B2M and neoplasm: In the B2m KO mice, two types of large tumor foci were present: (1) large foci negative for EGFP fluorescence, representing no TSPY protein expression (Fig. 6C & D, yellow arrow heads) and (2) large green fluorescent tumor foci (Fig. 6C, D, white arrows) positive for TSPY, but negative for B2M protein (Fig. 6G & H).