Development and Characterization of a Multiplex Bead-Based Immunoassay To Quantify Pneumococcal Capsular Polysaccharide- Specific Antibodies

Enzyme-linked immunosorbent assay (ELISA), the traditional antibody quantification technique, has several limitations, espe-cially when used to evaluate multivalent and/or infant vaccines. We have developed a multiplex bead-based antibody quantifica-tion assay (MBIA) to measure antibody response to multiple pneumococcal (Pn) serotypes (St) in a single assay. MBIA was com-pared with theWHO ELISA using aWHO panel of 12 international calibration sera for 7 Pn Sts. An agreement of 75 to 92%was obtained for all 7 Sts. MBIA exhibited good robustness, with the assay variability at<16%. Amajor contributor to MBIA vari-ability was the cell wall polysaccharide (CWPs) content in Pn St-specific capsular Ps. This necessitated careful CWPs (20g/ml) preadsorption of sera. MBIA is specific, robust, and reproducible and offers high throughput. The use of MBIA will greatly re-duce the cost and time required to evaluate the immune response to multiple Pn Sts and could help promote the licensure of fu-ture Pn and other multivalent vaccines. A number of immunoassays have been developed to measurethe concentration of serotype (St)-specific human IgG anti-pneumococcal (anti-Pn) capsular polysaccharide (Ps) antibodies following induced and natural immunization. The standard mea-surement of Pn antibody in most laboratories today relies on the World Health Organization (WHO) enzyme-linked immunosor-bent assay (ELISA) (3, 17). This standardized assay has severa