FUTILE SEARCH. “The failure of grafted normal cells to replicate indefinitely in vivo means that, given the “perfect” conditions of nutrition and environment that an isologous animal represents, transplanted normal cells are still incapable of immortality. This leads to the further conclusion that a search for perfect in vitro conditions in which normal cells might reveal immortality is futile.”
http://protein.bio.msu.ru/biokhimiya/contents/v62/full/62111380.html