Detection of Spontaneous CD4+ T-Cell Responses in Melanoma Patients against a Tyrosinase-Related Protein-2–Derived Epitope Identified in HLA-DRB1*0301 Transgenic Mice

Abstract

Abstract Purpose: The frequently expressed differentiation antigen tyrosinase-related protein-2 (TRP-2) has repeatedly been described as a target of spontaneous cytotoxic T-cell responses in melanoma patients, suggesting that it might be an ideal candidate antigen for T cell–based immunotherapy. As a prerequisite for immunization, T-cell epitopes have to be identified. Whereas a number of HLA class I–presented TRP-2–derived epitopes are known, information about HLA class II–presented antigenic ligands recognized by CD4+ T helper (Th) cells is limited. Experimental Design: The search for TRP-2–derived Th epitopes was carried out by competitive in vitro peptide binding studies with predicted HLA-DRB1*0301 ligands in combination with peptide and protein immunizations of HLA-DRB1*0301 transgenic mice. In vivo selected candidate epitopes were subsequently verified for their immunogenicity in human T-cell cultures. Results: This strategy led to the characterization of TRP-260-74 as an HLA-DRB1*0301–restricted Th epitope. Importantly, TRP-260-74–reactive human CD4+ Th cell lines, specifically recognizing target cells loaded with recombinant TRP-2 protein, could be established by repeated peptide stimulation of peripheral blood lymphocytes from several HLA-DRB1*03+ melanoma patients. Even short-term peptide stimulation of patients' peripheral blood lymphocytes showed the presence of TRP-260-74–reactive T cells, suggesting that these T cells were already activated in vivo. Conclusion: Peptide TRP-260-74 might be a useful tool for the improvement of immunotherapy and immune monitoring of melanoma patients.