Background Information: Our immune system protects us from disease by killing bacteria and viruses. It also helps fight cancer. A T-cell is one type of immune cell that does this. T-cells have proteins on them that turn on the immune system when it needs to fight infection and other proteins that turn off the immune system when it is no longer needed. These proteins are called checkpoints. Cancer cells can trick the immune system by turning off the T-cells, stopping them from recognizing the cancer cells. Drugs called “checkpoint inhibitors” turn back on the T-cells so they can recognize...