Expression of a large, nontoxic fragment of botulinum neurotoxin serotype A and its use as an immunogen.

Using the polymerase chain reaction, a large fragment of botulinum toxin was placed in two expression systems, one designed to produce a fusion protein product and another designed to produce only the toxin fragment. Expression of the fragment in the latter system was inconsistent. Expression of the fusion protein was easily measurable by ELISA. Mice were vaccinated with crude fusion protein, then challenged with native toxin. Mice receiving two immunizations were partially protected from up to 1200 LD50, suggesting that this toxin fragment may be a good vaccine candidate to replace the currently used toxoid.