"Pan-myeloid" reagent: the monoclonal antibody MCS-2 in the routine immunodiagnostic service of leukemia phenotyping

This retrospective analysis describes the reactivity of several monoclonal antibodies (MoAbs) which detect myelomonocytic antigens of the cells of 182 leukemias. These leukemias were assigned to definite subtypes of lymphocytic and myelo(mono)-cytic leukemias on the basis of standard leukemia phenotyping using morphological, cytochemical, isoenzymatic and mainly immunological criteria. The MoAb MCS-2 was negative in all cases of lymphocytic leukemia, whereas two of the three other commonly used "myeloid MoAbs" MCS-1, OKM-1 and 1/12/13 showed positivity in B-chronic lymphocytic leukemia (B-CLL), B-lymphoma (MCS-1), T-acute lymphoblastic leukemia (T-ALL) and Sézary syndrome (OKM-1). MCS-2 was positive in all samples of acute myelomonoblastic leukemia (AMMoL), chronic myelocytic leukemia (CML) and CML-myeloid blast crisis, which was not the case for MCS-1, OKM-1, or 1/12/13. In 14 cases (11 acute myeloblastic leukemia (AML), 3 CML-myeloid blast crisis) where MCS-2 was positive and one or all of the three other MoAbs were negative, the cells were mainly Ia-positive and peroxidase-negative. MCS-2 is a diagnostically important MoAb in the routine leukemia phenotyping of myelomonocytic leukemias. After having tested a large number of normal and malignant specimens, we would like to term MCS-2 a "pan-myeloid MoAb" reacting with the myelomonocytic cell lineage from the earliest myeloblast to granulocytes and monocytes.