FCGR2B and neoplasm: Importantly, although IFN-γ production was undetectable in WT tumor-infiltrating CD8+ T cells (Figure 4, L and M), Fcgr2b–/– T cells contained a high frequency (approximately 7%) of IFN-γ–producing effector CD8+ T cells on day 10 after tumor inoculation (Figure 4, L and M).