Inclusion Criteria:

          -  Patients ≥ 18 years of age

          -  BCR-ABL positive chronic myeloid leukaemia in chronic phase treated with imatinib as
             first line therapy

          -  CHR, CCyR after at least 18 months of imatinib treatment

          -  Adequate organ function, defined as the following:

               -  total bilirubin < 1.5 x ULN,

               -  AST and ALT < 2.5 x ULN,

               -  creatinine < 1.5 x ULN,

               -  ANC > 1.5 x 109/L,

               -  platelets > 100 x 109/L

          -  Written, voluntarily signed informed consent

        Exclusion Criteria:

          -  CMR (molecular remission 4.5 or BCR-ABL transcripts undetectable)

          -  Patient has received any other investigational treatment within 28 days before study
             entry

          -  Treatment with a second generation tyrosine kinase inhibitor (dasatinib, nilotinib)

          -  ECOG performance status ≥ 3

          -  Patients with a primary of a different histological origin than the study indication
             (unless relapse-free interval is ≥ 5 years, except cervical carcinoma, basal cell
             epithelioma or squamous cell carcinoma of the skin)

          -  Evidence of severe or uncontrolled systemic disease (e.g. unstable or uncompensated
             respiratory, cardiac, hepatic or renal disease etc.)

          -  Acute chronic infections

          -  Known autoimmune disease (e.g. collagen disease, polyarthritis, immune
             thrombocytopenia, thyroiditis, psoriasis, lupus nephritis or any other autoimmune
             disorder)

          -  Female patients who are pregnant or breast-feeding

          -  Known diagnosis of HIV