The druggable transcription factor Fli-1 regulates T cell immunity and tolerance in graft-versus-host disease

Graft-versus-host disease (GVHD), manifesting as either acute (aGVHD) or chronic (cGVHD), presents significant life-threatening complications following allogeneic hematopoietic cell transplantation. Here, we investigated Friend virus leukemia integration 1 (Fli-1) in GVHD pathogenesis and validated Fli-1 as a therapeutic target. Using genetic approaches, we found that Fli-1 dynamically regulated different T cell subsets in allogeneic responses and pathogenicity in the development of aGVHD and cGVHD. Compared with homozygous Fli1-deficient or WT T cells, heterozygous Fli1-deficient T cells induced the mildest GVHD, as evidenced by the lowest Th1 and Th17 cell differentiation. Single-cell RNA-Seq analysis revealed that Fli-1 differentially regulated CD4+ and CD8+ T cell responses. Fli-1 promoted the transcription of Th1/Th17 pathways and T cell receptor-inducible (TCR-inducible) transcription factors in CD4+ T cells, while suppressing activation- and function-related gene pathways in CD8+ T cells. Importantly, a low dose of camptothecin, topotecan, or etoposide acted as a potent Fli-1 inhibitor and significantly attenuated GVHD severity, while preserving the graft-versus-leukemia (GVL) effect. This observation was extended to a xenograft model, in which GVHD was induced by human T cells. In conclusion, we provide evidence that Fli-1 plays a crucial role in alloreactive CD4+ T cell activation and differentiation and that targeting Fli-1 may be an attractive strategy for treating GVHD without compromising the GVL effect.

Interleukin-23 receptor signaling by interleukin-39 potentiates T cell pathogenicity in acute graft-versus-host disease

IL-12 (p35/p40) and IL-23 (p19/p40) signal through IL-12R (IL-12Rβ2/β1) and IL-23R (IL-23Rα/IL-12Rβ1), respectively, which can promote pathogenic T lymphocyte activation, differentiation, and function in graft-versus-host disease (GVHD). With the use of murine models of allogeneic hematopoietic cell transplantation (HCT), we found that IL-12Rβ1 on donor T cells was dispensable to induce acute GVHD development in certain circumstances, while IL-23Rα was commonly required. This observation challenges the current paradigm regarding IL-12Rβ1 as a prerequisite to transmit IL-23 signaling. We hypothesized that p19/EBI3 (IL-39) may have an important role during acute GVHD. With the use of gene transfection and immunoprecipitation approaches, we verified that p19 and EBI3 can form biological heterodimers. We found that IL-39 levels in recipient serum positively correlated with development of acute GVHD in experimental models and in clinical settings, thereby implicating IL-39 in the pathogenesis of acute GVHD. Furthermore, we observed that human T cells can signal in response to IL-39. In chronic GVHD, IL-23Rα and IL-12Rβ1 were similarly required for donor T cell pathogenicity, and IL-39 levels were not significantly different from controls without GVHD. Collectively, we identify a novel cytokine, IL-39, as a pathogenic factor in acute GVHD, which represents a novel potential therapeutic target to control GVHD and other inflammatory disorders.