Task: Question Answering
Input (English): Context: 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. 
 Question: What is the target protein of the drug Idelalisib?
Output (English): phosphoinositol-3 kinase delta isoform