Immune checkpoint inhibition, conceptual illustration. T cells (blue), part of the body's immune system, are able to identify and kill cancer cells (red, spiked). The activity of T cells is regulated by proteins known as immune checkpoints (rectangles), which prevent them from attacking healthy cells (pink, round). Some cancer cells are able to take advantage of the immune checkpoints to prevent T cells from attacking them. These cancers can be treated with immune checkpoint inhibitors, a type of immunotherapy drug that blocks the checkpoint proteins, allowing the T cells to attack the cancer cells.