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Tumor-associated macrophages (TAM) are involved in tumor progression, metastasis, and immunosuppression. Because TAMs are highly plastic and could alter their phenotypes to proinflammatory M1 in response to environmental stimuli, reeducating TAMs has emerged as a promising approach to overcoming the challenges of solid cancer treatment. This study investigated the effect of IL9 on macrophage M1 polarization and verified its antitumor potential to retrain TAMs and promote chemokine secretion. We demonstrated that IL9 stimulated macrophage proliferation and polarized them toward the proinflammatory M1 phenotype in an IFNγ-dependent manner. Tumor-localized IL9 also polarized TAMs toward M1 in vivo and made them release CCL3/4 and CXCL9/10 to recruit antitumor immune cells, including T and natural killer cells, into the tumor microenvironment. Furthermore, peritoneal treatment with recombinant IL9 delayed the growth of macrophage-enriched B16F10 melanoma and 4T1 breast cancer in syngeneic mice, although IL9 treatment did not reduce tumor growth in the absence of macrophage enrichment. These results demonstrate the efficacy of IL9 in macrophage polarization to trigger antitumor immunity. Significance: These findings clarified the effect of IL9 on macrophage M1 polarization and verified its antitumor potential through retraining TAMs and chemokine secretion.

FACS gating strategy used for tumor-infiltrating immune cell analysis

Primers used in this study

Simple Summary Interleukin (IL) 15 is a proinflammatory cytokine and is well-known as an efficacious cytokine for cancer immunotherapy. Interestingly, the IL-15:IL-15Rα complex, a self-assembling form of IL-15 and its soluble receptor α (IL-15Rα), has shown greater antitumor activity than IL-15 itself. However, the development of a suitable multigene delivery system is needed for further applications of IL-15:IL-15Rα. Baculovirus, an arthropod-specific virus, is known for its adjuvant effect in cancer therapy. Here, we investigated the potential of the BacMam virus, a modified baculovirus for gene delivery into mammalian cells, as a novel multigene delivery system to generate a cell-based cancer vaccine secreting the self-assembling IL-15:IL-15Rα complex. Vaccination with a BacMam-based IL-15:IL-15Rα cancer vaccine triggered antitumor immune responses in a tumor antigen-specific manner. Our findings indicate that the BacMam system is a safe and effective method to produce protective and therapeutic cancer vaccines. Abstract This study reports the use of the BacMam system to deliver and express self-assembling IL-15 and IL-15Rα genes to murine B16F10 melanoma and CT26 colon cancer cells. BacMam-based IL-15 and IL-15Rα were well-expressed and assembled to form the biologically functional IL-15:IL-15Rα complex. Immunization with this IL-15:IL-15Rα cancer vaccine delayed tumor growth in mice by inducing effector memory CD4+ and CD8+ cells and effector NK cells which are tumor-infiltrating. It caused strong antitumor immune responses of CD8+ effector cells in a tumor-antigen specific manner both in vitro and in vivo and significantly attenuated Treg cells which a control virus-infected cancer vaccine could induce. Post-treatment with this cancer vaccine after a live cancer cell injection also prominently delayed the growth of the tumor. Collectively, we demonstrate a vaccine platform consisting of BacMam virus-infected B16F10 or CT26 cancer cells that secrete IL-15:IL-15Rα. This study is the first demonstration of a functionally competent soluble IL-15:IL-15Rα complex-related cancer vaccine using a baculovirus system and advocates that the BacMam system can be used as a secure and rapid method of producing a protective and therapeutic cancer vaccine.

IL-9 has been reported to play dual roles in the pathogenesis of autoimmune disorders and cancers. The collaboration of IL-9 with microenvironmental factors including the broader cytokine milieu and other cellular components may provide important keys to explain its conflicting effects in chronic conditions. In this review, we summarize recent findings on the cellular sources of, and immunological responders to IL-9, in order to interpret the role of IL-9 in the regulation of immune responses. This knowledge will provide new perspectives to improve clinical benefits and limit adverse effects of IL-9 when treating pathologic conditions.

Interleukin-9 (IL-9) is well known for its role in allergic inflammation. For cancer, both pro- and anti-tumor effects of IL-9 were controversially reported, but the impact of IL-9 on tumor metastasis has not yet been clarified. In this study, IL-9 was expressed as a secretory form (sIL-9) and a membrane-bound form (mbIL-9) on B16F10 melanoma cells. The mbIL-9 was engineered as a chimeric protein with the transmembrane and cytoplasmic region of TNF-α. The effect of either mbIL-9 or sIL-9 expressing cells were analyzed on the metastasis capability of the cancer cells. After three weeks of tumor implantation into C57BL/6 mice through the tail vein, the number of tumor modules in lungs injected with IL-9 expressing B16F10 was 5-fold less than that of control groups. The percentages of CD4+ T cells, CD8+ T cells, NK cells, and M1 macrophages considerably increased in the lungs of the mice injected with IL-9 expressing cells. Among them, the M1 macrophage subset was the most significantly enhanced. Furthermore, peritoneal macrophages, which were stimulated with either sIL-9 or mbIL-9 expressing transfectant, exerted higher anti-tumor cytotoxicity compared with that of the mock control. The IL-9-stimulated peritoneal macrophages were highly polarized to M1 phenotype. Stimulation of RAW264.7 macrophages with sIL-9 or mbIL-9 expressing cells also significantly increased the cytotoxicity of those macrophages against wild-type B16F10 cells. These results clearly demonstrate that IL-9 can induce an anti-metastasis effect by enhancing the polarization and proliferation of M1 macrophages.

IL-9 is a known T cell growth factor with pleiotropic immunological functions, especially in parasite infection and colitis. However, its role in tumor growth is controversial. In this study, we generated tumor clones expressing the membrane-bound form of IL-9 (MB-IL-9) and investigated their influences on immune system. MB-IL-9 tumor clones showed reduced tumorigenicity but shortened survival accompanied with severe body weight loss in mice. MB-IL-9 expression on tumor cells had no effect on cell proliferation or major histocompatibility complex class I expression in vitro. MB-IL-9 tumor clones were effective in amplifying CD4+ and CD8+ T cells and increasing cytotoxic activity against CT26 cells in vivo. We also observed a prominent reduction in body weights and survival period of mice injected intraperitoneally with MB-IL-9 clones compared with control groups. Ratios of IL-17 to interferon (IFN)-γ in serum level and tumor mass were higher in mice implanted with MB-IL-9 tumor clones than those observed in mice implanted with control cells. These results indicate that the ectopic expression of the MB-IL-9 on tumor cells exerts an immune-stimulatory effect with toxicity. To exploit its benefits as a tumor vaccine, a strategy to control the toxicity of MB-IL-9 tumor clones should be developed.