Delayed engraftment and mixed chimerism after HLA-identical sibling donor BMT in Fanconi anaemia

A 12-year-old girl with Fanconi anaemia (FA) received a bone marrow transpl ant from her HLA-identical brother following conditioning with cyclophospha mide (20 mg/kg), thoraco-abdominal radiation (TAI) (4 Gy) and equine anti-t hymocyte globulin (ATG) (90 mg/kg), Engraftment was delayed and initially t enuous, and was followed by mixed chimerism (MC) over a follow-up period of 2 years, DNA analysis of engraftment was performed on whole peripheral blo od and on separated granulocytes, B and T lymphocytes using PCR detection o f CA tandem repeat polymorphisms. At 10 weeks post BMT, granulocytes were p redominantly donor, but B and T lymphocytes recipient, in origin. Over the subsequent 90 weeks, granulocytes and B lymphocytes were donor-derived, whi lst T cells showed persistent MC but with an increasing donor component. Ma rrow haemopoietic function (Hb, ANC and platelet count) improved gradually in parallel with a rise in the proportion of donor lymphocyte engraftment, We postulate that a population of recipient lymphocytes survived conditioni ng and in turn delayed the development of full donor chimerism, Although tr ansient MC has been described after allogeneic BMT in FA, its association w ith delayed engraftment, and persistence for more than 1 year post BMT, has not been documented clearly.