328IMMUNE SURVEILLANCE FOR UTERINE MESENCHYMAL TUMOR IN THE FEMALE GENITAL SYSTEMUterine leiomyosarcomas (Ut-LMSs) are rare smooth muscle tumors accounting for approximately 1% of patients with uterine malignant tumor with an estimated annual incidence of 0.64 per 100,000 women. Ut-LMS are considered neoplasms of high metastatic potential with 5-year overall survival rates varying between 0 and 73%. The development of gynecologic tumors is often correlated with female hormone secretion; however, the development of Ut-LMS is not substantially correlated with hormonal conditions, and the risk factors of Ut-LMS are not clearly understood. The presentation of antigenic peptides by major histocompatibility complex (MHC) class I molecules is important for tumor rejection by cytotoxic T-lymphocytes (CTLs). Such antigenic peptides are generated as a result of the degradation of intracellular proteins by the ubiquitin proteasome pathway, a process that is influenced by the interferon (IFN)--inducible proteasome beta-subunit (PSMB)9/1i, which is -subunit of the 20S proteasome. Homozygous deficient mice for PSMB9/1i are now known to spontaneously develop Ut-LMS. Expression of PSMB9/1i is reportedly absent in human UtLMS, but present in human myometrium. Further studies revealed a few infiltrating CD56bright natural killer (NK) cells, which are known as "uterine NK cells" (uNK cells), in human Ut-LMS tissues. This short communication aims at summarizing recent insights into the regulation of NK cell function and the T lymphocyte-mediated immune system as tumor immune surveillance in the female genital systemyoyoyo224@hotmail.comReview5102015LMP2,Uterine leiomyosarcoma,T lymphocyte-mediated immunity,Natural killer cellsTakuma Hayashi,Akiko Horiuchi,Kenji Sano,Nobuyoshi Hiraoka,Tomoyuki Ichimura,Nobuo Yaegashi,Hiroyuki Aburatani,Susumu Tonegawa, Ikuo Konishi Dept. of Immunology and Infectious Disease, Shinshu University Graduate School of Medicine, Nagano, Japan,,Horiuch Ladies Clinic, Nagano, Japan, 3Dept. of Laboratory Medicine, Shinshu University Hospital, Nagano, Japan,,,Pathology Division, National Cancer Center Research Institute, Tokyo, Japan,Dept. of Obstetrics and Gynecology, Osaka City University Graduate School of Medicine, Osaka, Japan,Dept. of Obstetrics and Gynecology, Tohoku University Graduate School of Medicine, Miyagi, Japan,The Cancer System Laboratory, Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, Japan,Picower Institute and Dept. of Biology, Massachusetts Institute of Technology, MA, USA,Dept. of Obstetrics and Gynecology, Kyoto University Graduate School of Medicine, Kyoto, Japan, Promoting Business using Advanced Technology, Japan Science and Technology Agency (JST), Tokyo, Japan,