Inclusion Criteria:

          -  Willing and able to give informed consent

          -  Diagnosed with CML in chronic phase and have either the b3a2 (e14a2) or b2a2 (e13a2)
             variants that give rise to the p210 BCR-ABL protein.

          -  Must have a documented history of attempting only one prior TKI discontinuation under
             the guidance of a treating physician

          -  Must have met ALL the following criteria prior to first attempt to discontinue their
             TKI:

               -  Stable molecular response (MR4; <0.01% IS) for > 2 years, as documented on at
                  least 4 tests, performed at least 3 months apart

               -  Treatment with one of the following FDA approved TKI; imatinib, dasatinib,
                  nilotinib or bosutinib, at any dose for a minimum of 3 years prior to
                  discontinuing TKIs

               -  Has been on any number of TKIs, but has not been resistant to any TKI (changes
                  made for intolerance are allowed)

          -  Must have relapsed (defined as loss of major molecular response (MMR), RQ-PCR for
             BCR-ABL > 0.1% IS after first attempted discontinuation of TKI

          -  After first failed TFR attempt, must have a minimum duration of 1 year on a TKI, and
             must plan to remain on this same TKI for a minimum of 12 months during the combination
             treatment phase

          -  Current TKI must be the same as the TKI being taken prior to the initial TFR attempt
             (e.g., if patient is on imatinib prior to first TFR attempt, they should be on
             imatinib at time of enrollment on this study)

          -  Eastern Cooperative Oncology Group (ECOG) performance status 0-3

          -  Must have a RQ-PCR for BCR-ABL less than 0.01% IS reported by the trial designated
             central lab at time of study enrollment

          -  Must adhere to all study contraception guidelines

        Exclusion Criteria:

          -  History of accelerated or blast phase CML

          -  History of TKI resistance

          -  A second malignancy requiring active treatment

          -  Have previously received treatment with a JAK inhibitor.

          -  Platelet count less than 100 × 10^9/L or an absolute neutrophil count of less than 1 ×
             10^9/L or Hemoglobin less than 8 g/dL

          -  AST and ALT ≥ 3 times the institutional upper limit of normal (ULN)

          -  Creatinine ≥ 2 times ULN

          -  Total bilirubin ≥ 1.5 times ULN (unless direct bilirubin is within normal limits)

          -  Pregnant or lactating

          -  Unable to comply with lab appointments schedule and patient response outcome
             assessments

          -  Another investigational drug within 4 weeks of enrollment

          -  Any serious medical or psychiatric illness that could, in the investigator's opinion,
             interfere with the completion of treatment according to this protocol

          -  Have undergone a prior allogeneic transplant

          -  Screening 12-lead ECG showing a baseline corrected QT interval >500msec (patients with
             a pacemaker will still be eligible with QTc>500msec)