Induction of IL‐9‐producing CD8 + T cells by ascochlorin derivatives

Background and Purpose Ascochlorin (ASC) is an antiviral antibiotic from the fermented broth of Ascochyta viciae which exerts an inhibitory effect to cancers. Its impact on immune cells has not been examined. In this study, we obtained ASC derivatives with less cytotoxicity and determined whether they affected T cells, indicating possible immune‐mediated antitumour effects. Experimental Approach Newly synthesised ASC derivatives were screened for inhibitory effects on T‐cell antigen receptor (TCR)‐stimulated proliferative responses using murine CD4 + and CD8 + T cells. Two compounds were identified that exhibited >10‐fold less toxicity compared with ASC. N184, the less toxic of the two, was analysed for its in vivo antitumour effects, and in vitro effects on CD8 + T‐cell proliferation, survival, cytokine production and exhaustion, using microscopy, qPCR and flow cytometry. Key Results N184 induced limited IL‐9 production in CD8 + T cells following TCR stimulation, thereby improving cell survival. It also enhanced cytokine production in the late phase of proliferation and suppressed the induction of exhaustion. N184 suppressed tumour growth in mice in a CD8 + T cell‐dependent manner. The effect was partially prevented by an IL‐9‐neutralising antibody. Conclusion and Implications N184 induces differentiation of IL‐9‐producing CD8 + T cells in vitro and elicits antitumour immunity in an IL‐9‐dependent manner.