Escape from immune- and nonimmune-mediated tumor surveillance.

Surveillance against neoplastic transformation is dependent on intrinsic "nonimmune" control mechanisms that sense DNA damage and illegitimate cell growth. In addition, evidence from gene-targeted mice with a variety of immune defects demonstrates that the immune system is involved in tumor elimination. Induction of apoptosis is a common feature of most nonimmune surveillance mechanisms but also the downstream consequence of cytotoxic lymphocyte activity. Thus, mechanisms of tumor cell escape from nonimmune- and immune-surveillance share several features characterized by increased thresholds of apoptosis induction. In this review, tumor cell resistance to the effector mechanisms of cytotoxic lymphocytes are discussed in the context of the complementary actions of nonimmune- and immune-surveillance.