Background: Liver transplantation (LT) is the best available option for patients with end stage liver disease and HCC. However, recipients are at high risk of cancer recurrence and infection, due to immunosuppressive (IS) therapy. IS used in LT commonly consist of calcineurin inhibitor (CNI) or a mechanistic target of rapamycin (mTOR), anti-metabolite and corticosteroids. Liver is an important immunological organ with a unique microenvironment. Innate and adaptive immune responses shapes the balance between immune tolerance and activation. It is well-known that IS drugs targeting the adaptive component of immunity, while innate immune cells become the only self-defense mechanism against neoplastic cells and infectious agents. However, the effect of IS drugs on liver resident immune cells are not well known. In this study, we analyzed the effect of two main IS drugs, calcineurin inhibitors and mTOR inhibitors on adaptive and innate immune components of the liver in mice Method: C57/BL6 mice were treated by intraperitoneal injection of mTORi (rapamycin and everolimus) and CNI (cyclosporine) for 7 days. Twenty-four hours after the last injection, liver mononuclear cells (LMNCs), splenocytes were collected. The proportion of T cells, NKT cells and NK cells and various functional molecules were analyzed by flow cytometry. Result: The proportion of TCR+NK1.1- T cells, TCR+NK1.1+ NKT cells in LMNC did not differ in both CNI mTORi treated groups. TCR-NK1.1+NK fraction in LMNCs was significantly increased in mTORi group (9.5 in mTORi groups versus 7.8 in control group), CNI treatment had no effect on NK cells frequency. mTORi treatment significantly upregulated the TRAIL positive NK cells (38.5%±4.0 in mTORi group vs 21.0%±8.3 in untreated, p =0.003). CNI treatment oppositely significantly decreased the TRAIL positive NK cell population (16.4%±4.2 in CNI group vs 21.0%±8.3 in untreated, p <0.05). CD 69 and Nkp46 expression on liver NK cells were not changed significantly in both mTORi and CNI treated groups in comparison to control group. Moreover, liver NK cells from mTORi treated mice showed significantly higher cytotoxicity against TRAIL-sensitive Hepa1-6 cells (30.1% ± 13.0 vs 13.5 %± 6.0, p=0.009). Cytotoxicity against TRAIL resistant YAC-1 mouse lymphoma was not significantly enhanced after mTORi treatment (53.6 % ± 4.4 vs 39.9% ± 1.2). Conclusion: mTOR inhibitors has ability to enhance liver resident NK cell activity. This result suggests that mTOR inhibitors might be useful to maintain anti-microbe and anti-tumor immunity even under immunosuppressive condition after transplantation.
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