Hypothermic Oxygenated Machine Perfusion and Static Cold Storage Drive Distinct Immunomodulation During Liver Transplantation: A Pilot Study

Background. Organ injury is a major problem in liver transplant. Prolonged liver ischemia may result in ischemia/reperfusion injury (IRI), leading to inadequate activation of innate immunity. Hypothermic oxygenated machine perfusion (HOPE) of the graft emerges as a more physiologic method for liver preservation compared with static cold storage (SCS) by reducing IRI, which improves the quality of the graft. Despite being crucial, the immunological aspects of IRI in liver transplantation remained poorly explored. Methods. We designed a pilot study to assess intrahepatic immune responses to HOPE compared with SCS (6 patients in each group). We explored immunologic and inflammatory pathways using both bulk RNA-sequencing and single-cell multiparametric flow cytometry analyses from liver biopsies performed on the graft before and after transplantation. Results. Despite a limited number of patients and heterogeneous effects on IRI, we observed immune changes in liver biopsies before and after organ storage and distinct functional modulations of intrahepatic immune cells from the transplanted liver that underwent SCS versus HOPE. A significant increase of infiltrated monocytes, conventional type 2 dendritic cells (cDC2s), and neutrophils ( P < 0.05) and a trend toward reduced immune cell viability were observed after SCS but not after HOPE. Conclusions. This pilot study did not allow us to conclude on IRI but showed that HOPE perfusion dampens liver infiltration of some innate immune cells. It reveals that the inclusion of additional transplanted patients and analysis of later time points after transplantation are needed to draw a definitive conclusion. However, it can guide future studies evaluating the development of new strategies to prevent IRI.