Immune-cell recognition and killing of unwanted target cells, such as emergent tumor cells, is a critical component of the human host defense mechanism. Antibody-dependent cell-mediated cytotoxicity (ADCC) and T-cell killing are two mechanisms of cell-mediated immune response. Each of these processes involves the stimulation of immune cell sub-populations, such as natural killer (NK) cells or cytotoxic T-lymphocytes (CTL), which then actively lyse target cells. Understanding the interplay between immune and cancer cells and restoring and promoting the immune system’s capacity to fight and eliminate tumors ("cancer immunotherapy" or "immuno-oncology") is an exciting and promising research field.