Your T-Cells are responsible for recognizing, identifying (and some) killing pathogens in your body. A lot of research is currently being done on T-cell immunotherapy, that is taking your own cancerous cells and training your T-cells to attack only those cancerous cells. They are using this type of therapy for tumor cells specifically and it has shown to be semi-effective in many patients, but there are a lot of variables within the body that make it difficult to target only one specific type of cell. In some patients this method has completely reduced their tumor mass, or at least decreased it significantly. I personally find this information very exciting because what it means for the future of cancer patients. In the US alone in 2014 almost 2 million people have been diagnosed with cancer.