Figure 5. Intratumoral endothelial cells are not of human origin. Top row shows immunodetection of endothelial cells in tumors formed from DAPT-treated 029, 036, and 048 cells using a human-specific CD31 antibody. Arrows show negative endothelial cells. Bottom row shows immunodetection of the human-specific CD31 marker in a positive tissue control (human muscle) and a negative tissue control (mouse brain). 048 DAPT h&m is a section from the same tumor block as in the top row, but stained with a CD31 antibody detecting both human and mouse CD31.