EN
After a few cell divisions primary cell cultures enter into a terminally nondividing state. Replicative senescence of cells involves a wide range of cellular events including changes in gene expression. Using immortalization methods it is possible to immortalize many of the primary cell cultures. The major advantage is that the immortalized cells represent the tissue of origin. It is possible to distinguish spontaneous and induced immortalization. The spontaneous immortalization of cultured cells is quite a rare event. Carcinogenic agents, radiation and viral oncogens can induce immortalization of cells. Transfection of cells with oncogens and telomerase activation generates an extended lifespan of cells. This review discusses various approaches to cell immortalization and the application of such cell lines for studies on animal reproduction.