Liposomal co-encapsulation of a novel gemini lipopeptide and a CpG-ODN induces a strong Th1 response with the co-activation of a Th2/Th17 profile and high antibody levels

Abstract

A successful vaccine depends on its capacity to elicit a protective immune response against the target pathogen. The adjuvant used plays an important role in enhancing and directing the immune response. Liposomes are vaccine adjuvants that allow the co-encapsulation of antigens and immunostimulants. Our aim was to evaluate the adjuvanticity of a cationic liposome (Lip) formulated with a novel gemini lipopeptide (AG2-C16) alone or in combination with CpG-ODN as immunostimulants. To achieve this, we used the recombinant clumping factor of Staphylococcus aureus (rClfA) as a model antigen, in a murine model. We characterized the formulations by DLS, Cryo-SEM, and TEM, and analyzed the humoral and cellular immune responses induced in BALB/c and C57BL/6J mice injected with free rClfA and three formulations: Lip + CpG-ODN + rClfA, Lip + AG2-C16 + rClfA and Lip + AG2-C16 + CpG-ODN + rClfA. The addition of immunostimulants to the liposomes did not change the membrane diameter but affected their hydrodynamic diameter, z-potential, and homogeneity. All liposomal formulations were able to stimulate a specific humoral response, with high serum IgG, IgG1 and IgG2a or IgG2c titers in BALB/c or C57BL/6J mice, respectively. In addition, increased vaginal IgG levels were detected after injection, with no specific IgA. The cellular immunity induced by Lip + AG2-C16 + CpG-ODN + rClfA was characterized by a predominant Th1 profile, with the co-induction of Th2 and Th17 cells, and IFN-γ+ cytotoxic T cells. Furthermore, we studied the capacity of the different formulations to stimulate murine keratinocytes and fibroblasts in vitro. While no formulation activated keratinocytes, Lip + AG2-C16 + CpG-ODN increased the expression of CXCL9 in fibroblasts. These results suggest Lip + AG2-C16 + CpG-ODN as a promising adjuvant candidate to be used in vaccines against pathogens that require Th1/Th2/Th17 combined profiles, like S. aureus. Additionally, based on the IFN-γ+ cytotoxic T cells stimulation and the CXCL9 production by fibroblasts, we propose the use of this adjuvant formulation for the stimulation of a Th1 profile.