Immortalized cell lines are cells that have been modified to divide indefinitely in laboratory conditions. This process often involves altering the cells' genetic material, allowing them to bypass normal cellular aging and death. These cell lines are crucial for research, as they provide a consistent and renewable source of cells for experiments. Researchers use immortalized cell lines to study various biological processes, test drugs, and develop vaccines. Examples include the HeLa cell line, derived from cervical cancer cells, which has contributed significantly to medical research. These cell lines help scientists understand diseases and develop new treatments.