Graft TCR-Alpha/Beta Depletion and Peri-Transplant Use Of Eculizumab In Matched Unrelated Donor Transplantation For Severe Aplastic Anemia-Paroxysmal Nocturnal Hemoglobinuria: Report Of Two Cases

Introduction Inhibition of terminal complement components provides effective control of severe hemolytic PNH, but remains prohibitively expensive in countries with limited resources. Allogeneic hematopoietic stem cell transplantation offers a chance of permanent cure at the expense of increased risk of transplant-related morbidity and mortality in severe PNH. We report two patients with hemolytic PNH, associated with severe aplastic anemia, who were treated with limited eculizumab course to reduce the risk of complications of matched unrelated donor (MUD) transplantation. Patient #1 is a 22 y.o. young man. Severe aplastic anemia (SAA) was diagnosed at the age of 13 y.o. He received combined IST with ATG and cyclosporine A (CsA) and remained transfusion–free with complete hematologic response until 17 y.o., when SAA relapsed. CsA was re-administered as monotherapy due to severe anaphylaxis to ATG. At the age of 20 y.o. episodic hemolysis and severe abdominal pain bouts developed. PNH was diagnosed with standard flow cytometric assay. Two years later 10/10 matched unrelated donor was found and a decision was made to proceed to allogeneic transplantation. The preparative regimen included total doses of fludarabine - 150mg/m 2 , cyclophosphamide - 100mg/m 2 , thoracoabdominal irradiation - 6Gy and alemtuzumab 30 mg/m 2 . Eculizumab was administered weekly since day -14 till +14 at 600mg x2 and 300mg x3 resulting in prompt resolution of hemolysis. PBSC graft processing included TCR alpha/beta and CD19 depletion on CliniMACS instrument according to manufacturer9s instructions. The final graft contained 6,4*10 6 per kg NC, 6,6*10 6 per kg CD34+, 15*10 4 per kg TCR alpha/beta+ lymphocytes. GVHD prophylaxis included tacrolimus till day +30 and Mtx at +1,3,6,10. Engraftment was stable with Plt and WBC on day + 18. PNH clone in granulocytes and monocytes remained around detection limit. A peculiar feature of engraftment was stable split chimerism with all hematopoietic lineages except CD3 originating from the donor. T cells remained almost completely of recipient origin until thymic function recovered with dominant production of donor T cells (Fig. 1). Independent of this T-cell chimerism dynamics, the hematopoiesis remains stable and of donor origin for one year from transplant. No manifestations of acute or chronic GVHD were observed. Transplant toxicity included CMV reactivation controlled with standard antiviral treatment. Patient#2 is a 15 y.o. girl. The diagnosis of SAA was established at the age of 8 y.o. Combined IST with ATG and CsA induced partial hematologic response. Three years later she developed SAA relapse and hemolytic PNH complicated by cerebral sinus thrombosis and severe ischemic attack. She recovered upon endovascular thrombectomy and systemic thrombolysis eculizumab was started at 600 mg/biweekly leading to resolution of hemolysis. Four months later 10/10 MUD was identified and the patient proceeded to transplantation. The preparative regimen included fludarabine - 150mg/m 2 , cyclophosphamide - 100mg/m 2 , thoracoabdominal irradiation - 6Gy and ATG(horse) - 90 mg/m 2 . Eculizumab was administered weekly till day +21 at 300mg/week. Graft processing included TCR alpha/beta and CD19 depletion. The graft contained 13,8*10 6 per kg NC, 13,5*10 6 per kg CD34+, 31*10 4 per kg TCR alpha/beta+ lymphocytes. GVHD prophylaxis included tacrolimus till day +30 and Mtx at +1,3,6. Engraftment was rapid with Plt and WBC on day + 12 and + 15 respectively. Graft function is stable for 100 days post-transplant and PNH clone in granulocytes and monocytes is at the limits of detection. T-cell chimerism remains mixed with 10% of recipient cells. Grade 1-2 skin aGVHD was observed and controlled by short steroid course. No other early transplant-associated toxicity was observed. Conclusion Combined use of peri-transplant eculizumab and TCR alpha/beta depletion of the unrelated graft potentially protects patients with severe PNH from transplant-related toxicity. Disclosures: Boyakova: Alexion: Research Funding.