Treosulfan, Fludarabine, and Antithymocyte Globulin - A Low Toxicity Conditioning Regimen for Unrelated Donor - Hematopoietic Stem Cell Transplantation in Chronic Myeloid Leukemia.

Unrelated donor - hematopoietic stem cell transplantation (URD-HSCT) is the treatment of proved long-term efficacy for chronic myeloid leukemia (CML) patients not having an HLA-identical sibling. However, high procedure-related toxicity observed after oral busulfan- or TBI-based conditioning limits its applicability and deteriorates outcome [

Thirty patients (age 32, range 16–48 years) with CML in the 1^st chronic phase (n=29) or in 2^nd chronic phase (n=1) were included in the study. Median interval from diagnosis to alloHSCT equaled 1.0 (0.5–12.0) years. 63% of patients had previously been treated with Imatinib. The donors were selected based on high resolution typing for both HLA class I and II. 43% of donors were mismatched for a single HLA-C (n=9), HLA-DQB1 (n=3) or HLA-B locus (n=1). Bone marrow was used a source of stem cells in 19 patients, peripheral blood - in 11 cases. GVHD prophylaxis consisted of Cyclosporin A and short-course Methotrexate.

All patients engrafted with the median time to neutrophil recovery >0.5 G/L and PLT >50 G/L of 19 (10–30) days and 18 (12–29) days, respectively. Complete donor chimerism was achieved until day +100 in all but one patient. Grade 3–4 neutropenic infections occurred in 13% of patients. Grade 3–4 mucositis as well as hepatic toxicity including VOD were not observed. The incidence of grade II acute GVHD was 23%, whereas grade III-IV acute GVHD was not observed. The incidence of extensive chronic GVHD was 10%.

At 3 years the probability of the overall survival and hematological relapse-free survival equaled 82% (+/−7%). The cumulative incidence of non-relapse moratlity was 18% (+/−7%) (fungal infection n=3, bacterial infection n=1, EBV-LPD n=1). Four patients required donor lymphocyte infusion or additional interferon or imatinib treatment because of incomplete donor chimerism or molecular/cytogenetic relapse after initial response.

We conclude that treosulfan + fludarabine + ATG conditioning is associated with low organ toxicity, low incidence of severe GVHD and NRM. The regimen is feasible option for CML patients referred for URD-HSCT in tyrosine kinase inhibitors era.