Background: We previously showed that the bacterial lipopeptide Pam3Cys-Ser-Ser, meanwhile established as a
toll-like receptor (TLR) 1/2 ligand, acts as a strong adjuvant for the induction of virus specific CD8+ T cells in mice,
when covalently coupled to a synthetic peptide.
Case presentation: We now designed a new water-soluble synthetic Pam3Cys-derivative, named XS15 and
characterized it in vitro by a TLR2 NF-κB luciferase reporter assay. Further, the capacity of XS15 to activate immune
cells and stimulate peptide-specific CD8+ T and NK cells by 6-sulfo LacNAc+ monocytes was assessed by flow
cytometry as well as cytokine induction using immunoassays. The induction of a functional immune response after
vaccination of a volunteer with viral peptides was assessed by ELISpot assay and flow cytometry in peripheral blood
cells and infiltrating cells at the vaccination site, as well as by immunohistochemistry and imaging.
XS15 induced strong ex vivo CD8+ and TH1 CD4+ responses in a human volunteer upon a single injection of XS15
mixed to uncoupled peptides in a water-in-oil emulsion (Montanide™ ISA51 VG). A granuloma formed locally at the
injection site containing highly activated functional CD4+ and CD8+ effector memory T cells. The total number of
vaccine peptide-specific functional T cells was experimentally assessed and estimated to be 3.0 × 105 in the
granuloma and 20.5 × 106 in peripheral blood.
Conclusion: Thus, in one volunteer we show a granuloma forming by peptides combined with an efficient
adjuvant in a water-in-oil-emulsion, inducing antigen specific T cells detectable in circulation and at the vaccination
site, after one single vaccination only. The ex vivo T cell responses in peripheral blood were detectable for more
than one year and could be strongly boosted by a second vaccination. Hence, XS15 is a promising adjuvant
candidate for peptide vaccination, in particular for tumor peptide vaccines in a personalized setting.
Keywords: Adjuvant, Lipopeptide, TLR1/2 ligand, Immunotherapy, Vaccines