ERBB2 and breast neoplasm: In vivo antitumor activity of HER2-XPAT protein was assessed in the HER2-high BT-474 human breast tumor model (∼975,000 HER2 receptors per cell) and HER2-low HT-55 colorectal cancer model (∼25,000 HER2 receptors per cell) inoculated subcutaneously (s.c.)into immunodeficient mice and engrafted with huPBMCs as a source of T cells.