Development of a guinea pig model to assess immunogenicity of Haemophilus influenzae type b capsular polysaccharide 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.

Use of immuno assays during the development of a Hemophilus influenzae type b vaccine for technology transfer to emerging vaccine manufacturers

Quality control of Hemophilus Influenzae type b (Hib) conjugate vaccines is mainly dependent on physicochemical methods. Overcoming sample matrix interference when using physicochemical tests is very challenging, these tests are therefore only used to test purified samples of polysaccharide, protein, bulk conjugate, and final product. For successful development of a Hib conjugate vaccine, several ELISA (enzyme-linked immunosorbent assay) methods were needed as an additional tool to enable testing of in process (IP) samples. In this paper, three of the ELISA's that have been very valuable during the process development, implementation and scaling up are highlighted. The PRP-ELISA, was a very efficient tool in testing in process (IP) samples generated during the development of the cultivation and purification process of the Hib-polysaccharide. The antigenicity ELISA, was used to confirm the covalent linkage of PRP and TTd in the conjugate. The anti-PRP IgG ELISA was developed as part of the immunogenicity test, used to demonstrate the ability of the Hib conjugate vaccine to elicit a T-cell dependent immune response in mice. ELISA methods are relatively cheap and easy to implement and therefore very useful during the development of polysaccharide conjugate vaccines.

Preclinical evaluation of a Haemophilus influenzae type b conjugate vaccine process intended for technology transfer

Introduction of Haemophilus influenzae type b (Hib) vaccine in low- and middle-income countries has been limited by cost and availability of Hib conjugate vaccines for a long time. It was previously recognized by the Institute for Translational Vaccinology (Intravacc, originating from the former Vaccinology Unit of the National Institute of Public Health [RIVM] and the Netherlands Vaccine Institute [NVI]) that local production of a Hib conjugate vaccine would increase the affordability and sustainability of the vaccine and thereby help to speed up Hib introduction in these countries. A new affordable and a non-infringing production process for a Hib conjugate vaccine was developed, including relevant quality control tests, and the technology was transferred to a number of vaccine manufacturers in India, Indonesia, and China. As part of the Hib technology transfer project managed by Intravacc, a preclinical toxicity study was conducted in the Netherlands to test the safety and immunogenicity of this new Hib conjugate vaccine. The data generated by this study were used by the technology transfer partners to accelerate the clinical development of the new Hib conjugate vaccine. A repeated dose toxicity and local tolerance study in rats was performed to assess the reactogenicity and immunogenicity of a new Hib conjugate vaccine compared to a licensed vaccine. The results showed that the vaccine was well tolerated and immunogenic in rats, no major differences in both safety and immunogenicity in rats were found between the vaccine produced according to the production process developed by Intravacc and the licensed one. Rats may be useful to verify the immunogenicity of Hib conjugate vaccines and for preclinical evaluation. In general, nonclinical evaluation of the new Hib conjugate vaccine, including this proof of concept (safety and immunogenicity study in rats), made it possible for technology transfer partners, having implemented the original process with no changes in the manufacturing process and vaccine formulation, to start directly with phase 1 clinical trials.

Enhancement of serum and mucosal immune responses to a Haemophilus influenzae Type B vaccine by intranasal delivery

Intranasal (i.n.) vaccination is potentially the most direct method for conveying upper respiratory and mucosal immunity to respiratory pathogens. However, for unclear reasons, vaccines introduced into the nasal sinuses often have lower efficacy than vaccines administered by the more frequently used parenteral routes. We examined i.n. vaccination in a mouse immune-response model with a commonly used Haemophilus influenzae type B vaccine (Hibv) composed of the polyribosylribitol phosphate (PRP) capsule antigen conjugated to tetanus toxoid. Intranasal vaccination with Hibv using a Toll-like receptor 4 (TLR4) agonist as an adjuvant significantly increased the levels of IgA specific for the PRP capsule antigen in blood serum, saliva, and mucosal secretion specimens. In contrast, control mice vaccinated transdermally (t.d.) with Hibv did not produce significant levels of PRP-specific IgA in the blood serum and saliva, and anti-PRP IgG was increased only in serum. The i.n. and t.d. vaccinations resulted in equivalent bactericidal antibody responses in blood serum, suggesting that vaccine-derived IgG is protective against infection. Elevated levels of IgG specific for the tetanus toxoid carrier protein were measured in nasal sinuses and vaginal secretions in mice vaccinated by either the t.d. or i.n. route. Tissue culture studies confirmed that the nasopharynx-associated lymphoid tissue (NALT) was at least one of the sources of PRP-specific IgA and carrier-specific IgG within the nasal sinuses. We conclude that i.n. vaccination aided by a TLR4 agonist results in robust immune responses to both the carrier protein and bacterial polysaccharide components of the Hibv.

Survey of human-use adjuvants

Although there are only four adjuvants used in licensed vaccines for humans, a wealth of information on novel vaccine adjuvants has become available in both animal models and clinical studies over the past decade. Many vaccine candidates require immunopotentiation to achieve a satisfactory immune response, which is driving the search for new and safer approaches. In this review, we take a brief look at what is known of the mechanisms of action, consider some of the elements of product development, then survey several of the classes of adjuvants within the context of human trials.

Preclinical evaluation of group B streptococcal polysaccharide conjugate vaccines prepared with a modified diphtheria toxin and a recombinant duck hepatitis B core antigen

An effective vaccine against group B streptococcal (GBS) disease will undoubtedly include capsular polysaccharides (CPSs) from each of the five serotypes prevalent in the United States individually coupled to immunogenic proteins. This formulation may require the use of two or more different protein carriers. We preclinically examined the potential of two proteins to serve as effective carriers for GBS type III CPS. Recombinant duck hepatitis B core antigen (rdHBcAg), a particulate protein of viral origin, and a newly mutated form of diphtheria toxin (DTm) were covalently and directly coupled to purified type III CPS by reductive amination. Seventy-seven of 79 (97%) newborn pups born to mouse dams actively vaccinated with type III CPS-rdHBcAg conjugate survived GBS type III challenge, whereas none of the pups born to dams that received an uncoupled mixture of type III CPS and rdHBcAg or saline survived. Likewise, 64 (98%) of 65 pups born to dams vaccinated with type III CPS-DTm conjugate survived challenge, in sharp contrast to no survivors among the pups born to dams vaccinated with an uncoupled mixture of type III CPS and DTm. The presence of type III CPS-specific IgG in serum from dams correlated with pup survival in groups that received a conjugate vaccine, and this serum was opsonically active in vitro against GBS type III. In addition, carrier-specific IgG was also measured in serum from vaccinated mice. These data suggest that the rdHBcAg and DTm may be effective carriers for GBS CPSs.

Immunogenicity and specificity of the candidate multi-epitope-vaccines against HIV-1

The failure of some candidate HIV-1 vaccines may result from inducing very weak neutralization activity against representative primary viral isolates. Based on our hypothesis that epitope-vaccine may be a new strategy to induce high levels of neutralizing antibodies against HIV-1, we designed two candidate multi-epitope-vaccines, EP1 [C-G-(ELDKWA-GPGRAFY)2-K] and EP2 (CG-GPGRAFY-G-ELDKWA-G-RILAVERYLKD), containing three neutralizing epitopes (GPGRAFY, ELDKWA and RILAVERYLKD) on HIV-1 envelope protein, and expected them to induce epitope-specific antibodies of predefined epitope-specificity. The two peptides were conjugated to carrier protein bovine serum albumin (BSA) and used for immunization of rabbits. Proteins were purified from the rabbit sera induced by both candidate multi-epitope-vaccines (EP1-BSA and EP2-BSA) through affinity chromatography with epitope-peptide-conjugated sepharose-column, and identified as antibodies in silver-staining and immunoblotting. These antibodies were demonstrated to recognize three neutralizing epitopes on peptides and the recombinant gp41 in ELISA-assay and immunoblotting. These results indicated that both candidate multi-epitope-vaccines could induce high levels of antibodies of predefined epitope-specificity which recognized a few of neutralizing epitopes on peptides and protein, providing experimental evidence for the new strategy to develop an effective neutralizing-antibody-based multi-epitope-vaccine against HIV-1.

Induction of high levels of epitope-specific antibodies by epitope/peptide candidate vaccines against human immunodeficiency virus type-1 (HIV-1)

To test the immunogenicity of GPGRAFY-epitope-based candidate vaccines, a peptide with four repetitive GPGRAFY epitopes, V3-P1 [C-(GPGRAFY)4], and a peptide (PND) of the principal neutralizing domain (V3 loop: amino acid 301-328: C-TRPNNNTRKSIRIQRGPGRAFYTIGKI) on gp120 were synthesized and covalently coupled to a carrier protein BSA. Immunization of BALB/c mice and New Zealand White Rabbits with these conjugate vaccines engendered strong antibody responses against the PND (mouse serum titer by 1:12,800-25,600; rabbit serum titer by 1:6,400-12,800). Interestingly, the V3-P1-BSA conjugates and the PND-BSA conjugates could induce high levels of GPGRAFY-epitope-specific antibodies in the mice and rabbits (mouse serum titer by 1:25,600; rabbit serum titer by 1:12,800-25,600), while a recombinant gp160 subunit vaccine induced a low level of GPGRAFY-epitope-specific antibodies (serum titer by 1:400-1,600 in mice and rabbits). To confirm the above results, GPGRAFY-epitope-specific antibodies were isolated from rabbit sera induced by V3-P1-BSA, PND-BSA conjugates and rgp160 vaccine. In fact, 23-38 and 13-22 microg epitope-specific antibodies per milliliter serum were isolated from rabbit sera induced by V3-P1-BSA and PND-BSA conjugate, respectively, while 1.34 microg epitope-specific antibodies per milliliter serum were identified in rabbit serum induced by rgp160 vaccine. In the control group, only 0.069 microg proteins per milliliter serum were found in pooled pre-immune serum (normal serum). These results from mouse and rabbit experiments indicate that epitope and peptide vaccines both induce high levels of GPGRAFY-epitope-specific antibodies in comparison with rgp160 subunit vaccine, suggesting that epitope/peptide vaccines may be a new strategy to induce protective activity.

Induction of high level of specific antibody response to the neutralizing epitope ELDKWA on HIV-1 gp41 by peptide-vaccine

The monoclonal antibody 2F5 recognizing the neutralizing epitope ELDKWA on the C-domain could neutralize 90% of the investigated HIV-1 isolates. Low levels of ELDKWA-epitope-specific antibodies were observed in HIV-1-infected individuals. To induce high levels of antibodies to ELDKW-epitope, C-domain peptide (P2) was conjugated with a carrier peptide (KGGG)(7)-K (K/G). P2-K/G-conjugate induced high level of antibodies in mice by titer 1:25,600 to ELDKWA-epitope. P2-K/G-BSA-conjugate induced antibody response to ELDKWA-epitope (1:320-6400) in mice. The ELDKWA-epitope-specific antibodies of 19.8 and 34.6 microg/per milliliter serum were isolated from two rabbit antiserums (1:25,600). The levels of ELDKWA-epitope-specific antibodies induced in rabbits were greater than 1 microg/ml, a level considered to confer long-term protection. These results demonstrate the potential role of the C-domain peptide of gp41 to develop an effective ELDKWA-based epitope/peptide-vaccine against HIV-1.

Mutual interactions between DTaP-IPV and Haemophilus influenzae type b (Hib)-conjugated vaccines in laboratory animal models

Potency and/or immunogenicity of three different Haemophilus influenzae type b-conjugated vaccines (Hib) and a DTaP-IPV vaccine alone, and their mutual interactions in DTaP-IPV-Hib combination was tested. In a mouse model, only combination of Act-Hib, in which tetanus toxoid (TT) was as active as non-conjugated TT, significantly increased the immunogenicity and potency of TT component of DTaP-IPV vaccine. Also, only combination of Hib-TITER, in which CRM197 was used as the carrier with DTaP-IPV, increased the potency of diphtheria toxoid (DT) component of DTaP-IPV vaccine significantly. It shows that the additive effect of tested Hib vaccines on immunogenicity and/or potency of TT and DT was mostly due to the existence of TT and CRM197, respectively, as the carrier in the mentioned Hib vaccines. No difference was shown in inoculation of DTaP-IPV and Hib conjugated vaccines in the same syringe or at separate sites. DTaP-IPV had dual effects on anti-Hib capsular polysaccharide (HibCP) responses to Hib vaccines in the mouse model. This duality was probably related to the carrier B-cell epitopes activity of Hib conjugated vaccines. The immunogenicity of TT component of Act-Hib and Amvax Hib-TT in the guinea pig model was shown and combination of mentioned Hib vaccines with DTaP-IPV, remarkably increased anti-TT antibody responses to the TT component of DTaP-IPV vaccine. These confirmed our results in the mouse model. Using two different protocols to evaluate the guinea pig model for induction of anti-HibCP immunity showed that a "long interval" protocol does not have any advantage over the "short interval" protocol. Also, combination of DTaP-IPV with Hib vaccines did not have any noticeable effect on anti-HibCP antibodies in the guinea pig model. Taken together, our observations in laboratory animal models may facilitate a better understanding of the mutual interactions between the different antigen components of a combined vaccine such as DTaP-IPV-Hib vaccine.

Evaluation of a guinea pig model to assess interference in the immunogenicity of different components of a combination vaccine comprising diphtheria, tetanus and acellular pertussis (DTaP) vaccine and haemophilus influenzae type b capsular polysaccharide conjugate vaccine

A guinea pig model to assess the immunogenicity of a combination vaccine containing diphtheria, tetanus and acellular pertussis (DTaP) vaccine and Haemophilus influenzae type b (Hib) capsular polysaccharide conjugated to tetanus toxoid (HibT) was evaluated comparatively with the mouse immunogenicity test to study the effect of combining these antigens on the immunogenicity of various components. The immunogenicity test in mice was performed by subcutaneous injection of groups of 10 animals twice at an interval of four weeks with 1/10 of a single human dose of various formulations of combination vaccines, DTaP or HibT vaccine. The animals were bled at 4 and 6 weeks and IgG or total antibodies to various components were determined by ELISA or RIA. The guinea pig immunogenicity model included groups of animals injected subcutaneously twice at an interval of six weeks with 1.5 times the single human dose of various formulations. The animals were bled at 4, 6 and 8 weeks and serum samples were tested for antibodies to various components by ELISA, RIA and/or neutralization tests. Additionally, potency of tetanus and diphtheria components was assessed as per the US Food and Drug Administration's regulations. Aluminium phosphate (AIPO(4)) adsorbed HibT vaccine or HibT as a combination with AIPO(4)adsorbed DTaP vaccine showed significant increases in IgG antibodies to tetanus toxin in mice as well increased tetanus antitoxin levels in guinea pigs as compared to soluble HibT vaccine. In general, combining DTaP and HibT vaccines did not affect the antibody levels to tetanus and diphtheria toxoids whereas DTaP-HibT combination vaccine elicited significantly lower IgG antibodies to pertussis toxin and filamentous haemagglutinin than DTaP vaccine alone, particularly after first injection. Mice showed similar Hib antibody responses for the combination and HibT alone whereas guinea pigs consistently showed lower anamnestic responses to Hib for combination formulations than for HibT alone. Reducing the amount of HibT and/or tetanus toxoid in the combination formulations reduced this suppression of Hib antibody response in guinea pigs. Suppression of Hib antibody response in combination vaccines has also been reported from recent clinical trials. Based on the results from this study, it appears that the guinea pig model may be able to predict the human response to various components of combination vaccines.

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.

Effect of combination with an acellular pertussis, diphtheria, tetanus vaccine on antibody response to Hib vaccine (PRP-T)

Acellular pertussis vaccines provide protection against whooping cough with few adverse effects. Their introduction to routine immunisation programmes would be facilitated by their incorporation with other routinely administered vaccines. 262 infants were immunised with an acellular pertussis vaccine containing pertussis toxin and filamentous haemagglutinin, combined with diphtheria and tetanus toxoids. This vaccine was mixed with Haemophilus influenzae type b tetanus toxoid vaccine (PRP-T) so that infants received a single injection at age 2, 3 and 4 months. One month after the third dose the geometric mean titre of Hib IgG antibody was 0.48 microgram ml-1. Eighty-two percent of infants achieved a titre of 0.15 microgram ml-1, with only 27% achieving 1.0 microgram ml-1. This combination vaccine induced low Hib antibody responses when compared to other studies in which PRP-T was mixed with acellular or whole-cell pertussis vaccines. The combined vaccine did, however, appear to prime a subset of 35 infants for response to a fourth dose of PRP-T at 13 months of age, with a rise in GMT from 0.21 microgram ml-1 to 36.6 micrograms ml-1. These data have important implications for the introduction of combination acellular pertussis vaccines.

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.

MF59 adjuvant enhances antibody responses of infant baboons immunized with Haemophilus influenzae type b and Neisseria meningitidis group C oligosaccharide-CRM197 conjugate vaccine

The ability of the adjuvant MF59 to enhance the immunogenicity of polysaccharide-protein conjugate vaccines was investigated in infant baboons. MF59 consists of stable droplets (<250 nm) of the metabolizable oil squalene and two surfactants, polyoxyethylene sorbitan monooleate and sorbitan trioleate, in an oil-in-water emulsion. In humans, MF59 is well tolerated and enhances the immunogenicity of recombinant protein subunit or particle vaccines. Its effect on the immunogenicity of polysaccharide-protein conjugate vaccines is unknown. Baboons 1 to 4 months of age were immunized intramuscularly with Neisseria meningitidis group C and Haemophilus influenzae type b (Hib) oligosaccharide-CRM197 conjugate vaccines. The lyophilized vaccines were reconstituted with phosphate-buffered saline (PBS), Al(OH)3 (alum), or MF59. Groups of five animals each were given three injections of the respective formulations, with one injection every 4 weeks. Four weeks after each immunization, the MF59 group had up to 7-fold-higher geometric mean anticapsular-antibody titers than the alum group and 5- to 10-fold-higher N. meningitidis group C bactericidal-antibody titers. Twenty-one weeks after the third immunization, the MF59 group still showed 5- to 10-fold-higher anticapsular-antibody titers. The antibody responses of the animals given the vaccines reconstituted with PBS were low at all times measured. Both the MF59 and alum groups, but not the PBS group, showed booster antibody responses to unconjugated Hib and N. meningitidis group C polysaccharides, results consistent with induction of memory B cells. Thus, MF59 may be useful for accelerating and augmenting immunity to polysaccharide-protein conjugate vaccines in infants.

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.

Adjuvants for human vaccines--current status, problems and future prospects

Adjuvants help antigen to elicit an early, high and long-lasting immune response with less antigen, thus saving on vaccine production costs. In recent years, adjuvants received much attention because of the development of purified, subunit and synthetic vaccines which are poor immunogens and require adjuvants to evoke the immune response. With the use of adjuvants immune response can be selectively modulated to major histocompatibility complex (MHC) class I or MHC class II and Th1 or Th2 type, which is very important for protection against diseases caused by intracellular pathogens such as viruses, parasites and bacteria (Mycobacterium). A number of problems are encountered in the development and use of adjuvants for human vaccines. The biggest issue with the use of adjuvants for human vaccines, particularly routine childhood vaccines, is the toxicity and adverse side-effects of most of the adjuvant formulations. At present the choice of adjuvants for human vaccination reflects a compromise between a requirement for adjuvanticity and an acceptable low level of side-effects. Other problems with the development of adjuvants include restricted adjuvanticity of certain formulations to a few antigens, use of aluminum adjuvants as reference adjuvant preparations under suboptimal conditions, non-availability of reliable animal models, use of non-standard assays and biological differences between animal models and humans leading to the failure of promising formulations to show adjuvanticity in clinical trials. The most common adjuvants for human use today are still aluminum hydroxide and aluminum phosphate, although calcium phosphate and oil emulsions also have some use in human vaccinations. During the last 15 years much progress has been made on development, isolation and chemical synthesis of alternative adjuvants such as derivatives of muramyl dipeptide, monophosphoryl lipid A, liposomes, QS21, MF-59 and immunostimulating complexes (ISCOMS). Other areas in adjuvant research which have received much attention are the controlled release of vaccine antigens using biodegradable polymer microspheres and reciprocal enhanced immunogenicity of protein-polysaccharide conjugates. Biodegradable polymer microspheres are being evaluated for targeting antigens on mucosal surfaces and for controlled release of vaccines with an aim to reduce the number of doses required for primary immunization. Reciprocal enhanced immunogenicity of protein-polysaccharide conjugates will be useful for the development of combination vaccines.