Influenza virus-like particles as pandemic vaccines.

There is an urgent need to develop novel approaches for vaccination against emerging pathogenic avian influenza viruses as a priority for pandemic preparedness. Influenza virus-like particles (VLPs) have been suggested and developed as a new generation of non-egg-based cell culture-derived vaccine candidates against influenza infection. Influenza VLPs are formed by a self-assembly process incorporating structural proteins into budding particles composed of the hemagglutinin (HA), neuraminidase (NA) and M1 proteins, and may include additional influenza proteins such as M2. Animals vaccinated with VLPs were protected from morbidity and mortality resulting from lethal influenza infections. The protective mechanism of influenza VLP vaccines was similar to that of the currently licensed influenza vaccines inducing neutralizing antibodies and hemagglutination inhibition activities. Current studies demonstrate that influenza VLP approaches can be a promising alternative approach to developing a vaccine for pandemic influenza viruses. The first human clinical trial of a recombinant pandemic-like H5N1 influenza VLP vaccine was initiated in July 2007 (Bright et al., unpublished).

Epitopes recognized by antibodies to denatured core protein of hepatitis B virus.

Particulate and denatured core protein as well as e-antigen (HBe) of hepatitis B virus (HBV) differ in part immunologically but this has not been studied in sufficient detail. Therefore, in this study the B-cell immune response to native and denatured HBV core protein which both can exhibit HBe-specific epitopes was examined using a panel of mouse MABs and rabbit polyclonal antibodies to native and denatured core protein and polyclonal anti-HBe/anti-HBc antibodies from sera of infected patients. Epitope mapping was performed using a set of partially overlapping synthetic HBc peptides, carboxy-terminally truncated HBc proteins and various HBc fusion proteins. A major immunogenic region between amino acids 134-140 and two less immunogenic regions, one spanning amino acids 2-10 and one with three partially overlapping epitopes between amino acid positions 138 and 154, were defined by mouse MABs. Polyclonal rabbit antibodies to denatured HBc, woodchuck and ground squirrel hepatitis core proteins (WHc and GSHc) recognized similar epitopes but in addition occasionally region 61-85, and the latter was also recognized on particulate HBc. Two antigenic regions (amino acid positions 2-10 and 138-145) were found to be exposed on HBe from human serum, and were recognized by mouse anti-HBe but not by anti-HBc antibodies from sera of infected patients. This study demonstrates a more complex pattern of HBc and HBe epitopes than detected previously and provides tools to study conformational changes which may take place during HBc/HBe processing, transport and core particle assembly.

Anti-tumor effect of the alphavirus-based virus-like particle vector expressing prostate-specific antigen in a HLA-DR transgenic mouse model of prostate cancer.

The goal of this study was to determine if an alphavirus-based vaccine encoding human Prostate-Specific Antigen (PSA) could generate an effective anti-tumor immune response in a stringent mouse model of prostate cancer. DR2bxPSA F1 male mice expressing human PSA and HLA-DRB1(*)1501 transgenes were vaccinated with virus-like particle vector encoding PSA (VLPV-PSA) followed by the challenge with Transgenic Adenocarcinoma of Mouse Prostate cells engineered to express PSA (TRAMP-PSA). PSA-specific cellular and humoral immune responses were measured before and after tumor challenge. PSA and CD8 reactivity in the tumors was detected by immunohistochemistry. Tumor growth was compared in vaccinated and control groups. We found that VLPV-PSA could infect mouse dendritic cells in vitro and induce a robust PSA-specific immune response in vivo. A substantial proportion of splenic CD8 T cells (19.6 ± 7.4%) produced IFNγ in response to the immunodominant peptide PSA(65-73). In the blood of vaccinated mice, 18.4 ± 4.1% of CD8 T cells were PSA-specific as determined by the staining with H-2D(b)/PSA(65-73) dextramers. VLPV-PSA vaccination also strongly stimulated production of IgG2a/b anti-PSA antibodies. Tumors in vaccinated mice showed low levels of PSA expression and significant CD8+ T cell infiltration. Tumor growth in VLPV-PSA vaccinated mice was significantly delayed at early time points (p=0.002, Gehan-Breslow test). Our data suggest that TC-83-based VLPV-PSA vaccine can efficiently overcome immune tolerance to PSA, mediate rapid clearance of PSA-expressing tumor cells and delay tumor growth. The VLPV-PSA vaccine will undergo further testing for the immunotherapy of prostate cancer.

Subtype ayw variant of hepatitis B virus. DNA primary structure analysis.

The entire genome of human hepatitis B virus (HBV) occurring in Latvia was sequenced. This sequence, which is 3182 nucleotides long, was compared with the other previously published HBV genomes and was shown to share maximum homology with HBV subtype ayw DNA. The coordinates of 4 main open reading frames as well as hairpin structures are very well conserved in the two genomes. The distribution of nucleotide substitutions among different HBV genomes suggest that the open reading frames P and X can fulfil a coding function. On the basis of primary structure comparison for hepadnaviral DNAs several evolutionary conclusions can be drawn.

Recombinant core particles of hepatitis B virus exposing foreign antigenic determinants on their surface.

Insertion of foreign oligopeptide sequences (40-50 amino acids in length) into the Pro144 position of hepatitis B core antigen (HBcAg) leads to the formation of chimeric capsids in Escherichia coli cells. These capsids are morphologically and immunologically similar to native HBcAg, but expose the inserted oligopeptides on their outer surface and exhibit antigenic and immunogenic characteristics of the latter. As a source of model antigenic determinants, the appropriate DNA copies excised from cloned viral genes such as the pre-S region of hepatitis B virus, the transmembrane protein gp41 of human immunodeficiency virus 1 and the envelope protein gp51 of bovine leukemia virus have been used. The localization of the inserted antigenic determinants on the surface of chimeric capsids does not depend on the presence or absence of the arginine-rich, 39 amino acid-long C terminus of HBcAg.

Tetrapeptide QDPR is a minimal immunodominant epitope within the preS2 domain of hepatitis B virus.

A hepatitis B virus preS2 deletion library with the preS2 sequence fused to the coat protein of the RNA phage fr (fr CP) as a carrier has been constructed and used for the approximate localization of epitope recognized by a panel of murine monoclonal anti-preS2 antibodies. DNA copies of putative preS2 epitopes were synthesized and cloned within the fr CP gene. Tetrapeptide Gln-Asp-Pro-Arg (QDPR) corresponding to the preS (132-135) sequence was found to be the minimal sufficient recognition site for one of the monoclonal antibodies, S26. The closely related tetrapeptide EDPR did not mimic the epitope activity of QDPR.

[Genetically engineered mutants of the envelope protein of the RNA-containing bacteriophage]. / Gennoinzhenernye mutanty belka obolochki RNK-soderzhashchego bakteriofaga.

Expression of the coat protein gene of RNA bacteriophage fr in Escherichia coli cells leads to the formation of capsid-like structures of ca. 25 nm in diameter, which are immunologically indistinguishable from the native phage fr capsids. The modification strategy of the coat protein gene by gene engineering technique was developed in order to localize coat protein regions, which are exposed on the capsid surface and are capable to include foreign amino acid inserts without an appreciable effect on the capsid self-assembly. The oligonucleotide linkers, coding short amino acid sequences and bearing also convenient restriction sites, were synthesized and inserted into different regions of the coat protein gene. The mutant proteins, containing insertions of 2-12 amino acids in potentially exposed regions, were obtained. It was shown that N- and C-terminal insertions, as well as the insertion into codon 51 in the RNA-binding region, do not prevent the self-assembly. The regions (codons 96 and 112) were also revealed, insertions in them decreased drastically the protein yield as a consequence of a block in the self-assembly.

[Exposure of the major immunodominant epitope of the gp51 envelope protein of bovine leukosis virus on the surface of the hepatitis B core antigen capsid]. / Eksponirovanie mazhornogo immunodominantnogo épitopa obolochechnogo belka gp51 virusa leikoza krupnogo rogatogo skota na poverkhnosti kapsid kor-antigena virusa gepatita B.

Insertion of 48 amino acid long sequence of envelope protein gp51 of bovine leukemia virus (BLV), located from position 56 till 103 of mature protein, into Pro144 position of hepatitis B core antigen (HBcAg) leads to the formation of chimeric capsids. These capsids preserve morphology of intact HBcAg but expose on their outer surface BLV epitopes which are localised in the inserted gp51 fragment and responsible for the recognition of chimeras by monoclonal anti-gp51 antibodies MAK14. The anti-genicity of gp51 epitopes within chimeric capsids is not disturbed after shortening of C terminal part of inserted gp51 fragment by deletion of amino acids 73-103. The resulting chimeras show the same capsid-forming ability as well as HBcAg and gp51 antigenic properties.

Sequence variation in the capsid protein genes of human papillomavirus type 16.

We have cloned and sequenced the L1 and L2 genes from human papillomavirus type 16 (HPV16) DNA-containing cervical cytology samples collected from the U.K. and Trinidad. Samples containing high copy numbers of HPV16 DNA were selected as being likely to contain fully functional virus DNA molecules in an episomal state, rather than in an integrated and possibly altered state. In comparison with the previously published sequence of HPV16 isolated from an invasive cancer a variety of differences were detected in both L1 and L2. The pattern of changes appears to be different in samples from the two geographic regions. One of the differences (resulting in D at position 202 of the L1 protein) reported recently to be functionally important for virus particle assembly was found to occur in all the samples examined. Variations in L1 found within known immunoreactive regions or hydrophobic domains should be taken into account in design of prophylactic vaccines for HPV16 based on virus-like particles. All variations within L2 protein were found in hydrophilic domains in the carboxy-terminal half of L2. These positions were highly variable among other types of papillomavirus and are located outside the known L2 immunoreactive region.

Determination of the minimal length of preS1 epitope recognized by a monoclonal antibody which inhibits attachment of hepatitis B virus to hepatocytes.

The minimal amino acid sequence sufficient to be recognized efficiently by virus-attachment inhibiting murine monoclonal anti-preS1 antibody MA18/7 has been determined. We have constructed a recombinant gene library using the cloned coat protein gene of Escherichia coli RNA bacteriophage fr as a carrier. Different fragments of preS1 region from cloned hepatitis B virus (HBV) genomes, subtype ayw and adw, were inserted at position 2 of the 129 amino acid-long fr coat protein gene in the appropriate E. coli expression vectors. Fine mapping of preS1 epitope recognized by MA18/7 was accomplished by bidirectional shortening of the preS1 within original recombinant preS-fr coat protein genes with Bal31 exonuclease. Immunoblot analysis of the obtained recombinant protein library revealed that the tetrapeptide Asp-Pro-Ala-Phe (DPAF), located at the position preS(31-34) and conserved in all known HBV genomes, is sufficient to bind MA18/7 antibody. Recognition of the preS1 region by MA18/7 occurred irrespective of the amino acid context surrounding this DPAF tetrapeptide. Further shortening of this minimal epitope from the left or from the right side completely prevented antibody binding in immunoblots.

Marburg virus vaccines based upon alphavirus replicons protect guinea pigs and nonhuman primates.

Marburg virus (MBGV), for which no vaccines or treatments currently exist, causes an acute hemorrhagic fever with a high mortality rate in humans. We previously showed that immunization with either killed MBGV or a glycoprotein (GP) subunit prevented lethal infection in guinea pigs. In the studies reported here, an RNA replicon, based upon Venezuelan equine encephalitis (VEE) virus, was used as a vaccine vector; the VEE structural genes were replaced by genes for MBGV GP, nucleoprotein (NP), VP40, VP35, VP30, or VP24. Guinea pigs were vaccinated with recombinant VEE replicons (packaged into VEE-like particles), inoculated with MBGV, and evaluated for viremia and survival. Results indicated that either GP or NP were protective antigens while VP35 afforded incomplete protection. As a more definitive test of vaccine efficacy, nonhuman primates (cynomolgus macaques) were inoculated with VEE replicons expressing MBGV GP and/or NP. Three monkeys received packaged control replicons (influenza HA); these died 9 or 10 days after challenge, with typical MBGV disease. MBGV NP afforded incomplete protection, sufficient to prevent death but not disease in two of three macaques. Three monkeys vaccinated with replicons which expressed MBGV GP, and three others vaccinated with both replicons that expressed GP or NP, remained aviremic and were completely protected from disease.

Individual and bivalent vaccines based on alphavirus replicons protect guinea pigs against infection with Lassa and Ebola viruses.

Lassa and Ebola viruses cause acute, often fatal, hemorrhagic fever diseases, for which no effective vaccines are currently available. Although lethal human disease outbreaks have been confined so far to sub-Saharan Africa, they also pose significant epidemiological concern worldwide as demonstrated by several instances of accidental importation of the viruses into North America and Europe. In the present study, we developed experimental individual vaccines for Lassa virus and bivalent vaccines for Lassa and Ebola viruses that are based on an RNA replicon vector derived from an attenuated strain of Venezuelan equine encephalitis virus. The Lassa and Ebola virus genes were expressed from recombinant replicon RNAs that also encoded the replicase function and were capable of efficient intracellular self-amplification. For vaccinations, the recombinant replicons were incorporated into virus-like replicon particles. Guinea pigs vaccinated with particles expressing Lassa virus nucleoprotein or glycoprotein genes were protected from lethal challenge with Lassa virus. Vaccination with particles expressing Ebola virus glycoprotein gene also protected the animals from lethal challenge with Ebola virus. In order to evaluate a single vaccine protecting against both Lassa and Ebola viruses, we developed dual-expression particles that expressed glycoprotein genes of both Ebola and Lassa viruses. Vaccination of guinea pigs with either dual-expression particles or with a mixture of particles expressing Ebola and Lassa virus glycoprotein genes protected the animals against challenges with Ebola and Lassa viruses. The results showed that immune responses can be induced against multiple vaccine antigens coexpressed from an alphavirus replicon and suggested the possibility of engineering multivalent vaccines based upon alphavirus vectors for arenaviruses, filoviruses, and possibly other emerging pathogens.

Synthesis and assembly of virus-like particles of human papillomaviruses type 6 and type 16 in fission yeast Schizosaccharomyces pombe.

We have synthesized capsid proteins of human papillomavirus types 6 (HPV 6) and 16 (HPV 16) in fission yeast Schizosaccharomyces pombe and produced virus-like particles (VLP). The capsid proteins were localized in the nucleus by indirect immunofluorescence and cell fractionation analyses. The VLP were produced in both yeast clones synthesizing L1 alone and L/L2 and purified by sulfato-cellulofine chromatography. Electron microscopic examination showed that these VLP were similar in structure to native HPV particles. Two HPV 16 L1 variants (16 B27L1 and 16 T3L1), isolated from benign cervical samples, produced many more (68- and 14-fold) VLP than the prototype L1 (16 PL1) derived from cervical carcinoma. Coexpression of the HPV 6 L2 protein with 6 L1 and 16 B27L1 proteins increased the production level of the VLP four- and twofold, respectively. The L2 was not detected in the VLP purified with sulfato-cellulofine column, although the L2 was purified in the same fraction containing HPV 6 and 16 B27-VLP by size-fractionation using Sepharose column. Interaction between 6 L2 and 6/16 L1 proteins was not detected by the coimmunoprecipitation assays with either L1 or L2 antibodies. These results suggest that the L2 is not incorporated into the VLP synthesized in yeast.

Identification of hepatitis B virus core protein regions exposed or internalized at the surface of HBcAg particles by scanning with monoclonal antibodies.

Hepatitis B virus (HBV) core antigen (HBcAg) particles purified from Escherichia coli were probed in a competition enzyme immunoassay (EIA) with a panel of 16 murine monoclonal antibodies (MAbs) directed to different forms of core protein. The linear binding sites of the MAbs were mapped by combination of solid-phase and competition EIA using synthetic peptides covering the complete sequence of HBV core protein. Relative accessibilities of the linear binding sites at the HBcAg surface were investigated by comparing reactivities in solution of the MAbs to (i) two genetic variants of particulate HBcAg, (ii) denatured core protein, and (iii) synthetic peptides mimicking the appropriate linear binding sites. Further, accessibilities of HBV preS1 and preS2 epitopes (introduced into core protein at positions 77 or 144) at the surface of chimeric HBcAg particles were investigated. The previously described surface localization of core protein region 78-83 at the core particle surface was confirmed. In addition, another region, encompassing residues 127-133, was found to occupy a surface position at particulate HBcAg, whereas regions 9-20 and 133-145 were exposed after denaturation of the core protein and at synthetic peptides but not at particulate HBcAg.

Analysis of RNA phage fr coat protein assembly by insertion, deletion and substitution mutagenesis.

A structure-function analysis of the icosahedral RNA bacteriophage fr coat protein (CP) assembly was undertaken using linker-insertion, deletion and substitution mutagenesis. Mutations were specifically introduced into either pre-existing or artificially created restriction enzyme sites within fr CP gene expressed in Escherichia coli from a recombinant plasmid. This directs synthesis of wild type protein that undergoes self-assembly and forms capsid-like particles indistinguishable morphologically and immunologically from native phage particles. A series of fr CP variants containing sequence alterations in the regions which are (i) exposed on the external surface of capsid or (ii) located on the contacting areas between CP subunits were obtained and their assembly properties investigated. The majority of mutants demonstrated reduction of assembly ability and formed either CP dimers (mutations at residues 2, 10, 63 or 129) or both dimer and capsid structures (residue 2 or 69). The exceptions were variants demonstrating normal assembly and containing insertions at residues 2, 50 or 129 of the fr CP. A third type of assembled structure was formed by a variant with a single amino acid substitution I104T. The alpha A-helix region (residues 97-111) is particularly sensitive to mutation and any alteration in this region decreases accumulation of mutant protein in E. coli. The relative contributions of particular fr CP domains in maintenance of capsid structural integrity as well as the possible capsid assembly mechanism are discussed.

Candidate vaccine against botulinum neurotoxin serotype A derived from a Venezuelan equine encephalitis virus vector system.

A candidate vaccine against botulinum neurotoxin serotype A (BoNT/A) was developed by using a Venezuelan equine encephalitis (VEE) virus replicon vector. This vaccine vector is composed of a self-replicating RNA containing all of the VEE nonstructural genes and cis-acting elements and also a heterologous immunogen gene placed downstream of the subgenomic 26S promoter in place of the viral structural genes. In this study, the nontoxic 50-kDa carboxy-terminal fragment (H(C)) of the BoNT/A heavy chain was cloned into the replicon vector (H(C)-replicon). Cotransfection of BHK cells in vitro with the H(C)-replicon and two helper RNA molecules, the latter encoding all of the VEE structural proteins, resulted in the assembly and release of propagation-deficient, H(C) VEE replicon particles (H(C)-VRP). Cells infected with H(C)-VRP efficiently expressed this protein when analyzed by either immunofluorescence or by Western blot. To evaluate the immunogenicity of H(C)-VRP, mice were vaccinated with various doses of H(C)-VRP at different intervals. Mice inoculated subcutaneously with H(C)-VRP were protected from an intraperitoneal challenge of up to 100,000 50% lethal dose units of BoNT/A. Protection correlated directly with serum enzyme-linked immunosorbent assay titers to BoNT/A. The duration of the immunity achieved was tested at 6 months and at 1 year postvaccination, and mice challenged at these times remained refractory to challenge with BoNT/A.

Replicon-helper systems from attenuated Venezuelan equine encephalitis virus: expression of heterologous genes in vitro and immunization against heterologous pathogens in vivo.

A replicon vaccine vector system was developed from an attenuated strain of Venezuelan equine encephalitis virus (VEE). The replicon RNA consists of the cis-acting 5' and 3' ends of the VEE genome, the complete nonstructural protein gene region, and the subgenomic 26S promoter. The genes encoding the VEE structural proteins were replaced with the influenza virus hemagglutinin (HA) or the Lassa virus nucleocapsid (N) gene, and upon transfection into eukaryotic cells by electroporation, these replicon RNAs directed the efficient, high-level synthesis of the HA or N proteins. For packaging of replicon RNAs into VEE replicon particles (VRP), the VEE capsid and glycoproteins were supplied in trans by expression from helper RNA(s) coelectroporated with the replicon. A number of different helper constructs, expressing the VEE structural proteins from a single or two separate helper RNAs, were derived from attenuated VEE strains Regeneration of infectious virus was not detected when replicons were packaged using a bipartite helper system encoding the VEE capsid protein and glycoproteins on two separate RNAs. Subcutaneous immunization of BALB/c mice with VRP expressing the influenza HA or Lassa virus N gene (HA-VRP or N-VRP, respectively) induced antibody responses to the expressed protein. After two inoculations of HA-VRP, complete protection against intranasal challenge with influenza was observed. Furthermore, sequential immunization of mice with two inoculations of N-VRP prior to two inoculations of HA-VRP induced an immune response to both HA and N equivalent to immunization with either VRP construct alone. Protection against influenza challenge was unaffected by previous N-VRP immunization. Therefore, the VEE replicon system was characterized by high-level expression of heterologous genes in cultured cells, little or no regeneration of plaque-forming virus particles, the capability for sequential immunization to multiple pathogens in the same host, and induction of protective immunity against a mucosal pathogen.

Recombinant RNA replicons derived from attenuated Venezuelan equine encephalitis virus protect guinea pigs and mice from Ebola hemorrhagic fever virus.

RNA replicons derived from an attenuated strain of Venezuelan equine encephalitis virus (VEE), an alphavirus, were configured as candidate vaccines for Ebola hemorrhagic fever. The Ebola nucleoprotein (NP) or glycoprotein (GP) genes were introduced into the VEE RNA downstream from the VEE 26S promoter in place of the VEE structural protein genes. The resulting recombinant replicons, expressing the NP or GP genes, were packaged into VEE replicon particles (NP-VRP and GP-VRP, respectively) using a bipartite helper system that provided the VEE structural proteins in trans and prevented the regeneration of replication-competent VEE during packaging. The immunogenicity of NP-VRP and GP-VRP and their ability to protect against lethal Ebola infection were evaluated in BALB/c mice and in two strains of guinea pigs. The GP-VRP alone, or in combination with NP-VRP, protected both strains of guinea pigs and BALB/c mice, while immunization with NP-VRP alone protected BALB/c mice, but neither strain of guinea pig. Passive transfer of sera from VRP-immunized animals did not confer protection against lethal challenge. However, the complete protection achieved with active immunization with VRP, as well as the unique characteristics of the VEE replicon vector, warrant further testing of the safety and efficacy of NP-VRP and GP-VRP in primates as candidate vaccines against Ebola hemorrhagic fever.