Synergistic stimulation of antigen presenting cells via TLR by combining CpG ODN and poly(γ-glutamic acid)-based nanoparticles as vaccine adjuvants.

CpG oligodeoxynucleotide (ODN) encapsulated poly(γ-glutamic acid)-graft-l-phenylalanine ethyl ester (γ-PGA-Phe) nanoparticles (NPs) employing polycations were prepared to develop vaccine delivery and adjuvant systems. The CpG ODN was stably encapsulated into the NPs when protamine was used as the polycation. The CpG ODN-encapsulated γ-PGA-Phe NPs were taken up by macrophages and CpG ODN which was encapsulated into the NPs internalized into endo/lysosomes, where the toll-like receptor (TLR) 9, which recognizes CpG ODN, is expressed. The examination of release behavior in vitro revealed that the encapsulated CpG ODN into NPs was released when these NPs were immersed into the early endosomal environment. Interestingly, CpG ODN-encapsulated γ-PGA-Phe NPs synergistically activated macrophages. This may be due to the multiple stimulation of TLRs by γ-PGA-Phe NPs (TLR4 ligand) and CpG ODN (TLR9 ligand). We previously reported that γ-PGA-Phe NPs are excellent vaccine adjuvants for inducing potent innate and adaptive immune responses via TLR4. Moreover, coencapsulated CpG ODN and antigen in γ-PGA-Phe NPs induced potent antigen-specific cellular immunity at a higher level than the mixture of CpG ODN and antigen which is the conventional vaccine system. These findings suggest that the conjugation strategies of biologically derived adjuvant and polymeric NPs will aid the development of a novel approach for safe and effective vaccine delivery and adjuvant systems.