RESUMEN
Our previous study showed that malignant phenotype of human promyelocytic leukemia cells could he suppressed by fusion of them with mouse reticulocytes. In order to investigate the morphological changes for malignancy reversion, the present experiment was designed to study the microscepic and submicroscopic structure of cybrid cells and compared with their parental tumor cells. The results indicated that during the short period of cybrid cell cultivation, nuclei of numerous cybrid cells became pyknotic and eccentric, and some cells showed the process of nuclear expulsion (denucleation). The cybrids which cultivated for long period in vitro developed into more mature cells along both myeloid and erythroid differentiation pathway. The effects of mouse reticulocyte cytoplasmic factor on differentiation pathway of human promyelocytic leukemia cells were discussed.