Infant immunization with pneumococcal CRM197 vaccines: effect of saccharide size on immunogenicity and interactions with simultaneously administered vaccines

Exploring the variables influencing the immune response of traditional and innovative glycoconjugate vaccines

Vaccines are cost-effective tools for reducing morbidity and mortality caused by infectious diseases. The rapid evolution of pneumococcal conjugate vaccines, the introduction of tetravalent meningococcal conjugate vaccines, mass vaccination campaigns in Africa with a meningococcal A conjugate vaccine, and the recent licensure and introduction of glycoconjugates against S. Typhi underlie the continued importance of research on glycoconjugate vaccines. More innovative ways to produce carbohydrate-based vaccines have been developed over the years, including bioconjugation, Outer Membrane Vesicles (OMV) and the Multiple antigen-presenting system (MAPS). Several variables in the design of these vaccines can affect the induced immune responses. We review immunogenicity studies comparing conjugate vaccines that differ in design variables, such as saccharide chain length and conjugation chemistry, as well as carrier protein and saccharide to protein ratio. We evaluate how a better understanding of the effects of these different parameters is key to designing improved glycoconjugate vaccines.

Impact and Control of Sugar Size in Glycoconjugate Vaccines

Glycoconjugate vaccines have contributed enormously to reducing and controlling encapsulated bacterial infections for over thirty years. Glycoconjugate vaccines are based on a carbohydrate antigen that is covalently linked to a carrier protein; this is necessary to cause T cell responses for optimal immunogenicity, and to protect young children. Many interdependent parameters affect the immunogenicity of glycoconjugate vaccines, including the size of the saccharide antigen. Here, we examine and discuss the impact of glycan chain length on the efficacy of glycoconjugate vaccines and report the methods employed to size polysaccharide antigens, while highlighting the underlying reaction mechanisms. A better understanding of the impact of key parameters on the immunogenicity of glycoconjugates is critical to developing a new generation of highly effective vaccines.

Cross reacting material (CRM197) as a carrier protein for carbohydrate conjugate vaccines targeted at bacterial and fungal pathogens

This paper gives an overview of conjugate glycovaccines which contain recombinant diphtheria toxoid CRM197 as a carrier protein. A special focus is given to synthetic methods used for preparation of neoglycoconjugates of CRM197 with oligosaccharide epitopes of cell surface carbohydrates of pathogenic bacteria and fungi. Syntheses of commercial vaccines and laboratory specimen on the basis of CRM197 are outlined briefly.

Combined effects of glycan chain length and linkage type on the immunogenicity of glycoconjugate vaccines

The development and use of antibacterial glycoconjugate vaccines have significantly reduced the occurrence of potentially fatal childhood and adult diseases such as bacteremia, bacterial meningitis, and pneumonia. In these vaccines, the covalent linkage of bacterial glycans to carrier proteins augments the immunogenicity of saccharide antigens by triggering T cell-dependent B cell responses, leading to high-affinity antibodies and durable protection. Licensed glycoconjugate vaccines either contain long-chain bacterial polysaccharides, medium-sized oligosaccharides, or short synthetic glycans. Here, we discuss factors that affect the glycan chain length in vaccines and review the available literature discussing the impact of glycan chain length on vaccine efficacy. Furthermore, we evaluate the available clinical data on licensed glycoconjugate vaccine preparations with varying chain lengths against two bacterial pathogens, Haemophilus influenzae type b and Neisseria meningitidis group C, regarding a possible correlation of glycan chain length with their efficacy. We find that long-chain glycans cross-linked to carrier proteins and medium-sized oligosaccharides end-linked to carriers both achieve high immunogenicity and efficacy. However, end-linked glycoconjugates that contain long untethered stretches of native glycan chains may induce hyporesponsiveness by T cell-independent activation of B cells, while cross-linked medium-sized oligosaccharides may suffer from suboptimal saccharide epitope accessibility.

Pneumococcal conjugate vaccine dose-ranging studies in humans: A systematic review

BACKGROUND

Streptococcus pneumoniae is one of the most common bacterial pathogens of infants and young children. Antibody responses against the pneumococcal polysaccharide capsule are the basis of vaccine-mediated protection. We examined the relationship between the dose of polysaccharide in pneumococcal conjugate vaccines (PCVs) and immunogenicity.

METHODS

A systematic search of English publications that evaluated the immunogenicity of varying doses of pneumococcal conjugate vaccines was performed in Medline and Embase (Ovid Sp) databases in August 2019. We included only articles that involved administration of pneumococcal conjugate vaccine in humans and assessed the immunogenicity of more than one serotype-specific saccharide dose. Results were synthesised descriptively due to the heterogeneity of product valency, product content and vaccine schedule.

RESULTS

We identified 1691 articles after de-duplication; 9 studies met our inclusion criteria; 2 in adults, 6 in children and 1 in both. Doses of polysaccharide evaluated ranged from 0.44 mcg to 17.6 mcg. In infants, all doses tested elicited IgG geometric mean concentrations (GMCs) above the established correlate of protection (COP; 0.35 mcg/ml). A month after completion of the administered vaccine schedule, 95% confidence intervals of only three out of all the doses evaluated had GMCs that crossed below the COP. In the adult studies, all adults achieved GMCs that would be considered protective in children who have received 3 standard vaccine doses.

CONCLUSION

For some products, the mean antibody concentrations induced against some pneumococcal serotypes increased with increasing doses of the polysaccharide conjugate, but for other serotypes, there were no clear dose-response relationships or the dose response curves were negative. Fractional doses of polysaccharide which contain less than is included in currently distributed formulations may be useful in the development of higher valency vaccines, or dose-sparing delivery for paediatric use.

Immunochemical characteristics of Streptococcus pneumoniae type 3 capsular polysaccharide glycoconjugate constructs correlate with its immunogenicity in mice model

A panel of derivatives were prepared from Streptococcus pneumoniae polysaccharide type 3 (Ps3) modified with adipic acid dihydrazide (ADH). The degree of coupling between Ps3-adh derivatives and diphtheria (DTd) or tetanus (TTd) toxoids was varied by ADH linker loading. A series of Ps3 derivatives and the resultant glycoconjugates (GC) were tested for their immunochemical activity in an ELISA. Antigenic properties of components in GCs were estimated by interaction with serotype-specific and toxin-neutralizing antibodies to confirm the preservation of native protective epitopes both of Ps3 and DTd. After immunization of mice, a correlation was established between immunochemical activity and immunogenicity of these GCs. A correlation model developed for Ps3-DTd conjugates allowed to predict the immunogenicity of similar design Ps3-TTd conjugates based on ELISA testing data. The plausibility of this prediction was confirmed by the test immunization of mice with Ps3-TTds. The proposed immunochemical approach to the assessment and control of native structural and functional antigenic elements in GCs is important for the optimization of vaccine design and is an adequate alternative to extensive physicochemical characterization for assessing immunogenicity.

Higher mass meningococcal group C-tetanus toxoid vaccines conjugated with carbodiimide correlate with greater immunogenicity

To examine the link between meningococcal C (MenC) vaccine size and immunogenic response, a panel of MenC glycoconjugate vaccines were prepared differing in chain length, molar mass and hydrodynamic volume. The preparations consisted of different lengths of MenC polysaccharide (PS) covalently linked to monomeric purified tetanus toxoid (TT) carrier protein using the coupling reagent ethylcarbodiimide hydrochloride (EDC). Size exclusion chromatography with multi-angle light scattering (SEC-MALS) and viscometry analysis confirmed that the panel of MenC-TT conjugates spanned masses of 191,500 to 2,348,000 g/mol, and hydrodynamic radii ranging from 12.1 to 47.9 nm. The two largest conjugates were elliptical in shape, whereas the two smallest conjugates were more spherical. The larger conjugates appeared to fit a model described by multiple TTs with cross-linked PS, typical of lattice-like networks described previously for TT conjugates, while the smaller conjugates were found to fit a monomeric or dimeric TT configuration. The effect of vaccine conjugate size on immune responses was determined using a two-dose murine immunization. The two larger panel vaccine conjugates produced higher anti-MenC IgG1 and IgG2b titres after the second dose. Larger vaccine conjugate size also stimulated greater T-cell proliferative responses in an in vitro recall assay, although cytokines indicative of a T-helper response were not measurable. In conclusion, larger MenC-TT conjugates up to 2,348,000 g/mol produced by EDC chemistry correlate with greater humoral and cellular murine immune responses. These observations suggest that conjugate size can be an important modulator of immune response.

Interplay of Carbohydrate and Carrier in Antibacterial Glycoconjugate Vaccines

Bacterial infections are a serious health concern and are responsible for millions of illnesses and deaths each year in communities around the world. Vaccination is an important public health measure for reducing and eliminating this burden, and regions with comprehensive vaccination programs have achieved significant reductions in infection and mortality. This is often accomplished by immunization with bacteria-derived carbohydrates, typically in conjunction with other biomolecules, which induce immunological memory and durable protection against bacterial human pathogens. For many species, however, vaccines are currently unavailable or have suboptimal efficacy characterized by short-lived memory and incomplete protection, especially among at-risk populations. To address this challenge, new tools and techniques have emerged for engineering carbohydrates and conjugating them to carrier molecules in a tractable and scalable manner. Collectively, these approaches are yielding carbohydrate-based vaccine designs with increased immunogenicity and protective efficacy, thereby opening up new opportunities for this important class of antigens. In this chapter we detail the current understanding of how carbohydrates interact with the immune system to provide immunity; how glycoengineering, especially in the context of glycoconjugate vaccines, can be used to modify and enhance immune responses; and current trends and strategies being pursued for the rational design of next-generation glycosylated antibacterial vaccines. Graphical Abstract.

Pneumococcal 7-Valent Conjugate Vaccine

Each month, subscribers to The Formulary® Monograph Service receive five to six researched monographs on drugs that are newly released or are in late Phase III trials. The monographs are targeted to your Pharmacy and Therapeutics Committee. Subscribers also receive monthly one-page summary monographs on the agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation (DUE) is also provided each month. The monographs are published in printed form and on diskettes that allow customization. Subscribers to the The Formulary Monograph Service also receive access to a pharmacy bulletin board called The Formulary Information Exchange (The F.I.X). All topics pertinent to clinical pharmacy are discussed on The F.I.X.

Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. If you would like information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The July 2000 Formulary monographs are linezolid, insulin glargine, rivastigmine, pemirolast, and tacrolimus ointment. The DUE is on linezolid.

Structural correlates of carrier protein recognition in tetanus toxoid-conjugated bacterial polysaccharide vaccines

An analysis of structure-antibody recognition relationships in nine licenced polysaccharide-tetanus toxoid (TT) conjugate vaccines was performed. The panel of conjugates used included vaccine components to protect against disease caused by Haemophilus influenzae type b, Neisseria meningitidis groups A, C, W and Y and Streptococcus pneumoniae serotype 18C. Conformation and structural analysis included size exclusion chromatography with multi-angle light scattering to determine size, and intrinsic fluorescence spectroscopy and fluorescence quenching to evaluate the protein folding and exposure of Trp residues. A capture ELISA measured the recognition of TT epitopes in the conjugates, using four rat monoclonal antibodies: 2 localised to the HC domain, and 2 of which were holotoxoid conformation-dependent. The conjugates had a wide range of average molecular masses ranging from 1.8×10(6) g/mol to larger than 20×10(6) g/mol. The panel of conjugates were found to be well folded, and did not have spectral features typical of aggregated TT. A partial correlation was found between molecular mass and epitope recognition. Recognition of the epitopes either on the HC domain or the whole toxoid was not necessarily hampered by the size of the molecule. Correlation was also found between the accessibility of Trp side chains and polysaccharide loading, suggesting also that a higher level of conjugated PS does not necessarily interfere with toxoid accessibility. There were different levels of carrier protein Trp side-chain and epitope accessibility that were localised to the HC domain; these were related to the saccharide type, despite the conjugates being independently manufactured. These findings extend our understanding of the molecular basis for carrier protein recognition in TT conjugate vaccines.

Pneumococcal conjugate vaccines: emerging clinical information and its implications

Since 2000, when the first pneumococcal conjugate vaccine was introduced into routine use in the USA, it has had a substantial impact on invasive pneumococcal disease both in the immunized and nonimmunized population. It has also been shown to reduce pneumonia and otitis in young children and has reduced antibiotic nonsusceptible pneumococcal infections. In the USA, three primary doses and a booster dose are recommended (a so-called '3 + 1 schedule'). Some countries have or will soon introduce routine immunization with fewer doses, with either two primary doses and a booster dose ('2 + 1 schedule') or no booster dose ('3 + 0 schedule'). Some serotypes produce less antibody in a two-dose compared with a three-dose primary series. The booster dose may also be important in reducing nasopharyngeal carriage, hence absence of a booster dose may reduce indirect protection. It remains to be seen whether these schedule changes will reduce vaccine effectiveness within the population. Important future developments include extending the number of serotypes included in the vaccine and the possible extension of use into adults in whom indirect protection has been useful, but not as extensive as might be possible with direct immunization.

Protein carriers of conjugate vaccines: characteristics, development, and clinical trials

The immunogenicity of polysaccharides as human vaccines was enhanced by coupling to protein carriers. Conjugation transformed the T cell-independent polysaccharide vaccines of the past to T cell-dependent antigenic vaccines that were much more immunogenic and launched a renaissance in vaccinology. This review discusses the conjugate vaccines for prevention of infections caused by Hemophilus influenzae type b, Streptococcus pneumoniae, and Neisseria meningitidis. Specifically, the characteristics of the proteins used in the construction of the vaccines including CRM, tetanus toxoid, diphtheria toxoid, Neisseria meningitidis outer membrane complex, and Hemophilus influenzae protein D are discussed. The studies that established differences among and key features of conjugate vaccines including immunologic memory induction, reduction of nasopharyngeal colonization and herd immunity, and antibody avidity and avidity maturation are presented. Studies of dose, schedule, response to boosters, of single protein carriers with single and multiple polysaccharides, of multiple protein carriers with multiple polysaccharides and conjugate vaccines administered concurrently with other vaccines are discussed along with undesirable consequences of conjugate vaccines. The clear benefits of conjugate vaccines in improving the protective responses of the immature immune systems of young infants and the senescent immune systems of the elderly have been made clear and opened the way to development of additional vaccines using this technology for future vaccine products.

Use and interpretation of diagnostic vaccination in primary immunodeficiency: a working group report of the Basic and Clinical Immunology Interest Section of the American Academy of Allergy, Asthma & Immunology

A major diagnostic intervention in the consideration of many patients suspected to have primary immunodeficiency diseases (PIDDs) is the application and interpretation of vaccination. Specifically, the antibody response to antigenic challenge with vaccines can provide substantive insight into the status of human immune function. There are numerous vaccines that are commonly used in healthy individuals, as well as others that are available for specialized applications. Both can potentially be used to facilitate consideration of PIDD. However, the application of vaccines and interpretation of antibody responses in this context are complex. These rely on consideration of numerous existing specific studies, interpolation of data from healthy populations, current diagnostic guidelines, and expert subspecialist practice. This document represents an attempt of a working group of the American Academy of Allergy, Asthma & Immunology to provide further guidance and synthesis in this use of vaccination for diagnostic purposes in consideration of PIDD, as well as to identify key areas for further research.

Relevance of O-acetyl and phosphoglycerol groups for the antigenicity of Streptococcus pneumoniae serotype 18C capsular polysaccharide

Capsular polysaccharides are important virulence factors of Streptococcus pneumoniae. The polysaccharide has been used as a component of vaccines against pneumococcal diseases either as plain polysaccharide or better conjugated to a protein. The last one is the vaccine of choice to target child protection. The immune responses depend on several polysaccharide physicochemical properties that can be affected during either purification or modification in the case of conjugate vaccines. In serotype 18C, the repeating unit has a complex structure having a branched pentasaccharide with two apparently labile subtituents: glycerol-phosphate and O-acetyl group. The loss of these groups may potentially reduce the ability of the 18C polysaccharide to induce the desired immune response. Therefore, the relationship of both groups with the antigenicity and immunogenicity of 18C capsular polysaccharide is explored. It is shown that glycerol-phosphate must be preserved for conserving adequate antigenicity of the 18C capsular polysaccharide. At the same time, it was proved that O-acetyl groups do not play any role for the antigenicity and immunogenicity.

Determination of the glycation sites of Bacillus anthracis neoglycoconjugate vaccine by MALDI-TOF/TOF-CID-MS/MS and LC-ESI-QqTOF-tandem mass spectrometry

We present herein an efficient mass spectrometric method for the localization of the glycation sites of a model neoglycoconjugate vaccine formed by a construct of the tetrasaccharide side chain of the Bacillus anthracis exosporium and the protein carrier bovine serum albumin. The glycoconjugate was digested with both trypsin and GluC V8 endoproteinases, and the digests were then analyzed by MALDI-TOF/TOF-CID-MS/MS and nano-LC-ESI-QqTOF-CID-MS/MS. The sequences of the unknown peptides analyzed by MALDI-TOF/TOF-CID-MS/MS, following digestion with the GluC V8 endoproteinase, allowed us to recognize three glycopeptides whose glycation occupancies were, respectively, on Lys 235, Lys 420, and Lys 498. Similarly, the same analysis was performed on the tryptic digests, which permitted us to recognize two glycation sites on Lys 100 and Lys 374. In addition, we have also used LC-ESI-QqTOF-CID-MS/MS analysis for the identification of the tryptic digests. However, this analysis identified a higher number of glycopeptides than would be expected from a glycoconjugate composed of a carbohydrate-protein ratio of 5.4:1, which would have resulted in glycation occupancies of 18 specific sites. This discrepancy was due to the large number of glycoforms formed during the synthetic carbohydrate-spacer-carrier protein conjugation. Likewise, the LC-ESI-QqTOF-MS/MS analysis of the GluC V8 digest also identified 17 different glycation sites on the synthetic glycoconjugate.

Immunogenicity of a combination vaccine containing diphtheria toxoid, tetanus toxoid, three-component acellular pertussis, hepatitis B, inactivated polio virus, and Haemophilus influenzae type b when given concomitantly with 13-valent pneumococcal conjugate vaccine

Two randomized trials of 13-valent pneumococcal conjugate vaccine (PCV13) relative to PCV7 evaluated the immune responses of coadministered antigens comprising Infanrix(®) hexa/Infanrix(®)-IPV+Hib (diphtheria, tetanus, 3-component acellular pertussis, hepatitis B, inactivated poliovirus, and Haemophilus influenzae type b). After the 3-dose infant series, immunogenic noninferiority was demonstrated for all concomitantly administered antigens between the PCV13 and PCV7 groups. All antigens elicited good booster responses after the toddler dose except pertussis toxoid; however, 99.6% subjects achieved pertussis toxoid protective antibody level ≥5EU/mL in both groups. These results support the concomitant administration of PCV13 and Infanrix hexa/Infanrix-IPV+Hib as part of routine immunization schedules.

Evaluation of the immunogenicity and biological activity of the Citrobacter freundii Vi-CRM197 conjugate as a vaccine for Salmonella enterica serovar Typhi

Typhoid fever remains a major health problem in developing countries. Young children are at high risk, and a vaccine effective for this age group is urgently needed. Purified capsular polysaccharide from Salmonella enterica serovar Typhi (Vi) is licensed as a vaccine, providing 50 to 70% protection in individuals older than 5 years. However, this vaccine is ineffective in infants. Vi conjugated to a carrier protein (i.e., an exoprotein A mutant from Pseudomonas aeruginosa [rEPA]) is highly immunogenic, provides long-term protection, and shows more than 90% protective efficacy in children 2 to 5 years old. Here, we describe an alternative glycoconjugate vaccine for S. Typhi, Vi-CRM(197), where Vi was obtained from Citrobacter freundii WR7011 and CRM(197), the mutant diphtheria toxin protein, was used as the carrier. We investigated the optimization of growth conditions for Vi production from C. freundii WR7011 and the immunogenicity of Vi-CRM(197) conjugates in mice. The optimal saccharide/protein ratio of the glycoconjugates was identified for the best antibody production. We also demonstrated the ability of this new vaccine to protect mice against challenge with Vi-positive Salmonella enterica serovar Typhimurium.

Immunogenicity of alternative regimens of the conjugated 7-valent pneumococcal vaccine: a randomized controlled trial

BACKGROUND

The 7-valent CRM197 pneumococcal conjugated vaccine (PCV7) was originally licensed using 3 primary doses during infancy and a booster in the second year of life. We compared the originally licensed regimen to 2 widely used alternative regimens.

METHODS

Five hundred forty-three infants were randomized to receive PCV7 at 2, 4, 6, and 12 months (3 + 1), at 4, 6, and 12 months (2 + 1), or at 2, 4, and 6 months (3 + 0). Blood was drawn at 2, 7, 13, and 19 months. Serotype-specific IgG concentrations were determined by ELISA.

RESULTS

In the 2 + 1 group, postprimary IgG concentrations against serotypes 6B, 14, 18C, and 23F were reduced compared with the 3 + 1 or 3 + 0 groups. Both 3 + 1 and 2 + 1 groups showed marked booster response, but the 2 + 1 group had reduced concentrations against serotypes 6B, 18C, 23F. At 19 months, IgG antibodies decreased in both 3 + 1 and 2 + 1 groups but the 2 + 1 group had significantly lower concentrations against serotypes 6B, 18C, and 23F. IgG concentrations decreased in the 3 + 0 group during the second year and were significantly lower than those of 3 + 1 and 2 + 1 for all serotypes at 13 and 19 months.

CONCLUSIONS

Significant differences in immunogenicity were documented between the reduced and the licensed regimens. The clinical implications of these differences require further studies.

Immunology of combining CRM(197) conjugates for Streptococcus pneumoniae, Neisseria meningitis and Haemophilus influenzae in Chilean infants

We evaluated the immunogenicity and safety of an investigational combination of 9-valent pneumococcal conjugate vaccine (PCV9) and meningococcal group C conjugate (MnCC) vaccine (PCV9-MnCC) administered concomitantly with Haemophilus influenzae type b (Hib) conjugate vaccine, and of a combination of the three vaccines mixed together as a single injection (Hib-PCV9-MnCC), and compared them to separately administered PCV9 and MnCC dispensed to Chilean infants at 2, 4, and 6 months of age. The frequency of adverse events was similar among groups. Recipients of PCV9 alone or in combination with the other vaccines mounted significant antibody responses to the nine pneumococcal serotypes in PCV9, with >88% achieving protective levels of > or =0.35microg/mL. For serotypes 6B, 9V, and 5, recipients of PCV9 alone had significantly higher geometric mean concentrations (GMCs) than those of the other vaccine groups. Similarly, the GMC of anti-PRP antibodies was significantly lower among recipients of Hib-PCV9-MnCC than among those who received Hib vaccine separately from PCV9 or MnCC. In Chilean infants, PCV9, PCV9-MnCC, and Hib-PCV9-MnCC were highly immunogenic and safe. Overall, interactions of PCV9, MnCC and Hib affected the magnitude (GMC) of the primary antibody responses to some of the antigens, but not the percentage of subjects who achieved protective antibody thresholds.

Immunogenicity, reactogenicity, and safety of a seven-valent pneumococcal conjugate vaccine (PCV7) concurrently administered with a fully liquid DTPa-IPV-HBV-Hib combination vaccine in healthy infants

AIM OF THE STUDY

To evaluate the immunogenicity, safety and reactogenicity of a seven-valent pneumococcal conjugate vaccine (PCV7) when given concomitantly with a fully liquid DTaP-IPV-HBV-Hib combination vaccine.

METHODS

Two hundred and sixty-six healthy infants in France (n=136) and Germany (n=130) were randomized to receive DTaP-IPV-HBV-Hib and PCV7 (test group) at the age of 2, 3 and 4 months (primary series) and 12-15 months (booster dose), or to receive DTaP-IPV-HBV-Hib at the same time points but PCV7 at the ages of 5, 6, 7 and 13-16 months (control group). Antibody levels to all vaccine antigens were measured before dose 1, 1 month after dose 3, at the time of booster, and 1 month later. Safety data were collected after each vaccine dose.

RESULTS

Two hundred and fifty-seven infants (test group, 131; control group, 126) completed the primary immunization series and two hundred and forty-five received the booster dose (test group, 125; control group, 120). Depending on the serotype, 92.8-100% of subjects in the test group achieved antibody levels >or=0.15 microg/mL for PCV7 antigens at 5 months of age, and 89.7-99.1% of them antibody levels >or=0.50 microg/mL 1 month after booster. For DTaP-IPV-HBV-Hib, there was no statistically significant difference between the two groups in the proportion of infants that achieved pre-defined seroprotective levels for each antigen at 5 months and 1 month after booster. Frequency of local and systemic reactions was similar in both groups except for fever above 38.0 degrees C, which was more frequent in the test group after dose 1, 2 or 4. Fever >39.0 degrees C was only reported from three children in each group.

CONCLUSION

The PCV7 vaccine was highly immunogenic, well tolerated, and safe when coadministered with the DTPa-IPV-HBV-Hib vaccine at 2, 3, and 4 months of age and a booster dose at 12-15 months. In this study, PCV7 did not show any relevant influence on the immunogenicity and safety of the concurrently administered DTPa-IPV-HBV-Hib vaccine.

Combination conjugate vaccines

Increasingly, more diseases are becoming vaccine preventable, but maintaining community and provider acceptance demands that the number of injections does not increase. Combination conjugate vaccines represent an inevitable and important advance. This paper reviews the efficacy and safety of combination conjugate vaccines, including immunological mechanisms underlying interactions among vaccine epitopes, the role of immunological memory, and correlates of immunity. Specific attention is given to the experience with combination vaccines against each of Haemophilus influenzae type b, Streptococcus pneumoniae and Neisseria meningitidis. The implications of these findings for different communities are discussed, key areas for further research identified and implications for post-licensure monitoring addressed.

Could a single dose of pneumococcal conjugate vaccine in children be effective? Modeling the optimal age of vaccination

Using incidence rates from CDC's Active Bacterial Core surveillance and immunogenicity data from the Navajo/Apache trial of pneumococcal conjugate vaccine (PCV), we used Markov modeling to predict the optimal age to give a single dose of PCV. Antibody concentration thresholds of 0.35 and 1.0 mcg/ml were considered protective. Our outcome was vaccine serotype-specific invasive pneumococcal disease (IPD) incidence at 24 months. The models predicted the optimal age to vaccinate is 5-7 months with vaccine-induced immunologic memory and 8-10 months without memory. IPD reduction ranged from 15 to 62%, depending on model parameters. A single PCV dose in infants could prevent substantial IPD.

Assignment of weight-based immunoglobulin G1 (IgG1) and IgG2 units in antipneumococcal reference serum lot 89-S(F) for pneumococcal polysaccharide serotypes 1, 4, 5, 7F, 9V, and 18C

Weight-based assignments for immunoglobulin G1 (IgG1) and IgG2 subclass antibodies to Streptococcus pneumoniae capsular polysaccharides (PnPs) in antipneumococcal standard reference serum lot 89-S (lot 89-S), also known as lot 89-SF, have been determined for serotypes 1, 4, 5, 7F, 9V, and 18C. This extends the usefulness of lot 89-S beyond the IgG1 and IgG2 subclass assignments for serotypes 3, 6B, 14, 19F, and 23F made previously (A. Soininen, H. Kayhty, I. Seppala, and T. Wuorimaa, Clin. Diagn. Lab. Immunol. 5:561-566, 1998) to cover 11 major serotypes associated with the highest percentage of pneumococcal disease worldwide. A method of equivalence of absorbances in enzyme immunosorbent assays was used to determine the IgG1 and IgG2 antibody concentrations for the additional serotypes in lot 89-S, based on the subclass values previously assigned for PnPs serotypes 6B, 14, and 23F. This cross-standardization method assures consistency with previous antibody assignments in that reference serum. The newly assigned subclass values for serotype 9V, and previously assigned values for serotype 14, were used to quantitate PnPs antibodies in sera from adult and pediatric subjects immunized with a pneumococcal conjugate vaccine. There was a predominance of IgG1 anti-PnPs antibodies in pediatric sera and IgG2 anti-PnPs antibodies in the adult sera. The IgG1 and IgG2 subclass assignments for the 11 PnPs serotypes in antipneumococcal standard reference serum lot 89-S are useful for quantitating and characterizing immune responses to pneumococcal infection and vaccination regimens.

Assignment of weight-based antibody units for 13 serotypes to a human antipneumococcal standard reference serum, lot 89-S(f)

Weight-based immunoglobulin G (IgG), IgM, IgA, and total Ig antibody assignments were made to human antipneumococcal standard reference serum lot 89-S, also known as lot 89-SF, for Streptococcus pneumoniae capsular polysaccharide (PnPs) serotypes 2, 6A, 8, 9N, 10A, 11A, 12F, 15B, 19A, 17F, 20, 22F, and 33F, as well as for C-polysaccharide (C-Ps), extending the standard's usefulness for pneumococcal vaccine evaluation beyond the original serotype 1, 3, 4, 5, 6B, 7F, 9V, 14, 18C, 19F, and 23F assignments (S. A. Quataert, C. S. Kirch, L. J. Quackenbush Wiedl, D. C. Phipps, S. Strohmeyer, C. O. Cimino, J. Skuse, and D. V. Madore, Clin. Diagn. Lab. Immunol. 2:590-597, 1995). The additional 14 assignments were determined using an equivalence of absorbance method with an anti-PnPs serotype 6B reference enzyme-linked immunosorbent assay (EIA). To assure accuracy, anti-PnPs EIA for serotype 14 antibodies, a previously assigned serotype, was performed concurrently. This method assures consistency of the new microgram-per-microliter assignments with previous antiserotype assignments to lot 89-S. The sum of the experimentally derived isotype assignments for anti-PnPs serotypes in lot 89-S agrees well with the separately determined total Ig assignment for each serotype. The lot 89-S assignments for serotypes 1, 5, 6B, 14, 18C, 19F, and 23F were used for pneumococcal conjugate vaccine clinical trial evaluation and to generate data in efficacy trials where serological correlates for protection have been proposed. The assignment of antibody concentrations to additional pneumococcal serotypes in this reference reagent facilitates the consistent and accurate comparison of serum antibody concentrations across clinical trials.

Advances in Pneumococcal Vaccines

The introduction of Haemophilus influenzae type b (Hib) vaccine into the universal immunisation schedules of many industrialised countries and the subsequent remarkable decline in the incidence of invasive Hib disease has further highlighted the impact of invasive pneumococcal diseases. Streptococcus pneumoniae is now the leading cause of bacterial meningitis in children in many settings and a leading cause of vaccine-preventable bacterial disease in children worldwide. The currently marketed 23-valent pneumococcal polysaccharide vaccine provides large serotype coverage at a relatively low cost. However, it is not efficacious in young children. Pneumococcal conjugate vaccines (PCVs) are highly effective in preventing invasive disease in infants and young children, with favourable safety and immunogenicity profiles. These vaccines have also shown efficacy in reducing cases of non-invasive disease (i.e. otitis media), nasopharyngeal acquisition of vaccine-specific serotypes of S. pneumoniae, and protection against pneumococcal disease caused by resistant strains. However, PCV contains a limited number of pneumococcal serotypes and, given adequate ecological pressure, replacement disease by non-vaccine serotypes remains a threat, particularly in areas with very high disease burden. Furthermore, although capsular-specific antibodies have been shown to be highly protective, it remains unclear what concentration of these serotype-specific antibodies protect against disease and, more recently, it has become clear that opsonic activity and avidity of these antibodies are more critical determinants of protection than concentration. Therefore, monitoring disease burden and defining immune correlates of protection after widespread use of conjugate vaccines are crucial for the evaluation of these new generation vaccines. Furthermore, a need exists to develop pneumococcal vaccines with lower cost and larger serotype coverage. Development of one or more protein vaccines that might be easier and, thus, less expensive to manufacture, and which might provide protection against multiple serotypes, is in progress. This article reviews the current state of pneumococcal disease and pneumococcal vaccines in clinical use.

Pneumococcal conjugate vaccines for preventing vaccine-type invasive pneumococcal disease and pneumonia with consolidation on x-ray in children under two years of age

BACKGROUND

Pneumonia, most commonly caused by Streptococcus pneumoniae (Pnc), is a major cause of morbidity and mortality among young children especially in developing countries. Recently, the prevalence of antibiotic-resistant Pnc has increased worldwide such that the effectiveness of preventive strategies, like the new pneumococcal conjugate vaccines (PCV) on rates of invasive pneumococcal disease (IPD) and pneumonia, needs to be evaluated.

OBJECTIVES

To determine the efficacy of PCV in reducing the incidence of IPD due to vaccine serotypes (VT) and x-ray confirmed pneumonia with consolidation of unspecified etiology in children who received PCV before 12 months of age.

SEARCH STRATEGY

We searched the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, Issue 1 2004), MEDLINE (1990 to March 2004) and EMBASE (1990 to December 2003). Reference list of articles, and books of abstracts of relevant symposia, were hand searched. Researchers in the field were also contacted.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing PCV with placebo, or another vaccine, among children below two years with IPD and clinical/radiographic pneumonia as outcomes.

DATA COLLECTION AND ANALYSIS

Two reviewers independently identified eligible studies, assessed trial quality, and extracted data. Differences were resolved by discussion. The inverse variance method was used to pool effect sizes.

MAIN RESULTS

We identified four trials assessing the efficacy of PCV in reducing the incidence of IPD, two on x-ray confirmed pneumonia as outcome, and one on clinical pneumonia, with or without x-ray confirmation. Results from pooling HIV-1 negative children from the South African study with the other studies were as follows: the pooled vaccine efficacy (VE) for vaccine-type IPD was 88% (95% confidence interval (CI) 73% to 94%; fixed effect and random effects models), the effect measure was statistically significant (p <0.00001) and there was no heterogeneity (p = 0.77I2 0%); the pooled VE for all-serotype IPD was 66% (95% CI 46% to 79%; fixed effect model), the effect measure was statistically significant (p <0.00001) and there was no statistical heterogeneity (p = 0.09, I2 51%); the pooled VE for x-ray confirmed pneumonia was 22% (95% CI 11% to 31%; both fixed effect and random effects models) and there was no statistical heterogeneity (p = 0.80, I2 0%). Analyses that included all the children in the South African study (HIV-1 negative and HIV-1 positive children) and pooled with data from the other studies gave very similar results.

REVIEWERS' CONCLUSIONS

PCV is effective in reducing the incidence of IPD from all serotypes but exerts a greater effect in reducing VT IPD. Although PCV is also effective in reducing the incidence of x-ray confirmed pneumonia, there are still uncertainties about the definition of this outcome. Additional randomised controlled trials are currently in progress.

Pneumococcal conjugate vaccines—a European perspective

Streptococcus pneumoniae is a leading cause of bacterial pneumonia, meningitis, and acute otitis media in children and adults worldwide. In the age group of < 2 years the incidence of invasive pneumococcal disease ranges from approximately 14 cases per 100,000 in Germany and the Netherlands and more than 90 per 100,000 children in Spain. The vulnerability of children to S. pneumoniae can also be demonstrated by the high rate of sequelae (> 20% in Germany) and the high mortality (7.5%) in pneumococcal meningitis. Furthermore, antibiotic resistance of S. pneumoniae is increasing in Europe, particularly in France, Spain, and Eastern European countries, whereas Germany and Northern Europe are only marginally affected. A 7-valent pneumococcal conjugate vaccine (7vPCV) that was shown to be highly efficacious in preventing invasive pneumococcal disease in infants in the USA was licensed in Europe in 2001. It is expected that broad usage of the vaccine would reduce the incidence of invasive pneumococcal disease and the levels of pneumococcal resistance significantly. Important questions have been raised regarding the effectiveness of this vaccine in high-risk populations, serotype replacement, the efficacy of this vaccine in otitis media, and the co-administration of the new vaccine with other standard childhood vaccines used in various European countries. France and Spain currently have the most-wide ranging guidelines recommending pneumococcal vaccination for children. Overall, the development of pneumococcal conjugate vaccines is a significant step in the control of pneumococcal disease in children in Europe. Further progress in pneumococcal vaccine development can be expected from conjugate vaccines including more than seven serotypes (9-valent, 11-valent).

Preparation and characterization of group A meningococcal capsular polysaccharide conjugates and evaluation of their immunogenicity in mice

Epidemic and endemic meningitis caused by group A Neisseria meningitidis remains a problem in sub-Saharan Africa. Although group A meningococcal capsular polysaccharide (GAMP) vaccine confers immunity at all ages, the improved immunogenicity of a conjugate and its compatibility with the World Health Organization's Extended Program on Immunization offers advantages over GAMP alone. Conjugates of GAMP bound to bovine serum albumin (BSA) were synthesized, characterized, and evaluated for their immunogenicities in mice. Two methods, involving adipic acid dihydrazide (ADH) as a linker, were used. First, ADH was bound to GAMP activated with cyanogen bromide (CNBr) or with 1-cyano-4(dimethylamino)-pyridinium tetrafluoroborate (CDAP) to form GAMP(CNBr)AH and GAMP(CDAP)AH. These derivatives were bound to BSA by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) to form GAMP(CNBr)AH-BSA and GAMP(CDAP)AH-BSA. Second, ADH was bound to BSA with EDC to form AHBSA. AHBSA was bound to activated GAMP to form GAMP(CNBr)-AHBSA and GAMP(CDAP)-AHBSA. The yield of GAMP(CDAP)-AHBSA (35 to 40%) was higher than those of the other conjugates (5 to 20%). GAMP conjugates elicited immunoglobulin G (IgG) anti-GAMP in all mice after three injections of 2.5 or 5.0 microg of GAMP: the geometric mean (GM) was highest in recipients of GAMP(CDAP)-AHBSA (11.40 enzyme-linked immunosorbent assay units). Although the difference was not statistically significant, the 5.0- microg dose elicited a higher GM IgG anti-GAMP than the 2.5- microg dose. Low levels of anti-GAMP were elicited by GAMP alone. GAMP(CDAP)-AHBSA elicited bactericidal activity roughly proportional to the level of IgG anti-GAMP.

Current state of pneumococcal vaccines

Streptococcus pneumoniae is a leading cause of bacterial pneumonia, meningitis, and acute otitis media in children and adults worldwide. According to World Health Organization estimates, at least 1 million children under 5 years of age die each year from pneumococcal pneumonia. The emergence of resistant strains necessitates the development of an effective vaccine with a large serotype coverage. The 11 most common serotypes cause 72-83% of all serious pneumococcal diseases worldwide. Currently marketed 23-valent pneumococcal polysaccharide vaccine provides large serotype coverage and offers a less expensive option. However, it is efficacious only in adults but not in infants. Conjugate vaccines offer a solution by generating immunological memory already at early age. A recently licensed 7-valent conjugate vaccine is immunogenic and efficacious in infants. Its serotype coverage might be sufficient in Europe and North America, but not in Africa, Asia and Oceania. A need exists to develop pneumococcal vaccines with lower cost and larger serotype coverage. Several 11-valent pneumococcal conjugate vaccines are being evaluated in phase I-III trials. This study reviews the current state of pneumococcal problem and pneumococcal vaccines in clinical use.

Immune response to octavalent diphtheria- and tetanus-conjugated pneumococcal vaccines is serotype- and carrier-specific: the choice for a mixed carrier vaccine

BACKGROUND

Development of protein-conjugated pneumococcal vaccines for infants has led to formulations that are immunogenic in the age group at highest risk for pneumococcal diseases. This study focuses on the search for an optimal formulation.

METHODS

In a randomized trial Icelandic infants (n = 160) were immunized at age 3, 4 and 6 months with one of two octavalent pneumococcal conjugate vaccines (serotypes 3, 4, 6B, 9V, 14, 18C, 19F and 23F conjugated to diphtheria toxoid (PncD) or tetanus protein (PncT) followed with a booster of either the same conjugate or 23-valent polysaccharide vaccine at 13 months. Safety data were collected after each vaccination, and IgG responses (enzyme-linked immunosorbent assay) were measured at 3, 4, 6, 7, 13 and 14 months.

RESULTS

Both conjugates were safe and caused fewer local reactions than the routine vaccines (P < 0.0001). At 7 months both groups had significant IgG response to all serotypes. The geometric mean concentration range was 0.35 to 4.09 and 0.65 to 3.38 microg/ml for PncD and PncT, respectively, with 88.2 to 100% and 92.4 to 100% of subjects reaching > or = 0.15 microg/ml. The PncD gave better primary responses to serotypes 3, 9V and 18C, whereas PncT gave better response to serotype 4. Similar responses were induced to the other serotypes. Good booster IgG responses were obtained in all vaccine groups; 97.5 to 100% of subjects reached > or = 1 microg/ml.

CONCLUSIONS

Both octavalent pneumococcal conjugates were safe and immunogenic in infants. Based on the results from this and similar trials, a mixed diphtheria and tetanus pneumococcal conjugate vaccine was designed to provide the optimal immune response to each serotype.

Bridging phase 2 and phase 3 pneumococcal immunologic data for future combination vaccines

Pneumococcal conjugate vaccines (PncCs) will be introduced into childhood vaccination programs now that the first PncC has been licensed for use. The next generation of PncCs and possible combination vaccines containing PncC will most probably be approved on the basis of phase 2 immunogenicity and safety data. PncCs are combination vaccines that include, at present, 7-11 components. Immune response to different components may vary. Furthermore, there seem to be population-based differences in immune response. Whether these differences are due to the other vaccines that are given simultaneously or due to the genetic background remains to be seen. Immune response can be evaluated by determining both the quantity and the quality of antibodies after vaccination. However, data are still missing on the minimal protective immune response and serologic correlates or surrogates of protection.

Tolerability and immunogenicity of an eleven-valent pneumococcal conjugate vaccine in healthy toddlers

BACKGROUND

A need to increase the serotype coverage of pneumococcal conjugate vaccines exists. The use of a single carrier protein may cause overload of the carrier and decrease the immune response by not providing sufficient carrier-specific T helper cell support. A vaccine composed of a mixture of tetanus- and diphtheria-conjugated polysaccharides (PS) is a potential solution to this issue.

OBJECTIVES

The aim of this study was to assess the tolerability and immunogenicity in healthy toddlers of an 11-valent pneumococcal conjugate vaccine that uses both tetanus and diphtheria toxoids as carriers. We explored the effect of an aluminum adjuvant on safety and immunogenicity by comparing the vaccine with and without adjuvant.

METHODS

Twenty Finnish and 23 Israeli toddlers received the conjugate vaccine with or without aluminum adjuvant. Safety data were recorded for 5 days after vaccination. Sera were obtained before and 28 days after the immunization. IgG antibodies to the 11 vaccine-type PSs were determined by enzyme immunoassay.

RESULTS

No serious adverse events occurred. The formulation with the adjuvant tended to induce fewer local but more systemic reactions than the non-adjuvant-containing formulation. Both vaccine formulations induced significant IgG increases for the vaccine-specific PSs. Types 3 and 7F were the most immunogenic; antibodies reached a concentration of 1 microg/ml in all individuals. Conjugates of types 6B, 14 and 23F were the weakest immunogens; antibodies reached the concentration of 1 microg/ml in 36, 27 and 32% of the individuals in the nonadjuvant group and in 53, 38 and 53% in the adjuvant group, respectively.

CONCLUSIONS

An 11-valent mixed carrier pneumococcal conjugate vaccine is safe and immunogenic in toddlers. The use of an adjuvant do not seem to offer any significant benefit.

Serum and salivary anti-capsular antibodies in infants and children immunized with the heptavalent pneumococcal conjugate vaccine

AIM

To study the ability of seven-valent experimental pneumococcal polysaccharide CRM197 protein conjugate vaccine (PncCRM) to induce antibodies in serum and saliva of infants.

METHODS

Sixty Finnish infants received Pnc-CRM vaccine at 2, 4 and 6 months of age and were boosted with PncCRM (n = 30) or pneumococcal polysaccharide (PncPS) (n = 29) vaccine at the age of 15 months. Serum IgG antibody concentrations to vaccine serotypes 4, 6B, 9V, 14, 18C, 19F and 23F were measured by enzyme immunoassay at 2, 4, 6, 7, 15, 16 and 24 months of age. Salivary IgA, IgG and secretory Ig antibody titers at 7 and 16 months of ages were analyzed by enzyme immunoassay against the same serotypes, except 23F.

RESULTS

PncCRM induced systemic immune responses and immunologic memory. At 7 months of age 69 to 100% of children, depending on the serotype, had serum IgG antibody concentrations exceeding the value of 1.0 microg/ml. At 15 months the titers were still higher than before the vaccinations. Booster doses of either PncPS or PncCRM induced an increase in antibody concentrations. The titers were still elevated at 24 months of age. Salivary IgA and IgG antibodies were found rarely at 7 months of age, but in up to 80% of samples taken at 16 months of age, depending on the serotype and nature of the booster vaccine. Salivary IgG correlated with IgG in serum, supporting the theory that salivary IgG is derived from serum. Salivary IgA and secretory Ig correlated positively, which indicates that IgA was locally produced.

CONCLUSIONS

PncCRM induces both systemic and mucosal immune responses in infants.

Immunogenicity and reactogenicity of a pneumococcal conjugate vaccine administered combined with a haemophilus influenzae type B conjugate vaccine in United Kingdom infants

BACKGROUND

Streptococcus pneumoniae is a major disease burden in young children and the incidence of antibiotic-resistant pneumococcal strains is increasing. Multivalent pneumococcal saccharide-protein conjugate vaccines have recently been developed.

OBJECTIVES

To assess the immunogenicity and reactogenicity of a 7-valent pneumococcal conjugate vaccine (7VPnC) administered as a separate injection or as a combined injection with Haemophilus influenzae type b vaccine (HbOC) at 2, 3 and 4 months of age.

METHODS

Randomized controlled trial of 368 healthy UK infants receiving routine vaccines only (control group), routine vaccines and 7VPnC as a separate injection (separate group), or routine vaccines and 7VPnC combined with HbOC (combined group) at 2, 3 and 4 months. The control group received 7VPnC at 5, 6 and 7 months. All groups received pneumococcal polysaccharide vaccine at 13 to 16 months. Anticapsular IgG antibodies to 7VPnC serotypes were measured at 2, 5, 13 and 14 months and safety data collected.

RESULTS

IgG antibody concentrations at 5 months were higher in the two treatment groups compared with the controls for all 7VPnC serotypes (P < 0.001) and higher in the separate group than the combined group for five 7VPnC serotypes (P < 0.05). For both treatment groups antibody concentrations were higher at 14 months (range, 6.6 to 25.3 microg/ml) than at 5 months (range, 0.6 to 2.5 microg/ml) for all 7VPnC serotypes (P < 0.001).

CONCLUSION

7VPnC was well-tolerated, safe and immunogenic when administered as a separate or as a combined 7VPnC/HbOC injection. Although antibody responses were lower in the infants who received the combination compared with those who received 7VPnC as a separate injection, marked anamnestic responses to polysaccharide challenge were observed, suggesting that both groups were immunologically primed.

Pneumococcal pneumonia and bacteremia model in mice for the analysis of protective antibodies

Pneumococci cause infection by colonizing the nasopharynx and invading the mucosal surfaces. Infection models in mice, where the natural route of infection is mimicked, may be useful to study antibody mediated protection against pneumococcal pneumonia and bacteremia. We have established a pneumococcal pneumonia and bacteremia model in mice and investigated the protective capacity of human antibodies. Intranasal challenge with serotypes 1, 3, 6A and 8 caused lung infection and bacteremia which was lethal. Serotype 6B caused low, but detectable, infection and other serotypes tested were not virulent. Passive immunization with a human IgG preparation i.p. protected mice in a dose dependent manner against bacteremia caused by the virulent serotypes (except serotype 3) and partially or completely cleared pneumococci from the lungs of mice infected with serotypes 1, 6A and 8. Adsorption of antibodies with homologous capsular polysaccharides eliminated protection against disease but adsorption with cell wall polysaccharides (CWPS) did not. Furthermore, a good correlation was observed between protection of sera in vivo and opsonic activity in vitro. The results indicate that the model may be useful to analyse the levels, isotypes, specificity and other characteristics of human antibodies which protect against pneumococcal infection and to evaluate the protective potential of pneumococcal vaccine candidates.

Immunogenicity of a heptavalent pneumococcal conjugate vaccine in Apache and Navajo Indian, Alaska native, and non-native American children aged <2 years

High rates of invasive pneumococcal disease have been described among infants living in various Native American communities. In this study, we evaluated the immunogenicity of a 7-valent pneumococcal vaccine consisting of serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F covalently linked to the outer membrane protein complex of Neisseria meningitidis in Apache and Navajo Indian, Alaska Native, and non-Native American children. The vaccine was administered at ages 2, 4, and 6 months; a booster dose was given at age 15 months. Levels of serotype-specific immunoglobulin G (IgG) were measured by a standardized enzyme-linked immunosorbent assay. The responses after 3 primary doses of vaccine were similar in all 3 groups of children, except for those to serotypes 14 and 23F. One month after the booster dose, geometric mean concentrations (GMCs) of serotype-specific IgG antibodies increased significantly in all 3 groups of children, compared with GMCs of IgG antibodies to pneumococcal serotypes before the booster dose.

New combination vaccines

Physicians can achieve full vaccination at each of the recommended visits by administering three or four injections, but for infants, four injections seem to be a maximum in light of the size of the infant thigh, which is the preferred injection site. Thus, physicians must make room for all of the new vaccines on the horizon. To accomplish that task, combinations will be necessary. Progress toward that goal is occurring.

Preparation of pneumococcal capsular polysaccharide-protein conjugate vaccines utilizing new fragmentation and conjugation technologies

There is a global urgent need for a new efficient and inexpensive vaccine to combat pneumococcal disease, which should also be affordable in developing countries. In view of this need a simple low-cost technique to prepare such a vaccine was developed. The preparation of serotype 14 and 23F pneumococcal capsular polysaccharide (PnPS)-protein conjugates to be included in a forthcoming multivalent PnPS conjugate vaccine is described. Commercial lots of PnPSs produced according to Good Manufacturing Practice from Streptococcus pneumoniae serotype 14 (PS14) and 23F (PS23F) were partially depolymerized by sonication or irradiation in an electron beam accelerator. The PnPS fragments were conjugated to tetanus toxoid (TT) using a recently developed conjugation chemistry. The application of these new simple, efficient and inexpensive fragmentation and conjugation technologies allowed the synthesis of several PnPS-protein conjugates containing PnPS fragments of preselected sizes and differing in the degree of substitution. The PS14TT and PS23FTT conjugate vaccine candidates were characterized chemically and their immunogenicity was evaluated in rabbits and mice. All PnPS conjugate vaccines, unlike the corresponding plain polysaccharides, produced high IgG titres in both animal species. The PS14TT conjugates tended to be more immunogenic than the PS23FTT conjugates. The immune response to the PS14TT conjugates, but not to the PS23FTT conjugates, was related to the size of the conjugated polysaccharide hapten. Both types of conjugates elicited strong booster effects upon secondary immunizations, resulting in high IgG1, IgG2a and IgG2b titres.

Selection of an immunogenic and protective epitope of the PsaA protein of Streptococcus pneumoniae using a phage display library

Streptococcus pneumoniae is an important pathogen that causes disease in young and elderly individuals. The currently available polysaccharide vaccines have limited efficacy in those age groups most susceptible to pneumococcal infections. This study focuses on mapping the epitopes of a surface protein of S. pneumoniae by biopanning a 15 mer phage display library using 5 different monoclonal antibodies (MAbs) against the Pneumoccal surface adhesin A (PsaA). PsaA is a component of the bacterial cell wall that is highly species specific and is involved in bacterial adherence and virulence. Biopanning of the phage display library reveals three distinct epitopes on the PsaA protein. The sequence homology of these epitopes ranges from two to six amino acids when compared to the native PsaA protein type 2. Two of these epitopes have been evaluated for their immunogeneicity in mice. The peptide selected by the MAbs 8G12, 6F6, and 1B7 is referred to as the consensus peptide and is immunogenic in mice. Optimal anti-PsaA response is observed in mice immunized with 50microg of the consensus peptide complexed to proteosomes in 1:1 ratio. The anti-PsaA response is significantly lower than the response to the PsaA native protein. The peptide selected by monoclonal antibody 4E9 in its lipidated form is significantly protective in mice challenged with S. pneumoniae serotype 2 when compared to mice immunized with the native protein. These results show that the selected epitopes of PsaA protein are immunogenic and protective in mice. These epitopes need to be evaluated further as alternatives to currently available vaccines.

Salivary anti-capsular antibodies in infants and children immunised with Streptococcus pneumoniae capsular polysaccharides conjugated to diphtheria or tetanus toxoid

Saliva samples of infants and children immunised with pneumococcal vaccines were analysed for anti-polysaccharide (PS) antibodies against the Streptococcus pneumoniae (Pnc) vaccine serotypes 6B, 14, 19F, and 23F. The children received Pnc conjugate vaccine (1, 3, or 10 micrograms of PSs conjugated to diphtheria or tetanus toxoid) or placebo at 2, 4, and 6 months. At 7 months of age salivary PS antibodies were detected rarely. All children received Pnc conjugate or PS vaccine at 14 months of age. At 15 months, both IgA and IgG anti-Pnc PS were found, anti-19F and anti-14 antibodies occurring most frequently and in the highest concentrations. IgA was in the secretory form and predominantly IgA1. A negative dose dependency was observed in IgA anti-19F response. In general, no clear differences in salivary antibody responses were found between the children primed with conjugate vaccine in infancy and those who received their first Pnc vaccine at 14 months of age, suggesting that priming with Pnc conjugate vaccines does not lead to remarkable mucosal memory responses.

Dose dependency of antibody response in infants and children to pneumococcal polysaccharides conjugated to tetanus toxoid

Three injections of tetravalent pneumococcal polysaccharide-tetanus toxoid conjugate vaccine (PncT) were given to infants at 2, 4 and 6 months of age simultaneously with diphtheria-tetanus-pertussis and Haemophilus influenzae type b-tetanus toxoid conjugate vaccines. Three doses (1, 3 or 10 microg) of polysaccharides were used. Children were boosted with unconjugated polysaccharide vaccine at 14 months of age. No dose dependency was seen after primary immunization. However, booster response to three vaccine serotypes was highest in the group primed with the lowest dose of conjugate vaccine. As the magnitude of the response to booster may be related to the number of polysaccharide-specific memory B cells, we hypothesize that the 10 microg dose of the tetravalent conjugate vaccine is too high for optimal induction of immunologic memory.