<qa>  What is the name of the drug that collects blood?Participants will have ECP treatments for 2 consecutive days every 2 weeks for 24 weeks, for a total of 26 treatments. For ECP, patients undergo leukapheresis, a method of collecting large numbers of white blood cells, or leukocytes-cells that may be responsible for many of the medical problems in Crohns disease. Whole blood is collected through a needle in an arm vein, similar to donating a unit of blood. The blood flows through a machine that separates it into its components by spinning. The white cells are removed and collected in a plastic bag, and the red blood cells and plasma are returned to the patients bloodstream through the same needle. The collected white cells are mixed with a drug called UVADEX Registered Trademark, exposed to ultraviolet UVA light, and then returned to the patients bloodstream. The UVADEX allows the blood cells to absorb more UVA. The UVA changes the cells in a way that, once they are back in the body, they cause changes in other cells like them. Each ECP treatment takes 3 to 4 hours. On the first day of each 2-day treatment, patients will undergo a review of symptoms, check of vital signs, and blood draw. They will complete a CDAI diary for 7 days before the first of the two ECP treatments and a questionnaire about their life and activities at 4-week intervals. During the ECP treatment period, corticosteroids will be slowly reduced as long as disease symptoms do not worsen. 