Development and validation of a 6-plex Luminex-based assay for measuring human serum antibodies to group B streptococcus capsular polysaccharides

ABSTRACT

Six serotypes (Ia, Ib, II, III, IV, and V) cause nearly all group B streptococcal (GBS) disease globally. Capsular polysaccharide (CPS) conjugate vaccines aim to prevent GBS disease, however, licensure of a vaccine would depend on a standardized serological assay for measuring anti-CPS IgG responses. A multiplex direct Luminex-based immunoassay (dLIA) has been developed to simultaneously measure the concentration of serum IgG specific for the six prevalent GBS CPS serotypes. Assay validation was performed using serum samples obtained from human subjects vaccinated with an investigational 6-valent GBS CPS conjugate vaccine. Results for the assay are expressed as IgG concentrations (µg/mL) using a human serum reference standard composed of pooled sera from vaccinated subjects. The lower limits of quantitation (LLOQ) for all serotypes covered in the 6-plex GBS IgG dLIA fell within the range of 0.002-0.022 µg/mL IgG. Taken together, the 6-plex GBS IgG dLIA platform is specific for the six GBS serotypes included in Pfizer’s investigational vaccine, has a wide dilution adjusted assay range, and is precise (<18.5% relative standard deviation) for all serotypes, and, therefore, is suitable for quantitatively measuring vaccine-induced or naturally acquired serotype-specific anti-CPS IgG responses against GBS.

KEYWORDS:

• Streptococcus agalactiae
• group B streptococcus
• capsular polysaccharide
• serotype
• immunoassay
• IgG
• Luminex
• conjugate vaccine

Acknowledgments

The authors would like to thank Pfizer colleagues Natalie Silmon de Monerri for critically reviewing the manuscript, Christina D’Arco for editorial support, and laboratory analyst William Manzo.

Disclosure statement

All authors are current or past employees of Pfizer and may, as a consequence, be shareholders. Pfizer was involved in the design, analysis, and interpretation of the data in this research study, the writing of this report, and the decision to publish.

Author contributions statement

M. A. G. contributed to overall study design, conception of the work, data analysis, and original writing of the manuscript. M. L, D.G., D.P., and C. D. G. performed dLIA experiments, optimizations, data analysis and contributed to conception of the work; S. S. prepared the GBS-CPS poly lysine conjugates. H. H. N., A. M., and C. Y. T. performed statistical evaluation; P. G., W. V. K., and A. S. A. contributed to study conception, interpretation of data, and funding acquisition. All authors contributed to the development of the manuscript.

Data availability statement

All raw and processed data files are available upon request to the corresponding author. The data are not publicly available due to privacy restrictions.

Additional information

Funding

This work was supported by Pfizer Inc.