Instructions: Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.
Input: In a phase I study, Gilead Sciences' PI3K- inhibitor idelalisib produced rapid tumor shrinkage-a response that lasted for 17 months on average-in about half of the 54 patients with chronic lymphocytic leukemia who participated.
Output:
What is the target protein of the drug Idelalisib?