Assignment of weight-based antibody units for four additional serotypes to a human anti-pneumococcal standard reference serum 007sp.

The pneumococcal ELISA reference standard serum, Lot 89SF, has been in use since 1990 and was replaced with a new reference standard serum, 007sp in 2013. This serum was generated under an FDA-approved clinical protocol, where 278 adult volunteers were immunized with the 23-valent unconjugated polysaccharide vaccine, Pneumovax II®, and a unit of blood was obtained twice within 120 days following immunization. Pooled serum was prepared from the plasma, filled at 6ml per vial and lyophilised. Five independent laboratories participated in bridging the serotype specific IgG assignments for 89SF to 007sp to establish equivalent reference values for 13 pneumococcal capsular serotypes (1,3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, 23F) using the WHO reference ELISA. A subsequent follow up study established equivalent reference values for an additional seven serotypes (8, 10A, 11A, 12F, 15B, 22F, 33F). In this study three laboratories assigned weight-based IgG concentrations in mcg/mL of serum to 007sp for four additional serotypes; 2, 9N, 17F and 20A. This study completes the assignment of serotypes in 89SF to 007sp. In addition, the IgG antibody assignments for a 12 member WHO QC serum panel were extended to cover the four additional serotypes. Agreement was excellent with a concordance correlation coefficient (rc ) > 0.996 when each laboratory was compared to the assigned values for the 12 WHO QC sera. The 007sp preparation has replaced 89SF as the pneumococcal reference standard. Sufficient quantities of 007sp are projected to be available for the next 25 years.