Development and validation of a monocyte activation test for the control/safety testing of an OMV-based meningococcal B vaccine.

It is imperative to ensure biological products are free of contaminating pyrogenic material prior to administration to patients. Historically the rabbit pyrogen test (RPT) was used to screen for such contamination in medicines for intravenous delivery. This test was adapted for use to screen vaccines. However, some, including meningococcal vaccines containing outer membrane vesicles, are intrinsically pyrogenic. Indeed, this is the case for Bexsero which contains relatively high levels of endotoxin and other potential pyrogens such as lipoproteins and porins. The RPT proved a difficult method for measuring the pyrogenic content of Bexsero and differences between laboratories in different countries made repeat testing at the control laboratories problematic resulting in batches being wrongly identified as unsafe. At NIBSC a monocyte activation test (MAT) was adapted and validated as an alternative. This required setting of a specification in-house and deciding on a decisional procedure using multiple donors, allowing batches equally pyrogenic or less, than those batches shown to be safe in a clinical trial, to be certified as safe. The resulting format was a reference comparison method with an upper limit of 1.8 relative pyrogen units (RPU). The batch passed if an initial four donors had a response equal to or less than 1.8 RPU, if one donor is above this limit the batch was tested in a further four donors and seven of the eight must be equal to or below 1.8 RPU. If two donors have a response greater than 1.8 the batch failed.