Immortalization of Cultured Cells in Regenerative Biomedicine: Approaches, Opportunities, and Limitations

Primary cell cultures are one of the main research objects and promising tools in regenerative biomedicine. However, their application is significantly limited by the short lifespan and rapid aging. Existing approaches to prolong the "youth" of cultured cells inevitably alter their properties, which raises questions about their applicability in regenerative biomedicine. Our review examines the main mechanisms of aging of cultured cells, existing methods used to overcome it, and safety issues associated with the produced cultures. We analyzed the data on cell immortalization and its connection with tumor transformation. Among the methods for prolonging the proliferative activity of cells are spontaneous immortalization and immortalization induced by overexpression of the catalytic subunit of telomerase (TERT), viral oncogenes (T antigens of the polyomavirus SV40, proteins E6/E7 of human papillomavirus type 16, and adenoviral proteins E1A and E1B of adenoviruses), and cellular transcription factors, such as proto-oncogenes (c-MYC, BMI1). The accumulated data suggest that increasing the expression of the gene encoding TERT is one of the relatively safe approaches to prolonging the proliferative activity of a cell line, which does not lead to the tumor transformation of cell line. Based on the analyzed data, an attempt was made to identify the "boundary" between the permissible prolongation of cell culture life and its tumor transformation.