Leukemia cell-targeted STAT3 silencing and TLR9 triggering generate systemic antitumor immunity

Signal transducer and activator of transcription 3 (STAT3) is an oncogene and immune checkpoint commonly activated in cancer cells and in tumor-associated immune cells. We previously developed an immunostimulatory strategy based on targeted Stat3 silencing in Toll-like receptor 9 (TLR9)-positive hematopoietic cells using CpG-small interfering RNA (siRNA) conjugates. Here, we assessed the therapeutic effect of systemic STAT3 blocking/TLR9 triggering in disseminated acute myeloid leukemia (AML). We used mouse Cbfb-MYH11/Mpl-induced leukemia model, which mimics human inv(16) AML. Our results demonstrate that intravenously delivered CpG-Stat3 siRNA, but not control oligonucleotides, can eradicate established AML and impair leukemia-initiating potential. These antitumor effects require host’s effector T cells but not TLR9-positive antigen-presenting cells. Instead, CpG-Stat3 siRNA has direct immunogenic effect on AML cells in vivo upregulating major histocompatibility complex class-II, costimulatory and proinflammatory mediators, such as interleukin-12, while downregulating coinhibitory PD-L1 molecule. Systemic injections of CpG-Stat3 siRNA generate potent tumor antigen–specific immune responses, increase the ratio of tumor-infiltrating CD8+ T cells to regulatory T cells in various organs, and result in CD8+ T-cell–dependent regression of leukemia. Our findings underscore the potential of using targeted STAT3 inhibition/TLR9 triggering to break tumor tolerance an...

Source: Blood - January 2, 2014 Category: Hematology Authors: Hossain, D. M. S., Dos Santos, C., Zhang, Q., Kozlowska, A., Liu, H., Gao, C., Moreira, D., Swiderski, P., Jozwiak, A., Kline, J., Forman, S., Bhatia, R., Kuo, Y.-H., Kortylewski, M. Tags: Plenary Papers, Myeloid Neoplasia, Gene Therapy Source Type: research