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PubMedDate not supplied

Virosomes in vaccine development: induction of cytotoxic T lymphocyte activity with virosome-encapsulated protein antigens.

Virosomes are reconstituted viral envelopes which lack the genetic material but retain the cell entry and membrane fusion characteristics of the virus they are derived from. Thus, influenza virosomes are taken up by cells via receptor-mediated endocytosis, which directs the particles to the endosomal cell compartment. Subsequently, the virosomal membrane fuses with the endosomal membrane induced by the mildly acidic pH within the endosomes. This fusion process establishes continuity between the lumen of the virosome and the cell cytosol. Upon interaction of virosomes with antigen-presenting cells (APCs), protein antigens encapsulated within virosomes will be delivered to the cell cytosol, and thus, into the MHC class I presentation pathway. Indeed, virosome-mediated delivery of antigens in vivo results in efficient priming of a class I MHC-restricted cytotoxic T lymphocyte (CTL) response.

Animals↗

PubMed2005

The virosome concept for influenza vaccines.

There is a need for more efficacious inactivated influenza vaccines, since current formulations show suboptimal immunogenicity in at-risk populations, like the elderly. More effective vaccines are also urgently needed for an improved influenza pandemic preparedness. In this context, there is considerable interest in virosomes. Virosomes are virus-like particles, consisting of reconstituted influenza virus envelopes, lacking the genetic material of the native virus. Virosomes are produced from influenza virus through a detergent solubilization and removal procedure. Properly reconstituted virosomes retain the cell binding and membrane fusion properties of the native virus, mediated by the viral envelope glycoprotein haemagglutinin. These functional characteristics of virosomes form the basis for their enhanced immunogenicity. First, the repetitive arrangement of haemagglutinin molecules on the virosomal surface mediates a cooperative interaction of the antigen with Ig receptors on B lymphocytes, stimulating strong antibody responses. In addition, virosomes interact efficiently with antigen-presenting cells, such as dendritic cells, resulting in activation of T lymphocytes. In a murine model system, virosomes, as compared to conventional subunit vaccine, which consists of isolated influenza envelope glycoproteins, induce a more balanced T helper 1 versus T helper 2 response, virosomes in particular eliciting stronger T helper 1 responses than subunit vaccine. Also, as a result of fusion of the virosomes with the endosomal membrane, part of the virosomal antigen gains access to the major histocompatibility class I presentation pathway, thus priming cytotoxic T lymphocyte activity. Finally, virosomes represent an excellent platform for inclusion of lipophilic adjuvants for further stimulation of vaccine immunogenicity. By virtue of these characteristics, virosomes represent a promising novel class of inactivated influenza vaccines, which not only induce high virus-neutralizing antibody titres, but also prime the cellular arm of the immune system.

Antigen Presentation↗

PubMed1994

Cellular cytoplasmic delivery of a polypeptide toxin by reconstituted influenza virus envelopes (virosomes).

In this paper it is demonstrated that reconstituted influenza virus envelopes (virosomes) fuse efficiently with membranes of the endosomal cell compartment of cultured cells, after internalization through receptor-mediated endocytosis. As a consequence, molecules, encapsulated in the virosomal interior, are transferred to the cell cytoplasm. This process was monitored on the basis of delivery of subunit A of diphtheria toxin (DTA), initially encapsulated in the virosomal lumen. Virosome-mediated cytoplasmic delivery of DTA resulted in a virtually complete inhibition of cellular protein synthesis. DTA delivery was blocked by factors inhibiting the pH-dependent fusion activity of viral hemagglutinin, i.e., 20 mM NH4Cl, preincubation of the virosomes at low pH, and anti-hemagglutinin antibodies. Quantitation of the extent of virosome-mediated delivery of biologically active DTA demonstrated that a lower bound of approximately 10% of the virosomes entering the cells deposited their aqueous contents into the cytosol. This is in good agreement with the final extent of virosome fusion of 40%, as determined by a fluorescence lipid mixing assay based on the dilution of pyrene-labeled phosphatidylcholine from the virosomal into the endosomal membrane. At an added concentration of 1 microM virosomal lipid per 50,000 cells, depending on the condition of the experiment, a minimum of 4000 virosomes per cell were found to be internalized. Virosomes could also be induced to fuse with the cell plasma membrane by a transient lowering of the extracellular pH, as detected by appearance of virosome-encapsulated DTA in the cytoplasm.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1984

Binding to cells of virosomes containing herpes simplex virus type 1 glycoproteins and evidence for fusion.

Envelope proteins and lipids were extracted from purified herpes simplex virus type 1 virions with octyl glucoside and mixed with phosphatidylcholine for preparation of virosomes by removal of the detergent. Greater than 85% of the extracted envelope proteins, including all the glycoproteins and the nonglycosylated protein designated VP16, were associated with virosomes, which ranged in density from ca. 1.07 to 1.13 g/cm3. All the glycoproteins except gC were as susceptible to degradation by added protease in virosomes as in virions, indicating similar orientations in both. Approximately 30 to 40% of radiolabel incorporated into virosomes bound to HEp-2 cells within 1.5 h at either 4 or 37 degrees C. The cell-bound virosomes were enriched for gB and deficient in other glycoproteins, in comparison with unbound or total virosomes. Binding of virosomes to HEp-2 cells could be inhibited by purified virus, heparin, and monospecific antiviral antibodies. Polyclonal and monoclonal anti-gB antibodies were more effective at inhibiting virosome binding than were anti-gD or anti-gC antibodies. Virosomes depleted of gB or gD did not bind to cells as efficiently as did virosomes containing all the extracted enveloped components; this loss of binding activity was especially pronounced on depletion of gB. The binding of herpes simplex virus type 1 virosomes to cells is discussed in relation to possible heterogeneity of the virosomes and comparisons with binding of virions to cells. We also present electron microscopic evidence that bound virosomes can fuse with the cell surface.

Animals↗

PubMed2003

Influenza virosomes in vaccine development.

Influenza virosomes can be regarded as unilamellar liposomes carrying the spike proteins of influenza virus on their surface. Vaccination with influenza virosomes elicits high titers of influenza-specific antibodies, indicating that HA (and NA) reconstituted into a membranous environment exhibit strong immunogenicity. Moreover, virosomes can be used as presentation systems for unrelated antigens bound to the virosome surface. Because of their intrinsic adjuvant activity, virosomes support antibody formation and induction of T-helper cell responses against such surface-associated antigens. Provided that the fusogenic properties of the reconstituted HA are retained, virosomes can also be used to elicit cytotoxic T-cell responses against encapsulated antigens. Vaccines capable of activating the cellular branch of the immune response can be very important for protection against acute virus infections, especially for viruses with rapidly changing envelope glycoproteins like HIV and influenza virus. Moreover, virosomes can suit as powerful carriers in the development of prophylactic and immunotherapeutic strategies against cancer and premalignant disease. The use of virosomes as commercial influenza vaccine and as commercial adjuvant for a hepatitis A vaccine demonstrates that production of virosomes on an industrial scale is feasible, both technically and economically. The industrial production procedure currently followed has not been designed to retain the functional properties of HA. In fact, several steps in the procedure are probably incompatible with retention of fusion activity. As mentioned previously the fusogenic properties of virosomes are important for CTL activation and might also play a role in the induction of T-helper cell and antibody responses. Therefore, a number of key adaptations in the virosome production protocol will be necessary. Thus improved, virosomes are very attractive devices for the development of highly efficacious vaccines against a range of antigens.

Antigen Presentation↗

PubMed1998

Delivery to cancer cells of antisense L-myc oligonucleotides incorporated in fusogenic, cationic-lipid-reconstituted influenza-virus envelopes (cationic virosomes).

Antisense oligodeoxy-nucleoside phosphorothioates (OPTs) of L-myc were encapsulated into reconstituted influenza-virus-A envelopes (virosomes). The envelopes of the virosomes consisted of a single positively charged (cationic) lipid bilayer. Binding of cationic virosomes to cellular receptors that are membrane glycoproteins or glycolipids containing terminal sialic acid is mediated by the hemagglutinin glycoprotein (HA) of the influenza virus. After internalization through receptor-mediated endocytosis, cationic virosomes fuse efficiently with the membranes of the endosomal-cell compartment, and as a consequence the encapsulated OPT are delivered to the cell cytoplasma. Examination by fluorescence microscopy of the cellular uptake of cationic virosomes containing fluorescein-labeled OPT showed rapid and efficient incorporation of virosomes. Addition of cationic virosomes (75-150 microl) containing antisense L-myc OPT in the picomolar range to small-cell-lung-cancer (SCLC) cell cultures that expressed highly the L-myc oncogene led to strong inhibition of thymidine incorporation in a concentration-dependent manner. Virosome-entrapped sense L-myc OPT and random-order OPT had only minimal effects on the thymidine uptake. Cells of SCLC cell line NCI-H82 expressing a very low level of L-myc were not affected by antisense-L-myc virosomes. In Western-blot analysis, expression of L-myc protein was suppressed in the antisense-virosome-treated NCI-H209 cells but not in untreated control NCI-H209 cells. These results suggest that cationic virosomes may have great potential as an efficient delivery system for antisense oligonucleotides in cancer therapy.

Antibodies, Monoclonal↗

PubMed2004

Comparison of immunogenicity and tolerability of a virosome-adjuvanted and a split influenza vaccine in children.

OBJECTIVE: To compare the immunogenicity and safety of a virosome-adjuvanted influenza vaccine (Inflexal V; Berna Biotech, Berne, Switzerland) and a split influenza vaccine (Fluarix; GlaxoSmithKline Biologicals, Rixensart, Belgium) in children. SUBJECTS AND METHODS: The subjects, 453 children ages 6 to 71 months, were stratified into primed and unprimed and age groups (6 to 35 and 36 to 71 months) and then randomized 1:1 to receive virosome-adjuvanted (n = 224) or split influenza vaccine (n = 229), a half or full dose was given intramuscularly according to age. Unprimed children received a second dose after 4 weeks. Blood samples (n = 326) collected pre-and 28 days postvaccination were analyzed by hemagglutination inhibition test. Safety assessments were made at baseline and follow-up visits by the investigators and by parents for the 4 days after vaccinations. RESULTS: Both vaccines induced an effective immune response. Seroconversion rates (>4-fold titer rise) against the WHO recommended strains A/New Caledonia (H3N2), A/Moscow (H1N1) and B/Hongkong (B) were 80.1, 66.0 and 90.4% for the virosome-adjuvanted and 75.9, 62.9 and 89.4% for the split influenza vaccine, respectively. Unprimed children's seroconversion rates for H3N2 were significantly higher (P = 0.02) for the virosome-adjuvanted (88.8%) than for split influenza vaccine (77.5%). Seroprotection rates (titer of > 40) for H3N2, H1N1 and B, respectively, were 87.8, 80.1 and 90.4% after vaccination with the virosome-adjuvanted vaccine and 82.9, 78.2 and 89.4% after the split influenza vaccine. Unprimed children's seroprotection rate was significantly higher (P = 0.03) for H3N2 after the virosome-adjuvanted (88.8%) than those for the split influenza vaccine (78.3%). Equivalent geometric mean titer fold increases were evident for both vaccines. No serious adverse events were seen. Pain/ tenderness, redness and swelling/induration was found in 25.4, 11.2 and 8.9% for the virosome-adjuvanted vaccine and in 24.0, 9.2 and 6.1% for the split influenza vaccine, respectively. The rates of fever, malaise/irritability and shivering was 6.3, 11.6 and 2.7% for the virosome-adjuvanted vaccine and 8.3, 11.8 and 2.6% for the split influenza vaccine, respectively. CONCLUSIONS: The virosome-adjuvanted influenza vaccine showed greater immunogenicity over the split influenza vaccine in unprimed children and showed a trend toward better immunogenicity in the rest of the study population. Both vaccines were well-tolerated.

Child, Preschool↗

PubMed1996

Activation of murine lymphocytes by lipopolysaccharide incorporated in fusogenic, reconstituted influenza virus envelopes (virosomes).

We have studied the in vitro activation of murine lymphocytes with LPS incorporated in the membranes of both phospholipid vesicles (liposomes) and vesicles composed of fusogenic, reconstituted influenza virus envelopes (virosomes). The incorporation of Salmonella minnesota rough-LPS in liposomes reduced the potency of LPS to stimulate splenocyte proliferation and cell surface kappa-light chain expression on 70 Z/3 pre-B cells by over 100-fold. Salmonella minnesota rough-LPS inserted into virosomes was at least 10-fold more potent than free LPS, both when prebound virosomes were allowed to be taken up by the cells at neutral pH and when the virosomes were fused into the plasma membrane by low pH treatment. Inactivation of the virosomes by low pH pretreatment reduced the potency of the virosomal LPS to the level of liposome-incorporated LPS. The association of the various LPS forms with the cells was quantitated using radio-iodinated LPS. Correcting for uptake, virosomal LPS remained 2- to 10-fold more potent than free LPS in stimulating B lymphocytes and at least 100-fold more active than liposomal LPS or fusion-inactivated virosomes. After low pH-induced fusion with the plasma membrane, the majority (80%) of the prebound virosomes had fused with the cells, compared with about 8% after neutral uptake. From these results we conclude that LPS inserted into the plasma or endosomal membranes efficiently activates murine lymphocytes. The fusion data suggest that the incorporation into endosomal membranes might be a more effective stimulus.

Animals↗

PubMed2004

Virosome and ISCOM vaccines against Newcastle disease: preparation, characterization and immunogenicity.

The purpose of this study was to prepare and characterize virosomes and ISCOMs containing envelope proteins of Newcastle disease virus (NDV) and to evaluate their immunogenicity in target animals (chickens). Virosomes were prepared by solubilization of virus with either Triton X-100 or octyl glucoside (OG) followed by detergent removal. Biochemical analysis revealed that these virosomes contained both the haemagglutinin-neuraminidase protein (HN) and the fusion protein (F), with preserved biological activity. Acidic environment triggered the fusion between virosomes and chicken erythrocyte ghosts. Formation of ISCOMs was achieved by solubilizing phospholipids, cholesterol, envelope protein antigen and Quil A in Triton X-100. The ISCOM particles were formed by removal of the detergent. In each formulation the relative HN content correlated with the capability to agglutinate red blood cells. The immunogenicity of these lipid-based subunit vaccines was determined in chickens after subcutaneous immunization. The relative HN content of the subunit vaccines correlated with the haemagglutination-inhibition (HI) antibody titres. Virosomes prepared with Triton X-100 and ISCOMs offered high clinical protection (> 80%) upon challenge with virulent NDV. Virosomes prepared with OG yielded lower clinical protection despite high HI antibody titres. Virosomes with reduced antigen density showed poor immunogenicity and protection. In conclusion, ND virosomes and ISCOMs were found to be immunogenic and provided good protection.

Animals↗

PubMed2005

Virosome-mediated delivery of protein antigens in vivo: efficient induction of class I MHC-restricted cytotoxic T lymphocyte activity.

Induction of CTL responses against protein antigens is an important aim in vaccine development. In this paper we present fusion-active virosomes as a vaccine delivery system capable of efficient induction of CTL responses in vivo. Virosomes are reconstituted viral membranes, which do not contain the genetic material of the virus they are derived from. Foreign macromolecules, including protein antigens, can be encapsulated in virosomes during the reconstitution process. Functionally reconstituted virosomes retain the cell binding and fusion characteristics of the native virus. Thus, upon uptake by cells through receptor-mediated endocytosis, virosomes will deliver their content to the cell cytosol. In a previous study, we demonstrated that protein antigens delivered in this manner to dendritic cells are efficiently processed for both MHC class I and class II presentation. Here, we studied in vivo induction of cellular immune responses against virosome-encapsulated ovalbumin (OVA) in mice. As little as 0.75 microg OVA delivered by fusion-active virosomes was sufficient to induce a powerful class I MHC-restricted CTL response. All immunization routes that were used (i.m., i.p. and s.c.) resulted in efficient induction of CTL activity. The CTLs induced were cytotoxic in a standard 51Cr-release assay and produced IFNgamma in response to OVA peptide. Thus, virosomes represent an ideal antigen delivery system for induction of cellular immunity against encapsulated protein antigens.

Adjuvants, Immunologic↗

PubMedDate not supplied

Preparation of influenza virosome vaccine with muramyldipeptide derivative B30-MDP.

An influenza virosome vaccine, consisting of influenza hemagglutinin-neuraminidase antigens (HANA), the muramyldipeptide derivative 6-O-(2-tetra-decylhexadecanoyl)-N-acetyl-muramyl-L-alanyl-D-isoglu tamine (B30-MDP) and cholesterol, was prepared by the detergent removal method using a flow-through dialyzer, Liposomat. The shape of the influenza virosome vaccine mimicked that of the influenza virus, namely, B30-MDP/cholesterol vesicle covered with HANA spikes. THe particle size and size distribution of prepared virosomes were evaluated by quasi-elastic laser light scattering and gel permeation chromatography. The state of incorporation of HANA spikes at the membrane surface of virosome was confirmed by electron microscopy. The results indicated that virosome formation was influenced by initial B30-MDP concentration in the mixed micellar solution prior to dialysis. It is apparent that the initial concentration of B30-MDP, relative to the mixed-micelle-to-virosome transition, is an important factor for virosome preparation. Accordingly, the transition was evaluated and clarified by the changes in membrane fluidity and particle size during the dialysis process. The results indicated that it is important to adjust the initial B30-MDP concentration in the mixed micellar solution before dialysis so that the concentration for the mixed-micelle-to-vesicle transition coincides with that for mixed-micelle-to-rosette-transition appropriate for virosome formation.

Acetylmuramyl-Alanyl-Isoglutamine↗

PubMed2004

Influenza virosomes as an efficient system for adjuvanted vaccine delivery.

Immunopotentiating reconstituted influenza virosomes possess several characteristics defining them as vaccine adjuvants. Virosomes have been shown to provide vaccine components with protection from extracellular degradation; a regular, repetitive antigen structure aiding presentation to B lymphocytes and fully functional, fusion-active, influenza haemagglutinin envelope proteins that enables receptor-mediated uptake and intracellular processing of the antigen. In addition, virosomes, as vaccine delivery systems, have been shown to be safe and not to engender any antibodies against the phospholipid components. Through the use of virosomes as a delivery vehicle, a number of vaccines have been developed. In humans, virosome-based vaccines containing inactivated hepatitis A and influenza antigens have been found to be efficacious and well-tolerated and have been on the market for several years. Hepatitis B, nucleic acids, cytotoxic drugs, and tetanus and diphtheria toxoids have also been incorporated into virosomes. Further investigations are ongoing in order to define the full potential of virosomes in both prophylactic and immunotherapeutic applications.

Adjuvants, Immunologic↗

PubMed2005

Clinical experience with inactivated, virosomal influenza vaccine.

Current available influenza vaccines are safe and effective in preventing influenza. Nevertheless, there is a need for influenza vaccines with improved efficacy in the elderly. This need is underscored by both the observation that influenza has a major clinical and economic impact in the elderly and the fact that currently available vaccines are generally less effective in elderly than in younger subjects. Several approaches are currently being pursued in order to improve the efficacy of influenza vaccines in elderly individuals and others who have impaired immune responses to conventional influenza vaccines. A novel antigen-presenting strategy to overcome impaired immune responses is the use of virosomes. Previously, data on safety and reactogenicity have been published regarding the use of virosomal influenza vaccines. Data from three recent clinical trials are presented here. The first of these was a comparative study of a virosomal vaccine and a conventional subunit vaccine in "at-risk" adults with underlying chronic illness. The virosomal vaccine demonstrated comparable tolerability to the subunit vaccine, with about 98% of patients reporting tolerability to be good or very good. The vast majority of adverse events reported were mild to moderate in severity. With both vaccine types, mean HI titres decreased with age for both the A-H1N1 and B influenza virus strains, but for the A-H3N2 strain (the most virulent of the three strains), mean HI titres did not decrease with age, suggesting a better response with the virosomal vaccine when compared to the subunit vaccine. All three studies explored the long-term persistence of antibodies after vaccination with virosomal influenza vaccines. Immunogenicity declined over time but remained high at 4, 6 and 12 months post-vaccination compared to baseline, indicating that adequate seroprotection is achievable for the duration of the influenza season. Virosomal vaccines may induce better immunity in elderly subjects and may be more effective in reducing morbidity and mortality in this age group.

Adolescent↗

PubMed2002

Virosome-mediated delivery of protein antigens to dendritic cells.

Virosomes are reconstituted viral membranes in which protein can be encapsulated. Fusion-active virosomes, fusion-inactive virosomes and liposomes were used to study the conditions needed for delivery of encapsulated protein antigen ovalbumin (OVA) to dendritic cells (DCs) for MHC class I and II presentation. Fusion-active virosomes, but not fusion-inactive virosomes, were able to deliver OVA to DCs for MHC class I presentation at picomolar OVA concentrations. Fusion activity of virosomes was not required for MHC class II presentation of antigen. Therefore, virosomes are an efficient system for delivery of protein antigens for stimulation of both helper and CTL responses.

Animals↗

PubMed1993

Fusogenic properties of Sendai virosome envelopes in rat brain preparations.

Sendai virosomes were characterized with respect to their ability to bind to, fuse with, and introduce substances into several rat brain preparations. Encapsulation efficiency for Sendai virosomes was enhanced but binding to cerebral cortical P2 preparations was attenuated by addition of bovine brain phosphatidylcholine during reconstitution. A higher percentage of Sendai virosomes than phosphatidylcholine liposomes appeared to bind to, fuse with and subsequently deliver [14C]sucrose into osmotically labile pools of the P2 preparation. Fusogenic activity was estimated by measuring dequenching of fluorescently labelled N-NBD-phosphatidylethanolamine. More virosomally encapsulated [14C]sucrose was bound to the P2 fraction than introduced into osmotically labile organelles, and the fraction of vesicles undergoing fusion was intermediate between these two values. Non-encapsulated [14C]sucrose did not bind to and was not taken up by the P2 fraction in a quantifiable manner. Virosomal envelopes also bound to primary cultures of rat brain neurons and glia in an apparently saturable manner. Addition of increasing amounts of the adenoassociated virus-derived vector pJDT95 increased encapsulation efficiency, and virosomes reconstituted in the presence of 60 micrograms DNA retained most of their binding activity (5.4% of total label) compared to those containing [14C]sucrose alone (8.4%). These data indicate that Sendai virosomes may be useful in the delivery of substances into brain-derived tissues, potentially for the modulation of gene expression and neurotransmission.

Animals↗

PubMed2000

Induction of cytotoxic T lymphocyte activity by fusion-active peptide-containing virosomes.

Priming of cytotoxic T lymphocyte (CTL) activity with exogenous antigen requires introduction of the antigen into the MHC class I presentation pathway of antigen-presenting cells. In the present study, we used fusogenic reconstituted envelopes (virosomes), derived from influenza virus, as a carrier system for delivery of a synthetic soluble peptide corresponding to a major murine CTL epitope of the influenza virus nucleoprotein (NP). Virosomes containing encapsulated NP-peptide efficiently sensitized target cells for recognition by influenza-specific CTLs generated through priming of mice with infectious virus. Intramuscular immunization of mice with peptide-containing virosomes induced a potent class I MHC-restricted CTL response against influenza-infected target cells. By contrast, an equal dose of NP-peptide encapsulated in fusion-inactivated virosomes did not induce CTL activity, indicating an essential role of the membrane fusion activity of the virosomes in the induction of the response. Likewise, NP-peptide encapsulated in liposomes, NP-peptide mixed with empty virosomes and NP-peptide in IFA failed to induce a CTL response. These results demonstrate that fusion-active virosomes represent a promising delivery system for induction of class I MHC-restricted CTL activity with non-replicating viral antigens.

Animals↗

PubMedDate not supplied

Development of a virosome vaccine against avian metapneumovirus subtype C for protection in turkeys.

An avian metapneumovirus (aMPV) virosome vaccine was prepared and tested for protection of turkeys by aMPV challenge. The vaccine was produced using a detergent-based (Triton X-100) extraction of aMPV subtype C followed by detergent removal with SM2 Bio-Beads. Western blot and virus-neutralization analysis confirmed that the aMPV virosomes contained both the fusion and attachment glycoproteins. Specific-pathogen-free turkeys were immunized either intranasally (i.n.) or intramuscularly (i.m.) with two doses of the aMPV virosome vaccine. Vaccination decreased clinical signs of disease following virulent challenge, and IN vaccination was superior to i.m. vaccination in reducing clinical signs. Decreases in viral load in the respiratory tract were observed in turkeys receiving i.n. vaccination with aMPV virosomes compared to unvaccinated poults. Increased virus-neutralizing antibody levels against aMPV were observed in birds vaccinated with virosomes. These results demonstrate that immunization of turkeys with aMPV virosomes can be an effective strategy for control of disease.

Administration, Intranasal↗

PubMed1994

Immunogenicity of new virosome influenza vaccine in elderly people.

The safety and immunogenicity of a new virosome influenza vaccine was compared to commercial whole-virus vaccine and subunit vaccine in elderly people. The virosome vaccine was made by extracting the haemagglutinin from influenza virus and incorporating it into the membrane of liposomes composed of phosphatidylcholine (PC) and phosphatidylethanolamine (PE). 126 residents of a nursing home, aged 63-102, were randomised to receive one of the vaccines. All three were well tolerated and caused a significant rise in the geometric mean anti-haemagglutinin inhibiting (HAI) antibody titre to the 3 vaccine components (H1N1 Singapore, H3N2 Beijing, and B/Yamagata). The virosome formulation caused the highest geometric mean titres in addition to significantly (p = 0.039-0.0016) higher rates of more than four-fold or more titre rises to all 3 vaccine components. The percentage of those immunised who achieved protective levels of antibody (HAI > or = 40) was significantly (p = 0.035-0.0017) higher for the H1N1 and B/Yamagata strains following immunisation with virosome formulation. Participants with non-protective baseline titres to the H1N1 or B/Yamagata strains were more likely (p = 0.0049-0.006) to achieve protective levels of antibodies after immunisation with the virosome vaccine. Immunisation with the virosome formulation did not result in a significant rise in anti-PC or anti-PE antibodies.

Aged↗