Priming with diphtheria-tetanus-pertussis vaccine enhances the response to the Haemophilus influenzae type b tetanus conjugate vaccine in infancy

Peptide adjacent to glycosylation sites impacts immunogenicity of glycoconjugate vaccine

Glycoconjugate vaccine is composed of polysaccharides (PSs) covalently linked with carrier protein. Glycosylation site selection, as a significant factor leading to heterogeneities of glycoconjugate structure, draws more and more attentions for its impact on the immunogenicity of glycoconjugate vaccine. To elucidate the relationship between glycosylation connectivity and immunogenicity of glycoconjugate vaccine, in this study, anti-E. coli O157:H7 glycoconjugate O-PS-MBP with defined connectivity, and three selected peptide segments GS1, GS2, GS3 derived from O-PS-MBP was synthesized. Immunogenicity results showed that only peptides adjacent to the glycosylation sites (GS1 and GS2) promoted the generation of PS-specific IgG antibodies and contributed to PS-specific IgG subclass distribution. Furthermore, GS1 and GS2 had significant priming effect for eliciting PS-specific IgG antibodies. These results indicated that different locations of glycosylation sites could lead to diverse presentation of peptides and glycopeptides to APCs and influence the immunogenicity of glycoconjugate vaccine, which extend the current understanding of mechanism for adaptive immune system activation by glycoconjugate vaccine, and have implications for rational glycoconjugate vaccine design.

Tetanus-diphtheria-pertussis vaccine may suppress the immune response to subsequent immunization with pneumococcal CRM197-conjugate vaccine (coadministered with quadrivalent meningococcal TT-conjugate vaccine): a randomized, controlled trial⋆

BACKGROUND

: Due to their antigenic similarities, there is a potential for immunological interaction between tetanus/diphtheria-containing vaccines and carrier proteins presented on conjugate vaccines. The interaction could, unpredictably, result in either enhancement or suppression of the immune response to conjugate vaccines if they are injected soon after or concurrently with diphtheria or tetanus toxoid. We examined this interaction among adult Australian travellers before attending the Hajj pilgrimage of 2015.

METHODS

We randomly assigned each participant to one of three vaccination schedules. Group A received tetanus, diphtheria and acellular pertussis vaccine (Tdap) 3-4 weeks before receiving CRM197-conjugated 13-valent pneumococcal vaccine (PCV13) coadministered with TT-conjugated quadrivalent meningococcal vaccine (MCV4). Group B received all three vaccines concurrently. Group C received PCV13 and MCV4 3-4 weeks before Tdap. Blood samples collected at baseline, at each vaccination visit and 3-4 weeks after vaccination were tested for the pneumococcal opsonophagocytic assay (OPA).

RESULTS

A total of 166 participants aged 18-64 (median 42) years were recruited, 159 completed the study. Compared with the other groups, Group A had significantly ( P  <   0.05) lower geometric mean titres (GMTs) post-vaccination in seven serotypes of PCV13 (1, 3, 4, 5, 14, 18C and 9V). Additionally, Group A had lower frequency of serorises (≥ 4-fold rise in OPA titres) in serotype5 (79%, p = 0.01) and 18C (73.5%, p = 0.06); whereas Groups B and C had significantly lower frequencies of serorises in Serotype 4 (82%) and 6A (73.5%), respectively. No statistically significant difference was detected across the three groups in frequencies achieving OPA titre ≥ 1:8 post-vaccination.

CONCLUSIONS

Tdap vaccination 3-4 weeks before administration of PCV13 and MCV4 significantly reduced the GMTs to seven of the 13 pneumococcal serotypes in adults. If multiple vaccination is required before travel, deferring tetanus/diphtheria until after administering the conjugate vaccine is recommended to avoid immune interference.

Effect of Tdap when administered before, with or after the 13-valent pneumococcal conjugate vaccine (coadministered with the quadrivalent meningococcal conjugate vaccine) in adults: A randomised controlled trial

Sequential or co-administration of vaccines has potential to alter the immune response to any of the antigens. Existing literature suggests that prior immunisation of tetanus/diphtheria-containing vaccines can either enhance or suppress immune response to conjugate pneumococcal or meningococcal vaccines. We examined this interaction among adult Australian travellers before attending the Hajj pilgrimage 2014. We also investigated tolerability of these vaccines separately and concomitantly. We randomly assigned each participant to one of three vaccination schedules. Group A received adult tetanus, diphtheria and acellular pertussis vaccine (Tdap) 3-4weeks before receiving CRM197-conjugated 13-valent pneumococcal vaccine (PCV13) and CRM197-conjugated quadrivalent meningococcal vaccine (MCV4). Group B received all three vaccines on one day. Group C received PCV13 and MCV4 3-4weeks before Tdap. Blood samples collected at baseline, each vaccination visit and 3-4weeks after vaccination were tested using the pneumococcal opsonophagocytic assay (OPA) and by ELISA for diphtheria and tetanus antibodies. Funding for meningococcal serology was not available. Participants completed symptom diaries after each vaccination. A total of 111 participants aged 18-64 (median 40) years were recruited. No statistically significant difference was detected across the three groups in achieving OPA titre ⩾1:8 post vaccination. However, compared to other groups, Group A had a statistically significant lower number of subjects achieving ⩾4-fold rise in serotype 3, and also significantly lower geometric mean titres (GMTs) to six (of 13) pneumococcal serotypes (3, 5, 18C, 4, 19A and 9V). Group C (given prior PCV13 and MVC4) had statistically significant higher pre-Tdap geometric mean concentration (GMC) of anti-diphtheria IgG; however, there was no difference across the three groups following Tdap. Anti-tetanus IgG GMCs were similar across the groups before and after Tdap. No serious adverse events were reported. In conclusion, Tdap vaccination 3-4weeks before concomitant administration of PCV13 and MCV4 significantly reduced the antibody response to six of the 13 pneumococcal serotypes in adults. The trial is registered at the Australian New Zealand Clinical Trials Registry (ANZCTR): ACTRN12613000536763.

Carrier priming to improve pneumococcal disease control and reduce the international program's cost in children

Pneumococcal conjugate vaccine (PCV) has the potential to interact with other vaccines containing diphtheria toxin-like antigens (such as those found in the DTP vaccine) upon sequential administration. This is attributed to the similarity of the diphtheria toxoid antigen to the carrier protein used to make PCV, (known as cross reactive material [CRM]) to diphtheria toxin ₁₉₇ or CRM₁₉₇. The interaction could lead to enhanced immunogenicity of PCV as a result of a phenomenon called carrier priming, whereby DTP is given some weeks before the first dose of PCV. This phenomenon could be implemented in the immunisation schedule in developing countries and among vulnerable populations to enhance the immunogenicity of PCV, reduce the number of doses required, and produce a more cost-effective immunisation program in developing countries.

Potential carrier priming effect in Australian infants after 7-valent pneumococcal conjugate vaccine introduction

AIM: To investigate evidence of clinical protection in infants after one dose of 7-valent pneumococcal conjugate vaccine (7vPCV) owing to carrier priming.

METHODS: Using Australian National Notifiable Diseases Surveillance System data, we conducted a descriptive analysis of cases of vaccine type invasive pneumococcal disease (VT-IPD) during “catch-up” years, when 7vPCV was carrier primed by prior administration of DTPa vaccine. We compared the number of VT-IPD cases occurring 2-9 wk after a single dose of 7vPCV (carrier primed), with those < 2 wk post vaccination, when no protection from 7vPCV was expected yet. Further comparison was conducted to compare the occurrence of VT-IPD cases vs non-VT-IPD cases after a single carrier-primed dose of 7vPCV.

RESULTS: We found four VT-IPD cases occurring < 2 wk after one carrier primed dose of 7vPCV while only one case occurred 2-9 wk later. Upon further comparison with the non-VT-IPD cases that occurred after one carrier primed dose of 7vPCV, two cases were detected within 2 wk, whereas seven occurred within 2-9 wk later; suggesting a substantial level of protection from VT-IPD occurring from 2 wk after carrier-primed dose of 7vPCV.

CONCLUSION: This data suggest that infants may benefit from just one dose of 7vPCV, likely through enhanced immunity from carrier priming effect. If this is proven, an adjusted 2-dose schedule (where the first dose of PCV is not given until after DTPa) may be sufficient and more cost-effective.

Carrier priming or suppression: understanding carrier priming enhancement of anti-polysaccharide antibody response to conjugate vaccines

INTRODUCTION

With the availability of newer conjugate vaccines, immunization schedules have become increasingly complex due to the potential for unpredictable immunologic interference such as 'carrier priming' and 'carrier induced epitopic suppression'. Carrier priming refers to an augmented antibody response to a carbohydrate portion of a glycoconjugate vaccine in an individual previously primed with the carrier protein. This review aims to provide a critical evaluation of the available data on carrier priming (and suppression) and conceptualize ways by which this phenomenon can be utilized to strengthen vaccination schedules.

METHODS

We conducted this literature review by searching well-known databases to date to identify relevant studies, then extracted and synthesized the data on carrier priming of widely used conjugate polysaccharide vaccines, such as, pneumococcal conjugate vaccine (PCV), meningococcal conjugate vaccine (MenCV) and Haemophilus influenzae type b conjugate vaccines (HibV).

RESULTS

We found evidence of carrier priming with some conjugate vaccines, particularly HibV and PCV, in both animal and human models but controversy surrounds MenCV. This has implications for the immunogenicity of conjugate polysaccharide vaccines following the administration of tetanus-toxoid or diphtheria-toxoid containing vaccine (such as DTP).

CONCLUSION

Available evidence supports a promising role for carrier priming in terms of maximizing the immunogenicity of conjugate vaccines and enhancing immunization schedule by making it more efficient and cost effective.

Immunogenicity of a promiscuous T cell epitope peptide based conjugate vaccine against benzo[a]pyrene: redirecting antibodies to the hapten

The prototype polycyclic aromatic hydrocarbon benzo[a]pyrene (B[a]P) is an environmental pollutant and food contaminant of epidemiological importance. To protect against adverse effects of this ubiquitous carcinogen, we developed an immunoprophylactic strategy based on a B[a]P-protein conjugate vaccine to induce B[a]P specific antibodies (Grova et al., Vaccine. 2009;27:4142-51). Here, we investigated in mice the efficacy of B[a]P-peptide conjugates based on promiscuous T cell epitopes (TCE) into further improve this approach. We showed that B[a]P-peptide conjugates induced very different levels of hapten-specific antibodies with variable functional efficacy, depending on the carrier. In some cases peptide carriers induced a more efficient antibody response against B[a]P than tetanus toxoid as a protein carrier, with the capacity to sequester more B[a]P in the blood. Reducing the carrier size to a single TCE can dramatically shift the antibody bias from the carrier to the B[a]P. Conjugates based on the TCE FIGITEL induced the best anti-hapten response and no antibodies against the carrier peptide. Some peptide conjugates increased the selectivity of the antibodies for the activated metabolite 7,8-diol-B[a]P and B[a]P by one or two orders of magnitude. The antibody efficacy was also demonstrated in their ability to sequester B[a]P in the blood and modulate its faecal excretion (15-56%). We further showed that pre-existing immunity to the carrier from which the TCE was derived did not reduce the immunogenicity of the peptide conjugate. In conclusion, we showed that a vaccination against B[a]P using promiscuous TCEs of tetanus toxin as carriers is feasible even in case of a pre-existing immunity to the toxoid and that some TCE epitopes dramatically redirect the antibody response to the hapten. Further studies to demonstrate a long-term protection of an immunoprophylactic immunisation against B[a]P are warranted.

Recent advances in developing synthetic carbohydrate-based vaccines for cancer immunotherapies

Cancer cells can often be distinguished from healthy cells by the expression of unique carbohydrate sequences decorating the cell surface as a result of aberrant glycosyltransferase activity occurring within the cell; these unusual carbohydrates can be used as valuable immunological targets in modern vaccine designs to raise carbohydrate-specific antibodies. Many tumor antigens (e.g., GM2, Ley, globo H, sialyl Tn and TF) have been identified to date in a variety of cancers. Unfortunately, carbohydrates alone evoke poor immunogenicity, owing to their lack of ability in inducing T-cell-dependent immune responses. In order to enhance their immunogenicity and promote long-lasting immune responses, carbohydrates are often chemically modified to link to an immunogenic protein or peptide fragment for eliciting T-cell-dependent responses. This review will present a summary of efforts and advancements made to date on creating carbohydrate-based anticancer vaccines, and will include novel approaches to overcoming the poor immunogenicity of carbohydrate-based vaccines.

A polyvalent vaccine for high-risk prostate patients: "are more antigens better?"

We have shown the immunogenicity and safety of synthetic carbohydrate vaccines when conjugated to the carrier keyhole limpet hemocyanin (KLH) and given with the adjuvant, QS-21, in patients with biochemically relapsed prostate cancer. To determine whether immune response could be further enhanced with stimulation by multiple antigens, a hexavalent vaccine was prepared using previously determined doses and administered in a Phase II setting to 30 high-risk patients. The hexavalent vaccine included GM2, Globo H, Lewis(y), glycosylated MUC-1-32mer and Tn and TF in a clustered formation, conjugated to KLH and mixed with QS-21. Eight vaccinations were administered over 13 months. All 30 patients had significant elevations in antibody titers to at least two of the six antigens; 22 patients had increased reactivity with FACS. These serologic responses were lower than that seen previously in patients treated with the respective monovalent vaccines. The reciprocal median combined IgM and IgG antibody titers with ELISA against MUC1, Tn, TF, globo H and GM2 for these 30 patients were 640, 80, 120, 40 and 0, compared to 1280, 640, 1280, 320 and 160 seen in patients receiving individual monovalent vaccines. This hexavalent vaccine of synthetic "self" antigens broke immunologic tolerance against two or more antigens in all 30 vaccinated patients, was safe, but antibody titers against several of the antigens were lower than those seen in individual monovalent trials. No impact on PSA slope was detected. We address the relevance of the multivalent approach for prostate cancer treatment.

The nature and consequences of intra- and inter-vaccine interference

Vaccine interference may be intra- or inter-vaccine in nature. Intra-vaccine interference is determined by the nature and dose of the individual vaccine valences, the nature and quality of any additives and the pharmaceutical formulation of the product. Additionally, vaccinee factors including the presence of pre-existing immunity, the stage of immunological maturation, genetic and environmental background may also determine interference. The vaccine schedule and mode of delivery are further contributory factors. In practice, the phenomenon of vaccine interference argues that individual vaccines should not be combined or associated in the absence of specific data sheet recommendations to do so.

Effect of probiotics on vaccine antibody responses in infancy--a randomized placebo-controlled double-blind trial

Probiotics are immunomodulatory and may thus affect vaccine antibody responses. With the accumulating evidence of their health-promoting effects, probiotics are increasingly administered in allergy-prone infants. Therefore, we studied the effect of probiotics on antibody responses to diphtheria, tetanus and Haemophilus influenzae type b (Hib) vaccines in 6-month-old infants participating in a randomized placebo-controlled double-blind allergy-prevention trial. Mothers of unborn children at increased risk for atopy used a combination of four probiotic strains, or a placebo, for 4 wk before delivery. During 6 months from birth, their infants received the same probiotics and galacto-oligosaccharides, or a placebo. The infants were immunized with a DTwP (diphtheria, tetanus and whole cell pertussis) at ages 3, 4, and 5 months, and with a Hib polysaccharide conjugate at 4 months. Serum diphtheria, tetanus, and Hib IgG antibodies were measured at 6 months. In the probiotic group, protective Hib antibody concentrations (>/=1 microg/ml) occurred more frequently, 16 of 32 (50%) vs. six of 29 (21%) (p = 0.020), and the geometric mean (inter-quartile range) Hib IgG concentration tended to be higher 0.75 (0.15-2.71) microg/ml than in the placebo group 0.40 (0.15-0.92) microg/ml (p = 0.064). In these respective groups, diphtheria, 0.38 (0.14-0.78) vs. 0.47 (0.19-1.40) IU/ml (p = 0.449), and tetanus, 1.01(0.47-1.49) vs. 0.81 (0.56-1.39) IU/ml (p = 0.310), IgG titers were comparable. In conclusion, in allergy-prone infants probiotics seem not to impair antibody responses to diphtheria, tetanus, or Hib, but may improve response to Hib immunization.

Immunogenicity and reactogenicity of primary immunization with a hexavalent diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated polio-Haemophilus influenzae type B vaccine coadministered with two doses of a meningococcal C-tetanus toxoid conjugate vaccine

BACKGROUND

This study evaluated the concurrent use of meningococcal C tetanus conjugate (MenC-TT) vaccine (NeisVac-C) with DTaP-based combinations, according to 2 vaccination schedules, one of which included hepatitis B vaccination at birth (Trial DTaP-HBV-IPV/Hib-097).

METHODS

Healthy infants were randomized to receive either DTaP-HBV-IPV/Hib (Infanrix hexa) at 2, 4, and 6 months (N = 115) or HBV at birth followed by DTaP-HBV-IPV/Hib at 2 and 6 months and DTaP-IPV/Hib (Infanrix-IPV Hib) at 4 months (N = 115). In both groups 2 doses of MenC-TT conjugate were coadministered at 2 and 4 months, and compared with 3 doses of MenC-CRM197 conjugate (Meningitec) coadministered at 2, 4, and 6 months with DTaP-HBV-IPV/Hib (N = 120). Antibody concentrations were measured at 2, 6 and 7 months. Solicited local and general symptoms, unsolicited symptoms, and serious adverse events (SAEs) were recorded.

RESULTS

All MenC-TT recipients had seroprotective concentrations of anti-PRP antibodies (> or = 0.15 microg/mL) 1 month after the third vaccine dose and all had SBA-MenC titers > or = 1:8 after the second dose of MenC-TT. These responses were noninferior to those seen after 3 doses of DTaP-HBV-IPV/Hib and MenC-CRM. Anti-PRP antibody GMCs were significantly higher in MenC-TT than MenC-CRM vaccinees (7.9, 7.3, 3.8 microg/mL, respectively). Immune responses to all other coadministered antigens were unimpaired, with seroprotection/seropositivity rates > or = 98.1% in MenC-TT vaccinees. All schedules studied were well tolerated, with no differences in reactogenicity between the study groups.

CONCLUSIONS

Coadministration of DTaP-HBV-IPV/Hib or DTaP-IPV/Hib with 2 doses of MenC-TT conjugate vaccine is safe, well tolerated, and immunogenic, with no impairment of the response to the coadministered antigens.

Antibodies against Haemophilus influenzae type b capsular polysaccharide and tetanus toxoid before and after a booster dose of the carrier protein nine years after primary vaccination with a protein conjugate vaccine

IgG antibodies against Haemophilus influenzae type b (Hib) capsular polysaccharide (CPS) and tetanus toxoid (TT) were measured for 53 children, 10 years of age, before and 1 month after a booster dose of diphtheria-tetanus vaccine (DT). All children had been vaccinated at 3, 5 and 12 months of age with DT and a Hib-TT conjugate. Geometric mean concentrations of Hib CPS serum IgG antibody were 4.16 and 4.30 microg/mL before and after the DT booster, respectively. The geometric mean concentration of TT IgG antibody increased from 0.09 IU/mL to 4.58 IU/mL (P < 0.001). Hib CPS IgG levels remained well above protective titers for 9 years after 3 doses of Hib-TT appropriately spaced in infancy. A booster dose of TT did not affect Hib CPS antibody concentrations but induced a pronounced IgG response against TT.

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.

Humoral immune responses to a protective peptide-conjugate against measles after different prime-boost regimens

The current live-attenuated measles vaccine leaves many children unprotected until they reach the recommended age of vaccination. We have previously shown that the short peptide corresponding to the hemagglutinin noose epitope (HNE) of the measles virus (MV) hemagglutinin protein induced virus-neutralizing antibodies even in the presence of protective levels of anti-whole virus-specific antibodies. Here we investigate the immunogenicity of HNE peptide-conjugates of diphtheria or tetanus toxoid in mice after active and passive priming with antibodies against the peptide, toxoids and conjugates. Both conjugates induced high titers of peptide antibodies which crossreacted with the virus and protected against a lethal intracranial challenge with a rodent-adapted measles virus, even after active priming with homologous or heterologous toxoid or conjugate. Peptide-specific epitopic suppression was stronger after passive priming with carrier or conjugate antibodies, but diphtheria toxoid as a carrier was less susceptible to suppression than tetanus toxoid and suppression was overcome by an additional boost. Furthermore, prior immunization with peptide-conjugate did not interfere with the development of a complete response to a subsequent injection of MV, suggesting that the benefits of a follow-up vaccination with the current live-attenuated vaccine would not be lost. These results underline the potential of these peptide-based conjugates as vaccine candidates for use in early infancy to close the window of susceptibility before the live-attenuated vaccine can be administered.

Does antigenic overload exist? The role of multiple immunizations in infants

There is no evidence that currently recommended vaccines overload or weaken the infant immune system. Infants have an enormous capacity to respond safely and effectively to multiple vaccines. The schedule for the administration of childhood vaccines is tailored to the unique developmental pattern of the infant immune system. Childhood vaccines provide immediate protection from common childhood illness and establish the foundation for lifelong immunity that develops with subsequent vaccination or infection. Widespread vaccination of infants and children represents a public health triumph of the 20th century. This fact must be reinforced continually by health care workers and parent education to help maintain progress in the 21st century.

Greater antibody responses to an eleven valent mixed carrier diphtheria- or tetanus-conjugated pneumococcal vaccine in Filipino than in Finnish or Israeli infants

BACKGROUND

Antibody responses to pneumococcal conjugate vaccines may vary when administered in different populations or epidemiologic settings. Understanding the causes and significance of this variation could help to determine the number of doses and timing required for protection against pneumococcal diseases in each country.

METHODS

This report compares antibody responses to aluminum-adjuvanted and nonadjuvanted mixed carrier 11-valent diphtheria- or tetanus-conjugated pneumococcal vaccine (11-PncTD) formulations when given at 6, 10 and 14 weeks and 9 months of age to Filipino infants (n = 51) and at 2, 4, 6 and 12 months of age to Finnish (n = 127) and Israeli (n = 124) infants. The study populations differ in their natural exposure to pneumococcus and risk factors for pneumococcal carriage and disease.

RESULTS

Filipino and Israeli infants had slightly but significantly higher prevaccination geometric mean concentration (GMC) of antibodies than did the Finnish infants. After three doses of aluminum-adjuvanted 11-PncTD vaccine, the Filipino infants had 1.8 to 6.7 and 1.5 to 5.0 times higher GMC than the Finnish and Israeli infants, respectively, against pneumococcal serotypes conjugated to tetanus protein. The GMC of serotypes conjugated to diphtheria toxoid was 1.3 to 3.0 and 0.7 to 2.0 times the GMC in Finnish and Israeli infants, respectively. The nonadjuvanted vaccine formulation induced generally lower GMCs.

CONCLUSIONS

The antibody responses to the tetanus-conjugated polysaccharides were considerably higher in the Filipino than in the Finnish or Israeli infants. This may be a result of several factors including the priming effect of tetanus toxoid given to pregnant women, early pneumococcal nasopharyngeal acquisition and genetic differences among populations.

On the power of chemical synthesis: immunological evaluation of models for multiantigenic carbohydrate-based cancer vaccines

Synthetic carbohydrate cancer vaccines have been shown to stimulate antibody-based immune responses in both preclinical and clinical settings. The antibodies have been observed to react in vitro with the corresponding natural carbohydrate antigens expressed on the surface of tumor cells, and are able to mediate complement-dependent and/or antibody-dependent cell-mediated cytotoxicity. Furthermore, these vaccines have proven to be safe when administered to cancer patients. Until recently, only monovalent antigen constructs had been prepared and evaluated. Advances in total synthesis have now enabled the preparation of multivalent vaccine constructs, which contain several different tumor-associated carbohydrate antigens. Such constructs could, in principle, serve as superior mimics of cell surface antigens and, hence, as potent cancer vaccines. Here we report preclinical ELISA-based evaluation of a TF-Le(y)-Tn bearing construct (compound 3) with native mucin glycopeptide architecture and a Globo-H-Le(y)-Tn glycopeptide (compound 4) with a nonnative structure. Mice were immunized with one or the other of these constructs as free glycopeptides or as keyhole lymphet hemocyanin conjugates. Either QS-21 or the related GPI-0100 were coadministered as adjuvants. Both keyhole lymphet hemocyanin conjugates induced IgM and IgG antibodies against each carbohydrate antigen, however, the mucin-based TF-Le(y)-Tn construct was shown to be less antigenic than the unnatural Globo-H-Le(y)-Tn construct. The adjuvants, although related, proved significantly different, in that GPI-0100 consistently induced higher titers of antibodies than QS-21. The presence of multiple glycans in these constructs did not appear to suppress the response against any of the constituent antigens. Compound 4, the more antigenic of the two constructs, was also examined by fluorescence activated cell sorter analysis. Significantly, from these studies it was shown that antibodies stimulated in response to compound 4 reacted with tumor cells known to selectively express the individual antigens. The results demonstrate that single vaccine constructs bearing several different carbohydrate antigens have the potential to stimulate a multifaceted immune response.

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.

Comparison of antibody titers after immunization with monovalent or tetravalent KLH conjugate vaccines

Antigens such as ganglioside GD3, neutral glycolipid Lewis(y) (Le(y)) and mucins MUC1 and MUC2 are over-expressed on the cell surface of many tumors. We have shown previously that conjugation of antigens such as these to keyhole limpet hemocyanin (KLH) and the use of immunological adjuvant QS-21 is the optimal approach for inducing high titer IgM and IgG antibodies. These antibodies are able to bind with natural antigens on the tumor cell surface and mediate complement dependent cytotoxicity and/or antibody dependent cell mediated cytotoxicity. Immunization of patients with monovalent vaccines containing these and a variety of other antigens have demonstrated both the consistent immunogenicity and the safety of these vaccines. Now, in preparation for the use of polyvalent conjugate vaccines in the clinic, we have addressed for the first time with conjugate vaccines against cancer antigens several questions in the pre-clinical setting, including whether immunogenicity of the individual components is decreased in the polyvalent vaccine and issues relating to vaccine formulation and administration. We have immunized groups of mice with GD3-KLH, Le(y)-KLH, MUC1-KLH and MUC2-KLH conjugates and QS-21 separately or mixed and administered at one or four sites. High titer IgM and IgG antibodies were induced against each of the four antigens whether administered singly in separate mice, at separate sites in the same mice, or mixed and administered at a single site or at four sites, or administered subcutaneously (s.c.) or intraperitoneally (i.p.). These antibodies reacted specifically with the respective antigens and tumor cells expressing these antigens. There was no evidence of suppression of the antibody response against any one of the antigens by the presence of the other conjugates in the vaccine. Immunogenicity of the four individual antigens conjugated to KLH and QS-21 is not affected by mixing the four together and administering them at a single subcutaneous site.

Effect of pre-existing immunity for systemic and mucosal immune responses to intranasal immunization with group B Streptococcus type III capsular polysaccharide-cholera toxin B subunit conjugate

The effects of priming with a group B Streptococcus type III capsular polysaccharide (GBS CPS III)-recombinant cholera toxin B subunit (rCTB) conjugate, purified GBS CPS III or rCTB alone on the systemic and mucosal immune responses to CPS III after intranasal (i.n.) immunization were investigated in mice. Priming with purified GBS CPS III followed by boosting with GBS CPS III-rCTB conjugate or priming with the conjugate followed by boosting with free CPS induced comparable levels of specific IgG and IgA in both serum and in lungs and vagina. However, i.n. immunization comprising both priming and boosting with conjugate was superior to priming with CPS and boosting with conjugate or the reverse, especially with regard to inducing mucosal IgA anti-CPS responses. All the immunization schemes, except priming and boosting with free CPS, induced high and similar levels of IgG1 in serum. In contrast, mice primed with free CPS III and then boosted with CPS III-rCTB conjugate by the i.n. route failed to produce significant levels of IgG2a, IgG2b and IgG3 in serum, at difference from mice primed with the conjugate and boosted with either conjugate or free CPS. Pre-immunization with rCTB either i.n. or i.p. did not suppress specific serum IgG responses induced by GBS CPS III-rCTB conjugate intranasally, but did inhibit serum and especially mucosal IgA responses. Our findings suggest that priming with CPS affects the distribution of IgG subclasses to GBS CPS and that pre-existing anti-carrier rCTB immunity can have an inhibitory effect on mucosal immune responses elicited by the conjugate vaccine given by the i.n. route.

Pediatric combination vaccines

There will be an increasing demand for safe and effective combination vaccines as more paediatric vaccines are developed and licensed for new indications. The successful introduction of new combination vaccines into the childhood immunization schedule has the potential to improve vaccine coverage and thus reduce morbidity and mortality from childhood infections, and also possibly to reduce the cost of vaccines and their delivery. This article reviews the recent literature regarding new combination vaccines and discusses the main issues surrounding the simultaneous administration of multiple vaccine antigens to children.

Epitopic overload at the site of injection may result in suppression of the immune response to combined capsular polysaccharide conjugate vaccines

Capsular polysaccharide (CP) conjugate vaccines targeting a variety of bacterial infections are currently under development and clinical evaluation. The inclusion of multiple CP serotypes combined in a single injection is an important maneuver being evaluated. The combination of CP conjugate vaccines into a single multivalent injection may result in competition among the different components and adversely affect the immunogenicity of any individual conjugate. We observed a reduction of 30-90% in antibody responses to several serotypes in mice when immunogenicity of a 12-valent Escherichia coli (E. coli) lipopolysaccharide (LPS) conjugate vaccine was compared to the immunogenicity of each monovalent vaccine evaluated separately. A reduction of 30% was observed in the Staphylococcus aureus (S. aureus) type 8 CP antibodies when a type 8-rEPA conjugate was combined with a type 5-rEPA conjugate. S. aureus types 5 and 8-rEPA conjugates were combined with 100 micrograms of either rEPA (homologous) or diphtheria toxoid (DT) (heterologous) carrier proteins, and evaluated in rEPA or DT primed mice. The addition of the homologous protein resulted in a 64% reduction in type 5 CP antibodies. The heterologous protein did not affect the immunogenicity of the type 5. We postulate that the free protein competed with the conjugate and recruited most of the rEPA primed T cells. In the case of the DT conjugates, the DT targeted different populations of the T cells, thus interference was not observed. These data suggested that the epitopic load rather than the antigenic load at the site of injection caused reduced immunogenicity of the conjugates. We theorize that individual components of multivalent CP vaccines conjugated to the same carrier proteins would compete for a limited number of specific carrier protein primed T cells. This would result in one or more components being unavailable in eliciting a sufficient immune response. The use of multiple carrier proteins should be considered as an approach to reduce interference when multivalent conjugate vaccines are to be formulated into a single injection.

Murine immune responses to Neisseria meningitidis group C capsular polysaccharide and a thymus-dependent toxoid conjugate vaccine

The polysaccharide (PS) capsules of many pathogenic bacteria are poor immunogens in infants and young children as a result of the delayed response to PS antigens during ontogeny. The development of polysaccharide-protein conjugate vaccines for Haemophilus influenzae type b, which have proven to be efficacious in this age group, has led to active development by a number of investigators of conjugate vaccines for other diseases. We describe here the response of several mouse strains to the capsular PS of Neisseria meningitidis group C (MCPS) conjugated to tetanus toxoid (MCPS-TT) and the same response in BALB/c mice as a model of the immune consequences of conjugate vaccine immunization. The use of a conjugate vaccine results in a shift in the isotype elicited in response to the MCPS, from immunoglobulin M (IgM) and IgG3 to primarily IgG1. A response to MCPS-TT is seen even among mouse strains which respond poorly to MCPS itself, emphasizing the importance of a strain survey when choosing a mouse model for a vaccine. The marked increase in IgG1 antibody titer was accompanied by a large increase in bactericidal activity of sera from these animals. Animals primed with the conjugate vaccine demonstrated a booster response after secondary immunization with either the MCPS or the conjugate. The ability to produce a boosted IgG1 anti-MCPS response to the MCPS can be transferred to adoptive recipients by B cells alone from mice primed with MCPS-TT but not mice primed with MCPS alone. These data indicate that in BALB/c mice a single immunization with MCPS-TT is sufficient to induce a shift to IgG1 and generate a memory B-cell population that does not require T cells for boosting.

Reduced response to multiple vaccines sharing common protein epitopes that are administered simultaneously to infants

The plethora of newly discovered vaccines implies that, in the future, many vaccines will have to be administered simultaneously to infants. We examined the potential interference with the immune response of several coadministered vaccines containing the same protein component, namely, tetanus toxoid (TT). Infants simultaneously receiving a tetravalent pneumococcal vaccine conjugated to TT (PncT) and a diphtheria-tetanus-pertussis-poliovirus-Haemophilus influenzae type b-tetanus conjugate vaccine showed significantly lower anti-H. influenzae type b polysaccharide (polyribosylribitol phosphate [PRP]) antibody concentrations than those receiving either a tetravalent pneumococcal vaccine conjugated to diphtheria toxoid or placebo. A dose range study showed that anti-PRP antibody concentrations were inversely related to the TT content of the PncT vaccines administered in infancy. Postimmunization antitetanus antibody concentrations were also affected adversely as the TT content of the coadministered vaccines was increased. This phenomenon, which we believe derives from interference by a common protein carrier, should be taken into account when the introduction of an immunization program including multiple conjugate vaccines is considered.