All animal studies were performed using protocols approved by the Rhode Island Hospital Institutional Animal Care and Use Committee (cmtt# 0268-98). Athymic nude mice were purchased from Harlan (Indianapolis, IN). Twenty-four hours prior to transplantation of tumor cells, animals were injected intraperitoneally with anti-LY2.2 antibodies containing anti-asialo GM1 to suppress T-cell and NK cytotoxic activity, respectively [39, 40] . Cultured cells were harvested as described previously [13] . Subcutaneous injections with 5610 6 cells per site were performed under aseptic conditions into both of the upper flanks. For intraperitoneal injections, mice were injected with 2610 6 cells suspended in HBSS. Tumors were excised at three weeks postinjection, weighed, frozen in a hexane/acetone bath and stored at 280uC. Tumors were analyzed by indirect immunofluorescence as described above.