Toxicity and immunogenicity of pertussis whole cell vaccine in one animal model

The required in vivo assays for the release of Whole Cell Pertussis Vaccine are the Mouse Weight Gain test (MWGT) for assessment of specific toxicity and the Mouse Protection test (MPT) to estimate the potency. Despite the fact that both assays are criticised for the use of large number of animals, poor precision or insensitivity, more precise alternatives--such as the Leukocytosis Promotion test (LP-test) and Pertussis Serological Potency Test (PSPT)--are still not fully accepted. During the optimisation of the production process, the need for more accurate parameters to determine toxicity and potency became essential. To reduce substantially the number of animals, we have combined the MWGT with the LP-test and PSPT in one model, named the Mouse Toxicity and Immunogenicity test (MTI-test). Animals are inoculated with half a human dose and are weighed individually pre-immunisation and 16 hours (parameter for endotoxin), three and seven days post immunisation. Additionally, the number of leukocytes (parameter for PT) is determined on day 7 and after 28 days the animals are bled individually for immunogenicity testing (parameter for potency). A lyophilised reference vaccine is included as a positive control to standardise the assay and to determine its reproducibility. The advantage of this modified procedure is that the data on toxicity and immunogenicity are obtained from the individual mouse, which enables statistical analysis to be made. The leucocytosis data can be used to check whether mice were vaccinated correctly, allowing for the elimination of incorrectly vaccinated mice from the assay. Furthermore, this assay can be used to determine the consistency of production, the influence of adjuvant on toxicity, as well as the composition and stability of vaccines.