Co-encapsulation of antigen and Toll-like receptor ligand in cationic liposomes affects the quality of the immune response in mice after intradermal vaccination

Abstract

Enhanced immunogenicity of subunit antigens can be achieved by antigen encapsulation in liposomes and the addition of immune potentiators. In this study we co-encapsulated ovalbumin (OVA) and a Toll-like receptor (TLR) ligand (PAM3CSK4 (PAM) or CpG) in cationic liposomes and investigated the effect of the formulations on dendritic cell (DC) maturation in vitro and on the immune response in mice after intradermal immunisation. Co-encapsulation of PAM did not affect the OVA content of the liposomes, but co-encapsulation of CpG led to a decrease in OVA content by 25%. After liposomal encapsulation, both ligands retained the ability to activate TLR-transfected HEK cells, though PAM only induced activation at elevated concentrations. DC maturation induced by liposome-based adjuvant formulations was superior compared to the free adjuvants. Encapsulation of PAM and CpG in liposomes did not influence the total IgG titres compared to the antigen/adjuvant solution, but OVA/CpG liposomes shifted the IgG1/IgG2a balance more to the direction of IgG2a compared to non-encapsulated CpG. Moreover, only this formulation resulted in IFN-γ production by restimulated splenocytes from immunised mice. These data show that co-encapsulation of antigen and immune potentiator in cationic liposomes, can affect the type of immune response generated after intradermal immunisation.