Possible role of natural killer cells and other effector cells in immune surveillance against cancer.

The concept of immune surveillance against cancer was initially formulated with thymus-dependent immunity as a central and requisite effector mechanism. However, a substantial amount of evidence has accumulated to indicate that T cell-mediated immunity is mainly important for protection against tumors induced by oncogenic viruses and not for many other types of spontaneous or chemical carcinogen-induced tumors. It now appears likely that various components of the natural immune system also play major roles in immune surveillance. These include natural killer (NK) cells and macrophages. These existing evidence for the roles of these effector cells is discussed.