As the most lethal type of skin cancer, melanoma represents a significant health problem today as the incidence is rising and projected to continue its upward trend in years to come. The effective therapeutic options for patients with advanced disease are limited. One of the promising therapeutic modalities is antigen-specific immunotherapy. As a result of significant advances in identification of immunogenic tumor antigens, many clinical trials are ongoing to examine the therapeutic efficacy o f p e ptide-based vaccines for melanoma. However, peptide-specific immunotherapy has some drawbacks as it can only be applied to a group of patients who express immunogenic antigens. The anti-tumor immune response in the form of CTL response is also restricted by class I MHC molecules, although recent evidence suggests that some peptide epitopes may be presented by multiple HLA molecules. Therefore, in order to develop a clinically effective peptide-specific immunotherapeutic strategy, a large repertoire of immunogenic antigens or targets associated with a wide range of different HLA molecules needs to be identified to broaden applicability, and the immunogenicity of each target needs to be optimized. NY-ESO-1 antigen is one of the Cancer- Testis (CT) antigens that are tumor-specific. NY-ESO-1 appears to be the most immunogenic CT antigen identified to date, as a spontaneous but specific immune response occurs in a majority of these patients, and it promises to be an excellent target for a vaccine. However, only a few peptide epitopes from NY-ESO-1 are reported to be immunogenic and the natural expression of this and a d d itional novel immunogenic peptide epitopes has not been examined extensively. Therefore, the specific aims are: 1) To identify new immunogenic peptide epitopes derived from NY-ESO-1 that are naturally presented by HLA-A-locus encoded molecules on melanoma, 2) To examine the ability of known peptide epitopes from distinct melanoma-associated antigens to associate with different HLA-A molecules and to stimulate melanoma-reactive CTL.