Abstract Introduction Treatment-free remission (TFR) is successful in half of the patients with chronic myeloid leukemia who discontinue Imatinib (IM) after sustained molecular response. Methods In a prospective trial, we used pioglitazone for 3 months before stopping IM in 30 patients. Percentages of peripheral blood lymphocyte subsets were assessed before and after treatment. The relation of these data with duration of IM treatment and TRF were examined. Results The median time of IM treatment was 117.6 months. After discontinuation, 11 patients had molecular recurrence after 5.2 months (2.4 - 30). The observation time for those remaining in TFR was 46 (26 - 56) months. The independent factors for the maintenance of TFR were the duration of IM treatment and the percentage of double-positive T cells at IM stop. Conclusion A longer treatment with imatinib was associated with a longer TFR after discontinuation. Pioglitazone could act as an immunomodulator, increasing DP T cells which may contribute to prevent relapse. Treatmentfree Treatment free (TFR (IM response trial examined 1176 117 6 117. discontinuation 1 52 5 2 5. 2.4 24 4 (2. 30. . 30) 26 (2 56 doublepositive double positive stop immunomodulator relapse 2. (