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

Intradermal administration of the pneumococcal conjugate vaccine in mice results in lower antibody responses as compared to intramuscular administration

INTRODUCTION

Several studies have shown that intradermal vaccination leads to improved immune responses. In addition, lowering vaccine doses will reduce costs and therefore potentially increase coverage. To determine whether intradermal delivery enhances the antibody responses against the 13-valent pneumococcal conjugate vaccine (PCV13), we compared intradermally and intramuscularly vaccinated mice.

METHODS

Mice were immunized with PCV13, either intradermally or intramuscularly and CFU-counts in the nasal tissue were determined three or seven days after intranasal colonization with a serotype 4 clinical strain. Antibody concentrations against all thirteen polysaccharides were measured in blood and mucosal samples using a fluorescent-bead-based multiplex immunoassay.

RESULTS

Antibody levels in both serum and mucosal samples were higher in the intramuscularly vaccinated group as compared to the intradermally vaccinated group. No protection against S. pneumoniae intranasal colonization was observed for either vaccination route.

CONCLUSIONS

Intradermal vaccination was inferior to intramuscular immunization in inducing serotype-specific antibodies.

Development of a pneumococcal conjugate vaccine based on chemical conjugation of polysaccharide serotype 6B to PspA

The use of conjugate vaccines remains an effective intervention to prevent pneumococcal diseases. In order to expand vaccine coverage, the inclusion of pneumococcal proteins as carriers is a propitious alternative that has been explored over the past few years. In this study, pneumococcal surface protein A (PspA) clade 1, family 1 (PspA1) and clade 3, family 2 (PspA3) were used as carrier proteins for pneumococcal capsular polysaccharide serotype 6B (Ps6B). Employing an improved reductive amination chemistry, 50% of Ps6B was incorporated to each protein, PspA1 and PspA3. The effect of chemical modifications in Ps6B and PspA was assessed by an antigenicity assay and circular dichroism, respectively. Fragmentation and oxidation decreased the antigenicity of Ps6B while conjugation improved antigenicity. In the same manner, introduction of adipic acid dihydrazide (ADH) reduced PspA secondary structure content, which was partially restored after conjugation. Immunization of Ps6B-PspA1 and Ps6B-PspA3 conjugates in mice induced specific IgG antibodies against the Ps6B and the protein; and anti-PspA antibodies had functional activity against two pneumococcal strains with different serotypes. These results suggest that chemical coupling between Ps6B and PspA did not affect antigenic epitopes and support the further development of PspA as a carrier protein in pneumococcal conjugate vaccines to provide broader protection.

Booster immunization with a fractional dose of Prevnar 13 affects cell-mediated immune response but not humoral immunity in CD-1 mice

Achieving durable protective immunity following vaccination is dependent on many factors, including vaccine composition and antigen dose, and it has been investigated for various types of vaccines. Aim of the present study was to investigate the overall immune response elicited by two different booster doses in CD-1 mice, by exploiting the largely used 13-valent pneumococcal conjugate vaccine Prevnar 13® (PCV13). Immunization was performed by two primary doses of PCV13 two weeks apart, and a full or fractional (1/5) booster dose on week 10. Serotype-specific antibody titer, avidity, and opsonophagocytic activity were evaluated one week later, and compared to cell-mediated immunity (CMI) responses determined as the frequency of cytokines producing splenocytes by in vitro recall with the antigens (carrier protein and polysaccharides). Data showed that regardless of the booster dose, a comparable humoral response was produced, characterized by similar amounts of serotype-specific antibodies, with analog avidity and opsonophagocytic properties. On the other hand, when CMI was evaluated, the presence of CRM197-specific IL-5 and IL-2 producing cells was evident in splenocytes from mice immunized with the full dose, while in those immunized with the fractional booster dose, IFN-γ producing cells responsive to both protein and polysaccharide antigens were significantly increased, whereas the number of IL-5 and IL-2 positive cells remained unaffected. Overall the present findings show that PCV13 humoral response in mice is associated to a Th2 predominant response at the full booster dose, while the fractional one favors a mixed Th1/Th2 response, suggesting an important role of CMI besides measurement of functional protective antibodies, as an additional and important key information in vaccine development.

Immunogenicity differences of a 15-valent pneumococcal polysaccharide conjugate vaccine (PCV15) based on vaccine dose, route of immunization and mouse strain

Pneumococcal disease continues to be a medical need even with very effective vaccines on the market. Globally, there are extensive research efforts to improve serotype coverage with novel vaccines; therefore, conducting preclinical studies in different animal models becomes essential. The work presented herein focuses on evaluating a 15-valent pneumococcal conjugate vaccine (PCV15) in mice. Initially we evaluated several doses of PCV15 in Balb/c mice. The optimal vaccine dose was determined to be 0.4μg per pneumococcal polysaccharide (PS) (0.8μg of 6B) for subsequent studies. This PS dose was chosen for PCV evaluation in mice based on antibody levels determined by multiplexed electrochemiluminescent (ECL) assays, T-cell responses following in vitro stimulation with CRM197 peptides and protection from pneumococcal challenge. We then selected four mouse strains for evaluation: Balb/c, C3H/HeN, CD1 and Swiss Webster (SW), immunized with PCV15 by either intraperitoneal (IP) or intramuscular (IM) routes. We assessed IgG responses by ECL assays and functional antibody activity by multiplexed opsonophagocytic assays (MOPA). Every mouse strain evaluated responded to all 15 serotypes contained in the vaccine. Mice tended to have lower responses to serotypes 6B, 23F and 33F. The IP route of immunization resulted in higher antibody titers for most serotypes in Balb/c, C3H and SW. CD1 mice tended to respond similarly for most serotypes, regardless of route of immunization. Similar trends were observed with the four mouse strains when evaluating functional antibody activity. Given the differences in antibody responses based on mouse strain and route of immunization, it is critical to evaluate pneumococcal vaccines in multiple animal models to determine the optimal formulation before moving to clinical trials.

Molecular signatures of antibody responses derived from a systems biology study of five human vaccines

Many vaccines induce protective immunity via antibodies. Systems biology approaches have been used to determine signatures that can be used to predict vaccine-induced immunity in humans, but whether there is a 'universal signature' that can be used to predict antibody responses to any vaccine is unknown. Here we did systems analyses of immune responses to the polysaccharide and conjugate vaccines against meningococcus in healthy adults, in the broader context of published studies of vaccines against yellow fever virus and influenza virus. To achieve this, we did a large-scale network integration of publicly available human blood transcriptomes and systems-scale databases in specific biological contexts and deduced a set of transcription modules in blood. Those modules revealed distinct transcriptional signatures of antibody responses to different classes of vaccines, which provided key insights into primary viral, protein recall and anti-polysaccharide responses. Our results elucidate the early transcriptional programs that orchestrate vaccine immunity in humans and demonstrate the power of integrative network modeling.

Memory B and T cell responses induced by serotype 4 Streptococcus pneumoniae vaccines: longitudinal analysis comparing responses elicited by free polysaccharide, conjugate and carrier

We have conducted a 1-year longitudinal study in mice vaccinated by free serotype 4 Streptococcus pneumoniae PS (PS4), the corresponding tetanus toxoid (TT)-conjugated vaccine, or the TT carrier alone. B and T cell immunity induced by these three types of antigen, were compared by monitoring the (i) long-term persistence of specific serum antibodies, (ii) frequency of memory B cell precursors in spleen, and (iii) T cell responses against the carrier. While PS4-specific antibody response appeared later than the anti-carrier response upon primary immunization, PS4-specific B memory and serum responses were quantitatively and qualitatively similar to the ones observed against TT upon immunization by either the free carrier or the conjugate. We also observed a parallel persistent carrier-specific T cell response in the spleen. These data indicate that the nature and long-term kinetics of the anti-PS4 antibody response induced by the conjugate vaccine are similar to "classical" T-dependent response elicited by conventional protein antigens.

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.

B cell mediated priming following pneumococcal colonization

The primary reservoir for Streptococcus pneumoniae is the human nasopharynx, and colonization is often the initial step in pathogenesis. Recently we have demonstrated that pneumococcal colonization primes the immune response to subsequent vaccination with the pneumococcal conjugate vaccine (CPV). In this study we wished to determine if colonization stimulates the production of B cell memory that is activated following vaccination with CPV. To test this hypothesis, we colonized mice with S. pneumoniae serotype 14, adoptively transferred their B cells and CD4+ T cells into naïve recipients, and vaccinated the recipients with CPV. Our results indicate that pneumococcal colonization stimulates the production of memory B cells which are responsible for enhancing the immune response to CPV vaccination.