Virus-like particles: passport to immune recognition

Multiepitope peptide-loaded virus-like particles as a vaccine against hepatitis B virus-related hepatocellular carcinoma

To develop a hepatitis B virus (HBV) therapeutic vaccine that can induce a broad but specific immune response and significant antitumor effects both in vivo and in vitro, we inserted HBV X protein (HBx)-derived epitopes HBx(52-60), HBx(92-100), and HBx(115-123); a novel subdominant cytolytic T lymphocyte (CTL) epitope HBx(140-148); and the universal T helper epitope pan human leukocyte antigen DR-binding epitope into HBV core protein to form multiepitope peptide-loaded virus-like particles (VLPs). CTL responses against epitope-loaded VLPs were elicited by priming with VLP-pulsed dendritic cells in both HLA-A*0201 transgenic (Tg) mice and peripheral blood lymphocytes from HLA-A2(+)/HBx(+) HBV-infected hepatocellular carcinoma (HCC) patients. The multiepitope peptide-loaded VLPs demonstrated significantly higher immunogenicity in Tg mice than any single responsive epitope. Significant antitumor effects were demonstrated both with primary cultured autologous HCC cells in vitro and tumor-bearing Tg mice in vivo in an HLA-A2-restricted and epitope-specific fashion.

CONCLUSION

The significant antitumor effects both in vivo and in vitro demonstrate the potential of multiepitope peptide-loaded VLPs as a vaccine against HCC.

Simple high-cell density fed-batch technique for high-level recombinant protein production with Pichia pastoris: Application to intracellular production of Hepatitis B surface antigen

Background

Hepatitis B is a serious global public health concern. Though a safe and efficacious recombinant vaccine is available, its use in several resource-poor countries is limited by cost. We have investigated the production of Hepatitis B virus surface antigen (HBsAg) using the yeast Pichia pastoris GS115 by inserting the HBsAg gene into the alcohol oxidase 1 locus.

Results

Large-scale production was optimized by developing a simple fed-batch process leading to enhanced product titers. Cells were first grown rapidly to high-cell density in a batch process using a simple defined medium with low salt and high glycerol concentrations. Induction of recombinant product synthesis was carried out using rather drastic conditions, namely through the addition of methanol to a final concentration of 6 g L^-1. This methanol concentration was kept constant for the remainder of the cultivation through continuous methanol feeding based on the on-line signal of a flame ionization detector employed as methanol analyzer in the off-gas stream. Using this robust feeding protocol, maximum concentrations of ~7 grams HBsAg per liter culture broth were obtained. The amount of soluble HBsAg, competent for assembly into characteristic virus-like particles (VLPs), an attribute critical to its immunogenicity and efficacy as a hepatitis B vaccine, reached 2.3 grams per liter of culture broth.

Conclusion

In comparison to the highest yields reported so far, our simple cultivation process resulted in an ~7 fold enhancement in total HBsAg production with more than 30% of soluble protein competent for assembly into VLPs. This work opens up the possibility of significantly reducing the cost of vaccine production with implications for expanding hepatitis B vaccination in resource-poor countries.

Host responses from innate to adaptive immunity after vaccination: molecular and cellular events

The availability of effective vaccines has had the most profound positive effect on improving the quality of public health by preventing infectious diseases. Despite many successful vaccines, there are still old and new emerging pathogens against which there is no vaccine available. A better understanding of how vaccines work for providing protection will help to improve current vaccines as well as to develop effective vaccines against pathogens for which we do not have a proper means to control. Recent studies have focused on innate immunity as the first line of host defense and its role in inducing adaptive immunity; such studies have been an intense area of research, which will reveal the immunological mechanisms how vaccines work for protection. Toll-like receptors (TLRs), a family of receptors for pathogen-associated molecular patterns on cells of the innate immune system, play a critical role in detecting and responding to microbial infections. Importantly, the innate immune system modulates the quantity and quality of longterm T and B cell memory and protective immune responses to pathogens. Limited studies suggest that vaccines which mimic natural infection and/or the structure of pathogens seem to be effective in inducing long-term protective immunity. A better understanding of the similarities and differences of the molecular and cellular events in host responses to vaccination and pathogen infection would enable the rationale for design of novel preventive measures against many challenging pathogens.

Aspects of Microparticle Utilization for Potentiation of Novel Vaccines: Promises and Risks

Many recombinant vaccines against novel (HIV, HCV) or ever-changing (influenza) infectious agents require the presence of adjuvants/delivery vehicles to induce strong immune responses. The necessity of their improvement led to the major effort towards development of vaccine delivery systems that are generally particulate (e.g., nano- and microparticles) and have comparable dimensions to the pathogens (viruses or bacteria). The mode of action of these adjuvants is not fully understood but implies the stimulation of the innate or antigen-specific immune responses, and/or the increase of antigen uptake or processing by antigen-presenting cells (APC). Moreover, enhancement of adjuvant activity through the use of micro- and nanoparticulate delivery systems often resulted from the synergistic effects producing immune responses stronger than those elicited by the adjuvant or delivery system alone. Among particulate adjuvants, biodegradable micro- and nanoparticles of poly(D,L-lactide-co-glycoside) (PLGA) or poly(D,L-lactide) (PLA) have been reported to enhance both humoral and cellular immune responses against an encapsulated protein antigen. Cationic and anionic polylactide co-glycolide (PLG) microparticles have been successfully used to adsorb a variety of agents, which include plasmid DNA, recombinant proteins and adjuvant active oligonucleotides and are also currently tested in several vaccine applications. Another approach envisions specific targeting of APC, especially peripheral DC and exploitation of particulate systems that are small enough for lymphatic uptake (polystyrene nanobeads). Micro- and nanoparticles offer the possibility of enhancement of their uptake by appropriate cells through manipulation of their surface properties. Still, questions regarding toxicity and molecular interaction between micro- and nano-particles and immune cells, tissues and whole organisms remain to be addressed. These risks and other possible side effects should be assessed in detail especially if mass-production and massive administration of such preparations is to be considered.

Influenza virus-like particles produced by transient expression in Nicotiana benthamiana induce a protective immune response against a lethal viral challenge in mice

A strain-specific vaccine represents the best possible response to the threat of an influenza pandemic. Rapid delivery of such a vaccine to the world's population before the peak of the first infection wave seems to be an unattainable goal with the current influenza vaccine manufacturing capacity. Plant-based transient expression is one of the few production systems that can meet the anticipated surge requirement. To assess the capability of plant agroinfiltration to produce an influenza vaccine, we expressed haemagglutinin (HA) from strains A/Indonesia/5/05 (H5N1) and A/New Caledonia/20/99 (H1N1) by agroinfiltration of Nicotiana benthamiana plants. Size distribution analysis of protein content in infiltrated leaves revealed that HA was predominantly assembled into high-molecular-weight structures. H5-containing structures were purified and examination by transmission electron microscopy confirmed virus-like particle (VLP) assembly. High-performance thin layer chromatography analysis of VLP lipid composition highlighted polar and neutral lipid contents comparable with those of purified plasma membranes from tobacco plants. Electron microscopy of VLP-producing cells in N. benthamiana leaves confirmed that VLPs accumulated in apoplastic indentations of the plasma membrane. Finally, immunization of mice with two doses of as little as 0.1 microg of purified influenza H5-VLPs triggered a strong immune response against the homologous virus, whereas two doses of 0.5 microg of H5-VLPs conferred complete protection against a lethal challenge with the heterologous A/Vietnam/1194/04 (H5N1) strain. These results show, for the first time, that plants are capable of producing enveloped influenza VLPs budding from the plasma membrane; such VLPs represent very promising candidates for vaccination against influenza pandemic strains.

The coming of age of virus-like particle vaccines

Virus-like particles are supra-molecular assemblages, usually icosahedral or rod-like structures. They incorporate key immunologic features of viruses which include repetitive surfaces, particulate structures and induction of innate immunity through activation of pathogen-associated molecular-pattern recognition receptors. They carry no replicative genetic information and can be produced recombinantly in large scale. Virus-like particles thus represent a safe and effective vaccine platform for inducing potent B- and T-cell responses. In addition to being effective vaccines against the corresponding virus from which they are derived, virus-like particles can also be used to present foreign epitopes to the immune system. This can be achieved by genetic fusion or chemical conjugation. This technological innovation has greatly broadened the scope of their use, from immunizing against microbial pathogens to immunotherapy for chronic diseases. Towards this end, virus-like particles have been used to induce autoantibodies to disease-associated self-molecules involved in chronic diseases, such as hypertension and Alzheimer's disease. The recognition of the potent immunogenicity and commercial potential for virus-like particles has greatly accelerated research and development activities. During the last decade, two prophylactic virus-like particle vaccines have been registered for human use, while another 12 vaccines entered clinical development.

Nanotechnology in vaccine delivery

With very few adjuvants currently being used in marketed human vaccines, a critical need exists for novel immunopotentiators and delivery vehicles capable of eliciting humoral, cellular and mucosal immunity. Such crucial vaccine components could facilitate the development of novel vaccines for viral and parasitic infections, such as hepatitis, HIV, malaria, cancer, etc. In this review, we discuss clinical trial results for various vaccine adjuvants and delivery vehicles being developed that are approximately nanoscale (< 1000 nm) in size. Humoral immune responses have been observed for most adjuvants and delivery platforms while only viral vectors, ISCOMs and Montanide™ ISA 51 and 720 have shown cytotoxic T cell responses in the clinic. MF59 and MPL® have elicited Th1 responses, and virus-like particles, non-degradable nanoparticles and liposomes have also generated cellular immunity. Such vaccine components have also been evaluated for alternative routes of administration with clinical successes reported for intranasal delivery of viral vectors and proteosomes and oral delivery of a VLP vaccine.

Virus-like particles-universal molecular toolboxes

Virus-like particles (VLPs) are highly organised spheres that self-assemble from virus-derived structural antigens. These stable and versatile subviral particles possess excellent adjuvant properties capable of inducing innate and cognate immune responses. Commercialised VLP-based vaccines have been successful in protecting humans from hepatitis B virus (HBV) and human papillomavirus (HPV) infection and are currently explored for their potential to combat other infectious diseases and cancer. Much insight into VLP-mediated immune stimulation and optimised VLP design has been gained from human immunodeficiency virus (HIV)-derived VLPs presenting promising components of current AIDS vaccine approaches. Owing to their unique features, VLPs and virosomes, the in vitro-reconstituted VLP counterparts, have recently gained ground in the field of nanobiotechnology as organic templates for the development of new biomaterials.

Emerging vaccines for influenza

BACKGROUND

Influenza remains one of the leading causes of morbidity and mortality worldwide. The available vaccines are least effective in the populations at greatest risk--children, the elderly, and the immunocompromised. Furthermore, avian influenza and other novel strains have the potential to cause the next influenza pandemic. Research efforts have accelerated worldwide to develop new vaccines to provide better immunity against annual epidemics and a potential pandemic.

OBJECTIVE

To summarize the global research efforts at developing new influenza vaccines, adjuvants, and delivery devices.

METHOD

MEDLINE and Pharmaprojects databases were searched for publications and continuing research on new influenza vaccine technologies.

RESULTS/CONCLUSIONS

Technologies such as DNA vaccines, live recombinant viral vector vaccines, and virus-like particles have shown significant promise for immunogenicity and protection from experimental challenge to influenza. New modalities for vaccine delivery and methods for rapid vaccine production are also being investigated. With the possibility of an influenza pandemic increasing the need to develop new vaccines, the global research community has made large strides to meet this challenge.

Cancer vaccines: accomplishments and challenges

Advancements in knowledge in diverse fields of science, including genetics, cell biology, molecular biology and biochemistry, have shed light on the origins of cancer and cell intrinsic properties that allow it to grow, invade and metastasize. Many therapies currently in use or under development are based on this knowledge. Advances in immunology, on the other hand, have shed light on how the host responds to these malignant properties of cancer. Based on that knowledge, immunotherapy, in particular vaccines directed at improving the host response against cancer, is being developed as an alternative therapeutic approach. In this review, we address main issues that have driven development of cancer vaccines and the challenges that have been met and/or are anticipated.

The truncated virus-like particles of C6/36 cell densovirus: implications for the assembly mechanism of brevidensovirus

The brevidensovirus is one of the smallest viruses in the world and the capsid of Aedes albopictus C6/36 cell densovirus (C6/36DNV) is the simplest and most compact capsid in brevidensovirus. To understand the assembly mechanism of icosahedral-virus capsid from this simplest model, we tried to express various lengths of virus proteins (VPs) of C6/36DNV in Bac-to-Bac system and evaluate their self-assembly capacities in insect Spodoptera frugiperda 9 (Sf9) cells. The result showed that the N-terminal GGSG sequence (residue 23-26), highly conserved glycine-rich region in Parvoviridae, and C-terminal GTGGVVTCMP (residue 344-353) were essential for capsid assembly, while the N-terminal nuclear localization signal, GTKRKR sequence (residue 15-20), was nonessential for the virus-like particles (VLPs) assembly, but did effect the formation of crystalline arrays in infected Sf9 cells. These information provided clues for how icosahedral-virus capsids formed and showed the potential of C6/36DNV-VLPs becoming a powerful nanoparticle vector.

Cowpea mosaic virus capsid: a promising carrier for the development of carbohydrate based antitumor vaccines

Immunotherapy targeting tumor cell surface carbohydrates is a promising approach for cancer treatment. However, the low immunogenecity of carbohydrates presents a formidable challenge. We describe here the enhancement of carbohydrate immunogenicity by an ordered display on the surface of the cowpea mosaic virus (CPMV) capsid. The Tn glycan, which is overexpressed on numerous cancer cell surfaces, was selected as the model antigen for our study. Previously it has been shown that it is difficult to induce a strong T cell-dependent immune response against the monomeric form of Tn presented in several ways on different carriers. In this study, we first synthesized Tn antigens derivatized with either a maleimide or a bromoacetamide moiety that was conjugated selectively to a cysteine mutant of CPMV. The glycoconjugate was then injected into mice and pre- and post-immune antibody levels in the mice sera were measured by enzyme-linked immunosorbant assays. High total antibody titers and, more importantly, high IgG titers specific for Tn were obtained in the post-immune day 35 serum, suggesting the induction of T cell-dependent antibody isotype switching by the glycoconjugate. The antibodies generated were able to recognize Tn antigens presented in their native conformations on the surfaces of both MCF-7 breast cancer cells and the multidrug resistant breast cancer cell line NCI-ADR RES. These results suggest that the CPMV capsid can greatly enhance the immunogenicity of weak antigens such as Tn and this can provide a promising tool for the development of carbohydrate based anti-cancer vaccines.

Cowpea mosaic virus capsid: a promising carrier for the development of carbohydrate based antitumor vaccines

Immunotherapy targeting tumor cell surface carbohydrates is a promising approach for cancer treatment. However, the low immunogenecity of carbohydrates presents a formidable challenge. We describe here the enhancement of carbohydrate immunogenicity by an ordered display on the surface of the cowpea mosaic virus (CPMV) capsid. The Tn glycan, which is overexpressed on numerous cancer cell surfaces, was selected as the model antigen for our study. Previously it has been shown that it is difficult to induce a strong T cell-dependent immune response against the monomeric form of Tn presented in several ways on different carriers. In this study, we first synthesized Tn antigens derivatized with either a maleimide or a bromoacetamide moiety that was conjugated selectively to a cysteine mutant of CPMV. The glycoconjugate was then injected into mice and pre- and post-immune antibody levels in the mice sera were measured by enzyme-linked immunosorbant assays. High total antibody titers and, more importantly, high IgG titers specific for Tn were obtained in the post-immune day 35 serum, suggesting the induction of T cell-dependent antibody isotype switching by the glycoconjugate. The antibodies generated were able to recognize Tn antigens presented in their native conformations on the surfaces of both MCF-7 breast cancer cells and the multidrug resistant breast cancer cell line NCI-ADR RES. These results suggest that the CPMV capsid can greatly enhance the immunogenicity of weak antigens such as Tn and this can provide a promising tool for the development of carbohydrate based anti-cancer vaccines.

Chimeric coronavirus-like particles carrying severe acute respiratory syndrome coronavirus (SCoV) S protein protect mice against challenge with SCoV

We tested the efficacy of coronavirus-like particles (VLPs) for protecting mice against severe acute respiratory syndrome coronavirus (SCoV) infection. Coexpression of SCoV S protein and E, M and N proteins of mouse hepatitis virus in 293T or CHO cells resulted in the efficient production of chimeric VLPs carrying SCoV S protein. Balb/c mice inoculated with a mixture of chimeric VLPs and alum twice at an interval of four weeks were protected from SCoV challenge, as indicated by the absence of infectious virus in the lungs. The same groups of mice had high levels of SCoV-specific neutralizing antibodies, while mice in the negative control groups, which were not immunized with chimeric VLPs, failed to manifest neutralizing antibodies, suggesting that SCoV-specific neutralizing antibodies are important for the suppression of viral replication within the lungs. Despite some differences in the cellular composition of inflammatory infiltrates, we did not observe any overt lung pathology in the chimeric-VLP-treated mice, when compared to the negative control mice. Our results show that chimeric VLP can be an effective vaccine strategy against SCoV infection.

Production of recombinant HIV-1/HBV virus-like particles in Nicotiana tabacum and Arabidopsis thaliana plants for a bivalent plant-based vaccine

Human immunodeficiency virus (HIV-1) and hepatitis B virus (HBV) spread via similar transmission pathways, and infection by HBV occurs in up to 32% of HIV-1 cases. Here, we describe the successful expression of novel recombinant HIV-1/HBV virus-like particles (VLPs) in Nicotiana tabacum and Arabidopsis thaliana. The production levels and quality of the recombinant VLPs were comparable in the two plants, showing that parameters intrinsic to the recombinant proteins determined their assembly into VLPs. These heterologous VLPs can be used in a bivalent anti-HIV-1/-HBV vaccine, administrated via ingestion of transgenic plants.

Virus-like particles: flexible platforms for vaccine development

Virus-like particles (VLPs) consist of viral structural proteins that, when overexpressed, spontaneously self-assemble into particles that are antigenically indistinguishable from infectious virus or subviral particles. VLPs can be considered as dense, repetitive arrays of one or more protein subunits with properties that are highly advantageous for use as stand-alone vaccines or as vaccine platforms. This review discusses the development of VLP-based platform technologies for vaccines against pathogens, as well as nontraditional targets such as self-antigens involved in chronic diseases.

Strong and heterogeneous adsorption of infectious bursal disease VP2 subviral particle with immobilized metal ions dependent on two surface histidine residues

VP2, the single outer protein of infectious bursal disease virus capsid, can self-assemble into T = 1 subviral particle (SVP), which can be efficiently purified by immobilized metal ion affinity chromatography (IMAC). In this study, a systemic investigation of the adsorption behavior of VP2 SVP on Ni-NTA resin was performed to identify that His253 and His249 on the surface of SVP are the key factors accounted for the strong and heterogeneous interaction. First, an untagged VP2-441 SVP was constructed, expressed, and purified by IMAC to demonstrate that SVP can interact with immobilized Ni2+ ions on NTA resin without an inserted His tag. Second, equilibrium adsorption studies were used to demonstrate that SVP has a higher affinity to the immobilized Ni2+ ions than a model protein, bovine serum albumin, although the maximum amount of SVP bound per volume resin is limited by the pore size of the resin as verified by confocal microscopic analysis. Third, based on structural analysis and computer modeling, His253 and His249 on the surface of SVP are responsible for a strong heterogeneous and multiple adsorption with the immobilized Ni2+ ions; and this was confirmed by a point-mutation experiment. This is the first example to elucidate the interaction between the immobilized metal ions and viral particles at molecular level. A detailed understanding of SVP-immobilized metal ion interactions can provide useful strategies for engineering icosahedral protein nanoparticles to achieve a simple and one-step purification by IMAC.

Development of hepatitis B virus capsids into a whole-chain protein antigen display platform: new particulate Lyme disease vaccines

The immunogenicity of peptides and small protein fragments can be considerably enhanced by their presentation on particulate carriers such as capsid-like particles (CLPs) from hepatitis B virus (HBV). HBV CLPs are icosahedral nanoparticles formed by 90 or 120 core protein dimers. Insertions into the immunodominant c/e1 B cell epitope, a surface-exposed loop on the HBV capsid protein, are especially immunogenic. Here we investigated whether the HBV core protein can be exploited as a vaccine carrier for whole-chain protein antigens, using two clinically relevant proteins derived from a bacterial human pathogen, the Lyme disease agent Borrelia burgdorferi. For this purpose we analyzed CLP formation by core fusions with the entire 255-amino-acid ectodomain of outer surface lipoprotein A (OspA), and with two distinct, 189 amino acid long variants of the dimeric OspC (OspC(a), OspC(b)) of B. burgdorferi. OspA appropriately inserted into the HBV core protein yielded a multimerization-competent fusion protein, termed coreOspA. Although only partially assembling into regular CLPs, coreOspA induced antibodies to OspA, including the Ig isotype profile and specificity for the protective epitope "LA-2", with an efficiency similar to that of recombinant lipidated OspA, the first generation vaccine against Lyme disease. Moreover, coreOspA actively and passively protected mice against subsequent challenge with B. burgdorferi. Fusions with the two OspC variants were found to efficiently form regular CLPs, most probably by OspC dimerization across different core protein dimers. In mice, both coreOspC preparations induced high-titered antibody responses to the homologous but also to the heterologous OspC variant, which conferred protection against challenge with B. burgdorferi. The data demonstrate the principal applicability of HBV CLPs to act as potent immunomodulator even for structurally complex full-length polypeptide chains, and thus open new avenues for novel vaccine designs.

Generation of chimeric HBc proteins with epitopes in E.coli: formation of virus-like particles and a potent inducer of antigen-specific cytotoxic immune response and anti-tumor effect in vivo

The major aim of the project was to develop the virus-like particles (VLPs) displaying single or multi-epitope of hepatocellular carcinomas (HCC) in Escherichia coli and to evaluate the effect on inducing Ag-specific CD8(+) T cell response and antitumor efficacy as candidate vaccines. To this end, hepatitis B virus core (HBc) particles were used as a carrier of HCC epitopes. Four HCC epitopes MAGE-1(278-286aa), MAGE-3(271-279aa), AFP1 (158-166aa) or AFP2 (542-550aa) were fused to the 3' terminus of the truncated HBV core gene, respectively, or conjunctively. Not all recombinant plasmids led to expression of chimeric proteins in expression strain E. coli BL21 (DE3), but chimeric proteins which are expressed in inclusion bodies resulted in the formation of complete "mature" VLPs. E. coli-derived truncated HBc(1-144) chimeric protein self-assembled into VLPs that both morphologically and physically are similar to the wild-type ones and they still remained activity after purification and refolding from 6M urea solution. We also showed that they could be internalized and presented by DCs in vitro. Additionally, DCs pulsed with the chimeric HBc-VLPs could induce stronger CTL activity and greater IFN-gamma secretion by responding T cells compared with peptid-pulsed DCs. In the B16-pIR-HH tumor therapy model, the growth of established tumors was significantly inhibited by immunization using VLP-pulsed DCs, resulting in significantly higher survival rate of immunized animals. Thus, the results of the current study have demonstrated the principal possibility of using VLP on the basis of HBcAg for creation of a new type of HCC-specific immunogen.

Pathobiology of henipavirus entry: insights into therapeutic strategies

The recently emerged paramyxoviruses, Nipah (NiV) and Hendra (HeV), designated as Biosafety Level 4 pathogens, can cause lethal respiratory and neurological disease in both animals and humans. NiV outbreaks have been associated with efficient transmission amongst livestock (pigs) and mortality rates exceeding 70%, with documented cases of human-to-human transmission. Without vaccines or effective therapeutics, NiV and HeV continue to present an impending threat to global health and economies. The current understanding of henipavirus pathobiology has led to the development of small animal models reflecting certain aspects of the human pathology. In this review, we discuss how these animal models have been critical in testing vaccination strategies and in eliciting neutralizing antibodies against the envelope glycoproteins. Additionally, the discovery of the viral receptor and development of pseudotyped-viral systems have allowed us to explore the multiple opportunities for therapeutic intervention existing within the individual steps of the henipavirus entry pathway. Current research shows promise for the future development of effective strategies to limit the impact of these biological threats.