What Causes Aplastic Anaemia: Results of Transplants from Genetically-Identical Twins.

Background Aplastic anaemia has diverse aetiologies. Distinguishing between these is, in part, testable by analyzing results of haematopoietic cells transplants between genetically-identical twins one of whom has aplastic anaemia. Objective Describe outcomes of genetically-identical twin transplants for aplastic anaemia with and without pretransplant conditioning. Methods We interrogated data from an observational database of 59 consecutive recipients of genetically-identical twin transplants for aplastic anaemia reported to the Center for International Blood and Marrow Transplant Research (CIBMTR) 2000-2019. Results 38 subjects were male. Median age was 18 years (Interquartile Range [IQR], 11-32 years). Median interval from diagnosis to transplant was 2 months (IQR 1-3 months). 11 subjects received a 1 st transplant without pretransplant conditioning. 2 of recovered normal bone marrow function. The other 9 received a 2 nd transplant with pretransplant conditioning 7 of whom recovered. 48 subjects received pretransplant conditioning before a 1 st or 2 nd transplant all of whom recovered. Conclusion Only some genetically-identical twins with aplastic anaemia recover normal bone marrow function after a 1 st haematopoietic cell transplant without pretransplant conditioning whereas most subjects recover when a transplant is preceded by pretransplant conditioning. These data are consistent with an immune-mediated aetiology of aplastic anaemia in most cases.