Evolution of conjugate 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.

Polysaccharide Vaccines: A Perspective on Non-Typhoidal Salmonella

Polysaccharides are often the most abundant antigens found on the extracellular surfaces of bacterial cells. These polysaccharides play key roles in interactions with the outside world, and for many bacterial pathogens, they represent what is presented to the human immune system. As a result, many vaccines have been or currently are being developed against carbohydrate antigens. In this review, we explore the diversity of capsular polysaccharides (CPS) in Salmonella and other selected bacterial species and explain the classification and function of CPS as vaccine antigens. Despite many vaccines being developed using carbohydrate antigens, the low immunogenicity and the diversity of infecting strains and serovars present an antigen formulation challenge to manufacturers. Vaccines tend to focus on common serovars or have changing formulations over time, reflecting the trends in human infection, which can be costly and time-consuming. We summarize the approaches to generate carbohydrate-based vaccines for Salmonella, describe vaccines that are in development and emphasize the need for an effective vaccine against non-typhoidal Salmonella strains.

Evaluation of single-use tangential flow filtration technology for purification of activated polysaccharides used in conjugate vaccine manufacturing

Over the past decade, single‐use tangential flow filtration (TFF) technologies have emerged to reduce system preparation time, promote fast and flexible product change over, and ultimately shorten process development and manufacturing time/cost. In this study, the performance of a recently developed Pellicon® single‐use TFF capsule was compared against traditional Pellicon® cassettes by assessing TFF process performance (such as flux, residuals clearance, and yield) and post‐purification product attributes (such as concentration and mass‐weighted average molecular weight). Good scaling was shown by comparing process performance and product attributes across different scales and formats. Additionally, similar TFF process performance and post‐purification product attributes were observed for the single‐use capsule compared to the reusable TFF cassettes. The capsule requires a smaller flush than the cassette, and it is easier to use since it does not require a compression holder or pre‐sanitization. The results provide insight into the application of the single‐use TFF capsule and scalability of TFF processes for the purification of conjugate vaccines.

Effect of childhood pneumococcal vaccination and beta-lactam antibiotic use on the incidence of invasive pneumococcal disease in the adult population

Describe the incidence of invasive pneumococcal disease (IPD) in serotypes with reduced antibiotic sensitivity to penicillin (RAS-Pen) in adults over 59 years of age and its association with childhood anti-pneumococcal vaccination coverage (CVC) and community consumption of beta-lactam. We selected IPD cases in adults over 59 years of age reported in the Community of Madrid between 2007 and 2016. We estimated the incidence of cases caused by serotypes included in the 13-valent pneumococcal conjugate vaccine (PCV13), those not included (non-PCV13) and the six serotypes additional to the 7-valent (PCV13-no7). We compared the incidences of serotypes from the pre-vaccine period (2007-2009) and the vaccine period (2011-2016) by analysing the incidence trend (JointPoint Trend Analysis) and its association with the CVC and community consumption of beta-lactam (Poisson model). We identified 1936 cases of IPD, 29.2% (n = 565) in serotypes with RAS-Pen. The incidence decreased for PCV13 cases (annual percentage of change, APC: -12.2, p < 0.05) and increased for non-PCV13 (APC: 15.4, p < 0.05). The incidence of IPD due to non-PCV13 was associated with community beta-lactam consumption (IRR 1.156; CI95% 1.025-1.304) and that of cases of PCV13-no7 with CVC (IRR 0.574; 95% CI95% 0.413-0.797). The non-PCV13 strains that increased the most at the end of the period were 6C, 11A and 15A. The incidence of IPD due to PCV13 with RAS-Pen at > 59 years was decreasing and was associated with CVC. The incidence of cases due to non-PCV13 was increasing and was associated with community consumption of beta-lactam.

Immunogenicity and safety of a tetravalent E. coli O-antigen bioconjugate vaccine in animal models

BACKGROUND

Extra-intestinal pathogenic Escherichia coli (ExPEC) are major human pathogens; however, no protective vaccine is currently available. We assessed in animal models the immunogenicity and safety of a 4-valent E. coli conjugate vaccine (ExPEC-4V, serotypes O1, O2, O6 and O25 conjugated to Exotoxin A from Pseudomonas aeruginosa (EPA)) produced using a novel in vivo bioconjugation method.

METHODS

Three doses of ExPEC-4V (with or without aluminum hydroxide) were administered to rabbits (2μg or 20μg per O-antigen, subcutaneously), mice (0.2μg or 2μg per O-antigen, subcutaneously) and rats (0.4μg or 4μg per O-antigen, intramuscularly). Antibody persistence and boostability were evaluated in rats using O6-EPA monovalent conjugate (0.4μg O-antigen/dose, intramuscularly). Toxicity was assessed in rats (16μg total polysaccharide, intramuscularly). Serum IgG and IgM antibodies were measured by ELISA.

RESULTS

Robust antigen-specific IgG responses were observed in all animal models, with increased responses in rabbits when administered with adjuvant. O antigen-specific antibody responses persisted up to 168days post-priming. Booster immunization induced a rapid recall response. Toxicity of ExPEC-4V when administered to rats was considered to be at the no observed adverse effect level.

CONCLUSIONS

ExPEC-4V conjugate vaccine showed good immunogenicity and tolerability in animal models supporting progression to clinical evaluation.

Consensus Recommendation for India and Bangladesh for the Use of Pneumococcal Vaccine in Mass Gatherings with Special Reference to Hajj Pilgrims

Respiratory tract infections are prevalent among Hajj pilgrims with pneumonia being a leading cause of hospitalization. Streptococcus pneumoniae is a common pathogen isolated from patients with pneumonia and respiratory tract infections during Hajj. There is a significant burden of pneumococcal disease in India, which can be prevented. Guidelines for preventive measures and adult immunization have been published in India, but the implementation of the guidelines is low. Data from Bangladesh are available about significant mortality due to respiratory infections; however, literature regarding guidelines for adult immunization is limited. There is a need for extensive awareness programs across India and Bangladesh. Hence, there was a general consensus about the necessity for a rapid and urgent implementation of measures to prevent respiratory infections in pilgrims traveling to Hajj. About ten countries have developed recommendations for pneumococcal vaccination in Hajj pilgrims: France, the USA, Kuwait, Qatar, Bahrain, the UAE (Dubai Health Authority), Singapore, Malaysia, Egypt, and Indonesia. At any given point whether it is Hajj or Umrah, more than a million people are present in the holy places of Mecca and Madina. Therefore, the preventive measures taken for Hajj apply for Umrah as well. This document puts forward the consensus recommendations by a group of twenty doctors following a closed-door discussion based on the scientific evidence available for India and Bangladesh regarding the prevention of respiratory tract infections in Hajj pilgrims.

Design of glycoconjugate vaccines against invasive African Salmonella enterica serovar Typhimurium

Nontyphoidal salmonellae, particularly Salmonella enterica serovar Typhimurium, are a major cause of invasive disease in Africa, affecting mainly young children and HIV-infected individuals. Glycoconjugate vaccines provide a safe and reliable strategy against invasive polysaccharide-encapsulated pathogens, and lipopolysaccharide (LPS) is a target of protective immune responses. With the aim of designing an effective vaccine against S. Typhimurium, we have synthesized different glycoconjugates, by linking O-antigen and core sugars (OAg) of LPS to the nontoxic mutant of diphtheria toxin (CRM(197)). The OAg-CRM(197) conjugates varied in (i) OAg source, with three S. Typhimurium strains used for OAg extraction, producing OAg with differences in structural specificities, (ii) OAg chain length, and (iii) OAg/CRM(197) ratio. All glycoconjugates were compared for immunogenicity and ability to induce serum bactericidal activity in mice. In vivo enhancement of bacterial clearance was assessed for a selected S. Typhimurium glycoconjugate by challenge with live Salmonella. We found that the largest anti-OAg antibody responses were elicited by (i) vaccines synthesized from OAg with the highest glucosylation levels, (ii) OAg composed of mixed- or medium-molecular-weight populations, and (iii) a lower OAg/CRM(197) ratio. In addition, we found that bactericidal activity can be influenced by S. Typhimurium OAg strain, most likely as a result of differences in OAg O-acetylation and glucosylation. Finally, we confirmed that mice immunized with the selected OAg-conjugate were protected against S. Typhimurium colonization of the spleen and liver. In conclusion, our findings indicate that differences in the design of OAg-based glycoconjugate vaccines against invasive African S. Typhimurium can have profound effects on immunogenicity and therefore optimal vaccine design requires careful consideration.

Designing vaccines for the twenty-first century society

The history of vaccination clearly demonstrates that vaccines have been highly successful in preventing infectious diseases, reducing significantly the incidence of childhood diseases and mortality. However, many infections are still not preventable with the currently available vaccines and they represent a major cause of mortality worldwide. In the twenty-first century, the innovation brought by novel technologies in antigen discovery and formulation together with a deeper knowledge of the human immune responses are paving the way for the development of new vaccines. Final goal will be to rationally design effective vaccines where conventional approaches have failed.

Assessment of immunogenicity and safety following primary and booster immunisation with a CRM197 -conjugated Haemophilus influenzae type B vaccine in healthy Chinese infants

BACKGROUND

Invasive meningitis and pneumonia caused by Haemophilus influenzae type b (Hib) is an important cause of childhood mortality in countries where Hib vaccination is not routine. We evaluated the non-inferiority of a licensed Hib vaccine, PRP-CRM(197) compared with a second licensed Hib vaccine, PRP-T, following the recommended Chinese immunisation schedule for infants between 6 months and 1 year of age.

METHODS

In the first study phase, 6-12 month-old infants received two primary doses of either PRP-CRM(197) (n = 335) or PRP-T (n = 335) vaccine administered 1 month apart. In the second study phase 8 months later, the same children received a single booster dose of vaccine identical to that use for priming (PRP-CRM(197), n = 327; PRP-T, n = 333). Serum levels of anti-polyribosylribitol phosphate (PRP) antibodies were measured using enzyme-linked immunosorbent assay (ELISA). Non-inferiority of primary and booster doses was assessed in terms of percentages of subjects with anti-PRP antibody levels associated with providing short-term (≥ 0.15 μg/ml) and long-term (≥ 1.0 μg/ml) protection; the non-inferiority margin was set at -5%.

RESULTS

PRP-CRM(197) was demonstrated to be non-inferior to PRP-T. Anti-PRP antibodies levels ≥ 0.15 μg/ml and ≥ 1.0 μg/ml were achieved by 97% of infants in the PRP-CRM(197) group and 98% of infants in the PRP-T group 1 month after primary immunisation, and by all subjects (100%) in both vaccine groups 1 month after booster administration. Safety profiles for both vaccines were similar; no serious adverse events, deaths or adverse events leading to withdrawal occurred during the study.

CONCLUSION

PRP-CRM(197) was well-tolerated and immunologically non-inferior to a licensed comparator Hib vaccine in Chinese infants (Clinicaltrials.gov: NCT01044316 & NCT01226953).

Prospects for prevention of Salmonella infection in children through vaccination

PURPOSE OF REVIEW

Strains of Salmonella enterica subsp. enterica are amongst the most commonly identified invasive bacterial pathogens in resource-poor settings, and cause significant mortality, particularly in children. In this study we review recent progress in the development of vaccines against S. Typhi, S. Paratyphi and nontyphoidal Salmonella for children.

RECENT FINDINGS

Typhoid remains common and S. Paratyphi A is increasingly recognized as a cause of enteric fever in Asia. In rural Africa, nontyphoidal salmonellae are among the most common invasive bacterial infections, although S. Typhi predominates in some urban centres. Licensed vaccines against typhoid have moderate but useful efficacy but neither of the two available vaccines can be used in infants. Although Ty21a may afford some cross-protection against S. Paratyphi B, there are no vaccines that specifically target paratyphoid or any nontyphoidal Salmonella. Several live attenuated vaccines are under development and may offer some advantages over Ty21a. Vi-conjugate vaccines should offer children excellent protection from typhoid once licensed.

SUMMARY

There are few effective vaccines against Salmonella sp. and those that do exist target only one serovar, S. Typhi. Research is urgently needed to combat emerging agents of enteric fever such as S. Paratyphi A as well as nontyphoidal serovars, which commonly cause invasive disease in Africa.

Long-term protection after immunization with protein-polysaccharide conjugate vaccines in infancy

The polysaccharide-encapsulated bacteria, Haemophilus influenzae type b, Neisseria meningitidis and Streptococcus pneumoniae are important causes of invasive bacterial infection in childhood, accounting for most of the cases of bacterial pneumonia and meningitis worldwide. Protein-polysaccharide conjugate vaccines have been developed over the last 20 years and have proven very effective in controlling these infections. Although studies have consistently shown that herd immunity is critical for population protection, long-term individual protection against polysaccharide-encapsulated bacteria appears to depend on persisting antibody and, perhaps to a lesser extent, immunological memory. However, some studies have reported that the concentration of serum antibody and vaccine effectiveness are not sustained after infant immunization, despite persistence of immunological memory. In this article, we detail the mechanisms of protection against invasion by encapsulated bacteria, describe the age-dependent B-cell and antibody responses to protein-polysaccharide conjugate vaccines and propose strategies to guarantee protection during periods of increased disease burden.

Optimizing protection against meningococcal disease

Neisseria meningitidis is a leading cause of bacterial meningitis and septicemia in the United States. Vaccines directed against meningococcal disease must elicit high and persistent titers of bactericidal antibodies against prevalent meningococcal serogroups and be highly efficacious in preventing meningococcal infection. Currently, 2 quadrivalent (A, C, W-135, Y) vaccines-a polysaccharide meningococcal vaccine and a conjugate meningococcal vaccine-are licensed in the United States. Neither is approved for use in infants or toddlers younger than 2 years of age. Results of studies with an investigational quadrivalent (ACWY) meningococcal CRM(197) glycoconjugate vaccine in infants demonstrate that this vaccine has potential to protect this age group. The availability of an effective vaccine for routine universal infant immunization is particularly important because the incidence of invasive meningococcal disease is greatest in infants for all serogroups and because achievable vaccination rates are much greater for infants and young children than they are for adolescents.

10-valent pneumococcal nontypeable Haemophilus influenzae PD conjugate vaccine: Synflorix

The global burden of disease due to Streptococcus pneumoniae remains high. The licensed 7-valent pneumococcal conjugate vaccine (7vCRM, Prevenar/Prevnar) has successfully reduced invasive disease in the USA, but serotype coverage is incomplete and some evidence suggests that serotype replacement has occurred. Recently, a new 10-valent pneumococcal nontypeable Haemophilus influenzae (NTHi) protein D (PD) conjugate vaccine (PHiD-CV, Synflorix) has been licensed in more than 40 countries, including Europe, for the prevention of invasive disease and acute otitis media (AOM) due to pneumococcus in infants and children. PHiD-CV is immunogenic in infants when administered as a three-dose primary vaccination in a range of schedules and has a safety profile comparable to that of 7vCRM. Additional serotypes in PHiD-CV (1, 5 and 7F) increase overall serotype coverage and improve coverage in specific age groups and against specific disease syndromes. The use of the PD carrier, which provided protection against AOM caused by NTHi in a large efficacy trial testing a prototype of the final vaccine formulation, suggests that PHiD-CV will also provide some protection against AOM due to NTHi.

Evaluation of the immunogenicity and reactogenicity of a DTPa-HBV-IPV combination vaccine Co-administered with a hib conjugate vaccine either as a single injection of a hexavalent combination or as two separate injections at 3, 5 and 11 months of age

A combined DTPa-HBV-IPV/Hib vaccine containing diphtheria (D), tetanus (T), acellular pertussis (Pa), hepatitis B (HBV) and types 1, 2 and 3 inactivated polioviruses (IPV) extemporaneously mixed with a conjugated Haemophilus influenzae type b (Hib) vaccine (Group 1) was compared to the DTPa-HBV-IPV and Hib vaccines (Group 2) administered separately at 3, 5 and 11 months of age (n = 440). A microneutralization assay was used to detect antibodies against the 3 polio virus types (cut-off 1:8 dil), RIA for anti-HBs antibodies (cut-off 10 mIU/ml) and ELISA for antibodies against all other vaccine antigens (cut-off: 0.1 IU/ml for anti-tetanus and anti-diphtheria antibodies; 5 El.U/ml for antibodies against each of the 3 acellular pertussis antigens and 0.15 microg/ml for anti-PRP antibodies). Similar immune responses were observed in both groups 1 month after dose 2 as well as after dose 3. Six months after dose 2 however, the proportion of subjects maintaining an anti-tetanus antibody concentration > or = 0.1 IU/ml was lower in Group 2 and a slight group difference in favour of Group 1 was also observed for anti-PRP, anti-diphtheria and anti-polio type 1 antibody persistence prior to the third dose. The overall incidence of local and general solicited symptoms was similar in both groups. One subject discontinued study vaccination following an SAE considered to be related to vaccination. The DTPa-HBV-IPV/Hib combined vaccine is immunogenic and well tolerated when administered according to a 3, 5 and 11 month vaccination schedule and can therefore be considered as a feasible alternative to the separate administration of the pentavalent DTPa-HBV-IPV and the monovalent Hib vaccines.

A randomized trial to determine the tolerability and immunogenicity of a quadrivalent meningococcal glycoconjugate vaccine in healthy adolescents

BACKGROUND

Because of the well-documented increased risk of meningococcal disease among adolescents, vaccination is recommended for this population in many countries, including the United States. This study compared the tolerability and immunogenicity in adolescents of a candidate quadrivalent meningococcal CRM197 glycoconjugate vaccine against serogroups A, C, W-135, and Y (MenACWY-CRM) with that of the licensed unconjugated quadrivalent polysaccharide vaccine (MPSV4).

METHODS

This phase II study was conducted in the United States among 524 adolescents aged 11-17 years in 2 stages, with different randomization schemes. The first 334 participants, enrolled in Stage 1, were randomized (1:1) to receive either MenACWY-CRM(+) (with adjuvant) or MPSV4. The next 190 participants, enrolled in Stage 2, were randomized (4:1) to receive either MenACWY-CRM(-) (without adjuvant) or MPSV4. Safety data were collected using diary cards and active surveillance. Human complement serum bactericidal activity (hSBA) titers were measured 1 and 12 months postvaccination.

RESULTS

MenACWY-CRM and MPSV4 vaccines were well tolerated (local reactions, 63%-71% vs. 60%-62%; systemic reactions, 44%-56% vs. 46%-59%, respectively). One month postvaccination, similar hSBA titers were observed with the adjuvanted and nonadjuvanted MenACWY-CRM. The immunogenicity of MenACWY-CRM(-), measured by geometric mean titer, was significantly (P < 0.05) greater than that of MPSV4 for all 4 vaccine serogroups at 1 month. The percentage of subjects with hSBA titers > or =1:4 was also significantly greater (P < 0.01) for MenACWY-CRM(-) recipients for serogroups A, C, and Y and noninferior for W-135. The proportions of MenACWY-CRM(-) recipients with hSBA titers > or =1:4 to the vaccine serogroups at 1 month were 84% to 96% and geometric mean titers were 34 to 100. The percentage of subjects with hSBA titers > or =1:4 was significantly (P < 0.01) greater than MPSV4 for serogroups C, W-135, and Y 12 months postvaccination.

CONCLUSIONS

MenACWY-CRM was well tolerated and immunogenic, with evidence of persistence of bactericidal antibodies for at least 12 months postvaccination.

Immunochemical termination of self-tolerance

The ability to selectively induce a strong immune response against self-proteins, or increase the immunogenicity of specific epitopes in foreign antigens, would have a significant impact on the production of vaccines for cancer, protein-misfolding diseases, and infectious diseases. Here, we show that site-specific incorporation of an immunogenic unnatural amino acid into a protein of interest produces high-titer antibodies that cross-react with WT protein. Specifically, mutation of a single tyrosine residue (Tyr(86)) of murine tumor necrosis factor-alpha (mTNF-alpha) to p-nitrophenylalanine (pNO(2)Phe) induced a high-titer antibody response in mice, whereas no significant antibody response was observed for a Tyr(86) --> Phe mutant. The antibodies generated against the pNO(2)Phe are highly cross-reactive with native mTNF-alpha and protect mice against lipopolysaccharide (LPS)-induced death. This approach may provide a general method for inducing an antibody response to specific epitopes of self- and foreign antigens that lead to a neutralizing immune response.

Characterization of the IgD binding site of encapsulated Haemophilus influenzae serotype b

Encapsulated Haemophilus influenzae is a causative agent of invasive disease, such as meningitis and septicemia. Several interactions exist between H. influenzae and the human host. H. influenzae has been reported to bind IgD in a nonimmune manner, but the responsible protein has not yet been identified. To define the binding site on IgD for H. influenzae, full-length IgD and four chimeric IgDs with interspersed IgG sequences and Ag specificity for dansyl chloride were expressed in stably transfected Chinese hamster ovary cells. The binding of recombinant IgD to a panel of encapsulated H. influenzae serotype b (Hib) and nontypeable strains were investigated using a whole cell ELISA and flow cytometry. IgD binding was detected in 50% of the encapsulated Hib strains examined, whereas nontypeable H. influenzae did not interact with IgD. Finally, mapping experiments using the chimeric IgD/IgG indicated that IgD CH1 aa 198-224 were involved in the interaction between IgD and H. influenzae. Thus, by using recombinant IgD and chimeras with defined Ag specificity, we have confirmed that Hib specifically binds IgD, and that this binding involves the IgD CH1 region.

CRM197-conjugated serogroup C meningococcal capsular polysaccharide, but not the native polysaccharide, induces persistent antigen-specific memory B cells

Neisseria meningitidis is one of the leading causes of bacterial meningitis and septicemia in children. Vaccines containing the purified polysaccharide capsule from the organism, a T cell-independent antigen, have been available for decades but do not appear to provide protection in infancy or immunologic memory as measured by antibody responses. By contrast, T cell-dependent serogroup C protein-polysaccharide conjugate vaccines protect against serogroup C meningococcal disease from infancy onward and prime for immunologic memory. We compared the magnitude and kinetics of plasma cell and memory B-cell responses to a meningococcal plain polysaccharide vaccine and a serogroup C glycoconjugate vaccine in adolescents previously primed with the conjugate vaccine. Plasma cell kinetics were similar for both vaccines, though the magnitude of the response was greater for the glycoconjugate. In contrast to the glycoconjugate vaccine, the plain polysaccharide vaccine did not induce a persistent immunoglobulin G (IgG) memory B-cell response. This is the first study to directly show that serogroup C meningococcal glycoconjugate vaccines induce persistent production of memory B cells and that plain polysaccharide vaccines do not, supporting the use of the conjugate vaccine for sustained population protection. Detection of peripheral blood memory B-cell responses after vaccination may be a useful signature of successful induction of immunologic memory during novel vaccine evaluation.

The capsular polysaccharide biosynthesis of Streptococcus pneumoniae serotype 8: functional identification of the glycosyltransferase WciS (Cap8H)

CPS (capsular polysaccharide) is a major virulence factor in Streptococcus pneumoniae. Biosynthesis of CPS RU (repeat unit) proceeds by sequential transfer of sugar residues from the appropriate sugar donor to an activated lipid carrier by committed GTs (glycosyltransferases). While the nucleotide sequence of many cps loci is already known, the real substrate specificity of the hypothetical GTs, as well as the sequence of sugar addition is unclear. In the present paper, we report the biochemical characterization of one alpha-galactosyltransferase, WciS (Cap8H), a member of GT family 4. This enzyme is implicated in the tetrasaccharide RU biosynthetic pathway of Strep. pneumoniae CPS 8 ([-->4)-alpha-D-Glcp-(1-->4)-alpha-D-Galp-(1-->4)-beta-D-GlcAp-(1-->4)-beta-D-Glcp-(1-->]n). Expression of WciS-His6 in Escherichia coli BL21 (DE3) strains or BL21 (DE3)/DeltagalU strain resulted in synthesis of a 39 kDa membrane-associated protein identified by N-terminal sequencing and recognized by anti-His6-tag antibody. This protein was capable of adding a galactose residue cellobiuronic acid [beta-D-GlcAp-(1-->4)-D-Glcp]-pyrophosphate-polyprenol from UDP-Gal. The newly added galactose residue is removed by alpha-galactosidase, indicating that WciS is a retaining GT. Our results suggest that WciS catalyses the addition of the third sugar residue of the CPS 8 RU. The recombinant WciS-His6 was solubilized and purified as a soluble multimer, opening the way for structural studies.

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.

Engineering N-linked protein glycosylation with diverse O antigen lipopolysaccharide structures in Escherichia coli

Campylobacter jejuni has a general N-linked protein glycosylation system that can be functionally transferred to Escherichia coli. In this study, we engineered E. coli cells in a way that two different pathways, protein N-glycosylation and lipopolysaccharide (LPS) biosynthesis, converge at the step in which PglB, the key enzyme of the C. jejuni N-glycosylation system, transfers O polysaccharide from a lipid carrier (undecaprenyl pyrophosphate) to an acceptor protein. PglB was the only protein of the bacterial N-glycosylation machinery both necessary and sufficient for the transfer. The relaxed specificity of the PglB oligosaccharyltransferase toward the glycan structure was exploited to create novel N-glycan structures containing two distinct E. coli or Pseudomonas aeruginosa O antigens. PglB-mediated transfer of polysaccharides might be valuable for in vivo production of O polysaccharides-protein conjugates for use as antibacterial vaccines.

Haemophilus influenzae type b conjugate vaccines

Haemophilus influenzae type b (Hib) is one of the leading causes of invasive bacterial infection in young children worldwide. During childhood, acquisition of antibody directed against the polysaccharide capsule of the organism, presumably as a result of asymptomatic carriage, confers protection and disease is much less common after the age of 4 years. Like other polysaccharides, the polyribosyl ribitol phosphate (PRP) of the Hib capsule is a T-independent antigen and not immunogenic when administered as a vaccine in infancy. Because the highest rates of disease occur in the first 2 years of life, efficacious Hib vaccines have been designed by covalently linking the PRP capsule to a carrier protein that recruits T-cell help for the polysaccharide immune response and induces anti-PRP antibody production even in the first 6 months of life. Introduction of Hib protein-polysaccharide conjugate vaccines into many industrialized countries over the past 15 years has resulted in the virtual elimination of invasive Hib disease. However, despite the success of the vaccine programme several factors may interfere with the effectiveness of the vaccine in the routine programme, as observed in the UK recently. Such factors may include interference with other concomitant vaccines, waning immunity in the absence of booster doses of vaccine, and reduced natural boosting as a result of decreased transmission of the organism. However, the burden of disease remains highest in resource-poor countries and urgent efforts are needed to provide the benefits of this vaccine for children living in regions where it cannot be used for economic and logistical reasons.

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.