Differential B-cell memory around the 11-month booster in children vaccinated with a 10- or 13-valent pneumococcal conjugate vaccine.

BACKGROUND: Both the 10- and 13-valent pneumococcal conjugate vaccines (PCV10 and PCV13) induce immunological memory against Streptococcus pneumoniae infections caused by vaccine serotypes. In addition to comparing serum antibody levels, we investigated frequencies of serotype-specific plasma cells (PCs) and memory B-cells (Bmems) as potential predictors of long-term immunity around the booster vaccination at 11 months of age. METHODS: Infants were immunized with PCV10 or PCV13 at 2, 3, 4, and 11 months of age. Blood was collected before the 11-month booster or 7-9 days afterward. Serotype-specific immunoglobulin G (IgG) levels were determined in serum samples by multiplex immunoassay. Circulating specific PCs and Bmems against shared serotypes 1, 6B, 7F, and 19F and against PCV13 serotypes 6A and 19A were measured in peripheral blood mononuclear cells by enzyme-linked immunospot assay. RESULTS: No major differences in IgG levels and PC frequencies between groups were found for the 4 shared serotypes. Notably, PCV13 vaccination resulted in higher frequencies of Bmems than PCV10 vaccination, both before and after the booster dose, for all 4 shared serotypes except for serotype 1 postbooster. For PCV13-specific serotypes 6A and 19A, the IgG levels and frequencies of PCs and Bmems were higher in the PCV13 group, pre- and postbooster, except for PC frequencies prebooster. CONCLUSIONS: Both PCVs are immunogenic and induce measurable IgG, PC, and Bmem booster responses at 11 months. Compared to PCV10, vaccination with PCV13 was associated with overall similar IgG levels and PC frequencies but with higher Bmem frequencies before and after the 11-month booster. The clinical implications of these results need further follow-up. CLINICAL TRIALS REGISTRATION: NTR3069.

Preclinical safety and immunogenicity evaluation of a nonavalent PorA native outer membrane vesicle vaccine against serogroup B meningococcal disease.

BACKGROUND: An improved nonavalent PorA native outer membrane vesicle vaccine was developed with intrinsic adjuvating activity due to presence of less-toxic (lpxL1) LPS. In the present study, the safety and immunogenicity of this next-generation NonaMen vaccine were evaluated following repeated vaccination in rabbits and mice. METHODS: A repeated-dose toxicology study was performed in rabbits. Immunogenicity of next-generation NonaMen was evaluated by determining the serum bactericidal antibody (SBA) titers against meningococcal serogroup B strains containing several PorA subtypes. Release of the pro-inflammatory cytokine, interleukin-6 (IL-6), by the human monocytic cell line (MM6) was measured to estimate pyrogenic activity. RESULTS: No toxicologically relevant findings were noted in vaccinated rabbits receiving plain next-generation NonaMen. In agreement, next-generation NonaMen induced reduced amounts of the pro-inflammatory cytokine, IL-6, released by human monocyte cell line. In both rabbits and mice, next-generation NonaMen induced high SBA titers against all tested MenB strains regardless of whether or not aluminium phosphate adjuvant is used. CONCLUSIONS: The data suggest that next-generation NonaMen is a safe vaccine with the potential to develop a broadly protective immune response and encourage the start of the first clinical studies.

Differential effect of TLR2 and TLR4 on the immune response after immunization with a vaccine against Neisseria meningitidis or Bordetella pertussis.

Neisseria meningitidis and Bordetella pertussis are Gram-negative bacterial pathogens that can cause serious diseases in humans. N. meningitidis outer membrane vesicle (OMV) vaccines and whole cell pertussis vaccines have been successfully used in humans to control infections with these pathogens. The mechanisms behind their effectiveness are poorly defined. Here we investigated the role of Toll-like receptor (TLR) 2 and TLR4 in the induction of immune responses in mice after immunization with these vaccines. Innate and adaptive immune responses were compared between wild type mice and mice deficient in TLR2, TLR4, or TRIF. TRIF-deficient and TLR4-deficient mice showed impaired immunity after immunization. In contrast, immune responses were not lower in TLR2-/- mice but tended even to be higher after immunization. Together our data demonstrate that TLR4 activation contributes to the immunogenicity of the N. meningitidis OMV vaccine and the whole cell pertussis vaccine, but that TLR2 activation is not required.

Hyperproliferation of B cells specific for a weakly immunogenic PorA in a meningococcal vaccine model.

Highly homologous meningococcal porin A (PorA) proteins induce protective humoral immunity against Neisseria meningitidis group B infection but with large and consistent differences in the levels of serum bactericidal activity achieved. We investigated whether a poor PorA-specific serological outcome is associated with a limited size of the specific B-cell subpopulation involved. The numbers of PorA-specific splenic plasma cells, bone marrow (BM) plasma cells, and splenic memory B cells were compared between mice that received priming and boosting with the weakly immunogenic PorA (P1.7-2,4) protein and those that received priming and boosting with the highly immunogenic PorA (P1.5-1,2-2) protein. Immunoglobulin G (IgG) titers (except at day 42), bactericidal activity, and the avidity of IgG produced against P1.7-2,4 were significantly lower at all time points after priming and boosting than against P1.5-1,2-2. These differences, however, were not associated with a lack of P1.7-2,4-specific plasma cells. Instead, priming with both of the PorAs resulted in the initial expansion of comparable numbers of splenic and BM plasma cells. Moreover, P1.7-2,4-specific BM plasma cells, but not P1.5-1,2-2-specific plasma cells, expanded significantly further after boosting. Likewise, after a relative delay during the priming phase, the splenic P1.7-2,4-specific memory B cells largely outnumbered those specific for P1.5-1,2-2, upon boosting. These trends were observed with different vaccine formulations of the porins. Our results show for the first time that B-cell subpopulations involved in a successfully maturated antibody response against a clinically relevant vaccine antigen are maintained at smaller population sizes than those associated with poor affinity maturation. This bears consequences for the interpretation of immunological memory data in clinical vaccine trials.

Immunogenicity of a combination vaccine containing pneumococcal conjugates and meningococcal PorA OMVs.

The pre-clinical immunogenicity of a combination vaccine containing 13-valent pneumococcal conjugate (13vPnC) vaccine (serotypes 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F and 23F conjugated to CRM197) and nine-valent meningococcal B PorA vaccine (NonaMen; serosubtypes P1.7,16; P1.5-1,2-2; P1.19,15-1; P1.5-2,10; P1.12-1,13; P1.7-2,4; P1.22,14; P1.7-1,1 and P1.18-1,3,6), and any potential immunological interference between pneumococcal and MenB components of the vaccine were evaluated. NIH mice were immunized twice subcutaneously with the vaccines combined in one syringe, or given individually. Combining 13vPnC vaccine with NonaMen vaccine in one syringe had no negative effect on the induced antibody response against any MenB serosubtypes compared to separate injection of the vaccines, and the anti-pneumococcal antibody responses were enhanced. Furthermore, co-administration of the combination vaccine with a combined diphtheria/tetanus/acellular pertussis/inactivated poliomyelitis vaccine/Haemophilus influenzae type b-TT conjugate (DTaP/IPV-Hib) vaccine to New Zealand white rabbits at a different injection site did not affect the anti-pneumococcal polysaccharide and anti-PorA antibody titres. We conclude that no immunological interference was observed by combined administration of pneumococcal conjugate and meningococcal B vaccines in one syringe.

Porin A-specific antibody avidity in patients who are convalescing from meningococcal B disease.

Porin A (PorA), which determines the serosubtype of Neisseria meningitidis, is the main antigen of a candidate vaccine against serogroup B meningococci, which has been shown to induce high-avidity antibodies in children. We characterized the immune response of children after convalescing from meningococcal infection with a serosubtype P1.7-2,4 strain. Acute- and convalescent-phase sera of 21 children with meningococcal septic shock caused by strains with PorA subtype P1.7-2,4 were collected. The serum bactericidal antibody titers, IgG isotype distribution, and antibody avidity were measured. We determined whether the differences in avidity of anti-outer membrane vesicle antibodies were PorA specific. Serum bactericidal activity against H44/76 P1.7-2,4 was <4 in all convalescent sera. The IgG isotype distribution of the convalescent sera was dominated by IgG(1), followed by IgG(3), whereas no IgG(2) or IgG(4) was found. The geometric mean avidity index (GMAI) of convalescent sera measured against a strain with the identical subtype as the infective isolate was significantly higher than that against a strain with a heterologous PorA subtype or a PorA-negative mutant strain (57 versus 35 and 23%, respectively; p = 0.005 and p < 0.001). Geometric mean avidity titers were highest for P1.7-2,4, corresponding with the highest GMAI. The GMAI after invasive meningococcal disease was lower than after vaccination of healthy toddlers with a monovalent P1.7-2,4 outer membrane vesicle vaccine.