Particle bombardment-mediated DNA vaccination with rotavirus VP6 induces high levels of serum rotavirus IgG but fails to protect mice against challenge.

The rotavirus inner capsid protein VP6 contains conserved epitopes that are potential targets for eliciting protective immunity against different serotypes within the same group of rotavirus. In order to determine whether VP6 alone can induce protective immunity, an expression vector pcDNA1/EDIM6 containing gene 6 of rotavirus EDIM strain was constructed and used as a vaccine in an adult mouse model. Cloned gene 6 was determined to be 1356 nucleotides long and contained a 5' noncoding region of 23 nucleotides, a 3' noncoding region of 139 nucleotides, and a coding frame of 1194 nucleotides for a polypeptide of 397 amino acid residues. Recombinant VP6 was expressed in rabbit reticulocyte lysate and the heat-denatured recombinant VP6 migrated in SDS-gels with an apparent molecular weight of approximately 43 kDa. Five additional polypeptide bands corresponding to oligomers of recombinant VP6 were observed when the expressed product was not heat denatured. To determine the immunogenicity of recombinant VP6, female BALB/c mice were injected intramuscularly or intradermally with pcDNA1/EDIM6, or were inoculated epidermally with plasmid-coated gold beads using the Geniva Accell particle delivery device. Only intradermal injection and particle delivery elicited measurable serum anti-rotavirus IgG responses, but responses developed following particle delivery were significantly (P < 0.001) greater. However, none of the delivery methods induced serum or stool anti-rotavirus IgA responses and, when challenged with EDIM no protection against infection was observed in the immunized mice. Therefore, parenteral immunization with VP6 alone elicited large anti-rotavirus IgG responses but did not elicit protection against murine rotavirus infection in this model.