A feeder-cell independent subpopulation of the PICM-19 pig liver stem cell line capable of long-term growth and extensive expansion

A method for the feeder-independent culture of PICM-19 pig liver stem cell line was recently devised, but the cell line's growth was finite and the cells essentially ceased dividing after approximately 20 passages over a 1 year culture period. Here we report the isolation, continuous culture, and initial characterization of a spontaneously arising feeder-independent PICM-19 subpopulation, PICM-19FF, that maintained replication rate and hepatocyte functions over an extended culture period. PICM-19FF cells grew to 90-98 % confluency after each passage at 2 week intervals, and the cells maintained a high cell density after 2 years and 48 passages in culture (average of 2.6 x 10(6) cells/T25 flask or 1 x 10(5) cells/cm(2)). Morphologically, the PICM-FF cells closely resembled the finite feeder-independent PICM-19 cultures previously reported, and, as before, no spontaneous formation of 3D multicellular ductules occurred in the cells' monolayer. Their bipotent stem cell nature was therefore not evident. Over extensive passage, cytochrome P450 (EROD) activity was maintained, although urea production was reduced on a per mg protein basis at later passages. Two other attributes of fetal hepatocytes, gamma-glutamyl transpeptidase activity and serum-protein secretion, were also shown to be maintained by the PICM-19FF cells. The PICM-19FF cells therefore appear to have indefinite growth potential as a feeder-independent cell line and this should enhance the experimental usefulness of the cell line, in general, and may also improve its application to toxicological/pharmacological assays and artificial liver devices.