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First published online 28 June 2010 doi:10.1111/j.1365-2141.2010.08293.x Overcoming HLA-DPB1 donor specific antibody-mediated haematopoietic graft failure Primary and secondary graft failure (GF) remain a major complication of allogeneic haematopoietic stem cell transplan- tation (HSCT). Multiple factors have been implicated in GF, including the use of mismatched donors, T-cell depleted grafts, reduced-intensity conditioning and ABO blood group mis- match (Mattsson et al, 2008). However, most cases cannot be attributed to a single factor. Donor specific antibodies (DSA) have only recently been recognized as a factor implicated in graft failure(Ciurea et al, 2010; Spellman et al, in press), particularly in mismatched transplants(Ciurea et al, 2009). A 63-year-old man was referred to our centre for unrelated HSCT for relapsed lymphoplasmacytic lymphoma (LPL) and therapy-induced bone marrow failure. Prior treatments consisted of three different lines of combination chemotherapy, autologous peripheral blood HSCT, and, most recently, lenalidomide. His white blood cell (WBC) count was 1Æ7 · 10 9 /l, absolute neutrophil count (ANC) 0Æ6 · 10 9 /l, haemoglobin 105 g/l and platelet count 4 · 10 9 /l. Bone marrow biopsy revealed 20% overall cellularity, constituted mostly by LPL cells, marked reduction in myeloid and erythroid series, rare megakaryocytes and no dysplasia. Flow cytometry confirmed clonality of the B cell marrow population. Fluorescence in situ hybridization confirmed a previously identified deletion of 13q14 in 20% of analysed cells. Metaphase cytogenetics revealed 45,XY, add(3)(p22),-4, add(6)(q12), der(13)del(13)(q12q14) t(13;?)(q32;?), del(16) (q22), -17, ?add(19)(p13Æ3), +mar[4]/46,XY[16]. The patient did not have a HLA-matched sibling and the best unrelated donor identified had a mismatch in Cw (recipient Cw*0704, donor Cw*0202). Screening DSAs using FlowPRA TM (One Lambda, Inc., Canoga Park, CA, USA) and further evaluation with Luminex-based single antigen assay or single antigen flow beads (One Lambda, Inc.) was negative for DSAs directed at the mismatched Cw antigen. Conditioning regimen for the transplantation consisted of fludarabine 25 mg/m 2 days )5 to )1 and melphalan 70 mg/m 2 on days )2 and )1. Graft-versus-host disease (GVHD) prophylaxis consisted of oral tacrolimus and sirolimus. Both donor and recipient had O+ blood type. The patient received an unmodified bone marrow product containing 3Æ93 · 10 8 total nucleated cells/kg. By day 21, the patient continued to be platelet transfusion-dependent and WBC count was <0Æ1 · 10 9 /l. A biopsy showed the bone marrow to be 40% cellular, populated almost exclusively by LPL cells with very Correspondence 94 ª 2010 Blackwell Publishing Ltd, British Journal of Haematology, 151, 84–109