Graft-versus-host disease (GVHD) remains the most significant complication after allogeneic stem cell transplantation. Previously, acute GVHD had been considered to be mediated predominantly by Th1-polarized T cells. Recently, investigators have identified a second proinflammatory lineage of T cells termed Th17 that is critically dependent on the transcription factor retinoic acid-related orphan receptor (ROR)γt. In this study, we have evaluated the role of Th17 cells in murine acute GVHD by infusing donor T cells lacking RORC and as a consequence the isoform RORγt. Recipients given donor CD4+ and CD8+ T cells lacking RORC had significantly attenuated acute GVHD and markedly decreased tissue pathology in the colon, liver, and lung. Using a clinically relevant haploidentical murine transplantation model, we showed that RORC−/− CD4+ T cells alone diminished the severity and lethality of acute GVHD. This was not found when CD4+ T cells from RORC−/− mice were given to completely mismatched BALB/c mice, and it was correlated with absolute differences in the generation of TNF in the colon after transplant. Thus, CD4+ T cell expression of RORC is important in the pathogenesis of acute GVHD.

Tumor necrosis factor-alpha (TNF-alpha) is a key mediator of inflammatory diseases, including rheumatoid arthritis (RA), and anti-TNF-alpha drugs such as etanercept are effective treatments. Splice-switching oligonucleotides (SSOs) are a new class of drugs designed to induce therapeutically favorable splice variants of targeted genes. In this work, we used locked nucleic acid (LNA)-based SSOs to modulate splicing of TNF receptor 2 (TNFR2) pre-mRNA. The SSO induced skipping of TNFR2 exon 7, which codes the transmembrane domain (TM), switching endogenous expression from the membrane-bound, functional form to a soluble, secreted form (Delta7TNFR2). This decoy receptor protein accumulated in the circulation of treated mice, antagonized TNF-alpha, and altered disease in two mouse models: TNF-alpha-induced hepatitis and collagen-induced arthritis (CIA). This is the first report of upregulation of the endogenous, circulating TNF-alpha antagonist by oligonucleotide-induced splicing modulation.

• Extended donor T reg survival is required for protection from GVHD; donor T reg longevity depends on T reg CCR8 expression. • Donor CD11c1 APCs promote T reg longevity in vivo; host CD11c1 APCs do not appear to contribute to donor T reg reconstitution.The infusion of donor regulatory T cells (T regs) has been used to prevent acute graftversus-host disease (GVHD) in mice and has shown promise in phase 1 clinical trials. Previous work suggested that early T reg migration into lymphoid tissue was important for GVHD prevention. However, it is unclear how and where T regs function longitudinally to affect GVHD. To better understand their mechanism of action, we studied 2 T regassociated chemokine receptors in murine stem cell transplant models. CC chemokine receptor (CCR) 4 was dispensable for donor T reg function in the transplant setting. Donor T regs lacking CCR8 (CCR8 2/2 ), however, were severely impaired in their ability to prevent lethal GVHD because of increased cell death. By itself, CCR8 stimulation was unable to rescue T regs from apoptosis. Instead, CCR8 potentiated T reg survival by promoting critical interactions with dendritic cells. In vivo, donor bone marrow-derived CD11c 1 antigen-presenting cells (APCs) were important for promoting donor T reg maintenance after transplant. In contrast, host CD11c 1 APCs appeared to be dispensable for early activation and expansion of donor T regs . Collectively, our data indicate that a sustained donor T reg presence is critical for their beneficial properties, and that their survival depends on CCR8 and donor but not host CD11c

Key Points Allogeneic donor T cells establish stable contacts with dendritic cells in lymph nodes immediately (2 hours) after they are transplanted. Endogenous Tregs disrupt stable contacts between T cells and DCs, which are interleukin-10 dependent.

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