IL-39 promotes chronic graft-versus-host disease by increasing T and B Cell pathogenicity

Chronic graft-versus-host disease (cGVHD) remains a major complication during the late phase of allogeneic hematopoietic stem cell transplantation (allo-HSCT). IL-39, a newly described pro-inflammatory cytokine belonging to the IL-12 family, plays a role in lupus development. Recently, IL-39 has been identified as a pathogenic factor in acute GVHD (aGVHD). However, the role of IL-39 in the pathogenesis of cGVHD remains unclear.

We constructed a recombinant IL-39 plasmid and established scleroderma and lupus-like cGVHD models. Quantitative PCR and enzyme-linked immunosorbent assay (ELISA) were used to detect IL-39 expression in mice and patients post transplantation, respectively. Hydrodynamic gene transfer (HGT) was performed to achieve IL-39 overexpression in vivo. Multiparameter flow cytometry, western blotting, and assays in vitro were performed to investigate the effect of IL-39 on cGVHD.

The relative expression of IL-23p19 and EBi3 was significantly increased in the intestine of cGVHD mice on day 40 post allo-HSCT, and IL-39 levels were significantly elevated in the serum of patients following allo-HSCT. Overexpression of IL-39 significantly aggravated the severity of cGVHD. Increased IL-39 levels promoted T-cell activation and germinal center responses, and may exacerbate thymic damage. Consistently, blocking IL-39 markedly ameliorated immune dysregulation in the cGVHD mice. Furthermore, we found that IL-39 was produced by B cells, CD11b⁺ cells, and CD8⁺T cells after activation. Stimulation of IL-39 led to upregulation of the IL-39 receptor on CD4⁺T cells and further caused activation of the STAT1/STAT3 pathway, through which IL-39 may exert its pro-inflammatory effects.

Our study reveals a critical role for IL-39 in cGVHD pathogenesis and indicates that IL-39 may serve as a potential therapeutic target for cGVHD prevention.