Immunogenicity and protective efficiency in mice of a smallpox DNA vaccine candidate

The adverse reactions of the current live smallpox vaccine, and potential use of smallpox as a bioterrorism weapon, have highlighted the need to develop a new effective vaccine for this infectious disease. In the present study, a DNA vaccine vector was produced, which was optimized for expression of the vaccinia virus L1 antigen in a mouse model. Plasmid-encoded IgM-tL1R, which contains a truncated L1R gene fused to an IgM signal sequence, was constructed and expressed under the regulation of an SV40 enhancer. The expressed recombinant tL1 proteins were successfully secreted into the culture media. The DNA vaccine was administered to mice by electroporation, and animals were subsequently challenged with the lethal dose of vaccinia virus. We observed that immunization with IgM-tL1R induced robust neutralizing antibody responses and provided complete protection against a vaccinia virus infection. Isotyping studies revealed a lower IgG1/IgG2a ratio following vaccination with IgM-tL1R, suggesting the stimulation of Th1 immune responses. Our results propose that an optimized DNA vaccine, IgM-tL1R, can be effective in eliciting an anti-vaccinia virus immune response and provide protection against lethal orthopoxvirus challenge.