Circulating endothelial progenitor cells mobilized by acute phase small-for-size graft injury promote tumor recurrence after liver transplantation

Abstract

OBJECTIVE: We aim to investigate the impact of acute-phase small-for-size graft injury on mobilization of circulating endothelial progenitor cells (EPCs) in the patients with hepatocellular carcinoma (HCC) after liver transplantation and to explore the molecular mechanism in a series of in vivo and in vitro functional studies. METHODS: In clinical study, 115 HCC recipients were included. The intragraft gene signature of the grafts greater (Group 1) and less than 60% (Group 2) of standard liver weight (SLW) were characterized by microarry analysis. Circulating EPCs (CD34+CD133+CD45-) were compared by FACS analysis. Clinical-pathological data including the incidence of tumor recurrence and metastasis were compared. In animal study, a rat orthotopic liver transplantation model using the recipient with liver cirrhosis was established with the application of whole or small-for-size (50%) graft. Circulating EPCs and intragraft mRNA levels of CXCL10/CXCR3 were compared. EPCs migration and differentiation in liver graft was further confirmed using a rat model with green fluorescence protein labeling. The direct role of CXCL10 on EPCs mobilization was further studied in a CXCL10-/- mouse model and in vitro assays. RESULTS: The patients were grouped into Group 1 (>= 60% SLW, n=37) and Group 2 (<60% SLW, n=78). The numbers of patients beyond Milan criteria [15/37(40.5%) vs 29/49(59.2%), p=0.838] or UCSF criteria [9/37(24.3%) vs 19/60(31.7%), p=1] were similar. Much more patients in Group 2 developed tumor recurrence and lung metastasis [19/78(24.4%) vs 3/37(8%), p=0.04]. Level of circulating EPCs was significantly higher in Group 2 (Day 3: 0.09% vs 0.002%, p=0.019; Week 4: 0.12% vs 0.033%, p=0.037; Week 8: 0.0585% vs 0.025%, p=0.018; Week 12: 0.055% vs 0.028%, p=0.025). Intragraft gene expression of CXCL10 was significantly high in Group 2. Over-expression of CXCL10 and more circulating EPCs was confirmed in the rat liver transplantation model using small-for-size graft. The direct role of CXCL10 on mobilization of circulating EPCs was further confirmed in CXCL10-/- mouse. CONCLUSION: A significantly higher population of postoperative circulating EPCs, which are mobilized by small-for-size graft injury through CXCL10/CXCR3 signaling, may lead to a higher incidence of tumor recurrence and metastasis after liver transplantation using small-for-size graft.