Membrane marker and cell separation studies in Ph1-positive leukemia

Abstract From 32 patients with Ph1-positive leukemia whose cells reacted with a specific antiserum made against non-T, non-B acute lymphoid leukemia (ALL) cells, five typical patients were studied in detail. Three of these had had Ph1-positive chronic myeloid leukemia (CML) and later developed acute blast crisis with lymphoid involvement. The other two patients presented with acute leukemia with a mixture of myeloid and lymphoid blasts. In all five cases lymphoid blasts expressed the same phenotype as Ph1-negative non-T, non-B ALL: they reacted with anti-ALL and anti-p28,33 (anti-la) sera but lacked differentiation markers of thymocytes, B lymphocytes, and myeloid cells. In these cell populations high levels of terminal transferase enzyme activity were detected. Blast cells reacting with anti-ALL serum (ALL+) were separated from unreactive cells (ALL-) on a fluorescence-activated cell sorter. ALL+ cells had the morphology of ALL blasts, while ALL- cells appeared to be myeloid. These studies also suggest but do not prove that both ALL+ (lymphoid) and myeloid populations carried the Ph1 chromosome. The implication of these findings is that at least some Ph1-positive leukemias may arise from a prelymphoid, premyeloid progenitor and during blast crisis a variable proportion of blasts may retain their essentially stem cell-like characteristics. Since patients with lymphoid involvement sometimes respond to therapy designed for ALL, the early diagnosis is clinically important. Assays for ALL antigen and for terminal transferase have an important role in the diagnosis of lymphoid blast crisis, particularly if the lymphoblasts are present in the company of myeloid cells.