Failure of Identical Twin Bone Marrow to Restore Haemopoiesis in 2 Patients with Severe Aplastic Anemia (SAA) without Immunosuppressive (IS) Conditioning

The role of mononuclear cells (MNC) in the regulation of aplastic haemopoiesis is poorly understood.Evidence for an important role of T-lymphocytes in SAA is strengthened by a frequent clinical response after treatment with Anti-T-cellglobulin. The occurrence of SAA in patients who are fortunate enough to have an identical twin bone marrow donor can provide insight into “immune”-mediated aplasia,as half of these patients ultimately require pretreatment with Cyclophosphamide to obtain haemopoietic recovery.We had the rare opportunity to study mononuclear leucocytes and bone marrow cells from 2 patients with SAA who ultimately required Cyclophosphamide to recover following twin bone marrow grafting.In coculture studies performed with donor cells, major or minor histocompatibility differences as a cause of colony growth alteration could be excluded (1).