Polyglutamic acid-trimethyl chitosan-based intranasal peptide nano-vaccine induces potent immune responses against group A streptococcus.

Peptide-based vaccines have the potential to overcome the limitations of classical vaccines; however, their use is hampered by a lack of carriers and adjuvants suitable for human use. In this study, an efficient self-adjuvanting peptide vaccine delivery system was developed based on the ionic interactions between cationic trimethyl chitosan (TMC) and a peptide antigen coupled with synthetically defined anionic α-poly-(l-glutamic acid) (PGA). The antigen, possessing a conserved B-cell epitope derived from the group A streptococcus (GAS) pathogen and a universal T-helper epitope, was conjugated to PGA using cycloaddition reaction. The produced anionic conjugate formed nanoparticles (NP-1) through interaction with cationic TMC. These NP-1 induced higher systemic and mucosal antibody titers compared to antigen adjuvanted with standard mucosal adjuvant cholera toxin B subunit or antigen mixed with TMC. The produced serum antibodies were also opsonic against clinically isolated GAS strains. Further, a reduction in bacterial burden was observed in nasal secretions, pharyngeal surface and nasopharyngeal-associated lymphoid tissue of mice immunized with NP-1 in GAS challenge studies. Thus, conjugation of defined-length anionic polymer to peptide antigen as a means of formulating ionic interaction-based nanoparticles with cationic polymer is a promising strategy for peptide antigen delivery. STATEMENT OF SIGNIFICANCE: A self-adjuvanting delivery system is required for peptide vaccines to enhance antigen delivery to immune cells and generate systemic and mucosal immunity. Herein, we developed a novel self-adjuvanting nanoparticulate delivery system for peptide antigens by combining polymer-conjugation and complexation strategies. We conjugated peptide antigen with anionic α-poly-(l-glutamic acid) that in turn, formed nanoparticles with cationic trimethyl chitosan by ionic interactions, without using external crosslinker. On intranasal administration to mice, these nanoparticles induced systemic and mucosal immunity, at low dose. Additionally, nanoparticles provided protection to vaccinated mice against group A streptococcus infection. Thus, this concept should be particularly useful in developing nanoparticles for the delivery of peptide antigens.