Calibration of a serum reference standard for Group B streptococcal polysaccharide conjugate vaccine development using surface plasmon resonance

Abstract

Group B streptococcus (GBS) is a leading cause of neonatal morbidity and mortality worldwide. Development of a maternal vaccine to protect newborns through placentally transferred antibody is considered feasible based on the well-established relationship between anti-GBS capsular polysaccharide (CPS) IgG levels at birth and reduced risk of neonatal invasive GBS. An accurately calibrated serum reference standard that can be used to measure anti-CPS concentrations is critical for estimation of protective antibody levels across serotypes and potential vaccine performance. For this, precise weight-based measurement of anti-CPS IgG in sera is required. Here, we report an improved approach for determining serum anti-CPS IgG levels using surface plasmon resonance with monoclonal antibody standards, coupled with a direct Luminex-based immunoassay. This technique was used to quantify serotype-specific anti-CPS IgG levels in a human serum reference pool derived from subjects immunized with an investigational six-valent GBS glycoconjugate vaccine.

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

“… 24 The serotype-specific nature of IgG antibodies targeting the envelope CPS also makes it difficult to provide a basis for protective thresholds for less common capsular GBS serotypes. 25 The 6-plex GBS IgG dLIA permits direct cross-serotype comparison of CPS-specific IgG, 27 and in combination with the validation presented in this work, positions the assay as a powerful tool to serve as the primary serological readout for global seroepidemiology studies and vaccine clinical trials.…”

“… 10 , 28 This reference standard has weight-based assigned IgG antibody concentrations for all six serotypes and is self-calibrating, as previously described. 27 The reference standard uses log–log linear regression to interpolate test sample IgG concentrations (µg/mL) from median fluorescence intensity (MFI) values.…”

“…The signal output was expressed as MFI which were evaluated against the human serum reference standard curve with weight-based IgG assignments (in µg/mL) for each serotype, as previously described. 27 …”

“… 11 The development of a human serum reference standard with weight-based IgG assignments was previously described using surface plasmon resonance (SPR) and permits the comparison of anti-CPS IgG across serotypes. 27 The present study describes the validation of the 6-plex GBS IgG dLIA, and the results presented here were generated using the cross-standardized reference standard. 27 …”

“… 27 The present study describes the validation of the 6-plex GBS IgG dLIA, and the results presented here were generated using the cross-standardized reference standard. 27 …”