Direct killing of interleukin-2-transfected tumor cells by human neutrophils

We have previously established that human polymorphonuclear cells (PMN) express IL-2R beta- and gamma-chains and that addition of IL-2 maintains the viability of PMN by preventing these cells from undergoing programmed cell death. The purpose of this study was to examine whether IL-2-releasing tumor cells are capable of stimulating PMN tumoricidal activity. We therefore investigated the ability of PMN to kill IL-2-transfected tumor cells using normal human PMN directed against the murine mammary adenocarcinoma TS/A engineered to release high amounts of murine IL-2 (3,600 U, B6) compared with TS/A parental cells and TS/A tumor cells transfected with the neomycin-resistance (NEO) gene only. The potency of PMN as IL-2-induced killer cells was indicated by the low number of cells required for killing (effector cell:target cell ratio 10:1) and the degree of tumor cell lysis (68+/-10%). Evidence for the role of IL-2 as a mediator of tumor cytotoxicity by PMN was substantiated by inhibition of tumor killing with anti-IL-2 and anti-IL-2R beta monoclonal antibodies (MAbs). Furthermore, in vivo depletion of mature granulocytes using MAb RB6-8C5 resulted in B6 adenocarcinoma growth, thereby confirming a direct role for IL-2-activated PMN in tumor cytolysis. Lastly, we suggest that one possible mechanism involved in IL-2-induced PMN cytotoxicity against the B6 clone occurs via the nitric oxide pathway, which could be inhibited upon addition of the arginine analog, N(G)-monomethyl-L-arginine.