Lysozyme M-Cre mice, CD8 knockout mice and perforin knockout mice were purchased from Jackson laboratory (Bar Harbor, ME, USA), and STAT3flx/flx mice have been described (15 (link)). These mice were backcrossed to the FVB/N background more than 10 times. All animals were housed under specific pathogen-free conditions at the Hillman Cancer Center of the University of Pittsburgh Cancer Institute. Animal experiments were approved by the Institutional Animal Care and Use Committee (IACUC) of the University of Pittsburgh.