Immunization with HIV-1 gp41 subunit virosomes induces mucosal antibodies protecting nonhuman primates against vaginal SHIV challenges.

Human immunodeficiency virus (HIV)-1 is mainly transmitted mucosally during sexual intercourse. We therefore evaluated the protective efficacy of a vaccine active at mucosal sites. Macaca mulatta monkeys were immunized via both the intramuscular and intranasal routes with an HIV-1 vaccine made of gp41-subunit antigens grafted on virosomes, a safe delivery carrier approved in humans with self-adjuvant properties. Six months after 13 vaginal challenges with simian-HIV (SHIV)-SF162P3, four out of five vaccinated animals remained virus-negative, and the fifth was only transiently infected. None of the five animals seroconverted to p27gag-SIV. In contrast, all 6 placebo-vaccinated animals became infected and seroconverted. All protected animals showed gp41-specific vaginal IgAs with HIV-1 transcytosis-blocking properties and vaginal IgGs with neutralizing and/or antibody-dependent cellular-cytotoxicity activities. In contrast, plasma IgGs totally lacked virus-neutralizing activity. The protection observed challenges the paradigm whereby circulating antiviral antibodies are required for protection against HIV-1 infection and may serve in designing a human vaccine against HIV-1-AIDS.

Immunogenicity of a virosomally-formulated Plasmodium falciparum GLURP-MSP3 chimeric protein-based malaria vaccine candidate in comparison to adjuvanted formulations.

BACKGROUND: In clinical trials, immunopotentiating reconstituted influenza virosomes (IRIVs) have shown great potential as a versatile antigen delivery platform for synthetic peptides derived from Plasmodium falciparum antigens. This study describes the immunogenicity of a virosomally-formulated recombinant fusion protein comprising domains of the two malaria vaccine candidate antigens MSP3 and GLURP. METHODS: The highly purified recombinant protein GMZ2 was coupled to phosphatidylethanolamine and the conjugates incorporated into the membrane of IRIVs. The immunogenicity of this adjuvant-free virosomal formulation was compared to GMZ2 formulated with the adjuvants Montanide ISA 720 and Alum in three mouse strains with different genetic backgrounds. RESULTS: Intramuscular injections of all three candidate vaccine formulations induced GMZ2-specific antibody responses in all mice tested. In general, the humoral immune response in outbred NMRI mice was stronger than that in inbred BALB/c and C57BL/6 mice. ELISA with the recombinant antigens demonstrated immunodominance of the GLURP component over the MSP3 component. However, compared to the Al(OH)(3)-adjuvanted formulation the two other formulations elicited in NMRI mice a larger proportion of anti-MSP3 antibodies. Analyses of the induced GMZ2-specific IgG subclass profiles showed for all three formulations a predominance of the IgG1 isotype. Immune sera against all three formulations exhibited cross-reactivity with in vitro cultivated blood-stage parasites. Immunofluorescence and immunoblot competition experiments showed that both components of the hybrid protein induced IgG cross-reactive with the corresponding native proteins. CONCLUSION: A virosomal formulation of the chimeric protein GMZ2 induced P. falciparum blood stage parasite cross-reactive IgG responses specific for both MSP3 and GLURP. GMZ2 thus represents a candidate component suitable for inclusion into a multi-valent virosomal malaria vaccine and influenza virosomes represent a versatile antigen delivery system suitable for adjuvant-free immunization with recombinant proteins.

Design and pre-clinical profiling of a Plasmodium falciparum MSP-3 derived component for a multi-valent virosomal malaria vaccine.

BACKGROUND: Clinical profiling of two components for a synthetic peptide-based virosomal malaria vaccine has yielded promising results, encouraging the search for additional components for inclusion in a final multi-valent vaccine formulation. This report describes the immunological characterization of linear and cyclized synthetic peptides comprising amino acids 211-237 of Plasmodium falciparum merozoite surface protein (MSP-3). METHODS: These peptides were coupled to phosphatidylethanolamine (PE); the conjugates were intercalated into immunopotentiating reconstituted influenza virosomes (IRIVs) and then used for immunizations in mice to evaluate their capacity to elicit P. falciparum cross-reactive antibodies. RESULTS: While all MSP-3-derived peptides were able to elicit parasite-binding antibodies, stabilization of turn structures by cyclization had no immune-enhancing effect. Therefore, further pre-clinical profiling was focused on FB-12, a PE conjugate of the linear peptide. Consistent with the immunological results obtained in mice, all FB-12 immunized rabbits tested seroconverted and consistently elicited antibodies that interacted with blood stage parasites. It was observed that a dose of 50 microg was superior to a dose of 10 microg and that influenza pre-existing immunity improved the immunogenicity of FB-12 in rabbits. FB-12 production was successfully up-scaled and the immunogenicity of a vaccine formulation, produced according to the rules of Good Manufacturing Practice (GMP), was tested in mice and rabbits. All animals tested developed parasite-binding antibodies. Comparison of ELISA and IFA titers as well as the characterization of a panel of anti-FB-12 monoclonal antibodies indicated that at least the majority of antibodies specific for the virosomally formulated synthetic peptide were parasite cross-reactive. CONCLUSION: These results reconfirm the suitability of IRIVs as a carrier/adjuvant system for the induction of strong humoral immune responses against a wide range of synthetic peptide antigens. The virosomal formulation of the FB-12 peptidomimetic is suitable for use in humans and represents a candidate component for a virosomal multi-valent malaria subunit vaccine.

Contribution of influenza immunity and virosomal-formulated synthetic peptide to cellular immune responses in a phase I subunit malaria vaccine trial.

We have demonstrated recently in a phase Ia clinical trial that synthetic malaria peptides delivered by immuno-potentiating reconstituted influenza virosomes (IRIV) induced long-lived peptide-specific antibody responses in all volunteers. In the current ancillary study to this clinical trial we have investigated the cellular immune responses specific for IRIV and the surface bound synthetic malaria peptides tested. After vaccination, in 50% (8/16) of the volunteers at least one positive lymphoproliferative response specific for the 49mer peptide derived from the Plasmodium falciparum apical membrane antigen-1 (AMA-1) was observed with stimulation indices ranging from 2 to 4.5. All volunteers showed pre-existing IRIV specific cellular immunity assessed by ex vivo IFN-gamma ELISpot analysis and lymphoproliferation. The pre-existing influenza specific T cell responses did not interfere negatively with the induction of malaria peptide-specific humoral and cellular immune responses. Our results support the view that IRIV constitute a safe antigen delivery system for induction of peptide-specific immune responses in human populations.

Anti-angiogenetic effects of immune-reconstituted influenza virosomes assembled with parathyroid hormone-related protein derived peptide vaccine.

BACKGROUND: C-IRIV/PTR-4 is a novel anticancer vaccine construct composed of immune-reconstituted influenza virosomes (IRIV) assembled with the PTH-rP derived peptide (PTR)-4, a synthetic CTL epitope with HLA-A(*)02.01 amino acid binding motifs. This peptide is able to generate a human PTH-rP specific CTL response with anti-tumor activity in vitro and in mice. MATERIALS AND METHODS: We have investigated the immunological and preventive anti-tumor activity of C-IRIV/PTR-4 compared with the soluble PTR-4 peptide, in HHD mice inoculated with autologous PTH-rP+ tumor cells. RESULTS: Peptide vaccination with either a soluble and an IRIV formulation showed similar immunological activity and the ability to purge the tumor tissue of tumor cell clones able to produce the target antigen (PTR-rP). The most efficient protection from tumor growth was however observed in animals vaccinated with C-IRIV/PTR-4 in which an additional IRIV related anti-angiogenetic effect was detected in the tumor tissue. CONCLUSIONS: These results confirm the immunological activity of PTR-4 vaccination and suggest a more efficacious therapeutic potential of C-IRIV/PTR-4 against bone metastases and malignancies like breast, prostate and lung which very often over-express PTH-rP.

Structure-activity-based design of a synthetic malaria peptide eliciting sporozoite inhibitory antibodies in a virosomal formulation.

The circumsporozoite protein (CSP) of Plasmodium falciparum is a leading candidate antigen for inclusion in a malaria subunit vaccine. We describe here the design of a conformationally constrained synthetic peptide, designated UK-39, which has structural and antigenic similarity to the NPNA-repeat region of native CSP. NMR studies on the antigen support the presence of helical turn-like structures within consecutive NPNA motifs in aqueous solution. Intramuscular delivery of UK-39 to mice and rabbits on the surface of reconstituted influenza virosomes elicited high titers of sporozoite crossreactive antibodies. Influenza virus proteins were crucially important for the immunostimulatory activity of the virosome-based antigen delivery system, as a liposomal formulation of UK-39 was not immunogenic. IgG antibodies elicited by UK-39 inhibited invasion of hepatocytes by P. falciparum sporozoites, but not by antigenically distinct P. yoelii sporozoites. Our approach to optimized virosome-formulated synthetic peptide vaccines should be generally applicable for other infectious and noninfectious diseases.

Preclinical profiling of the immunogenicity of a two-component subunit malaria vaccine candidate based on virosome technology.

Presentation of synthetic peptides on immunopotentiating reconstituted influenza virosomes is a promising technology for subunit vaccine development. An optimized virosomally delivered peptide representing 5 NPNA repeats of P. falciparum circumsporozoite protein is highly immunogenic in mice. Antibodies against this peptide (UK-39) inhibit sporozoite invasion of human hepatocytes. A second peptide (AMA49-C1) based on domain III of apical membrane antigen 1, induces antibodies that inhibit blood-stage parasite growth in vitro. Here we show a detailed pre-clinical profiling of these virosomally formulated peptides alone and in combination in mice and rabbits. Two immunizations with virosomally formulated UK-39 or AMA49-C1 were enough to elicit high titers of parasite cross-reactive antibodies in both species. A low dose of 10 microg UK-39 was enough to induce maximal titers in rabbits. Higher doses of peptide did not increase antibody titers. In contrast, AMA49-C1 induced higher antibody titers with 25 and 50 microg peptide. Combination of UK-39 and AMA49- C1 on separate virosomes did not have any negative effect on anti-peptide antibody titers in mice or rabbits. No MHC restriction was observed in the development of humoral responses in outbred rabbits with different immunogenetic backgrounds. All vaccine formulations were safe in toxicity studies in rabbits and rats. Taken together, low amounts of synthetic peptides delivered on virosomes induced high antibody titers in mice and rabbits. Moreover, different peptides could be combined without interfering with individual anti-peptide responses, augmenting the value of this system for the development of a multivalent malaria vaccine.

Humoral and cellular immune responses to airway immunization of mice with human papillomavirus type 16 virus-like particles and mucosal adjuvants.

Cervical cancer results from cervical infection by human papillomaviruses (HPV), especially HPV16. Intramuscular administrations of HPV16 virus-like particle (VLP) vaccines have been shown to induce strong neutralizing antibody responses and protect women against genital HPV16 infection and associated lesions. However, an alternative route of administration that avoids parenteral injection might facilitate vaccine implementation, particularly in developing countries which account for the majority of the worldwide cases of cervical cancer. In addition, inducing mucosal immunity could partially overcome the substantial variation in HPV16 antibodies at the cervix seen in ovulating women. Aerosol vaccination with HPV16 VLPs was previously shown to be immunogenic in mice and in women. Here, we examine whether exposure to other respiratory viral antigens may interfere with the HPV16 VLP-specific humoral response and whether two known mucosal adjuvants, CpG oligodeoxynucleotides and a natural non-toxic Escherichia coli heat-labile enterotoxin (HLT), can enhance the immunogenicity of airway immunization (nasal or aerosol-like) of mice with HPV16 VLPs. Our data show that HLT can significantly improve anti-VLP humoral responses in serum and mucosal secretions, as well as VLP-specific proliferative responses and IFN-gamma production by CD8 T cells, and that recent exposure to influenza surface antigens can diminish mucosal, but not systemic, antibody responses to the VLPs.

Antibodies elicited by a virosomally formulated Plasmodium falciparum serine repeat antigen-5 derived peptide detect the processed 47 kDa fragment both in sporozoites and merozoites.

Serine repeat antigen-5 (SERA5) is a candidate antigen for inclusion into a malaria subunit vaccine. During merozoite release and reinvasion the 120 kDa SERA5 precursor protein (P120) is processed, and a complex consisting of an N-terminal 47 kDa (P47) and a C-terminal 18kDa (P18) processing product associates with the surface of merozoites. This complex is thought to be involved in merozoite invasion of and/or egress from host erythrocytes. Here we describe the synthesis and immunogenic properties of virosomally formulated synthetic phosphatidylethanolamine (PE)-peptide conjugates, incorporating amino acid sequence stretches from the N-terminus of Plasmodium falciparum SERA5. Choosing an appropriate sequence was crucial for the development of a peptide that elicited high titers of parasite cross-reactive antibodies in mice. Monoclonal antibodies (mAbs) raised against the optimized peptide FB-23 incorporating amino acids 57-94 of SERA5 bound to both P120 and to P47. Western blotting analysis proved for the first time the presence of SERA5 P47 in sporozoites. In immunofluorescence assays, the mAbs stained SERA5 in all its predicted localizations. The virosomal formulation of peptide FB-23 is suitable for use in humans and represents a candidate component for a multi-valent malaria subunit vaccine targeting both sporozoites and blood stage parasites.

Optimized Malaria-antigens delivered by immunostimulating reconstituted influenza virosomes.

Malaria remains a serious cause of morbidity and mortality in millions of individuals each year. The development of widespread resistance of the parasite to drugs as well as resistance of the transmitting mosquito-vector to insecticides in combination with the poor economic situation of many malaria-endemic countries make the development of an effective and inexpensive treatment and prevention a main focus of research. Vaccines remain to be one of the most cost effective and feasible means of disease control and have remarkable success in the control of many infectious disease: eradication of small pox, virtual eradication of polio and the reduction of measles and diphtheria. Next generation vaccines should focus on specific antigens rather than whole inactivated or attenuated pathogens, since the requirements by regulatory authorities concerning safety are becoming more stringent over time. But sub-unit and in particular peptide-based vaccines are poorly immunogenic themselves, and alum represents only a sub-optimal adjuvant for recombinant proteins and synthetic peptides. This emphasizes the need for suitable carrier- and adjuvant systems promoting protective immune responses by delivering protein and peptide antigens in an appropriate conformation. Here, we review the development of a new approach combining peptide-based malaria vaccine candidate antigens with an immune stimulatory carrier-system based on influenza virosomes focusing on the induction of protective antibodies.

Virosome-based active immunization targets soluble amyloid species rather than plaques in a transgenic mouse model of Alzheimer's disease.

Active vaccination with amyloid peptides shows promise for the treatment and prevention of Alzheimer's disease (AD). Several studies in transgenic mouse models of AD have revealed the potency of vaccination to prevent or even clear amyloid plaques from mouse brain. However, the idea that soluble oligomeric species of beta-amyloid (Abeta), rather than plaques, trigger the disease has gained momentum, and current active vaccination strategies affect the levels of total or soluble brain Abeta little or not at all. We describe an active vaccination method based on Abeta1-16 presented on the surface of virosomes, which triggered a dramatic decrease in both soluble Abeta40 (75% reduction; p=0.01) and soluble Abeta42 (62% reduction; p=0.03) in a double transgenic mouse model of AD. Whereas Abeta40 and Abeta42 levels in the insoluble fraction tended to be reduced (by 30% and 27%, respectively), the number of thioflavine-S-positive amyloid plaques was not affected. The high specific antibody responses, obtained without eliciting T-cell reactivity, demonstrate that immunostimulating reconstituted influenza virosomes are a promising antigen carrier system against the neuropathology of AD.

Nonclinical safety evaluation of Escherichia coli heat-labile toxin mucosal adjuvant as a component of a nasal influenza vaccine.

Conventional influenza vaccines currently in use are administered parenterally and generally confer good protection against systemic disease through the induction of high titers of serum virus-neutralizing antibodies. Parenteral vaccines are suboptimal in that they fail to induce a local mucosal response that may prevent the early stages of virus infection. Thus, the intranasal administration of a vaccine may provide a viable alternative to the parenteral route. Indeed, intranasal administration of vaccine antigens when formulated with an appropriate mucosal adjuvant (e.g., bacterial toxins), results in a vigorous local and systemic immune response. This review discusses the nonclinical safety evaluation of Escherichia coli heat-labile toxin as a mucosal adjuvant for an intranasally administered influenza vaccine.

A virosomal vaccine against candidal vaginitis: immunogenicity, efficacy and safety profile in animal models.

A novel vaccine (PEV7) consisting of a truncated, recombinant aspartyl proteinase-2 of Candida albicans incorporated into influenza virosomes was studied. This vaccine candidate generated a potent serum antibody response in mouse and rat following intramuscular immunization. Anti-Sap2 IgG and IgA were also detected in the vaginal fluid of rats following intravaginal or intramuscular plus intravaginal administration. In a rat model of candidal vaginitis, PEV7 induced significant, long-lasting, likely antibody-mediated, protection following intravaginal route of immunization. PEV7 was also found to be safe in a repeated-dose toxicological study in rats. Overall, these data provide a sound basis to envisage the clinical development of this new candidate vaccine against candidal vaginitis.

Influenza virosomes as a vaccine adjuvant and carrier system.

Influenza virosomes have been used for more than 10 years in commercial vaccines. The technology has been further developed as a carrier and adjuvant system for subunit vaccines, in particular for synthetic peptides. The extensive amount of preclinical and clinical data supports the notion that influenza virosomes represent a platform technology that ensures robust and long-lasting immune responses against subunit antigens with an excellent safety profile. Structurally and functionally, virosomes are enveloped virus-like particles, although they are assembled in vitro. This unique feature ensures a tight control of their composition and at the same time provides the flexibility to adapt the particle to various types of antigens. The mode of action of virosomes is complex and includes carrier as well as immune-stimulatory functions.

Virosome-formulated Plasmodium falciparum AMA-1 & CSP derived peptides as malaria vaccine: randomized phase 1b trial in semi-immune adults & children.

BACKGROUND: This trial was conducted to evaluate the safety and immunogenicity of two virosome formulated malaria peptidomimetics derived from Plasmodium falciparum AMA-1 and CSP in malaria semi-immune adults and children. METHODS: The design was a prospective randomized, double-blind, controlled, age-deescalating study with two immunizations. 10 adults and 40 children (aged 5-9 years) living in a malaria endemic area were immunized with PEV3B or virosomal influenza vaccine Inflexal®V on day 0 and 90. RESULTS: No serious or severe adverse events (AEs) related to the vaccines were observed. The only local solicited AE reported was pain at injection site, which affected more children in the Inflexal®V group compared to the PEV3B group (p = 0.014). In the PEV3B group, IgG ELISA endpoint titers specific for the AMA-1 and CSP peptide antigens were significantly higher for most time points compared to the Inflexal®V control group. Across all time points after first immunization the average ratio of endpoint titers to baseline values in PEV3B subjects ranged from 4 to 15 in adults and from 4 to 66 in children. As an exploratory outcome, we found that the incidence rate of clinical malaria episodes in children vaccinees was half the rate of the control children between study days 30 and 365 (0.0035 episodes per day at risk for PEV3B vs. 0.0069 for Inflexal®V; RR  = 0.50 [95%-CI: 0.29-0.88], p = 0.02). CONCLUSION: These findings provide a strong basis for the further development of multivalent virosomal malaria peptide vaccines. TRIAL REGISTRATION: ClinicalTrials.gov NCT00513669.

Respiratory syncytial virus subunit vaccine based on a recombinant fusion protein expressed transiently in mammalian cells.

Although respiratory syncytial virus (RSV) causes severe lower respiratory tract infection in infants and adults at risk, no RSV vaccine is currently available. In this report, efforts toward the generation of an RSV subunit vaccine using recombinant RSV fusion protein (rRSV-F) are described. The recombinant protein was produced by transient gene expression (TGE) in suspension-adapted human embryonic kidney cells (HEK-293E) in 4 L orbitally shaken bioreactors. It was then purified and formulated in immunostimulating reconstituted influenza virosomes (IRIVs). The candidate vaccine induced anti-RSV-F neutralizing antibodies in mice, and challenge studies in cotton rats are ongoing. If successful in preclinical and clinical trials, this will be the first recombinant subunit vaccine produced by large-scale TGE in mammalian cells.

Development of influenza virosome-based synthetic malaria vaccines.

BACKGROUND: The development of a malaria vaccine represents one of the most important scientific public health challenges of our time. One possible approach is based on subunit vaccines that use distinct malarial antigens for which there is some evidence of protective immunity from epidemiological data in the field or animal challenge models. It is generally accepted that an effective malaria subunit vaccine will target antigens of several developmental stages of the parasite. OBJECTIVE: At present, the development of peptide-based vaccines is hampered by their poor immunogenicity and lack of in vivo stability of synthetic peptides and suitable antigen delivery systems driving appropriate immune responses in humans. Most importantly, the synthetic structures delivered have to mimic closely the corresponding native malaria protein to induce effective antibody responses. METHODS: Review of recent publications highlighting the design as well as preclinical and clinical development of conformationally constrained synthetic peptides of two malaria proteins delivered on the surface of influenza virosomes. RESULTS/CONCLUSION: The great potential of influenza virosomes as a flexible, human-compatible antigen delivery platform for the development of a multivalent malaria subunit vaccine is described.

Evidence of blood stage efficacy with a virosomal malaria vaccine in a phase IIa clinical trial.

BACKGROUND: Previous research indicates that a combination vaccine targeting different stages of the malaria life cycle is likely to provide the most effective malaria vaccine. This trial was the first to combine two existing vaccination strategies to produce a vaccine that induces immune responses to both the pre-erythrocytic and blood stages of the P. falciparum life cycle. METHODS: This was a Phase I/IIa study of a new combination malaria vaccine FFM ME-TRAP+PEV3A. PEV3A includes peptides from both the pre-erythrocytic circumsporozoite protein and the blood-stage antigen AMA-1. This study was conducted at the Centre for Clinical Vaccinology and Tropical Medicine, University of Oxford, Oxford, UK. The participants were healthy, malaria naïve volunteers, from Oxford. The interventions were vaccination with PEV3A alone, or PEV3A+FFM ME-TRAP. The main outcome measure was protection from malaria in a sporozoite challenge model. Other outcomes included measures of parasite specific immune responses induced by either vaccine; and safety, assessed by collection of adverse event data. RESULTS: We observed evidence of blood stage immunity in PEV3A vaccinated volunteers, but no volunteers were completely protected from malaria. PEV3A induced high antibody titres, and antibodies bound parasites in immunofluorescence assays. Moreover, we observed boosting of the vaccine-induced immune response by sporozoite challenge. Immune responses induced by FFM ME-TRAP were unexpectedly low. The vaccines were safe, with comparable side effect profiles to previous trials. Although there was no sterile protection two major observations support an effect of the vaccine-induced response on blood stage parasites: (i) Lower rates of parasite growth were observed in volunteers vaccinated with PEV3A compared to unvaccinated controls (p = 0.012), and this was reflected in the PCR results from PEV3A vaccinated volunteers. These showed early control of parasitaemia by some volunteers in this group. One volunteer, who received PEV3A alone, was diagnosed very late, on day 20 compared to an average of 11.8 days in unvaccinated controls. (ii). Morphologically abnormal parasites were present in the blood of all (n = 24) PEV3A vaccinated volunteers, and in only 2/6 controls (p = 0.001). We describe evidence of vaccine-induced blood stage efficacy for the first time in a sporozoite challenge study.

Virosome-mediated delivery of tumor antigen to plasmacytoid dendritic cells.

Cytotoxic T lymphocytes (CTL) are crucial in viral clearance and tumor growth control. Thus the induction of CTL activity is an important aim in vaccine development. We investigate an innovative delivery system for peptide transfer to the MHC class I processing pathway of APC with the aim to trigger CTL in the context of an antitumoral response. The strategy relies on a novel antigen delivery system termed "chimeric immunopotentiating reconstituted influenza virosomes" (CIRIV) targeting plasmacytoid dendritic cells (PDC). By using virosomes containing encapsulated Melan-A peptide and a PDC line developed in our laboratory, we evaluated the response of Melan-A specific T cells. Virosomes have the capacity to bind PDC and are endocyted within vesicles in the cytosol. This endocytosis is inhibited by neuraminidase, suggesting that it is mediated by sialic acid present on cell surface. Furthermore, PDC loaded with Melan-A virosomes can induce a Melan-A specific T cell activation. Interestingly, they activate T cells with a better efficiency than PDC loaded with a free peptide and when PDC where previously activated by a TLR ligand. These results indicate that virosomes could be a suitable delivery system for tumor peptide in immunotherapy of cancer.