Histochemical staining of tumor grown in mice with severe combined immunodeficiency with the human-specific anti-CEACAM1 monoclonal antibody 4D1/C2.

Panel (A) shows negative staining with 4D1/C2 in tumors grown after subcutaneous injection of A549 lung cancer cells. Panels (B) and (C) show positive staining of endothelial cells lining blood vessels in tumors initiated with A549 lung cancer cells plus AC133-derived putative endothelial cells. (D) Negative control (tumor tissue of mice injected subcutaneously with A549 lung cancer cells and AC133-derived putative endothelial cells). Tumor cells are indicated by arrowheads. Endothelial cells are indicated by arrows. Original magnification ×100.