Bone marrow transplantation (BMT) is the most effective therapy for many patients with leukemia. Three possible situations of chimerism can be encountered during assessment of the hematological status in patients after allogeneic BMT: 1) complete chimerism (CC), where the marrow and circulating blood cells are all of donor origin; 2) near-complete chimerism (NCC), where over 90% of the cell components are of donor origin; 3) mixed chime­rism (MC), where the cell components are of both donor and recipient origins. In CC or NCC, durable engraftment is achieved.
Evaluation of the chimerism status after BMT provides substantial information about the replacement of host cells with donor cells. Since hematopoietic chimerism is predictive of the early relapse of acute leukemia [1-3], development of effective molecular-diagnostic methods for monitoring of chimerism is an important tool for determining the risk of relapse in patients after BMT [4-6].
Methods for detection of chimerism include conversion of blood group, karyotyping, analysis of variable number of tandem repeat (VNTR) and microsatellite assay [7-11]. The most sensitive and accurate methods are fluorescent in situ hybridization (FISH) with specific probes for the sex chromosomes (XY-FISH) and multiplex short tandem repeat polymerase chain reaction (STR-PCR) with capillary electrophoresis for quantification of chimerism [12-14]. The latter approach is sex-independent and can be applied to virtually all patients. In this article we describe our experience in the detection of chimerism after BMT in Bulgaria.