A non-toxic recombinant Clostridium septicum α toxin induces protective immunity in mice and rabbits

Clostridium septicum alpha toxin (CSA) plays significant roles in ruminant's braxy. Genetically engineered CSA has been shown to function as a potential vaccine candidate in the prevention of the disease caused by Clostridium septicum. In the present study, we synthesized a non-toxic recombinant, rCSA_m4/TMD by introducing four amino acid substitutions (C86L/N296A/H301A/W342A) and 11-amino-acid deletion (residues 212 to 222). Compared to recombinant CSA, rCSA_m4/TMD showed no cytotoxicity to MDCK cells and was not fatal to mice. Moreover, rCSA_m4/TMD could protect immunized mice against 5 × mouse LD₁₀₀ (100% lethal dose) of crude CSA without obvious pathological change. Most importantly, rabbits immunized with rCSA_m4/TMD produced high titers of neutralizing antibodies which protected the rabbits against crude CSA challenge. These data suggest that genetically detoxified rCSA_m4/TMD is a potential subunit vaccine candidate against braxy.