Abstract
Background: Small-for-size liver graft in living donor liver transplantation (LDLT) may provide favorable immune microenvironment for tumor growth compared to deceased donor liver transplantation (DDLT). The role of NK cells on hepatic ischemia-reperfusion (IR) injury is controversial. CD56brightCD16dimNK cells are retained within hepatic sinusoids via the engagement of CCR5 pathway. We aim to investigate the role of CCR5(+) NK cells in tumor recurrence after liver transplantation.
Methods: To investigate the clinical relevance of circulating NK cells, 80 HCC patients who underwent liver transplantation were recruited. To explore the association between NK cells and HCC development, a rat orthotopic liver transplantation model with tumor development was established. Wild-type and TLR4(-/-) mice were subject to hepatic IR injury and major hepatectomy. The underlying mechanism was explored using the immunity-humanized NSG mice with orthotopic liver cancer.
Results: Less peripheral blood CD56brightCD16dimCD3(-) NK cells (Fig.A) and higher intragraft TLR4/PD-L1/CCR5 mRNA levels (Fig.B) were observed in LDLT recipients and significantly associated with higher tumor recurrence compared to DDLT after liver transplantation. These findings were further validated in a rat transplantation model. Besides, the expression of PD-L1 in tumor was higher in small-forsize graft compared to whole graft (Fig.C). In a mouse hepatic IR model, the liver-resident CCR5(+) NK cells and PD-L1 expression were decreased in TLR4-/-mice compared to wild type mice. Blocking PDL1 in TLR4-/-mice decreased CCR5(+) NK cells recruited into the liver. In a humanized NSG mouse model, TLR4 was highly expressed in the tumor area compared to non-tumor area (Fig.D). The tumor induced expression of PD-1 on CCR5(+) NK cells functionally exhausted intratumor NK cells characterized by upregulated NK-cell-inhibitory receptors.
Conclusions: PD-L1/TLR4 signaling upregulated during liver graft injury directly induced the exhaustion of CCR5(+) NK cells, which further promoted HCC recurrence after transplantation.