Immune surveillance of senescent cells--biological significance in cancer- and non-cancer pathologies.

Cellular senescence, a state of stable growth arrest, can occur in response to various stress stimuli such as telomere shortening, treatment with chemotherapeutic drugs or the aberrant activation of oncogenes. Senescent cells communicate with their environment by secreting various cytokines and growth factors, and it has become clear that this 'secretory phenotype' can have pro- as well as anti-tumorigenic effects. Recent work from our laboratory showed that premalignant, senescent hepatocytes are recognized and cleared through an antigen-specific immune response and that this immune response, designated as 'senescence surveillance' is crucial for tumor suppression in the liver [(Kang,T.W. et al. (2011) Senescence surveillance of pre-malignant hepatocytes limits liver cancer development. Nature, 479, 547-551]. It is an emerging concept that immune responses against senescent cells have a broader biological significance in cancer- as well as non-cancer pathologies and current data suggest that distinct immune responses are engaged to clear senescent cells in different disease settings. In this review article, we will discuss different examples how immune responses against senescent cells are involved to restrict disease progression in cancer- and non-cancer pathologies.