Post-Vaccination Delivery of CpG ODNs Enhances the Th2-Associated Protective Immunity of the Smallpox DNA Vaccine

Potential threat of smallpox bioterrorism and concerns related to the adverse effects of currently licensed live-virus vaccines suggest the need to develop novel vaccines with better efficacy against smallpox. Use of DNA vaccines containing specific antigen-encoding plasmids prevents the risks associated with live-virus vaccines, offering a promising alternative to conventional smallpox vaccines. In this study, we investigated the efficiency of toll-like receptor (TLR) ligands in enhancing the immunogenicity of smallpox DNA vaccines. BALB/c mice were immunized with a DNA vaccine encoding the vaccinia virus L1R protein, along with the cytosine–phosphate–guanine (CpG) motif as a vaccine adjuvant, and their immune response was analyzed. Administration of B-type CpG oligodeoxynucleotides (ODNs) as TLR9 ligands 24 h after DNA vaccination enhanced the Th2-biased L1R-specific antibody immunity in mice. Moreover, B-type CpG ODNs improved the protective effects of the DNA vaccine against the lethal Orthopoxvirus challenge. Therefore, use of L1R DNA vaccines with CpG ODNs as adjuvants is a promising approach to achieve effective immunogenicity against smallpox infection.