Synthetic bacterial lipopeptide analogs facilitate naive CD4+ T cell differentiation and enhance antigen-specific HLA-II-restricted responses.

Synthetic di- and tri-palmitoylated bacterial lipopeptide analogs (BLpA) can enhance HLA-I-restricted immune responses. Here we show that BLpA indirectly promote antigen-driven differentiation of naive CD4+ T lymphocytes in vitro, with mechanisms that require DC and are inhibited by CTLA-4/Ig. In mixed cultures of cord blood-derived PBMC and allogeneic DC, P3CSK4 lipopeptide facilitated the transition from CCR7(+)/CD45RA(+)/CD62L+ to CCR7(-)/CD45RA(-)/CD62L(dim) T cells with kinetics significantly exceeding those obtained with the unlipidated CSK4 analog. Moreover, P3CSK4 and P2CSK4, but neither the mono-palmitoylated PCSK4 analog nor the CSK4 peptide, increased the frequency of IFN-gamma-producing T cells expanded under similar conditions. Along with this, P2CSK4 and P3CSK4, but not PCSK4, restored the in vitro antigenicity of MDP-OspA, a non-immunogenic analog of Borrelia burgdorferi major outer surface lipoprotein A, and enhanced the frequency of in vitro expanded T cells specific for the tetanus toxoid (TT) and hepatitis B surface antigen (HBsAg) peptides TT(947-967) and HBsAg(19-33) and for TT. Altogether, BLpA bearing at least two ester-bonded palmitoyl side chains indirectly enhance antigen-driven CD4+ T cell differentiation. BLpA adjuvanticity is independent of covalent bonding to Ag and Ag formulation. This information may be helpful to generate more potent recombinant vaccines.