Guanidinylated cationic nanoparticles as robust protein antigen delivery systems and adjuvants for promoting antigen-specific immune responses in vivo.

Weak immunogenicity and transient humoral or cellular immune responses are the major limitations of modern protein vaccines. Using delivery adjuvants is a good strategy to promote their immune response in vivo. In this study, a type of guanidinylated and cationic nanoparticle adjuvant self-assembled by monomethoxy poly(ethylene glycol)-block-poly(2-(diisopropyl amino)ethyl methacrylate)-block-poly(2-(guanidyl)ethyl methacrylate) (mPEG-b-PDPA-b-PGEM, PEDG) copolymers was used as an antigen delivery carrier. PEDG nanoparticles could encapsulate the model antigen ovalbumin (OVA) by facile electrostatic absorption with a loading efficiency of approximately 200 μg of OVA per 1 mg of the polymer. Rapid OVA release within 4 hours in acidic lysosomal compartments of antigen-presenting cells was observed. PEDG nanoparticles could stimulate the maturation of mouse bone marrow-derived dendritic cells and enhance antigen uptake and presentation by 4 fold compared to free OVA. The nanoparticles also induced the activation of macrophages (RAW 264.7) to produce a high level of cytokines including TNF-α, IL-6 and IL-10. OVA-loaded PEDG nanoparticles efficiently induced a superior antigen cross-presentation effect in vitro and in vivo compared to free OVA vaccination. In vivo stimulation of mice using nanoparticle-formulated OVA robustly enhanced the antigen-specific CD8+ T cell proliferation and the secretion of antigen-specific IgG, serum IgG2a/IgG1 antibodies and cytokines (IFN-γ, IL-2). The strategy of nanoparticle delivery prolonged the antigen duration at the injection site and enhanced its migration to draining lymph nodes as indicated by fluorescence tracking. In all, the novel guanidinylated nanoparticles could act as an effective adjuvant delivery system for protein antigens to elicit both potent antigen-specific cellular immune responses, including Th1-based adaptive immunity and CD8+ T cell response, and humoral immune responses.