Sustained release of inactivated H1N1 virus from degradable microparticles for extended vaccination.

Influenza vaccines administered as intramuscularly injected inactivated viruses or intranasally administered live-attenuated viruses usually provide short-term protection against influenza infections. Biodegradable particles that provide sustained release of the antigen has been studied as an approach to extend vaccine protection. Here, we investigate sustained release of ultraviolet killed influenza A virus (A/PR/8/34(H1N1)) (kPR8) loaded into poly(D,L-lactic-co-glycolic acid) (PLGA) microparticles. Particles were prepared using the double emulsion method, and polymer molecular weight (MW), polymer hydrophobicity, polymer concentration in the organic phase, and the amount of killed virus were varied to obtain a range of particles. Formulations included PLGA 50:50 (2-6, 7-17 kDa), PLGA 75:25 (4-15 kDa), and 50/50 PLGA 75:25 (4-15 kDa)/PCL (14 kDa). Additionally, NaOH was co-encapsulated in some cases to enhance particle degradation. The structure of the particles was explored by size measurements and electron microscopy. The kPR8 release profiles were measured using hemagglutinin ELISA. The concentration of the polymer (PLGA) in the organic phase and polymer MW significantly influenced virus loading, while polymer MW and co-encapsulation of NaOH modulated the release profiles. Mice receiving a single intramuscular injection of NaOH microparticle-encapsulated kPR8 were partially protected against a lethal influenza challenge 32 weeks post immunization. Microparticle (MP) vaccination induced a gradual increase in PR8-specific IgGs dominated by IgG1 in contrast to the rapid IgG2a-biased response elicited by soluble kPR8 immunization. Our results indicate that vaccine-NaOH co-loaded PLGA particles show potential as a single dose vaccination strategy for extended protection against influenza virus infection.