Analysis of immunophenotype, genotype, and lineage fidelity in blastic transformation of chronic myelogenous leukemia: A study of 20 cases

We have examined the immunophenotype and genotype of leukemic cells from 20 patients with the blastic phase of chronic myelogenous leukemia (CML), which is known to arise from a pluripotential hematopoletic stem cell. The phenotypic analysis of surface antigens with a panel of lineage-specific monoclonal antibodies revealed that six of 20 cases expressed phenotypes of lymphoid blastic transformation with pre-B cell markers. One of these cases was shown to coexpress cluster designation 2 of T cell marker on the same cells by two-color immunofluorescence analysis. Eight cases, including two cases that also had a megakaryocytic component, showed phenotypes expressing differentiation antigens of myeloid series. Three expressed a phenotype of megakaryoblastic transformation. The remaining three cases had no surface marker characteristic of any cellular lineage. The genotypic analysis by Southern blot hybridization showed that immunoglobulin heavy chain genes were rearranged in all of six lymphoid blastic transformations and that rearrangement of a T cell receptor beta chain gene was present in only one lymphoid blastic transformation that had no T cell surface marker. DNA samples in all cases of nonlymphoid blastic transformation were retained in the germ line configuration for both immunoglobulin and T cell receptor genes. Although these findings support the concept of lineage fidelity in nonlymphoid blastic transformation of CML, lymphoid blastic transformation committed to B cell lineage may, in some cases, present a few phenotypic or genotypic expressions of T cell-associated features with the pre-B cell phenotype and genotype.