Steatotic Livers Are More Susceptible to Ischemia Reperfusion Damage after Transplantation and Show Increased γδ T Cell Infiltration.

Liver transplantation (LTx) is often the only possible therapy for many end-stage liver diseases, but successful long-term transplant outcomes are limited by multiple factors, including ischemia reperfusion injury (IRI). This situation is aggravated by a shortage of transplantable organs, thus encouraging the use of inferior quality organs. Here, we have investigated early hepatic IRI in a retrospective, exploratory, monocentric case-control study considering organ marginality. We analyzed standard LTx biopsies from 46 patients taken at the end of cold organ preparation and two hours after reperfusion, and we showed that early IRI was present after two hours in 63% of cases. Looking at our data in general, in accordance with Eurotransplant criteria, a marginal transplant was allocated at our institution in about 54% of cases. We found that patients with a marginal-organ LTx showing evidence of IRI had a significantly worse one-year survival rate (51% vs. 75%). As we saw in our study cohort, the marginality of these livers was almost entirely due to steatosis. In contrast, survival rates in patients receiving a non-marginal transplant were not influenced by the presence or absence of IRI. Poorer outcomes in marginal organs prompted us to examine pre- and post-reperfusion biopsies, and it was revealed that transplants with IRI demonstrated significantly greater T cell infiltration. Molecular analyses showed that higher mRNA expression levels of CXCL-1, CD3 and TCRγ locus genes were found in IRI livers. We therefore conclude that the marginality of an organ, namely steatosis, exacerbates early IRI by enhancing effector immune cell infiltration. Preemptive strategies targeting immune pathways could increase the safety of using marginal organs for LTx.

Unconventional RORγt+ T cells drive hepatic ischemia reperfusion injury.

An emerging body of evidence suggests a pivotal role of CD3(+) T cells in mediating early ischemia reperfusion injury (IRI). However, the precise phenotype of T cells involved and the mechanisms underlying such T cell-mediated immune responses in IRI, as well as their clinical relevance, are poorly understood. In this study, we investigated early immunological events in a model of partial warm hepatic IRI in genetically targeted mice to study the precise pathomechanistic role of RORγt(+) T cells. We found that unconventional CD27(-)γδTCR(+) and CD4(-)CD8(-) double-negative T cells are the major RORγt-expressing effector cells in hepatic IRI that play a mechanistic role by being the main source of IRI-mediating IL-17A. We further show that unconventional IRI-mediating T cells are contingent on RORγt, as highlighted by the fact that a genetic deficiency for RORγt, or its therapeutic antagonization via digoxin, is protective against hepatic IRI. Therefore, identification of CD27(-)γδTCR(+) and CD4(-)CD8(-) double-negative T cells as the major source of IL-17A via RORγt in hepatic IRI opens new therapeutic options to improve liver transplantation outcomes.