Answer:
B. Genetically engineered mammalian cells
Explanation:
Herceptin is a monoclonal antibody that binds (attach) to specific antigens in cancer cells to destroy them. This antibody is used in the treatment of different types of cancers including breast and gastric carcinoma, in which HER2/neu protein is overexpressed. Herceptin targets HER2/neu receptors present in cancer cells to kill them. HER2/neu is a protein signaling receptor involved in cell proliferation, thereby this antibody works to selectively target cells that have an excess of HER2/neu receptors such as gastric and breast cancer cells.