes important for growth and development. Viroids belong to two families, the Avsunviroidae and the Pospiviroidae. Viroids of the Avsunviroidae family adopt a branched or quasi rod-like secondary structure in their native state. Members of the Pospiviroidae family adopt a rod-like secondary structure. In such native structures five structural/functional domains have been identified: central (C), pathogenicity, variable and two terminal domains. The central conserved region (CCR) within the C domain characterizes viroids of the Pospiviroidae. Specific secondary structures of this region play an important role in viroid replication and processing. Viroids of the Avsunviroidae family lack a CCR but possess self-cleaving properties by forming hammerhead ribozyme structures; they accumulate and replicate in chloroplasts, whereas members of the Pospiviroidae family have a nuclear localization. Viroid replication occurs via a rolling circle mechanism using either a symmetric or asymmetric pathway in three steps, RNA transcription, processing and ligation.

Viroids: unusual small pathogenic RNAs

Viroids are small (about 300 nucleotides), single-stranded, circular, non-encapsidated pathogenic RNA molecules. They do not code for proteins and thus depend on plant host enzymes for their replication and other functions. They induce plant diseases by direct interaction with host factors but the mechanism of pathogenicity is still unknown. They can alter the expression of selected plant genes important for growth and development. Viroids belong to two families, the Avsunviroidae and the Pospiviroidae. Viroids of the Avsunviroidae family adopt a branched or quasi rod-like secondary structure in their native state. Members of the Pospiviroidae family adopt a rod-like secondary structure. In such native structures five structural/functional domains have been identified: central (C), pathogenicity, variable and two terminal domains. The central conserved region (CCR) within the C domain characterizes viroids of the Pospiviroidae. Specific secondary structures of this region play an important role in viroid replication and processing. Viroids of the Avsunviroidae family lack a CCR but possess self-cleaving properties by forming hammerhead ribozyme structures; they accumulate and replicate in chloroplasts, whereas members of the Pospiviroidae family have a nuclear localization. Viroid replication occurs via a rolling circle mechanism using either a symmetric or asymmetric pathway in three steps, RNA transcription, processing and ligation.

Genetic variability of potato spindle tuber viroid RNA replicon

The genetic continuity of the potato spindle tuber viroid (PSTVd) genome was analysed after infection of tomato plants with cloned cDNAs of parental strains. During the six weeks of the experiment, several new sequence variants appeared. The sequence variants detected in the progeny population induced sequence-specific disease symptoms. The PSTVd genome therefore follows the pattern expected for typical pseudo-strains propagating in plants as a population of similar sequences. Assessing further the replicon continuity, a PSTVd cDNA mutant with a deletion in the central conserved region was constructed and proven to be non-infectious. Surprisingly, in a sub-population of potato transformants expressing the same deleted PSTVd RNA an infectious viroid was detected. This suggests specific transcript conversion followed by recovery of the full-length pathogen genome.

Genetic variability of potato spindle tuber viroid RNA replicon

The genetic continuity of the potato spindle tuber viroid (PSTVd) genome was analysed after infection of tomato plants with cloned cDNAs of parental strains. During the six weeks of the experiment, several new sequence variants appeared. The sequence variants detected in the progeny population induced sequence-specific disease symptoms. The PSTVd genome therefore follows the pattern expected for typical pseudo-strains propagating in plants as a population of similar sequences. Assessing further the replicon continuity, a PSTVd cDNA mutant with a deletion in the central conserved region was constructed and proven to be non-infectious. Surprisingly, in a sub-population of potato transformants expressing the same deleted PSTVd RNA an infectious viroid was detected. This suggests specific transcript conversion followed by recovery of the full-length pathogen genome.

Restoration of secondary hairpin II is associated with restoration of infectivity of a non-viable recombinant viroid

Mutagenesis and/or construction of recombinants by exchange of genomic regions between parental molecules constitute powerful tools for the study of viroids. However, a large proportion of such modifications results in molecules, which have lost their infectivity. Such is the case for a recombinant viroid named CECS, obtained by replacing the right half of a citrus exocortis viroid (CEVd) by the same region from chrysanthemum stunt viroid (CSVd). In an effort to recover viable infectious progeny from this recombinant, tomato plants were inoculated with an Agrobacterium strain carrying a dimer of the CECS viroid in positive orientation under the control of the CaMV 35S promoter. About 20% of the plants treated in this way were found to be infected with a replicating viroid, which was further propagated. Sequence analysis of six cloned full-length cDNAs derived from progeny molecules revealed the presence of mutations as compared with the parental CECS sequence. However, only two types of mutations were consistently recovered in all progeny molecules, the addition of a G in a string of four at positions 70-73, a mutation frequently observed in CEVd isolates and mutations leading to the restoration of the correct base pairing in secondary hairpin II. These results show that agro-infection is a suitable technique for the recovery of viable molecules from non-infectious viroid mutants and confirm that the ability to form secondary hairpin II is a prerequisite for viroid infectivity.

The genetic stability of potato spindle tuber viroid (PSTVd) molecular variants

RNA viruses propagate as a population of genetically related entities composing a quasi-species. Specific representatives are the result of both a high mutation rate during replication and competition between the continuously arising sequence variants. Similar to other RNA pathogens, potato spindle tuber viroid (PSTVd) propagates as a population of similar but nonidentical sequences. The sequence of progeny molecules derived from cloned molecular variants of PSTVd were studied after one and six consecutive plant passages. Although the severe parental sequence S23 was found to be genetically stable, all five other parental sequences analyzed, irrespective of their pathogenicity, led to the appearance of complex populations. Divergence of the progeny was observed at the sequence level, but also, more surprisingly, at the level of the pathogenicity of individual progeny molecules. In two cases, the parental sequence was retained in the progeny population. In the other cases, it was completely out-competed and eliminated, sometimes in as little as one plant passage. Although it has been observed previously that artificially mutated PSTVd molecules may revert rapidly to the wild-type sequence, this study presents direct evidence for the rapid evolution of naturally occurring PSTVd sequence variants.