CHARACTERIZATION OF LEUKEMIC-CELLS IN CD2 CD19 DOUBLE-POSITIVE ACUTE LYMPHOBLASTIC-LEUKEMIA/

In the diagnosis of leukemia, CD2 which is a T-cell associated marker and CD19 which is a B-cell associated marker are widely used to determ ine the lineage of leukemic cells. It is known that the cells of acute lymphoblastic leukemia (ALL) express both CD2 and CD19 in some cases. The origins of these cells are generally thought to be a common precu rsor for T- and B-lymphocytes. However, cytoplasmic staining of CD3 wh ich is a more specific marker for T-lineage and cytoplasmic staining o f mb-1 (CD79a) which is more specific for B-lineage were not performed in previous reports and the determination of the cell lineages of the se cells was unclear. We had two cases of ALL whose blasts were CD2/CD 19 double positive. The first case was assessed as B-lineage because t he cells expressed cytoplasmic CD79a and lacked cytoplasmic CD3. The i mmunoglobulin (Ig) heavy chain gene was rearranged. The other cell sur face markers including CD22 and HLA-DR also suggested that these cells were B-lineage. The CD? expression may be a coincidence and should no t be taken as a T-cell marker in this case. It was difficult to determ ine the lineage in the second case because both cytoplasmic CD79a and cytoplasmic CD3 were expressed and neither TCR beta chain nor Ig heavy chain genes were rearranged. The other surface markers were not usefu l to determine the lineage. We concluded that this case was really an unclassified ALL. Accordingly, cytoplasmic staining of CD3 and CD79a s hould be carried out in the diagnosis of leukemia when it is difficult to determine the cell lineage. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.