Tyrosinase has many advantages as a target
antigen for the
immunotherapy of patients with
melanoma because it is expressed in nearly all
melanoma specimens with a high degree of cellular homogeneity, and its distribution in normal tissues is limited to melanocytes. To broaden our ability to direct cellular immune responses against this
protein, we pursued an investigation to identify new shared
human leukocyte antigen (HLA)-A2.1 restricted
epitopes from
tyrosinase.
Peptides were synthesized that fit a permissive HLA-A2.1 binding motif and did not span common sites of polymorphism. The binding affinity of each
peptide to HLA-A2.1 relative to a standard
peptide with intermediate binding affinity was evaluated in a competitive inhibition assay. Twelve
peptides were selected that had binding affinities within 80% of that of the standard
peptide, and these were used to stimulate peripheral blood mononuclear cells (PBMC) in vitro from three HLA-A2.1+ patients with metastatic
melanoma. Cytotoxic T lymphocytes that specifically recognized
peptide-pulsed target cells as well as HLA-A2.1+ tyrosinase+
melanoma cells were raised from one patient with
tyrosinase:8-17 (CLLWSFQTSA). To evaluate further the immunogenicity of this
peptide, PBMC from 23 HLA-A2.1+ patients were stimulated in vitro with
tyrosinase:8-17. Eleven bulk T-cell cultures demonstrated specific
peptide recognition, and six of these also recognized HLA-A2.1+ tyrosinase+
melanoma cells. These data suggest that
tyrosinase:8-17 may be clinically useful for the treatment of patients with
melanoma.