Killer cells of the immune system eliminate cancer cells. Cytotoxic T lymphocytes (CTL) and natural killer (NK) cells are the two main killer cell types in the human body. A11 has developed quantitative single cell killing assays for human CTL and NK cells which allow kinetic analyses and distinguish cancer cell apoptosis, necrosis and combined forms. These assays will be used to analyze the killing efficiencies of individual CTL and NK cells, quantify the mode of cancer cell death, and analyze CTL and NK cells simultaneously to understand potential cooperativities.