Given that patients evaluated a shorter time after LT had a higher incidence of chimerism than those patients evaluated a longer time after LT, the observed blood chimerism may
be derived from residual lymphocytes in the liver graft. We therefore assessed blood chimerism over time after LT. LT patients 723, 739, and 860 displayed STR loci of donor origin in the blood on day 2 after LT, but these loci disappeared 1 week or longer after LT (Table 3). One female LT recipient (case Tamoxifen mouse 823) was positive for the amelogenin Y locus (from a male donor) on 1 day after LT; the presence of this locus became undetectable 1 month after LT, although another locus persisted 3 months after LT (Fig. 1B; Table 3). For case 887, although STR could not be measured shortly after LT, 3 loci of donor origin were detectable 7 months after LT (Fig. 1C; Table 3). These were unlikely to be derived from residual leucocytes/lymphocytes
from the donor liver graft. The data suggest that there could be two types of blood cells present in liver grafts: residual mature leucocytes/lymphocytes responsible for short-term chimerism and putative HSPCs resulting in long-term chimerism of donor origin. These two types of chimerism might occur simultaneously, as demonstrated by the fact that partial chimerism patients showed selleck inhibitor multiple loci of donor origin shortly after LT, but were positive for only a single locus of donor origin at later time points after LT (Table 3). The blood chimerism phenomenon raises the question of whether HSPCs exist in the adult liver or that residual leukocytes/lymphocytes in liver grafts could be the source of the chimerism. Attempts have been made to isolate hematopoietic stem cells from mouse adult livers using disparate panels of different cell-surface markers.13, 14 There has not been any report regarding HSPCs in human adult livers. A Lin−CD34+CD38−CD90+ population purified
from human umbilical cord blood has been demonstrated to have the ability to give rise to long-term multipotent grafts in serial transplantations.18, 19 We therefore attempted to determine whether Lin−CD34+CD38−CD90+ HSCs were present in the human adult liver. Single-cell suspensions isolated from healthy donor livers were analyzed using either the total cell population (n = 9) or cells Thiamet G sorted for CD45+ (n = 7). Average sizes of the Lin−CD34+CD38−CD90+ populations were 0.03% ± 0.017% in total liver cells and 0.05% ± 0.012% in CD45+ liver cells (Fig. 2A). The Lin−CD34+CD38−CD90+ population was significantly higher in CD45+ liver cells than in total liver cells (Fig. 2A; P = 0.043), indicating that CD45+ selection enriched for potential HSPCs. Representative flow-cytometry results of the population are shown in Fig. 2B,C. These results suggest the presence of a Lin−CD34+CD38−CD90+ HSPC population in human adult livers.