NK cells kill many types of tumor cells,especially cells that have reduced class I MHC expression and express ligands for NK cell- activating receptors. higu to Macrophages are capable of both inhibiting and promoting the growth and spread of cancers,depending on their activation state. zyme NK cells kill many types of tumor cells, especially cells that have reduced class I MHC expression and express ligands for NK cell– activating receptors. Macrophages are capable of both inhibiting and promoting the growth and spread of cancers, depending on their activation state