Expression of an oncofetal 65-kDa phosphoprotein in lymphocytic and granulocytic leukemias.

We examined the expression of an oncofetal 65-kDa phosphoprotein, termed p65, in patients with lymphocytic and granulocytic leukemia. This protein was previously identified in rat fetal tissues and in epithelial cancers of rat and human origin. Using the anti-p65 monoclonal antibodies MB2 and MF11 in a double-antibody sandwich enzyme-linked immunosorbent assay (ELISA), we analyzed the expression of the protein in sera of 80 normal, healthy controls and in 61 patients with benign, nonneoplastic diseases. We established that the upper level of normal p65 concentration 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 71 patients with leukemia in different stages of development. The level of p65 was well above normal in 95% of acute lymphocytic leukemia (ALL; 19 cases), 83% of acute myeloblastic leukemia (AML; 23 cases), 37% of chronic lymphocytic leukemia (CLL; 19 cases), and 30% of chronic myelogenous leukemia (CML; 10 cases). MB2 monoclonal antibodies were used for immunocytochemical staining of isolated lymphocytes from normal peripheral blood and from blood of leukemic patients (in 12 CLL patients, 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 tumor marker in leukemia.