Development and evaluation of alternative testing methods for the in vivo NIH potency test used for the quality control of inactivated rabies vaccines

The potency control of rabies vaccines is routinely performed in a vaccination-challenge test (NIH test), which induces substantial distress and suffering in laboratory mice. Although, according to the recommendations by the WHO, partial replacement of this in vivo potency test by in vitro antigenicity testing is permitted, no internationally accepted alternative testing method is yet available. In the present study, we focussed on the use of monoclonal antibody-based ELISA systems for the quantitative detection of rabies glycoprotein in vaccines for human and veterinary use. Results in the newly developed competitive binding ELISA for glycoprotein quantification showed good correlation with NIH potencies. Also, the applicability for vaccines based on different virus strains was demonstrated. Quantification methods were remodelled to convenient ELISA kits for interlaboratory evaluation of the sensitivity and reproducibility in an internal collaborative study. The relevance of the data generated with these assays is currently assessed by parallel studies evaluating vaccine-induced B and T cell-mediated immunity. We speculate that the assays developed will provide, at least in part, a suitable replacement for the NIH potency test.