Flow cytometric detection of CD79a expression in T-cell acute lymphoblastic leukemias

We evaluated the lineage specificity of CD79a in acute leukemias using 3-co lor flow cytometry in 58 consecutive cases. A panel of cell-surface antigen s, including myeloid-associated markers, B-cell-associated markers, and T-c ell associated markers, was used. All cases of acute myeloid leukemia were CD79a-, whereas all cases of B-lineage acute lymphoblastic leukemia (ALL) w ere CD79a+. Three of 8 cases of T-cell ALL showed variable CD79a expression , indicating the presence of a blast subset expressing a relatively high le vel of CD79a. We investigated the clinical and pathologic characteristics o f these 3 cases. All 3 cases had L1 or L2 morphology and expressed surface CD3. None of the other B cell-associated markers were positive, although 1 case expressed CD13 and CD33. Uncommon random karyotypic abnormalities were identified in all 3 cases. Molecular studies demonstrated monoclonal gene rearrangement of T-cell receptor gamma in 2 of 3 cases. All 3 patients were 18 years old or younger; 1 patient did not enter remission and 1 had disea se relapse in 8 months. Our findings provide further support for the existe nce of a subset of T-cell ALL coexpressing CD3 and CD79a. Further study of the clinical and biologic significance of this subset may be warranted.