Methods
Ten pediatric patients with TM (5 males and 5 females, 5 - 14 years old) were enrolled in the study (Table 1). The study was done in accordance with the principles of Good Clinical Practice, the Declaration of Helsinki, and all local regulations (approved by the Independent Ethics Committee of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology. All of the parents of the patients signed a written informed consent).
The inclusion criteria were as follows: an established diagnosis of TM, a high blood transfusion-dependency (at least one unit of RBC every 2-3 weeks for at least 1 year) and an enlarged spleen.
The exclusion criteria were as follows: platelet count < 75 × 109/L, an absolute neutrophil count < 1.5 × 109/L; a cardiac ejection fraction of < 50% or impaired renal, hepatic or gastrointestinal functions.
All patients were heavily transfused and had moderately severe iron overload. Liver iron concentration was measured by MRI (GE Signa 1.5). Chelation therapy continued during the study. All patients had very low pre-transfusion Hb level (<80 g/L) before enrolling in this study, heralding severe IE.
The dose of ruxolitinib was age-adjusted and based on previously published reports on ruxolitinib pharmacokinetics in children: for patients younger than 11 years it was 40-100 mg/m2total dose three times daily; for patients older than 12 years it was 20 - 30 mg/m2 total dose twice daily. Toxicities were graded according to the Common Terminology Criteria for Adverse Events version 4.0 (http://ctep.cancer.gov).
Eight patients received ruxolitinib for 6 months, while patient 1 and 9 received ruxolitinib for 1 and 1.5 years, respectively.
HSCT was performed in 8 out of 10 patients. The source of stem cells was bone marrow from matched sibling donor (MSD; n = 2), bone marrow from matched unrelated donor (MUD; n = 1) and peripheral blood from MUD (n=1) or haploidentical related donor (MMRD; n = 2). Two of the patients (2 and 4) have not received HSCT.
Conditioning regimen for the first transplant was treosulfan (42 g/m2 total dose; days -4, -3 and -2), thiotepa and (300 mg/m2 total dose; day - 5) and fludarabine (150 mg/m2 total dose; days -5, -4, -3, and -2). In addition patients received serotherapy with rabbit antithymocyte globulin (ATG;) (5 mg/kg total dose); days -5 and -4). On day -7 and - 1 patients received 375 mg/m2 rituximab for reducing the risk of Epstein-Barr virus related post-transplant lymphoproliferative disease. Grafts from MUD and MMRD (n=5) were TCRab+/CD19+ depleted by using an immunomagnetic method in accordance with the manufacturer’s instructions (Miltenyi Biotec, Bergisch Gladbach, Germany). Donor-specific anti-HLA antibodies were not detected in any of patients.
A decrease in spleen volume as assessed by MRI was chosen as the main criterion of ruxolitinib suppression of IE. Additional efficacy criteria were as follows: a decrease of soluble transferrin receptor (sTfR) concentration, a decline in proerythroblast (CD45-/CD71+/CD117+) and erythroblast (CD45-/CD71+/CD235+) count in the bone marrow, assessed by flow cytometry. Data obtained from previously published studies were used for interpreting the results.27-29 Also percentage changes of RBC transfusion volume (ml/kg) which was required to maintain Hb at 11.0 – 12.0 g/L compared to baseline and graft failure/rejection rate were used for efficacy evaluation.