Various patterns of chimerism after allogeneic bone marrow transplantation for advanced chronic lymphocytic leukemia.

Chimerism studies after allogeneic BMT are performed to determine the donor and/or recipient origin of peripheral blood and marrow lymphoid and hematopoietic cells. These studies have been performed mostly in leukemias and aplastic anemia. We report DNA-based chimerism studies in three patients transplanted for advanced CLL from a histocompatible sibling. Following conditioning with chlorambucil, cyclophosphamide and TBI all three successfully engrafted. One has remained in continuous complete remission (CR) with a complete donor chimerism (CDC) for 110 months post-BMT. Another was in mixed chimerism (MC) with minimal residual disease (MRD) at 3 months post-BMT but was in CR and in CDC at 6 months, suggesting that the persistent CLL cells has disappeared between these two studies. The third patient has been in persistent MC since BMT (24 months follow-up), although he is in CR with no evidence of persistent CLL. We postulate that this patient's MC status is due to normal residual recipient lymphohematopoietic cells that survived the conditioning regimen. In conclusion, various patterns of chimerism can be observed in CLL patients after BMT while remaining in CR and with no evidence of residual CLL.