TSAs may be unique to a single tumor or shared among several tumors. 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.