Peptide-loaded chimeric influenza virosomes for efficient in vivo induction of cytotoxic T cells

Protein and lipid expansion microscopy with trypsin and tyramide signal amplification for 3D imaging

Expansion microscopy, whereby the relative positions of biomolecules are physically increased via hydrogel expansion, can be used to reveal ultrafine structures of cells under a conventional microscope. Despite its utility for achieving super-resolution imaging, expansion microscopy suffers a major drawback, namely reduced fluorescence signals caused by excessive proteolysis and swelling effects. This caveat results in a lower photon budget and disfavors fluorescence imaging over a large field of view that can cover an entire expanded cell, especially in 3D. In addition, the complex procedures and specialized reagents of expansion microscopy hinder its popularization. Here, we modify expansion microscopy by deploying trypsin digestion to reduce protein loss and tyramide signal amplification to enhance fluorescence signal for point-scanning-based imaging. We name our new methodology TT-ExM to indicate dual trypsin and tyramide treatments. TT-ExM may be applied for both antibody and lipid staining. TT-ExM displayed enhanced protein retention for endoplasmic reticulum and mitochondrial markers in COS-7 cell cultures. Importantly, TT-ExM-based lipid staining clearly revealed the complex 3D membrane structures in entire expanded cells. Through combined lipid and DNA staining, our TT-ExM methodology highlighted mitochondria by revealing their DNA and membrane structures in cytoplasm, as well as the lipid-rich structures formed via phase separation in nuclei at interphase. We also observed lipid-rich chromosome matrices in the mitotic cells. These high-quality 3D images demonstrate the practicality of TT-ExM. Thus, readily available reagents can be deployed in TT-ExM to significantly enhance fluorescence signals and generate high-quality and ultrafine-resolution images under confocal microscopy.

Virosome: An engineered virus for vaccine delivery

The purpose of immunization is the effective cellular and humoral immune response against antigens. Several studies on novel vaccine delivery approaches such as micro-particles, liposomes & nanoparticles, etc. against infectious diseases have been investigated so far. In contrast to the conventional approaches in vaccine development, a virosomes-based vaccine represents the next generation in the field of immunization because of its balance between efficacy and tolerability by virtue of its mechanism of immune instigation. The versatility of virosomes as a vaccine adjuvant, and delivery vehicle of molecules of different nature, such as peptides, nucleic acids, and proteins, as well as provide an insight into the prospect of drug targeting using virosomes. This article focuses on the basics of virosomes, structure, composition formulation and development, advantages, interplay with the immune system, current clinical status, different patents highlighting the applications of virosomes and their status, recent advances, and research associated with virosomes, the efficacy, safety, and tolerability of virosomes based vaccines and the future prospective.

Cooperation Between Systemic and Mucosal Antibodies Induced by Virosomal Vaccines Targeting HIV-1 Env: Protection of Indian Rhesus Macaques Against Low-Dose Intravaginal SHIV Challenges

A virosomal vaccine inducing systemic/mucosal anti-HIV-1 gp41 IgG/IgA had previously protected Chinese-origin rhesus macaques (RMs) against vaginal SHIV_SF162P3 challenges. Here, we assessed its efficacy in Indian-origin RMs by intramuscular priming/intranasal boosting (n=12/group). Group K received virosome-P1-peptide alone (harboring the Membrane Proximal External Region), Group L combined virosome-rgp41 plus virosome-P1, and Group M placebo virosomes. Vaccination induced plasma binding but no neutralizing antibodies. Five weeks after boosting, all RMs were challenged intravaginally with low-dose SHIV_SF162P3 until persistent systemic infection developed. After SHIV challenge #7, six controls were persistently infected versus only one Group L animal (vaccine efficacy 87%; P=0.0319); Group K was not protected. After a 50% SHIV dose increase starting with challenge #8, protection in Group L was lost. Plasmas/sera were analyzed for IgG phenotypes and effector functions; the former revealed that protection in Group L was significantly associated with increased binding to FcγR2/3(A/B) across several time-points, as were some IgG measurements. Vaginal washes contained low-level anti-gp41 IgGs and IgAs, representing a 1-to-5-fold excess over the SHIV inoculum's gp41 content, possibly explaining loss of protection after the increase in challenge-virus dose. Virosomal gp41-vaccine efficacy was confirmed during the initial seven SHIV challenges in Indian-origin RMs when the SHIV inoculum had at least 100-fold more HIV RNA than acutely infected men's semen. Vaccine protection by virosome-induced IgG and IgA parallels the cooperation between systemically administered IgG1 and mucosally applied dimeric IgA2 monoclonal antibodies that as single-agents provided no/low protection - but when combined, prevented mucosal SHIV transmission in all passively immunized RMs.

Targeted Delivery of CRISPR/Cas13 as a Promising Therapeutic Approach to Treat SARS-CoV-2

On a worldwide scale, the outbreak of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has led to extensive damage to the health system as well as the global economy. Hitherto, there has been no approved drug or vaccine for this disease. Therefore, the use of general antiviral drugs is at the first line of treatment, though complicated with limited effectiveness and systemic side effects. Given the pathophysiology of the disease, researchers have proposed various strategies not only to find a more specific therapeutic way but also to reduce the side effects. One strategy to accomplish these goals is to use CRISPR/Cas13 system. Recently, a group of scientists has used the CRISPR/Cas13 system, which is highly effective in eliminating the genome of RNA viruses. Due to the RNA nature of the coronavirus genome, it seems that this system can be effective against the disease. The main challenge regarding the application of this system is to deliver it to the target cells efficiently. To solve this challenge, it seems that using virosomes with protein S on their membrane surface can be helpful. Studies have shown that protein S interacts with its specific receptor in target cells named Angiotensin-Converting Enzyme 2 (ACE2). Here, we propose if CRISPR/Cas13 gene constructs reach the infected cells efficiently using a virosomal delivery system, the virus genome will be cleaved and inactivated. Considering the pathophysiology of the disease, an important step to implement this hypothesis is to embed protein S on the membrane surface of virosomes to facilitate the delivery of gene constructs to the target cells.

The next generation of HCV vaccines: a focus on novel adjuvant development

INTRODUCTION

Considerable efforts have been made to treat and prevent acute and chronic infections caused by the hepatitis C virus (HCV). Current treatments are unable to protect people from reinfection. Hence, there is a need for development of both preventive and therapeutic HCV vaccines. Many vaccine candidates are in development to fight against HCV, but their efficacy has so far proven limited partly due to low immunogenicity.

AREAS COVERED

We explore development of novel and powerful adjuvants to achieve an effective HCV vaccine. The basis for developing strong adjuvants is to understand the innate immunity pathway, which subsequently stimulates humoral and cellular immune responses. We have also investigated immunogenicity of developed adjuvants that have been used in recent studies available in online databases such as PubMed, PMC, ScienceDirect, Google Scholar, etc.

EXPERT OPINION

Adjuvants are used as a part of vaccine formulation to boost vaccine immunogenicity and antigen delivery. Several FDA-approved adjuvants are used in licensed human vaccines. Unfortunately, no adjuvant has yet been proven to boost HCV immune responses to the extent needed for an effective vaccine. One of the promising approaches for developing an effective adjuvant is the combination of various adjuvants to trigger several innate immune responses, leading to activation of adaptive immunity.[Figure: see text].

Virosome-based nanovaccines; a promising bioinspiration and biomimetic approach for preventing viral diseases: A review

Vaccination is the most effective means of controlling infectious disease-related morbidity and mortality. However, due to low immunogenicity of viral antigens, nanomedicine as a new opportunity in new generation of vaccine advancement attracted researcher encouragement. Virosome is a lipidic nanomaterial emerging as FDA approved nanocarriers with promising bioinspiration and biomimetic potency against viral infections. Virosome surface modification with critical viral fusion proteins is the cornerstone of vaccine development. Surface antigens at virosomes innovatively interact with targeted receptors on host cells that evoke humoral or cellular immune responses through antibody-producing B cell and internalization by endocytosis-mediated pathways. To date, several nanovaccine based on virosome formulations have been commercialized against widespread and life-threatening infections. Recently, Great efforts were made to fabricate a virosome-based vaccine platform against a new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. Thus, this review provides a novel overview of the virosome based nanovaccine production, properties, and application on the viral disease, especially its importance in SARS-CoV-2 vaccine discovery.

Pulmonary Delivery of Virosome-Bound Antigen Enhances Antigen-Specific CD4+ T Cell Proliferation Compared to Liposome-Bound or Soluble Antigen

Pulmonary administration of biomimetic nanoparticles loaded with antigen may represent an effective strategy to directly modulate adaptive immune responses in the respiratory tract. Depending on the design, virosomes may not only serve as biomimetic antigen carriers but are also endowed with intrinsic immune-stimulatory properties. We designed fluorescently labeled influenza-derived virosomes and liposome controls coupled to the model antigen ovalbumin to investigate uptake, phenotype changes, and antigen processing by antigen-presenting cells exposed to such particles in different respiratory tract compartments. Both virosomes and liposomes were captured by pulmonary macrophages and dendritic cells alike and induced activation in particle-bearing cells by upregulation of costimulatory markers such as CD40, CD80, CD86, PD-L1, PD-L2, and ICOS-L. Though antigen processing and accumulation of both coupled and soluble antigen was similar between virosomes and liposomes, only ovalbumin-coupled virosomes generated a strong antigen-specific CD4⁺ T cell proliferation. Pulmonary administrated antigen-coupled virosomes therefore effectively induced adaptive immune responses and may be utilized in novel preventive or therapeutic approaches in the respiratory tract.

Virosome-bound antigen enhances DC-dependent specific CD4+ T cell stimulation, inducing a Th1 and Treg profile in vitro

There is considerable interest to develop antigen-carriers for immune-modulatory clinical applications, but insufficient information is available on their effects on antigen-presenting cells. We employed virosomes coupled to ovalbumin (OVA) to study their interaction with murine bone marrow-derived dendritic cells (BMDCs) and modulation of downstream T cell responses. BMDCs were treated in vitro with virosomes or liposomes prior to determining BMDC phenotype, viability, and intracellular trafficking. Antigen-specific CD4⁺ T cell activation was measured by co-culture of BMDCs with DO11.10 CD4⁺ T cells. Compared to liposomes, virosomes were rapidly taken up. Neither nanocarrier type affected BMDC viability, nor did a moderate degree of activation differ for markers such as CD40, CD80, CD86. Virosome uptake occurred via clathrin-mediated endocytosis and phagocytosis, with co-localization in late endosomes. Only BMDCs treated with OVA-coupled virosomes induced enhanced OVA-specific CD4⁺ T cell proliferation. Antigen-coupled virosomes are endowed with an intrinsic ability to modulate DC-dependent adaptive immune responses.

Virosome engineering of colloidal particles and surfaces: bioinspired fusion to supported lipid layers

Immunostimulating reconstituted influenza virosomes (IRIVs) are liposomes with functional viral envelope glycoproteins: influenza virus hemagglutinin (HA) and neuraminidase intercalated in the phospholipid bilayer. Here we address the fusion of IRIVs to artificial supported lipid membranes assembled on polyelectrolyte multilayers on both colloidal particles and planar substrates. The R18 assay is used to prove the IRIV fusion in dependence of pH, temperature and HA concentration. IRIVs display a pH-dependent fusion mechanism, fusing at low pH in analogy to the influenza virus. The pH dependence is confirmed by the Quartz Crystal Microbalance technique. Atomic Force Microscopy imaging shows that at low pH virosomes are integrated in the supported membrane displaying flattened features and a reduced vertical thickness. Virosome fusion offers a new strategy for transferring biological functions on artificial supported membranes with potential applications in targeted delivery and sensing.

[Way to the peptide vaccine against hepatitis C]

In order to surpass the problem of genetic variability of hepatitis C virus envelope proteins during vaccine development, we used the so-called "reverse vaccinology"approach--"from genome to vaccine". Database of HCV protein sequences was designed, viral genome analysis was performed, and several highly conserved sites were revealed in HCV envelope proteins in the framework of this approach. These sites demonstrated low antigenic activity in full-size proteins and HCV virions: antibodies against these sites were not found in all hepatitis C patients. However, two sites, which contained a wide set of potential T-helper epitope motifs, were revealed among these highly conserved ones. We constructed and prepared by solid-phase peptide synthesis several artificial peptide constructs composed of two linker-connected highly conserved HCV envelope E2 protein sites; one of these sites contained a set of T-helper epitope motifs. Experiments on laboratory animals demonstrated that the developed peptide constructs manifested immunogenicity compared with one of protein molecules and were able to raise antibodies, which specifically bound HCV envelope proteins. We succeeded in obtaining antibodies reactive with HCV from hepatitis C patient plasma upon the immunization with some constructs. An original preparation of a peptide vaccine against hepatitis C is under development on the basis of these peptide constructs.

Influenza T-cell epitope-loaded virosomes adjuvanted with CpG as a potential influenza vaccine

Purpose

Influenza CD8⁺ T-cell epitopes are conserved amongst influenza strains and can be recognized by influenza-specific cytotoxic T-cells (CTLs), which can rapidly clear infected cells. An influenza peptide vaccine that elicits these CTLs would therefore be an alternative to current influenza vaccines, which are not cross-reactive. However, peptide antigens are poorly immunogenic due to lack of delivery to antigen presenting cells, and therefore need additional formulation with a suitable delivery system. In this study, the potential of virosomes as a delivery system for an influenza T-cell peptide was investigated.

Methods

The conserved human HLA-A2.1 influenza T-cell epitope M1_58–66 was formulated with virosomes. The immunogenicity and protective effect of the peptide-loaded virosomes was assessed in HLA-A2 transgenic mice. Delivery properties of the virosomes were studied in mice and in in vitro dendritic cell cultures.

Results

Immunization of HLA-A2.1 transgenic C57BL/6 mice with peptide-loaded virosomes in the presence of the adjuvant CpG-ODN 1826 increased the number of peptide-specific CTLs. Vaccination with adjuvanted peptide-loaded virosomes reduced weight loss in mice after heterologous influenza infection. Association with fusion-active virosomes was found to be crucial for antigen uptake by dendritic cells, and subsequent induction of CTLs in mice.

Conclusions

These results show that influenza virosomes loaded with conserved influenza epitopes could be the basis of a novel cross-protective influenza vaccine.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-014-1556-3) contains supplementary material, which is available to authorized users.

An H1-H3 chimeric influenza virosome confers complete protection against lethal challenge with PR8 (H1N1) and X47 (H3N2) viruses in mice

Annual health threats and economic damages caused by influenza virus are still a main concern of the World Health Organization and other health departments all over the world. An influenza virosome is a highly efficient immunomodulating carrier mimicking the natural antigen presentation pathway and has shown an excellent tolerability profile due to its biocompatibility and purity. The major purpose of this study was to construct a new chimeric virosome influenza vaccine containing hemagglutinin (HA) and neuraminidase (NA) proteins derived from the A/PR/8/1934 (H1N1) (PR8) and A/X/47 (H3N2) (X47) viruses, and to evaluate its efficacy as a vaccine candidate in mice. A single intramuscular vaccination with the chimeric virosomes provided complete protection against lethal challenge with the PR8 and X47 viruses. The chimeric virosomes induced high IgG antibody responses as well as hemagglutination inhibition (HAI) titers. HAI titers following the chimeric virosome vaccination were at the same level as the whole inactivated influenza vaccine. Mice immunized with the chimeric virosomes displayed considerably less weight loss and exhibited significantly reduced viral load in their lungs compared with the controls. The chimeric virosomes can be used as an innovative vaccine formulation to confer protection against a broad range of influenza viruses.

Influenza virosomes as vaccine adjuvant and carrier system

The basic concept of virosomes is the controlled in vitro assembly of virus-like particles from purified components. The first generation of influenza virosomes developed two decades ago is successfully applied in licensed vaccines, providing a solid clinical safety and efficacy track record for the technology. In the meantime, a second generation of influenza virosomes has evolved as a carrier and adjuvant system, which is currently applied in preclinical and clinical stage vaccine candidates targeting various prophylactic and therapeutic indications. The inclusion of additional components to optimize particle assembly, to stabilize the formulations, or to enhance the immunostimulatory properties have further improved and broadened the applicability of the platform.

Adjuvant effect of cationic liposomes for subunit influenza vaccine: influence of antigen loading method, cholesterol and immune modulators

Cationic liposomes are potential adjuvants for influenza vaccines. In a previous study we reported that among a panel of cationic liposomes loaded with influenza hemagglutinin (HA), DC-Chol:DPPC (1:1 molar ratio) liposomes induced the strongest immune response. However, it is not clear whether the cholesterol (Chol) backbone or the tertiary amine head group of DC-Chol was responsible for this. Therefore, in the present work we studied the influence of Chol in the lipid bilayer of cationic liposomes. Moreover, we investigated the effect of the HA loading method (adsorption versus encapsulation) and the encapsulation of immune modulators in DC-Chol liposomes on the immunogenicity of HA. Liposomes consisting of a neutral lipid (DPPC or Chol) and a cationic compound (DC-Chol, DDA, or eDPPC) were produced by film hydration-extrusion with/without an encapsulated immune modulator (CpG or imiquimod). The liposomes generally showed comparable size distribution, zeta potential and HA loading. In vitro studies with monocyte-derived human dendritic cells and immunization studies in C57Bl/6 mice showed that: (1) liposome-adsorbed HA is more immunogenic than encapsulated HA; (2) the incorporation of Chol in the bilayer of cationic liposomes enhances their adjuvant effect; and (3) CpG loaded liposomes are more efficient at enhancing HA-specific humoral responses than plain liposomes or Alhydrogel.

Virus-like particles as a highly efficient vaccine platform: diversity of targets and production systems and advances in clinical development

Virus-like particles (VLPs) are a class of subunit vaccines that differentiate themselves from soluble recombinant antigens by stronger protective immunogenicity associated with the VLP structure. Like parental viruses, VLPs can be either non-enveloped or enveloped, and they can form following expression of one or several viral structural proteins in a recombinant heterologous system. Depending on the complexity of the VLP, it can be produced in either a prokaryotic or eukaryotic expression system using target-encoding recombinant vectors, or in some cases can be assembled in cell-free conditions. To date, a wide variety of VLP-based candidate vaccines targeting various viral, bacterial, parasitic and fungal pathogens, as well as non-infectious diseases, have been produced in different expression systems. Some VLPs have entered clinical development and a few have been licensed and commercialized. This article reviews VLP-based vaccines produced in different systems, their immunogenicity in animal models and their status in clinical development.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

Nanocarrier possibilities for functional targeting of bioactive peptides and proteins: state-of-the-art

This review attempts to provide an updated compilation of studies reported in the literature pertaining to production of nanocarriers encasing peptides and/or proteins, in a way that helps the reader direct a bibliographic search and develop an integrated perspective of the subject. Highlights are given to bioactive proteins and peptides, with a special focus on those from dairy sources (including physicochemical characteristics and properties, and biopharmaceutical application possibilities of e.g. lactoferrin and glycomacropeptide), as well as to nanocarrier functional targeting. Features associated with micro- and (multiple) nanoemulsions, micellar systems, liposomes and solid lipid nanoparticles, together with biopharmaceutical considerations, are presented in the text in a systematic fashion.

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.

Synthetic peptide vaccines

This review considers the stages of the development of synthetic peptide vaccines against infectious agents, novel approaches and technologies employed in this process, including bioinformatics, genomics, proteomics, large-scale peptide synthesis, high-throughput screening methods, the use of transgenic animals for modelling human infections. An important role for the development and selection of efficient adjuvants for peptide immunogens is noted. Examples of synthetic peptide vaccine developments against three infectious diseases (malaria, hepatitis C, and foot-and-mouth disease) are given.

Enhancement of immunogenicity of a virosome-based avian influenza vaccine in chickens by incorporating CpG-ODN

Influenza virosomes are virus-like particles, representing a platform for vaccine development. In this study, we examined the immunogenicity of avian influenza virosomes with or without inclusion of recombinant chicken interferon-gamma (rChIFN-γ) or CpG-ODN in chickens. Immunization with virosomes adjuvanted with CpG-ODN elicited the highest haemagglutination inhibition antibody titres, as well as IgG and IgA serum antibody responses. Moreover, Virosomes+CpG-ODN formulation induced an antigen-specific spleen cell proliferation and IFN-γ expression. In conclusion, our results demonstrated that virus-specific antibody- and cell-mediated responses may be induced in chickens immunized with virosomes and these responses can be enhanced by incorporating CpG-ODN in the virosome vaccine formulation.

Nanoparticle delivery systems in cancer vaccines

Therapeutic strategies that involve the manipulation of the host's immune system are gaining momentum in cancer research. Antigen-loaded nanocarriers are capable of being actively taken up by antigen-presenting cells (APCs) and have shown promising potential in cancer immunotherapy by initiating a strong immunostimulatory cascade that results in potent antigen-specific immune responses against the cancer. Such carrier systems offer versatility in that they can simultaneously co-deliver adjuvants with the antigens to enhance APC activation and maturation. Furthermore, modifying the surface properties of these nanocarriers affords active targeting properties to APCs and/or enhanced accumulation in solid tumors. Here, we review some recent advances in these colloidal and particulate nanoscale systems designed for cancer immunotherapy and the potential for these systems to translate into clinical cancer vaccines.

Structural modifications of outer membrane vesicles to refine them as vaccine delivery vehicles

In an effort to devise a safer and more effective vaccine delivery system, outer membrane vesicles (OMVs) were engineered to have properties of intrinsically low endotoxicity sufficient for the delivery of foreign antigens. Our strategy involved mutational inactivation of the MsbB (LpxM) lipid A acyltransferase to generate OMVs of reduced endotoxicity from Escherichia coli (E. coli) O157:H7. The chromosomal tagging of a foreign FLAG epitope within an OmpA-fused protein was exploited to localize the FLAG epitope in the OMVs produced by the E. coli mutant having the defined msbB and the ompA::FLAG mutations. It was confirmed that the desired fusion protein (OmpA::FLAG) was expressed and destined to the outer membrane (OM) of the E. coli mutant from which the OMVs carrying OmpA::FLAG are released during growth. A luminal localization of the FLAG epitope within the OMVs was inferred from its differential immunoprecipitation and resistance to proteolytic degradation. Thus, by using genetic engineering-based approaches, the native OMVs were modified to have both intrinsically low endotoxicity and a foreign epitope tag to establish a platform technology for development of multifunctional vaccine delivery vehicles.

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.

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.

A virosomal malaria peptide vaccine elicits a long-lasting sporozoite-inhibitory antibody response in a phase 1a clinical trial

OBJECTIVES

Peptides delivered on the surface of influenza virosomes have been shown to induce solid humoral immune responses in experimental animals. High titers of peptide-specific antibodies were also induced in a phase 1a clinical trial in volunteers immunized with virosomal formulations of two peptides derived from the circumsporozoite protein (CSP) and the apical membrane antigen 1 (AMA-1) of Plasmodium falciparum. The main objective of this study was to perform a detailed immunological and functional analysis of the CSP-specific antibodies elicited in this phase 1a trial.

METHODOLOGY/PRINCIPAL FINDINGS

46 healthy malaria-naïve adults were immunized with virosomal formulations of two peptide-phosphatidylethanolamine conjugates, one derived from the NANP repeat region of P. falciparum CSP (designated UK-39) the other from P. falciparum AMA-1 (designated AMA49-C1). The two antigens were delivered in two different concentrations, alone and in combination. One group was immunized with empty virosomes as control. In this report we show a detailed analysis of the antibody response against UK-39. Three vaccinations with a 10 microg dose of UK-39 induced high titers of sporozoite-binding antibodies in all volunteers. This IgG response was affinity maturated and long-lived. Co-administration of UK-39 and AMA49-C1 loaded virosomes did not interfere with the immunogenicity of UK-39. Purified total IgG from UK-39 immunized volunteers inhibited sporozoite migration and invasion of hepatocytes in vitro. Sporozoite inhibition closely correlated with titers measured in immunogenicity assays.

CONCLUSIONS

Virosomal delivery of a short, conformationally constrained peptide derived from P. falciparum CSP induced a long-lived parasite-inhibitory antibody response in humans. Combination with a second virosomally-formulated peptide derived from P. falciparum AMA-1 did not interfere with the immunogenicity of either peptide, demonstrating the potential of influenza virosomes as a versatile, human-compatible antigen delivery platform for the development of multivalent subunit vaccines.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00400101.

A new and versatile virosomal antigen delivery system to induce cellular and humoral immune responses

The purpose of a vaccine is the induction of effective cellular and/or humoral immune responses against antigens. Because defined antigens are often poor immunogens when administered alone, an adjuvant is required to potentiate the immune response. Most of these adjuvants are designed to induce humoral immune responses, including immunopotentiating reconstituted influenza virosomes (IRIVs). IRIVs are one of the few adjuvants currently licensed for human use with the advantage of an excellent safety profile. To induce a potent cytotoxic T lymphocyte (CTL) immune response CTL epitopes have to be encapsulated into IRIVs. However, the existing encapsulation methods are inefficient or rather laborious. We have developed and characterised a new generation of influenza virosomes (TIRIVs) that induced both, strong CTL and antibody responses against specific antigens of choice. In addition, these virosomes were stabilised and offer the possibility of lyophilisation while retaining all their structural, functional and immunogenic properties after reconstitution. TIRIVs induce strong cellular and humoral immune responses and are a versatile and efficient carrier system with adjuvant properties for a variety of antigens. TIRIVs are not only stabilised but also allow easy formulation of new and/or labile T cell and B cell antigens. Considering their immunogenic properties, their flexibility and their superior storage characteristics TIRIVs provide a versatile technology platform for any vaccination strategy.

Viral peptide immunogens: current challenges and opportunities

Synthetic peptide vaccines have potential to control viral infections. Successful experimental models using this approach include the protection of mice against the lethal Sendai virus infection by MHC class I binding CTL peptide epitope. The main benefit of vaccination with peptide epitopes is the ability to minimize the amount and complexity of a well-defined antigen. An appropriate peptide immunogen would also decrease the chance of stimulating a response against self-antigens, thereby providing a safer vaccine by avoiding autoimmunity. In general, the peptide vaccine strategy needs to dissect the specificity of antigen processing, the presence of B-and T-cell epitopes and the MHC restriction of the T-cell responses. This article briefly reviews the implications in the design of peptide vaccines and discusses the various approaches that are applied to improve their immunogenicity.

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-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.

Clinical applications of virosomes in cancer immunotherapy

Cancer immunotherapy is increasingly accepted as a treatment option for advanced stage disease. The identification of tumour-associated antigens in 1991 has prompted the development of antigen-specific immunotherapeutic strategies for a variety of cancers. Many of them result in some immunological responses in cancer patients; however, clinical results were not observed concomitantly with immunological responses; therefore, further improvements in the field of immunotherapy are urgently needed. Virosomes are lipidic envelopes devoid of genetic information, but which retain the antigenic profile and fusogenic properties from their viral origin. Virosomes are versatile antigen carriers and can be engineered to perform various tasks in cancer immunotherapy. Preclinical data have fostered the development of innovative clinical protocols. Hence, immunopotentiating reconstituted influenza virosomes will be assessed in breast and melanoma immunotherapy, and may contribute to the development of clinically effective cancer vaccines and ultimately improve patient outcomes. The objective of this review is to provide an overview of the potential clinical applications of virosomes as innovative and potentially effective reagents in active specific cancer immunotherapy.

Efficient induction of tumoricidal cytotoxic T lymphocytes by HLA-A0201 restricted, melanoma associated, L27Melan-A/MART-126–35 peptide encapsulated into virosomes in vitro

Cancer immunotherapy requires the induction of HLA class I restricted cytotoxic T lymphocytes (CTL) specific for tumor associated antigens (TAA). While a number of TAA have been identified, there is an urgent need for the development of adjuvants capable of stimulating CTL responsiveness. Previously, we reported the capacity of immunopotentiating reconstituted influenza virosomes (IRIV) to enhance CTL responses specific for synthetic peptides simultaneously added to cultures in soluble form. This effect was based on IRIV mediated activation of CD4(+) T cells. Here we investigated the "in vitro" immunogenicity of a novel virosome formulation coupling in a single reagent the adjuvant power of IRIV to the capacity of liposomes to efficiently encapsulate synthetic peptides. As a model epitope we chose L(27)Melan-A/Mart-1(26-35) HLA-A0201 restricted peptide from a melanoma-associated antigen widely used in tumor immunotherapy. The reagent thus developed induced the proliferation of CD4(+) T cells characterized by a T helper 1 cytokine profile and CXCR3 expression. Most importantly, it significantly enhanced the generation of L(27)Melan-A/Mart-1(26-35) specific CTL, as compared to soluble peptides, in particular at low nominal epitope concentrations (<1 microg/ml). These effector cells were able to efficiently kill HBL melanoma cells expressing Melan-A/MART-1 and HLA-A0201. The adjuvant effects observed were also detectable in the absence of CD4(+) T cells. Taken together our results suggest that this highly immunogenic antigenic formulation might qualify for clinical use in active, antigen-specific, melanoma immunotherapy.

Peptides delivered by immunostimulating reconstituted influenza virosomes

Vaccines have been well accepted and used effectively for more than 100 years. Traditional vaccines are generally composed of whole inactivated or attenuated microorganisms that have lost their disease-causing properties. These classical prophylactic live vaccines evoke protective immune responses, but have often been associated with an unfavorable safety profile, as observed, for example, for smallpox and polio myelitis vaccines [1,2]. First improvements were subunit vaccines that do not focus on attenuation of whole organisms but concentrate on particular proteins. These vaccines are able to generate protective immune responses (e.g. diphtheria, tetanus, pertussis)3. However, next generation vaccines should focus on specific antigens (e.g. proteins, peptides), since the requirements by regulatory authorities to crude biological material are becoming more stringent over time. An increasing number of such antigens capable of inducing protective humoral or cellular immune responses have been identified in the last few years. But most of these are weak immunogens. This reemphasizes the need for adjuvants to promote a potent immune response and also for delivery antigens to the immune system in an appropriate way (carrier capability). Here we review a new approach for prophylactic and therapeutic vaccines, which focuses on the induction of highly specific immune responses directed against antigen-derived peptides using a suitable carrier system.