EXPRESSION OF AN ONCOFETAL 65-KDA PHOSPHOPROTEIN IN LYMPHOCYTIC AND GRANULOCYTIC LEUKEMIAS

We examined the expression of an oncofetal 65-kDa phosphoprotein, term ed p65, in patients with lymphocytic and granulocytic leukemia. This p rotein was previously identified in rat fetal tissues and in epithelia l cancers of rat and human origin. Using the anti-p65 monoclonal antib odies MB2 and MF11 in a double-antibody sandwich enzyme-linked immunos orbent assay (ELISA), we analyzed the expression of the protein in ser a of 80 normal, healthy controls and in 61 patients with benign, nonne oplastic diseases. We established that the upper level of normal p65 c oncentration is 115 U/ml p65 (mean plus two standard deviations above the mean in a control group). We also analyzed p65 levels in sera of 7 1 patients with leukemia in different stages of development. The level of p65 was well above normal in 95% of acute lymphocytic leukemia (AL L; 19 cases), 83% of acute myeloblastic leukemia (AML; 23 cases), 37% of chronic lymphocytic leukemia (CLL; 19 cases), and 30% of chronic my elogenous leukemia (CML; 10 cases). MB2 monoclonal antibodies were use d for immunocytochemical staining of isolated lymphocytes from normal peripheral blood and from blood of leukemic patients (in 12 CLL patien ts, the p65 positivity was 83%, in 2 ALL patients, 100%, and in 4 AML patients, 75%). Our data suggest that p65 protein may be of use as a t umor marker in leukemia.