Pharmaceutical and immunological evaluation of human papillomavirus viruslike particle as an antigen carrier.

We report the preparation and the immunogenicity of a conjugate vaccine obtained by chemically conjugating a variant of the extracellular peptide fragment of influenza type A M2 protein to the human papillomavirus (HPV) viruslike particle (VLP). Conjugates comprised of approximately 4,000 copies of the antigenic peptide per VLP are obtained as the result of the reaction between a C-terminal cysteine residue on the peptide and the maleimide-activated HPV VLP. The resulting conjugates have an average particle size slightly larger than the carrier and present enhanced overall stability against chemical and thermal-induced denaturation. The M2-HPV VLP conjugates lost the binding affinity for anti-HPV conformational antibodies but retained reactivity to a M2-specific monoclonal antibody. The conjugate vaccine formulated with aluminum adjuvant and delivered in two doses of 30-ng peptide was found to be highly immunogenic and conferred good protection against lethal challenge of influenza virus in mice. These results suggest that HPV VLP can be used as a carrier for synthetic or small antigens for the development of subunit vaccines.