Outer Membrane Vesicle Vaccine Research Articles

Teasing apart structural determinants of `toxicity' and `adjuvanticity': implications for meningococcal vaccine development

The use of lipopolysaccharide (LPS) as an adjuvant is limited by its high endotoxic activity. In particular, the fatty-acyl pattern of the lipid A part of LPS has been demonstrated to determine its biological activity. By genetic modification of the lipid A biosynthesis pathway in Neisseria meningitidis, a panel of recombinant strains with specific alterations in the lipid A acylation pattern, as well as a strain completely lacking LPS were isolated. Whereas all variations in the fatty-acyl pattern resulted in reduced endotoxic activity, as measured by TNF-α induction in the human macrophage cell line MM6, the adjuvant activity of the modified LPS was, in most cases, barely affected. The in vivo adjuvant properties of N. meningitidis wild-type and mutant LPS was found to correlate with induction of co-stimulatory molecules, in particular CD80 and CD40, and with IL-12 production by LPS-stimulated bone marrow-derived BALB/c dendritic cells in vitro. Our results suggest that the ability of LPS to stimulate pro-inflammatory cytokine induction is not necessarily linked to its adjuvant activity. The availability of this novel set of lipid A variants with improved pharmacological properties will be of great importance for the improvement of future outer membrane vesicle vaccines against N. meningitidis.

Teasing apart structural determinants of 'toxicity' and 'adjuvanticity': implications for meningococcal vaccine development.

The use of lipopolysaccharide (LPS) as an adjuvant is limited by its high endotoxic activity. In particular, the fatty-acyl pattern of the lipid A part of LPS has been demonstrated to determine its biological activity. By genetic modification of the lipid A biosynthesis pathway in Neisseria meningitidis, a panel of recombinant strains with specific alterations in the lipid A acylation pattern, as well as a strain completely lacking LPS were isolated. Whereas all variations in the fatty-acyl pattern resulted in reduced endotoxic activity, as measured by TNF-alpha induction in the human macrophage cell line MM6, the adjuvant activity of the modified LPS was, in most cases, barely affected. The in vivo adjuvant properties of N. meningitidis wild-type and mutant LPS was found to correlate with induction of co-stimulatory molecules, in particular CD80 and CD40, and with IL-12 production by LPS-stimulated bone marrow-derived BALB/c dendritic cells in vitro. Our results suggest that the ability of LPS to stimulate pro-inflammatory cytokine induction is not necessarily linked to its adjuvant activity. The availability of this novel set of lipid A variants with improved pharmacological properties will be of great importance for the improvement of future outer membrane vesicle vaccines against N. meningitidis.

PorA-specific differences in antibody avidity after vaccination with a hexavalent Men B outer membrane vesicle vaccine in toddlers and school children

A clinical phase II trial with an experimental hexavalent outer membrane vesicle (OMV) vaccine (HexaMen) containing six different porin A (PorAs) was carried out in toddlers (2–3 years) and schoolchildren (7–8 years) in The Netherlands. HexaMen exists of two OMVs each containing three different PorA types. The serum bactericidal activity (SBA) after vaccination against the six PorAs was significantly different and was higher in toddlers than in schoolchildren. After vaccination the SBA against P1.5-2,10 was 4–6 times higher than against P1.7–2,4. The aim of this study was to test whether the differences in SBA could be explained by a difference in subtype-specific antibody avidity maturation. The avidity index (AI) of antibodies against three subtypes (PorA types P1.5-2,10; P1.12-1,13 and P1.7-2,4) was measured by ELISA and evaluated in relation to SBA. A significant avidity maturation for the 3 PorA subtypes was found. This maturation was most pronounced for P1.5-2,10 (mean AI=72%), correlating with the highest SBA titres. Generally, the avidity titre correlated best with SBA. No differences in avidity indices against the three tested PorAs were found between toddlers and school children indicating that avidity maturation induced by this vaccine is not age-dependent.

Immunisation schedules for non-replicating nasal vaccines can be made simple by allowing time for development of immunological memory

Mice immunised intranasally with multiple doses of outer membrane vesicles (OMVs) from group B meningococci developed antibody responses that depended on the interval between doses. High levels of antibodies in saliva and extracts of faeces were induced within 4 weeks after an OMV vaccine had been given at weekly intervals, whereas the antibody responses in these samples were negligible when given four times at 1-day or 1-h intervals, or as one large dose. Only modest responses were obtained in serum after 4 weeks, however, whether the vaccine had been given repeatedly at any schedule, including the 1-week interval, or as one dose. On the other hand, two large doses given 8 weeks apart induced booster antibody responses in both serum and secretions that matched the responses from a second series of the four smaller doses. Intranasal immunisations may thus stimulate immunological memory more rapidly in secretions than in serum. In order to secure adequate systemic responses by a minimum of doses, nasal vaccines should therefore be given at intervals longer than 4 weeks, in harmony with the intervals recommended for injectable vaccines.

Direct isolation of recombinant human antibodies against group B Neisseria meningitidis from scFv expression libraries

The successful generation of human antibodies from large naı̈ve antibody libraries requires iterative selection steps. Here, we describe a new and fast method for the isolation of high affinity antibodies directly from human single chain Fv antibody (scFv) expression libraries. Escherichia coli scFv expression libraries were made from peripheral blood lymphocytes from four individuals vaccinated with group B Neisseria meningitidis outer membrane vesicle (OMV) vaccine. Forty thousand clones were directly screened for antibodies binding N. meningitidis strain 44/76 (B:15:P1.7,16). Of 430 specific clones detected, 225 candidates were isolated and re-screened against the N. meningitidis strains NZ-98/254 (B:4:P1.7b,4) giving 4% cross-reactive clones. Antibodies were further characterized by DNA sequencing, ELISA and surface plasmon resonance (SPR) analysis, showing broad V-gene diversity and nanomolar scFv affinities. Antibodies derived by this method may assist in the discovery and development of new vaccine antigens as well as therapeutic antibody agents for the treatment of meningococcal diseases.

Stability of mono- and trivalent meningococcal outer membrane vesicle vaccines

The stability during storage of outer membrane vesicles (OMVs) of Neisseria meningitidis group B was studied. Three types of OMVs were compared for their stability, containing either one (monovalent) or three different PorA subtypes (trivalent), the latter with and without class 4 outer membrane protein (OMO, RmpM).Aqueous formulations were stored freeze-dried (4°C), frozen (−70°C) and in liquid form at 4, 37 and 56°C. Physico-chemical properties and immunogenicity of the OMVs as well as PorA conformation and antigenicity (P1.7-2,4, the subtype present in all formulations) were monitored during 1 year. At −70 or 4°C, the structure and immunogenicity of OMVs was preserved. Storage of OMVs at high temperatures (37 or 56°C) induced destruction of the OMV structure and denaturation of PorA, followed by chemical degradation. Immunogenicity decreased or was lost completely. Changes observed in the fluorescence spectra of degraded OMVs were also seen in tryptophan (Trp) and tyrosine (Tyr) derivatives incubated at 56°C, indicating the occurrence of chemical degradation of tryptophan and tyrosine residues in PorA. Trivalent OMVs were slightly more stable at 37°C than monovalent OMVs as assessed by in vitro methods, but these differences did not result in differences in the immunogenicity. The stability of trivalent OMVs was not affected by the presence of RmpM. Both trivalent and monovalent OMVs could be freeze-dried with preservation of their immunogenicity.In conclusion, OMVs are sensitive to elevated temperatures, but are stable in the frozen or freeze-dried state or when stored at 4°C in the liquid state.

Antibody specificities and effect of meningococcal carriage in icelandic teenagers receiving the Norwegian serogroup B outer membrane vesicle vaccine.

Antibody specificities of pre- and postvaccination serum samples from 40 (53%) teenagers who received three doses of the Norwegian Neisseria meningitidis serogroup B vaccine (B:15:P1.7,16) during a previous trial in Iceland (Perkins et al., J. Infect. Dis. 177:683-691, 1998) were analyzed with serum bactericidal activity (SBA) and immunoblotting assays with reference and isogenic meningococcal H44/76 vaccine strains. The H44/76 variants demonstrated significant vaccine-induced SBA to P1.7,16 PorA and Opc but not to PorB, Opa5.5, and a heterologous PorA protein. On blots, immunoglobulin G levels to all these proteins increased significantly after vaccination. Measurement of SBA to the two main variable regions (P1.7 and P1.16) on the P1.7,16 PorA with PorA deletion mutants revealed significantly higher activity to the P1.7,- and P1.-,16 mutants compared to the P1.7,16 strain, indicating exposure of new accessible epitopes. Only 12 (30%) serum samples showed distinct decreases with these or the P1.-,- mutant, with most samples containing SBA to the P1.7 and P1.16 combination. In contrast, P1.16-specific antibodies were mainly found on blots. Thirteen of the vaccinees (32.5%) were carriers of meningococci at the time of the third dose, of whom four (30.8%) harbored strains of the ET-5 complex. Carriage of P1.15 strains was generally reflected in > or =4-fold increases in SBA and distinct immunoglobulin G binding to the P1.19,15 PorA on blots. Although vaccination did not elicit bactericidal activity to the serotype 15 PorB, most carriers of serotype 15 strains showed > or =4-fold increases in SBA to this antigen.

Comparison of functional immune responses in humans after intranasal and intramuscular immunisations with outer membrane vesicle vaccines against group B meningococcal disease

A serogroup B meningococcal outer membrane vesicle (OMV) vaccine was delivered either intranasally or intramuscularly to 12 and 10 volunteers, respectively. The mucosal vaccine was given as four weekly doses followed by a fifth dose after 5 months; each dose consisted of OMVs equivalent to 250 μg of protein. The intramuscular (i.m.) vaccine, consisting of the same OMVs but adsorbed to Al(OH) 3, was administered as three doses each of 25 μg of protein, with 6 weeks interval between first and second doses and the third dose after 10 months. Both groups of vaccinees demonstrated significant immune responses when measured as specific IgG antibodies against live meningococci, as serum bactericidal activity (SBA) and as opsonophagocytic activity. Two weeks after the last dose, the anti-meningococcal IgG concentrations were significantly higher in the i.m. group (median IgG concentration: 43.1 μg/ml) than in the intranasal group (10.6 μg/ml) ( P=0.001). The corresponding opsonophagocytic activity was 7.0 and 3.0 (median log 2 titre) ( P=0.001), and the SBA was 5.0 and 2.0 (median log 2 titre) ( P=0.005), for the i.m. and intranasal groups, respectively. The last immunisation induced an enhanced immune response in the i.m. group, whereas the intranasal group showed no significant booster response. Accordingly, affinity maturation of anti-OMV-specific IgG antibodies was seen only after i.m. vaccination. The IgG1 subclass dominated the responses in both groups, whereas the significant IgG3 responses observed in the i.m. group were absent in the intranasal group. Although the intranasal OMV vaccination schedule used here induced functional immune responses relevant to protection, an improved vaccine formulation and/or a modified mucosal immunisation regimen may be needed to achieve a systemic effect comparable to that seen after three doses of intramuscular vaccination.

Serum bactericidal activity correlates with the vaccine efficacy of outer membrane vesicle vaccines against Neisseria meningitidis serogroup B disease

For evaluation of serum bactericidal activity (SBA) as surrogate for the efficacy of outer membrane vesicle (OMV) vaccines against Neisseria meningitidis serogroup B disease, we have reanalyzed data from a randomized double blind placebo-controlled efficacy trial involving 172,000 secondary school students (aged 13–14 years) in Norway (1988–1991). A cohort of the efficacy trial consisting of 880 individuals was selected for immunogenicity studies. An efficacy of 87% was calculated for a 10-month observation period. However, after an observation period of 29 months, the estimated efficacy against group B disease induced by vaccination was 57%. The immunogenicity study showed that the SBA geometric mean titer (GMT) for the vaccinees was 2.4 before vaccination and 19.0 six weeks after the second vaccine dose. One year after vaccination the GMT was reduced to 2.8. A separate three-dose study with 304 adolescents showed that with a third dose at 10 months after the second dose (i.e. when cases of disease started to appear) a strong booster response was induced. Ten months after the second dose the SBA was reduced to near pre-immunization level. Following the third dose the SBA geometric mean titer of 2.7 increased to 62.3. One year after the third dose, the GMT was markedly higher than 6 weeks after the second dose (12.6 versus 8.8). Thus, protection after vaccination corresponds with the level of SBA. In order to reach lasting protective levels of SBA in a population, three vaccine doses are probably required. Measurements of SBA are likely to be useful for evaluating various upcoming formulations and improvements of immunization regimens for OMV vaccines.

Influence of intravenous anesthesia on mucosal and systemic antibody responses to nasal vaccines.

Inhalation of antigens may stimulate the immune system by way of the upper as well as the lower airways. We have shown that at least 1,000 times more live pneumococci were recovered from pulmonary tissue after being presented as drops of a liquid suspension onto the nares of anesthetized mice compared to the number of bacteria recovered from animals that were not anesthetized in the course of the challenge. Mice that were similarly immunized intranasally by inhalation of three different nonreplicating particulate vaccine formulations, i.e., a meningococcal outer membrane vesicle (OMV) vaccine, a formalin-inactivated whole-virus influenza (INV) vaccine, and the INV vaccine with OMVs as a mucosal adjuvant, during general intravenous anesthesia developed concentrations of vaccine-specific serum immunoglobulin G (IgG) antibodies that were four to nine times higher than in mice that were fully awake during immunizations. The concentrations of IgA antibodies in serum were also higher in anesthetized than in nonanesthetized mice and correlated positively with the corresponding levels of serum IgG antibodies in the anesthetized but not in the nonanesthetized mice. In saliva and feces, however, the concentrations of IgA antibodies were equally high whether or not the animals were dormant during immunizations. The results indicate that intrapulmonary antigen presentation, as a part of an intranasal immunization strategy, is of importance for systemic but not for mucosal antibody responses. A major portion of IgA antibodies in serum may thus be derived from nonmucosal sites.

Avidity maturation following vaccination with a meningococcal recombinant hexavalent PorA OMV vaccine in UK infants

To date, there are no data assessing the utility of avidity indices as a surrogate marker for the induction of immunological memory following meningococcal serogroup B outer membrane vesicle (OMV) vaccination. We studied infants who had been immunized with three doses of a recombinant hexavalent PorA OMV vaccine at ages 2–4 months, together with a fourth dose at age 12–18 months. A control group had received a single dose of the same vaccine at age 12–18 months. As previously reported, serum bactericidal antibody (SBA) titres increased after each of the first three doses, with a significant increase observed from 6 months post third dose to 1 month post fourth dose. The geometric mean avidity indices (GMAI), against strain H44/76 OMVs, increased from 1 month post first dose to 1 month post third dose. Significant increases in GMAI were observed at 6 months post third dose and again following the fourth dose. At 32–42 months of age, though the SBA titres had returned to post first dose levels, the GMAI remained elevated. No increase in avidity was observed in the control group. Antibody avidity indices are useful laboratory markers for the priming of immunological memory following vaccination with meningococcal serogroup B OMV vaccines.

Meningococcal vaccines

The successful introduction of a protein–polysaccharide conjugate vaccine against serogroup C meningococci into the UK infant immunization schedule, in combination with a catch-up campaign for individuals less than 18 years of age, has seen virtually all group C disease eliminated in childhood. From being a devastating disease with a very high mortality, the possibility of eradicating invasive meningococcal disease now seems eminently feasible. Since similar technology is likely to facilitate prevention of disease caused be serogroup A, Y and W135 meningococci, the major hurdle in achieving the goal of eradication is development of a safe and immunogenic vaccine against serogroup B infections. Outer membrane vesicle vaccines remain in development and further trials are anticipated. Through the recent availability of the meningococcal genome sequence, many new vaccine candidates are being identified and there is increasing optimism that a solution to the problem can be found.

Quantification of Lipopolysaccharides in Outer Membrane Vesicle Vaccines Against Meningococcal Disease. High-performance Liquid Chromatographic Determination of the Constituent 3-Hydroxy-lauric Acid

A high-performance liquid chromatographic (HPLC) assay for quantification of lipopolysaccharides (LPSs, endotoxins) in outer membrane vesicle vaccines against meningococcal disease has been developed. The LPS constituent, 3-hydroxy-lauric acid, served as marker substance for the quantification. LPS from the vaccine was precipitated by ethanol and the fatty acid constituents, including 3-hydroxy-lauric acid, were released by acidic hydrolysis, collected and purified by solid phase extraction on C18 disc-cartridges and converted into phenacyl esters for UV detection at 240nm. Quantification of the derivatized 3-hydroxy-lauric acid was achieved by HPLC using a Brownlee RP-18 reversed phase column with acetonitrile/water (68:32, v/v) as mobile phase. The method was found to be linear over the range 3–49μg LPS/ml with a sensitivity of 1·6 (μg/ml)−1. The repeatability (within-day precision) of the method at three levels (3–49μg LPS/ml) was 6–14% relative standard deviation and the intermediate (between-day) precision was 7% relative standard deviation (at level 15μg LPS/ml). The method has been successfully used in the quality control of a meningococcal B outer membrane vesicle vaccine, containing 4–8% LPS relative to protein (w/w), in our laboratory for three years.

Meningococcal outer membrane vesicle (OMV) antibody avidity indices as a surrogate marker of priming for the induction of immunological memory following vaccination with a meningococcal hexavalent PorA OMV vaccine

Meningococcal outer membrane vesicle (OMV) antibody avidity indices as a surrogate marker of priming for the induction of immunological memory following vaccination with a meningococcal hexavalent PorA OMV vaccine

Antibody Avidity and Immunoglobulin G Isotype Distribution following Immunization with a Monovalent Meningococcal B Outer Membrane Vesicle Vaccine

The avidity maturation and immunoglobulin G (IgG) isotype distribution of antibodies after vaccination with a meningococcal B outer membrane vesicle (OMV) vaccine were evaluated as indicators of protective immunity. Pre- and postvaccination sera from 134 healthy toddlers (ages, 2 to 3 years) immunized with a monovalent meningococcal B OMV (serosubtype P1.7-2,4) vaccine adsorbed with AlPO(4) or Al(OH)(3) were analyzed by enzyme-linked immunosorbent assay (ELISA) methods. The children were vaccinated three times with intervals of 3 to 6 weeks between vaccinations or twice with an interval of 6 to 10 weeks between vaccinations. A booster was given after 20 to 40 weeks. The avidity index (AI) of antibodies increased significantly during the primary series of vaccinations and after the booster was given. No differences in AIs were found when the results obtained with the two vaccination schedules or with the two adjuvants were compared. After vaccination, IgG1 was the predominant IgG isotype, followed by IgG3. No IgG2 or IgG4 was detected. There was a strong correlation between serum bactericidal activity (SBA) and ELISA titers (r = 0.85 [P < 0.0001] for total IgG, r = 0.83 for IgG1 [P < 0.0001], r = 0.82 for IgG3 [P < 0.0001], and r = 0.84 [P < 0.0001] for the avidity titer). When two subgroups with similar anti-OMV IgG levels were compared before and after the booster vaccination, the higher AI after the booster vaccination was associated with significantly increased SBA. We concluded that avidity maturation occurs after vaccination with a monovalent meningococcal B OMV vaccine, especially after boosting, as indicated by a significant increase in the AI. Vaccination with the monovalent OMV vaccine induced mainly IgG1 and IgG3 isotypes, which are considered to be most important for protection against meningococcal disease. An increase in the AI of antibodies is associated with increased SBA, independent of the level of specific IgG and the IgG isotype distribution. Measuring the AI and IgG isotype distribution of antibodies after vaccination can be a supplementary method for predicting protective immunity for evaluation in future phase III trials with meningococcal serogroup B vaccines.

Health economics of a hexavalent meningococcal outer-membrane vesicle vaccine in children: potential impact of introduction in the Dutch vaccination program

The cost-effectiveness of universal vaccination of infants with a new hexavalent meningococcal B outer-membrane vesicle vaccine is projected for The Netherlands by applying decision analysis. The societal perspective is taken and direct and productivity costs (friction costs method) are considered. Future costs and effects are discounted at 4% (base year 1998). In this simulation model, vaccination would prevent 19 deaths and eight cases with severe long-term sequelae per year, rendering 526 additional quality adjusted life years (QALYs) per year. Yearly costs of acute phase of illness due to meningococcal infections in children are estimated at ▪ 1,426,634, while the future costs due to sequelae are estimated at ▪ 3,801,121 per year. Of all these costs, the vaccination program could prevent ▪ 3,334,052 per year. The program costs of meningococcal vaccination are estimated at ▪ 11,601,356, resulting in a cost-effectiveness ratio (CER) of ▪ 15,721 per QALY. These results are sensitive to the vaccine dose price (conservatively estimated at ▪ 10), efficacy, and coverage of meningococcal sero-subtypes.

Meningococcal outer membrane vesicle vaccine given intranasally can induce immunological memory and booster responses without evidence of tolerance.

We have studied the ability of outer membrane vesicle (OMV) vaccines from Neisseria meningitidis serogroup B to induce vaccine-specific antibody and spleen cell proliferative responses in mice after being administered intranasally (i.n.) and/or subcutaneously (s.c.). A series of four weekly i.n. doses (25 microg) without adjuvant or a single s.c. dose (2.5 microg) with aluminum hydroxide was followed 2 months later by secondary i.n. or s.c. immunizations. After i.n. priming, both immunoglobulin G (IgG) antibody responses in serum, measured by enzyme-linked immunosorbent assay, and IgA antibodies in saliva and extracts of feces were significantly boosted by later i.n. immunizations. The IgG antibody responses in serum were also significantly augmented by secondary s.c. immunization after i.n. as well as s.c. priming. Sera from mice immunized i.n. reached the same level of bactericidal activity as after s.c. immunizations. The s.c. immunizations alone, however, had no effect on mucosal IgA antibody responses, but could prime for booster antibody responses in secretions to later i.n. immunizations. The i.n. immunizations also led to marked OMV-specific spleen cell proliferation in vitro. Both serum antibody responses and spleen cell proliferation were higher after i.n. priming and later s.c. immunizations than after s.c. immunizations alone. There was thus no evidence that i.n. priming had induced immunological tolerance within the B- or T-cell system. Our results indicate that a nonproliferating meningococcal OMV vaccine given i.n. can induce immunological memory and that it may be favorably combined with similar vaccines for injections.

IgG antibody subclass responses determined by immunoblot in infants’ sera following vaccination with a meningococcal recombinant hexavalent PorA OMV vaccine

The introduction of meningococcal serogroup C conjugate vaccines into the UK immunisation schedule has led to the decline of serogroup C disease in those vaccinated but there is no imminent vaccine solution for serogroup B disease. The PorA outer membrane protein (OMP) is a potential serogroup B vaccine candidate and an outer membrane vesicle (OMV) vaccine containing six different PorA OMPs (each representing a different serosubtype) has been evaluated in phase II trials with encouraging results. Little is known about the IgG subclass response to the various antigens contained within this vaccine. These responses are important due to the different half-lives and complement fixing abilities of these antibodies. In this study, immunoblotting was undertaken with infants’ sera following either three or four doses of vaccine, and OMVs from six isogenic meningococcal strains differing only in their PorA serosubtype. Following either three or four doses of the vaccine, IgG 3 and IgG 1 subclass antibodies were induced to all six of the isogenic strains, although sera collected after four doses of vaccine showed stronger antibody levels. IgG 3 was found in more sera than IgG 1. For both sets of sera, the two isogenic strains expressing P1.5,2 and P1.5 c,10 induced stronger IgG subclass antibody responses than the other four meningococcal strains. The recombinant hexavalent PorA OMV vaccine stimulates both IgG 1 and IgG 3 subclass antibodies, the subclasses that are most effective in activating the complement system.

OUTER MEMBRANE VESICLES FROM NEISSERIA MENINGITIDIS: EFFECTS ON CYTOKINE PRODUCTION IN HUMAN WHOLE BLOOD

The Norwegian group B meningococcal outer membrane vesicle (OMV) vaccine consists of outer membrane proteins (OMPs) as main antigens with significant amounts of lipopolysaccharide (LPS; 5–9% relative to protein). We have studied the ability of this OMV vaccine preparation to induce secretion of pro-inflammatory cytokines, tumour necrosis factor α (TNF-α), interleukin 1β (IL-1β), interleukin 6 (IL-6), interleukin 8 (IL-8) and anti-inflammatory cytokines, interleukin 4 (IL-4), interleukin 10 (IL-10) and interleukin 13 (IL-13) in a human whole blood model. Plasma levels of TNF-α, IL-1β, IL-6 and IL-8 were massively increased; mean peak levels of TNF-α 44696±7764, IL-1β 38043±5411, IL-6 10057±1619 and IL-8 30449±5397pg/ml were obtained with an OMV-LPS concentration of 1μg/ml; corresponding levels in control plasmas were below the detection limit of the assay. Mean maximal level of IL-10 (2540±144pg/ml) was obtained at OMV-LPS concentration of 10μg/ml, after 24h; while the level in control plasma was below detection limit. OMV-LPS did not induce release of IL-4 and IL-13 in doses from 0.001–10μg/ml. The present results show that OMVs from meningococci have potent pro-inflammatory properties and are likely to contribute to the observed local and systemic inflammatory effects.

Immunogenicity and safety of monovalent P1.7 h,4 meningococcal outer membrane vesicle vaccine in toddlers: comparison of two vaccination schedules and two vaccine formulations

The safety and immunogenicity of two PorA-based meningococcal outer membrane vesicle (OMV) vaccines against the P1.4 serosubtype adsorbed with AlPO 4 or Al(OH) 3 were studied in 134 toddlers. Vaccinations were given three times with an interval of 3–6 weeks or twice with an interval of 6–10 weeks. A vaccination was repeated after 20–40 weeks. Pre- and post-immunization sera were tested for bactericidal activity against an isogenic strain expressing P1.7 h,4 PorA. Both meningococcal OMV vaccines were well tolerated. The percentage of children with a fourfold increase in bactericidal activity was 96% (AlPO 4-adjuvated vaccine/2+1 schedule), 100% (AlPO 4-adjuvated vaccine/3+1 schedule), 93% (Al(OH) 3-adjuvated vaccine/2+1 schedule) and 97% (Al(OH) 3-adjuvated vaccine/3+1 schedule). Adsorption with AlPO 4 makes the OMV vaccine more immunogenic than adsorption with Al(OH) 3. Bactericidal activity was highest after the 3+1 schedule, although the response shortly after the primary series was higher in the two-dose priming group.