Quantitative determination of pneumococcal capsular polysaccharides in the polyvalent vaccine. I. Standardization of an immunoelectrophoretic method

Principles of vaccine potency assays

Compared with biologics, vaccine potency assays represent a special challenge due to their unique compositions, multivalency, long life cycles and global distribution. Historically, vaccines were released using in vivo potency assays requiring immunization of dozens of animals. Modern vaccines use a variety of newer analytical tools including biochemical, cell-based and immunochemical methods to measure potency. The choice of analytics largely depends on the mechanism of action and ability to ensure lot-to-lot consistency. Live vaccines often require cell-based assays to ensure infectivity, whereas recombinant vaccine potency can be reliably monitored with immunoassays. Several case studies are presented to demonstrate the relationship between mechanism of action and potency assay. A high-level decision tree is presented to assist with assay selection.

Relation between structure and immunologic properties of the Vi capsular polysaccharide

The Vi capsular polysaccharide of Salmonella typhi is a linear homopolymer of poly-alpha(1----4)GalNAcp variably O acetylated at the C-3 position. Serum antibodies elicited by this antigen confer protective immunity against typhoid fever. The relation between the immunologic properties and structure of Vi was investigated by carboxyl reduction, O deacetylation, and acid hydrolysis. The immunogenicity of Vi was closely related to its degree of O acetylation. Partial O deacetylation slightly increased immunogenicity; complete O deacetylation eliminated the immunogenicity of Vi. O-deacetylated Vi, however, still reacted with antisera prepared by injection of whole bacteria. Carboxyl reduction, in contrast, had a comparatively slight effect upon both the immunogenicity and antigenicity of Vi. Retention levels of antigenicity after acid treatment were greater for both the native and carboxyl-reduced Vi than for the O-deacetylated product. The Courtauld-Koltun space-filling model of a pentamer of Vi demonstrated that the bulky nonpolar O-acetyls, which protrude in rows on both sides, make up most of the surface. The carboxyls are less exposed and are partially shielded by the O-acetyls. The molecular model thus provides an explantation for the dominant role of the O-acetyls, as well as the lesser effect of carboxyl reduction, upon the immunologic properties of Vi.

Virulence, immunity, and vaccine related to Streptococcus pneumoniae

The pathogenesis of bacterial infection involves a series of interactions between the virulence determinants of the microorganisms and the immunity of the host. Studies on the molecular structure and immunological properties of pneumococcal virulence factors have provided general knowledge for the chemical basis of immunogenicity and prevention of bacterial infection. Antibody responses to PS and protein antigens can be greatly affected by their physicochemical properties, e.g., molecular size, specific determinants, conformation, etc. Characterization of group 19 pneumolysins and cloning of their ply genes were studied to examine the relationship of ply to virulence. Group 19 pneumococci all contained ply; the disease-isolated types of 19F and 19A appeared to show a higher specific hemolytic activity and yield than the nonpathogenic types, 19B and 19C. Genomic DNA that contained the ply gene from group 19 strains were analyzed by the polymerase chain reaction (PCR). Type 2 oligonucleotide primers recognized and initiated synthesis of an identical 1.5 kb DNA fragment in types 2, 19F, 19A, 19B, and 19C. Their sizes of restriction DNA fragments were also found to be homologous. Thus, group 19 ply genes showed remarkably similar characteristics. A difficult problem in the development of vaccines against bacterial diseases is the poor immune response of young children to purified PSs. The efficacy of pneumococcal vaccine might be improved by supplementation with inactivated pneumolysin in the form of a PS-protein conjugate.

C-polysaccharide in a pneumococcal vaccine

The 14-valent pneumococcal vaccine, Pneumovax, was found to contain approximately 25o micrograms per ml of the cell-wall antigen, C-polysaccharide (C-Ps), in addition to 100 micrograms per ml of each of the 14 capsular polysaccharides. Rabbit anti-C-Ps antiserum recognized four components of this C-Ps with different antigenic determinants, corresponding to four fragments with different molecular sizes. By lectin affinity chromatography it was demonstrated that some of the C-Ps in the vaccine contained cell-wall residues. The methods used in this study can also be used for the characterization of other polysaccharide preparations.

Molecular sizing of individual polysaccharides in polyvalent pneumococcal and meningococcal vaccines by column chromatography and immunoelectrophoresis

We determined the molecular size of meningococcal and pneumococcal polysaccharides in final vaccines, using a combination of column chromatography and simple rocket immunoelectrophoresis. We found a good correlation between the distribution coefficients obtained with UV monitoring or ELISA and immunoelectrophoresis.

The quantitative immunochemical determination of pneumococcal and meningococcal capsular polysaccharides by light scattering rate nephelometry

A quantitative nephelometric method was used for the measurement of the individual pneumococcal, as well as meningococcal, polysaccharides in the polyvalent vaccine final containers. This method is simple, rapid, inexpensive, and provides both qualitative and quantitative analyses of the polyvalent polysaccharide vaccines. By this method the individual pneumococcal types, 1, 2, 3, 4, 6A, 7F, 8, 9N, 12F, 14, 18C, 19F, 23F and 25 polysaccharides, were found to be present at 90-114% of the manufacturer's indicated concentrations; meningococcal group A, C, Y and W135 polysaccharides were at 90-108% of the manufacturer's listed concentrations. This nephelometric method coupled with gel filtration can also be used for measurement of the molecular sizes or stability of individual polysaccharides in the final container. Pneumococcal polysaccharide types 3, 6A, 9N and 19F, used as representative types, were treated with 0.5 N hydrochloric acid. The molecular sizes for types 3 and 9 N polysaccharides were stable to acid treatment. In contrast, types 6A and 19F polysaccharides were degraded. Heating meningococcal groups A, C, Y and W135 polysaccharides at 37 degrees C for 48 h did not affect their molecular size in the polyvalent vaccine.

Immunoelectrophoretic characterization of the molecular weight polydispersion of polysaccharides in multivalent bacterial capsular polysaccharide vaccines

The molecular weight polydispersion of single antigens present in multivalent bacterial capsular polysaccharide vaccines has been characterized by an immunoelectrophoretic method. Chromatographic effluents from Sepharose gel of bacterial capsular polysaccharide vaccines were tested by fused-rocket immunoelectrophoresis and the distribution coefficient (Kd) of each polysaccharide present in the mixture was calculated. The method appeared to be efficient and reproducible. However, different Kd values were obtained by immunoelectrophoretic and chemical or physical analysis of the chromatographic effluents of each single polysaccharide component. The use of this immunoelectrophoretic procedure was extended to the potency control of multivalent meningococcal and pneumococcal polysaccharide vaccines in order to detect changes in the molecular weight polydispersion of each antigen with time.

Detection of "neutral" type 7F and type 14 pneumococcal capsular polysaccharides by immunoelectrophoresis

Type 7F and type 14 pneumococcal capsular polysaccharides, neutral at pH 8.6, were studied by immunoelectrophoresis at pH 5. Three techniques were used: rocket, countercurrent, and reversed immunoelectrophoresis. Our results show that these two capsular polysaccharides types can be detected at pH 5 with high sensitivity.

Cross-immunogenicity of pneumococcal group 9 capsular polysaccharides in adult volunteers

Group 9 organisms (types 9N, 9A, 9L, and 9V) account for about 3 to 4% of pneumococcal disease isolates throughout the world. Types 9N and 9V comprise about 90% of the group 9 disease isolates. Type 9N is more common than type 9V in adults, and type 9V predominates in infants and children. In the United States there have been eight reported cases due to group 9 pneumococci in individuals previously vaccinated; six were type 9V and two were type 9N. To ascertain the cross-immunogenicity of group 9 polysaccharides, volunteers were injected with vaccines of monovalent types 9N, 9A, 9V, or 9L, or bivalent (9N and 9A) or trivalent (9N, 9A, and 9V) polysaccharide vaccines. Monovalent types 9N, 9V, and 9L each stimulated a 5.8- to 7.5-fold geometric mean rise, and at least 80% of the volunteers responded with a twofold or greater homologous antibody rise. Type 9V induced a 5.8-fold geometric mean rise, but only 66% of the volunteers responded with a twofold or greater homologous antibody rise. Type 9N induced only a 2.1-fold geometric increase, and only 54% of the volunteers responded with a twofold or greater rise in anti 9V antibodies. Types 9L and 9A were the most cross-immunogenic. The trivalent preparation (9N, 9A, and 9V) gave the highest geometric mean titer and seroconversion rate to each of the group 9 polysaccharides. These results suggest that the polyvalent pneumococcal vaccine with its type 9N does not induce a satisfactory anti-type 9V response and should contain additional components in order to achieve greater protection against group 9 organisms.