Effects of different immunomodulating liposome-based adjuvants and injection sites on immunogenicity in pigs
Vaccine adjuvants are able to boost immune responses and steer immunity towards a desired direction. Liposome-based cationic adjuvant formulations (CAFs) are effective in inducing cell-mediated immune responses in mice, non-human primates and humans. In the translation from mouse to humans, pigs could play an important role. In this study, we thus used commercial pigs housed under field conditions to investigate the effects of four different CAFs incorporating distinct immunomodulators: C-type lectin receptor ligands trehalose-6,6-dibehenate and monomycolyl glycerol, toll-like receptor ligand Poly(I:C) or retinoic acid. The vaccines were formulated with a recombinant Chlamydia model protein antigen and administered via distinct injection routes. All adjuvants significantly increased antigen-specific IgA and IgG in serum, compared to non-adjuvanted antigen. Administering the vaccines through intramuscular and intraperitoneal routes induced significantly higher antigen-specific IgA and IgG serum antibodies, than the perirectal route. Although the immunizations triggered cell-mediated immunity, no significant differences between the adjuvants or injection sites were detected by intracellular flow cytometry or cytokine-release assays. Genes depicting T cell subtypes were monitored by qPCR, which revealed minor differences only. Our findings suggest that the adjuvant-specific signature of the tested adjuvant immunomodulation does not translate well from mice to pigs. This study provides new insights into immune responses to CAFs in the pig model, and highlights that adjuvant studies should be ideally carried out in the intended species of interest.