obsolete immortal cell line cell true OBSOLETE: A cell line cell that is expected to be capable of an unlimited number of divisions, and is thus able to support indefinite growth/propagation in vitro as part of a immortal cell line. continuous cell line cell permanent cell line cell Obsoleted in July 2013 and replaced by the CLO 'immortal cell line cell' class, as a result of CLO-OBI-CL alignment efforts. Covers cells actively being cultured or stored in a quiescent state for future use.