What is the difference between primary cells and cell lines?

Primary cells are directly derived from the patient and have limited proliferation cycles. cell lines are formed when normal cells are cultured and allowed to divide and expand in number, which is usually due to genetic modifications. cell lines are often derived from a tumour of the cell type of interest or by transforming and immortalising a primary cell with an oncogene. contrary to primary cells, cell lines can be maintained indefinitely in culture and are able to generate large number of cells.