This study is designed to assess the safety and preliminary efficacy of five different doses of DTA-H19 given as six intravesical infusions into the bladder of patients with superficial bladder cancer who have failed intravesical therapy with Bacille Calmette-Guérin (BCG).DTA-H19 is a DNA plasmid that contains H19 gene regulatory sequences that drive the expression of an intracellular toxin [diphtheria toxin A (DTA) chain]only in cancer cells and not in normal cells. In line with the standard procedure for DNA plasmid pharmaceutical products, another chemical component will be added to the solution, called PEI (polyethlenimine) in a liquid solution, which improves the ability of the DNA plasmid to enter the cells.