Immunopotentiator-Loaded Polymeric Microparticles as Robust Adjuvant to Improve Vaccine Efficacy

Adjuvants are required to ensure the efficacy of subunit vaccines. Incorporating molecular immunopotentiators within particles could overcome drawbacks of molecular adjuvants (such as solubility and toxicity), and improve adjuvanticity of particles, achieving stronger adjuvant activity. Aim of this study is to evaluate the adjuvanticity of immunopotentiator-loaded polymeric particles for subunit vaccine.

PLGA microparticles (PMPs) and imiquimod (TLR-7 ligand)-loaded PLGA microparticles (IPMPs) were prepared by SPG premix membrane emulsification. In vitro and in vivo studies were performed to their adjuvant activity, using ovalbumin and H5N1 influenza split vaccine as antigens.

Incorporating imiquimod into microparticles significantly improved the efficacy of PLGA microparticles in activating BMDCs and pMΦs, and antigen uptake by pMΦs was also promoted. IPMPs showed stronger adjuvanticity to augment OVA-specific immune responses than PMPs. IgG subclass profiles and cytokine secretion levels by splenocytes indicated that IPMPs elicited more Th1-polarized immune response, compared to PMPs. In vivo study using H5N1 influenza split vaccine as antigen also confirmed the effects of IPMPs on antigen-specific cellular immunity.

Considering adjuvanticity and safety profiles (PLGA and IMQ, both approved by FDA), we conclude that IMQ-loaded PLGA microparticles are promising robust adjuvant for subunit vaccines.