Rosenberg and his group wanted to know whether they could take the patient's normal, undirected cells and treat them in a way that would produce the specific killer T-cells needed to destroy a tumor. They began by going back to the most successful killer cells in the earlier experiment. These were cells that recognized a cancer antigen called MART-1. They then isolated the T-cell gene that controlled the MART-1 recognition site. Next, they created an artificial virus that carried the cloned anti-MART-1 gene and used this virus to install the gene in lymphocytes taken from the patient's blood. This changed the patient's white blood cells into killer T-cells directed exclusively at the MART-1 cancer antigen found on the surface of malignant melanoma cells. Finally, Rosenberg's team used some laboratory tricks learned earlier to pump up the number of these anti-MART-1 killer cells and then inject them back into the patient.