Immunohistology of the liver of a high-RI HLCM. A representative liver section of a high-RI HLCM (RI: 91.2%) was subjected to immunohistochemical staining using STEM 121 antibody for the detection of engrafted human hepatocytes. The area stained in brown and unstained foci show xenografted human hepatocytes (H) and residual murine hepatocytes (M), respectively. The RI was determined by the proportion of area occupied by xenograft to the total area of the liver section. CV, central vein; HLCM, humanized liver chimeric mouse; RI, replacement index; PV, portal vein.