We previously demonstrated that the switch from non- to highly tumorigenic phenotype of human melanoma cells is directly related to procathepsin L secretion, which increased cell resistance to complement-mediated cell lysis. Involvement of procathepsin L secretion in tumor growth was clearly demonstrated by three different strategies: (1) inhibition of secreted procathepsin L activity; (2) increase of procathepsin L secretion; and (3) inhibition of procathepsin L secretion. This latter strategy was triggered by intracellular expression of anti-human cathepsin L single-chain variable fragment (ScFv). These previous experiments were performed by processing melanoma cells before their injection into nude mice. We herein designed a new lentiviral vector in which this anti-cathepsin L ScFv was cloned. This lentiviral vector was optimized to allow the highest intracellular expression of anti-cathepsin L ScFv in transduced melanoma cells. In these transduced cells, procathepsin L secretion was strongly inhibited. In addition, injection of this anti-cathepsin L ScFv lentiviral vector into tumors already induced in nude mice inhibited tumor growth and associated angiogenesis. This is the first report to demonstrate that targeting procathepsin L secretion with anti-cathepsin L ScFv lentiviral construct constitutes a new gene therapy in the challenge to inhibit the growth of tumors induced by human melanoma cells.