Immunomodulation by juglone alleviates acute graft‐versus‐host disease without compromising the graft‐versus‐leukaemia activity in mice

Background and Purpose Acute graft‐versus‐host disease (GVHD) remains a major barrier to successful transplantation outcomes. Recent studies have shown that pharmacotherapy for GVHD should target both the innate and adaptive inflammatory immune responses. Juglone, a redox‐active phytochemical found in walnuts, has shown potent anti‐inflammatory effects in models of colitis and inflammatory bowel disease. However, its effects on T‐cell‐mediated immune responses remain largely unknown. Considering the overlapping mediators of inflammation in GVHD and the aforementioned conditions, we investigated the use of juglone as a prophylactic agent for GVHD. Experimental Approach Immunomodulatory activity and mechanism of action of juglone were studied using murine splenic leukocytes in vitro. The GVHD prophylactic efficacy of orally administered juglone was evaluated using a murine model of allogeneic haematopoietic stem cell transplantation based on an MHC mismatch. Key Results Juglone exhibited immunomodulatory activity by (i) inhibiting the activation of dendritic cells and CD4 + T‐cells, (ii) inhibiting cytokine secretion and lymphocyte proliferation, and (iii) inducing exhaustion of CD4 + T‐cells, as shown by increased expression of CTLA‐4 (CD152) and Fas (CD95). Oral administration of juglone significantly reduced mortality and morbidity associated with GVHD while maintaining graft‐versus‐leukaemia activity. This was accompanied by a decrease in the number of naïve CD4 + cells, and an increase in the number of CD4 + and CD8 + central memory T‐cells. Conclusion and Implications Juglone is a potent immunomodulator for GVHD prophylaxis. Our study is the first to provide a dosage framework for the oral administration of juglone that can be used for clinical development.