Nucleocapsid-like particles of dengue-2 virus enhance the immune response against a recombinant protein of dengue-4 virus

In this study, we evaluate in mice a novel formulation containing nucleocapsid-like particles of dengue-2 virus (recNLP) co-immunized with a chimeric protein composed of the dengue-4 envelope domain III fused twice within the meningococcal P64k protein of Neisseria meningitidis (PD24). The animals receiving the PD24–recNLP mixture showed the highest levels of antiviral antibodies. Similar results were obtained for IFNγ secretion levels, indicating a functional Th1 cellular response. Consistently, the percentage of mice surviving after viral challenge was significantly higher for those immunized with the mixture than for those inoculated with PD24 protein alone. In addition, in vivo depletion experiments demonstrated the decisive role of CD4⁺ and CD8⁺ cells in the protection conferred by immunization with PD24–recNLP. In conclusion, this report demonstrates for the first time the adjuvant capacity of dengue-2 virus recNLP. Additionally, the evidence presented highlights the potential of these particles for enhancing the immune response against heterologous recombinant proteins.     

Purified and highly aggregated chimeric protein DIIIC-2 induces a functional immune response in mice against dengue 2 virus

It was previously reported that DIIIC-2 (a fusion protein composed of domain III of the envelope protein and the capsid protein from dengue 2 virus), as an aggregate antigen from a partially purified preparation, induced a functional protective immune response against dengue 2 virus in the mouse encephalitis model. In the present work, a purification procedure was developed for DIIIC-2, and soluble and aggregated fractions of the purified protein were characterized and evaluated in mice. The purification process rendered a protein preparation of 91 % purity, and the remaining 9 % consisted of fragments and aggregates of the same recombinant protein. After the in vitro aggregation process, upon addition of oligodeoxynucleotides, 80 % of the protein formed aggregates, whereas 20 % remained as soluble protein. An immunological evaluation revealed the proper immunogenicity of the aggregated purified protein in terms of induction of antiviral and neutralizing antibodies, cell-mediated immunity and protection upon dengue 2 virus challenge in the mouse encephalitis model. Based on these results, we can assert that the purified protein DIIIC-2 is functional and could be used for further scalable steps and preclinical studies in non-human primates.     

A novel fusion protein domain III-capsid from dengue-2, in a highly aggregated form, induces a functional immune response and protection in mice

Based on the immunogenicity of domain III from the Envelope protein of dengue virus as well as the proven protective capacity of the capsid antigen, we have designed a novel domain III-capsid chimeric protein with the goal of obtaining a molecule potentially able to induce both humoral and cell-mediated immunity (CMI). After expression of the recombinant gene in Escherichia coli, the domain III moiety retained its antigenicity as evaluated with anti-dengue sera. In order to explore alternatives for modulating the immunogenicity of the protein, it was mixed with oligodeoxynucleotides in order to obtain particulated aggregates and then immunologically evaluated in mice in comparison with non-aggregated controls. Although the humoral immune response induced by both forms of the protein was equivalent, the aggregated variant resulted in a much stronger CMI as measured by in vitro IFN-γ secretion and protection experiments, mediated by CD4⁺ and CD8⁺ cells. The present work provides additional evidence in support for a crucial role of CMI in protection against dengue virus and describes a novel vaccine candidate against the disease based on a recombinant protein that can stimulate both arms of the acquired immune system.     

A hemagglutinin-based multipeptide construct elicits enhanced protective immune response in mice against influenza A virus infection

Multipeptide constructs, comprising adjacent sequences of the 317–341 intersubunit region of immature influenza A hemagglutinin (H1N1), were designed and the functional properties of these branched peptides were compared to that of the corresponding linear peptides. In vivo studies revealed that the immunogenicity of the peptides was dependent on the presence of the hydrophobic fusion peptide (comprised in FP3), encompassing the N-terminal 1–13 sequence of the HA2 subunit. Antibody and T cell recognition, however, was directed against the 317–329 HA1 sequence, comprised in the P4 peptide. Multiple copies of P4, covalently linked by branched lysine residues, significantly enhanced the efficiency of antibody binding and the capacity of peptides to elicit B- and T-cell responses. A fraction of peptide induced antibodies reacted with immature or with proteolitically cleaved hemagglutinin (HA) molecules pretreated at low pH. Immunization with a multipeptide construct, (P4)₄–FP3, not only resulted in elevated antibody and T cell responses but conferred enhanced protection against lethal A/PR/8/34 (H1N1) infection as compared to its subunit peptides. The beneficial functional properties of this artificial peptide antigen may be acquired by multiple properties including: (i) stabilized peptide conformation which promotes strong, polyvalent binding to both antibodies and MHC class II molecules; (ii) appropriate P4 conformation for antibody recognition stabilized by the covalently coupled fusion peptide, resulting in the production of virus cross reactive antibodies which inhibit the fusion activity of the virus; (iii) activation of peptide specific B cells which potentiate antigen presentation and peptide specific T cell responses; and (iv) generation of helper T cells which secrete lymphokines active in the resolution of infection.     

Segments of puumala hantavirus nucleocapsid protein inserted into chimeric polyomavirus-derived virus-like particles induce a strong immune response in mice

Insertion of a short-sized epitope at four different sites of yeast-expressed hamster polyomavirus major capsid protein VP1 has been found to result in the formation of chimeric virus-like particles. Here, we demonstrate that the insertion of 45 or 120 amino acid-long segments from the N-terminus of Puumala hantavirus nucleocapsid protein into sites 1 (amino acids 80-89) and 4 (amino acids 288-295) of VP1 allowed the highly efficient formation of virus-like particles. In contrast, expression level and assembly capacity of fusions to sites 2 (amino acids 222-225) and 3 (amino acids 243-247) were drastically reduced. Immunization of BALB/c mice with chimeric virus-like particles induced a high-titered antibody response against the hantavirus nucleocapsid protein, even in the absence of any adjuvant. The strongest response was observed in mice immunized with virus-like particles harboring 120 amino acids of hantavirus nucleocapsid protein. According to the immunoglobulin subclass distribution of nucleocapsid protein-specific antibodies a mixed Th1/Th2 response was detected. The VP1 carrier itself also induced a mixed Th1/Th2 response, which was found to be reduced in mice immunized with virus-like particles harboring 120 amino acid-long inserts. In conclusion, hamster polyomavirus VP1 represents a promising carrier moiety for future vaccine development.     

Identification of Toxoplasma gondii protein fractions induce immune response against melanoma in mice

Dendritic cells (DCs) play a crucial role in the initiation of adaptive immune responses against tumor cells. We recently found that protein components of Toxoplasma gondii (T. gondii) could mature DCs efficiently. Therefore, in this study, we aimed to find the most effective protein components of T. gondii which are able to mature DCs and consequently instruct immune responses in tumor‐bearing mice. Soluble tachyzoite antigens (STAgs) were fractionated by ammonium sulfate precipitation and subsequently by anion‐exchange HPLC. Immature DCs (iDCs) were treated by these protein fractions and were monitored for IL‐12p70 and IL‐10 production. Moreover, the capacity of mature DCs (mDCs) to induce lymphocyte proliferation was investigated. Ultimately, we analyzed the ability of mDCs in instructing immune responses in tumor‐bearing mice. We found that ammonium sulfate fraction one (A1) matured‐DCs produced higher IL‐12 level and IL‐12/IL‐10 ratio; therefore, this fraction was selected for further fractionation by anion‐exchange HPLC. The results showed that anion‐exchange HPLC fraction 14 (C14) matured‐DCs secrete higher levels of IL‐12p70 and IL‐12p70/IL‐10 ratio. Survival of the mice matured by A1 fraction increased significantly compared to other groups. Moreover, SDS‐PAGE electrophoresis showed that different obtained fractions have distinct proteins based on their size. These results demonstrate that two protein fractions of T. gondii are able to mature DCs more efficient.     

Protective efficacy in mice of a secreted form of recombinant dengue-2 virus envelope protein produced in baculovirus infected insect cells

Summary We constructed a recombinant baculovirus encoding a dengue (DEN)-2 virus envelope glycoprotein truncated of 102 amino acids (aa) at its C-terminus (D2E102). The production, processing and transportation of the recombinant protein in baculovirus-infectedSpodoptera frugiperda (Sf9) cells and its immunogenic properties in mice were compared to those of a previously characterized recombinant DEN-2 E-protein with a 71aa C-terminal truncation (D2E71). Both proteins were transported through the Golgi complex and their N-oligosaccharides of the high man-nose type were processed to the complex mannose type. D2E102 transited to the plasma membrane and was secreted whereas D2E71 presumably remained associated with the plasma membrane. The reactivities of the recombinant proteins with neutralizing monoclonal antibodies were similar. Both intracellular and extracellular D2E102 induced neutralizing antibodies in mice and were thus immunogenic. The level of protective immunity to DEN-2 virus encephalitis challenge in mice vaccinated with intracellular D2E102 (80%, p<0.01) was lower than that induced with D2E71 (90%, P<0.001). Sixty-eight percent (P<0.001) of mice vaccinated with 5 µg of extracellular D2E102 protein were protected against lethal challenge.     

Long-lasting protective immune response to the 19-kilodalton carboxy-terminal fragment of Plasmodium yoelii merozoite surface protein 1 in mice

Merozoite surface protein 1 (MSP1) is the major protein on the surface of the plasmodial merozoite, and its carboxy terminus, the 19-kDa fragment (MSP1(19)), is highly conserved and effective in induction of a protective immune response against malaria parasite infection in mice and monkeys. However, the duration of the immune response has not been elucidated. As such, we immunized BALB/c mice with a standard four-dose injection of recombinant Plasmodium yoelii MSP1(19) formulated with Montanide ISA51 and CpG oligodeoxynucleotide (ODN) and monitored the MSP1(19)-specific antibody levels for up to 12 months. The antibody titers persisted constantly over the period of time without significant waning, in contrast to the antibody levels induced by immunization with Freund's adjuvant, where the antibody levels gradually declined to significantly lower levels 12 months after immunization. Investigation of immunoglobulin G (IgG) subclass longevity revealed that only the IgG1 antibody level (Th2 type-driven response) decreased significantly by 6 months, while the IgG2a antibody level (Th1 type-driven response) did not change over the 12 months after immunization, but the boosting effect was seen in the IgG1 antibody responses but not in the IgG2a antibody responses. After challenge infection, all immunized mice survived with negligibly patent parasitemia. These findings suggest that protective immune responses to MSP1(19) following immunization using oil-based Montanide ISA51 and CpG ODN as an adjuvant are very long-lasting and encourage clinical trials for malaria vaccine development.     

A tetravalent dengue vaccine containing a mix of domain III-P64k and domain III-capsid proteins induces a protective response in mice

Recombinant fusion proteins containing domain III of the dengue virus envelope protein fused to the P64k protein from Neisseria meningitidis and domain III of dengue virus type 2 (D2) fused to the capsid protein of this serotype were immunogenic and conferred protection in mice against lethal challenge, as reported previously. Combining the domain III-P64k recombinant proteins of dengue virus types 1, 3 and 4 (D1, D3, and D4) with the domain III-capsid protein from D2, we obtained a novel tetravalent formulation containing different antigens. Here, the IgG and neutralizing antibody response, the cellular immune response, and the protective capacity against lethal challenge in mice immunized with this tetravalent formulation were evaluated. The neutralizing antibody response obtained against D1, D2 and D3, together with the high levels of IFNγ secretion induced after stimulation with the four dengue serotypes, supports the strategy of using a new tetravalent formulation containing domain III of the envelope protein fused to the capsid protein of each dengue virus serotype.     

A recombinant 15-kilodalton carboxyl-terminal fragment of Plasmodium yoelii yoelii 17XL merozoite surface protein 1 induces a protective immune response in mice.

Since the developmental stages of malarial parasites which replicate within erythrocytes are responsible for the morbidity and mortality associated with this disease, antigens produced by these stages have been proposed as candidates for a vaccine. One surface protein of merozoites (MSP-1) has been shown to immunize both rodents and primates against virulent challenge infection in experimental systems. However, little is known of relevant epitopes on the molecule, and attempts to obtain recombinant MSP-1 polypeptides in a native configuration have proven difficult. We have found that the cysteine-rich, carboxyl-terminal region of the MSP-1 protein from the rodent malarial parasite Plasmodium yoelii yoelii can be expressed in a native configuration as a fusion protein in Escherichia coli. This recombinant polypeptide containing 15 kDa of the predicted 197-kDa protein elicits antibodies in mice which recognize the native parasite MSP-1. Most significantly, both inbred and outbred mice immunized with the fusion protein in Ribi adjuvant are partially and in some cases completely protected against challenge infection with an otherwise lethal parasite strain. This is the first observation of such significant protection obtained with a small portion of the MSP-1 produced in recombinant systems.     

Adjuvant modulation of the immune response of mice against the LcrE protein of Chlamydophila pneumoniae

LcrE protein is a TTSS component of Chlamydophila pneumoniae. The immunogenicity and protective effect of recombinant LcrE protein combined either with Freund's or Alum adjuvant were investigated in mice. The immunization with both protocols resulted in a significant reduction of the number of viable C. pneumoniae in the lungs after challenge. Lower IgG2a/IgG1 ratio in Alum-immunized mice suggested a shift towards Th2 type immune response, but the presence of LcrE-specific IFN-γ-producing cells in LcrE+Alum-immunized mice also indicates Th1 type response. LcrE-specific IgA level was higher in both the sera and the lungs after using Freund's adjuvant. Phenotype of LcrE-specific IFN-γ-producing cells was CD4+ in Alum- and Freund's-immunized mice, but CD8+ cells were also detected in Freund's-immunized mice.These results confirm that LcrE induces protective immunity in mice. The results also show that Alum is able to activate the CD4+ cell-based cellular immunity, thus it can be regarded as an alternative adjuvant during vaccine screening and a useful adjuvant in a potential protein vaccine against C. pneumoniae infection.     

The effect of the carrier protein on the immune response and on the induction of tolerance in mice to the 2,4-dinitrophenyl determinant

The role of the protein carrier on the primary and anamnestic response to the 2,4-dinitrophenyl (DNP) determinant was studied in randombred ICR and in an inbred BALB/c AnNIcr strain of mice. It was found that the level of the response was related to the immunogenicity of the carrier molecule. Mouse γ-globulin (MGG) was the most effective carrier for inducing tolerance to DNP regardless of the route of administration, while only occasional tolerance was achieved with the highly immunogenic haemocyanin. When human γ-globulin (HGG) served as a carrier, hyporesponsiveness to the DNP group was induced in the majority of neonate and adult mice when injected intraperitoneally, while an immune response ensued when the antigen was incorporated in adjuvant and injected into the footpads. Conversely, the most effective carrier for immunization against the DNP determinant was haemocyanin, while little immunity against either DNP or the protein carrier resulted from immunization with DNP—MGG. The antibody response of the mice when measured by the passive tanned haemagglutinating test was directed mostly against the hapten carrier complex and the protein carrier rather than the DNP-determinant alone, regardless of the initial route of administration. In contrast to the results obtained in vitro, the antibody responsible for the PCA reaction in mice is directed exclusively against the hapten and the hapten—protein conjugate but not against the protein carrier.     

Evaluation of transferrin-binding protein 2 within the transferrin-binding protein complex as a potential antigen for future meningococcal vaccines.

Because the meningococcal transferrin receptor was shown to elicit bactericidal and protective antibodies in laboratory animals, we undertook a study of the protective role of each of the polypeptides within the Tbp1-Tbp2 complex. We developed a procedure to purify from Neisseria meningitidis B16B6 the two proteins in milligram amounts and raised specific antisera in rabbits and mice. Only antisera specific for Tbp2 displayed bactericidal activity against the parent strain. Mice immunized with purified Tbp2 survived a lethal challenge to a similar degree as animals immunized with the Tbp1-Tbp2 complex, demonstrating that Tbp2 played an important role in the protective activity observed with the complex. Both Tbp1- and Tbp2-specific antisera inhibited transferrin binding to the purified receptor in a solid-phase binding assay, suggesting that the antibodies were able to interact with the Tbp1 molecule only when it was removed from its membrane environment. Finally, Tbp2-specific immunoglobulins were able to lower the growth rate of the meningococci when human transferrin was their sole iron source. Therefore, in all four different systems tested, Tbp2 or antibodies specific for Tbp2 displayed biological characteristics close to those of the Tbp1-Tbp2 complex. This suggests that Tbp2 plays an important role in the protective activity of the complex, eliciting antibodies that are not only bactericidal but also inhibitory for meningococcal growth.     

Adaptive immune response to Shigella flexneri 2a cydC in immunocompetent mice and mice lacking immunoglobulin A

Shigella flexneri cydC, which is deficient in cytochrome bd, was rapidly cleared from the lungs of intranasally inoculated mice and was Sereny negative, yet it induced 93% protection against challenge with wild-type S. flexneri. Mice that lack immunoglobulin A (IgA) were fully protected, suggesting that IgA may not be required for adaptive immunity in this model system.     

Virus-specific immune response in the lungs of mice infected with influenza virus.

The time course of primary humoral immune response in NFS/N mice infected with the adapted influenza virus A/Aichi 2/68(H3N2) was followed by determination of the different class immunoglobulins in lungs, lung washings, and in blood serum. The quantity of antibody-producing cells (APC) was estimated by local haemolysis in gel. The presence of antibodies in serum and lavage fluid was tested by the methods of radial haemolysis and radial immunodiffusion. It was shown that the local immune response had developed earlier than systemic antibodies occurred in the serum.     

Structural and functional complexity of the humoral response against the Trypanosoma cruzi ribosomal P2 beta protein in patients with chronic Chagas' heart disease

High levels of antibodies against the C-terminus of the Trypanosoma cruzi TcP2 beta ribosomal protein, defined by the peptide EEEDDDMGFGLFD, named R13, have been measured in sera from patients with chronic Chagas' Heart Disease (cChHD). These antibodies also recognize an epitope on the second extracellular loop of the beta 1-adrenergic receptor, inducing a functional response on cardiomyocytes. The aim of this study was to gain novel insights into the structural basis of this cross-reactivity as well as to evaluate the origin of anti-M2- cholinergic receptor antibodies, which are also commonly found in cChHD patients. To address these questions we immunopurified anti-R13 antibodies and studied the structural requirements of epitope recognition. Results showed that the immunopurified antibodies recognized a conformation of R13 in which the third Glu residue was essential for binding, explaining their low affinity for the mammalian homologue (peptide H13: EESDDDMGFGLFD). Alanine mutation scanning showed individual variations in epitope recognition in each of the studied patients. The importance of a negatively charged residue at position 3 for the recognition of anti-R13 antibodies was further confirmed by competition experiments using a Ser3-phosphorylated H13 analogue, which had 10 times more affinity for the anti-R13 antibody than the native H13 peptide. Moreover, anti-R13 antibodies stimulated either the beta 1-adrenergic or the M2-cholinergic receptor, in strict agreement with the functional properties of the IgG fractions from which they derived, demonstrating that the same parasite antigen may generate antibody specificities with different functional properties. This may be a clue to explain the high variability of electrophysiological disturbances found in cChHD.     

Immunogenicity of a truncated enterovirus 71 VP1 protein fused to a Newcastle disease virus nucleocapsid protein fragment in mice

Enterovirus 71 (EV71) is one of the viruses that cause hand, foot and mouth disease. Its viral capsid protein 1 (VP1), which contains many neutralization epitopes, is an ideal target for vaccine development. Recently, we reported the induction of a strong immune response in rabbits to a truncated VP1 fragment (Nt-VP1t) displayed on a recombinant Newcastle disease virus (NDV) capsid protein. Protective efficacy of this vaccine, however, can only be tested in mice, since all EV71 animal models thus far were developed in mouse systems. In this study, we evaluated the type of immune responses against the protein developed by adult BALB/c mice. Nt-VP1t protein induced high levels of VP1 IgG antibody production in mice. Purified VP1 antigen stimulated activation, proliferation and differentiation of splenocytes harvested from these mice. They also produced significant levels of IFN-γ, a Th1-related cytokine. Taken together, Nt-VP1t protein is a potent immunogen in adult mice and our findings provide the data needed for testing of its protective efficacy in mouse models of EV71 infections.     

Effects of a Th1- versus a Th2-biased immune response in protection against Helicobacter pylori challenge in mice

The roles that T helper type 1 (Th1) and T helper type 2 (Th2) Helicobacter pylori-specific immune responses play in protection from H. pylori challenge are poorly understood. It is expected that Th2 immune responses are required for protection against extracellular bacteria, such as H. pylori. However, recent studies have suggested that Th1 immunity is required for protection. The mechanisms by which this might occur are unknown. Our goal in this study was to more clearly define the effects of a Th1- versus a Th2-promoting H. pylori vaccine on immunity and protection. Therefore, we tested a Th1 vaccine consisting of an H. pylori sonicate and CpG oligonucleotides (CpG) and a Th2 vaccine consisting of a lipopolysaccharide (LPS)-depleted H. pylori sonicate combined with cholera toxin (CT). We demonstrate that although the Th2-promoting vaccine induced stronger systemic and local immune responses, only the Th1-promoting vaccine was protective.     

The VR2 epitope on the PorA P1.7-2,4 protein is the major target for the immune response elicited by the strain-specific group B meningococcal vaccine MeNZB

A protracted epidemic of group B meningococcal disease in New Zealand led to the testing of a strain-specific tailor-made vaccine, MeNZB. Immunogenicity levels achieved during age group trials enabled New Zealand's regulatory authority to grant licensure to deliver MeNZB to all individuals under age 20. During the trials target strains for serum bactericidal antibody measurements included the vaccine target strain NZ98/254 and two comparator epidemic-type strains (NZ94/167 and NZ02/09). In this study, 12 other strains differing variously from the vaccine strain by their capsular group, PorB type, and PorA variable region specificities, or PorA expression, were used as target strains. The PorA specificity of the serum bactericidal antibody responses to the vaccine was determined for 40 vaccinees. Sets of 10 pre- and postvaccination sera were chosen randomly from the young infant, older infant, toddler, and school-age group trials. Antibody recognition of linearized PorA proteins was also determined using immunoblotting. Across all age groups vaccine-induced serum bactericidal antibodies specifically targeted the VR2 P1.4 epitope of the PorA P1.7-2,4 protein irrespective of the PorB type and/or capsular type of the target strain. Deletion of amino acids within the VR2 epitope or replacement of the epitope through genetic exchange allowed strains variously to resist antibody-directed complement-mediated lysis and negated PorA-specific antibody recognition in immunoblots. The demonstration that the immunodominant antibody response was specifically for the VR2 P1.4 epitope of the PorA protein supports the public health decision to use a strain-specific vaccine for the control of New Zealand's epidemic of meningococcal disease.