Influence of immunosuppressive drugs on natural killer cells in therapeutic drug exposure in liver transplantation

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: . 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.