Protection with a recombinant Hc of Clostridium Botulinum neurotoxin serotype A from Escherichia coli as an effective subunit vaccine.

A recombinant Hc of Clostridium botulinum neurotoxin serotype A (AHc) was successfully expressed in Escherichia coli for use as an antigen, and the purified AHc was used to vaccinate mice and evaluate their survival against challenge with active botulinum neurotoxin serotype A. The mice, given twice or third subcutaneous vaccinations with a dosage of 1 microg AHc mixed with Freund adjuvant, were completely protected against an intraperitoneal administration of 1,000,000 50% lethal doses (LD(50)) of neurotoxin serotype A. Following the administration of AHc using alhydrogel adjuvant via the intramuscular route, a strong protective immune response was also elicited in the vaccinated mice. A dose-response was observed in protective efficacy with increasing AHc dosage and number of vaccinations. Mice that received two injections of >or= 0.2 microg and three injections of >or= 0.04 microg were completely protected when challenged with 100,000 LD(50) of neurotoxin serotype A. These results clearly suggest that the recombinant AHc highly expressed in Escherichia coli is very efficacious in protecting against challenge with active botulinum neurotoxin serotype A in mouse model and a good subunit candidate vaccine against botulinum neurotoxin serotype A for human use.