Through a combination of flow cytometry, 3H‐Thymidine (3H‐TdR) incorporation, cytotoxicity assays, and in vivo mouse experiments, we comprehensively evaluated the effects of CD2 on CTL activation, proliferation, and its capacity to recognize, induce apoptosis in, and suppress the metastatic potential of breast cancer cells. The gene discussed is CD2; the disease is breast cancer.