Artist interpretation: Cytotoxic T cells (blue) attack a cancer cell (orange). The immune system hosts an army of white blood cells dedicated to helping the body fight infections. One faction of this army includes T cells, a type of white blood cell that develops from stem cells in bone marrow. There are three main types of T cells that each play a different role in the highly-coordinated defense of the body against illness: Regulatory T cells modulate the immune response and prevent other immune cells from becoming overactive. Helper T cells help activate other immune cells once they detect evidence of a foreign invader, such as a virus or cancer.  Killer, or cytotoxic, T cells directly attack and destroy cells they recognize as being foreign. Over the past few decades, advancements in immunotherapy have come a long way, and it is now an important part of treating some [...]