IHC staining of humanized ENG of the blood vessels in the 4T1 tumor from GEMs. Seven (i.e., SN6h, SN6j, SN6, SN6c, SN6d, SN6f and SN6i) of the eight anti-hENG mAbs show strong staining with tumor vasculature from both homozygous and hemizygous GEMs, but show minimal or no significant staining of tumors from wild-type control mice. A portion (indicated by a red square) of each panel of the top row was enlarged to show the larger images of the stained tumor vessels in the second row (Fig. 2a). Rat anti-mENG mAb MJ7/18 shows strong staining with tumor vasculature from a wild-type mouse and hemizygous mouse but does not stain homozygous mouse tumor (Fig. 2a). The result indicates that the MJ7/18 epitope is lost in the humanized ENG. An isotype-matched control IgG (MOPC195v; IgG1-κ; Fig. 2a) does not show any staining with the tumors from the three types of mice.