Human IgG subclass responses in relation to serum bactericidal and opsonic activities after immunization with three doses of the Norwegian serogroup B meningococcal outer membrane vesicle vaccine

Ten adult volunteers, with low prevaccination levels of serum IgG antibodies against meningococcal antigens (< 1 microg ml(-1)), received three doses of the Norwegian group B meningococcal outer membrane vesicle (OMV) vaccine intramuscularly at weeks 0, 6 and 46. Anti-OMV IgG subclass responses were measured and compared with serum bactericidal activity (SBA) and opsonic activity against the vaccine strain 44/76. All vaccinees showed an IgG1 antibody response after each vaccine dose. The vaccine-induced median serum IgG1 antibody levels were 16, 17 and 18 microg ml(-1) 2-6 weeks after the first, second and third dose, respectively. Three vaccinees showed a weak IgG3 response after the first dose, whereas 8 and 9 showed a response after the second (median = 10 microg ml(-1)) and third dose (median = 10 microg ml(-1)), respectively. Low levels of anti-OMV IgG2 antibodies were found, whilst specific IgG4 antibodies were only detected for one vaccinee. The vaccine induced at least a fourfold increase in SBA titre in 8 vaccinees after the first dose, in 9 vaccinees after 2 doses and in all vaccinees after 3 doses. A positive correlation was found between IgG1 subclass antibody levels and SBA (r = 0.62, P < 0.0001). Elevated opsonophagocytic activity, measured as respiratory burst (RB), was observed in all vaccinees after one vaccine dose and usually increased after 2 and 3 doses. A strong positive correlation was found between IgG1 antibody levels and RB (r = 0.76, P < 0.0001). In conclusion, we have shown that systemic meningococcal OMV vaccination in adult vaccinees mainly induced IgG1 antibodies which correlated with bactericidal and opsonic activity, but also a considerable amount of IgG3 antibodies, which, in contrast to the IgG1 response, was induced only after 2 or 3 vaccine doses and declined more rapidly.     

Development and characterisation of outer membrane vesicle vaccines against serogroup A Neisseria meningitidis

Neisseria meningitidis bacteria of serogroup A are causing recurring meningitis epidemics on the African continent. An outer membrane vesicle (OMV) vaccine against serogroup A meningococci made from a subgroup III serogroup A meningococcal strain was previously shown to induce antibodies with serum bactericidal activity (SBA) in mice. We have here further investigated the properties of OMV vaccines made from five different subgroup III serogroup A meningococcal strains grown in a synthetic medium with low iron content. In addition to the major outer membrane proteins (PorA, PorB, RmpM, Opa and OpcA), small amounts of the NadA, TdfH, Omp85, FetA, FbpA and NspA outer membrane proteins, as well as lipooligosaccharides, were detected in the vaccines. The OMV vaccines were used to immunise mice. Anti-meningococcal IgG antibodies in the mouse sera were analysed by immunoblotting and by enzyme-linked immunosorbent assay against OMVs, and against live meningococcal cells in SBA and a flow-cytometric assay. The vaccines induced antibodies with high SBA and opsonophagocytic activity. The strongest IgG responses were directed against PorA. Significant SBA responses were also observed against a subgroup III strain, which did not express PorA, whereas no SBA was observed against a clone IV-1 serogroup A strain. An OMV vaccine from serogroup A meningococci may be an alternative to polysaccharide and conjugate polysaccharide vaccines for Africa.     

A bivalent outer membrane vesicle-based intranasal vaccine to prevent infection of periodontopathic bacteria

Periodontal disease has become a serious public health problem, not only causing tooth loss, but also inducing chronic disorders of extra-oral organs. The present study assessed an intranasal vaccine strategy to prevent periodontal disease using outer membrane vesicles (OMVs) of two major periodontopathic bacteria, Porphyromonas gingivalis (Pg) and Aggregatibacter actinomycetemcomitans (Aa). We compared the morphology, composition, and immune activity between OMVs of Pg strain ATCC 33277 and Aa strain Y4. Aa OMVs had a smoother surface and stronger lipid A activity compared to Pg OMVs. The in vitro immune activity elicited by Aa OMVs in macrophage-like cells was remarkably stronger than that of Pg OMVs. Intranasal immunization of mice with Aa OMVs alone resulted in robust, humoral immune responses in blood and saliva. Despites the intrinsically low mucosal immunogenicity of Pg OMVs alone, using Aa OMVs as a mucosal adjuvant strongly enhanced Pg-specific immune responses, resulting in both serum IgG and salivary IgA, both of which aggregated Pg and Aa cells. Furthermore, Aa OMVs were found to be a more potent mucosal adjuvant than Poly(I:C) in the context of enhancing the production of Pg-specific IgG (especially IgG2a) and IgA. In addition, in a randomized, blinded study, mice oral challenged with Pg and Aa after intranasal immunization with Pg OMVs and Aa OMVs had significantly decreased numbers of both microorganisms compared to mock-immunized mice. Furthermore, in an intracerebral injection mouse model, there were no serious adverse effects on the brain even after administrating a dose of OMVs as same as that used for intranasal administration. Taken together, the bivalent OMV intranasal vaccine may be effective in preventing colonization of periodontopathic bacteria in the oral cavity and related systemic disorders associated with periodontal diseases.     

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.     

Response of steroid-treated former preterm infants to a single dose of meningococcal C conjugate vaccine

Attenuated antibody responses have been reported in preterm infants who received neonatal dexamethasone treatment. The duration of immunosuppression may extend into later infancy. This study assessed the immune response of former preterm infants to a single meningococcal serogroup C conjugate (MCC) immunisation given after infancy. A cohort of 49 toddlers born at less than 33 weeks' gestation were given an initial dose of MCC vaccine at a median age of 13 months; 11 had received dexamethasone in the neonatal period. Sera obtained 4 weeks post immunisation were analysed for serum bactericidal antibody (SBA) and serogroup C-specific IgG antibody concentrations. Immune responses were compared with those of an historical cohort of 70 term toddlers given a single dose of the same vaccine at age 13 months. An SBA titre of > or =8 was taken to indicate a protective response. Following a single MCC dose, the SBA geometric mean titre (GMT) for former preterm infants was 249 (95% C.I. 111, 558), not significantly different from that of the historical term cohort whose SBA GMT was 141 (95% C.I. 89, 224) (p=0.06). A significantly lower proportion of former preterm infants achieved a protective SBA titre of > or =8 compared with term infants, 37/48 (77%) versus 64/70 (91%), (p=0.03). For steroid-treated and non steroid-treated subgroups, SBA GMTs were 1237 (95% C.I. 250, 6132) and 154 (62, 385), respectively, and numbers achieving an SBA titre of > or =8 were 10/11 (91%) and 27/37 (73%), (p=0.42). Most children born at <33 weeks' gestation mount a protective immune response to a single MCC vaccine dose given at age 13 months, but fewer former preterm infants attain a protective SBA titre of 8 compared with term infants. Previous neonatal dexamethasone treatment does not appear to attenuate immune response after infancy.     

A murine model for the study of immune memory in response to pneumococcal conjugate vaccination

We developed a murine model for assessment of immunological memory and antibody-induced protection to nasopharyngeal (NP) challenges. BALB/c female mice (n = 10 mice per study parameter) were immunized with two priming doses of the licensed 7-valent pneumococcal (Pnc) conjugate vaccine and immune responses [antibody immunoglobulin G (IgG) levels, avidity and opsonophagocytic activity] were monitored for 26 weeks until IgG levels decreased to nearly baseline. A booster dose of either 2 microg conjugate or 5 microg polysaccharide vaccine was given at week 26. The ability of these two treatments to recall immune memory established by the conjugate vaccine was determined for types 4 and 14 for up to 63 days post-booster. The ability of challenge with pneumococcal type 14 to recall the immune response was also evaluated, as well as, the number of antibody secreting cells (ASC) specific to polysaccharide (Ps) 4, 6B, and 14. A higher dose of conjugate vaccine (2 microg) was necessary to elicit a significant increase in IgG levels after priming with one dose. Priming with lower doses (0.5 and 1.0 microg) only elicited modest increases in IgG levels. Recall of the immune response was found with either conjugate or Ps vaccines. NP challenge with type 14 at week 26 did not recall the immune response, although reduction in NP Pnc load was seen post-primary immunization at 5, 10 and 26 weeks. ASCs were detected in response to either conjugate or Ps booster doses. This model allows for the screening and determination of potential alternative vaccination regimens and the study of immunological markers of memory following Pnc vaccination.     

Immunogenicity studies with a genetically engineered hexavalent PorA and a wild-type meningococcal group B outer membrane vesicle vaccine in infant cynomolgus monkeys

The immunogenicity of two meningococcal outer membrane vesicle (OMV) vaccines, namely the Norwegian wild-type OMV vaccine and the Dutch hexavalent PorA OMV vaccine, were examined in infant cynomolgus monkeys. For the first time, a wild-type- and a recombinant OMV vaccine were compared. Furthermore, the induction of memory and the persistence of circulating antibodies were measured. The Norwegian vaccine contained all four classes of major outer membrane proteins (OMP) and wild-type L3/L8 lipopolysaccharide (LPS). The Dutch vaccine consisted for 90% of class 1 OMPs, had low expression of class 4 and 5 OMP, and GalE LPS. Three infant monkeys were immunised with a human dose at the age of 1.5, 2.5 and 4.5 months. Two monkeys of each group received a fourth dose at the age of 11 months. In ELISA, both OMV vaccines were immunogenic and induced booster responses, particularly after the fourth immunisation. The Norwegian vaccine mostly induced sero-subtype P1.7,16 specific serum bactericidal antibodies (SBA), although some other SBA were induced as well. The antibody responses against P1.7,16, induced by the Norwegian vaccine, were generally higher than for the Dutch vaccine. However, the Dutch vaccine induced PorA specific SBA against all six sero-subtypes included in the vaccine showing differences in the magnitude of SBA responses to the various PorAs.     

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 172000 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.     

Heterologous prime-boost strategy to overcome weak immunogenicity of two serosubtypes in hexavalent Neisseria meningitidis outer membrane vesicle vaccine

In the hexavalent meningococcal B OMV vaccine (HexaMen), two of the six Porin A proteins present are weakly immunogenic in mice and humans. We investigated the possibility that the lower immunogenicity of these serosubtypes (P1.7-2,4 and P1.19,15-1) could be overcome by using HexaMen and monovalent OMVs in heterologous immunisation protocols. Whereas HexaMen priming on day 0 followed by a monovalent P1.7-2,4 OMV boosting on day 28 (specific boost) did not result in higher titres against P1.7-2,4 (on day 42), the reverse order of immunisations (specific priming) resulted in significantly higher ELISA and SBA titres, but with lower avidity. For the strongly immunogenic PorA P1.5-1,2-2, all strategies gave high antibody responses, while avidity was highest after two monovalent P1.5-1,2-2 OMV immunisations. Based on the improved antibody titres obtained by specific priming with the weakly immunogenic PorA, we extended our study with combined P1.7-2,4 and P1.19,15-1 priming followed by two HexaMen booster immunisations. This resulted in higher ELISA and SBA titres against these weakly immunogenic PorAs, while the response against the other four PorAs was unaffected. Also, we observed an increase in antibody avidity using this schedule, indicating that affinity maturation has occurred. In conclusion, we found that specific priming, rather than specific boosting with monovalent OMVs, gave a significant rise in the serosubtype-specific immune response against a weakly immunogenic PorA, with high avidity antibodies in an extended immunisation schedule.     

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.     

Evaluation and validation of a serum bactericidal antibody assay for Haemophilus influenzae type b and the threshold of protection

Prior to routine immunisation, Haemophilus influenzae serotype b (Hib) was a major cause of serious bacterial infections, particularly in young children. In the United Kingdom, introduction of the Hib conjugate vaccine into the national childhood immunisation schedule has led to a sustained decline in invasive Hib disease across all age-groups. Evaluation of the immune response to Hib conjugate vaccines involves measurement of serum IgG antibodies against the capsular polyribosyl-ribitol-phosphate (PRP) polysaccharide by enzyme-linked immunosorbent assay (ELISA), with accepted short-term and long-term protective thresholds of ≥0.15 μg/mL and ≥1.0 μg/mL, respectively. These levels were derived by passive immunisation or immunisation with pure polysaccharide, and their relevance for protection following immunisation with conjugate vaccines remains unclear. This study aimed to modify and optimise a serum bactericidal antibody (SBA) assay to evaluate the functional activity of Hib antibodies generated following Hib conjugate vaccination. Validation of the Hib SBA assay was deemed acceptable for all assay parameters tested. A strong correlation between anti-PRP IgG concentrations and SBA titres was observed in vaccinated adults (r = 0.81), as well as infants after primary immunisation at 2, 3, and 4 months (r = 0.635) and after the 12-month booster (r = 0.746). The assay identified some children with high anti-PRP IgG but low SBA activity and vice versa. The predictive protective SBA titre corresponding to a post-booster anti-PRP IgG of 1.0 μg/mL was 8. Thus, the optimised Hib SBA assay was specific and reproducible and correlated with anti-PRP IgG. Such assays may have a role in evaluating immune responses to conjugate vaccines in addition to measuring capsular antibodies.     

Head-to-head comparison of four nonadjuvanted inactivated cell culture-derived influenza vaccines: effect of composition, spatial organization and immunization route on the immunogenicity in a murine challenge model

In order to study the influence of antigen composition, spatial organization of antigen and the route of administration, four cell culture-derived, inactivated, nonadjuvanted influenza vaccine formulations, i.e. whole inactivated virus (WIV), split, subunit and virosome vaccines were prepared from a single antigen batch. We directly compared the immunogenicity and efficacy of these vaccine formulations after intramuscular (i.m.) or intranasal (i.n.) administration in mice. Prime and boost vaccination were followed by a potentially lethal homologous aerosol challenge. For all vaccines, the i.m. route induced higher serum humoral immune responses as compared to the i.n. route and protected all mice against challenge at a dose of 5 microg. Upon i.n. immunization only WIV and split vaccines induced detectable IgG titers and partial protection against challenge but only very low HI titers were induced in almost all mice. WIV induced mainly IgG2a/c titers via both routes, whereas split vaccine induced exclusively IgG1 titers via both routes. Subunit and virosome vaccines induced exclusively IgG1 via the i.m. route. Mucosal sIgA levels were only detected after i.n. vaccination with WIV. Furthermore, vaccines containing all viral components (WIV and split vaccine) induced higher serum HI titers and serum antibody titers than subunit and virosome vaccines. The differences in magnitude and quality of immune responses of split and WIV, having the same composition, are likely related to their distinct spatial organization. In conclusion, the direct comparison between WIV, split, subunit and virosomes, shows that the differences in immune responses between these well known influenza vaccines can be explained by both the composition and particulate structure of these vaccine formulations.     

Effective nasal influenza vaccine delivery using chitosan

Nasal influenza vaccination may prove to be a good alternative to parenteral injection because of the enhancement of the mucosal immune response and the ease of vaccine administration. This study investigated the use of chitosan, a bioadhesive polymer, as a nasal delivery system with inactivated, subunit influenza vaccine. Subjects received nasally 15 or 7.5 microg of the standard inactivated trivalent influenza vaccine with chitosan or 15 microg of the same vaccine intramuscularly. Serum haemagglutination inhibition (HI) titres for all three vaccine components were measured prior to, and at time points up to 14 weeks after dosing. Serum HI titres following intranasal vaccination with the nasal chitosan-influenza vaccine met the criteria set by the Committee for Proprietary Medicinal Products in terms of seroprotection rate, seroconversion rate and mean fold increase of HI titre for at least one of the three antigens in the vaccination schedules used. These data show that nasal immunisation with chitosan plus trivalent inactivated influenza is a potentially effective, easily-administered form of vaccination.     

Preclinical immunogenicity study of trivalent meningococcal AWX-OMV vaccines for the African meningitis belt

In the recent decade, epidemic meningitis in the African meningitis belt has mostly been caused by Neisseria meningitidis of serogroups A, W and X (MenA, MenW and MenX, respectively). There is at present no licensed vaccine available to prevent MenX meningococcal disease. To explore a trivalent MenAWX vaccine concept, we have studied the immunogenicity in mice of MenX outer membrane vesicles (X-OMV) or MenX polysaccharide (X-PS) when combined with a bivalent A-OMV and W-OMV (AW-OMV) vaccine previously shown to be highly immunogenic in mice. The vaccine antigens were produced from three representative wild type strains of MenA (ST-7), MenW (ST-11) and MenX (ST-751) isolated from patients in the African meningitis belt. Groups of mice were immunized with two doses of X-OMV or X-PS combined with the AW-OMV vaccine or as individual components. All vaccine preparations were adsorbed to Al(OH)₃. Sera from immunized mice were tested by ELISA and immunoblotting. Functional antibody responses were measured as serum bactericidal activity (SBA) and opsonophagocytic activity (OPA). Immunization of mice with X-OMV, alone or in combination with AW-OMV induced high levels of anti-X OMV IgG. Moreover, X-OMV alone or in combination with the AW-OMV vaccine induced high SBA and OPA titers against the MenX target strain. X-PS alone was not immunogenic in mice; however, addition of the AW-OMV vaccine to X-PS increased the immunogenicity of X-PS. Both AWX vaccine formulations induced high levels of IgG against A- and W-OMV and high SBA titers against the MenA and MenW vaccine strains. These results suggest that a trivalent AWX vaccine, either as a combination of OMV or OMV with X-PS, could potentially prevent the majority of meningococcal disease in the meningitis belt.     

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.     

Influence of administration dose and route on the immunogenicity and protective efficacy of BBG2Na, a recombinant respiratory syncytial virus subunit vaccine candidate

The immunogenicity and protective efficacy of BBG2Na, a novel recombinant respiratory syncytial virus subunit vaccine candidate, was assessed in BALB/c mice under various conditions of dose, administration route and number of immunisations. A single intra-peritoneal (i.p.) dose of 2 microg, or two doses of 0.2 microg, were sufficient to induce elevated RSV-A serum antibodies and sterilising lung protective immunity. Serum antibody titres were significantly boosted following second immunisations, but not a third. Of three routes of immunisation, i.p. induced the highest RSV-A antibody titres, followed in efficacy by the intra-muscular (i. m.) and subcutaneous (s.c.) routes. Nonetheless, all three routes induced comparable and sterilising lung protection. In contrast, upper respiratory tract protection was observed only after i.p. vaccination, although significant viral titre reductions were evident following i.m. or s.c. immunisations. Interestingly, Pepscan analyses indicated that antibody epitope usage was highest in i.p. and lowest in i.m. immunised mice, respectively. Nonetheless, all routes resulted in antibody responses to known lung protective epitopes (protectopes). Thus, the prevention of serious lower respiratory tract disease, the principle goal of a RSV vaccine, but not URT infection, is dose dependent but unlikely to be influenced by the route of BBG2Na administration.     

Genetic immunisation against hepatitis B using whole bacteriophage lambda particles

Mice and rabbits have been vaccinated with whole bacteriophage lambda particles containing a DNA vaccine expression cassette under the control of the CMV promoter (enhanced green fluorescent protein [lambda-EGFP] or hepatitis B surface antigen [lambda-HBsAg]). Mice were vaccinated twice intramuscularly (i.m.) with 5x10(9) of lambda-EGFP phage (containing 250 ng DNA) and exhibited specific anti-EGFP responses 28 days post-vaccination. Rabbits were vaccinated i.m. with 4x10(10) of lambda-HBsAg phage (2 microg DNA) or recombinant HBsAg protein. Following two vaccinations with lambda-HBsAg, one out of four rabbits exhibited high level anti-HBsAg responses (comparable to those seen using the recombinant HBsAg protein). Following a third vaccination with lambda-HBsAg, all four rabbits showed similar high level responses which have not decreased after more than 6 months. High anti-phage responses were observed in all animals following the first immunization with lambda-HBsAg, indicating that a high antibody titre against the phage carrier did not prevent a subsequent immune response against the DNA vaccine component. Compared to results in mice using equivalent lambda-HBsAg doses, anti-HBsAg responses were much higher in rabbits, which could indicate a swamping effect in mice. Since phage lambda DNA is approximately 50 kb in size (tenfold larger than most plasmid vectors used for naked DNA immunisation), a comparable dose of phage lambda DNA given as intact phage particles actually delivers tenfold less vaccine DNA on a per gene copy (molar) basis. Thus the efficiency of the technique may be even higher than the data at first suggests.     

Prior meningococcal A/C polysaccharide vaccine does not reduce immune responses to conjugate vaccine in young adults

The immune responses induced in young adults by a meningococcal A/C polysaccharide-diphtheria toxoid conjugate vaccine (Mcj) and a meningococcal A/C plain polysaccharide vaccine (Mps) were evaluated in unvaccinated subjects and those who had received either vaccine previously. 195 subjects aged 17-30 years received either Mps or Mcj. After 12 months, they were randomised again to receive a second dose of either vaccine. Serogroup specific serum bactericidal assay (SBA) titers and IgG antibody responses were assayed before and 4-8 weeks after primary and booster immunisation. Both vaccines were immunogenic in previously unvaccinated subjects. Administration of a dose of Mps after previous Mps or Mcj induced lower bactericidal titers to group C Neisseria meningitidis than those seen after a single dose of Mps. Bactericidal antibody responses to Mcj were not reduced in subjects who had previously received Mps.     

Outer membrane vesicles of Neisseria lactamica as a potential mucosal adjuvant

The muscosal delivery of vaccines has many advantages including ease of administration and the induction of a mucosal immune response at the natural site of infection for many pathogens. Mice were immunised with outer membrane vesicles (OMV) prepared from Neisseria lactamica or Neisseria meningitidis by subcutaneous (SC) or intranasal (IN) routes, or live cells of N. lactamica given IN or by SC injection. A systemic IgG and mucosal IgA response was demonstrated and N. lactamica OMV induced antibodies cross-reactive with N. meningitidis; however, a cross-reactive response following IN administration was only evident after three doses of vaccine. OMV from both organisms were also an effective intranasal adjuvant for a co-administered model antigen, hepatitis B surface antigen (HBsAg), inducing systemic IgG against HBsAg and IgA in lung and vaginal washes. IN administration of N. meningitidis OMV elicited serum antibodies that were bactericidal for meningococci and provided passive protection in an infant rat model of meningococcal bacteraemia. The antibody response to N. lactamica OMV given IN was only weakly bactericidal but still afforded passive protection. Thus, OMV from N. lactamica given IN elicit immune responses cross-reactive with N. meningitidis and act as an effective mucosal adjuvant.     

Combined administration of serogroup B meningococcal vaccine and conjugated serogroup C meningococcal vaccine is safe and immunogenic in college students

This study evaluated the first use of a combination of the lyophilized components of the conjugated group C vaccine Menjugate reconstituted with the liquid group B outer membrane vesicle (OMV) vaccine MeNZB. At 6-week intervals, healthy residential students received three doses of MeNZB alone or concomitantly with one dose of Menjugate (MeNZB+MenC). Short-lasting injection-site reactions of mild or moderate intensity were frequent in both groups. There were no vaccine-related serious adverse events. After three doses, the percentage of subjects with serum bactericidal assay (SBA) titres > or = 1:8 against the serogroup B strain NZ98/254 was 82% for MeNZB+MenC and 78% for MeNZB. All subjects in the MeNZB+MenC group achieved SBA titres > or = 1:8 against serogroup strain C11 and 67% in the MeNZB group. All SBA and ELISA responses of the combined vaccine were at least as good as for MeNZB alone. After vaccination, the pharyngeal carriage rate of any meningococcus in the vaccinated group had declined from 40% to 21%.