The long-term outcome and efficacy of PR1/BCR-ABL multipeptides vaccination in chronic myeloid leukemia: results of a 7-year longitudinal investigation

Background: Although Imatinib has revolutionized the treatment of chronic myeloid leukemia (CML), not all patients reach complete remission and a considerable proportion of the patients develop resistance to Imatinib. Material and Methods: In an attempt to increase the tail on the survival curve, we conducted a Phase I/II study of PR1/BCR-ABL multipeptides vaccination trial in CML patients with at least 15 months of Imatinib treatment and 5 months of persistent molecular residual disease. Results: One month after the completion of the vaccinations, 4 patients nearly developed a 1-log fall in their BCR-ABL transcript level, with 4 patients achieving a major molecular response (MMR). Nine patients were followed for more than a period of 7 years. The vaccinations were associated with a MMR in five patients and a complete molecular response (CMR) in one patient. The removal of Imatinib in two patients who achieved MMR after the vaccinations led to a resurgence of the leukemia population and relapse. Conclusion: Our study suggests that a combination of immunotherapy with Imatinib targeted therapy keeps the leukemia population under control, improving the long-lasting clinical and molecular response of CML patients, for at least 7 years.