Role of Spontaneous and Interleukin-2–Induced Natural Killer Cell Activity in the Cytotoxicity and Rejection of Fas+and Fas− Tumor Cells

Abstract

Abstract In the current study, we investigated whether the naive, poly I:C or interleukin-2 (IL-2)–induced natural killer (NK)/lymphokine-activated killer (LAK) cells use perforin and/or Fas ligand (FasL) to mediated cytotoxicity. We correlated these findings with the ability of mice to reject syngeneic Fas+ and Fas− tumor cells either spontaneously or after IL-2 treatment. The spontaneous NK-cell–mediated cytotoxicity was primarily perforin based, whereas the poly I:C and IL-2–induced NK/LAK activity was both FasL and perforin dependent. L1210 Fas+ tumor targets were more sensitive than L1210 Fas− targets to poly I:C and IL-2–induced cytotoxicity in wild-type, gld/gld, and perforin knockout mice. When L1210 Fas+ and Fas– tumor cells were injected subcutaneously (sc) or intraperitoneally into syngeneic mice, Fas− tumor cells caused mortality earlier than Fas+ tumor cells. Also, approximately 20% of the mice injected sc with L1210 Fas+ tumor cells survived the challenge(>60 days), whereas all mice injected similarly with L1210 Fas− tumor cells died. When immunotherapy using IL-2 (10,000 U, three times/d for a week, followed by once/d for an additional week) was attempted in mice injected sc with tumor cells, IL-2 treatment was very effective against mice bearing L1210 Fas+ (40% survival) but not L1210 Fas− (0% survival) tumors. These data correlated with the finding that the LAK cells from IL-2–injected mice caused increased cytotoxicity against L1210 Fas+ when compared with L1210 Fas− targets. Also, L1210 Fas+tumor-bearing mice showed increased tumor-specific cytotoxic T lymphocyte (CTL) activity when compared with those bearing L1210 Fas− tumor cells. Together our studies show for the first time that expression of Fas on tumor targets makes them more immunogenic as well as susceptible to CTL- and IL-2–induced LAK activity. The Fas+ tumor cells are also more responsive to immunotherapy with IL-2.