Chimeric influenza virus replicating predominantly in the murine upper respiratory tract induces local immune responses against human immunodeficiency virus type 1 in the genital tract

Globular Head-Displayed Conserved Influenza H1 Hemagglutinin Stalk Epitopes Confer Protection against Heterologous H1N1 Virus

Significant genetic variability in the head region of the influenza A hemagglutinin, the main target of current vaccines, makes it challenging to develop a long-lived seasonal influenza prophylaxis. Vaccines based on the conserved hemagglutinin stalk domain might provide broader cross-reactive immunity. However, this region of the hemagglutinin is immunosubdominant to the head region. Peptide-based vaccines have gained much interest as they allow the immune system to focus on relevant but less immunogenic epitopes. We developed a novel influenza A hemagglutinin-based display platform for H1 hemagglutinin stalk peptides that we identified in an epitope mapping assay using human immune sera and synthetic HA peptides. Flow cytometry and competition assays suggest that the identified stalk sequences do not recapitulate the epitopes of already described broadly neutralizing stalk antibodies. Vaccine constructs displaying 25-mer stalk sequences provided up to 75% protection from lethal heterologous virus challenge in BALB/c mice and induced antibody responses against the H1 hemagglutinin. The developed platform based on a vaccine antigen has the potential to be either used as stand-alone or as prime-vaccine in combination with conventional seasonal or pandemic vaccines for the amplification of stalk-based cross-reactive immunity in humans or as platform to evaluate the relevance of viral peptides/epitopes for protection against influenza virus infection.

Attenuated Recombinant Influenza A Virus Expressing HPV16 E6 and E7 as a Novel Therapeutic Vaccine Approach

Persistent infection with high-risk human papillomavirus (HPV) types, most often HPV16 and HPV18, causes all cervical and most anal cancers, and a subset of vulvar, vaginal, penile and oropharyngeal carcinomas. Two prophylactic virus-like particle (VLPs)-based vaccines, are available that protect against vaccine type-associated persistent infection and associated disease, yet have no therapeutic effect on existing lesions or infections. We have generated recombinant live-attenuated influenza A viruses expressing the HPV16 oncogenes E6 and E7 as experimental immunotherapeutic vaccine candidates. The influenza A virus life cycle lacks DNA intermediates as important safety feature. Different serotypes were generated to ensure efficient prime and boost immunizations. The immune response to vaccination in C57BL/6 mice was characterized by peptide ELISA and IFN-γ ELISpot, demonstrating induction of cell-mediated immunity to HPV16 E6 and E7 oncoproteins. Prophylactic and therapeutic vaccine efficacy was analyzed in the murine HPV16-positive TC-1 tumor challenge model. Subcutaneous (s.c.) prime and boost vaccinations of mice with recombinant influenza A serotypes H1N1 and H3N2, followed by challenge with TC-1 cells resulted in complete protection or significantly reduced tumor growth as compared to control animals. In a therapeutic setting, s.c. vaccination of mice with established TC-1 tumors decelerated tumor growth and significantly prolonged survival. Importantly, intralesional vaccine administration induced complete tumor regression in 25% of animals, and significantly reduced tumor growth in 50% of mice. These results suggest recombinant E6E7 influenza viruses as a promising new approach for the development of a therapeutic vaccine against HPV-induced disease.

RNA-based viral vectors

The advent of reverse genetic approaches to manipulate the genomes of both positive (+) and negative (-) sense RNA viruses allowed researchers to harness these genomes for basic research. Manipulation of positive sense RNA virus genomes occurred first largely because infectious RNA could be transcribed directly from cDNA versions of the RNA genomes. Manipulation of negative strand RNA virus genomes rapidly followed as more sophisticated approaches to provide RNA-dependent RNA polymerase complexes coupled with negative-strand RNA templates were developed. These advances have driven an explosion of RNA virus vaccine vector development. That is, development of approaches to exploit the basic replication and expression strategies of RNA viruses to produce vaccine antigens that have been engineered into their genomes. This study has led to significant preclinical testing of many RNA virus vectors against a wide range of pathogens as well as cancer targets. Multiple RNA virus vectors have advanced through preclinical testing to human clinical evaluation. This review will focus on RNA virus vectors designed to express heterologous genes that are packaged into viral particles and have progressed to clinical testing.

Novel mucosal DNA-MVA HIV vaccination in which DNA-IL-12 plus cholera toxin B subunit (CTB) cooperates to enhance cellular systemic and mucosal genital tract immunity

Induction of local antiviral immune responses at the mucosal portal surfaces where HIV-1 and other viral pathogens are usually first encountered remains a primary goal for most vaccines against mucosally acquired viral infections. Exploring mucosal immunization regimes in order to find optimal vector combinations and also appropriate mucosal adjuvants in the HIV vaccine development is decisive. In this study we analyzed the interaction of DNA-IL-12 and cholera toxin B subunit (CTB) after their mucosal administration in DNA prime/MVA boost intranasal regimes, defining the cooperation of both adjuvants to enhance immune responses against the HIV-1 Env antigen. Our results demonstrated that nasal mucosal DNA/MVA immunization schemes can be effectively improved by the co-delivery of DNA-IL-12 plus CTB inducing elevated HIV-specific CD8 responses in spleen and more importantly in genital tract and genito-rectal draining lymph nodes. Remarkably, these CTL responses were of superior quality showing higher avidity, polyfunctionality and a broader cytokine profile. After IL-12+CTB co-delivery, the cellular responses induced showed an enhanced breadth recognizing with higher efficiency Env peptides from different subtypes. Even more, an in vivo CTL cytolytic assay demonstrated the higher specific CD8 T-cell performance after the IL-12+CTB immunization showing in an indirect manner its potential protective capacity. Improvements observed were maintained during the memory phase where we found higher proportions of specific central memory and T memory stem-like cells T-cell subpopulations. Together, our data show that DNA-IL-12 plus CTB can be effectively employed acting as mucosal adjuvants during DNA prime/MVA boost intranasal vaccinations, enhancing magnitude and quality of HIV-specific systemic and mucosal immune responses.

Influenza reverse genetics: dissecting immunity and pathogenesis

Reverse genetics systems allow artificial generation of non-segmented and segmented negative-sense RNA viruses, like influenza viruses, entirely from cloned cDNA. Since the introduction of reverse genetics systems over a decade ago, the ability to generate ‘designer’ influenza viruses in the laboratory has advanced both basic and applied research, providing a powerful tool to investigate and characterise host–pathogen interactions and advance the development of novel therapeutic strategies. The list of applications for reverse genetics has expanded vastly in recent years. In this review, we discuss the development and implications of this technique, including the recent controversy surrounding the generation of a transmissible H5N1 influenza virus. We will focus on research involving the identification of viral protein function, development of live-attenuated influenza virus vaccines, host–pathogen interactions, immunity and the generation of recombinant influenza virus vaccine vectors for the prevention and treatment of infectious diseases and cancer.

A recombinant influenza A virus expressing domain III of West Nile virus induces protective immune responses against influenza and West Nile virus

West Nile virus (WNV) continues to circulate in the USA and forms a threat to the rest of the Western hemisphere. Since methods for the treatment of WNV infections are not available, there is a need for the development of safe and effective vaccines. Here, we describe the construction of a recombinant influenza virus expressing domain III of the WNV glycoprotein E (Flu-NA-DIII) and its evaluation as a WNV vaccine candidate in a mouse model. FLU-NA-DIII-vaccinated mice were protected from severe body weight loss and mortality caused by WNV infection, whereas control mice succumbed to the infection. In addition, it was shown that one subcutaneous immunization with 10⁵ TCID₅₀ Flu-NA-DIII provided 100% protection against challenge. Adoptive transfer experiments demonstrated that protection was mediated by antibodies and CD4+T cells. Furthermore, mice vaccinated with FLU-NA-DIII developed protective influenza virus-specific antibody titers. It was concluded that this vector system might be an attractive platform for the development of bivalent WNV-influenza vaccines.

Mucosal HIV transmission and vaccination strategies through oral compared with vaginal and rectal routes

IMPORTANCE OF THE FIELD

There are currently over thirty million people infected with HIV and there are no vaccines available to prevent HIV infections or disease. The genitourinary, rectal and oral mucosa are the mucosal HIV transmission routes. An effective vaccine that can induce both systemic and local mucosal immunity is generally accepted as a major means of protection against mucosal HIV transmission and AIDS.

WHAT THE READER WILL GAIN

Structure and cells that comprise the oral, vaginal and rectal mucosa pertaining to HIV transmission and vaccination strategies through each mucosal route to prevent mucosal and systemic infection will be discussed.

AREAS COVERED IN THIS REVIEW

Covering publications from 1980s through 2010, mucosal transmission of HIV and current and previous approaches to vaccinations are discussed.

TAKE HOME MESSAGE

Although oral transmission of HIV is far less common than vaginal and rectal transmissions, infections through this route do occur through oral sex as well as vertically from mother to child. Mucosal vaccination strategies against oral and other mucosal HIV transmissions are under intensive research but the lack of consensus on immune correlates of protection and lack of safe and effective mucosal adjuvants and delivery systems hamper progress towards a licensed vaccine.

The effects of preexisting immunity to influenza on responses to influenza vectors in mice

The use of viral vectors as vaccine candidates has shown promise against a number of pathogens. However, preexisting immunity to these vectors is a concern that must be addressed when deciding which viruses are suitable for use. A number of properties, including the existence of antigenically distinct subtypes, make influenza viruses attractive candidates for use as viral vectors. Here, we evaluate the ability of influenza viral vectors containing inserts of foreign pathogens to elicit antibody and CD8(+) T cell responses against these foreign antigens in the presence of preexisting immunity to influenza virus in mice. Specifically, responses to an H3N1-based vector expressing a 90 amino acid polypeptide derived from the protective antigen (PA) of Bacillus anthracis or an H1N1-based vector containing a CD8(+) T cell epitope from the glycoprotein (GP) of lymphocytic choriomeningitis virus were evaluated following infections with either homosubtypic or heterosubtypic influenza viruses. We found that mice previously infected with influenza viruses, even those expressing HA and NA proteins of completely different subtypes, were severely compromised in their ability to mount an immune response against the inserted epitopes. This inhibition was demonstrated to be mediated by CD8(+) T cells, which recognize multiple strains of influenza viruses. These CD8(+) T cells were further shown to protect mice from a lethal challenge by a heterologous influenza subtype. The implication of these data for the use of influenza virus vectors and influenza vaccination in general are discussed.

A live bivalent influenza vaccine based on a H9N2 virus strain

The purpose of this study was to construct an H9N2 virus-based bivalent live vaccine expressing the protective antigen of a different subtype of influenza virus. Reverse genetics was used to generate an influenza virus containing nine gene segments derived from the A/Chicken/Jiangsu/11/2002 (H9N2) strain, including independent M1 and M2 matrix gene segments. A recombinant virus expressing the H1N1 HA1 hemagglutinin protein was produced on this framework by substituting the extracellular domain of the H9N2 M2 gene with the H1N1 HA1 fragment from A/PR/8/34 (PR8, H1N1). The resulting hybrid virus H9N2-PR8/HA1 was genetically stable and of low pathogenicity. Intra-nasal immunization of BALB/c mice with H9N2-PR8/HA1 virus induced both anti-H9N2 virus and anti-PR8 HA antibodies and conferred protection to mice against lethal challenge (40x LD(50)) with either H1N1 or H9N2 viruses. This study provides a new influenza H9N2 virus model for the expression and/or delivery of foreign antigens.

Crystallographic definition of the epitope promiscuity of the broadly neutralizing anti-human immunodeficiency virus type 1 antibody 2F5: vaccine design implications

The quest to create a human immunodeficiency virus type 1 (HIV-1) vaccine capable of eliciting broadly neutralizing antibodies against Env has been challenging. Among other problems, one difficulty in creating a potent immunogen resides in the substantial overall sequence variability of the HIV envelope protein. The membrane-proximal region (MPER) of gp41 is a particularly conserved tryptophan-rich region spanning residues 659 to 683, which is recognized by three broadly neutralizing monoclonal antibodies (bnMAbs), 2F5, Z13, and 4E10. In this study, we first describe the variability of residues in the gp41 MPER and report on the invariant nature of 15 out of 25 amino acids comprising this region. Subsequently, we evaluate the ability of the bnMAb 2F5 to recognize 31 varying sequences of the gp41 MPER at a molecular level. In 19 cases, resulting crystal structures show the various MPER peptides bound to the 2F5 Fab'. A variety of amino acid substitutions outside the 664DKW666 core epitope are tolerated. However, changes at the 664DKW666 motif itself are restricted to those residues that preserve the aspartate's negative charge, the hydrophobic alkyl-pi stacking arrangement between the beta-turn lysine and tryptophan, and the positive charge of the former. We also characterize a possible molecular mechanism of 2F5 escape by sequence variability at position 667, which is often observed in HIV-1 clade C isolates. Based on our results, we propose a somewhat more flexible molecular model of epitope recognition by bnMAb 2F5, which could guide future attempts at designing small-molecule MPER-like vaccines capable of eliciting 2F5-like antibodies.

Characterization of recombinant influenza A virus as a vector for HIV-1 p17Gag

We have generated a recombinant influenza A virus with the HIV-1 p17(Gag) (rFlu-p17) gene inserted into the influenza virus neuraminidase (NA) gene. Expression of HIV-1 p17 protein was detected by conventional Western blot analysis and also by liquid chromatography/tandem mass spectrometry (LC-MS/MS) analysis of rFlu-p17 infected cells. The latter method does not depend on protein-specific antibody preparations and proved to be a powerful tool to detect proteins of interest. Next, antigen presentation of p17 expressed after infection of antigen-presenting cells was determined. Cloned p17-specific CD8+ T-cells were co-cultured with rFlu-p17 infected B-cells and produced IFN-gamma upon stimulation. Furthermore, we showed that immunization with rFlu-p17 elicited a humoral immune response in mice. This study shows that replication-deficient rFlu-p17 is antigenic in vitro and immunogenic in vivo and warrants further development as a candidate vaccine vector.

Partial humanization and characterization of an anti-idiotypic antibody against monoclonal antibody 2F5, a potential HIV vaccine?

We recently developed a murine anti-idiotypic antibody (Ab2/3H6) versus the human monoclonal antibody 2F5, one of a few antibodies yet known to neutralize a broad range of HIV-1 primary isolates. Ab2/3H6 was not only able to bind to the paratope of mAb 2F5 but also significantly inhibited the binding of 2F5 to its synthetic epitope ELDKWA on gp41. In the present work we describe the partial humanization, expression, and characterization of Ab2/3H6 variants followed by several corresponding interaction studies with 2F5. The results of these studies support the high specificity of the recombinantly expressed Ab2s to the idiotype. Apparent affinities were designated by end point measurement and were similar compared to the murine Ab2/3H6. Moreover, the inhibition potency of chimeric Ab2/3H6 analyzed by in vitro studies could be shown to be the same as that detected for the hybridoma-derived murine Ab2/3H6.

Attachment of infectious influenza A viruses of various subtypes to live mammalian and avian cells as measured by flow cytometry

At present there is much interest in the cell tropism and host range of influenza viruses, especially those of the H5N1 subtype. We wished to develop a method that would enable investigation of attachment of infectious virus through the interaction of the hemagglutinin molecule and live mammalian and avian cells and the subsequent infection of these cells. To this end, influenza viruses of various HA subtypes were constructed that either carry the green fluorescent protein (GFP) instead of the neuraminidase protein, or that express GFP in the cytoplasm of infected cells. The HA genes were derived from influenza viruses A/PR/8/34 (H1N1), A/Netherlands/178/95 (H3N2) and A/Vietnam/1194/04 (H5N1). Using these pairs of viruses, attachment and post-attachment events in the virus replication cycle can be distinguished. In general, the expression of NeuAc(alpha2-3)Gal or NeuAc(alpha2-6)Gal receptors on the cells tested corresponded with the attachment of the viruses that were studied with respect to predicted receptor specificity. Virus attachment was not always predictive for efficient infection of the cells.

Live attenuated influenza virus expressing human interleukin-2 reveals increased immunogenic potential in young and aged hosts

Despite the reported efficacy of commercially available influenza virus vaccines, a considerable proportion of the human population does not respond well to vaccination. In an attempt to improve the immunogenicity of live influenza vaccines, an attenuated, cold-adapted (ca) influenza A virus expressing human interleukin-2 (IL-2) from the NS gene was generated. Intranasal immunization of young adult and aged mice with the IL-2-expressing virus resulted in markedly enhanced mucosal and cellular immune responses compared to those of mice immunized with the nonrecombinant ca parent strain. Interestingly, the mucosal immunoglobulin A (IgA) and CD8(+) T-cell responses in the respiratory compartment could be restored in aged mice primed with the IL-2-expressing virus to magnitudes similar to those in young adult mice. The immunomodulating effect of locally expressed IL-2 also gave rise to a systemic CD8(+) T-cell and distant urogenital IgA response in young adult mice, but this effect was less distinct in aged mice. Importantly, only mice immunized with the recombinant IL-2 virus were completely protected from a pathogenic wild-type virus challenge and revealed a stronger onset of virus-specific CD8(+) T-cell recall response. Our findings emphasize the potential of reverse genetics to improve the efficacy of live influenza vaccines, thus rendering them more suitable for high-risk age groups.

Influenza virus NS vectors expressing the mycobacterium tuberculosis ESAT-6 protein induce CD4+ Th1 immune response and protect animals against tuberculosis challenge

Infection with Mycobacterium tuberculosis remains a major cause of morbidity and mortality all over the world. Since the effectiveness of the only available tuberculosis vaccine, Mycobacterium bovis bacillus Calmette-Guérin (BCG), is suboptimal, there is a strong demand to develop new tuberculosis vaccines. As tuberculosis is an airborne disease, the intranasal route of vaccination might be preferable. Live influenza virus vaccines might be considered as potential vectors for mucosal immunization against various viral or bacterial pathogens, including M. tuberculosis. We generated several subtypes of attenuated recombinant influenza A viruses expressing the 6-kDa early secretory antigenic target protein (ESAT-6) of M. tuberculosis from the NS1 reading frame. We were able to demonstrate the potency of influenza virus NS vectors to induce an M. tuberculosis-specific Th1 immune response in mice. Moreover, intranasal immunization of mice and guinea pigs with such vectors induced protection against mycobacterial challenge, similar to that induced by BCG vaccination.

Simian immunodeficiency virus engrafted with human immunodeficiency virus type 1 (HIV-1)-specific epitopes: replication, neutralization, and survey of HIV-1-positive plasma

To date, only a small number of anti-human immunodeficiency virus type 1 (HIV-1) monoclonal antibodies (MAbs) with relatively broad neutralizing activity have been isolated from infected individuals. Adequate techniques for defining how frequently antibodies of these specificities arise in HIV-infected people have been lacking, although it is generally assumed that such antibodies are rare. In order to create an epitope-specific neutralization assay, we introduced well-characterized HIV-1 epitopes into the heterologous context of simian immunodeficiency virus (SIV). Specifically, epitope recognition sequences for the 2F5, 4E10, and 447-52D anti-HIV-1 neutralizing monoclonal antibodies were introduced into the corresponding regions of SIVmac239 by site-directed mutagenesis. Variants with 2F5 or 4E10 recognition sequences in gp41 retained replication competence and were used for neutralization assays. The parental SIVmac239 and the neutralization-sensitive SIVmac316 were not neutralized by the 2F5 and 4E10 MAbs, nor were they neutralized significantly by any of the 96 HIV-1-positive human plasma samples that were tested. The SIV239-2F5 and SIV239-4E10 variants were specifically neutralized by the 2F5 and 4E10 MAbs, respectively, at concentrations within the range of what has been reported previously for HIV-1 primary isolates (J. M. Binley et al., J. Virol. 78:13232-13252, 2004). The SIV239-2F5 and SIV239-4E10 epitope-engrafted variants were used as biological screens for the presence of neutralizing activity of these specificities. None of the 92 HIV-1-positive human plasma samples that were tested exhibited significant neutralization of SIV239-2F5. One plasma sample exhibited >90% neutralization of SIV239-4E10, but this activity was not competed by a 4E10 target peptide and was not present in concentrated immunoglobulin G (IgG) or IgA fractions. We thus confirm by direct analysis that neutralizing activities of the 2F5 and 4E10 specificities are either rare among HIV-1-positive individuals or, if present, represent only a very small fraction of the total neutralizing activity in any given plasma sample. We further conclude that the structures of gp41 from SIVmac239 and HIV-1 are sufficiently similar such that epitopes engrafted into SIVmac239 can be readily recognized by the cognate anti-HIV-1 monoclonal antibodies.

Intranasal delivery of vaccines against HIV

HIV poses a serious health threat in the world. Mucosal transmission of HIV through the genitourinary tract may be the most important route of transmission. Intranasal immunisations induce vaginal and systemic immune responses. Various protein-, DNA- and RNA-based immunopotentiating adjuvants/delivery systems and live bacterial and viral vectors are available for intranasal immunisations, and these systems may differ in their ability to induce a specific type of immune response (e.g., a cytotoxic T cell versus an antibody response). As the protection against HIV may require both cytotoxic T cell and antibodies, a combination of adjuvants/delivery systems for combinations of mucosal and parenteral immunisations may be required in order to develop a protective anti-HIV vaccine.

Recombinant poxviruses as mucosal vaccine vectors

The majority of infections initiate their departure from a mucosal surface, such as Human immunodeficiency virus (HIV), a sexually transmitted virus. Therefore, the induction of mucosal immunity is a high priority in the development of vaccines against mucosal pathogens. The selection of an appropriate antigen delivery system is necessary to induce an efficient mucosal immune response. Poxvirus vectors have been the most intensively studied live recombinant vector, and numerous studies have demonstrated their ability to induce mucosal immune responses against foreign expressed antigens. Previous studies have demonstrated that recombinants based on the attenuated modified vaccinia virus Ankara (MVA) vector were effective in inducing protective responses against different respiratory viruses, such as influenza and respiratory syncytial virus, following immunization via mucosal routes. Recent studies performed in the murine and macaque models have shown that recombinant MVA (rMVA) does not only stimulate HIV-specific immunity in the genital and rectal tracts following mucosal delivery, but can also control simian/human immunodeficiency viraemia and disease progression. In addition, a prime-boost vaccination approach against tuberculosis emphasized the importance of the intranasal rMVA antigen delivery to induce protective immunity against Mycobacterium tuberculosis. The aim of this review is to summarize the studies employing recombinant poxviruses, specifically rMVA as a mucosal delivery vector. The results demonstrate that rMVAs can activate specific immune responses at mucosal surfaces, and encourage further studies to characterize and improve the MVA mucosal immunogenicity of poxvirus vectors.

Generation of an influenza A virus vector expressing biologically active human interleukin-2 from the NS gene segment

Engineering of the influenza A virus NS1 protein became an attractive approach to the development of influenza vaccine vectors since it can tolerate large inserts of foreign proteins. However, influenza virus vectors expressing long foreign sequences from the NS1 open reading frame (ORF) are usually replication deficient in animals due to the abrogation of their NS1 protein function. In this study, we describe a bicistronic expression strategy based on the insertion of an overlapping UAAUG stop-start codon cassette into the NS gene, allowing the reinitiation of translation of a foreign sequence. Although the expression level of green fluorescent protein (GFP) from the newly created reading frame was significantly lower than that obtained previously from an influenza virus vector expressing GFP from the NS1 ORF, the bicistronic vector appeared to be replication competent in mice and showed outstanding genetic stability. All viral isolates derived from mouse lungs at 10 days postinfection were still capable of expressing GFP in infected cells. Utilizing this bicistronic approach, we constructed another recombinant influenza virus, allowing the secretion of biologically active human interleukin-2 (IL-2). Although this virus also replicated to high titers in mouse lungs, it did not display any mortality rate in infected animals, in contrast to control viruses. Moreover, the IL-2-expressing virus showed an enhanced CD8+ response to viral antigens in mice after a single intranasal immunization. These results indicate that influenza viruses could be engineered for the expression of biologically active molecules such as cytokines for immune modulation purposes.

Chimeric influenza virus hemagglutinin proteins containing large domains of the Bacillus anthracis protective antigen: protein characterization, incorporation into infectious influenza viruses, and antigenicity

Large polypeptides of the Bacillus anthracis protective antigen (PA) were inserted into an influenza A virus hemagglutinin glycoprotein (HA), and the chimeric proteins were functionally characterized and incorporated into infectious influenza viruses. PA domain 1', the region responsible for binding to the other toxin components, the lethal factor and edema factor, and domain 4, the receptor binding domain (RBD), were inserted at the C-terminal flank of the HA signal peptide and incorporated into the HA1 subunit of HA. The chimeric proteins, designated as LEF/HA (90 amino acid insertion) and RBD/HA (140 amino acid insertion), were initially analyzed following expression using recombinant vaccinia viruses. Both chimeric proteins were shown to display functional phenotypes similar to that of the wild-type HA. They transport to the cell surface, can be cleaved into the HA1 and HA2 subunits by trypsin to activate membrane fusion potential, are able to undergo the low-pH-induced conformational changes required for fusion, and are capable of inducing the fusion process. We were also able to generate recombinant influenza viruses containing the chimeric RBD/HA and LEF/HA genes, and the inserted PA domains were maintained in the HA gene segments following several passages in MDCK cells or embryonated chicken eggs. Furthermore, DNA immunization of mice with plasmids that express the chimeric RBD/HA and LEF/HA proteins, and the recombinant viruses containing them, induced antibody responses against both the HA and PA components of the protein. These approaches may provide useful tools for vaccines against anthrax and other diseases.

Functional chimeras of human immunodeficiency virus type 1 Gp120 and influenza A virus (H3) hemagglutinin

In an attempt to produce a protein that will allow determination of the native human immunodeficiency virus type 1 (HIV-1) gp120 (Env) structure in its trimeric state, we fused the globular head of gp120 to the stalk region of influenza virus A (X31) hemagglutinin (HA). The chimeric protein (EnvHA) has been expressed by using a recombinant vaccinia virus system, and its functional characteristics were determined. EnvHA is expressed as a 120- to 150-kDa protein that can oligomerize to form dimers and trimers. It retains the low-pH (5.2 to 5.4) requirement of X31-HA to trigger membrane fusion but, unlike X31-HA, it is not absolutely dependent on exogenously added trypsin for protein processing to release the HA2 fusion peptide. In terms of receptor binding the chimeric protein retains specificity for human CD4 but, in relation to the membrane fusion event, it appears to lose the Env coreceptor specificity of the parental HIV-1 strains: NL43 for CXCR4 and JRFL for CCR5. These properties suggest that stable, functional EnvHAs are being produced and that they may be exploited in terms of structural studies. Further, the potential of introducing the envHA genes into influenza viruses, by use of reverse genetics, and their use as a therapeutic vaccine for HIV are discussed.

Immunogenicity and protection efficacy of replication-deficient influenza A viruses with altered NS1 genes

We explored the immunogenic properties of influenza A viruses with altered NS1 genes (NS1 mutant viruses). NS1 mutant viruses expressing NS1 proteins with an impaired RNA-binding function or insertion of a longer foreign sequence did not replicate in murine lungs but still were capable of inducing a Th1-type immune response resulting in significant titers of virus-specific serum and mucosal immunoglobulin G2 (IgG2) and IgA, but with lower titers of IgG1. In contrast, replicating viruses elicited high titers of serum and mucosal IgG1 but less serum IgA. Replication-deficient NS1 mutant viruses induced a rapid local release of proinflammatory cytokines such as interleukin-1beta (IL-1beta) and IL-6. Moreover, these viruses also elicited markedly higher levels of IFN-alpha/beta in serum than the wild-type virus. Comparable numbers of virus-specific primary CD8(+) T cells were determined in all of the groups of immunized mice. The most rapid onset of the recall CD8(+)-T-cell response upon the wild-type virus challenge was detected in mice primed with NS1 mutant viruses eliciting high levels of cytokines. It is noteworthy that there was one NS1 mutant virus encoding NS1 protein with a deletion of 40 amino acids predominantly in the RNA-binding domain that induced the highest levels of IFN-alpha/beta, IL-6 and IL-1beta after infection. Mice that were immunized with this virus were completely protected from the challenge infection. These findings indicate that a targeted modification of the RNA-binding domain of the NS1 protein is a valuable technique to generate replication-deficient, but immunogenic influenza virus vaccines.

Characterization of molecular features, antigen-binding, and in vitro properties of IgG and IgM variants of 4E10, an anti-HIV type 1 neutralizing monoclonal antibody

The human monoclonal antibody 4E10 has been generated previously by immortalization of peripheral blood cells from an HIV-1-infected individual. This antibody binds to the linear epitope NWFDIT on gp41 and exhibits exceptional neutralizing activity against a broad spectrum of primary HIV-1 isolates. In the present study, molecular features, immunoreactivity, and functional activity of 4E10 were studied. The original hybridoma-derived 4E10 was of subtype IgG(3). Analysis of the variable segment of the heavy chain (VH) demonstrated extensive somatic mutations compared to the closest homologous germline gene VH1-69. Most amino acid substitutions occurred in the complementarity-determining region (CDR) 2, characteristic for an antigen-driven somatic maturation. The heavy chain of the CDR3 (H3) is of unusual length and cannot be attributed with certainty to any specific D(H) locus. To enable mass production and to prolong the in vivo half-life, 4E10 was subsequently cloned as IgG(1) in Chinese hamster ovary (CHO) cells. In additional studies, 4E10 was class switched to the IgM isotype. Binding to the linear epitope NWFDIT was not significantly changed after the cloning procedures. However, in vitro studies revealed dramatic differences in the neutralizing potential. The antiviral activity could be greatly enhanced by change of IgG(3) to IgG(1). In contrast, the IgM isotype almost completely lost its neutralizing potential.

Human immunodeficiency virus type 1-neutralizing monoclonal antibody 2F5 is multispecific for sequences flanking the DKW core epitope

Human monoclonal antibody 2F5 is one of a few human antibodies that neutralize a broad range of HIV-1 primary isolates. The 2F5 epitope on gp41 includes the sequence ELDKWA, with the core residues, DKW, being critical for antibody binding. HIV-neutralizing antibodies have never been elicited by immunization with peptides bearing ELDKWA, suggesting that important part(s) of the 2F5 paratope remain unidentified. The use of longer peptides extending beyond ELDKWA has resulted in increased epitope antigenicity, but neutralizing antibodies have not been generated. We sought to develop peptides that bind to 2F5, and that function as specific probes of the 2F5 paratope. Thus, we used 2F5 to screen a set of phage-displayed, random peptide libraries. Tight-binding clones from the random peptide libraries displayed sequence variability in the regions flanking the DKW motif. To further reveal flanking regions involved in 2F5 binding, two semi-defined libraries were constructed having 12 variegated residues either N-terminal or C-terminal to the DKW core (X(12)-AADKW and AADKW-X(12), respectively). Three clones isolated from the AADKW-X(12) library had similar high affinities, despite a lack of sequence homology among them, or with gp41. The contribution of each residue of these clones to 2F5 binding was evaluated by Ala substitution and amino acid deletion studies, and revealed that each clone bound 2F5 by a different mechanism. These results suggest that the 2F5 paratope is formed by at least two functionally distinct regions: one that displays specificity for the DKW core epitope, and another that is multispecific for sequences C-terminal to the core epitope. The implications of this second, multispecific region of the 2F5 paratope for its unique biological function are discussed.

Induction of HIV Immunity in the Genital Tract After Intranasal Delivery of a MVA Vector: Enhanced Immunogenicity After DNA Prime-Modified Vaccinia Virus Ankara Boost Immunization Schedule

Vaccines intended to prevent mucosal transmission of HIV should be able to induce multiple immune effectors in the host including Abs and cell-mediated immune responses at mucosal sites. The aim of this study was to characterize and to enhance the immunogenicity of a recombinant modified vaccinia virus Ankara (MVA) expressing HIV-1 Env IIIB Ag (MVAenv) inoculated in BALB/c mice by mucosal routes. Intravaginal inoculation of MVAenv was not immunogenic, whereas intranasally it induced a significant immune response to the HIV Ag. Intranasal codelivery of MVAenv plus cholera toxin (CT) significantly enhanced the cellular and humoral immune response against Env in the spleen and genitorectal draining lymph nodes, respectively. Heterologous DNAenv prime-MVAenv boost by intranasal immunization, together with CT, produced a cellular immune response in the spleen 10-fold superior to that in the absence of CT. A key finding of these studies was that both MVAenv/MVAenv and DNAenv/MVAenv schemes, plus CT, induced a specific mucosal CD8(+) T cell response in genital tissue and draining lymph nodes. In addition, both immunizations also generated systemic Abs, and more importantly, mucosal IgA and IgG Abs in vaginal washings. Specific secretion of beta-chemokines was also generated by both immunizations, with a stronger response in mice immunized by the DNA-CT/MVA-CT regimen. Our findings are of relevance in the area of vaccine development and support the optimization of protocols of immunization based on MVA as vaccine vectors to induce mucosal immune responses against HIV.

Characterization of a neuraminidase-deficient influenza a virus as a potential gene delivery vector and a live vaccine

We recently identified a packaging signal in the neuraminidase (NA) viral RNA (vRNA) segment of an influenza A virus, allowing us to produce a mutant virus [GFP(NA)-Flu] that lacks most of the NA open reading frame but contains instead the gene encoding green fluorescent protein (GFP). To exploit the expanding knowledge of vRNA packaging signals to establish influenza virus vectors for the expression of foreign genes, we studied the replicative properties of this virus in cell culture and mice. Compared to wild-type virus, GFP(NA)-Flu was highly attenuated in normal cultured cells but was able to grow to a titer of >10(6) PFU/ml in a mutant cell line expressing reduced levels of sialic acid on the cell surface. GFP expression from this virus was stable even after five passages in the latter cells. In intranasally infected mice, GFP was detected in the epithelial cells of nasal mucosa, bronchioles, and alveoli for up to 4 days postinfection. We attribute the attenuated growth of GFP(NA)-Flu to virion aggregation at the surface of bronchiolar epithelia. In studies to test the potential of this mutant as a live attenuated influenza vaccine, all mice vaccinated with >/==" BORDER="0">10(5) PFU of GFP(NA)-Flu survived when challenged with lethal doses of the parent virus. These results suggest that influenza virus could be a useful vector for expressing foreign genes and that a sialidase-deficient virus may offer an alternative to the live influenza vaccines recently approved for human use.

Toward novel vaccines and therapies based on negative-strand RNA viruses

The study of negative-strand RNA viruses has suggested new strategies to produce more attenuated viruses. Reverse genetics has allowed the implementation of the strategies, and new or improved monovalent vaccines are being developed. In addition, recombinant viruses expressing foreign proteins or epitopes have been produced with the aim of developing multivalent vaccines capable of stimulating humoral and cellular immune responses against more than one pathogen. Finally, recombinant viruses that selectively enter cells expressing tumor markers or the HIV envelope protein have been engineered and shown to lyse target cells. Preclinical and clinical trials of improved and multivalent vaccines and therapeutic (oncolytic) viruses are ongoing.

Prime-boost immunization schedules based on influenza virus and vaccinia virus vectors potentiate cellular immune responses against human immunodeficiency virus Env protein systemically and in the genitorectal draining lymph nodes

Vaccines that elicit systemic and mucosal immune responses should be the choice to control human immunodeficiency virus (HIV) infections. We have previously shown that prime-boost immunizations with influenza virus Env and vaccinia virus (VV) WR Env recombinants induced an enhanced systemic CD8(+) T-cell response against HIV-1 Env antigen. In this report, we analyzed in BALB/c mice after priming with influenza virus Env the ability of two VV recombinants expressing HIV-1 Env B (VV WR Env and the highly attenuated modified VV Ankara [MVA] Env) to boost cellular immune responses in the spleen and in the lymph nodes draining the genital and rectal tracts. Groups of mice were primed by the intranasal route with 10(4) PFU of influenza virus Env and boosted 14 days later by the intraperitoneal or intranasal route with 10(7) PFU of MVA Env or VV WR Env, while the control group received two immunizations with influenza virus Env. We found that the combined immunization (Flu/VV) increased more than 60 times the number of gamma interferon-specific CD8(+) T cells compared to the Flu/Flu scheme. Significantly, boosting with MVA Env by the intraperitoneal route induced a response 1.25 or 2.5 times (spleen or genital lymph nodes) higher with respect to that found after the boost with VV WR Env. Mice with an enhanced CD8(+) T-cell response also had an increased Th1/Th2 ratio, evaluated by the cytokine pattern secreted following in vitro restimulation with gp160 protein and by the specific immunoglobulin G2a (IgG2a)/IgG1 ratio in serum. By the intranasal route recombinant WR Env booster gave a more efficient immune response (10 and 1.3 times in spleen and genital lymph nodes, respectively) than recombinant MVA Env. However, the scheme influenza virus Env/MVA Env increased four times the response in the spleen, giving a low but significant response in the genital lymph nodes compared with a single intranasal immunization with MVA Env. These results demonstrate that the combination Flu/MVA in prime-booster immunization regimens is an effective vaccination approach to generate cellular immune responses to HIV antigens at sites critical for protective responses.

Mucosal immunity induced by intramuscular administration of free peptides in-line with PADRE: IgA antibodies to the ELDKWA epitope of HIV gp41

To improve the mucosal antibody response against a short amino acid (aa) sequence (ELDKWA) of HIV gp41, we have investigated a construction including this peptide in-line with the Pan DR epitope (PADRE). ELDKWA is a conserved peptide playing a key role in the pathogenicity of HIV transmission. PADRE is a non-natural peptide with multipotential immunogenic properties. The results show striking differences between mucosal and systemic immune systems, with a preferential response of the mucosal organs. In contrast with most mucosal immunizations, the intracellular response persists for over two months after the last injection. This strongly suggests that further investigations of conserved key epitopes from various pathogens may lead to safe and chemically defined mucosal vaccines with synthetic peptides. These candidate vaccines with free peptides may be suitable for mass campaigns even in developing countries.

Anti-idiotypic antibody Ab2/3H6 mimics the epitope of the neutralizing anti-HIV-1 monoclonal antibody 2F5

Anti-idiotypic antibodies directed against potentially neutralizing anti-HIV-1 antibodies may mimic epitopes on gp41 otherwise cryptic to the immune system. This study reports the generation of murine monoclonal antibody Ab2/3H6 blocking the binding of human Ab1 2F5 to the synthetic epitope and to gp160 in an enzyme-linked immunosorbent competition assay. Ab2/2H6 diminished the neutralizing potency of 2F5 in an in-vitro neutralization assay. Ab2/3H6 Fab fragments were capable of inducing neutralizing immune and 2F5-specific responses in B6D2F1 mice applying a simple prime-boost regimen of immunization.

Intranasal inoculation of a recombinant influenza virus containing exogenous nucleotides in the NS segment induces mucosal immune response against the exogenous gene product in mice

To establish a mucosal vaccine system, we evaluated the immunogenicity of a recombinant influenza virus, designated NS2Acat, in which the chloramphenicol acetyltransferase (CAT) reporter gene is fused in frame to the NS1 gene in the NS gene segment. The NS2Acat replicated slightly within the lungs in BALB/c mice after intranasal administration, accompanying expression of the CAT and the viral HA mRNA. NS2Acat induced delayed-type hypersensitivity (DTH) and sensitized the CAT-specific T lymphocytes in the regional lymph nodes, which proliferated and synthesized several cytokines in vitro upon antigenic challenge. These results suggest that NS2Acat is capable of eliciting a respiratory immune response against the fused gene product.

Hyperattenuated recombinant influenza A virus nonstructural-protein-encoding vectors induce human immunodeficiency virus type 1 Nef-specific systemic and mucosal immune responses in mice

We have generated recombinant influenza A viruses belonging to the H1N1 and H3N2 virus subtypes containing an insertion of the 137 C-terminal amino acid residues of the human immunodeficiency virus type 1 (HIV-1) Nef protein into the influenza A virus nonstructural-protein (NS1) reading frame. These viral vectors were found to be genetically stable and capable of growing efficiently in embryonated chicken eggs and tissue culture cells but did not replicate in the murine respiratory tract. Despite the hyperattenuated phenotype of influenza/NS-Nef viruses, a Nef and influenza virus (nucleoprotein)-specific CD8(+)-T-cell response was detected in spleens and the lymph nodes draining the respiratory tract after a single intranasal immunization of mice. Compared to the primary response, a marked enhancement of the CD8(+)-T-cell response was detected in the systemic and mucosal compartments, including mouse urogenital tracts, if mice were primed with the H1N1 subtype vector and subsequently boosted with the H3N2 subtype vector. In addition, Nef-specific serum IgG was detected in mice which were immunized twice with the recombinant H1N1 and then boosted with the recombinant H3N2 subtype virus. These findings may contribute to the development of alternative immunization strategies utilizing hyperattenuated live recombinant influenza virus vectors to prevent or control infectious diseases, e.g., HIV-1 infection.

Viral vectors as potential HIV-1 vaccines

Vaccine vectors based on recombinant viruses have great promise to play an important role in the development of an effective HIV-1 vaccine. Within the last 10 years a wide range of viruses have been investigated for their ability to express protein(s) from foreign pathogens and to induce specific immunological responses against these antigen(s) in vivo. Each viral vector has its own unique biological characteristics and thus far none of them has proven to be an ideal candidate as a vaccine vehicle for HIV-1. This review focuses on both replication competent and non-replication competent viral vectors as a potential HIV-1 vaccine. Other approaches for the development of an HIV-1 vaccine are reviewed elsewhere and are beyond the scope of this review.

History of biotechnology in Austria

Austria has contributed significantly to the progress of the biotechnologies in the past and is actively engaged in doing so today. This review describes the early history of biotechnology in Austria, beginning with the Vienna process of baker's yeast manufacture in 1846, up to the achievements of the 20th century, e.g. the submerged vinegar process, penicillin V, immune biotechnology, biomass as a renewable source of fermentation products (power alcohol, biogas, organic acids etc.), biopulping, biopolymers, biocatalysis, mammalian cell technology, nanotechnology of bacterial surface layers, and environmental biotechnology.