Embodiments of a novel platform for delivering a peptide antigen to a subject to induce an immune response to the peptide antigen are provided. For example, nanoparticle polyplexes are provided that comprise a polymer linked to a peptide conjugate by an electrostatic interaction. The conjugate comprises a peptide antigen linked to a peptide tag through an optional linker. An adjuvant may be included in the nanoparticle polyplex, linked to either the polymer or the conjugate, or admixed with the nanoparticles. The nanoparticle polyplex can be administered to a subject to induce an immune response to the peptide antigen.