Low Dose Alemtuzumab Achieves Long-Term Engraftment with Low Level Mixed Chimerism in Related Haemopoietic Stem Cell Transplantation for Haemoglobinopathies

Haemopoietic stem cell transplantation (HSCT) is the only proven curative treatment available for haemoglobinopathies. To reduce transplant-related mortality and morbidity associated with graft-versus-host disease (GvHD) and facilitate donor engraftment we have used low-dose alemtuzumab in 43 consecutive patients (36 with thalassaemia and 7 with sickle cell disease; median age 6 years; range 2 to 16 years) transplanted since 2000. Donors were HLA-matched family donors in all cases. All patients were conditioned with oral busulfan 14 mg/kg (days -9 to -6), cyclophosphamide 200 mg/kg (days -5 to -2) and alemtuzumab 0.3 mg/kg (days -8 to -6) with post-HSCT methotrexate (10 mg/m² days +4 and +7) and ciclosporin for six months. Hypertransfusion was initiated six weeks before conditioning and maintained until day +28 to suppress endogenous haemopoiesis and minimise graft rejection. Patients with thalassaemia were Pesaro class I or II. Patients with sickle cell disease were transplanted for stroke or recurrent vasooclusive crisis and/or acute chest syndrome not responding to hydroxycarbamide. The source of stem cells was bone marrow in all cases except one patient who received PBSC with a median cell dose of 3.08 x 10⁸ TNC/kg (range 1.69 – 10.90 x 10⁸ TNC/kg). Median follow up was 25.8 months (range 6.5 – 94.3 months). Chimerism studies were performed on peripheral blood genomic DNA using 8 microsatellites markers by genescanning. All patients are alive (43/43), 42 with long-term transfusion-independence and donor haematological values (5 years DFS 97.7%). One patient failed to engraft and was re-infused with autologous cells. Donor haemopoiesis was ≥ 95% on day +28 in all 42 patients who engrafted and was maintained at ≥ 95% in the majority of patients at 12 months post-HSCT. Eleven patients (11/42; 31%) have stable mixed chimerism at ≥ 12 months post-HSCT: donor haemopoiesis 90–94% (n=4); <90% (n=7; median 85%; range 45 – 89%). There have been no late relapses and no patients had falling donor haemopoiesis <90% after day +90. Acute GvHD ≥ grade 2 occurred in 5 patients (11.6%) and was steroid-responsive in all cases except the patient who received PBSC. Limited chronic GvHD was present in 2 patients (4.6%) >18 months post-HSCT (on no treatment) and Karnofsky score is 100% in all engrafted patients (42/42). In conclusion, addition of low-dose alemtuzumab (total dose 0.3 mg/kg) achieved long-term engraftment in almost all children undergoing HLA-matched family donor HSCT for haemoglobinopathies with minimal chronic GvHD and excellent DFS (97.7%).