T-cell receptor (TCR) gene transfer for cancer immunotherapy is limited by the availability of large numbers of tumorspecific T cells. TCR α and β chains were isolated from a highly lytic HLA-A2-restricted cytotoxic T lymphocyte (CTL) clone recognizing the melanoma-associated Melan-A/MART-1 antigen and inserted into a lentiviral vector carrying a bidirectional promoter capable of robust and coordinated expression of the two transgenes. Lentiviral vector-based gene delivery systems have shown increased transfer efficiency and transgene expression compared with the widely used γ-retroviral vectors. This vector performed more efficiently than a γ-retrovirus-based vector containing the same expression cassette, resulting in a T-cell population with 60% to 80% of transgenic TCR expression with mainly CD8+ intermediate effector phenotype. Transgenic T cells specifically produced cytokine in response to and killed antigen-expressing melanoma cells, retained an overlapping functional avidity in comparison with the TCR donor CTL clone, and exerted significant therapeutic effects in vivo upon adoptive transfer in melanoma-bearing severe combined immunodeficient mice. Optical imaging showed their accumulation in the tumor site. Overall, our results indicate that lentiviral vectors represent a valid tool for stable and high-intensity expression of transgenic TCR and support clinical exploitation of this approach for therapeutic application. ©2009 American Association for Cancer Research.