Testing of veterinary clostridial vaccines: from mouse to microtitre plate

Vaccines to protect against clostridial diseases are among the most common veterinary biologicals. Each batch of these materials is subjected to a variety of toxicity and antigenicity tests. The potency of the final vaccine is then assessed by Toxin Neutralisation Test (TNT). All of these tests use mice and have lethal endpoints. Development of alternatives for potency testing was based on ELISAs able to measure antibody levels to the specific toxins relative to a standard serum with a defined unitage. These alternative assays were shown to correlate with the relevant TNTs and have been accepted by European Regulatory Authorities as batch release potency tests. Recently we have developed in vitro cell line alternatives for the toxicity and antigenicity tests for Cl. septicum using the VERO cell line. With this cell line it has been possible to develop in vitro assays which, when compared with the in vivo tests, gave correlations of 87% to 100%. Having shown proof of principle, similar cell line assays have been developed for Cl. novyi and Cl. perfringens types C and D.