Synthetic insertion signal sequences enhance MHC class I presentation of a peptide from the melanoma antigen MART-1.

Cytotoxic T lymphocytes (CTL) recognize minimal peptides of eight to ten residues which are the products of intracellularly processed proteins and are presented at the cell surface by MHC class I molecules. An important step in this process is the translocation of processed proteins from the cytosol across the endoplasmic reticulum membrane mediated by transporter associated with antigen processing (TAP) proteins, or as an alternative, by endoplasmic reticulum insertion signal sequences. We report here that the addition of synthetic signal sequences at the N terminus, but not at the C terminus, of an epitope from the human melanoma antigen MART-1 greatly enhances its presentation in both TAP-deficient and TAP-expressing cells. A newly designed peptide construct, composed of the epitope replacing the hydrophobic part of a natural signal sequence, was also very effective. Interestingly, an artificial signal sequence containing the same epitope was the most efficient construct for enhancing its presentation. These peptide constructs facilitated epitope presentation when loaded into the cytosol of TAP-deficient T2 cells, TAP-expressing melanoma cells and human dendritic cells. These findings may be of practical significance for the development of synthetic anti-cancer vaccines and in vitro immunization of CTL for adoptive immunotherapy.