Study of chimerism in long-term survivors after bone marrow transplantation for severe acquired aplastic anemia.

Chimerism studies employing PCR and Southern techniques targeting VNTR loci were performed in 17 severe acquired aplastic anemia patients who were long-term survivors after BMT. They were studied a median of 4 years after BMT (1-12). All patients had normal blood counts. All patients conditioned with radiation-based schemes showed a full donor pattern of hemopoiesis. Conversely, out of five patients who received only cyclophosphamide as conditioning therapy, two of them had a late graft failure (2.4 and 3 years after BMT). One of these relapsing patients had a durable mixed chimerism, which was first detected 1 month after BMT. Our results seem to suggest that durable mixed chimerism can antecede graft failure in some patients conditioned only with cyclophosphamide, and that a more stringent monitoring can be clinically rewarding in this group of patients.