The innate immune system is one of two limbs of the human immune system. It is comprised mainly of natural killer cells (NK cells), macrophages and eosinophils. The other limb, the adaptive immune system, is comprised of T and B cells. Dendritic cells and T cells, which reside between the two limbs, facilitate cross-talk between the innate and adaptive immune system. Both the innate and adaptive immune system are important in controlling cancer; however, the interplay between the two is very complicated and not completely understood.