Identification of a new shared HLA-A2.1 restricted epitope from the melanoma antigen tyrosinase

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.