Differential immunogenicity of a DNA vaccine containing the Streptococcus mutans wall-associated protein A gene versus that containing a truncated derivative antigen A lacking in the hydrophobic carboxyterminal region.

Two plasmid DNA constructs were obtained by cloning separately into the eukaryotic expression vector pcDNA3.1/V5-His-TOPO the wall-associated protein A (wapA) gene of Streptococcus mutans GS-5 or its truncated derivative antigen A (agA) gene encoding a known candidate antigen for dental caries vaccine. The immunogenicity of the two constructs, designated pcDNA-wapA and pcDNA-agA, was compared by intranasal immunization of two groups of mice using the cationic DMRIE-C (1,2-dimyristyloxypropyl-3-dimethylhydroxy ethyl ammonium bromide-cholesterol) as an adjuvant. Immunization with pcDNA-wapA or pcDNA- agA resulted in specific salivary IgA and systemic IgG antibodies to the target antigens after two doses given at 3-week intervals. Higher salivary IgA level was observed in the mice immunized with the pcDNA-wapA vaccine compared to those immunized with the pcDNA-agA vaccine. Furthermore, anti-WapA antibody inhibited S. mutans sucrose-dependent adherence suggesting a potential protection against S. mutans colonization of the tooth, while anti-AgA had no significant effect. Indeed, prediction and analysis of protein epitopes showed that WapA contains highly promiscuous MHC-II binding motifs in addition to those found in AgA. Immunodot assay confirmed that WapA bound biotin-labeled dextran, whereas AgA did not. These data indicated that full-length WapA is a better candidate vaccine antigen than the soluble AgA, which is truncated in the hydrophobic membrane and wall-spanning region.