Flow cytometry of p53 protein expression in some hematological malignancies.

p53 is a tumor suppressor gene encoding a nuclear phosphoprotein that plays an important role in the control of normal cell proliferation. We have tried to establish the value of the p53 protein expression in peripheral blood (PB) and/or bone marrow (BM) cells of patients with some hematological malignancies. A recently developed fixation/permeabilization method was modified for flow cytometric assessment of p53 protein expression using two anti-p53 monoclonal antibodies. p53 quantitation expressed as molecules of equivalent soluble fluorochrome per cell (MESF) providing valuable data contributing to a more precise definition of leukemic cells, was also applied. Our findings showed higher percentage of p53 expression in cells of AML patients at the time of diagnosis opposite to the controls. These data, in association with immunophenotype of cells, accompanied diagnosis of relapse or definition of remission after allogeneic BM transplantation. We observed also elevated levels of p53 protein at initial diagnosis of early B-ALL. According to our results quantitation of p53 protein allows better characterization of selected population of BM cells and should be used for the monitoring of blast persistence during and after therapy and might also be one of the methods to indicate early relapse. Percentage of p53 protein positivity varied in our group of B-CLL patients tested in connection with progression of disease. We documented also one case of Burkitt's lymphoma with high percentage of p53 positivity. Measurement of p53 protein expression by flow cytometry may be of clinical importance by indicating levels of positivity. Our results suggest, that p53 alteration is frequently involved at initial diagnosis of AML, in some T-cell disorders and on the contrary more frequently during early B-ALL relapse, in advanced stages of B-CLL and in Burkitt's lymphoma. p53 protein quantitation is of value to ascertain malignancy and provides additional parameter suitable for the evaluation of residual disease and for the monitoring of therapy.