RAPAMYCIN INHIBITS NK CELL FUNCTION

Abstract

A307 Aims: Host-derived NK cells infiltrate solid organ allografts early after transplantation. In the DA to Lewis, high-responder, orthotopic model of liver transplantation 56.4±6.2% of the mononuclear cells in the allograft 24 hours after transplant are NK cells. Previous studies have shown that graft-infiltrating NK cells are a significant source of the proinflammatory cytokine IFNγ. NK cells are likely affecting the cytokine milieu in the graft and are capable of cytotoxicity against stressed or foreign cells. We have found that cyclosporine (CsA) treatment does not prevent the infiltration of NK cells into liver allografts. It is still unclear if there are direct effects of immunosuppression on NK cells. The purpose of this study was to determine the effects of immunosuppressive drugs on primary rat NK cell proliferation and function. Methods: NK cells were purified from normal Lewis rat spleens and primary NK cell lines were established and analyzed for proliferation, cytotoxicity, and IFNγ secretion. For the proliferation assays, thymidine incorporation was measured in the presence of increasing doses of CsA (0-100 ng/ml), FK506 (FK, 0.1-100 ng/ml) or Rapamycin, (RAPA, 0-10 ng/ml). Proliferation was analyzed 1-7 days after initial culture. To determine if immunosuppressive drugs alters the ability of NK cells to kill, thymidine-based cytotoxicity assays or JAM assays were performed against tumor targets in the absence or presence of immunosuppressive drugs (CSA, 100 ng/ml, FK,100 ng/ml and RAPA,10 ng/ml). In addition, IFNγ secretion of NK cells was analyzed by ELISA after treatment with immunosuppressive drugs (CsA, 100 ng/ml, FK,100 ng/ml and RAPA,10 ng/ml). Results: NK cells demonstrated robust proliferation both in the absence and presence of CsA. In contrast, FK significantly (p< 0.05) inhibited proliferation at high doses. RAPA significantly (p< 0.05) inhibited the proliferation of NK cells in a dose-dependent manner. CsA and FK did not effect NK cell–mediated killing while cytotoxicity was significantly (p< 0.05) inhibited in the presence of RAPA. Primary NK cells secrete robust levels of IFNγ and Neither CsA, FK nor RAPA inhibited IFNγ production by NK cells. Conclusions: NK cells proliferate and function in the presence of CsA and low doses of FK. These data indicate that activated NK cells may contribute to the rejection response in CsA and FK treated allograft recipients. In contrast to CsA and FK, RAPA can significantly diminish NK cell proliferation and killing. RAPA may inhibit NK cells from actively contributing to the elimination of virally infected or transformed cells in transplant patients. Understanding the differential effects of these immunosuppressive drugs on NK cell effector function is important in clinical transplantation.