Successful allogeneic bone marrow transplantation in juvenile CML: conditioning or graft-versus-leukaemia effect?

Allogeneic BMT is the treatment of choice for juvenile CML (JCML). This has been successful following conditioning with cyclophosphamide (120 mg/kg) and total body irradiation (TBI) (10-15.75 Gy). However, busulphan (16 mg/kg) and cyclophosphamide (200 mg/kg) (Bu/Cy) conditioning has been reported to be insufficient to eradicate the malignant clone in JCML. We report successful BMT and eradication of the disease at 18 months follow-up in a child 15 months old at presentation, who was conditioned with busulphan 20 mg/kg and cyclophosphamide 200 mg/kg, with the addition of splenic irradiation. Despite using higher than conventional doses of busulphan, pharmacokinetic analysis revealed very low busulphan peak levels and rapid excretion. As a possible consequence, only partial chimerism was achieved, but full engraftment ensued following the discontinuation of cyclosporin A, rebound donor lymphocytosis and the onset of acute GVHD. We suggest that host resistance to engraftment and tumour elimination was overcome by removing a suppressive effect on donor lymphocytes, allowing a graft-versus-leukaemia effect.