The significance of additional transplant-related risk factors for hemolysis, including potentially severe hemolysis due to Kidd group incompatibility, is unknown in BMT from matched unrelated donors (MUD). We report MUD BMT for 35y old male PNH patient (pt) diagnosed 1,5y before, with CD59 defect on 95% of erythrocytes (Er), with refractory hemolysis (LDH 1886 U/l, haptoglobin 0.08 g/l) and IgG autoantibodies on Er, previously treated with steroids and multiple transfusions with increasing frequency. BMT-related risk factors for hemolysis were: major Kidd incompatibility (Jk(b)+ donor and detectable anti-Jk(b) alloantibodies in titer 2 in pt), minor AB0 incompatibility (pt B, donor 0 with anti-B titer 1:16) and different Rh (pt−, donor+). Other risk factors included CMV seronegativity of the donor and seropositivity of the pt, arterial hypertension, steroid-related diabetes mellitus and probable former thrombotic episode leading to nasal septum perforation. MUD was ten alleles HLA-matched 38y old male. Myeloablative conditioning consisted of Treosulfan, Fludarabine and Thymoglobulin. Graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporin-A and methotrexate. Gancyclovir and IgG were used for CMV-reactivation prophylaxis. Transplanted bone marrow was depleted of Er on Fenwall CS3000 plus and contained 0.5x10(8) NC/kg, 2.1x10(6) CD34+ cells/kg and 12.5x10(6) CD3+ cells/kg. No serious complications were observed during the treatment and post-transplant aplasia. Filtered washed Er 0Rh-Jk(b)- were transfused 7x and single-donor platelets 7x. Following 11 days of absolute agranulocytosis full reconstitution of haematopoiesis was achieved with granulocyte count of 1.0x10(9)/l and platelets 50x10(9)/l on day +22, Hb 10 g/dl on day +26. Acute GVHD grade II was transiently present since day +21 and responded well to low-dose methylprednisolone. No chronic GVHD was observed. CMV reactivation with transient severe pancytopenia developed after day +70 and was overcome with ganciclovir, foscarnet and immunoglobulins. Hemolysis gradually decreased (LDH less than 400 U/L since day +5, normal haptoglobin >0.7 g/l since day +38). Anti-Jk(b) alloantibodies titer reached 0 on day +31 and since then they were detectable only with use of a micro-method. Full 100% donor chimerism was achieved on day +28 and was re-confirmed on days +71 and +99. Recipient-type population of erythrocytes gradually decreased (24%, 7% and 1% on days +30, +70 and +98, respectively). Complete eradication of PNH clone was confirmed by absence of complement inhibitor CD55 (DAF) and CD59 (MIRL) defects on 100% of erythrocytes and granulocytes in flow-cytometric evaluation performed on day +160. The patient stays at home without any signs of GVHD, hemolysis nor PNH over 9 months following BMT. We conclude that MUD BMT can be offered as an effective treatment option despite multiple transplant-related risk factors for hemolysis including Kidd group incompatibility.

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