Inclusion Criteria:  Males or females ≥18 years Histologically confirmed relapsed/refractory CLL who received ≥1 lines of prior therapy At least one bi-dimensionally measurable nodal lesion >1.5 cm Adequate renal, hepatic function Adequate hematologic parameters at screening  Exclusion Criteria:  Subjects who relapsed or progressed on BCL-2 inhibitor Relapsed within 2 years of discontinuation of prior PI3K inhibitor (PI3Ki) therapy or disease progression on PI3Ki therapy History or currently active HBV, HCV; any uncontrolled active infection, HIV infection; HIV-related lymphoma History of Richter's transformation or prolymphocytic leukemia Known allergies to both xanthine oxidase inhibitors and rasburicase, or any excipients of the drug products Currently active, clinically significant cardiovascular disease, such as uncontrolled arrhythmia or Class 3 or 4 congestive heart failure Pregnant women