Background: Natural killer (NK) cells are enriched in the liver and are the main regulators in liver transplantation regarding rejection or tolerance, viral infection, or tumor recurrence. Immunosuppression consists of a triple drug standard regimen comprising tacrolimus (TAC) and corticosteroids (CS) with either mycophenolate mofetil (MMF) or sirolimus (SIR)/everolimus (EVE). The aim of this study was to evaluate the impact of trough levels of these regimens under clinical conditions and exposure on human NK-cell activity and function in order to better understand the antiviral and anti-tumor effects of mammalian target of rapamycin inhibitor (mTORI).
Methods: Peripheral blood mononuclear cells (PBMCs) were collected from liver transplant recipients and healthy controls. Number and phenotypes of NK cells in vivo were analyzed by flow cytometry. In this study we simulated the immunosuppressive microenvironment in vitro. PBMCs were cultured at the clinically effective plasma concentration of drugs for 3 d to detect the effect of immunosuppressants on NK cells. Drug type and concentration: single drug [EVE, 5 ng/mL; SIR, 5 ng/mL; TAC, 5 ng/mL; cyclosporine A (CSA), 125 ng/mL; MMF, 15 µg/mL; CS, 0.5 µg/mL] and combined immunosuppressants (Group 1: TAC, 5 ng/mL + MMF, 15 µg/mL + CS, 0.5 µg/mL; Group 2: TAC, 5 ng/mL + SIR, 5 ng/mL + CS, 0.5 µg/mL; Group 3: TAC, 5 ng/mL + EVE, 5 ng/mL + CS, 0.5 µg/mL). In addition, NK cells were sorted from PBMCs and treated under the above conditions to detect NK cell killing function and RNA transcription characteristics.
Results: CS significantly impaired the cytolytic activity of NK cells, followed by MMF and SIR/EVE. CS and TAC/CSA significantly decreased the secretion of IFN-γ and CD107a. NK cell function in liver transplant recipients was most pronouncedly inhibited by a triple immunosuppressive regimen, with CS playing the most prominent role compared with the other drugs. The MMF-containing regimen demonstrated a significant increase in the expression of suppressive genes, especially of the Siglec7/9 family. The SIR group had stronger NK cell activity compared with that of the MMF group, although liver transplantation patients have lower NK cell activity and function.
Conclusions: Despite an overall comparable immunosuppressive efficiency in terms of prevention of acute rejection, a mTORIs-including regimen might be considered as having less impact on NK cell function.
Keywords: Liver transplantation; NK cells; calcineurin inhibitor (CNI); everolimus; immunosuppressants.
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