T-LYMPHOID MYELOID BILINEAL CRISIS IN CHRONIC MYELOGENOUS LEUKEMIA/

We describe 2 cases of ''bilineal'' crisis in chronic myelogenous leuk emia (CML) with T cell and myeloid phenotypes. In both cases, morphocy tochemically distinct myeloid and T lymphoid blast populations prolife rated simultaneously in the phase of blastic crisis-myeloperoxidase (M PO)-positive, CD7(+)/CD33(+) myeloblasts in the peripheral blood, and MPO-negative, periodic acid Schiff (PAS)-positive lymphoblasts in the lymph nodes. In each case, common karyotypes containing Ph(1) transloc ation were demonstrated in both the peripheral blood and the lymph nod e samples. In Case 1, the lymph nodes were occupied by >90% lymphoblas ts, which were positive for CD2, cytoplasmic CD3 (cCD3), CD5 and CD7 a nd terminal deoxynucleotidyl transferase (TdT), but negative for myelo id antigens. Myeloblasts and T lymphoblasts showed an identical rearra ngement of the bcr gene by Southern blotting analysis, although the cl onal rearrangement of the T cell receptor (TcR)-delta gene was seen on ly in T lymphoblasts. In Case 2, simultaneous proliferation of myelobl asts and lymphoblasts was documented morphocytochemically in the lymph node, and a flow cytometric analysis revealed the coexistence of CD7( +)/CD33(+) and CD7(+)/CD33(-) blast populations. Each blast population was enriched by antibody-conjugated immuno-magnetic beads; the former was positive for MPO by 64% but negative for cCD3 and TdT, whereas th e latter was positive for cCD3 and TdT but negative for MPO (<1%). CD7 (+)/CD33(+) myeloblasts and CD7(+)/CD33(-) lymphoblasts showed an iden tical rearrangement of the bcr gene. Neither TcR-beta, TcR-gamma nor t he TcR-delta gene was clonally rearranged in either population. These observations clearly indicate that T lymphoid and myeloid blasts share common Ph(1)-positive progenitors, and that Ph(1)-positive T lymphoid /myeloid progenitors are probably involved in the development of blast ic transformation in some percentage of CML patients.