Collaborative study for the characterisation of the BINACLE Assay for in vitro detection of tetanus toxicity in...

Tetanus vaccines for human and veterinary use are produced by formaldehyde-induced inactivation of tetanus neurotoxin (TeNT) purified from Clostridium tetani cultures. Due to the high morbidity caused by exposure to TeNT it is essential that the quality control of tetanus vaccines includes testing for absence of tetanus toxin as prescribed by European Pharmacopoeia monographs 0452 and 0697. Currently this test is carried out in guinea pigs for each bulk of tetanus toxoid. To test the applicability of the in vitro BINACLE ("binding and cleavage") assay as an alternative method for the quality control of tetanus vaccines, two collaborative studies were run by the European Directorate for the Quality of Medicines & HealthCare under the aegis of the Biological Standardisation Programme. The first collaborative study indicated that the method allows sensitive TeNT detection. However, a clear conclusion could not be drawn due to the high variability of the results. To address the variability, the protocol was optimised and further standardised for the second study. The study results demonstrated good assay precision, both with respect to repeatability and reproducibility. Importantly, the limit of detection was 0.11 ng/mL TeNT in five out of nine laboratories and 0.33 ng/mL in four out of nine laboratories, suggesting that the BINACLE assay can detect TeNT with similar sensitivity as in vivo toxicity tests and can thus be taken into consideration as an alternative method to the current compendial in vivo test.