Allogeneic hematopoietic stem cell transplantation (allo-HCT) is an effective means by which to treat a wide variety of diseases resulting from hematological dysfunction. However, the development of graft-versus-host disease (GVHD) remains a major cause of morbidity and mortality post transplantation. The IL-12 family of cytokines is comprised of IL-12, IL-23, IL-27, IL-35, and potentially IL-39. IL-12 family members are unique in that each cytokine and cognate receptor is comprised of heterodimers in which either the a or b subunit is shared among the others. IL-12 (p35+p40) and IL-23 (p19+p40) have well documented proinflammatory functions responsible for Th1 differentiation and Th17 stabilization, respectively, and play critical roles in GVHD development. IL-12R and IL-23R share a β-chain (IL-12Rβ1) yet use distinct α-chains to mediate their respective receptor signaling. While both IL-12R and IL-23R are widely implicated in inflammatory disorders, the role of IL-12Rβ1 in this context remains much less defined. We therefore studied the impact of eliminating the common IL-12Rβ1 chain or the unique IL-23Rα chain in T cells on GVHD using murine models of allogeneic bone marrow transplantation (BMT). In agreement with previous publications, we found a pathogenic role for IL-23Rα on donor T cells in aGVHD. Strikingly, a similar effect was not seen for IL-12Rβ1 (Figure 1A, B). These data suggest that that IL-23Rα contributes to GVHD pathogenesis via a pathway independent of IL-12Rβ1. To confirm that functional differences existed between T cells deficient for IL-23Rα or IL-12Rβ1 in GVHD, we assessed cytokine profiles of these T cells in target organs 14 days post-BMT. We found that, while production of IFNγ and IL-17 in the spleen was similarly decreased in both cohorts, GM-CSF production by CD4+ T cells was reduced exclusively in T cells deficient for IL-23Rα. Further, a significant reduction of IFNγ and GM-CSF in target organs, such as the liver and gut, was only observed in T cells deficient for IL-23Rα. The newest member of the IL-12 family, IL-39, was recently shown to contribute to SLE pathogenesis; this cytokine has been described to be composed of IL-23p19 and EBI3. Given the cognate receptor for IL-39 includes IL-23Rα and gp130, we hypothesized that IL-39 may play a role in aGVHD as this would explain why IL-12Rβ1 is dispensable. To validate that p19 and EBI3 can form a heterodimer, we transfected SV40 cells with vectors containing control, IL-23p19, EBI3 or both cDNAs. We detected IL-39 heterodimers only in the supernatant of cells transfected with both IL-23p19 and EBI3 via ELISA (Figure 1C). Furthermore, we observed significantly increased levels of IL-39 in allogeneic recipients at day 14 post BMT compared to naïve mice or recipients of BM alone in two models of aGVHD (Figure 1D). This may implicate IL-39 in the GVHD development. Taken together, our studies indicate that IL-23Rα plays an essential role, whereas IL-12Rβ1 is dispensable, for donor T cells to induce aGVHD. Our proposed model is that in the absence of IL-12Rβ1, IL-39 could transmit IL-23Rα signaling, hypothetically by forming a heterodimer with gp130. This new finding indicates that IL-23Rα and IL-39 are potential therapeutic targets for controlling aGVHD in the clinic.
Figure 1. Effect of IL-12R 𝛃 1 in aGVHD and the potential role of IL-39 Lethally irradiated BALB/c mice were transplanted with 5x106 TCD-BM alone or plus 1x106 purified T cells from WT B6, IL-12R𝛃1KO, or IL-23RαKO mice. Survival (A) and body weight loss (B) are shown. Supernatant from SV40 cells transiently transfected with vectors containing control, IL-23p19, EBI3 or both cDNAs. p19 and EBI3 heterodimers were detected via ELISA (C). Serum was collected from naïve or lethally irradiated mice transplanted with 5x106 TCD-BM alone or plus 1x106 purified T cells. Formation of p19 and EBI3 heterodimers were tested in serum at 14 days post BMT via ELISA (D).
Disclosures
No relevant conflicts of interest to declare.
Inhibition of ITK differentiates GVT and GVHD in allo-HSCT
