Interlaboratory study to assess precision and reproducibility of the meningococcal antigen surface expression (MEASURE) assay to quantify factor H binding protein expression at the surface of meningococcal serogroup B strains.

Background: The serum bactericidal antibody using human complement (hSBA) assay, the accepted surrogate measure of meningococcal vaccine efficacy, is limited by human sera and complement requirements. Pfizer developed and validated the flow-cytometry-based Meningococcal Antigen Surface Expression (MEASURE) assay to quantify surface-expressed factor H binding protein (fHbp) levels on intact meningococci. Surface expression of fHbp is correlated with hSBA assay killing by MenB-fHbp (Trumenba)-induced antibody, meaning the MEASURE assay can be used to predict meningococcal serogroup B (MenB) strain susceptibility to antibodies elicited by MenB-fHbp. This study aimed to evaluate interlaboratory precision and reproducibility of the MEASURE assay.

Methods: The MEASURE assay was transferred to UK Health Security Agency (UKHSA) and US Centers for Disease Control and Prevention (CDC) laboratories. MEASURE assay results from 42 MenB strains encoding sequence-diverse fHbp variants that express fHbp at different levels were compared between the UKHSA, CDC, and Pfizer laboratories. Intermediate precision within each laboratory was determined.

Results: Pairwise comparisons of fHbp expression levels for all 42 MenB test strains showed >97 % agreement across the 3 laboratories when strains were grouped above or below a mean fluorescence intensity level of 1000, the threshold previously established as indicative of susceptibility to MenB-fHbp-induced antibodies in the hSBA assay. Each laboratory met assay precision criteria of ≤30 % total relative standard deviation.

Conclusions: Quantification of fHbp surface expression using the MEASURE assay is robust and reproducible across different laboratories. Previously determined cutoffs corresponding to predicted susceptibility to vaccine-induced antibodies can be applied to MEASURE data generated across laboratories.