Retro-inversion enhances the adjuvant and CpG co-adjuvant activity of host defence peptide Bac2A

Abstract Host defence peptides (HDPs) have a variety of potential therapeutic applications, including as vaccine adjuvants, energizing efforts for modification strategies to address their toxicity and instability. Here we compare l , d and RI-Bac2A as vaccine adjuvants. d and RI-Bac2A are equally resistant to proteolytic degradation with no increases in toxicity, however, only RI-Bac2A maintains adjuvant activity of the natural peptide through conserved induction of a Th2 immune response. As HDPs potentiate the adjuvant activity of CpG ODNs, the isomers were also evaluated as co-adjuvants. l -Bac2A has no significant co-adjuvant activity while CpG/RI-Bac2A induces antibody titres significantly higher than CpG ( P l -Bac2A ( P d -Bac2A ( P l and RI-Bac2A promote ODN uptake into B cells and antigen presenting cells. The enhanced adjuvant and co-adjuvant of RI-Bac2A is hypothesized to result from an undefined combination of increased stability and retained biological activity supporting application of retro-inversion to this, and potentially other HDPs.