Metronomic chemotherapy with low-dose cyclophosphamide plus gemcitabine can induce anti-tumor T cell immunity in vivo |
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Authors: | Miki Tongu Nanae Harashima Hiroyuki Monma Touko Inao Takaya Yamada Hideyuki Kawauchi Mamoru Harada |
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Affiliation: | 1. Department of Experimental Animals, Center for Integrated Research in Science, Shimane University, Izumo, Shimane, Japan 2. Department of Immunology, Faculty of Medicine, Shimane University, Izumo, Shimane, 693-8501, Japan 3. Department of Surgery, Faculty of Medicine, Shimane University, Izumo, Shimane, Japan 4. Department of Otorhinolaryngology, Faculty of Medicine, Shimane University, Izumo, Shimane, Japan
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Abstract: | Several chemotherapeutic drugs have immune-modulating effects. For example, cyclophosphamide (CP) and gemcitabine (GEM) diminish immunosuppression by regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs), respectively. Here, we show that intermittent (metronomic) chemotherapy with low-dose CP plus GEM can induce anti-tumor T cell immunity in CT26 colon carcinoma-bearing mice. Although no significant growth suppression was observed by injections of CP (100 mg/kg) at 8-day intervals or those of CP (50 mg/kg) at 4-day intervals, CP injection (100 mg/kg) increased the frequency of tumor peptide-specific T lymphocytes in draining lymph nodes, which was abolished by two injections of CP (50 mg/kg) at a 4-day interval. Alternatively, injection of GEM (50 mg/kg) was superior to that of GEM (100 mg/kg) in suppressing tumor growth in vivo, despite the smaller dose. When CT26-bearing mice were treated with low-dose (50 mg/kg) CP plus (50 mg/kg) GEM at 8-day intervals, tumor growth was suppressed without impairing T cell function; the effect was mainly T cell dependent. The metronomic combination chemotherapy cured one-third of CT26-bearing mice that acquired tumor-specific T cell immunity. The combination therapy decreased Foxp3 and arginase-1 mRNA levels but increased IFN-γ mRNA expression in tumor tissues. The percentages of tumor-infiltrating CD45+ cells, especially Gr-1high CD11b+ MDSCs, were decreased. These results indicate that metronomic chemotherapy with low-dose CP plus GEM is a promising protocol to mitigate totally Treg- and MDSC-mediated immunosuppression and elicit anti-tumor T cell immunity in vivo. |
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