Serum Bactericidal Antibody Responses Research Articles

Immunogenicity of a single 4CMenB vaccine booster in adolescents 11 years after childhood immunisation

The clinical development of the meningococcal vaccine, 4CMenB, included 2 doses in vaccine-naïve adolescents, which was considered unlikely to be cost-effective for implementation. Theoretically, priming with 4CMenB in early childhood might drive strong immune responses after only a single booster dose in adolescents and reduce programmatic costs. To address this question, children over 11 years old who took part in previous trials involving the administration of 3–5 doses of 4CMenB at infant/preschool age from 2006 were recruited into a post licensure single-centre trial, and were divided into two groups: those who received their last dose at 12 months old (infant group) and those who received their last dose at 3 years old (infant + preschool group). Naïve age-matched controls were randomised to receive one (adolescent 1 group) or two doses at days 0 and 28 (adolescent 2 group) of 4CMenB. Serum bactericidal antibody (SBA) assays using human complement were performed against three reference strains prior to vaccination, and at 1, 6 and 12 months. Previous vaccination was associated with a higher response to a single booster dose at 11 years of age, one-month post-vaccination, when compared with a single dose in naïve age-matched controls. At day 180, the highest responses were observed in participants in the infant + preschool group against strain 5/99 (GMT 316.1 [CI 158.4 to 630.8]), as compared with naïve adolescents who received two doses (GMTs 84.5 [CI 57.7 to 123.6]). When the last dose was received at 12-months of age, responses to a single adolescent dose were not as robust (GMT 61.1 [CI 14.8 to 252.4] to strain 5/99). This descriptive study indicates that the highest SBA responses after a single dose in adolescence were observed in participants who received a preschool dose, suggesting that B cell memory responses are not sufficiently primed at less than 12 months of age.Trial registration EudraCT 2017-004732-11, ISRCTN16774163.

Association between circulating exhausted CD4+ T cells with poor meningococcal C conjugate vaccine antibody response in HIV-infected children and adolescents

OBJECTIVES:To investigate the expression levels of surface markers of activation (CD38 and HLA-DR), inhibition (PD-1, TIGIT and CD57) and co-stimulation (CD28 and CD127) on CD4+ T cells of children/adolescents with vertical HIV infection (HI patients) and HIV-uninfected (HU) controls vaccinated with the meningococcal C conjugate vaccine (MCC).METHODS:HI patients (n=12), aged 8-17 years, were immunized with two MCC injections, while HU controls (n=9), aged 5.3-10.7 years, received a single MCC dose (as per national recommendation at the time of this study, a single MCC vaccine dose should be given for healthy children and youth aged 1-18 years). The HI patients were categorized according to the combined antiretroviral therapy (cART) treatment. Blood samples were obtained before vaccination, after priming, and after the administration of a booster dose of vaccine to determine the serum bactericidal antibody (SBA) titers and the expression levels of surface markers on CD4+ T cells by flow cytometry. The levels of serum cytokines, IL-4 and CXCL-13 were also measured using Luminex kits.RESULTS:The co-expression of the TIGIT-HLA-DR-CD38 molecules increased in the CD4+ T cells of HI patients/no-cART who also showed a lower frequency of CD127+CD28+ CD4+ T cells than HI patients/cART and HU group subjects. There were significant negative correlations between the frequency of exhausted CD4+ T cells and the SBA response. IL-4 levels were higher in HI patients/cART and positively correlated with SBA titers but negatively associated with the expression of exhaustion markers. Moreover, the CXCL-13 levels were positively correlated with the exhausted CD4+ T cells.CONCLUSION:The results of our study suggest that the co-expression of exhaustion markers and/or loss of co-stimulatory molecules influence the SBA response in HI patients.

A Meningococcal Outer Membrane Vesicle Vaccine with Overexpressed Mutant FHbp Elicits Higher Protective Antibody Responses in Infant Rhesus Macaques than a Licensed Serogroup B Vaccine.

MenB-4C (Bexsero; GlaxoSmithKline Biologicals) is a licensed meningococcal vaccine for capsular B strains. The vaccine contains detergent-extracted outer membrane vesicles (dOMV) and three recombinant proteins, of which one is factor H binding protein (FHbp). In previous studies, overexpression of FHbp in native OMV (NOMV) with genetically attenuated endotoxin (LpxL1) and/or by the use of mutant FHbp antigens with low factor H (FH) binding increased serum bactericidal antibody (SBA) responses. In this study, we immunized 13 infant macaques with 2 doses of NOMV with overexpressed mutant (R41S) FHbp with low binding to macaque FH (NOMV-FHbp). Control macaques received MenB-4C (n = 13) or aluminum hydroxide adjuvant alone (n = 4). NOMV-FHbp elicited a 2-fold higher IgG anti-FHbp geometric mean titer (GMT) than MenB-4C (P = 0.003), and the anti-FHbp repertoire inhibited binding of FH to FHbp, whereas anti-FHbp antibodies to MenB-4C enhanced FH binding. MenB-4C elicited a 10-fold higher GMT against strain NZ98/254, which was used to prepare the dOMV component, whereas NOMV-FHbp elicited an 8-fold higher GMT against strain H44/76, which was the parent of the mutant NOMV-FHbp vaccine strain. Against four strains with PorA mismatched to both of the vaccines and different FHbp sequence variants, NOMV-FHbp elicited 6- to 14-fold higher SBA GMTs than MenB-4C (P ≤ 0.0002). Two of 13 macaques immunized with MenB-4C but 0 of 17 macaques immunized with NOMV-FHbp or adjuvant developed serum anti-FH autoantibodies (P = 0.18). Thus, the mutant NOMV-FHbp approach has the potential to elicit higher and broader SBA responses than a licensed group B vaccine that contains wild-type FHbp that binds FH. The mutant NOMV-FHbp also might pose less of a risk of eliciting anti-FH autoantibodies.IMPORTANCE There are two licensed meningococcal capsular B vaccines. Both contain recombinant factor H binding protein (FHbp), which can bind to host complement factor H (FH). The limitations of these vaccines include a lack of protection against some meningococcal strains and the potential to elicit autoantibodies to FH. We immunized infant macaques with a native outer membrane vesicle (NOMV) vaccine with genetically attenuated endotoxin and overproduced mutant FHbp with low binding to FH. The NOMV-FHbp vaccine stimulated higher levels of protective serum antibodies than a licensed meningococcal group B vaccine against five of six genetically diverse meningococcal strains tested. Two of 13 macaques immunized with the licensed vaccine, which contains FHbp that binds macaque FH, but 0 of 17 macaques given NOMV-FHbp or the negative control developed serum anti-FH autoantibodies Thus, in a relevant nonhuman primate model, the NOMV-FHbp vaccine elicited greater protective antibodies than the licensed vaccine and may pose less of a risk of anti-FH autoantibody.

Effect on meningococcal serogroup W immunogenicity when Tdap was administered prior, concurrent or subsequent to the quadrivalent (ACWY) meningococcal CRM197-conjugate vaccine in adult Hajj pilgrims: A randomised controlled trial

Immune responses to the capsular polysaccharide administered in the polysaccharide-protein conjugate vaccines can be either improved or suppressed by the pre-existence of immunity to the carrier protein. Receiving multiple vaccinations is essential for travellers such as Hajj pilgrims, and the use of conjugated vaccines is recommended.We studied the immune response to meningococcal serogroup W upon prior, concurrent and sequential administration of a quadrivalent meningococcal conjugate vaccine (MCV4) conjugated to CRM197 (coadministered with 13 valent pneumococcal vaccine conjugate CRM197 [PCV13]), and tetanus-diphtheria-acellular pertussis (Tdap) vaccine in Australian adults before attending the Hajj pilgrimage in 2014.Participants were randomly assigned, by computer-generated numbers, to three study arms by 1:1:1 ratio. Group A received Tdap followed by MCV4-CRM197 (+PCV13) 3–4 weeks later. Group B received all three vaccines in a single visit. Group C received MCV4-CRM197 (+PCV13) followed by Tdap 3–4 weeks later. Blood samples obtained prior to and 3–4 weeks after immunisation with MCV4-CRM197 were tested for meningococcal serogroup W-specific serum bactericidal antibody responses using baby rabbit complement (rSBA).One hundred and seven participants aged between 18 and 64 (median 40) years completed the study. No significant difference in meningococcal serogroup W rSBA geometric mean titre (GMT) was observed between the study arms post vaccination with MCV-CRM197 but Group A tended to have a slightly lower GMT (A = 404, B = 984 and C = 1235, p = 0.15). No statistical difference was noticed between the groups in proportions of subjects achieving a ≥4-fold rise in rSBA titres or achieving rSBA titre ≥8 post vaccination.In conclusion, receipt of MCV4-CRM197 vaccine prior, concurrent or subsequent to Tdap has similar immunologic response, and hence concurrent administration is both immunogenic and practical. However, further investigation into whether carrier induced suppression is a public health issue is suggested.Clinical trial registration: ANZCTR no. ACTRN12613000536763.

Exposure to low-dose arsenic in early life alters innate immune function in children

Early-life exposure to arsenic (As) increases risks of respiratory diseases/infections in children. However, data on the ability of the innate immune system to combat bacterial infections in the respiratory tracts of As-exposed children are scarce. To evaluate whether persistent low-dose As exposure alters innate immune function among children younger than 5 years-of-age, mothers and participating children (N = 51) that were members of the Health Effects of Arsenic Longitudinal Study (HEALS) cohort in rural Bangladesh were recruited. Household water As, past and concurrent maternal urinary As (U-As) as well as child U-As were all measured at enrollment. In addition, U-As metabolites were evaluated. Innate immune function was examined via measures of cathelicidin LL-37 in plasma, ex vivo monocyte-derived-macrophage (MDM)-mediated killing of Streptococcus pneumoniae (Spn), and serum bactericidal antibody (SBA) responses against Haemophilus influenzae type b (Hib). Cyto-/chemokines produced by isolated peripheral blood mononuclear cells (PBMC) were assayed using a Multiplex system. Multivariable linear regression analyses revealed that maternal (p < 0.01) and child (p = 0.02) U-As were positively associated with plasma LL-37 levels. Decreased MDM-mediated Spn killing (p = 0.05) and SBA responses (p = 0.02) were seen to be each associated with fractions of mono-methylarsonic acid (MMA; a U-As metabolite) in the children. In addition, U-As levels were seen to be negatively associated with PBMC formation of fractalkine and IL-7, and positively associated with that for IL-13, IL-17 and MIP-1α. These findings suggested that early-life As exposure may disrupt the innate host defense pathway in these children. It is possible that such disruptions may have health consequences later in life.

Baseline Circulating Activated TFH and Tissue-Like Exhausted B Cells Negatively Correlate With Meningococcal C Conjugate Vaccine Induced Antibodies in HIV-Infected Individuals.

Since 2006, meningococcal serogroup C (MenC) conjugate (MCC) vaccines have been supplied by the Brazilian government for HIV-infected children under 13 years old. For measuring protection against MenC, the serum bactericidal antibody (SBA) assay is the method of choice. The characterization of T follicular helper cells (TFH) cells has been an area of intensive study because of their significance in multiple human diseases and in vaccinology. The objective of this study was to characterize the phenotype of peripheral TFH cells and B cells and how they associated with each other and with SBA levels induced by vaccination as well as with serum cytokine levels of HIV-infected and non-infected children and adolescents. We found that CD27−IgD−CD21−CD38+ (exhausted B cells) as well as short-lived plasmablasts (CD27+IgD−CD21−CD38+) are increased in cART treated HIV patients and negatively associated with MCC vaccine induced SBA levels. Baseline frequency of activated peripheral TFH cells was a negative correlate for SBA response to MCC vaccine but positively correlated with circulating plasmablast frequency. Baseline IL4-levels positively associated with SBA response but showed a negative correlation with activated peripheral TFH cells frequency. The increased frequency of activated peripheral TFH cells found in non-responders to the vaccine implies that higher activation/differentiation of CD4 T cells within the lymph node is not necessarily associated with induction of vaccine responses.

A Meningococcal Native Outer Membrane Vesicle Vaccine With Attenuated Endotoxin and Overexpressed Factor H Binding Protein Elicits Gonococcal Bactericidal Antibodies.

Meningococcal outer membrane vesicle (OMV) vaccines are prepared with detergents to remove endotoxin, which also remove desirable antigens such as factor H binding protein (FHbp). Native OMV (NOMV) vaccines with genetically attenuated endotoxin do not require detergent treatment and elicit broader serum bactericidal antibody (SBA) responses than OMV or recombinant FHbp (rFHbp) vaccines. We measured human complement-mediated SBA responses in mice immunized with NOMV with overexpressed FHbp subfamily B (NOMV-FHbp), NOMV with FHbp genetically inactivated (NOMV-KO), and/or a control rFHbp vaccine against meningococcal and gonococcal strains. Despite having 36-fold less FHbp per dose, the NOMV-FHbp vaccine elicited a ≥3-fold higher serum IgG anti-FHbp geometric mean titer than control vaccines containing rFHbp (P ≤ .003). Against 2 meningococcal outbreak strains with mismatched PorA and heterologous FHbp subfamily B sequence variants, the NOMV-FHbp vaccine produced ≥30-fold higher SBA titers than control vaccines. Mice immunized with NOMV-FHbp and NOMV-KO vaccines also elicited SBA against a gonococcal strain (P < .0001 vs the adjuvant-only control group). In contrast, 2 licensed meningococcal serogroup B vaccines, including one containing detergent-extracted OMV, did not produce gonococcal SBA in humans. A meningococcal NOMV vaccine elicits SBA against gonococci and with overexpressed FHbp elicits SBA against meningococci.

Breadth and Duration of Meningococcal Serum Bactericidal Activity in Health Care Workers and Microbiologists Immunized with the MenB-FHbp Vaccine.

MenB-FHbp is a meningococcal serogroup B vaccine with two factor H binding protein (FHbp) antigens from subfamilies A and B. For licensure, efficacy was inferred from serum bactericidal antibody (SBA) responses to four reference strains. Only limited information is available on the breadth or duration of protective SBA responses to genetically diverse disease-causing strains. Seventeen health care or laboratory workers were immunized with two (n = 2) or three (n = 15) doses of MenB-FHbp at 0, 2, and 6 months. SBA levels were measured against 14 serogroup B case isolates, including 6 from U.S. college outbreaks and 2 from Quebec during hyperendemic disease. Compared with preimmunization titers, the proportion of subjects with ≥4-fold increases in SBA titer 1 month after 2 doses of vaccine ranged from 35% to 94% for six isolates with FHbp subfamily A and from 24% to 76% for eight isolates with subfamily B FHbp. The respective proportions with ≥4-fold titer increases at 1 month after dose 3 were 73% to 100% and 67% to 100%. At that time point, the proportion of subjects with titers of ≥1:4 (presumed sufficient for short-term protection) ranged from 93% to 100% for all 14 isolates. By 9 to 11 months after dose 3, 50% or fewer of the subjects with follow-up sera had protective titers of ≥1:4 for 4 of 9 isolates tested. Three doses of MenB-FHbp elicited short-term protective SBA responses to diverse disease-causing serogroup B strains. For some strains, serum titers declined to <1:4 by 9 to 11 months, which raises concerns about the duration of broad, long-term protection. (This study has been registered at ClinicalTrials.gov under registration no. NCT02569632.).

Serum Bactericidal Antibody Responses of Students Immunized With a Meningococcal Serogroup B Vaccine in Response to an Outbreak on a University Campus.

MenB-4C is a recently licensed meningococcal serogroup B vaccine. For vaccine licensure, short-term efficacy was inferred from serum bactericidal antibody (SBA) titers against 3 antigen-specific indicator strains, which are not necessarily representative of US disease-causing strains. A total of 4923 students were immunized with MenB-4C in response to an outbreak at a university. Serum samples were obtained at 1.5-2 months from 106 students who received the recommended 2 doses and 52 unvaccinated students. Follow-up serum samples were obtained at 7 months from 42 vaccinated and 24 unvaccinated participants. SBA was measured against strains from 4 university outbreaks. At 1.5-2 months, the proportion of immunized students with protective titers ≥1:4 against an isolate from the campus outbreak was 93% (95% confidence interval [CI], 87%-97%) vs 37% (95% CI, 24%-51%) in unvaccinated students. The proportion with protective titers against strains from 3 other university outbreaks was 73% (95% CI, 62%-82%) vs 26% (95% CI, 14%-41%) in unvaccinated; 71% (95% CI, 61%-79%) vs 19% (95% CI, 10%-33%) in unvaccinated; and 53% (95% CI, 42%-64%) vs 9% (95% CI, 3%-22%) in unvaccinated (P < .0001 for each strain). At 7 months, the proportion of immunized students with titers ≥1:4 was 86% (95% CI, 71%-95%) against the isolate from the campus outbreak and 57% (95% CI, 41%-72%), 38% (95% CI, 24%-54%), and 31% (95% CI, 18%-47%), respectively, for the other 3 outbreak strains. MenB-4C elicited short-term protective titers against 4 strains responsible for recent university campus outbreaks. By 7 months the prevalence of protective titers was <40% for 2 of the 4 outbreak strains. A booster dose of MenB-4C may be needed to maintain protective titers.

Association of serum bactericidal antibody and opsonic antibody levels after Neisseria meningitidis serogroup C conjugate vaccine in Brazilian children and adolescents infected or not infected with HIV

Neisseria meningitidis serogroup C (MenC) is the main causative agent of meningitis in Brazil. HIV infection affects the quality of the immune system. HIV+ children have an increased risk of infection to encapsulated bacteria such as N. meningitidis. We evaluated the opsonic antibody (OPA) levels and its correlation with serum bactericidal antibody (SBA) levels induced by one and two doses of a MenC conjugate vaccine in children and adolescents HIV+ and HIV-exposed but uninfected children (HEU) group. Overall the data show the importance of two doses of vaccine for HIV+ individuals. About 79% and 58% of HIV+ patients showed SBA and OPA positive response after two doses of vaccine, respectively. For HEU group, 62% and 41% of patients showed SBA and OPA positive response after one dose of vaccine, respectively. A positive and significant association between SBA and OPA levels was seen after two doses of vaccine in HIV+ patients.

Serum Bactericidal Antibody Responses of Adults Immunized with the MenB-4C Vaccine against Genetically Diverse Serogroup B Meningococci.

MenB-4C is a meningococcal vaccine for the prevention of serogroup B disease. The vaccine contains factor H binding protein (FHbp) and three other antigens that can elicit serum bactericidal antibodies (SBA). For vaccine licensure, efficacy was inferred from the SBA responses against three antigen-specific indicator strains. The relation between those results and broad protection against circulating genetically diverse strains is not known. Twenty adults were immunized with two doses of MenB-4C given 1 to 2 months apart. SBA activity against 3 reference strains and 15 serogroup B test strains (6 from college outbreaks) was measured. Compared to the preimmunization titers, 70%, 95%, and 95% of subjects had ≥4-fold increases in the titers of anti-PorA P1.4, anti-NadA, and anti-FHbp antibodies against the reference strains, respectively. In contrast, only 25 to 45% of the subjects had ≥4-fold increases in responses to 10 of the 15 test strains, including 8 that expressed one to three of the antigens in the vaccine. At 1 month, the majority of subjects with <4-fold titer increases had serum titers of ≥1:4, which are considered sufficient for protection. However, the titers against four strains declined to <1:4 by 4 to 6 months in one-third to greater than 50% of the subjects tested. Clinically relevant isolates are often more resistant to SBA than the indicator strains used to measure antigen-specific SBA. A working model is that the percentage of subjects with titers of ≥1:4 at 1 month postimmunization correlates with short-term protection against that strain, whereas the percentage of subjects with ≥4-fold titer increases represents a more robust response. (The protocol used at the Oxford Vaccine Group has been registered at ClinicalTrials.gov under registration no. NCT02398396.).

A meningococcal NOMV-FHbp vaccine for Africa elicits broader serum bactericidal antibody responses against serogroup B and non-B strains than a licensed serogroup B vaccine

BackgroundMeningococcal epidemics in Sub-Sahara caused by serogroup A strains are controlled by a group A polysaccharide conjugate vaccine. Strains with serogroups C, W and X continue to cause epidemics. Protein antigens in licensed serogroup B vaccines are shared among serogroup B and non-B strains. PurposeCompare serum bactericidal antibody responses elicited by an investigational native outer membrane vesicle vaccine with over-expressed Factor H binding protein (NOMV-FHbp) and a licensed serogroup B vaccine (MenB-4C) against African serogroup A, B, C, W and X strains. MethodsHuman Factor H (FH) transgenic mice were immunized with NOMV-FHbp prepared from a mutant African meningococcal strain containing genetically attenuated endotoxin and a mutant sub-family B FHbp antigen with low FH binding, or with MenB-4C, which contains a recombinant sub-family B FHbp antigen that binds human FH, and three other antigens, NHba, NadA and PorA P1.4, capable of eliciting bactericidal antibody. ResultsThe NOMV-FHbp elicited serum bactericidal activity against 12 of 13 serogroup A, B, W or X strains from Africa, and four isogenic serogroup B mutants with sub-family B FHbp sequence variants. There was no activity against a serogroup B mutant with sub-family A FHbp, or two serogroup C isolates from a recent outbreak in Northern Nigeria, which were mismatched for both PorA and sub-family of the FHbp vaccine antigen. For MenB-4C, NHba was expressed by all 16 African isolates tested, FHbp sub-family B in 13, and NadA in five. However, MenB-4C elicited titers ≥1:10 against only one isolate, and against only two of four serogroup B mutant strains with sub-family B FHbp sequence variants. ConclusionsNOMV-FHbp has greater potential to confer serogroup-independent protection in Africa than the licensed MenB-4C vaccine. However, the NOMV-FHbp vaccine will require inclusion of sub-family A FHbp for coverage against recent serogroup C strains causing outbreaks in Northern Nigeria.

Impaired Immunogenicity of Meningococcal Neisserial Surface Protein A in Human Complement Factor H Transgenic Mice.

Neisserial surface protein A (NspA) is a highly conserved outer membrane protein previously investigated as a meningococcal vaccine candidate. Despite eliciting serum bactericidal activity in mice, a recombinant NspA vaccine failed to elicit serum bactericidal antibodies in a phase 1 clinical trial in humans. The discordant results may be explained by the recent discovery that NspA is a human-specific ligand of the complement inhibitor factor H (FH). Therefore, in humans but not mice, NspA would be expected to form a complex with FH, which could impair human anti-NspA protective antibody responses. To investigate this question, we immunized human FH transgenic BALB/c mice with three doses of recombinant NspA expressed in Escherichia coli microvesicles, with each dose being separated by 3 weeks. Three of 12 (25%) transgenic mice and 13 of 14 wild-type mice responded with bactericidal titers of ≥1:10 in postimmunization sera (P = 0.0008, Fisher's exact test). In contrast, human FH transgenic and wild-type mice immunized with a control meningococcal native outer membrane vesicle vaccine had similar serum bactericidal antibody responses directed at PorA, which is not known to bind human FH, and a mutant factor H binding protein (FHbp) antigen with a >50-fold lower level of FH binding than wild-type FHbp antigen binding.Thus, human FH can impair anti-NspA serum bactericidal antibody responses, which may explain the poor immunogenicity of the NspA vaccine previously tested in humans. A mutant NspA vaccine engineered to have decreased binding to human FH may increase protective antibody responses in humans.

Effect of complement Factor H on anti-FHbp serum bactericidal antibody responses of infant rhesus macaques boosted with a licensed meningococcal serogroup B vaccine

FHbp is a major serogroup B meningococcal vaccine antigen. Binding of complement Factor H (FH) to FHbp is specific for human and some non-human primate FH. In previous studies, FH binding to FHbp vaccines impaired protective anti-FHbp antibody responses. In this study we investigated anti-FHbp antibody responses to a third dose of a licensed serogroup B vaccine (MenB-4C) in infant macaques vaccinated in a previous study with MenB-4C. Six macaques with high binding of FH to FHbp (FHhigh), and six with FHlow baseline phenotypes, were immunized three months after dose 2. After dose 2, macaques with the FHlow baseline phenotype had serum anti-FHbp antibodies that enhanced FH binding to FHbp (functionally converting them to a FHhigh phenotype). In this group, activation of the classical complement pathway (C4b deposition) by serum anti-FHbp antibody, and anti-FHbp serum bactericidal titers were lower after dose 3 than after dose 2 (p<0.02). In macaques with the FHhigh baseline phenotype, the respective anti-FHbp C4b deposition and bactericidal titers were similar after doses 2 and 3. Two macaques developed serum anti-FH autoantibodies after dose 2, which were not detected after dose 3. In conclusion, in macaques with the FHlow baseline phenotype whose post-dose 2 serum anti-FHbp antibodies had converted them to FHhigh, the anti-FHbp antibody repertoire to dose 3 was skewed to less protective epitopes than after dose 2. Mutant FHbp vaccines that eliminate FH binding may avoid eliciting anti-FHbp antibodies that enhance FH binding, and confer greater protection with less risk of inducing anti-FH autoantibodies than FHbp vaccines that bind FH.

Interchangeability of meningococcal group C conjugate vaccines with different carrier proteins in the United Kingdom infant immunisation schedule

An open, non-randomised study was undertaken in England during 2011–12 to evaluate vaccine antibody responses in infants after completion of the routine primary infant immunisation schedule, which included two doses of meningococcal group C (MenC) conjugate (MCC) vaccine at 3 and 4 months. Any of the three licensed MCC vaccines could be used for either dose, depending on local availability. Healthy term infants registered at participating general practices (GPs) in Hertfordshire and Gloucestershire, UK, were recruited prospectively to provide a single blood sample four weeks after primary immunisation, which was administered by the GP surgery. Vaccination history was obtained at blood sampling. MenC serum bactericidal antibody (SBA) and IgG antibodies against Haemophilus influenzae b (Hib), pertussis toxin (PT), diphtheria toxoid (DT), tetanus toxoid (TT) and thirteen pneumococcal serotypes were analysed according to MCC vaccines received. MenC SBA responses differed significantly (P<0.001) according to MCC vaccine schedule as follows: MenC SBA geometric mean titres (GMTs) were significantly lower in infants receiving a diphtheria cross-reacting material-conjugated MCC (MCC-CRM) vaccine followed by TT-conjugated MCC (MCC-TT) vaccine (82.0; 95% CI, 39–173; n=14) compared to those receiving two MCC-CRM (418; 95% CI, 325–537; n=82), two MCC-TT (277; 95% CI, 223–344; n=79) or MCC-TT followed by MCC-CRM (553; 95% CI, 322–949; n=18). The same group also had the lowest Hib geometric mean concentrations (0.60μg/mL, 0.27–1.34) compared to 1.85μg/mL (1.23–2.78), 2.86μg/mL (2.02–4.05) and 4.26μg/mL (1.94–9.36), respectively. Our results indicate that MCC vaccines with different carrier proteins are not interchangeable. When several MCC vaccines are available, children requiring more than one dose should receive MCC vaccines with the same carrier protein or, alternatively, receive MCC-TT first wherever possible.

Human factor H (FH) impairs protective meningococcal anti-FHbp antibody responses and the antibodies enhance FH binding.

ABSTRACTThe meningococcal 4CMenB vaccine (Bexsero; Novartis) contains four antigens that can elicit serum bactericidal activity, one of which is factor H (FH)-binding protein (FHbp). FHbp specifically binds human complement FH. When humans are immunized, FHbp is expected to form a complex with FH, which could affect immunogenicity and safety. Wild-type mice (whose FH does not bind to FHbp) and human FH transgenic mice were immunized with three doses of 4CMenB, and their responses were compared. There were no significant differences between the serum bactericidal responses of transgenic and wild-type mice to strains with all of the antigens mismatched for 4CMenB except PorA or NadA. In contrast, against a strain mismatched for all of the antigens except FHbp, the transgenic mice had 15-fold weaker serum bactericidal antibody responses (P = 0.0006). Binding of FH downregulates complement. One explanation for the lower anti-FHbp serum bactericidal activity in the transgenic mice is that their postimmunization serum samples enhanced the binding of FH to FHbp, whereas the serum samples from the wild-type mice inhibited FH binding. Control antiserum from transgenic mice immunized with a low-FH-binding mutant FHbp (R41S) vaccine inhibited FH binding. Two 4CMenB-vaccinated transgenic mice developed serum IgM autoantibodies to human FH. Thus, human FH impairs protective serum anti-FHbp antibody responses, in part by skewing the antibody repertoire to FHbp epitopes outside the FH binding site. FHbp vaccines that bind FH may elicit FH autoantibodies. Mutant FHbp antigens with low FH binding could improve protection and, potentially, vaccine safety in humans.

Meningococcal factor H-binding protein vaccines with decreased binding to human complement factor H have enhanced immunogenicity in human factor H transgenic mice

Factor H-binding protein (fHbp) is a component of a meningococcal vaccine recently licensed in Europe for prevention of serogroup B disease, and a second vaccine in clinical development. The protein specifically binds human factor H (fH), which down-regulates complement activation and enhances resistance to bactericidal activity. There are conflicting data from studies in human fH transgenic mice on whether binding of human fH to fHbp vaccines decreases immunogenicity, and whether mutant fHbp vaccines with decreased fH binding have enhanced immunogenicity. fHbp can be classified into two sub-families based on sequence divergence and immunologic cross-reactivity. Previous studies of mutant fHbp vaccines with low fH binding were from sub-family B, which account for approximately 60% of serogroup B case isolates. In the present study, we evaluated the immunogenicity of two mutant sub-family A fHbp vaccines containing single substitutions, T221A or D211A, which resulted in 15- or 30-fold lower affinity for human fH, respectively, than the corresponding control wild-type fHbp vaccine. In transgenic mice with high serum concentrations of human fH, both mutant vaccines elicited significantly higher IgG titers and higher serum bactericidal antibody responses than the control fHbp vaccine that bound human fH. Thus, mutations introduced into a sub-family A fHbp antigen to decrease fH binding can increase protective antibody responses in human fH transgenic mice. Collectively the data suggest that mutant fHbp antigens with decreased fH binding will result in superior vaccines in humans.

Does Binding of Complement Factor H to the Meningococcal Vaccine Antigen, Factor H Binding Protein, Decrease Protective Serum Antibody Responses?

Factor H binding protein (fHbp) is a principal antigen in a multicomponent meningococcal vaccine recently licensed in Europe for prevention of serogroup B diseases. The protein recruits the complement downregulator, factor H (fH), to the bacterial surface, which enables the organism to resist complement-mediated bacteriolysis. Binding is specific for human fH. In preclinical studies, mice and rabbits immunized with fHbp vaccines developed serum bactericidal antibody responses, which in humans predict protection against developing meningococcal disease. These studies, however, were in animals whose fH did not bind to the vaccine antigen. Here we review the immunogenicity of fHbp vaccines in human fH transgenic mice. The data suggest that animals with high serum human fH concentrations have impaired protective antibody responses. Further, mutant fHbp vaccines with single amino acid substitutions that decrease fH binding are superior immunogens, possibly by unmasking epitopes in the fH binding site that are important for eliciting serum bactericidal antibody responses. Humans immunized with fHbp vaccines develop serum bactericidal antibody, but achieving broad coverage in infants required incorporation of additional antigens, including outer membrane vesicles, which increased rates of fever and local reactions at the injection site. The experimental results in transgenic mice predict that fHbp immunogenicity can be improved in humans by using mutant fHbp vaccines with decreased fH binding. These results have important public health implications for developing improved fHbp vaccines for control of serogroup B meningococcal disease and for development of vaccines against other microbes that bind host molecules.

Importance of Inhibition of Binding of Complement Factor H for Serum Bactericidal Antibody Responses to Meningococcal Factor H-binding Protein Vaccines

Factor H (fH) binding protein (fHbp) is part of vaccines developed for prevention of meningococcal serogroup B disease. More than 610 fHbp amino acid sequence variants have been identified, which can be classified into 2 subfamilies. The extent of cross-protection within a subfamily has been difficult to assess because of strain variation in fHbp expression. Using isogenic mutant strains, we compared cross-protective serum antibody responses of mice immunized with 7 divergent fHbp variants in subfamily B, including identification numbers (ID) 1 and 55, which were chosen for vaccine development. In the presence of the human complement downregulator fH, the ability of the anti-fHbp antibodies to deposit sufficient complement C3b on the bacterial surface to elicit bactericidal activity required inhibition of binding of fH by the anti-fHbp antibodies. With less bound fH, the bacteria became more susceptible to complement-mediated bactericidal activity. Among the different fHbp sequence variants, those more central in a phylogenic network than ID 1 or 55 elicited anti-fHbp antibodies with broader inhibition of fH binding and broader bactericidal activity. Thus, the more central variants show promise of extending protection to strains with divergent fHbp sequences that are covered poorly by fHbp variants in clinical development.

Immunogenicity of a meningococcal native outer membrane vesicle vaccine with attenuated endotoxin and over-expressed factor H binding protein in infant rhesus monkeys

We previously investigated immunogenicity of meningococcal native outer membrane vesicle (NOMV) vaccines prepared from recombinant strains with attenuated endotoxin (ΔLpxL1) and over-expressed factor H binding protein (fHbp) in a mouse model. The vaccines elicited broad serum bactericidal antibody responses. While human toll-like receptor 4 (TLR-4) is mainly stimulated by wildtype meningococcal endotoxin, mouse TLR-4 is stimulated by both the wildtype and mutant endotoxin. An adjuvant effect in mice of the mutant endotoxin would be expected to be much less in humans, and may have contributed to the broad mouse bactericidal responses. Here we show that as previously reported for humans, rhesus primate peripheral blood mononuclear cells incubated with a NOMV vaccine from ΔLpxL1 recombinant strains had lower proinflammatory cytokine responses than with a control wildtype NOMV vaccine. The cytokine responses to the mutant vaccine were similar to those elicited by a detergent-treated, wildtype outer membrane vesicle vaccine that had been safely administered to humans. Monkeys (N=4) were immunized beginning at ages 2–3 months with three doses of a NOMV vaccine prepared from ΔLpxL1 recombinant strains with over-expressed fHbp in the variant 1 and 2 groups. The mutant NOMV vaccine elicited serum bactericidal titers ≥1:4 against all 10 genetically diverse strains tested, including 9 with heterologous PorA to those in the vaccine. Negative-control animals had serum bactericidal titers <1:4. Thus, the mutant NOMV vaccine elicited broadly protective serum antibodies in a non-human infant primate model that is more relevant for predicting human antibody responses than mice.