Post-transplant Bregs promote the tumor recurrence via CXCL10/CXCR3 signaling

Abstract

Background & Aims: The circulating immune cells mobilized during liver transplantation may play important roles in acute phase graft injury and late phase tumor recurrence. However, the precise mechanism of circulating immune cell mobilization during liver transplantation has not been explored. In this study, we aim to investigate the impact of acute-phase small-for-size graft injury on mobilization of circulating regulating B cells (Bregs) in the patients with hepatocellular carcinoma (HCC) after liver transplantation and to explore the underlying molecular mechanism therein. Methods: We first investigated the association of circulating Bregs with clinical-pathological parameters in liver cancer patients underwent liver transplantation. Next, we explored the role and the mechanism of acute phase liver graft injury on mobilizing Bregs using a clinically relevant model of rat orthotopic liver transplantation. The role of CXCL10/CXCR3 signaling on Breg mobilization was further investigated in CXCL10-/- and CXCR3-/- mice model with hepatic ischemia/ reperfusion and major hepatectomy. Results: Clinically, the percentage of human circulating Bregs in living donor liver transplantation (LDLT) group was higher compared to that in deceased donor liver transplantation (DDLT) group. While comparing the recurrence group and none-recurrence group, HCC patients with high expression levels of circulating Bregs on 3 and 6 month after orthotopic liver transplantation (OLT) had high HCC recurrence. In an orthotopic rat OLT model, we found that small-for-size liver graft injury induced the increase of both circulating and hepatic Bregs. There were more circulating Bregs in the rats receiving small-for-size liver graft at day3 after OLT. Consistently, higher level of hepatic Bregs were also found in small-for-size liver graft at day5 after OLT. The accumulations of intragraft B cells were also detected after OLT. The numbers of B cells were higher at day3 and day5 in small-for-size liver graft. In the CXCL10-/- and CXCR3-/- mice model, the percentage of circulating Bregs in PBMCs or total blood B cells in CXCL10-/- mice were lower than that in WT mice. Similar phenomenon was also found in CXCR3-/- mice. Bregs promoted HCC proliferation, invasion and epithelial-mesenchymal transition in vitro. Conclusions: A significantly higher population of circulating Bregs, which were mobilized by small-for-size graft injury, may lead to a higher incidence of tumor recurrence and metastasis after LDLT. Post-transplant enhanced CXCL10/CXCR3 signaling may play important roles on Bregs mobilization, which further promoted tumor growth and metastasis.