Immunophenotype of blast cells in acute myelofibrosis.

The immunophenotype of peripheral blood blast cells from six patients with acute myelofibrosis was studied using a panel of monoclonal antibodies directed against granulocytic, erythroid, megakaryocytic and lymphoid antigenic determinants. In all patients most of the blast cells were labeled with anti-HLA-DR and with the early myelomonocytic antibodies My7 (CD13), My9 (CD33) and B1-3C5 (CD34) (3/3). In three cases, platelet antibodies Edu3 (CD41) and GPIIIa (CD61) reacted with about 30% of blast cells. TdT was positive in two out of six samples studied. Lymphoid markers T3 (CD3), Leu9 (CD7), J5 (CD10), B4 (CD19) and B1 (CD20) were negative in all cases. These results suggest that blast cells are mainly of immature myelocytic origin. However, the coexistence of megakaryoblasts cannot be ruled out in the cases with a proportion of cells that are positive with Edu3 and GPIIIa antibodies.