Most unique tumor antigens arise due to point mutations in DNA induced by chemical carcinogens, ultraviolet light, or X-irradiation. Shared TSAs are usually encoded by oncogenic viruses. An aberrant disaccharide moiety associated with cancer is the Thomsen- Friedenreich antigen. The most important effector cells in anti-tumor immunity are macrophages, NK cells, and Tc cells. Effector cells kill tumors using the same mechanisms they use to kill microorganisms.
Tumors evade the immune system by a number of mechanisms.
Many tumors lack the co- stimulator B7 and thus do not present antigen efficiently to T cells. Tumors may shed surface antigen, which binds to blocking antibodies, which in turn saturate Fc receptors on effector cells. Lymphocyte proliferation is measured by assaying the uptake of 3 H-thymidine into the DNA of T cells cultured with inactivated tumors. The cytotoxic capability of lymphocytes is determined by measuring the amount of 51 Cr released from lysed tumor cells. Reinfusion of LAK cells along with IL-2 causes tumor regression in some humans.