Virosomes

Virosomes are virus-mimicking systems that contain liposomal bilayer and pH-dependent protein impregnated in the liposomal wall. Virosomes are produced by a detergent dialysis procedure. Many researchers have demonstrated that the virosomes facilitate the leakage of the encapsulated drugs from the endosomes into the cytoplasm. This is, however, complicated technology and, so far, no virosome products are used in the clinical practice. 

Felnerova D, et al. Liposomes and virosomes as delivery systems for antigens, nucleic acids, and drugs. Curr Opin Biotechnol 2004 15 518. 

Immunopotentiating reconstituted influenza virosomes (IRTV) are spherical 150-nm sized particles consisting of a phospholipid bilayer in which influenza virus A/Singapore strain-derived hemagglutinin (HA) and neuraminidase (NA) are intercalated. As such, they resemble and mimic the influenza virus envelope. The difference from conventional liposome formulations lies in the inclusion of the viral envelope proteins HA and NA as well as viral phospholipids. Especially, the inclusion of influenza virus HA provides IRIV with delivery and immimogenic capacities. IRTV are licensed for human use as adjuvant in hepatitis A vaccination and as influenza subunit vaccine (1). 

Figure 1 Continued on next page) Immunopotentiating reconstituted influenza virosomes (IRIV) induced antigen specific proliferation of CD4+CD45RO+ cells. (A) Peripheral blood mononuclear cells (PBMQ from healthy donors n=3) were cultured in the absence of stimuli (Neg), in the presence of IRIV (V), and in the presence of control liposomes (L) at the indicated dilutions. Proliferation was measured on day 6 of culture by H-thymidine incorporation. (B) Cord blood mononuclear cells from two donors were cultured in the absence of stimuli (Neg) or in the presence of phytohaemag-glutinin (PHA), concanavalin A (ConA), IRIV (V) or L at the indicated concentrations. Proliferation was measured on day 3 of culture for PHA and ConA cultures and on day 6 for IRIV and L stimulated cultures. (Q Purified CD4+ or CD8+ cells were cocultured with autologous irradiated PBMC in the absence of stimuli (Neg) and in the presence of IRIV (V) at the indicated concentrations. Proliferation was measured on day 6 of culture by H-thymidine incorporation. (D) Purified CD4/CD45RA+ cells and CD4/CD45RO-I-cells were isolated from PBMC of one healthy donor and cocultured with autologous irradiated PBMC in the presence of IRIV (V) or L at the indicated concentration. Proliferation was measured on day 6 of culture by H-thymidine incorporation. Source From Ref 6.

Figure 2 Cytokine gene expression in immunopotentiating reconstituted influenza virosomes (IRIV) stimulated peripheral blood mononuclear cells (PBMC). PBMC were cultured in the presence or absence of IRIV. On days 1 and 2, culture cells were harvested and total cellular RNA was extracted and reverse transcribed. The cDNAs thus obtained were tested in real time polymerase chain reaction assays in the presence of primers specific for the indicated cytokine genes. Source From Refs. 6 and 9.

Figure 5 Immunopotentiating reconstituted influenza virosomes (IRIV) adjuvance on cytotoxic T-cell (CTL) induction. PBMC from a healthy donor were cultured in the presence of influenza matrix (IM)58 66 (A), IMss-eo and control liposomes (B) or IMss-ee and IRIV (C). After a seven-day culture, percentages of IMss-ee speciflc CTL within cultured cells were quantifled by HLA-A0201/IM58 gfi phosphatidylethanolamine tetramer staining (fluorescence 2) and anti CDS fluorescein isothiocyanate staining (fluorescence 1). CTL precursor frequencies detected in IMss-ee and IRIV stimulated cultures within the same experiment are shown in (D). Source From Ref 6.

Figure 6 Immunopotentiating reconstituted influenza virosomes (IRIV) adjuvant effects in the induction of tumor associated antigen-specific cytotoxic T cell. CD14-negative cells from a healthy donor peripheral blood mononuclear cells were cocultured with autologous immature dendritic cells (iDC) in the presence of Melan-A/Mart-l27-35, alone (A) or supplemented with either control liposomes (B) or IRIV (1 50, C). On day 7, culture cells were restimulated with Melan-A/MART-127-35 pulsed iDC and cultured for six further days [see Materials and Methods ]. On day 7 after restimulation cells were stained with fluorescein isothiocyanate-conjugated anti-CD8 and phosphatidylethanolamine-conjugated HL A-A0201 /Melan-A/MART -127-3 5 tetramers. Source From Ref. 6.

Figure 7 Immunopotentiating reconstituted influenza virosomes (IRIV) mediated adjuvance in cytotoxic T-cell induction requires CD4+ T cells. CD8+ and CD14+ cells were cultured in the presence of autologous intact or irradiated CD4+ cells. These cultures were stimulated with influenza matrix (IM)58 66 (1 Pg/mL) alone (A) or supplemented with IRIV (1 50) (B). After seven days of incubation both cocultures were restimulated with irradiated IMss-ee pulsed CD14+ cells and cultured for six further days in the presence of interleukin-2 [see Materials and Methods ]. Six days after restimulation, cultures were stained with HLA-A0201 /IM58-66 PE-specilic tetramers and anti-CD8 fluorescein isothiocyanate monoclonal antibodies. Source. From Ref 6.

Schumacher R, Adamina A, Zurbriggen R, et al. Influenza virosomes enhance class I restricted CTL induction through CD4+ T cell activation. Vaccine 2004 22 714. 

Virosomes are viral glycoproteins encapsulated in lipid vesicles, which have been shown to be effective as experimental vaccines delivered by both mucosal and systemic routes. Viruses and their surface glycoproteins have a high affinity for receptors on mucosal surfaces, especially along the respiratory tract. 

Liposomes are phospholipid vesicles that have been evaluated both as adjuvants and as vehicles for antigens and adjuvants (17). A liposomal hepatitis A (Hep A) vaccine (virosomes) has been extensively evaluated in the clinic and is currently licensed for a Hep A vaccine (18). Alternative adjuvants that have been used in a few products include L-tyrosine (allergy vaccine) and MPL (cancer treatment). The various adjuvants (mainly alum salts) used in vaccine formulations and their quantities per dose are listed in Table 1. 

Bungener DT, Huckriede A, Wilschut J. Virosomes as an antigen delivery system. J Liposome Res 2000 10 329-338. 

Kaneda, Y. (2000) Virosomes evolution of the liposome as a targeted drug delivery system. Adv. Drug Deliv. Rev., 43, 197-205. 

Proteohposomes, also known as virosomes or chimerasomes, incorporate viral proteins, fusogenic peptides, nuclear proteins or nuclear localization peptides, which induce fusion of hposomes with the cell membranes and facilitate DNA release and transport through the cytoplasm. 

Mineral Salts Immunostimulatory adjuvants Lipid particles Particulate adjuvants Mucosal adjuvants Aluminium hydroxide, aluminium phosphate, calcium phosphate Saponins (e.g., QS21), MDP derivatives, bacterial DNA (CpG oligos), LPS, MPL and synthetic derivatives, lipopeptides, cytokines (e.g., GM-CSF, IL-2, IL-12) Liposomes, virosomes, iscoms, cochleates, emulsions (e.g., Freunds adjuvant, SAF, MF59 ) Poloxamer particles, virus-like particles, PLG microparticles Cholera toxin (CT), mutant toxin (e.g., LTK63, LTR72), heat labile enterotoxin (LT), microparticles, polymerized liposomes, chitosan... 

Virosomes are liposomes containing viral fusion proteins that allow efficient entering into cells fusion with endosome membranes. Viral fusion proteins become activated in the low pH environment in the endosome to release its contents into the cytosol. Hepatitis A and influenza vaccines constructed on virosomes elicited fewer local adverse reactions than did their classic counterparts and displayed enhanced immunogenicity. Virosome-formulated influenza vaccine has also been shown to be safe and immunogenic when administered by the intranasal route. Other studies have suggested that immunopotentiating reconstituted influenza virosomes can be a suitable delivery system for synthetic... 

Poltl-Frank, F. Zurbriggen, R. Helg, A. Stuart, F. Robinson, J. Gluck, R. Pluschke, G. Use of reconstituted influenza virus virosomes as an immunopotentiating delivery system for a peptide-based vaccine. Clin. Exp. Immunol. 1999, 117, 496-503. 

To increase immunogenicity, the hepatitis A vaccines commercially available are coupled to adjuvant aluminium phosphate or aluminium hydroxide. However, alum precipitates provoke inflammatory responses at the injection site. Immunostimulating reconstituted influenza virosomes have therefore been used as an alternative adjuvant. In 1994, a hepatitis A vaccine using the new adjuvant was licensed in Switzerland, and it was later approved for use in other countries the vaccine was well tolerated and highly immunogenic (SEDA-20,290) (SEDA-22,344). Nine people with a history of ocular sensitivity were immunized with hepatitis B, without untoward reactions. However, this result in such a small series should not be overestimated (75). There have been reports of three cases of inflammatory nodular reactions after hepatitis B immunization aluminium allergy was confirmed (76-78). 

The current status of adjuvanted influenza vaccines has been reviewed (26). The authors concluded that the vaccine produces a higher titer of antibodies than non-adjuvanted or virosomal vaccines. Local reactions occur more often, but are mild and transient. The results of a trial with two doses of an intranasally administered inactivated virosome-formulated influenza vaccine containing Escherichia coli heat-labile toxin as a mucosal adjuvant in 106 volunteers aged 33-63 years have been reported (27). About 50% of vaccinees had local adverse reactions (44% after the first dose and 54% after the second dose) or systemic adverse reactions (48 and 46%) after administration of the vaccine. Rhinorrhea, sneezing, and headache were the most common reactions they were mild and transient and resolved within 24-48 hours. No febrile reactions were associated with immunization. Between 77 and 92% of vaccinees developed protective hemagglutination inhibition antibody titers against the two influenzae A strains of the vaccine, whereas protective antibody titers against the B strain of the vaccine were achieved in only 49-58%. 

Gluck R, Mischler R, Durrer P, Furer E, Lang AB, Herzog C, Cryz SJ Jr. Safety and immunogenicity of intranasally administered inactivated trivalent virosome-formulated influenza vaccine containing Escherichia coli heat-labile toxin as a mucosal adjuvant J Infect Dis 2000 181(3) 1129-32. 

Two commercial vaccines based on virosome technology are currendy on the market. Epaxal (Berna Biotech Ltd, Bern, Switzerland), a hepatitis A vaccine, has inactivated hepatitis A virus particles adsorbed on the surface of the immunopotentiating reconstituted influenza virosomes (IRIV). In Inflexal V (Berna Biotech Ltd) the virosome components themselves are the vaccine protective antigens (185). Recently, in phase I study liposome-encapsulated malaria vaccine (containing monophosphoryl lipid A as adjuvant in the bilayer), the formulation showed induction of higher level of anti-malaria antibody in human volunteers (186). Some liposomal formulations are under investigation in preclinical studies against Yersina pestis, ricin toxin and Ebola Zaire virus (77, 187). 

Cusi MG et al (2004) Efficient delivery of DNA to dendritic cells mediated by influenza virosomes. Vaccine 22 735-739... 

Bungener L, Huckriede A, Wilschut J, Daemen T (2002) Delivery of protein antigens to the immune system by fusion-active virosomes A comparison with liposomes and ISCOMs. Biosci Rep 22 323-338... 

Bungener L et al (2002) Virosome-mediated delivery of protein antigens to dendritic cells. Vaccine 20 2287-2295... 

Huckriede A, Bungener L, Daemen T, Wilschut J (2003) Influenza virosomes in vaccine development. Meth Enzymol 373 74-91... 

Herzog C, Metcalfe IC, Schaad UB (2002) Virosome influenza vaccine in children. Vaccine 20(Suppl 5) B24-B28... 

Usonis V et al (2003) Antibody titres after primary and booster vaccination of infants and young children with a virosomal hepatitis A vaccine (Epaxal). Vaccine 21 4588-4592... 

Ambrosch F et al (2004) Rapid antibody response after vaccination with a virosomal hepatitis a vaccine. Infection 32 149-152... 

Ruf BR, Colberg K, Frick M, Preusche A (2004) Open, randomized study to compare the immunogenicity and reactogenicity of an influenza split vaccine with an MF59-adjuvanted subunit vaccine and a virosome-based subunit vaccine in elderly. Infection 32 191-198... 

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