Extension of HLA-A*0201-Restricted Minimal Epitope by Nε-Palmitoyl-lysine Increases the Life Span of Functional Presentation to Cytotoxic T Cells

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Abstract
The delineation of the minimal requirements for efficient delivery of functional cytotoxic epitopes into APC could be a step toward the definition of “minimal length” lipopeptides for the modulation of CTL activity. Several analogues of the HLA-A*0201-restricted HIV-1 polymerase (pol476–484) minimal cytotoxic epitope were obtained by modifying P0, P1, or P10 positions by a single Nε-palmitoyl-lysine residue. The use of fluorescent derivatives confirmed the cell-permeating activities and suggested that a P0- and a P1-modified lipopeptide possessing ionizable extremities fulfills the structural requirements for MHC loading. The expressions of HLA-peptide complexes at the surface of TAP-deficient cells incubated with the parent epitope or lipopeptide derivatives were compared, in terms of intensity and stability. Both lipopeptides induced a considerably prolonged expression of conformationally correct complexes, which were dependent on the integrity of the exocytosis pathway, suggesting a dynamic mechanism of formation or reloading of the complexes from an intracellular pool. The agonistic activities of the different HLA-peptide complexes were evaluated using two independent T cell lines from HIV-infected donors. We report that a lipodecapeptide obtained by N-terminal addition of a Nε-palmitoyl-lysine to the pol476–484 epitope was able to increase the life span of functional presentation to cytotoxic T cells specific for the parent peptide.

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