Synthesis and physicochemical and immunological characterization of pneumococcus type 12F polysaccharide-diphtheria toxoid conjugates

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

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

Future vaccine development at NICHD

Using published data and the results of our studies, we hypothesized that a critical level of serum IgG antibodies to the surface structures of invasive pathogens (capsular polysaccharides of Haemophilus influenzae type b, pneumococcus, meningococcus, Salmonella typhi, Escherichia coli, and Staphylococcus aureus, the O-specific polysaccharide LPS domain of the LPS of Shigella, non-typhoidal Salmonella, and E. coli, and the capsular polypeptide of Bacillus anthraces) confer immunity to these pathogens. Covalent attachment to a protein increases their immunogenicity and bestows T-cell properties to these antigens. We have also shown that a critical level of serum IgG antibodies to pertussis toxin alone induces immunity on both an individual and on a community basis (herd immunity) to Bordetella pertussis. It is likely that all the above conjugates and pertussis toxoid will be incorporated into vaccines for routine infant immunization.

Vaccines based on the cell surface carbohydrates of pathogenic bacteria

Glycoconjugate vaccines, in which a cell surface carbohydrate from a micro-organism is covalently attached to an appropriate carrier protein are proving to be the most effective means to generate protective immune responses to prevent a wide range of diseases. The technology appears to be generic and applicable to a wide range of pathogens, as long as antibodies against surface carbohydrates help protect against infection. Three such vaccines, against Haemophilus influenzae type b, Neisseria meningitidis Group C and seven serotypes of Streptococcus pneumoniae, have already been licensed and many others are in development. This article discusses the rationale for the development and use of glycoconjugate vaccines, the mechanisms by which they elicit T cell-dependent immune responses and the implications of this for vaccine development, the role of physicochemical methods in the characterisation and quality control of these vaccines, and the novel products which are under development.

Surface organization and nanopatterning of collagen by dip-pen nanolithography

Collagen is a key fibrous protein in biological systems, characterized by a complex structural hierarchy as well as the ability to self-assemble into liquid crystalline mesophases. The structural features of collagen influence cellular responses and material properties, with importance for a wide range of biomaterials and tissue architectures. The mechanism by which fibrillar collagen structures form from liquid crystalline mesophases is not well characterized. We report positive printing of collagen and a collagen-like peptide down to 30-50-nm line widths, using the atomic force microscopy technique of dip-pen nanolithography. The method preserved the triple-helical structure and biological activity of collagen and even fostered the formation of characteristic higher levels of structural organization. The "direct-write" capability of biologically relevant molecules, while preserving their structure and functionality, provides tremendous flexibility in future biological device applications and in proteomics arrays, as well as a new strategy to study the important hierarchical assembly processes of biological systems.

Group B Streptococcus capsular polysaccharide-cholera toxin B subunit conjugate vaccines prepared by different methods for intranasal immunization

Group B Streptococcus (GBS) type III capsular polysaccharide (CPS III) was conjugated to recombinant cholera toxin B subunit (rCTB) using three different methods which employed (i) cystamine and N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP), (ii) carbodiimide with adipic acid dihydrazide (ADH) as a spacer, or (iii) reductive amination (RA). The CPS III-rCTB conjugates were divided into large- and small-molecular-weight (M(r)) fractions, and the immunogenicities of the different preparations after intranasal (i.n.) immunization were studied in mice. Both large- and small-M(r) conjugates of CPS III-rCTB(RA) or CPS III-rCTB(ADH) induced high, almost comparable levels of CPS-specific immunoglobulin G (IgG) in serum, lungs, and vagina that were generally superior to those obtained with CPS III-rCTB(SPDP) conjugates or a CPS III and rCTB mixture. However, the smaller-M(r) conjugates of CPS III-rCTB(RA) or CPS III-rCTB(ADH) in most cases elicited a lower anti-CPS IgA immune response than the large-M(r) conjugates, and the highest anti-CPS IgA titers in both tissues and serum were obtained with the large-M(r) CPS III-rCTB(RA) conjugate. Serum IgG anti-CPS titers induced by the CPS III-rCTB(RA) conjugate had high levels of specific IgG1, IgG2a, IgG2b, and IgG3 antibodies. Based on the effectiveness of RA for coupling CPS III to rCTB, RA was also tested for conjugating GBS CPS Ia with rCTB. As for the CPS III-rCTB conjugates, the immunogenicity of CPS Ia was greatly increased by conjugation to rCTB. Intranasal immunization with a combination of CPS Ia-rCTB and CPS III-rCTB conjugates was shown to induce anti-CPS Ia and III immune responses in serum and lungs that were fully comparable with the responses to immunization with the monovalent CPS Ia-rCTB or CPS III-rCTB conjugates. These results suggest that the GBS CPS III-rCTB and CPS Ia-rCTB conjugates prepared by the RA method may be used in bivalent and possibly also in multivalent mucosal GBS conjugate vaccines.

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

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

Protective efficacy and immunogenicity of Vi-porin conjugate against Salmonella typhi

A conjugate vaccine against Salmonella typhi was prepared by covalently binding capsular polysaccharide (Vi) with porin, both isolated from S. typhi. First, Vi and porins were extracted. The Vi was purified from S. typhi Ty2. The purified Vi conformed to the requirements of the World Health Organization. Porins were purified from S. typhi 0901. The Vi was bound to the porins by a heterobifunctional cross-linking reagent, N-succinimidyl-3-(2-pyridyl dithio)-propionate (SPDP). After preparing the Vi-porin conjugate, its protective ability and immunogenicity were studied in mice following systemic immunization. The results showed that the conjugate is 6.5-fold more protective than Vi alone against S. typhi. The mice immunized with conjugate elicited higher anti-Vi antibody (IgG) levels (P < 0.01) than the mice immunized with Vi alone. Anti-porin antibodies were also induced by the conjugate. To study the mucosal immune responses, secretory IgA (sIgA) in the intestinal fluid was measured. Conjugate-immunized mice showed the induction of sIgA as compared to Vi alone. The results showed that when Vi is bound to porins, both isolated from same organism, the resultant conjugate induced both systemic and mucosal immune responses and provided better protection against S. typhi than Vi alone.

Streptococcus pneumoniae type 14 polysaccharide-conjugate vaccines: length stabilization of opsonophagocytic conformational polysaccharide epitopes

A simple and convenient method was developed for the preparation of Streptococcus pneumoniae type 14 polysaccharide (Pn14PS)-tetanus toxoid (TT) conjugate vaccines, using terminally linked Pn14PS fragments of different lengths. Native Pn14PS was simultaneously depolymerized and activated for conjugation by partial N-deacetylation followed by nitrous acid deamination which yielded fragments (1.4 to 150.0 kDa) having a free aldehyde at the reducing end. These were then conjugated to TT through their terminal aldehydic groups, using the reductive amination procedure. All of the above conjugates, when injected in rabbits, induced anti-Pn14PS antibodies, whereas the native Pn14PS did not. The amounts of anti-Pn14PS antibodies elicited by these conjugates, as determined by enzyme-linked immunosorbent assay, followed a trend with conjugates containing the highest-molecular-weight Pn14PS eliciting the highest titers. The same trend was also observed in the ability of the antibodies to opsonize and kill live type 14 pneumococci, although the increase in opsonophagocytic activity was more pronounced and did not correlate linearly with increases in antibody titer. Competitive inhibition of the binding of different conjugate antisera to the native Pn14PS, using Pn14PS fragments as inhibitors, established that the conjugates induced antibodies with specificities for different lengths of Pn14PS beginning at 2 repeating units (RU). It was also established, both immunologically and antigenically, that at least 4 RU of Pn14PS were required to form an extended conformational epitope and that approximately 22 RU of Pn14PS were required to duplicate the same epitope on the same saccharide chain. The conformational epitope was found to be essential for the induction of antibodies with high opsonophagocytic activity and that augmentation of opsonophagocytic activity was also dependent on further chain extension.

New vaccines for the prevention of pneumococcal infections

Streptococcus pneumoniae is a major cause of acute otitis media, pneumonia, bacteremia, and meningitis. Because in recent years antibiotic-resistant pneumococcal strains have been emerging throughout the world, vaccination against pneumococcal infections has become more urgent. The capsular polysaccharide vaccine that has been available is neither immunogenic nor protective in young children and other immunocompromised patients. Several pneumococcal proteins have been proposed as candidate vaccines, but no human studies associated with them have been reported. Clinical trials of first-generation pneumococcal conjugate vaccines have shown that covalent coupling of pneumococcal capsular polysaccharides to protein carriers improves the immunogenicity of the polysaccharides. The protective efficacy of the conjugate vaccines against carriage, acute otitis media, and invasive infections is being studied.

Comparative immunogenicity of conjugates composed of Escherichia coli O111 O-specific polysaccharide, prepared by treatment with acetic acid or hydrazine, bound to tetanus toxoid by two synthetic schemes

Escherichia coli O111, of various H types and virulence factors, causes enteritis throughout the world, especially in young children. This O type is found rarely in healthy individuals. Serum antibodies to the O-specific polysaccharide of O111 lipopolysaccharide (LPS) protect mice and dogs against infection with this E. coli serotype. The O111 O-specific polysaccharide is composed of a pentasaccharide repeat unit with two colitoses bound to the C-3 and C-6 of glucose in a trisaccharide backbone; this structure is identical to that of Salmonella adelaide (O35), another enteric pathogen. Nonpyrogenic O111 O-specific polysaccharide was prepared by treatment of its LPS with acetic acid (O-SP) or the organic base hydrazine (DeA-LPS). The O-SP had a reduced concentration of colitose. These products were derivatized with adipic acid dihydrazide (ADH) or thiolated with N-succinimidyl-3(2-pyridyldithio) propionate (SPDP). The four derivatives were covalently bound to tetanus toxoid (TT) by carbodiimide-mediated condensation or with SPDP to form conjugates. Immunization of BALB/c and general-purpose mice by a clinically acceptable route showed that DeA-LPS-TTADH, of the four conjugates, elicited the highest level of LPS antibodies. Possible reasons to explain this differential immunogenicity between the four conjugates are discussed.

Local and systemic antibody responses to dextran-cholera toxin B subunit conjugates

This study was designed to test local and systemic immunity following mucosal immunization with a polysaccharide-protein conjugate. After preparing and characterizing dextran-cholera toxin B subunit (CTB) conjugates, we studied their immunogenicity in mice following systemic or mucosal immunizations. Dextran was chosen as a model polysaccharide antigen and conjugated via adipic acid dihydrazide and N-succinimidyl-3-(2-pyridyldithio)propionate to CTB. Mice were immunized either subcutaneously, intranasally, or perorally three times, and cholera toxin was used as an adjuvant for the mucosal immunizations. Three conjugates with different molecular weights for dextran (40,000 and 76,000) or varying dextran/CTB molar ratios were tested. Peroral immunizations with all conjugates evoked local immunoglobulin A (IgA) antibody responses against dextran in the small intestine, and intranasal immunizations did the same in the lung. Intranasal immunizations also elicited serum antibody titers that were significantly higher than or equal to those after subcutaneous immunizations. Intranasal immunizations evoked serum IgG antidextran titers which were dependent on the dextran/CTB molar ratio and inversely related to the local IgA response, which was not the case for subcutaneous immunizations. This is the first study of local and systemic immunity following mucosal immunization with a polysaccharide-protein conjugate. The results show that it is possible to evoke a local as well as a systemic antibody response against a polysaccharide by conjugating it to CTB and using an appropriate route of immunization.

Serum antibody responses to vaccination with 23-valent pneumococcal vaccine in splenectomized patients

Sixty-three patients that have been splenectomized for various disorders were vaccinated with Pneumovax 23, the currently available pneumococcal vaccine. Before and one month after splenectomy, IgG antibodies against 8 pneumococcal polysaccharide antigens (types 3, 4, 6B, 7F, 10A, 14, 19F, and 20) were determined by a highly reproducible and type-specific enzyme-linked immunosorbent assay (ELISA). In order to increase the specificity of the assay, this method involved the use of a capture antibody (F(ab')2-fragments of a type-specific rabbit antipneumococcal hyperimmune serum) to bind the pneumococcal antigens to the plastic surface of microtiter plates and the absorption of these sera with the cross-reacting C polysaccharide. Rates of patients showing a two-fold antibody increase were dependent on pneumococcal type, ranging from 12.7% to 33.3%. Antibody responses of single patients were not uniform for all pneumococcal serotypes investigated. Only one patient responded to all of the eight antigens tested. In spite of relatively low response rates, splenectomized patients should be routinely vaccinated with the pneumococcal vaccine, especially when the low rate of adverse reactions is taken into consideration. It is emphasised that the results of the present study and those reported in the literature have to be compared and interpreted with caution, because the available data on the antibody response to pneumococcal vaccination are based on assays that differ substantially in methodology.

Immunogenicity of conjugate vaccines consisting of pneumococcal capsular polysaccharide types 6B, 14, 19F, and 23F and a meningococcal outer membrane protein complex

In an effort to prepare pneumococcal (Pn) capsular polysaccharide (Ps) vaccines that would be immunogenic in infants, covalent conjugates were prepared for Pn types 6B, 14, 19F, and 23F. Each Ps type was covalently bound to an outer membrane protein complex from Neisseria meningitidis serogroup B and evaluated for immunogenicity in mice and infant monkeys. The conjugates induced specific anti-Ps antibody responses in mice and in infant rhesus and African green monkeys; a conjugate of 6B and outer membrane protein complex was immunogenic at Ps doses as low as 20 ng. Although low levels of the Pn group-common cell wall polysaccharide were present in all type-specific Ps preparations, anti-cell wall polysaccharide responses induced by covalent conjugates were < 1% of the total anti-Ps response after two doses of vaccine. In contrast, the anti-cell wall polysaccharide response of a noncovalent conjugate represented 41% of the anti-Ps response after two doses. Relative T-cell dependence, a requirement for the human target population of infants less than 18 months old, was demonstrated for all four Pn Ps conjugates in an athymic mouse model. Therefore, these Pn Ps-outer membrane protein complex conjugate vaccines are excellent candidates for evaluation in human infants.

Enzyme immunoassay for detection of immunoglobulin G (IgG), IgM, and IgA antibodies against type 6B pneumococcal capsular polysaccharide and cell wall C polysaccharide in chinchilla serum

Conjugation of the capsular polysaccharides of Streptococcus pneumoniae to protein carriers has introduced a new generation of pneumococcal vaccines which may be efficacious in preventing pneumococcal otitis media during infancy. The chinchilla model has been used extensively for studying the pathogenesis of pneumococcal otitis media and for testing the efficacy of early pneumococcal capsular polysaccharide (PCP) vaccines, but immunologic studies in the chinchilla have been limited by the lack of antibodies against specific immunoglobulin isotypes. By using affinity-purified rabbit immunoglobulin G (IgG) anti-chinchilla IgG, IgM, and IgA, we developed a sensitive enzyme immunoassay that is highly specific for IgG, IgM, and IgA antibodies against type 6B PCP (anti-6B) and against C polysaccharide in chinchilla serum. Antibody titers increased in serum from five chinchillas immunized with a type 6B outer membrane protein complex vaccine. Increases of anti-6B IgG and IgM antibody titers were more striking than increases of anti-6B IgA or anti-C polysaccharide IgG, IgM, or IgA titers were.

Production of anti-peptide specific antibody in mice following immunization with peptides conjugated to mannan

In order to investigate the usefulness of polysaccharides as carriers for the induction of antibody to synthetic peptides, peptides representing residues 139-147 of the surface antigen of hepatitis B and residues 129-140 of the pre-S2 region of the protein were coupled to mannan and dextran via an aminocaproic spacer molecule. Of the two conjugates studied, only mannan was useful as a carrier for the efficient production of anti-peptide antibodies.

Pneumococcal polysaccharide vaccines: indications, efficacy and recommendations

Streptococcus pneumoniae is the primary cause of community-acquired pneumonia, meningitis in adults and otitis media in infants and children and the third cause of meningitis in infants and children. Despite the availability of effective therapeutic agents against this pathogen, mortality has remained high, particularly for infections complicated by bacteremia. For many years, there has been a plea for vaccination. The first steps, using whole bacterial vaccines, were taken during the early decades of this century in the gold mining camps of South Africa, where pneumonia was endemic. The efficacy of purified pneumococcal polysaccharide vaccines has since been demonstrated in young adults, such as gold miners and military recruits, as well as for several other groups at risk, such as institutionalized elderly, patients with sickle cell anemia or those who have undergone a splenectomy, and elderly patients with underlying conditions such as chronic obstructive pulmonary disease and chronic cardiovascular disease, but not in infants and severely immunocompromised patients. Serological studies on the immune response to inoculation of pneumococcal polysaccharide antigens have demonstrated a severely impaired antibody response in the last two groups. Therefore, development of more highly immunogenic vaccines, e.g. by linking pneumococcal polysaccharides or parts of them to protein carriers, should be continued in an attempt to offer adequate protection to those who are insufficiently protected by the current 23-valent polysaccharide vaccine. Opportunities to immunize other patients who are at risk for pneumococcal infection and are capable of responding to the current vaccine should not be missed.

Preparation, characterization, and immunogenicity of meningococcal immunotype L2 and L3,7,9 phosphoethanolamine group-containing oligosaccharide-protein conjugates

A method was developed for the well-defined coupling of phosphoethanolamine group (PEA)- and carboxylic acid group-containing polysaccharides and oligosaccharides to proteins without the need for extensive modification of the carbohydrate antigens. The carboxylic acid group of the terminal 2-keto-3-deoxyoctulosonic acid moiety was utilized to introduce a thiol function in meningococcal immunotype L2 and L3,7,9 lipopolysaccharide-derived oligosaccharides. The thiol group-containing oligosaccharides were subsequently coupled to bromoacetylated proteins. Immunotype L2 and L3,7,9 PEA group-containing oligosaccharide-tetanus toxoid conjugates were prepared, and their immunogenicities were studied in rabbits. Both the immunotype L2 and immunotype L3,7,9 conjugates evoked high immunoglobulin G (IgG) antibody titers after the first booster injection. These conjugates also displayed an ability to induce long-lasting IgG antibody levels which could be detected until 9 months after one booster injection at week 3. The adjuvant Quil A enhanced the immune response to all the conjugates to a minor extent, which is in contrast with reported adjuvant effects of Quil A on these types of antigens in mice. A conjugate prepared from the dephosphorylated L3,7,9 oligosaccharides evoked a significantly lower IgG response than a similar PEA-containing conjugate, and enzyme-linked immunosorbent assay inhibition studies indicated a different epitope specificity. Furthermore, antisera elicited with the complete bacteria contained antibodies directed against PEA-containing epitopes, which stresses the importance of the presence of unmodified PEA groups in meningococcal lipopolysaccharide-derived oligosaccharide-protein conjugates. The procedure developed offers an elegant solution for the specific coupling of meningococcal PEA-containing oligosaccharides to proteins and may therefore be a very useful tool in the development of a vaccine against group B meningococci.

Antibody-secreting peripheral blood lymphocytes induced by immunization with a conjugate consisting of Streptococcus pneumoniae type 12F polysaccharide and diphtheria toxoid

Healthy adult volunteers were injected either with one of two conjugates composed of Streptococcus pneumoniae type 12F polysaccharide (Pn12F) covalently coupled to diphtheria toxoid or with Pn12F alone (as a component of Pnu-Imune, a 23-valent pneumococcus vaccine). The conjugates induced Pn12F-specific antibody-secreting cells in peripheral blood with numbers and isotype distribution similar to those induced by Pnu-Imune, with immunoglobulin A (IgA) as the predominant isotype. The conjugates also elicited high numbers of diphtheria toxoid-specific antibody-secreting cells of the IgG class. There was no distinct booster effect, since a second dose of the conjugates induced antibody-secreting cells at significantly lower numbers than after the first dose. In contrast to the cell numbers, the conjugate vaccines induced higher increases of IgA1 Pn12F antibodies in serum than did Pnu-Imune. However, neither the conjugates nor Pnu-Imune induced a secretory antibody response. Antibody levels in serum and saliva correlated poorly with the frequency of antigen-specific antibody-secreting cells. Circulating antibody-secreting cells present 7 days postimmunization were probably not responsible for the high increase of antibodies in serum but rather represented a population of in vivo-activated B cells with the ability to disseminate the humoral response from the antigen recognition site to distant locations of antibody production.

Pneumococcal vaccination: work to date and future prospects

In our opinion, the conclusion from all these studies is that pneumococcal polysaccharides in the form in which they have been administered are relatively poor immunogens when compared, for example, to certain proteins such as tetanus toxoid. Had pneumococcal vaccination been the success that might reasonably have been predicted, there would be no argument, this many years later, over its merits. Although polysaccharide vaccines appear to have been effective in mass vaccination programs and in epidemic situations where presumably healthy adults have been involved, it has been more difficult to document their efficacy in individuals who are most in need of them, namely those with aberrant or senescent immune systems. There seems to be no disagreement that antibody at some concentration (the precise level remains to be determined) will, in general, be associated with protection, although in any one individual, for a variety of reasons, infection with a vaccine serotype might still occur. Thus, the clear direction for the future should be not to argue further the merits of currently available vaccine preparations, but rather to work rapidly and efficiently to develop and test new and more effective polysaccharide antigens. Studies in the past 10 years have shown that the polyribosyl ribitolphosphate (PRP) of Haemophilus influenzae type b is a far more effective antigen when conjugated to diphtheria toxoid. For example, in a study in our laboratory, vaccination of healthy young adults with PRP-conjugated diphtheria toxoid yielded serum antibody levels 10- to 100-fold higher than after PRP alone. Responses may be even better if other proteins are used.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and immunologic properties in mice of vaccines composed of Staphylococcus aureus type 5 and type 8 capsular polysaccharides conjugated to Pseudomonas aeruginosa exotoxin A

Epidemiological, serological and in vitro phagocytosis experiments provide evidence that the newly discovered type 5 and type 8 capsular polysaccharides (CPs) are both virulence factors and protective antigens for bacteremia caused by Staphylococcus aureus. Neither type 5 nor type 8 CP elicited serum antibodies when injected into mice. These two CPs were bound to Pseudomonas aeruginosa exotoxin A (ETA) to form conjugates by using the synthetic scheme devised for the CP (Vi) of Salmonella typhi and of pneumococcus type 12F (A. Fattom, W. F. Vann, S. C. Szu, A. Sutton, X. Li, D. Bryla, G. Schiffman, J. B. Robbins, and R. Schneerson, Infect. Immun. 56:2292-2298, 1988; S. C. Szu, A. L. Stone, J. D. Robbins, R. Schneerson, and J. B. Robbins, J. Exp. Med. 166:1510-1524, 1987). Both S. aureus CP-ETA conjugates elicited a rise in CP antibodies. As components of conjugates, both S. aureus CPs acquired T-cell-dependent properties, as shown by their ability to respond to carrier priming and to stimulate booster responses. The conjugate-induced antibodies facilitated type-specific opsonization of S. aureus by human polymorphonuclear leukocytes. The conjugates also induced ETA antibodies which neutralized the native toxin in vitro. Clinical studies of these two conjugates for active or passive immunization of patients at risk for S. aureus bacteremia are planned.

Serum antibody response in adult volunteers elicited by injection of Streptococcus pneumoniae type 12F polysaccharide alone or conjugated to diphtheria toxoid

Conjugates of an uronic acid-containing capsular polysaccharide (CP), pneumococcous type 12F (Pn12F) bound to diphtheria toxoid (DT), were studied for safety and immunogenicity in adult volunteers. In mice, these conjugates, prepared with the same lot of DT and Pn12F-40234-006, a homogenous CP of high molecular weight, or Pn12-812408, a polydisperse CP with lower-molecular-weight material, were more immunogenic than the Pn12F alone and had T-cell dependent properties (A. Fattom, W. F. Vann, S.C. Szu, A. Sutton, X. Li, B. Bryla, G. Schiffman, J. B. Robbins, and R. Schneerson, Infect. Immun. 56:2292-2298, 1988). Adult volunteers, randomized into three groups, were injected either with one of these two conjugates or with Pnu-Imune, the 23 valent pneumococcus vaccine containing 25 micrograms of Pn12F as one of its components. Volunteers were injected two times, 4 weeks apart, with the Pn12F-DT conjugates and once with the Pnu-Imune. Side reactions following injection of the conjugates of Pnu-Imune were mild and short-lived. At 4 weeks and at 7 months after the first injection, higher levels of Pn12F antibodies were found in the volunteers injected with the conjugates than in the Pnu-Imune group (P less than 0.001). The conjugate prepared with the higher-molecular-weight Pn12F elicited higher levels of antibodies than the conjugate prepared with a lower-molecular-weight Pn12F preparation (P = 0.05). Both conjugates elicited about a 13-fold rise in DT antibodies.

Introduction of sulfhydryl groups into proteins at carboxyl sites

A two-step procedure for introduction of sulfhydryl groups at protein carboxyl groups is described. The resultant proteins contain 2-aminoethanethiol residues bound by amide linkages to the protein carboxyl groups. First an amide bond is formed between a carboxyl group of the protein and one of the amino groups of cystamine. Then the disulfide bond is reduced with dithiothreitol, yielding the amide of 2-aminoethanethiol. This procedure was used to incorporate sulfhydryl groups into carbonic anhydrase and adrenocorticotropic hormone. The effect of carbodiimide concentration and pH of the coupling reaction on stoichiometry of sulfhydryl group incorporation was examined. The method was used to prepare bovine carbonic anhydrase containing up to nine sulfhydryl groups per molecule with no loss of enzymatic activity and biologically active adrenocorticotropic hormone containing one sulfhydryl group per molecule.

Comparative immunogenicities of Vi polysaccharide-protein conjugates composed of cholera toxin or its B subunit as a carrier bound to high- or lower-molecular-weight Vi

The effect of molecular weight or size of the components on the immunogenicity of polysaccharide-protein conjugates prepared with the native Vi capsular polysaccharide (Vi) (approximately 3 x 10(3) kilodaltons) or lower-molecular-weight Vi (Vis; approximately 46 kilodaltons) abound to cholera toxin (CT) or to its B subunit (CTB) was studied. In mice, Vi-CT, Vi-CTB, and Vis-CTB elicited higher Vi antibody levels than the Vi alone (P less than 0.0001). Vi-CT and Vi-CTB were more immunogenic than Vis-CTB (P less than 0.01). CT or Vi-CT elicited higher levels of CT antibodies, as measured by enzyme-linked immunosorbent assay, than did CTB or Vi-CTB. In rhesus monkeys, the Vi conjugates elicited higher Vi antibody levels than the Vi alone (P less than 0.01). Vi-CTB elicited higher levels of Vi antibody after each injection than did Vis-CTB. Similar levels of CT antibodies, as measured by enzyme-linked immunosorbent assay, were elicited by all three conjugates. In contrast, Vi-CT elicited higher levels of neutralizing antibodies than Vi-CTB or Vis-CTB when either CT or the related heat-labile toxin of Escherichia coli was used as the antigen. These results indicate that the holotoxin and the native Vi provide the most immunogenic components for conjugates designed to induce both Vi and CT antibodies.