The repopulation potential of hepatocyte populations differing in size andprior mitotic expansion

Recently the stem cell-like regenerative potential of adult liver cells was demonstrated by serial transplantation. This repopulation capacity could b e useful for the treatment of genetic liver diseases by cell transplantatio n and/or expansion of genetically manipulated cells. However, previous expe riments used unfractionated populations of liver cells, and therefore it re mained undetermined whether all hepatocytes or only a subpopulation (stem c ells) possessed this high regenerative ability. To address this question we used centrifugal elutriation to separate hepatocytes by cell density. Unex pectedly, small hepatocytes (16 mu m) had lower repopulation capacity durin g the first round of transplantation when compared with both the medium-siz ed (21 mu m) and large (27 mu m) cells. We also compared the repopulation c apacity of hepatocytes that had undergone different degrees of in vivo expa nsion. Previous cell division neither reduced nor increased the repopulatio n capacity of transplanted liver cells. Finally, retroviral tagging experim ents demonstrated that liver-repopulating cells occur at a frequency of >1: 10,000. We conclude that short-term therapeutic liver repopulation does not require progenitor or stem cells.