IL-18R-dependent and independent pathways account for IL-18-enhanced antitumor ability of CAR-T cells

Abstract

Interleukin-18 (IL-18) has been demonstrated to augment the antitumor capacity of chimeric antigen receptor-T cells (CAR-T) but the underlying mechanisms are largely unknown. Here we explored the effects and mechanisms of exogenous IL-18 on the antitumor response of CAR-T cells. IL-18 boosted the cytotoxicity of human epidermal growth factor receptor-2 (HER2)-specific CAR-T cells ex vivo and enhanced the antitumor efficacy of the CAR-T cells in immunodeficient mice, moreover, IL-18 improved the antitumor capacity of OVA-specific T cells in immunocompetent mice, indicating the universal enhancing function of IL-18 for adoptive cell therapy. To address the roles of IL-18 receptor (IL-18R) in the enhancing function, we evaluated the effects of IL-18R knockout (IL-18R−/−) condition in immunocompetent host and CAR-T cells on the IL-18-enhanced antitumor activities. Interestingly, IL-18 persisted to improve the antitumor ability of IL-18R intact CAR-T cells in IL-18R−/− mice. For IL-18R−/− CAR-T cells, however, IL-18 still holds the enhancing ability to boost the antitumor efficacy in IL-18R−/− mice, albeit the ex vivo tumor-killing ability was lower than that of IL-18R intact CAR-T cells, indicating that IL-18R-independent pathway is involved in the enhancement. Furthermore, tagged IL-18 binded to the membrane of IL-18R−/− splenic and lymph node cells and IL-18R intact and IL-18R−/− CAR-T cells showed distinct transcriptomic profiles when stimulated by IL-18. These data demonstrate that IL-18R-independent pathways contribute to functions of IL-18.