We are developing strategies to target tumor-associated antigens (TAA) and viral antigens by genetically modifying patient peripheral blood lymphocytes to produce antitumor or antiviral reactive cytotoxic T-lymphocyte (CTL). To this end, we have succeeded in redirecting the specificity of peripheral blood T-cells and T-lymphocyte clones by the transfer of T-cell-receptor (TCR) genes from antigen specific T-cell clones into these lymphocytes. The TAA MART-1 is expressed by the majority of human melanoma tumors (1 ,2 ), making it an excellent potential target for therapeutic strategies utilizing TCR gene transfer. A single HLA-A2-restricted peptide epitope has been identified in the MART-1 protein (amino acids 27-35: MART-1(27 _35 )). HLA-A2 is present in approx 50% of Caucasian melanoma patients. Therefore, a TCR gene transfer approach using a TCR that recognizes this particular major histocompatibility complex (MHC)-peptide complex could potentially treat 50% of Caucasian melanoma patients. We have previously described the cloning of the TCR genes from a tumor-reactive CTL clone (clone 5) derived from a tumor-infiltrating lymphocyte (TIL) culture from patient 501 (3 ,4 ). The clone 5 TCR is HLA-A2 restricted and is specific for the m9-27 peptide epitope (MART-127 _35 ) of MART-1. Transfection of the α and β TCR genes from clone 5 into Jurkat cells resulted in the expression of a functional TCR on the cell surface (4 ).