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.