Different components of the immune system target leukemia cells for elimination. In the GVL effect, T cells and NK cells play a major role in eliminating leukemia cells. The target structures for immune attack by T cells may be leukemia-specific antigens or minor histocompatibility antigens, which are expressed on all cells or limited to expression on hematopoietic cells. NK cells attack allogeneic target cells which do not express class I ligands that interact with their KIR (alloreactive groups). Dendritic cells, macrophages, and cytokines play roles in modulating the GVL effect.