Abstract 3961: IL-15 improves the effect of adoptive T cell therapy through cellular senescence delay.
Authors: Weng Jinsheng , Kim Sung-Doo , Li Haiyan , He Jin , Qian Jianfei , Torikai Hiroki , Zhang Liang , Yang Jing , yi qing , Kwak Larry W. 
Published: August 2014

Abstract
Adoptive T-cell therapy is one of the most effective forms of immunotherapy in the clinical setting. However, the mechanism that regulates the in vivo effect of T-cell therapy still remains unclear. Using T cells generated from normal donors against previously identified T-cell epitopes in U266 idiotype light chain model, we expanded the antigen-specific T cells with IL-2 or IL-15 cytokines, we found that antigen specific T cells expanded with IL-2 have temperate inhibitory effect in vivo, whereas IL-15-expanded antigen-specific T cells provide a much stronger in vivo effect. Approximately 30% experimental mice remained tumor free after adoptive transfer with IL-15 expanded- antigen-specific T cells. Detailed analysis revealed that IL-15-expanded T cells have down-regulated expression of cellular senescence signature genes, decreased SA-ß-Gal activity, and decreased P53, P21WAF1 and P16INK4a expression. The expression level of CD27 and CD28 is significantly greater in IL-15-expanded T cells, indicating that IL-15-expanded T cells have delayed cellular senescence. This result is also confirmed by the memory CD8+ T cells purified from general normal donors. Memory CD8+ T cells cultured with IL-15 have significantly greater levels of CD27 and CD28 expression, lower SA-ß-Gal activity and lower P53, P21WAF1 and P16INK4a protein level after 5 days culture in vitro. To identify the molecular mechanism of the effect of IL-15 on the cellular senescence, we cultured the memory CD8+ T cells with IL-15 in the presence of different signaling pathway inhibitors and we found that IL-15 regulated cellular senescence through JAK3-STAT3 and JAK3-STAT5 signaling pathways. DNA damage molecules ATM, MDC1, and TP53bp1 are also down-regulated by IL-15, and there are three STATs potential binding sites in the promoter of TP53bp1. Using a CHIP assay, we found that IL-15 directly regulates p-STAT3 and p-STAT5 binding to the -123 site of TP53bp1 promoter. This site is also bound by tri-methy-H3(Lys27) and P300 after IL-15 stimulation, indicating that IL-15 induces both epigenetic and transcriptional mechanism to repress TP53bp1 expression. Cellular senescence was initially reported in human fibroblast cells of irreversible growth arrest, active metabolism, and specific gene signatures, and recent studies showed that senescence can be reversed and delayed by certain treatments. Our study provides the first evidence of IL-15 in memory CD8+ T cell senescence delay, which has provided a detailed molecular mechanism. Our study provides important information for the future improvement of adoptive T cell therapy in the clinic.
Citation Format: Jinsheng Weng, Sung-Doo Kim, Haiyan Li, Jin He, Jianfei Qian, Hiroki Torikai, Liang Zhang, Jing Yang, qing yi, Larry W. Kwak. IL-15 improves the effect of adoptive T cell therapy through cellular senescence delay. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3961. doi:10.1158/1538-7445.AM2013-3961