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 .