[Megakaryocytic leukemia cell lines and megakaryocytic leukemia]

Using the megakaryocytic leukemia cell lines, K-562 and CMK established from a Down's patient with acute megakaryoblastic leukemia, we studied the changes of antigen expression, cytosolic Ca2+ mobilization, thromboxane (TX) A2 formation and gene expression during megakaryocyte differentiation. We found that thrombospondin synthesis and platelet factor (PF)-4 gene expression were specific for mature megakaryoblasts, whereas collagen unresponsiveness and prostaglandin E1-induced Ca2+ mobilization were noted in immature megakaryoblasts alone. This experiment shows that functional and genetic analysis are useful for characterizing the leukemic megakaryoblastic cells. We analyzed the clinical, hematologic and genetic features of 4 patients with M7, and acute megakaryoblastic transformation of CML, MDS and essential thrombocythemia. In two patients, prednisolone and 6-MP were effective in cytoreduction. In 3 patients with increased platelet counts, normal CFU-Meg formation, the megakaryoblasts with platelet production, or the coexistence of immature megakaryoblasts with mature megakaryocytes were observed, thus indicating that some megakaryoblastic leukemia cells still have the capacity of differentiation. One patient had megakaryoblastic cells with PF-4 gene expression. These clinical findings suggest that the megakaryoblastic leukemia could not be characterized as usual leukemia and a more sensitive marker is required to differentiate leukemic megakaryoblasts from normal megakaryoblasts.