Conversion of acute undifferentiated leukemia phenotypes: analysis of clonal development

Phenotype switch in acute leukemia patients after intensive chemotherapy

According to Stass et al. the percentage of a lineage switch occurs in 6.7%-8.6% of patients with acute leukemia. Mostly, a conversion from the lymphoid to the myeloid phenotype is seen. In our three cases we found two switches from the myeloid to the lymphoid phenotype and only one from lymphoid to myeloid. This lineage switch is seen in relapsing and resistant leukemia cases. Different hypotheses have been discussed concerning the phenotype switch. Cytostatic chemotherapy may eradicate one leukemic cell clone, allowing another one to proliferate. Otherwise, the leukemic transformed stem cell could be influenced by the chemotherapy, resulting in a change of the differentiation program of the cell and following with a switch of marker expression. Perhaps there is some clinical importance to monitoring the phenotype switch in order to administer the best treatment.

Induction of myeloperoxidase in five cases of acute unclassified leukaemia

For further analysis of their lineage affinity the differentiation capacity of five cases of acute unclassified leukaemias were studied in vitro using 5 nM 12-O-tetradecanoyl-phorbol-13-acetate as an inducing agent. After 4 d in vitro a co-expression of both myeloid and early B-lymphoid or myeloid and early T-lymphoid antigens on the same population of cells was found. While ultrastructural analysis of the blasts prior to culture revealed the morphology of undifferentiated blasts without any specific endogenous peroxidase activity, the cultured blasts displayed monoblastic features and myeloperoxidase activity after 4 d in vitro. Since this type of peroxidase is highly specific for the myelomonocytic lineage the data indicate myelomonocytoid differentiation of all five cases studied. The co-expression of lymphoid as well as myeloid antigens and myeloperoxidase by the same blasts after culture could be indicative of bilineage differentiation capacity characterizing the original blasts as bipotential progenitor cells.