Monoclonal antibody MCS-2 as the marker of phorbol diester-induced myeloid differentiation in acute undifferentiated leukemia.

Leukemic cells from 32 cases of acute leukemia were cultured in vitro with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) to study their differentiative potential. Three cases of acute undifferentiated leukemia (AUL) were studied intensively. We found that culturing of leukemic cells with TPA can induce changes in cell surface antigens. In particular, MCS-2, a "pan" granulocyte/monocyte marker, was inducible in vitro in AUL and in acute myelogenous leukemia, while it was not inducible in acute lymphoblastic leukemia. BA-2 (recognizing the Mr 24,000 protein) and TA-1 (recognizing the Mr 170,000 and Mr 95,000 proteins) were also inducible in cases of AUL, acute myelocytic leukemia, and acute monoblastic leukemia, although these antigens are not limited only to leukemias of the myelomonocytic lineage. Our studies also indicate that undifferentiated cells could be induced to nonspecific esterase and sometimes to chloroacetate esterase reactivity while losing terminal deoxynucleotidyl transferase. Morphological studies in these cases revealed cytological maturation following TPA treatment. In most cases, these changes were also partially inducible by culturing cells in medium alone or with the addition of dimethyl sulfoxide but not to the extent that was demonstrated by TPA. Our studies showed that MCS-2 is a very good, specific marker of acute nonlymphocytic leukemia. A potential use for TPA to aid in the subclassification of patients with AUL is also suggested.