Having observed that (i) 291OVA cells were not or only poorly rejected in IFN-γ−/−, IFN-γR−/−, and STAT1−/− recipient mice (Figure 4), and (ii) that IFN-γ expression in the host was required to upregulate MHC expression in tumor cells (Figure 5A), we asked whether antigen expression was maintained or lost in IFN-γ−/−, IFN-γR−/−, and STAT1−/− recipient mice after inoculation of 291OVA cells. This evidence concerns the gene STAT1 and neoplasm.