Inclusion Criteria:

   1. Men and women ≥ 18 years of age.

   2. Prior diagnosis of CLL

   3. Must have received ≥ 1 prior therapy for CLL

   4. Intolerant of ibrutinib

   5. Willing and able to participate in all required evaluations and procedures in this
   study protocol including swallowing capsules without difficulty.

   6. ECOG performance status of ≤ 2.

Exclusion Criteria:

   1. Ongoing AE attributed to ibrutinib therapy

   2. Treatment with systemic anticancer therapy for CLL is prohibited between
   discontinuation of ibrutinib and enrollment on this trial.

   3. Prior exposure to a BCL-2 inhibitor (eg, venetoclax/ABT-199)

   4. Prior malignancy (other than CLL), except for adequately treated basal cell or
   squamous cell skin cancer, in situ cancer, or other cancer from which the subject has
   been disease free for ≥ 2 years.

   5. Significant cardiovascular disease such as uncontrolled or symptomatic untreated
   arrhythmias, congestive heart failure, or myocardial infarction within 6 months of
   screening, or any Class 3 or 4 cardiac disease as defined by the New York Heart
   Association Functional Classification, or QTc > 480 msec at screening. Exception:
   Subjects with controlled, asymptomatic atrial fibrillation during screening are
   allowed to enroll on study.