A murine hybridoma-derived
monoclonal antibody, PM-81, was obtained from a fusion of cells of the
NS-1 myeloma cell line with cells from a mouse immunized with the HL-60 promyelocytic
leukemia cell line. This cytotoxic
IgM monoclonal antibody was specific for myeloid cells. Employing indirect immunofluorescence and flow cytometry, we determined that this antibody reacts strongly with normal human granulocytes, eosinophils, and monocytes but not lymphocytes (including
phytohemagglutinin-activated lymphocytes), null cells, red blood cells, or platelets. Moreover, the PM-81 antibody reacts with
leukemia cells from 19 of 22 patients with
acute myelocytic leukemia of all FAB subclasses, three of three patients with common
acute lymphocytic leukemia, four of four patients with
chronic myelocytic leukemia (CML) in myeloid
blast crisis (terminal
transferase (TdT)-negative) but did not react with cells from two patients with CML in lymphoid
blast crisis (TdT-positive) or five patients with
chronic lymphocytic leukemia. The myeloid cell lines HL-60, K562, KG-1, and U937 were all reactive with PM-81. The lymphoid lines CCRF-CEM and Daudi did not express PM-81 but HSB-2 was positive. The PM-81
antigen was absent on myeloid and erythroid progenitor cells as determined by their insusceptibility to
complement-dependent lysis. In addition, only PM-81-unreactive cells were capable of colony formation. Furthermore, the PM-81 antibody does not appear to induce modulation of the
antigen to which it binds. Thus, this
monoclonal antibody appears to fulfill several criteria for clinical utility in the diagnosis and treatment of both acute myelocytic and
acute lymphocytic leukemia.