It is a miracle of billion-years evolution that vertebrates, including us – the humans, are constantly thwarting attacks from an ever-expanding universe of foreign invaders such as bacteria, viruses and other pathogenic organisms throughout our lifetime. The miracle that makes this happen is our adaptive immune system, comprising of B and T cells, and a host of other regulatory cell-types that function as a central command to activate, mobilize and eventually suppress the army of rogue killers, once the threat is eliminated.