Pneumococcal vaccine development

Development and qualification of an automated capillary Western method for the identification of polysaccharide serotypes in pneumococcal conjugate vaccine (PCV)

Streptococcus pneumoniae bacterial infection causes mortality in both adults and infants. To mitigate the impact of the disease, several Pneumococcal conjugate vaccines (PCVs) have been manufactured for the U.S. market, including the recent approval of the 15-valent PCV Vaxneuvance™ from MSD. These vaccines demonstrate high efficacy for both the adult and pediatric dose. These PCVs contain multiple unique serotypes in the final, formulated vaccine product, and identifying a specific polysaccharide, in the presence of other serotypes, is a critical quality attribute that must be demonstrated through analytical testing. Here we describe the development and qualification of an identity assay using an automated capillary western system, called Simple Western, implementing a multi-valent system suitability sample (SSS) to determine individual polysaccharide components. The assay was optimized through rigorous analytical development and was successfully qualified for use in the clinical release of the PCV.

Rationale and methods of a randomized controlled trial of immunogenicity, safety and impact on carriage of pneumococcal conjugate and polysaccharide vaccines in infants in Papua New Guinea

BACKGROUND

Children in third-world settings including Papua New Guinea (PNG) experience early onset of carriage with a broad range of pneumococcal serotypes, resulting in a high incidence of severe pneumococcal disease and deaths in the first 2 years of life. Vaccination trials in high endemicity settings are needed to provide evidence and guidance on optimal strategies to protect children in these settings against pneumococcal infections.

METHODS

This report describes the rationale, objectives, methods, study population, follow-up and specimen collection for a vaccination trial conducted in an endemic and logistically challenging setting in PNG. The trial aimed to determine whether currently available pneumococcal conjugate vaccines (PCV) are suitable for use under PNG's accelerated immunization schedule, and that a schedule including pneumococcal polysaccharide vaccine (PPV) in later infancy is safe and immunogenic in this high-risk population.

RESULTS

This open randomized-controlled trial was conducted between November 2011 and March 2016, enrolling 262 children aged 1 month between November 2011 and April 2014. The participants were randomly allocated (1:1) to receive 10-valent PCV (10vPCV) or 13-valent PCV (13vPCV) in a 1-2-3-month schedule, with further randomization to receive PPV or no PPV at age 9 months, followed by a 1/5th PPV challenge at age 23 months. A total of 1229 blood samples were collected to measure humoral and cellular immune responses and 1238 nasopharyngeal swabs to assess upper respiratory tract colonization and carriage load. Serious adverse events were monitored throughout the study. Of the 262 children enrolled, 87% received 3 doses of PCV, 79% were randomized to receive PPV or no PPV at age 9 months, and 67% completed the study at 24 months of age with appropriate immunization and challenge.

CONCLUSION

Laboratory testing of the many samples collected during this trial will determine the impact of the different vaccine schedules and formulations on nasopharyngeal carriage, antibody production and function, and immune memory. The final data will inform policy on pneumococcal vaccine schedules in countries with children at high risk of pneumococcal disease by providing direct comparison of an accelerated schedule of 10vPCV and 13vPCV and the potential advantages of PPV following PCV immunization.

TRIAL REGISTRATION

ClinicalTrials.gov CTN NCT01619462, retrospectively registered on May 28, 2012.

Inactivated pep27 mutant as an effective mucosal vaccine against a secondary lethal pneumococcal challenge in mice

Purpose

A pep27 mutant may be able to elicit mucosal immunity against pneumococcal diseases, and could be employed as an inexpensive attenuated vaccine. However, this particular mutant contains an erythromycin-resistance marker. The purpose of the current study is to develop a markerless pep27 mutant and assess whether this inactivated mutant is able to induce mucosal immunity.

Materials and Methods

Mice were vaccinated intranasally with the inactivated markerless pep27 mutant every 2 weeks for a total of three times, after which time serum samples were analyzed for antibody titers. The mice were then challenged with a lethal D39 strain and their survival time was measured. The cross-reactivity of the antisera against pep27 was also compared to other mutant serotypes.

Results

Intranasal immunization of mice with the inactivated markerless pep27 mutant provides effective protection and rapidly cleared bacterial colonization in vivo. Moreover, antisera raised against the pep27 mutant may cross-react with several other serotype strains.

Conclusion

Intranasal immunization with the inactivated pep27 mutant may be able to provide mucosal immunity, and could represent an efficient mucosal vaccine.

The wciN gene encodes an α-1,3-galactosyltransferase involved in the biosynthesis of the capsule repeating unit of Streptococcus pneumoniae serotype 6B

Almost all Streptococcus pneumoniae (pneumococcus) capsule serotypes employ the Wzy-dependent pathway for their capsular polysaccharide (CPS) biosynthesis. The assembly of the CPS repeating unit (RU) is the first committed step in this pathway. The wciN gene was predicted to encode a galactosyltransferase involved in the RU assembly of pneumococcus type 6B CPS. Herein, we provide the unambiguous in vitro biochemical evidence that wciN encodes an α-1,3-galactosyltransferase catalyzing the transfer of galactosyl from UDP-Gal onto the Glcα-pyrophosphate-lipid (Glcα-PP-lipid) acceptor to form Galα(1-3)Glcα-PP-lipid. A chemically synthesized acceptor (Glcα-PP-O(CH(2))(10)CH(3)) was used to characterize the WciN activity. The disaccharide product, i.e., Galα(1-3)Glcα-PP-O(CH(2))(10)CH(3), was characterized by mass and NMR spectroscopy. Substrate specificity study indicated that the acceptor structural region composed of pyrophosphate and lipid moieties may play an important role in the enzyme-acceptor recognition. Furthermore, divalent metal cations were found indispensable to the WciN activity, suggesting that this glycosyltransferase (GT) belongs to the GT-A superfamily. By analyzing the activities of six WciN mutants, a DXD motif involved in the coordination of a divalent metal cation was identified. This work provides a chemical biology approach to characterize the activities of pneumococcal CPS GTs in vitro and will help to better understand the pneumococcal CPS biosynthetic pathway.

The yin yang of bacterial polysaccharides: lessons learned from B. fragilis PSA

Over the past several years, there have been remarkable advances in our understanding of how commensal organisms shape host immunity. Although the full cast of immunogenic bacteria and their immunomodulatory molecules remains to be elucidated, lessons learned from the interactions between bacterial zwitterionic polysaccharides (ZPSs) and the host immune system represent an integral step toward better understanding how the intestinal microbiota effect immunologic changes. Somewhat paradoxically, ZPSs, which are found in numerous commensal organisms, are able to elicit both proinflammatory and immunoregulatory responses; both these outcomes involve fine-tuning the balance between T-helper 17 cells and interleukin-10-producing regulatory T cells. In this review, we discuss the immunomodulatory effects of the archetypal ZPS, Bacteroides fragilis PSA. In addition, we highlight some of the opportunities and challenges in applying these lessons in clinical settings.

Protection against Streptococcus pneumoniae serotype 1 acute infection shows a signature of Th17- and IFN-γ-mediated immunity

Acute pneumonia caused by Streptococcus pneumoniae is a major cause of child mortality. Antibodies are considered the main effectors of protection in this clinical presentation of pneumococcal invasive disease. To get new insights into the mechanisms involved in the protective immunity, we established a murine experimental model of protection against acute pneumococcal pneumonia and then evaluated the transcriptional, humoral and cellular responses in protected and non-protected animals. We found that intranasal inoculation of a sublethal dose of S. pneumoniae serotype 1 conferred complete protection against a subsequent challenge with a lethal dose of the same strain. Sublethal infection elicited a strong IgM and IgG antibody response against the capsular polysaccharide, as assessed one week later, and an exacerbated influx of neutrophils into the lungs immediately after the lethal challenge. Genome-wide microarray-based transcriptional analysis of whole lungs showed 149 differentially expressed genes among which we found upregulation of Il17a, Ifng and several IL-17A- and IFN-γ-related genes in protected versus non-protected mice. Kinetics analysis showed higher expression levels of Il17a in protected animals at all time points whereas Ifng was upregulated early in the protected mice and later in the non-protected animals. Intracelluar cytokine staining demonstrated that CD4(+) T cells account for a great proportion of the IL-17A produced in the lungs of protected animals. Overall, these results showed that an upregulation of IL-17A- and a timely regulation of IFN-γ-related gene expression, together with development of a Th17 response, are relevant characteristics of the protective immunity against S. pneumoniae acute pneumonia.

Immunogenicity, safety, and reactogenicity of the 10-valent pneumococcal nontypeable Haemophilus influenzae protein D conjugate vaccine and DTPa-IPV-Hib when coadministered as a 3-dose primary vaccination schedule in The Netherlands: a randomized controlled trial

BACKGROUND

Recent reviews have highlighted the unpredictability of immunologic interference when multivalent conjugated vaccines are coadministered with other pediatric vaccines.

OBJECTIVE

To evaluate immunogenicity, safety, and reactogenicity of the 10-valent pneumococcal nontypeable Haemophilus influenzae protein D conjugate vaccine (PHiD-CV; Synflorix, GlaxoSmithKline Biologicals) and DTPa-IPV-Hib (Pediacel, Sanofi Pasteur MSD) when coadministered as a 3-dose primary vaccination course.

MATERIAL AND METHODS

In a single-blind, single-center, randomized controlled trial in the Netherlands, healthy infants (n = 780) were randomly assigned (1:1:1) to receive either (1) PHiD-CV + DTPa-HBV-IPV/Hib (Infanrix Hexa, GlaxoSmithKline Biologicals), (2) PHiD-CV + DTPa-IPV-Hib, or (3) 7-valent pneumococcal conjugate vaccine (Prevenar/Prevnar, Pfizer Inc.) + DTPa-IPV-Hib at 2, 3, and 4 months of age. Blood samples were collected 1 month after dose 3. Diary cards were used to record safety and reactogenicity.

RESULTS

Antibody concentrations elicited by PHiD-CV coadministered with DTPa-IPV-Hib were noninferior to those following DTPa-HBV-IPV/Hib coadministration for 9 of 10 vaccines pneumococcal serotypes and protein D. For serotype 18C (conjugated to tetanus toxoid), the antibody concentration was higher with DTPa-HBV-IPV/Hib coadministration (1.73 vs. 1.07 μg/mL). The percentages of infants with antibody concentrations ≥0.2 μg/mL (68.9%-100% in the PHiD-CV + DTPa-HBV-IPV/Hib group vs. 64.9%-100% in the PHiD-CV + DTPa-IPV-Hib group) and with measurable opsonophagocytic activity (56.1%-100% in the PHiD-CV + DTPa-HBV-IPV/Hib group vs. 61.1%-100% in the PHiD-CV + DTPa-IPV-Hib group) were comparable for all serotypes in both PHiD-CV groups. Group differences in antibody responses to the DTPa-IPV-Hib antigens remained within the predefined limit for noninferiority. Safety and reactogenicity profiles were comparable across groups.

CONCLUSIONS

: PHiD-CV and DTPa-IPV-Hib were immunogenic and well tolerated when coadministered as a 3-dose primary vaccination course.

Immunogenicity of a 2-dose priming and booster vaccination with the 10-valent pneumococcal nontypeable Haemophilus influenzae protein D conjugate vaccine

BACKGROUND

The immunogenicity of the 10-valent pneumococcal nontypeable Haemophilus influenzae protein D-conjugate vaccine (PHiD-CV) was determined following a simplified 2-dose priming and the more commonly employed 3-dose priming both followed by a booster dose.

METHODS

A total of 351 healthy subjects were primed with PHiD-CV at either 3 and 5 or 3, 4 and 5 months of age followed in all subjects by a booster dose at 11 to 12 months of age. Serotype-specific pneumococcal responses were measured by 22F-inhibition ELISA and opsonophagocytic assays 1 month following primary and booster vaccinations.

RESULTS

Depending on the serotype, the percentages of subjects reaching the ELISA antibody threshold of 0.2 microg/mL were 92.8% to 98.0% following 2 primary doses and 96.1% to 100% following 3 primary doses except for serotype 6B (55.7% and 63.1%, respectively) and serotype 23F (69.3% and 77.6%, respectively). Opsonophagocytic activity (OPA) could be measured in 74.4% to 100% and 88.9% to 100% of the subjects after the 2-dose or 3-dose priming, respectively, except for serotype 1 (60.8% and 62.9%, respectively). In both groups, robust increases in ELISA antibodies and OPA titers were observed for all serotypes after the booster dose. Higher postprimary and postbooster ELISA antibody levels and OPA titers were observed for most serotypes following the 3+1 schedule.

CONCLUSION

PHiD-CV was immunogenic in both schedules, but further effectiveness data are needed to fully understand the public health benefit to be expected from these schedules in terms of prevention against invasive and mucosal infections.

The clinical consequences of antimicrobial resistance

The continued evolution of antimicrobial resistance in the hospital and more recently in the community threatens to seriously compromise our ability to treat serious infections. The major success of the seven-valent Streptococcus pneumoniae vaccine at reducing both infection and resistance has been followed by the emergence of previously minor serotypes that express multiresistance. The almost universal activity of cephalosporins and fluoroquinolones against community Escherichia coli strains has been compromised by the spread of CTX-M beta-lactamase-producing, fluoroquinolone-resistant strains, and the emergence of community-onset methicillin-resistant Staphylococcus aureus, particularly in the United States, has forced us to re-think our empirical treatment guidelines for skin and soft-tissue infections. Finally, our most potent and reliable class of antibiotics, the carbapenems, is compromised by the growth, primarily in intensive care units, of multiresistant Klebsiella pneumoniae, Acinetobacter baumanni, and Pseudomonas aeruginosa. The lack of a robust pipeline of new agents, particularly against resistant Gram-negative bacteria, emphasizes the importance of optimizing our use of current antimicrobials and promoting strict adherence to established infection control practices.

Immunogenicity of the 10-valent pneumococcal non-typeable Haemophilus influenzae protein D conjugate vaccine (PHiD-CV) compared to the licensed 7vCRM vaccine

BACKGROUND

The immunogenicity of the 10-valent pneumococcal nontypeable Haemophilus influenzae protein D-conjugate vaccine (PHiD-CV) was assessed and compared with the 7-valent pneumococcal conjugate vaccine (7vCRM).

METHODS

Healthy subjects (1650) were randomized to be vaccinated with 3 doses of PHiD-CV or 7vCRM (Prevenar/Prevnar) at 2-3-4 months of age and a fourth booster dose at 12-18 months. Serotype-specific pneumococcal responses (GlaxoSmithKline's ELISA with 22F-inhibition) and opsonophagocytic activity (OPA) were measured 1 month after primary and booster vaccinations.

RESULTS

The primary objective to demonstrate noninferiority of PHiD-CV versus 7vCRM (in terms of percentage of subjects with antibody concentration >or=0.2 microg/mL) for at least 7 of the 10 vaccine serotypes was reached as noninferiority was demonstrated for 8 serotypes. Although, noninferiority could not be demonstrated for ELISA responses against serotypes 6B and 23F, a post-hoc analysis of the percentage of subjects with OPA titers >or=8 suggested noninferiority for the 7 serotypes common to both vaccines including 6B and 23F.Priming of the immune system against all vaccine serotypes was confirmed by robust increases in ELISA antibody levels ( approximately 6.0-17 fold) and OPA titers ( approximately 8-93 fold) after a fourth consecutive dose of PHiD-CV.

CONCLUSIONS

PHiD-CV induces ELISA and functional OPA antibodies for all vaccine serotypes after primary vaccination and is noninferior to 7vCRM in terms of ELISA and/or OPA threshold responses. Effective priming is further indicated by robust booster responses.

ELISA IgG concentrations and opsonophagocytic activity following pneumococcal protein D conjugate vaccination and relationship to efficacy against acute otitis media

We explored the relationship between efficacy against acute otitis media (AOM) and both ELISA anti-polysaccharide IgG geometric mean concentrations (GMCs) and opsonophagocytic (OPA) geometric mean titres (GMTs) following primary and booster vaccination with pneumococcal protein D (Haemophilus influenzae-derived) conjugate vaccine. It was possible to distinguish between the OPA GMTs of low and high efficacy serotypes, however no such distinction was evident for ELISA GMCs. Also, there was a trend towards lower ELISA and OPA serotype-specific responses in subjects who developed AOM compared to controls. We conclude that serotype-specific OPA GMTs are an important endpoint to consider for evaluation of pneumococcal conjugate vaccines with respect to the protective efficacy against AOM (Study ID: 347414/NCT00119743).

Non-response to specific serotypes likely cause for failure to 23-valent pneumococcal polysaccharide vaccine in the elderly

During a randomised controlled trial with the 23-valent pneumococcal vaccine in older persons, antibody concentrations and opsonophagocytic activity (OPA) were compared between eight patients who developed culture-verified pneumococcal pneumonia and 38 controls, matched for age, sex and vaccination status. Patients who developed pneumococcal pneumonia did not respond with a significant increase of antibody concentration (>1microg/ml) post-vaccination to the infecting serotype, but responded equally well as controls to most other serotypes. Neither was there any significant difference in the OPA post-vaccination between patients and controls. In conclusion, the 23-valent pneumococcal vaccine should be regarded as 23 different vaccines, rather than one. Older persons who fail to respond to one serotype may well be protected against infection by the other 22 serotypes.

Immunization of aged mice with a pneumococcal conjugate vaccine combined with an unmethylated CpG-containing oligodeoxynucleotide restores defective immunoglobulin G antipolysaccharide responses and specific CD4+-T-cell priming to young adult levels

Polysaccharide (PS)-protein conjugate vaccines, in contrast to purified PS vaccines, recruit CD4+-T-cell help and restore defective PS-specific humoral immunity in the immature host. Surprisingly, in the immunocompromised, aged host, anti-PS responses to conjugate vaccines are typically no better than those elicited by purified PS vaccines. Although aging leads to defects in multiple immune cell types, diminished CD4+-T-cell helper function has recently been shown to play a dominant role. We show that in response to immunization with purified pneumococcal capsular PS serotype 14 (PPS14) in saline, the T-cell-independent immunoglobulin G (IgG) anti-PPS14 response in aged mice was comparable to that in young mice. In contrast, the T-cell-dependent IgG anti-PPS14 response to a soluble conjugate of PPS14 and pneumococcal surface protein A (PspA) (PPS14-PspA) in saline was markedly defective. This was associated with defective priming of PspA-specific CD4+ T cells. In contrast, immunization of aged mice with PPS14-PspA combined with an unmethylated CpG-containing oligodeoxynucleotide (CpG-ODN) restored IgG anti-PPS14 responses to young adult levels, which were substantially higher than those observed using purified PPS14. This was associated with enhanced PspA-specific CD4+-T-cell priming. Similarly, intact Streptococcus pneumoniae capsular type 14, which contains Toll-like receptor (TLR) ligands, also induced substantial, though modestly reduced, T-cell-dependent (TD) IgG ant-PPS14 responses in aged mice. Spleen and peritoneal cells from aged and young adult mice made comparable levels of proinflammatory cytokines in response to CpG-ODN, although cells from aged mice secreted higher levels of interleukin-10. Collectively, these data suggest that inclusion of a TLR ligand, as an adjuvant, with a conjugate vaccine can correct defective TD IgG anti-PS responses in elderly patients by augmenting CD4+-T-cell help.

Streptococcus pneumoniae enolase is important for plasminogen binding despite low abundance of enolase protein on the bacterial cell surface

Enolase represents one of the anchorless surface proteins of Streptococcus pneumoniae and has previously been identified as a plasminogen-binding protein, endowing this pathogen with host proteolytic activity. In this study the mAb 245,C-6 (IgG1) was produced in a BALB/c mouse after immunizing with a protein fraction from S. pneumoniae. The mAb reacted with recombinant pneumococcal enolase both under non-denaturing and denaturing conditions. The epitope for the mAb was mapped to residues 55DKSRYGGLG63 of pneumococcal enolase using a peptide array. By applying the previously reported structure of enolase, this epitope was localized in a surface-exposed loop in each of the monomers of the octameric enolase. Previous immunoelectron microscopic studies, using polyclonal rabbit antibodies against enolase, depicted enolase on the cell surface but did not quantify the amount of surface-exposed enolase on viable pneumococci. Here, flow cytometry revealed no binding of mAb 245,C-6 to viable pneumococci, including TIGR4 and its non-encapsulated isogenic mutant, and only a minor increase of fluorescence intensity was measured when the polyclonal anti-enolase antibodies were used. In contrast, control antibodies recognizing the choline-binding proteins (CBPs) PspA and PspC showed high reactivities. The non-encapsulated TIGR4 did not show increased levels of antibody binding for mAb 245,C-6 or polyclonal anti-enolase antibodies, but revealed increased binding of polyclonal antibodies reacting with PspA or PspC. These results suggest that, compared to other surface-exposed proteins such as CBPs, the amount of enolase under the selected conditions is low. Flow cytometry, however, with FITC-labelled plasminogen demonstrated that the amount of surface-exposed enolase is important for plasminogen binding and, therefore, is also important for pneumococcal pathogenesis.

Serotype distribution and antibiotic susceptibility of invasive and nasopharyngeal isolates of Streptococcus pneumoniae among children in rural Mozambique

OBJECTIVE

To describe and compare serotype distribution and antibiotic susceptibility of invasive and nasopharyngeal isolates of Streptococcus pneumoniae from children in rural Mozambique.

METHODS

From August 2002 to July 2003, we prospectively obtained invasive pneumococcal isolates from children <15 years of age admitted to the paediatric ward of Manhiça District Hospital. During a cross-sectional study of children <5 years of age with mild illnesses, attending the outpatient department of the hospital in March and April 2003, we collected nasopharyngeal isolates. Serotypes and antibiotic susceptibilities were determined using standardized methods.

RESULTS

The two most common pneumococcal serotypes among invasive isolates were types 1 (40% of 88 isolates serotyped) and 5 (10%), but these types were rare among nasopharyngeal isolates. Compared with invasive isolates, nasopharyngeal isolates were more likely to be serotypes in the licensed seven-valent conjugate vaccine (49%vs. 20%, P < 0.01), to have intermediate-level penicillin resistance (52%vs. 14%, P < 0.01) and to be non-susceptible to trimethoprim-sulfamethoxazole (61%vs. 45%, P < 0.01). Recent receipt of antibiotics or sulfadoxine/pyrimethamine were associated with carriage of antibiotic non-susceptible isolates.

CONCLUSIONS

These data indicate that a pneumococcal conjugate vaccine containing serotypes 1 and 5 could substantially reduce pneumococcal invasive disease among young children in rural Mozambique. Carriage surveys can overestimate potential coverage of the seven-valent pneumococcal conjugate vaccine in settings where serotypes 1 and 5 predominate.

Prior pneumococcal vaccination is associated with reduced death, complications, and length of stay among hospitalized adults with community-acquired pneumonia

BACKGROUND

Vaccination with pneumococcal polysaccharide reduces the incidence of bacteremic pneumococcal disease in adults. We investigated the impact of prior pneumococcal vaccination on in-hospital mortality and the probability of respiratory failure among hospitalized adults with community-acquired pneumonia.

METHODS

Consecutive individuals hospitalized with community-acquired pneumonia (diagnosed by International Classification of Diseases, Ninth Revision, Clinical Modification codes 480.0-487.0) at 109 community and teaching hospitals in the United States were identified using the Quality and Resource Management System, a database constructed by Tenet HealthCare to improve the quality of patient care. Vaccination status, comorbidities, and outcomes were abstracted by case managers concurrently with patient care. Associations between vaccination, survival, and respiratory failure were defined using multivariable logistic regression models.

RESULTS

Of 62,918 adults hospitalized with community-acquired pneumonia between 1999 and 2003, 7390 (12%) had a record of prior pneumococcal vaccination. Vaccine recipients were less likely to die of any cause during hospitalization than were individuals with no record of vaccination (adjusted odds ratio [OR], 0.50; 95% confidence interval [CI], 0.43-0.59), even after adjustment for the presence of comorbid illnesses, age, smoking, and influenza vaccination and under varying assumptions about missing vaccination data. Vaccination also lowered the risk of respiratory failure (adjusted OR, 0.67; 95% CI, 0.59-0.76) and other complications and reduced median length of stay by 2 days, compared with nonvaccination (P<.001).

CONCLUSIONS

Prior vaccination against pneumococcus is associated with improved survival, decreased chance of respiratory failure or other complications, and decreased length of stay among hospitalized patients with community-acquired pneumonia. These observations reinforce current efforts to improve compliance with existing pneumococcal vaccination recommendations for adults.

Genetic analysis of the capsular biosynthetic locus from all 90 pneumococcal serotypes

Several major invasive bacterial pathogens are encapsulated. Expression of a polysaccharide capsule is essential for survival in the blood, and thus for virulence, but also is a target for host antibodies and the basis for effective vaccines. Encapsulated species typically exhibit antigenic variation and express one of a number of immunochemically distinct capsular polysaccharides that define serotypes. We provide the sequences of the capsular biosynthetic genes of all 90 serotypes of Streptococcus pneumoniae and relate these to the known polysaccharide structures and patterns of immunological reactivity of typing sera, thereby providing the most complete understanding of the genetics and origins of bacterial polysaccharide diversity, laying the foundations for molecular serotyping. This is the first time, to our knowledge, that a complete repertoire of capsular biosynthetic genes has been available, enabling a holistic analysis of a bacterial polysaccharide biosynthesis system. Remarkably, the total size of alternative coding DNA at this one locus exceeds 1.8 Mbp, almost equivalent to the entire S. pneumoniae chromosomal complement.

Combined conjugate vaccines: enhanced immunogenicity with the N19 polyepitope as a carrier protein

The N19 polyepitope, consisting of a sequential string of universal human CD4(+)-T-cell epitopes, was tested as a carrier protein in a formulation of combined glycoconjugate vaccines containing the capsular polysaccharides (PSs) of Neisseria meningitidis serogroups A, C, W-135, and Y. Good antibody responses to all four polysaccharides were induced by one single immunization of mice with N19-based conjugates. Two immunizations with N19 conjugates elicited anti-MenACWY antibody titers comparable to those induced after three doses of glycoconjugates containing CRM197 as carrier protein. Compared to cross-reacting material (CRM)-based constructs, lower amounts of N19-MenACWY conjugates still induced high bactericidal titers to all four PSs. Moreover, N19-MenACWY-conjugated constructs induced faster and higher antibody avidity maturation against meningococcal C PS than CRM-based conjugates. Very importantly, N19-specific antibodies did not cross-react with the parent protein from which N19 epitopes were derived, e.g., tetanus toxoid and influenza virus hemagglutinin. Finally, T helper epitopes of the N19 carrier protein were effectively generated both in vivo (after immunization with the N19 itself) and in vitro (after restimulation of epitope-specific spleen cells). Taken together, these data show that the N19 polyepitope represents a strong and valid option for the generation of improved or new combined glycoconjugate vaccines.

Pneumococcal vaccination in adults

Pneumococci remain the most common etiology of community-acquired pneumonia in adults, with significant attendant mortality in the elderly. With the recognition of increasing rates of drug-resistant Streptococcus pneumoniae in recent years, efforts to prevent disease through vaccination have gained greater impetus. The 23-valent pneumococcal vaccine is used widely in the United States and provides effective protection against bacteremic pneumococcal disease, particularly in the immunocompetent host. The 7-valent pneumococcal conjugate vaccine, licensed in the United States in 2000, has had a dramatic impact on pneumococcal disease in the pediatric population, and its use in children has had effects on incidence rates in nonimmunized adults as well. Future directions include efforts to improve vaccination coverage in targeted populations and the development of more immunogenic and efficacious vaccines for high-risk groups.

Vaccines against bacterial meningitis

Meningitis remains an important cause of morbidity and mortality among children >5 years of age and is especially prevalent in developing countries. Effective routine immunization against Hib, pneumococcus and serogroupC meningococcus has had a significant impact on both invasive disease and carriage caused by these encapsulated bacteria. The major challenge in prevention of meningitis remains the delivery of vaccines worldwide, especially to resource-poor regions with the greatest disease burden.