Allogeneic Stem Cell Transplantation in Chronic Myeloid Leukemia Failing TKIs Therapy

Patients newly diagnosed with chronic phase chronic myeloid leukemia undergo treatment with TK inhibitors (TKI). A possible cause of TK failure is represented by the insufficient recovery of normal Ph- hematopoiesis during TKI treatment, with consequent severe cytopenias that limit TKI adequate administration. Although rare, this event happens in a proportion of 4-5% of CML patients. Our hypothesis is to circumvent this peculiar condition by providing a normal hematopoiesis from a HLA-matched donor (Human Leukocyte Antigen). The transplant procedure is therefore intended in providing a sustained hematopoiesis that will allow an early treatment with an adequate dosing of TKI. The transplant procedure planned in our study is built on all available evidences to provide the lowest incidence of acute and chronic GvHD (Graft-versus-host disease). Therefore, a bone marrow will be the preferential source and a GvHD prophylaxis based on Anti-thrombocyte globulin (ATG) and Cyclosporine/Methotrexate will be used according to standard current experience in the field of family and unrelated donors. The pre-transplant TKI will be continued until aplasia will develop, in order to decrease the tumor load as much as possible.The use of TKIs shortly after transplant carries the risk of inhibiting the newly transplanted hematopoietic cells, as Kit, an important kinase in normal bone marrow cells, is frequently blocked by Abl inhibitors. The use of bosutinib as post-transplant therapy is justified by the lack of Kit inhibition that distinguishes bosutinib from all other TKIs, and which could allow a minimal inhibitory activity against the transplanted normal bone marrow.