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Development of a Novel Vaccinia Neutralization Assay |
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In anticipation of large-scale smallpox vaccination, clinical trials of new vaccine candidates with improved safety profiles, and new vaccinia immune globulin (VIG) products, there is an immediate need to develop new assays to measure vaccinia-specific immune responses. The classical assay to measure vaccinia neutralization, the Plaque Reduction Neutralization Test (PRNT), is slow, labor intensive, and difficult to validate and transfer. CBER investigators developed a novel vaccinia neutralization assay based on the expression of a reporter gene, b-galactosidase. The new neutralization assay is rapid (24 hr), sensitive and reproducible and easy to validate. The read-out is automated. The results obtained with the new assay are in agreement with those obtained in the traditional PRNT assays, but it has the advantage of being high throughput requiring much smaller volumes of specimens per assay. In addition, a new FDA VIG standard was established for distribution to other laboratories. The new assay will serve as an important tool for pre-clinical and clinical trials of new smallpox vaccines, and evaluation of therapeutic agents to treat vaccine associated adverse reactions. The establishment of the new reporter-gene vaccinia-neutralization assay allowed CBER to determine the potency of new VIG products and also to measure anti-vaccinia neutralizing antibodies in IVIG products from multiple manufacturers in the U.S. and other countries. Recently, the assay was transferred to other laboratories that will be involved in the evaluation of specimens from new vaccine trials designed to test the safety and efficacy of more attenuated strains of vaccinia. CBER also helped WRAIR in their smallpox vaccination campaign by testing serum specimens from recent vaccinees with questionable vaccine take.
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