THE PNEUMOCOCCAL POLYSACCHARIDES

Chemical Synthesis of Rare, Deoxy-Amino Sugars Containing Bacterial Glycoconjugates as Potential Vaccine Candidates

Bacteria often contain rare deoxy amino sugars which are absent in the host cells. This structural difference can be harnessed for the development of vaccines. Over the last fifteen years, remarkable progress has been made toward the development of novel and efficient protocols for obtaining the rare sugar building blocks and their stereoselective assembly to construct conjugation ready bacterial glycans. In this review, we discuss the total synthesis of a variety of rare sugar containing bacterial glycoconjugates which are potential vaccine candidates.

Semisynthetic glycoconjugate vaccine candidate against Streptococcus pneumoniae serotype 5

Glycoconjugate vaccines based on isolated capsular polysaccharide (CPS) save millions of lives annually by preventing invasive pneumococcal disease caused by Streptococcus pneumoniae Some components of the S. pneumoniae glycoconjugate vaccine Prevnar13 that contains CPS antigens from 13 serotypes undergo modifications or degradation during isolation and conjugation, resulting in production problems and lower efficacy. We illustrate how stable, synthetic oligosaccharide analogs of labile CPS induce a specific protective immune response against native CPS using S. pneumoniae serotype 5 (ST-5), a problematic CPS component of Prevnar13. The rare aminosugar l-PneuNAc and a branched l-FucNAc present in the natural repeating unit (RU) are essential for antibody recognition and avidity. The epitope responsible for specificity differs from the part of the antigen that is stabilized by chemical modification. Glycoconjugates containing stable, monovalent synthetic oligosaccharide analogs of ST-5 CPS RU induced long-term memory and protective immune responses in rabbits superior to those elicited by the ST-5 CPS component in multivalent Prevnar13.

Production of capsular polysaccharide of Streptococcus pneumoniae type 14 and its purification by affinity chromatography

We describe a rapid and efficient method for producing the capsular polysaccharide of Streptococcus pneumoniae by fermentation on tryptic soy broth and purification of this compound by using immobilized soybean lectin as an affinity adsorbent. In principle, the same strategy can be used to produce purified capsular polysaccharides from other streptococcal serotypes by selecting the appropriate lectin adsorbents.

Alteration of antibody response to pneumococcal polysaccharide type III in rats by neonatal immobilization stress

Our previous studies showed that stressing newborn animals by immobilization during the first 2 weeks of life caused significant changes in the capacity of adult rats to respond to stress as measured by the adrenal and circulating levels of catecholamines. In this report the effect of stress on the antibody response to the capsular polysaccharide of Type III Streptococcus pneumoniae (SSS-III) was investigated in two different strains of rats: Sprague-Dawley (SD) and Fischer (F) 344 rats. Animals were stressed 1 h each day for a total period of 10 days. Following this period of stress, animals were reared together along with littermate controls up to 40 days of age, when they were immunized with an optimally immunogenic dose of SSS-III. The results of experiments done with SD rats showed a substantial suppression of the antibody response when the response of the neonatally stressed animals was compared to the controls. In contrast, stressing adult SD animals for 10 days, followed by a 3-week recovery period prior to immunization with SSS-III, did not result in any significant (p greater than .05) suppression of antibody response. When F rats were used, the antibody response of the neonatally stressed rats was also significantly (p less than .05) lower than that of the controls. Thus, the effects of chronic, immobilization stress on antibody response can be long-lasting when the stressor is applied during the neonatal period.

Biosynthesis of a galactose-and galacturonic acid-containing polysaccharide in Rhizobium meliloti

Previous work showed that two different strains derived from a culture of Rhizobium meliloti 102F51 differed with respect to phage specificity, agglutinability by alfalfa seed lectin, and synthesis of a galactose-containing polysaccharide (R. A. Ugalde, H. Handelsman, and W. J. Brill, J. Bacteriol. 166:148-154, 1986). Inner membranes from the more competitive strain incorporated galactose from UDP-galactose when a thermostable factor was present. This factor has now been identified as UDP-galacturonic acid. UDP-glucuronic acid was also active as a donor; however, this activity may be due to the presence of a 4-epimerase. Galacturonic acid, together with galactose, is incorporated into the reaction product, which appears to be a polysaccharide formed by several repeating units of these two monosaccharides. Partial acid hydrolysis liberates the disaccharide with galactose at the reducing end.

The immune response to pneumococcal polysaccharide type III is followed by increased production of an antibody antifactor

The study shows that serum from pneumococcal polysaccharide type III (SSSIII)-immunized and nonimmunized mice that has been absorbed until devoid of anti-SSSIII antibodies inhibits anti-SSSIII plaque-forming cells (PFC) but not antisheep red blood PFC in antibody plaque assay. A large fraction of the inhibitions activity can be absorbed by and eluted from anti-SSSIII-Sepharose, but not normal mouse serum-Sepharose. It has low or no affinity for protein A and concanavalin A. The titre of the inhibitor increases with repeated immunizations and inhibits the anti-SSSIII PFC of rats or mice of different allotypes. On the basis of these characteristics, I classify the inhibitor as an anti-idiotypic nonimmunoglobulin factor directed against a common determinant of anti-SSSIII antibodies of mouse and rat, with an immuno-regulatory function.

The role of antigen in the activation of regulatory T cells by immune B cells

The transfer of B cells from mice immunized with Type III pneumococcal polysaccharide (SSS-III) results in the activation of suppressor and amplifier T cells that control the magnitude of the antibody response in recipient mice, immunized subsequently with SSS-III. Prior treatment of transferred B cells with an excess of enzyme (polysaccharide depolymerase) capable of hydrolyzing SSS-III, does not alter the capacity of these cells to activate regulatory T cells. These findings indicate that the activation of regulatory T cells by immune B cells is not mediated by residual antigen on the surface of transferred cells.

Influence of carrier-specific, thymus-derived cells on the immunologlobulin M antibody response to staphylococcal lipoteichoic acid

The immunoglobulin M antibody response to the lipoteichoic acid (LTA) of Staphylococcus aureus ATCC 6538P was examined by a procedure in which erythrocytes sensitized with periodate-activated LTA were used for the detection of immunoglobulin M-producing plaque-forming cells LTA-specific plaque-forming cells were first detected 2 days after immunization with heat-killed bacterial cells, and maximal numbers of plaque-forming cells, mostly of the immunoglobulin M class rather than the immunoblogulin G or immunoglobulin A class, were attained by day 4; specificity for LTA was affirmed by plaque inhibition tests. No plaque-forming cells were found in mice given isolated LTA over a 10,000-fold range of immunizing doses. Mice pretreated with a carrier known to activate thymus-derived helper lymphocytes produced a plaque-forming cell response to LTA only when immunized with LTA bound to the same carrier. This suggests that carrier-specific thymus-derived cells are needed to initiate an antibody response to poorly immunogenic LTA. Since an antibody response can be elicited in mice given heat-killed cells, other cell wall and/or cell membrane constituents may play an important role as immunologically active carriers for this antigen.

Structural studies of the capsular polysaccharide from Streptococcus pneumoniae type 1

The capsular polysaccharide from Streptococcus pneumoniae type 1 is composed of D-galactopyranosyluronic acid residues and 2-acetamido-4-amino-2,4,6-trideoxy-D-galactopyranosyl residues. The latter sugar, previously unknown in Nature, was not isolated but was identified from the products obtained on deamination of the polymer. Using n.m.r. spectroscopy, methylation analysis, and Smith degradation as the principal methods of structural investigation, it is concluded that the polysaccharide is composed of trisaccharide repeating-units having the structure: leads to 3)-alpha-Sugp-(1 leads to 4)-alpha-D-GalpA-(1 leads to 3)-alpha-D-GalpA-(1 leads to, in which Sug denotes the new sugar.

Use of the periodate oxidation coupling method for the detection of antibody and antibody-producing cells specific for staphylococcal lipoteichoic acid

The periodate oxidation and chromium chloride coupling methods were compared for their ability to sensitize indicator erythrocytes with staphylococcal lipoteichoic acid (LTA) for the detection of specific antibody. Erythrocytes, sensitized with periodiate-activated lipoteichoic acid, were found to be superior for use in both passive immune hemagglutination and hemolysis tests as well as in the technique of localized hemolysis-in-gel for the detection of specific antibody-producing cells against LTA.

Mechanisms by which hapten conjugates of pneumococcal polysaccharide interfere with the challenge of anti-hapten memory cells

Incubation of trinitrophenylated hemocyanin (TNP-KLH)-primed spleen cells with microgram amounts of 2,4-dinitrophenyl (DNP) or 2,4,6-trinitrophenyl (TNP) conjugates of pneumococcal polysaccharide type 3 (SIII) for as little as 5 min at 4 degrees C results in a specific "block" of the 19 S and 7 S adoptive memory response to TNP-KLH. This hapten-SIII-induced block of anti-hapten memory B cell responsiveness seems to be an example of specific receptor blockade. The block is specific and can be prevented by simultaneous incubation of the primed cells with hapten-protein conjugates which presumably compete with the hapten-polysaccharide for attachment to the B cell surface via anti-hapten Ig receptors. Removal via capping of these Ig receptors by exposure of TNP-KLH-primed memory cells to rabbit anti-mouse Fab serum for 45 min at 37 degrees C renders these cells refractory to the blocking effect of hapten-SIII. Once the hapten-SIII has attached to the memory cells, these blocked cells can be "rescued" (i.e. returned to a state of responsiveness) by incubating these cells with either mouse anti-SIII at 37 degrees C or rabbit anti-DNP serum at 4 degrees C. Since a papain digest of the IgG fraction of rabbit anti-DNP did not rescue the cells while the intact IgG did, a capping off of the TNP-SIII was proposed as the mechanims for this return to responsiveness of the hitherto blocked cells. A rescue was not seen by treatment of recipient mice with such B cell mitogens as dextran sulfate, endotoxin or purified protein derivative of tuberculin.

Genetic control of the antibody response to type 3 pneumococcal polysaccharide in mice. II. Relationship between IgM immunoglobulin levels and the ability to give an IgM antibody response

Serum IgM immunoglobulin levels and antibody responses to an optimally immunogenic dose of Type III pneumococcal polysaccharide (SSS-III) were assessed for F(1), F(2), and backcross progeny derived from crosses between high responding BALB/cAnN (B) and low responding CBA/HN (C) mice. The results obtained confirmed our original hypothesis, namely, that a major component, present on the X chromosome, governs the ability to respond to SSS-III in a decisive manner. Although all low responding C mice had low IgM levels, both intermediate and high responders had high IgM levels of the same magnitude. Treatment with bacterial lipopolysaccharides (LPS) resulted in a significant increase in the IgM levels of low responding C mice. While the IgM levels attained were similar to those of high responding B mice, not given LPS, no antibody specific for LPS appeared to be produced. These findings suggest that C mice are unable to make an IgM antibody response to SSS-III and other polysaccharide antigens, despite the fact that they possess the capacity to synthesize normal amounts of IgM immunoglobulin.

The type-specific substance from Pneumococcus type 13

1. The type-specific substance, S.13, from Pneumococcus type 13 was subjected to hydrolysis with alkali, followed by enzymic dephosphorylation, to yield a pentasaccharide. 2. The pentasaccharide, corresponding to the dephosphorylated repeating unit of S.13, was shown to be O-beta-d-galactopyranosyl-(1-->4)-O-beta- d-glucopyranosyl-(1-->3)-O-beta-d- galactofuranosyl-(1-->4)-O-2-acetamido-2-deoxy-beta-d- glucopyranosyl-(1-->2)-ribitol. 3. The phosphodiester linkages in S.13 join the hydroxyl group at position 1 of ribitol and the hydroxyl group at position 4 of a galactopyranosyl residue in the next repeating unit. 4. Ester groups, presumably O-acetyl, are located on positions 2 or 3 of most glucopyranosyl residues in S.13. 5. A partial structure for S.13 is proposed.

The type-specific substance from Pneumococcus type 29

1. A pentasaccharide, corresponding to the dephosphorylated repeating unit of the specific substance, S.29, from Pneumococcus type 29, was obtained by hydrolysis with alkali followed by enzymic dephosphorylation. 2. The pentasaccharide was shown to be O-2-acetamido-2-deoxy-beta-d-galactopyranosyl-(1-->6)-O-beta-d-galactofuranosyl-(1-->3)-O-beta-d-galactopyranosyl-(1-->6)-O-beta-d-galactofuranosyl-(1-->1)-ribitol. 3. The phosphodiester linkages in S.29 join the hydroxyl group at position 5 of ribitol and the hydroxyl group at position 3 or 4 of a 2-acetamido-2-deoxy-d-galactose residue in the next repeating unit. 4. A partial structure for S.29 was deduced from these experiments.

The type-specific substance from Pneumococcus type 10A(34). Structure of the dephosphorylated repeating unit

1. A hexasaccharide unit was isolated from the specific substance S. 10A from Pneumococcus type 10A (34) by hydrolysis with alkali followed by enzymic dephosphorylation. 2. The hexasaccharide was shown to be O-d-galactofuranosyl-(1-->3)-O-d- galactopyranosyl-(1-->4)-O-[d-galactofuranosyl- (1-->6)]-O-2-acet-amido-2-deoxy-d-galactopyranosyl- (1-->3)-O-d-galactopyranosyl-(1-->2)-ribitol.