A 32-year-old man with a 5-year history of Crohn disease presents with active ileocolonic inflammation despite adequate dietary modification and mesalamine therapy. He has 4–5 loose stools daily with blood, abdominal pain, and a CRP of 8.2 mg/dL. Colonoscopy confirms patchy transmural inflammation with skip lesions. What is the drug of choice for induction of remission in this patient?