Development and characterization of microencapsulated nanoparticle systems for oral vaccination by protein-antigens
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A composite platform strategy for oral vaccination with subunit antigens was developed to improve i) ease of administration and distribution; and ii) induction of mucosal immunity. The platform is referred to as Polyanhdyride-Releasing MicroParticle Technology, or PROMPT. In its core, polyanhydride nanoparticles based on 1,6-bis-(p-carboxyphenoxy)hexane (CPH) and sebacic acid (SA) served simultaneously as adjuvant and delivery vehicle of subunit antigens, while microencapsulation by pH-responsive polymers based on poly(ethylene glycol) (PEG) and poly(methacrylic acid) (PMAA) enabled targeted intestinal delivery of the nanoparticle payload. PROMPT formulations were synthesized by pH-mediated self-assembly to encapsulate nanoparticles. The reversible pH-responsive transition of these formulations coincided with the pH transition experienced during intestinal delivery, such that particles dissociated to release nanoparticles above pH 5. The physicochemical characteristics of the composite microgels were evaluated by Fourier transform infrared spectroscopy, electron microscopy, and confocal microscopy. PROMPT formulations demonstrated pH-dependent burst release of the encapsulated model antigen, ovalbumin, and then sustained release thereafter in both neutral pH and simulated gastrointestinal conditions. The biocompatibility and immunostimulatory capabilities of PROMPT formulations were evaluated in relevant cell lines to identify lead candidates for in vivo immunization experiments. PROMPT composite formulations demonstrated greater than 85% viability at microgel concentrations less than 1mg/mL, as indicated by cellular proliferation and membrane integrity. PROMPT microgels also demonstrated the ability to activate bone marrow-derived dendritic cells in vitro by stimulating cell surface marker expression and cytokine secretion. Finally, the ability of lead formulations to elicit immune responses was assessed in vivo by administering PROMPT formulations to BALB/c mice by oral gavage. PROMPT formulations induced measurable ovalbumin-specific IgA and IgG in mucosal fluids and blood serum, respectively, while soluble antigen and nanoparticles alone did not. This work shows that microencapsulation of nanoparticles for oral vaccine administration is a promising platform for developing safe, effective subunit-based vaccines.