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Multilaboratory Evaluation of a Viability Assay for Measurement of Opsonophagocytic Antibodies Specific to the Capsular Polysaccharides of Streptococcus pneumoniae

Sandra Romero-Steiner,^1* Carl Frasch,² Nelydia Concepcion,² David Goldblatt,³ Helena Käyhty,⁴ Merja Väkeväinen,^4, Craig Laferriere,⁵ Dominique Wauters,⁵ Moon H. Nahm,⁶ Mark F. Schinsky,^1, Brian D. Plikaytis,¹ and George M. Carlone¹

Centers for Disease Control and Prevention, Atlanta, Georgia,¹ U.S. Food and Drug Administration, Bethesda, Maryland,² University of London, London, United Kingdom,³ National Public Health Institute, Helsinki, Finland,⁴ Glaxo SmithKline Biologicals, Rixensart, Belgium,⁵ University of Rochester, Rochester, New York⁶

Received 24 June 2003/ Returned for modification 23 July 2003/ Accepted 18 August 2003

Opsonophagocytosis is a correlate of protection that measures the functional activity of vaccine-induced antibodies. A standardized opsonophagocytosis assay (OPA) should be used as part of the evaluation of current and future pneumococcal (Pnc) polysaccharide (Ps)-based vaccines. We enrolled five laboratories to evaluate a previously standardized viability OPA. Each laboratory was provided with a detailed OPA protocol, seven target Pnc strains (serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F), two quality control sera and 12 paired sera (blinded) from adult donors who received one dose of the 23-valent Pnc Ps vaccine. Laboratories sent their results to the Centers for Disease Control and Prevention for analysis. Sera were tested in duplicate (single run), and the results were averaged to yield a single OPA titer (50% killing) for each serum sample. The percentage of sera within one or two dilutions of the calculated median OPA titer was determined for each laboratory and for each serotype. In general, laboratories were capable of detecting OPA titers within one or two dilutions of the median for at least 75 and 88%, respectively, of the sera tested. The level of agreement with the median OPA titers varied depending on the participating laboratory (overall agreement = 0.8 [99% confidence interval = 0.75 to 0.85]). All OPA median titers reported for quality control sera were within one dilution of the expected titer. We conclude that this OPA can be done in multiple laboratories with a high degree of interlaboratory reproducibility.

Present address: University of Texas Southwestern Medical Center, Dallas, Tex.

Present address: School of Medicine, Washington University, St. Louis, Mo.

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