IL-23 suppresses innate immune response independently of IL-17A during carcinogenesis and metastasis

Abstract

IL-23 is an important molecular driver of Th17 cells and has strong tumor-promoting proinflammatory activity postulated to occur via adaptive immunity. Conversely, more recently it has been reported that IL-17A elicits a protective inflammation that promotes the activation of tumor-specific CD8(+) T cells. Here we show the much broader impact of IL-23 in antagonizing antitumor immune responses primarily mediated by innate immunity. Furthermore, the majority of this impact was independent of IL-17A, which did not appear critical for many host responses to tumor initiation or metastases. IL-23-deficient mice were resistant to experimental tumor metastases in three models where host NK cells controlled disease. Immunotherapy with IL-2 was more effective in mice lacking IL-23, and again the protection afforded was NK cell mediated and independent of IL-17A. Further investigation revealed that loss of IL-23 promoted perforin and IFN-gamma antitumor effector function in both metastasis models examined. IL-23-deficiency also strikingly protected mice from tumor formation in two distinct mouse models of carcinogenesis where the dependence on host IL-12p40 and IL-17A was quite different. Notably, in the 3'-methylcholanthrene (MCA) induction of fibrosarcoma model, this protection was completely lost in the absence of NK cells. Overall, these data indicate the general role that IL-23 plays in suppressing natural or cytokine-induced innate immunity, promoting tumor development and metastases independently of IL-17A.

Fig. 1.

Host IL-23p19 suppresses NK cell-mediated control of lung metastases. Groups of 5–15 WT, IL-23p19^−/−, IL-12p40^−/−, IL-12p35^−/−, IL-17^−/−, and RAG-1^−/− mice were injected i.v. with either (A–C) 2 × 10⁵ or (D) 1 × 10⁵ B16F10 melanoma cells. In B and C, mice were additionally treated with control Ig (cIg), anti-IL-12p40 (α-p40), or anti-IL-23p19 (α-p19) cells by treatment with antibodies (500 μg i.p.) on day −1, 0, and 7 relative to tumor inoculation. In D, mice were additionally depleted of CD8⁺ T cells (αCD8) or NK (αASGM1 or αNK1.1) cells by treatment with antibodies (100 μg i.p.) on day −1, 0, and 7 relative to tumor inoculation. Fourteen days after tumor inoculation, the lungs of these mice were harvested and fixed, and the colonies counted and recorded for individual mice as shown. Asterisks indicate the groups that are significantly different from untreated or cIg-treated mice in each strain. Mann–Whitney, *P < 0.05.

Fig. 2.

Host IL-23p19 suppresses IL-2 therapy of tumor metastases. Groups of 5–15 WT, IL-23p19^−/−, IL-12p40^−/−, IL-17^−/−, pfp^−/−, IFN-γ^−/−, IL-23p19^−/−xpfp^−/−, or IL-23p19^−/−xIFN-γ^−/− mice were injected i.v. with either (A–D) 7.5 × 10⁵ B16F10 melanoma cells or (E and F) 2 × 10⁵ RM-1 tumor cells. Mice received PBS (−) or 100,000 U IL-2 (+) i.p. on day -1 before tumor inoculation. Some IL-23p19^−/−xpfp^−/− mice were additionally treated with anti-IFN-γ mAb (100 μg i.p.) on days −1, 0, and 7 to neutralize IFN-γ. Fourteen days after tumor inoculation, the lungs of these mice were harvested and fixed, and the colonies counted and recorded for individual mice as shown. Asterisks indicate the groups that are significantly different from IL-2-treated WT mice or IL-2–treated IL-23p19^−/− mice (for those strains on p19^−/− background). Mann–Whitney, *P < 0.05.

Fig. 3.

IL-23p19 promotes the formation of DMBA/TPA-induced skin papillomas. Groups of 15–30 female WT, IL-23p19^−/−, IL-12p40^−/−, and IL-17^−/− mice were injected with 25 μg DMBA, and 1 week later, twice weekly with 4 μg TPA for 20 weeks as described in Materials and Methods. Mice were subsequently monitored for skin papilloma development for 25 weeks (n = 15 mice/group). Results are shown as (A) the mean lesion number per mouse over time and (B) percentage of mice in the group with papillomas over time. Significant differences in mean lesion number per mouse were observed by the unpaired Mann–Whitney U test (*, gene-targeted vs. WT, P < 0.05; **, p19^−/− vs. p17^−/−, P < 0.05). Significant differences in proportion with papilloma at any one-time point were determined by the Fisher's exact test (*, gene-targeted vs. WT, P < 0.05; **, p19^−/− vs. p17^−/−, P < 0.05).

Fig. 4.

IL-23p19 promotes the formation of MCA-induced fibrosarcomas. Groups of 10–25 male WT and IL-23p19^−/− mice as indicated were injected with either 5, 25,100, or 400 μg MCA as described in Materials and Methods and subsequently monitored for tumor development over 300 days (proportion of mice with tumors in each group shown in each panel). Mice were injected with 400 μg MCA (A and B), 100 μg (C and D), 25 μg (E and F), or 5 μg (G and H). Results are shown as the growth curves of individual mice with sarcoma in each group after MCA inoculation. Proportion of mice developing lethal tumors is shown on right of each panel. Statistical differences in tumor-free mice as determined by Fisher's exact test: (A and B) WT vs. p19^−/− (P = 0.0009); (C and D) WT vs. p19^−/− (P = 0.2443); (E and F) WT vs. p19^−/− (0.6614); and (H and I) WT vs. p19^−/− (0.4737).

Fig. 5.

IL-23p19 suppression of NK cells promotes the formation of MCA-induced fibrosarcomas. Groups of 14–15 male WT and IL-23p19^−/− mice as indicated were injected with 400 μg MCA as described in Materials and Methods and subsequently monitored for tumor development over 300 days (proportion of mice with tumors in each group shown). WT or IL-23p19^−/− mice were additionally treated with control Ig (cIg) or depleted of CD8⁺ T cell or NK cells weekly from the time of MCA inoculation to day 42. Results are shown as the growth curves of individual mice with sarcoma in each group after MCA inoculation. Statistical differences as determined by Fisher's exact test: (A–D) p19^−/− + cIg vs. p19^−/− + anti-CD8 (ns), p19^−/− + cIg vs. p19^−/− + anti-ASGM1 (P = 0.0027).