Virus-Like Particle (VLP) Vaccine Conferred Complete Protection against a Lethal Influenza Virus Challenge

A novel intranasal virus-like particle (VLP) vaccine designed to protect against the pandemic 1918 influenza A virus (H1N1)

We have prepared a virus-like particle (VLP) vaccine bearing the surface glycoproteins HA and NA of the 1918 influenza A virus by infecting Sf9 cells with a quadruple recombinant baculovirus that expresses the four influenza proteins (HA, NA, M1, and M2) required for the assembly and budding of the VLPs. The presence of HA and M1 in the purified VLPs was confirmed by Western blot, and that of NA by a neuraminidase enzymatic assay. For in vivo studies, the 1918 VLP vaccine was formulated with or without an oligonucleotide containing two CpG motifs and administered in two doses 2 wk apart via the intranasal route. The antibody titers in mice immunized with VLP vaccines were higher than in mice vaccinated with an inactivated swine virus (H1N1) control, when CHO cells expressing 1918 HA were used as antigen. The opposite result was obtained when disrupted swine virus was the antigen for the ELISA test. Vaccine efficacy was evaluated by challenging immunized mice with the 1918 antigenically related influenza virus A/swine/Iowa/15/30 (H1N1) and measuring viral titers in the upper and lower respiratory tract. Mice immunized with VLP vaccine plus CpG demonstrated significantly lower viral titers in the nose and lungs than did the control on days 2 and 4 postchallenge and completely cleared the virus by day 6. Furthermore, they did not show symptoms of disease although there was a minor decrease in body weight. Mice vaccinated with VLP alone also demonstrated significantly lower viral titers in the nose and lungs than did the placebo group as well as the inactivated virus group on days 4 and 6 postchallenge. These results suggest that it is feasible to make a safe and immunogenic vaccine to protect against the extremely virulent 1918 virus, using a novel and safe cell-based technology.

Hydrophilicity dependent budding and secretion of chimeric HIV Gag-V3 virus-like particles

Virus-like particles (VLPs) of numerous viruses have been considered as possible candidates for vaccine development. We have constructed HIV chimeric genes by coupling the gag gene of HIV-2 with the V3 domain of the gp120 gene of either HIV-1 or HIV-2 and expressed the chimeric genes in SF21 cells using the recombinant baculovirus expression system. Although the level of expression of the chimeric HIV-2 gag gene with the V3 domain of either HIV-1 gp120 (gagC-1V3) or HIV-2 gp120 (gagC-2V3) was high, the VLP assembly and extracellular release of GagC-1V3 was very poor. In contrast, GagC-2V3 chimeric proteins formed VLPs and released efficiently. We have constructed substitution mutants to investigate the effects of the hydrophobic region of the V3 domain of HIV-1 Gp120 (1V3) in VLP assembly and release. The substitution mutant analyses revealed that in replacing the hydrophobic region of the 1V3 in GagC-1V3 with the hydrophilic sequence of the V3 domain of HIV-2 Gp120 (2V3) enhanced the extracellular VLP. We demonstrate here that disruption of the hydrophobic character of the C-terminus of the chimeric protein improves assembly and release of the VLPs. Our results suggest that the poor GagC-1V3 VLP release was attributed to the hydrophobic region in the V3 sequence of the chimeric protein, and that not only the N-terminal myristylation and positively charged domain of the Gag protein functioned as a targeting signal to direct membrane binding, but also that the C-terminal hydrophobic region affected release of chimeric VLPs.

Vaccination, immune and gene therapy based on virus-like particles against viral infections and cancer

Virus-like particles (VLPs) are self-assembling, non-replicating particles lacking the viral genome that are formed by one or several viral structural proteins. VLPs can be purified after expression in yeast cells, insect cells using baculoviruses, Escherichia coli or mammalian cells. Recently, vaccines based on VLPs have come into focus with the FDA approval of a VLP-based vaccine against human papilloma viruses. However, this application of VLPs is just one of many developments within the VLP field. Other potential applications under development besides vaccines against viruses or cancers also include gene delivery and treatment of different disorders.

Immune responses against severe acute respiratory syndrome coronavirus induced by virus-like particles in mice

Virus-like particles (VLPs) represent a promising vaccine against severe acute respiratory syndrome coronavirus (SARS CoV). In this study, recombinant baculovirus vAcS and vAcME were constructed to express the S protein and the M and E proteins of SARS CoV, respectively. Electron microscope analysis demonstrated the formation of VLPs in vAcME and vAcS coinfected insect cells. Mice immunized four times with VLPs developed high antibody titres against SARS CoV. In addition, VLPs elicited cell-mediated immunity as demonstrated by enhanced interferon-γ and interleukin-4 production. VLPs also conferred protective immunity against the infection of Spike protein pseudotyped murine leukaemia virus. Our findings demonstrate that SARS CoV VLPs are immunogenic and can elicit strong SARS CoV-specific humoral and cellular immune responses in mice. This is the first study describing the immunogenicity of SARS CoV VLPs, providing valuable data for developing a protective vaccine against SARS CoV infection.

Evaluation of influenza virus-like particles and Novasome adjuvant as candidate vaccine for avian influenza

The development of safe and effective vaccines for avian influenza viruses is a priority for pandemic preparedness. Adjuvants improve the efficacy of vaccines and may allow antigen sparing during a pandemic. We have previously shown that influenza virus-like particles (VLPs) comprised of HA, NA, and M1 proteins represent a candidate vaccine for avian influenza H9N2 virus [Pushko P, Tumpey TM, Fang Bu, Knell J, Robinson R, Smith G. Influenza virus-like particles comprised of the HA, NA, and M1 proteins of H9N2 influenza virus induce protective immune responses in BALB/c mice. Vaccine 2005;23(50):5751-9]. In this study, an H9N2 VLP vaccine and recombinant HA (rH9) vaccine were evaluated in three animal models. The H9N2 VLP vaccine protected mice and ferrets from challenge with A/Hong Kong/1073/99 (H9N2) virus. Novasome adjuvant improved immunogenicity and protection. Positive effect of the adjuvant was also detected using the rH9 vaccine. The results have implications for the development of safe and effective vaccines for avian influenza viruses with pandemic potential.

Pandemic vaccines: promises and pitfalls

Prototype vaccines against influenza A/H5N1 may be poorly immunogenic, and two or more doses may be required to induce levels of neutralising antibody that are deemed to be protective. The actual levels of antibody required to protect against a highly pathogenic virus that potentially can spread beyond the large airways is unknown. The global capacity for vaccine manufacture in eggs or tissue culture is considerable, but the number of doses that can theoretically be produced in a pandemic context will only be sufficient for a small fraction of the world's population, even less if a high antigen content is required. The safety of new pandemic vaccines should be addressed in an internationally coordinated way. Steps are underway through the Therapeutic Goods Administration to evaluate mock-up vaccines now, so that the time to registration of a new product can be minimised. It will be 3-6 months into the pandemic before an effective vaccine becomes available, so other control measures will be important in the early stages of a pandemic. The primary goal of a pandemic influenza vaccine must be to prevent death, and not necessarily to prevent infection.

Immunogenicity of virus-like particles containing modified human immunodeficiency virus envelope proteins

Extensive glycosylation and variable loops of the HIV envelope protein (Env) are reported to shield some neutralizing epitopes. Here, we investigated the immunogenicity of mutated HIV Envs presented in virus-like particles (VLPs). We immunized mice with simian human immunodeficiency virus (SHIV) VLPs containing mutant HIV Env with reduced glycosylation (3G), variable loop-deleted mutations (dV1V2), or combinations of both types of mutations (3G-dV2-1G), and evaluated immune responses. Immune sera from mice that received VLPs with modified HIV Envs (3G or dV1V2) showed higher neutralizing activities against the homologous HIV 89.6 virus as well as heterologous viruses when compared with wild type SHIV VLP-immunized mice. Lymphocytes from immunized mice produced HIV Env-specific cytokines, with the 3G-dV2-1G mutant producing high levels of cytokines. Interestingly, both dendritic cells and B cells were found to interact with VLPs suggesting that VLPs are effective immunogens. Therefore, this study suggests that VLPs containing modified HIV Env have the potential to be developed as candidate vaccines capable of inducing cellular and humoral immune responses including neutralizing activities.

Virus-like particle vaccine induces protective immunity against homologous and heterologous strains of influenza virus

Recurrent outbreaks of highly pathogenic avian influenza virus pose the threat of pandemic spread of lethal disease and make it a priority to develop safe and effective vaccines. Influenza virus-like particles (VLPs) have been suggested to be a promising vaccine approach. However, VLP-induced immune responses, and their roles in inducing memory immune responses and cross-protective immunity have not been investigated. In this study, we developed VLPs containing influenza virus A/PR8/34 (H1N1) hemagglutinin (HA) and matrix (M1) proteins and investigated their immunogenicity, long-term cross-protective efficacy, and effects on lung proinflammatory cytokines in mice. Intranasal immunization with VLPs containing HA induced high serum and mucosal antibody titers and neutralizing activity against PR8 and A/WSN/33 (H1N1) viruses. Mice immunized with VLPs containing HA showed little or no proinflammatory lung cytokines and were protected from a lethal challenge with mouse-adapted PR8 or WSN viruses even 5 months postimmunization. Influenza VLPs induced mucosal immunoglobulin G and cellular immune responses, which were reactivated rapidly upon virus challenge. Long-lived antibody-secreting cells were detected in the bone marrow of immunized mice. Immune sera administered intranasally were able to confer 100% protection from a lethal challenge with PR8 or WSN, which provides further evidence that anti-HA antibodies are primarily responsible for preventing infection. Taken together, these results indicate that nonreplicating influenza VLPs represent a promising strategy for the development of a safe and effective vaccine to control the spread of lethal influenza viruses.

Virus-like particles: passport to immune recognition

Virus-like particles (VLPs) are formed by the self-assembly of envelope and/or capsid proteins from many viruses. In many cases such VLPs have structural characteristics and antigenicity similar to the parental virus, and some have already proven successful as vaccines against the cognate virus infection. The structural components of some VLPs have also proven amenable to the insertion or fusion of foreign antigenic sequences, allowing the production of chimeric VLPs exposing the foreign antigen on their surface. Other VLPs have been used as carriers for foreign antigens, including non-protein antigens, via chemical conjugation. This review outlines some of the advantages, disadvantages, and technical considerations for the use of a wide range of VLP systems in vaccine development.

Oropharyngeal aspiration of a silica suspension produces a superior model of silicosis in the mouse when compared to intratracheal instillation

Instillation of crystalline silica into the lungs of mice is a common experimental model of pulmonary fibrosis. Typically, a suspension of silica in saline is injected into the trachea via intubation or surgical tracheostomy. These techniques require a high degree of technical skill, have a lengthy training period, and can suffer from a high failure rate. In oropharyngeal aspiration, a droplet of liquid is placed in the animal's mouth while simultaneously holding its tongue (to block the swallow reflex) and pinching its nose shut, forcing it to breathe through its mouth, aspirating the liquid. To determine whether oropharyngeal aspiration (OA) could replace intratracheal instillation (IT) in a model of silica-induced fibrosis, a comparison was performed. Crystalline silica was introduced into the lungs of male C57BL/6 mice by the IT or OA procedure, and the resulting inflammation and fibrosis was assessed after 3 weeks. IT and OA instillation of silica both resulted in neutrophilic inflammation and fibrotic changes, including interstitial fibrosis and dense fibrotic foci. Mice treated via IT demonstrated a few large lesions proximal to conducting airways with little involvement of the distal parenchyma and large interanimal variability. In contrast, OA resulted in a diffuse pathology with numerous fibrotic foci distributed throughout the lung parenchyma, which is more representative of human fibrotic lung disease. OA- but not IT-treated mice exhibited significantly increased lung collagen content. Furthermore, the interanimal variability within the OA group was significantly less than in the IT group. Oropharyngeal aspiration should be considered as an alternative to intratracheal instillation of silica and other particulates in studies of respiratory toxicity and lung disease.

Making better influenza virus vaccines?

Better influenza vaccines are possible and necessary.

Killed and live influenza virus vaccines are effective in preventing and curbing the spread of disease, but new technologies such as reverse genetics could be used to improve them and to shorten the lengthy process of preparing vaccine seed viruses. By taking advantage of these new technologies, we could develop live vaccines that would be safe, cross-protective against variant strains, and require less virus per dose than conventional vaccines. Furthermore, pandemic vaccines against highly virulent strains such as the H5N1 virus can only be generated by reverse genetics techniques. Other technologic breakthroughs should result in effective adjuvants for use with killed and live vaccines, increasing the number of available doses. Finally, universal influenza virus vaccines seem to be within reach. These new strategies will be successful if they are supported by regulatory agencies and if a robust market for influenza virus vaccines against interpandemic and pandemic threats is made and sustained.

Vaccines for viral and parasitic diseases produced with baculovirus vectors

The baculovirus-insect cell expression system is an approved system for the production of viral antigens with vaccine potential for humans and animals and has been used for production of subunit vaccines against parasitic diseases as well. Many candidate subunit vaccines have been expressed in this system and immunization commonly led to protective immunity against pathogen challenge. The first vaccines produced in insect cells for animal use are now on the market. This chapter deals with the tailoring of the baculovirus-insect cell expression system for vaccine production in terms of expression levels, integrity and immunogenicity of recombinant proteins, and baculovirus genome stability. Various expression strategies are discussed including chimeric, virus-like particles, baculovirus display of foreign antigens on budded virions or in occlusion bodies, and specialized baculovirus vectors with mammalian promoters that express the antigen in the immunized individual. A historical overview shows the wide variety of viral (glyco)proteins that have successfully been expressed in this system for vaccine purposes. The potential of this expression system for antiparasite vaccines is illustrated. The combination of subunit vaccines and marker tests, both based on antigens expressed in insect cells, provides a powerful tool to combat disease and to monitor infectious agents.