The enzyme-linked immunosorbent assay of meningococcal and some related Escherichia coli polysaccharides

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.

Two enzyme linked immunosorbent assays for detecting antibodies against meningococcal capsular polysaccharides A and C

AIMS

To evaluate two of the recent methods of coating microtitre plates in the enzyme linked immunosorbent assay (ELISA) for detecting human antibodies against meningococcal capsular polysaccharides A and C with a view to validating a specific meningococcal antibody assay for routine clinical use.

METHODS

Two four-layer ELISA protocols were standardised: one method utilised meningococcal polysaccharides conjugated to poly-L-lysine polypeptide for coating the microtitre plates; another used polysaccharides mixed with methylated human serum albumin (mHSA). Titration curves were plotted for the ELISAs and the squared Pearson correlation coefficient (R2) was used to determine the degree of accuracy of fit of the curves. Specificity tests were performed by inhibition and adsorption studies.

RESULTS

Both methods gave good titration curves with a high R2 of > 0.98, indicating a high degree of accuracy in forming the curves. The titration end point after vaccination, obtained by the mHSA method, was 20 times higher, however, than that obtained by the poly-L-lysine method. Specificity tests showed that in the ELISA using polysaccharide/poly-L-lysine, antibody activity of a pre-vaccination serum sample was inhibited by 37%, and of post-vaccination serum by 50% with 1000-fold excess antigen. Antibody activity (post-vaccination) was reduced by 51% and 59%, respectively, by adsorption with antigen-coated Sepharose beads or adsorption with suspensions of killed meningococci. In contrast, antibody activity of a pre-vaccination serum was inhibited by 60% and a post-vaccination serum by 90% in ELISA employing polysaccharides mixed with mHSA. Reproducibility was better with the use of methylated human serum albumin than with poly-L-lysine; the former showed intrabatch and interbatch coefficients of variation of 4% and 2%, respectively, compared with 43% (intrabatch) and 16% (interbatch) obtained with the poly-L-lysine.

CONCLUSION

It is concluded that the antibody assay using meningococcal polysaccharides groups A and C mixed with mHSA is much better than that using polysaccharides coupled with poly-L-lysine.

Multicenter comparison of levels of antibody to the Neisseria meningitidis group A capsular polysaccharide measured by using an enzyme-linked immunosorbent assay

There is no standard immunoassay for evaluating immune responses to meningococcal vaccines. We developed an enzyme-linked immunosorbent assay to measure total levels of antibody to Neisseria meningitidis group A capsular polysaccharide. Five laboratories measured the antibody levels in six paired pre- and postvaccination serum samples by using the enzyme-linked immunosorbent assay. Methylated human serum albumin was used to bind native group A polysaccharide to microtiter plate surfaces. The between-laboratory coefficients of variation for pre- and postvaccination sera had ranges of 31 to 91 and 17 to 31, respectively. The mean laboratory coefficients of variation for pre- and postvaccination sera, respectively, were 17 and 11 (Molecular Biology Laboratory, Centers for Disease Control), 12 and 15 (Immunodiagnostic Methods Laboratory, Centers for Disease Control), 22 and 19 (Dana-Farber Cancer Institute), 38 and 38 (Bacterial Polysaccharide Laboratory, U.S. Food and Drug Administration), and 11 and 10 (Praxis Biologics, Inc.). Standardization of this enzyme-linked immunosorbent assay should allow interlaboratory comparison of meningococcal vaccine immunogenicity, thus providing a laboratory-based assessment tool for evaluating meningococcal vaccines.

Comparison of radioimmunoassay and enzyme-linked immunosorbent assay in measurement of antibodies to Neisseria meningitidis group A capsular polysaccharide

Antibodies to meningococcal group A polysaccharide were determined by radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) in serum samples from 16 adults vaccinated with bivalent meningococcal group A and C polysaccharide vaccine. The specific antibody levels in the serum samples were expressed as micrograms of antibody protein per milliliter of serum. For RIA the polysaccharide was radiolabeled extrinsically with 125I. Both native polysaccharide and polysaccharide labeled with 127I were used in ELISA. Because these antigens gave similar results, it can be concluded that the introduction of tyramine and iodine by the labeling procedure did not alter the antigenic activity of the polysaccharide. The reproducibility of RIA was clearly better than that of ELISA. The antibody levels detected by the methods were equal, which means that ELISA can be used satisfactorily to measure antibodies to meningococcal group A polysaccharide quantitatively. Some discrepant results were found due to an underestimation of immunoglobulin M antibodies in ELISA. This was shown by a correlation test in which a weakly significant negative correlation was found between the immunoglobulin M antibody level/immunoglobulin G antibody level ratio and the RIA antibody level/ELISA antibody level ratio.

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.