The study is designed to evaluate the clinical efficacy and safety of daily treatment for 12 weeks of oral administration of a delayed release, locally delivered 6MP (mercaptopurine) drug (80 mg), as compared to standard Purinethol (at a dose of 1-1.5 mg/kg/body weight), in alleviating the clinical, immunological and mucosal signs and symptoms of moderately active Crohn's Disease