Thrombospondin as a Marker for Leukemic Megakaryoblasts

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Abstract
Four cases of acute leukemia are reported in which the blast cells were reactive with a monoclonal antibody to the platelet alpha granule glycoprotein thrombospondin (TSP). Blasts in all four cases were also terminal deoxynucleotidyl transferase (TdT)-positive. Two cases demonstrated the presence of the Philadelphia chromosome, t(9;22). The only cells in normal bone marrow which reacted with antibody to TSP were megakaryocytes. Blasts in nine cases of acute myelogenous leukemia, six cases of acute lymphocytic leukemia, four cases of undifferentiated leukemia, and three cases of myelodysplastic syndrome were negative for TSP. Thus, TSP is useful in the identification of normal megakaryocytes and a subset of acute leukemia cells. The presence of both TSP and TdT in the leukemic blasts of our four patients suggests evolution from a pluripotent stem cell capable of multi-lineage differentiation.