Inclusion Criteria:

          1. Signed written informed consent form.

          2. Capability and willingness to comply with study procedures and ability to
             self-administration of the study drug.

          3. Male or female aged ≥ 18 years.

          4. At least three years of TKI therapy.

          5. BCR-ABL-positive, chronic phase CML patients with a transcript level according to the
             international scale (IS) of at least MR4, or better (MR4.5, MR5). MR4 is defined as
             (i) detectable disease ≤0.01% BCR-ABL IS or (ii) undetectable disease in cDNA with
             ≥10,000 ABL or ≥24,000 GUS transcripts for at least one year. There have to be at
             least three consecutive PCR-results with MR4 or better within the last year (+ months)
             before study entry. The latest of these PCRs must be a confirmatory MR4 measurement
             prior to randomization by the EUTOS-certified Study Reference Laboratories for PCR
             (BCR-ABL mRNA). No PCR-results in the last year before randomisation can be worse than
             MR4. If the last PCR was not done within two months from baseline (day 0) in an
             EUTOS-certified study Reference Laboratory; the PCR sample must be sent to an
             EUTOS-certified study Reference Laboratory at screening.

          6. Patients who had failed to discontinue TKI in a prior discontinuation attempt are
             eligible for this protocol, if they fulfil criterion 5 after retreatment with TKI. A
             prior TKI discontinuation failure must be specifically indicated at inclusion and
             documented.

          7. Adequate organ function:

             especially total bilirubin, lactate dehydrogenase [LDH], aspartate aminotransferase
             [AST], alanine aminotransferase [ALT] and coagulation parameters ≤ 2 × upper limit of
             normal (ULN)

          8. Adequate hematological parameters:

             platelet count ≥ 100 × 1000000000/L; white blood cell count ≥ 2.5 × 1000000000/L;
             lymphocytes ≥ 1.0 × 1000000000/L; hemoglobin ≥ 9.0 g/dL or 5.59 mmol/L.

          9. Female patients with reproductive potential must agree to maintain highly effective
             methods of contraception by practicing abstinence or by using at least two methods of
             birth control from the date of consent through the end of the study. If abstinence
             could not be practiced, a combination of hormonal contraceptive (oral, injectable, or
             implants) and a barrier method (condom, diaphragm with a vaginal spermicidal agent)
             has to be used. Male patients must agree to use condoms during study participation.

         10. Negative serum pregnancy test in women of childbearing potential.

         11. Date of diagnosis of CML confirmed by laboratory PCR must be known.

        Exclusion Criteria:

          1. Rare variants of BCR-ABL not quantifiable by RT-PCR according to the international
             scale (IS).

          2. Current or previous autoimmune diseases requiring treatment.

          3. Immunosuppressive treatment of any kind; transplant recipients

          4. Prior allogeneic stem cell transplantation.

          5. Prior pegylated IFN therapy. Prior low dose conventional IFN treatment with ≤ 3 x 3
             Mio I.E. / week for less than 1 year is acceptable.

          6. History of TKI resistance within the last 4 years of TKI therapy.

          7. History of accelerated phase or blast crisis.

          8. Hypersensitivity/allergy to the active substance or excipients of the formulation.

          9. Severe hepatic dysfunction or decompensated cirrhosis.

         10. End stage renal disease (GFR <15 ml/min)

         11. Thyroid disease that cannot be controlled by conventional therapy.

         12. Uncontrolled diabetes mellitus

         13. Epilepsy or other disorders of the central nervous system.

         14. Severe cardiac disease history including unstable or uncontrolled cardiac disease in
             the previous 6 months.

         15. Uncontrolled hypertension

         16. Any history of retinopathy e.g. retinal detachment, degeneration or thromboembolic
             events.

         17. Clinically significant concomitant diseases or conditions, which, in the opinion of
             the investigator, would lead to an unacceptable risk for the patient to participate in
             the study (please refer also to the actual Investigator Brochure).

         18. Other malignancy, except adequately treated superficial bladder cancer, basal or
             squamous cell carcinoma of the skin, or other cancer(s) for which the patient has been
             disease free for more than 3 years.

         19. Active or uncontrolled infections at the time of randomization.

         20. Pregnant and/or nursing women.

         21. Use of antibiotic therapy within the last 2 weeks prior to randomization

         22. Concurrent use of molecular targeted therapy.

         23. Tested HIV sero-positivity or tested active hepatitis B or C infection.

         24. Participation in another clinical study with other investigational drugs within 14
             days prior to randomization.

         25. Vaccination within 1 month prior to randomization.

         26. Any medical, mental, psychological or psychiatric condition (particularly severe
             depression, suicidal ideation or suicide attempt) that in the opinion of the
             investigator would not permit the patient to complete the study or comply to study
             procedures.

         27. Drug and/or alcohol abuse.