Polyclonal hemopoiesis in leukemia patients following molecularly documented remission

We performed clonality studies of hemopoietic reconstitution in 24 female patients (pts) with leukemias characterized by specific tumor markers. Thirteen pts had Acute Promyelocytic Leukemia (APL) with rearrangements of the RAR-a and PML genes, 8 BCR rearranged (BCR+)/Ph+ Chronic Myeloid Leukemia (CML) and 3 BCR+/Ph+ Acute Lymphoid Leukemia (ALL). Bone marrow (BM) DNA samples were obtained at diagnosis and at remission after Southern blot documented suppression of specific markers. The clonal or non-clonal nature of hemopoietic reconstitution was assessed by hybridizing the same DNAs with the M27 beta probe, in order to detect methylation differences at the X-linked DXS255 locus. Twenty four pts showed a polyclonal methylation pattern at remission, whereas in 3 cases an apparently clonal pattern was observed despite no evidence of specific gene rearrangement. In 2 of these 3 cases, however, DNAs derived from non-affected tissues (T lymphocytes, skin and BM fibroblasts) revealed the presence of the same DXS255 unmethylated allele detected at diagnosis, while in the third case we found the same apparently clonal pattern in blood mononuclear cells obtained from her healthy female BM donor. These data indicate that polyclonal hematopoiesis occur in APL and CML pts after therapy induced suppression of specific tumor markers, and that unbalanced or aberrant X chromosome methylation patterns are observed in some cases, most likely reflecting constitutional features.