Enhanced antibody responses in infants given different sequences of heterogeneous Haemophilus influenzae type b conjugate vaccines

A mechanism for glycoconjugate vaccine activation of the adaptive immune system and its implications for vaccine design

Although glycoconjugate vaccines have provided enormous health benefits globally, they have been less successful in significant high-risk populations. Exploring novel approaches to the enhancement of glycoconjugate effectiveness, we investigated molecular and cellular mechanisms governing the immune response to a prototypical glycoconjugate vaccine. In antigen-presenting cells, a carbohydrate epitope is generated upon endolysosomal processing of group B streptococcal type III polysaccharide coupled to a carrier protein. In conjunction with a carrier protein-derived peptide, this carbohydrate epitope binds to major histocompatibility class II (MHCII) and stimulates carbohydrate-specific CD4+ T-cell clones to produce interleukins 2 and 4—cytokines essential for providing T-cell help to antibody-producing B cells. An archetypical glycoconjugate vaccine constructed to maximize the presentation of carbohydrate epitopes recognized by T cells is 50–100 times more potent and significantly more protective in an animal model of infection than is a currently used vaccine construct.

Immediate and longer term immunogenicity of a single dose of the combined haemophilus influenzae type B-Neisseria meningitidis serogroup C-tetanus toxoid conjugate vaccine in primed toddlers 12 to 18 months of age

Hib-primed but MenC-naive toddlers (N = 433) were randomized to receive 1 dose of Hib-MenC-TT or separate Hib-TT and MenC-CRM197 vaccines. One month later, noninferiority was demonstrated for serum bactericidal anti-MenC antibodies (rSBA) and Hib antipolyribosylribitol phosphate (PRP) antibodies; >99% in both groups had rSBA titer ≥ 8 or anti-PRP concentration ≥ 0.15 μg/mL. After 12 months, rSBA titer ≥ 8 persisted in 86.7% and 76.4%, and anti-PRP concentration ≥ 0.15 μg/mL persisted in 98.8% and 100% of children, respectively.

Antigen processing of glycoconjugate vaccines; the polysaccharide portion of the pneumococcal CRM(197) conjugate vaccine co-localizes with MHC II on the antigen processing cell surface

Pneumococcal (Pn) polysaccharides (PS) are T-independent (TI) antigens and do not induce immunological memory or antibodies in infants. Conjugation of PnPS to the carrier protein CRM(197) induces PS-specific antibody in infants, and memory similar to T-dependent (Td) antigens. Conjugates have improved immunogenicity via antigen processing and presentation of carrier protein with MHC II and recruitment of T cell help, but the fate of the PS attached to the carrier is unknown. To determine the location of the PS component of PnPS-CRM(197) in the APC, we separately labeled PS and protein and tracked their location. The PS of types 14-CRM(197) and 19F-CRM(197) was specifically labeled by Alexa Fluor 594 hydrazide (red). The CRM(197) was separately labeled red in a reaction that did not label PS. Labeled antigens were incubated with APC which were fixed, permeabilized and incubated with anti-MHC II antibody labeled green by Alexa Fluor 488, followed by confocal microscopy. Labeled CRM(197) was presented on APC surface and co-localized with MHC II (yellow). Labeled unconjugated 14 or 19F PS did not go to the APC surface, but PS labeled 14-CRM(197) and 19F-CRM(197) was internalized and co-localized with MHC II. Monoclonal antibody to type 14 PS bound to intracellular type 14 PS and PS-CRM(197). Brefeldin A and chloroquine blocked both CRM(197) and PS labeled 14-CRM(197) and 19F-CRM(197) from co-localizing with MHC II. These data suggest that the PS component of the CRM(197) glycoconjugate enters the endosome, travels with CRM(197) peptides to the APC surface and co-localizes with MHC II.

Interchangeability of two diphtheria and tetanus toxoids, acellular pertussis, inactivated poliovirus, Haemophilus influenzae type b conjugate vaccines as a fourth dose in 15–20-month-old toddlers

BACKGROUND

Since 1998, all children in Canada have been immunized with a pentavalent diphtheria and tetanus toxoids, acellular pertussis, inactivated poliovirus, Haemophilus influenzae type b conjugate vaccine (DTaP-IPV-Hib) produced by one manufacturer (Pentacel). Recently, another DTaP-IPV-Hib (Infanrix-IPV-Hib) became available. Data on the interchangeability of these products was lacking.

METHODS

In this multicentered, observer-blind study, healthy 15-20-month-old children previously immunized with three doses of Pentacel were randomly allocated to receive a single dose of Pentacel or Infanrix-IPV-Hib. Adverse events were documented by diary for 7 days post-immunization and unsolicited adverse events were documented for 30 days.

RESULTS

433 participants were enrolled (mean age 17.1 months). Rates of fever, anorexia and irritability were similar in both groups. Injection-site redness >20 mm (11.5% versus 5.6%; p = 0.038), injection-site pain (52.1% versus 39.4%; p = 0.009) and moderate or greater drowsiness (13.8% versus 7.4%; p = 0.042) were more common after Pentacel than Infanrix-IPV-Hib. The proportions of participants who were sero-protected or who sero-responded were similar for all antigens. Geometric mean titers or concentrations were similar for antibodies against diphtheria toxoid and poliovirus type 3. Geometric mean concentrations or titers were higher in the Infanrix-IPV-Hib group against pertussis toxin (88.5 EU/mL versus 65.6 EU/mL), filamentous hemagglutinin (207.3 EU/mL versus 132.1 EU/mL), pertactin (251.9 EU/mL versus 166.9 EU/mL) and poliovirus type 1 (1293.7 versus 976.2 reciprocal dilution). Geometric mean titers or concentrations were higher in the Pentacel group against H. influenzae type b (29 microg/mL versus 19 microg/mL), tetanus toxoid (5.6 IU/mL versus 4.7 IU/mL) and poliovirus type 2 (1437.3 versus 1134.2 reciprocal dilution).

CONCLUSIONS

A booster dose of Infanrix-IPV-Hib after three priming doses of Pentacel is well-tolerated and immunogenic in 15-20-month-old toddlers and can be used interchangeably.

Ventrogluteal area—a suitable site for intramuscular vaccination of infants and toddlers

Buttock vaccination has lower reactogenicity and similar immunogenicity to the two other recommended paediatric vaccination sites (deltoid and anterolateral thigh). Safety concerns about buttock injection derived from injections with neurotoxic agents, like penicillin but not vaccines, have become entrenched. However, the ventrogluteal area is considered safe for intramuscular injection. This study outlines the development of the ventrogluteal area as a suitable site for intramuscular vaccination of infants and toddlers. Measurement was made in 642 children, aged 2-18 months and age-specific templates were prepared. These were used in an untrasonographic study of 57 children aged 2-18 months to determine the tissue composition of the ventrogluteal area compared with the recommended anterolateral thigh vaccination site. The ventrogluteal area was found to be clearly defined by the template and suitable for intramuscular injection. Subsequent vaccination studies with the area showed that it was:

Staphylococcus aureus types 5 and 8 capsular polysaccharide-protein conjugate vaccines

BACKGROUND

Staphylococcus aureus, the first or second most common pathogen isolated from patients, is capsulated; there are at least 12 capsular types, and types 5 and 8 comprise approximately 85% of blood. Types 5 and 8, composed of a trisaccharide repeat unit including a mannose uronic acid and 2 fucoses, are non-immunogenic. As protein conjugates, they induce opsonophagocytic antibodies that confer type-specific active and passive protection in mice.

METHODS

A phase II study of patients with end-stage renal disease showed that these conjugates induced approximately one third of the immunoglobulin G antibody of healthy individuals. Increasing the dose to 100 microg of polysaccharide induced levels similar to that in healthy individuals injected with 25 microg.

RESULTS

In a double-blinded randomized and controlled study of patients undergoing renal dialysis, the conjugates induced statistically significant protection against bacteremia for as long as 10 months after immunization. The estimated protective level was 80 microg Ab/mL. At re-injection approximately 2 years later, 83 of 83 recipients responded with protective levels.

CONCLUSIONS

Conjugate vaccine-induced antibodies to the types 5 and 8 capsular polysaccharide antibodies of S aureus prevent bacteremia caused by this pathogen. The extent and duration of conjugate-induced immunity can be extended by re-immunization approximately 1 year later. Studies of patients undergoing cardiovascular surgery who would be immunized with the staphylococcus conjugates when they are immunologically intact are planned.

Vaccine interchangeability

The recommended childhood immunization schedule is complex, with multiple doses of vaccines required to complete the series. For a variety of reasons, a single manufacturer's product may not be available for all of the doses needed. In addition, combination products may become available, allowing for fewer injections to be administered but resulting in a change of vaccine components. To ensure the timely immunization of children and to avoid missed opportunities to vaccinate, it is important to be familiar with data documenting the interchangeability of vaccines. Although clear evidence is available to demonstrate the interchangeability of some vaccines (i.e., hepatitis B vaccines and Haemophilus influenzae type b vaccines), it is more difficult to evaluate the interchangeability of others (i.e., diphtheria-tetanus-acellular pertussis [DTaP] vaccines). Limited data support the interchangeability of some DTaP products when necessary. This article presents the safety and immunogenicity data for immunization regimens that use vaccines from different manufacturers.

Interchangeability of vaccines

BACKGROUND

The delivery of childhood immunizations can be complex, often requiring numerous injections over months or years to complete the recommended schedule. The ability to interchange similar vaccines from different manufacturers during a vaccination series is important because the product administered previously may be unknown or no longer available.

METHODS

The current vaccine literature was reviewed to identify available data and determine the consensus on the interchangeability of current vaccines.

RESULTS

In the instance of diphtheria-tetanus toxoids-acellular pertussis (DTPa) vaccine, no serologic markers of protective efficacy against Bordetella pertussis exist; therefore it is difficult to evaluate interchangeability of available products. Consequently the ACIP, AAP and AAFP have recommended that the same DTPa product be used for the first three doses of the immunization series. However, if the previously administered product is unknown or not readily available, any licensed DTPa product may be used. More recent data suggest that at least some of the DTPa products have similar immunogenicity and appear to be interchangeable. For other families of vaccines, such as those designed to prevent infection with hepatitis B virus, poliovirus and Haemophilus influenzae type b, there is good evidence attesting to sustained immunogenicity when products from different manufacturers are used to complete a series.

CONCLUSIONS

The use of approved combination vaccine products whenever possible is advocated by the ACIP, AAP and AAFP because such products decrease the number of injections needed to complete the recommended immunizations and may reduce health care costs, improve program performance and aid in documentation of administered vaccines.

Active immunization in the United States: developments over the past decade

The Centers for Disease Control and Prevention has identified immunization as the most important public health advance of the 20th century. The purpose of this article is to review the changes that have taken place in active immunization in the United States over the past decade. Since 1990, new vaccines have become available to prevent five infectious diseases: varicella, rotavirus, hepatitis A, Lyme disease, and Japanese encephalitis virus infection. Improved vaccines have been developed to prevent Haemophilus influenzae type b, pneumococcus, pertussis, rabies, and typhoid infections. Immunization strategies for the prevention of hepatitis B, measles, meningococcal infections, and poliomyelitis have changed as a result of the changing epidemiology of these diseases. Combination vaccines are being developed to facilitate the delivery of multiple antigens, and improved vaccines are under development for cholera, influenza, and meningococcal disease. Major advances in molecular biology have enabled scientists to devise new approaches to the development of vaccines against diseases ranging from respiratory viral to enteric bacterial infections that continue to plague the world's population.

Carrier-mediated enhancement of cognate T cell help: the basis for enhanced immunogenicity of meningococcal outer membrane protein polysaccharide conjugate vaccine

Haemophilus influenzae type b capsular polysaccharide (PRP) conjugate vaccines, which are thought to induce T cell-dependent antibody production, induce protective responses after a single dose in individuals under 15 months of age. However, multiple doses of these vaccines are required to induce protective antibody responses in infants, with the exception of PRP conjugated to meningococcal outer membrane proteins (OMPC), which does so after a single dose. The basis for this difference is not fully understood, although others have proposed that OMPC and porins, the major protein component of OMPC, act as adjuvants or mitogens. In this report OMPC is shown to enhance CD40 ligand-mediated, T cell-dependent antibody production in mice. This paralleled the induction by OMPC of CD86, CD80 and CD40 costimulatory molecules on human neonatal and murine B cells and of Th1 cytokines. Neither porins nor lipopolysaccharide fully reproduced the effects of OMPC. These studies indicate that OMPC acts both as carrier and adjuvant, and thereby enhances T cell-dependent antibody responses in human infants.

Experience with the prevention of invasive Haemophilus influenzae type b disease by vaccination in Alaska: the impact of persistent oropharyngeal carriage

OBJECTIVES

To report the epidemiology of invasive Haemophilus influenzae type b (Hib) disease in high-risk Alaska Native infants before and after universal infant Hib vaccination and evaluate an increase in invasive Hib disease in 1996 after changing Hib vaccine type.

STUDY DESIGN

Statewide laboratory surveillance for invasive Hib disease has been conducted since 1980. Three cross-sectional Hib carriage studies were conducted in 1997 and 1998.

RESULTS

The invasive Hib disease rate in Alaska Natives decreased from 332 cases per 100,000 children <5 years old in 1980-1991 to 17:100,000 in 1992-1995 but increased primarily in rural areas to 57.9:100,000 after a switch in Hib vaccine types. Carriage studies in 5 rural Alaska Native villages showed oropharyngeal Hib carriage as high as 9.3% in children aged 1 to 5 years; in contrast, carriage in urban Alaska Native children was <1%.

CONCLUSIONS

Although Hib disease has decreased in Alaska, the rate of Hib disease and carriage in rural Alaska Natives did not decrease to the same extent as in non-Natives and urban Alaska Natives. Use of polyribosylribitol phosphate-outer-membrane protein conjugate vaccine for the first vaccine dose is critical to disease control in this population with continued transmission in infants <6 months of age. The ability to eliminate Hib carriage and disease may be affected by population characteristics, vaccination coverage, and Hib vaccine type used. This may pose a challenge to global elimination of Hib.

Cellular immune responses to Neisseria meningitidis in children

There is an urgent need for effective vaccines against serogroup B Neisseria meningitidis. Current experimental vaccines based on the outer membrane proteins (OMPs) of this organism provide a measure of protection in older children but have been ineffective in infants. We postulated that the inability of OMP vaccines to protect infants might be due to age-dependent defects in cellular immunity. We measured proliferation and in vitro production of gamma interferon (IFN-gamma), tumor necrosis factor alpha, and interleukin-10 (IL-10) in response to meningococcal antigens by peripheral blood mononuclear cells (PBMCs) from children convalescing from meningococcal disease and from controls. After meningococcal infection, the balance of cytokine production by PBMCs from the youngest children was skewed towards a TH1 response (low IL-10/IFN-gamma ratio), while older children produced more TH2 cytokine (higher IL-10/IFN-gamma ratio). There was a trend to higher proliferative responses by PBMCs from older children. These responses were not influenced by the presence or subtype of class 1 (PorA) OMP or by the presence of class 2/3 (PorB) or class 4 OMP. Even young infants might be expected to develop adequate cellular immune responses to serogroup B N. meningitidis vaccines if a vaccine preparation can be formulated to mimic the immune stimulus of invasive disease, which may include stimulation of TH2 cytokine production.

Conjugated polysaccharide vaccines

The joining of polysaccharide antigens to various proteins can result in increased immunogenicity of vaccines composed of such antigens. This article discusses conjugated polysaccharide vaccines for Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitis. Increased availability and use of such vaccines may result in the ability to give more effective vaccines earlier in life, further reducing the incidence of diseases caused by these organisms.

Haemophilus influenzae type b vaccines: history, choice and comparisons

The conjugate Haemophilus influenzae type b (Hib) vaccines are safe and far more immunogenic among infants and young children than is the unconjugated H. influenzae type b polysaccharide. The vaccines differ in their immunogenicity when used for primary immunization of infants, and these differences appear to be predictive of efficacy, such that some vaccines might be more suitable than others in certain populations.

A strategy for rational design of fully synthetic glycopeptide conjugate vaccines

The present study describes a strategy to rationally design fully synthetic glycopeptide conjugate vaccines. Glycopeptide immunogens were constructed by coupling synthetic oligosaccharides comprising repeating units of synthetic 3-beta-D-ribose-(1-1)-D-ribitol-5-phosphate (sPRP) to synthetic peptides containing potent T-helper cell determinants and B-cell epitopes of the Haemophilus influenzae type b (Hib) outer membrane proteins (OMPs) P1, P2, and P6. Rabbit immunogenicity studies revealed that some of these fully synthetic glycoconjugates were capable of eliciting high titers of both anti-PRP and anti-OMP immunoglobulin G antibodies. In addition, we systematically investigated the factors which could influence their immunogenicity. We observed that the magnitude of the anti-PRP antibody response markedly depended on the relative spatial orientation of sPRP and T-cell epitopes, the anti-PRP antibody response was enhanced when a multiple antigenic peptide was used as a carrier, the anti-PRP antibody response was optimal for three PRP repeating units, and lipidation of peptide-PRP conjugates had a minimal effect on the magnitude of the anti-PRP antibody response. The results of this study clearly demonstrate that coupling a carbohydrate hapten to a peptide can provide T-cell help and convert it into a T-cell-dependent antigen. The antisera raised against these conjugates were also found to be protective against Hib infection in the infant rat model of bacteremia.

The increasing burden of disease in Bangladeshi children due to Haemophilus influenzae type b meningitis

A laboratory-based study of diagnosed bacterial meningitis in the national paediatric hospital identified 852 cases of meningitis in the 8-year period 1987-1994. There were 587 culture-positive cases, of which Haemophilus influenzae (47%) and Streptococcus pneumoniae (32%) accounted for 80%. H. influenzae showed a remarkable increase of 700% during the study period. Most of the H. influenzae cases (90%) occurred in the 1st 2 years of life. Analysis of culture-negative specimens by antigen detection in the last 2 years also revealed the predominance of H. influenzae (71.4%) and S. pneumoniae (22.4%). Typing of H. influenzae isolates during this time showed that 98% of the strains were type b. This retrospective hospital-based study indicated a pronounced increase in the incidence of H. influenzae meningitis and strongly supports the need for large-scale Hib vaccination for young children. However, such nationwide intervention will probably need to be based on a prospective on a prospective and population-based surveillance of H. influenzae infections.

Chemical synthesis of Haemophilus influenzae glycopeptide conjugates

A simple procedure for conjugating synthetic fragments of the capsular polysaccharide of Haemophilus influenzae type b, poly-3-beta-D-ribose-(1,1)-D-ribitol-5-phosphate (sPRP) to linear peptides is described. The procedure consists of (i) reacting the amino group of amino-heptyl sPRP with m-maleimidobenzoyl-N-hydroxysuccinimide (MBS) in phosphate buffer, pH 7.5; (ii) selectively coupling the MBS-modified sPRP to the sulfhydryl group of the cysteine residue of peptides containing functional T-helper cell epitope(s). The glycopeptide conjugates were purified by gel filtration chromatography, biochemically characterized, and elicited protective level of anti-PRP antibody responses in rabbits.

Effect of neonatal immunization with diphtheria and tetanus toxoids on antibody responses to Haemophilus influenzae type b conjugate vaccines

We randomly assigned 150 newborn infants to receive diphtheria and tetanus toxoids (DT) or Hib oligosaccharide conjugate (HbOC) at birth to determine whether exposure to the Haemophilus influenzae type b (Hib) conjugate vaccines' carrier proteins would enhance immune responses to subsequent administrations of HbOC or PRP-tetanus toxoid conjugate (PRP-T) at 2, 4, and 6 months of age. Their antibody responses were compared with those of 100 children immunized with HbOC or PRP-T beginning at 2 months of age. No serious adverse reactions were associated with neonatal vaccination. Administration of HbOC at birth did not lead to earlier or higher antibody levels. Newborn immunization with DT did not prime children for enhanced antibody responses. Moreover, Hib antibody levels were lower in DT-primed children than in children immunized beginning at 2 months of age. Diphtheria antibody levels, but not tetanus antibody levels, were also lower in children immunized with DT at birth. We conclude that neonatal immunization with Hib conjugate vaccines is not a means to provide earlier protection against invasive Hib disease. Newborn DT administration does not enhance subsequent antibody responses to Hib conjugate vaccines, and may lead to suppression of Hib and diphtheria antibody responses.