Immunogenicity of a subunit vaccine against Bacillus anthracis.

The current approved vaccine against anthrax is based on protective antigen (PA) of Bacillus anthracis, requires six injections over an 18-month period and has a known history of side effects. Therefore, there is significant effort towards developing an improved vaccine against B. anthracis. Here we separately engineered and expressed domain 4 of PA (PAD4) and domain 1 of lethal factor (LFD1) as fusions to lichenase (LicKM), a thermostable enzyme from Clostridium thermocellum, and transiently expressed these fusions in Nicotiana benthamiana. Plant-produced antigens were combined and immunogenicity was evaluated in mice. All animals that received the experimental vaccine developed high antibody titers that were predominantly IgG1 and were able to neutralize the effects of LeTx in vitro.