Research Findings: Of over 200 LT patients
investigated, the overall incidence of blood
chimerism was around 6%. The incidence was
significantly higher among patients tested shortly
after LT (1 day to < 6 months) than in long-term
LT patients (6 months to 8 years), although blood
chimerism was indeed observed in long-term LT
survival patients (4-5
years after LT). In human adult liver graft, we
detected a small amount of hematopoietic Lin–CD34+CD38–CD90+
population representing putative HSPCs. Both Lin–CD34+
and Lin–CD45+ liver cells were capable of forming
myeloid-lineage and erythroid-lineage
methylcellulose colonies; more importantly, Lin–CD45+
or CD45+ liver cells could be engrafted into
hematopoietic cells in immunodeficient mice. Thus,
we provide the first evidence of a putative HSPC
population in the adult human liver, with the liver
acting as a good ectopic niche.
Implications: For the first time, our study
demonstrates the presence of the putative HSPC
population in adult human liver. Therefore, for LT
patients, transient chimerism results from mature
leucocytes and long-term chimerism derives from
putative HSPCs in the liver graft. The discovery of
existence of HSPCs in adult liver will have new
implications for the understanding of extra-marrow
hematopoiesis, liver regeneration, mechanisms of
tolerance in organ transplantation and de novo
cancer recurrence in LT patients.
Dr Xiao-Qi WANG
Department of Surgery
The University of Hong Kong
xqwang@hku.hk