Recipient mucosal-associated invariant T cells control GVHD within the colon

Mucosal-associated invariant T (MAIT) cells are a unique innate-like T cell subset that responds to a wide array of bacteria and yeast through recognition of riboflavin metabolites presented by the MHC class I–like molecule MR1. Here, we demonstrate using MR1 tetramers that recipient MAIT cells are present in small but definable numbers in graft-versus-host disease (GVHD) target organs and protect from acute GVHD in the colon following bone marrow transplantation (BMT). Consistent with their preferential juxtaposition to microbial signals in the colon, recipient MAIT cells generate large amounts of IL-17A, promote gastrointestinal tract integrity, and limit the donor alloantigen presentation that in turn drives donor Th1 and Th17 expansion specifically in the colon after BMT. Allogeneic BMT recipients deficient in IL-17A also develop accelerated GVHD, suggesting MAIT cells likely regulate GVHD, at least in part, by the generation of this cytokine. Indeed, analysis of stool microbiota and colon tissue from IL-17A–/– and MR1–/– mice identified analogous shifts in microbiome operational taxonomic units (OTU) and mediators of barrier integrity that appear to represent pathways controlled by similar, IL-17A–dependent mechanisms. Thus, MAIT cells act to control barrier function to attenuate pathogenic T cell responses in the colon and, given their very high frequency in humans, likely represent an important population in clinical BMT

Cytokines in graft-versus-host disease

Graft-versus-host disease (GVHD) is a complication of allogeneic bone marrow transplantation whereby transplanted naive and marrow-derived T cells damage recipient tissue through similar mechanisms to those that allow destruction of malignant cells, the therapeutic intent of bone marrow transplantation. The manifestations and severity of GVHD are highly variable and are influenced by the proportions of naive cells maturing along regulatory T cell, Th1, Th2, or Th17 phenotypes. This maturation is largely influenced by local cytokines, which, in turn, activate transcription factors and drive development toward a dominant phenotype. In addition, proinflammatory cytokines exert direct effects on GVHD target tissues. Our knowledge of the role that cytokines play in orchestrating GVHD is expanding rapidly and parallels other infective and inflammatory conditions in which a predominant T cell signature is causative of pathology. Because a broad spectrum of cytokine therapies is now routinely used in clinical practice, they are increasingly relevant to transplant medicine

Donor T-cell–derived GM-CSF drives alloantigen presentation by dendritic cells in the gastrointestinal tract

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has recently emerged as an important pathogenic cytokine in acute graft-versus-host disease (GVHD), but the nature of the T-cell lineages secreting the cytokine and the mechanisms of action are less clear. Here we used interleukin 17A-fate reporter systems with transcriptional analysis and assays of alloantigen presentation to interrogate the origins of GM-CSF-secreting T cells and the effects of the cytokine on antigen-presenting cell (APC) function after experimental allogeneic stem cell transplantation (SCT). We demonstrated that although GM-CSF-secreting Th17 and non-Th17 cells expanded in the colon over time after SCT, the Th17 lineage expanded to represent 10% to 20% of the GM-CSF secreting T cells at this site by 4 weeks. Donor T-cell-derived GM-CSF expanded alloantigen-presenting donor dendritic cells (DCs) in the colon and lymph nodes. In the mesenteric lymph nodes, GM-CSF-dependent DCs primed donor T cells and amplified acute GVHD in the colon. We thus describe a feed-forward cascade whereby GM-CSF-secreting donor T cells accumulate and drive alloantigen presentation in the colon to amplify GVHD severity. GM-CSF inhibition may be a tractable clinical intervention to limit donor alloantigen presentation and GVHD in the lower gastrointestinal tract

IL-6 dysregulation originates in dendritic cells and initiates graft-versus-host disease via classical signaling

Graft-versus-host-disease (GVHD) after allogeneic stem cell transplantation (alloSCT) is characterized by interleukin 6 (IL-6) dysregulation. IL-6 can mediate effects via various pathways, including classical, trans and cluster signaling. Given the recent availability of agents that differentially inhibit these discrete signaling cascades, understanding the source, signaling and cellular targets of this cytokine is paramount to inform the design of clinical studies. Here we demonstrate that IL-6 secretion from recipient dendritic cells (DC) initiates the systemic dysregulation of this cytokine. Inhibition of DC-driven classical signaling following targeted IL-6 receptor (IL-6R) deletion in T-cells eliminated pathogenic donor Th17/Th22 cell differentiation and resulted in long-term survival. Following engraftment, donor DC assume the same role, maintaining classical IL-6 signaling-dependent GVHD responses. Surprisingly, cluster-signaling was not active after transplant, while inhibition of trans-signaling with sgp130Fc promoted severe, chronic cutaneous GVHD. The latter was a result of exaggerated polyfunctional Th22 cell expansion that was reversed by IL-22 deletion or IL-6R inhibition. Importantly, inhibition of IL-6 classical-signaling did not impair the graft-versus-leukemia effect. Together, these data highlight IL-6 classical-signaling and downstream Th17/Th22 differentiation as key therapeutic targets after alloSCT

Pegylated interferon-2 alpha invokes graft-versus-leukemia effects in patients relapsing after allogeneic stem cell transplantation

Allogeneic stem cell transplantation (SCT) is a curative therapy for patients with hematological malignancies related largely to an immunological graft-versus-leukemia (GVL) effect mediated by donor T cells and natural killer cells. Relapse of disease after SCT represents failure of GVL and is now the major cause of treatment failure. We sought to augment GVL effects in patients (n = 29) relapsing after SCT in a prospective phase I/II clinical trial of dose-escalated pegylated interferon-2 alpha (peg-IFN alpha). The administration of peg-IFN alpha after reinduction chemotherapy, with or without subsequent donor lymphocyte infusion (DLI), resulted in a 2-year overall survival (OS) of 31% (95% confidence interval, 17.3%-49.2%), which rejects the null hypothesis of 7% generated by observations in an institutional historical cohort. As expected, peg-IFN alpha was associated with graft-versus-host disease (GVHD) and hematological toxicity, which was manageable with scheduled dose modifications. Progression-free survival (PFS) was greatest in patients who experienced GVHD, although the majority of those patients still eventually progressed. Higher PFS and OS were associated with pretreatment proportions of immune cell populations with regulatory function, including mucosal invariant T cells, regulatory T cells, and plasmacytoid dendritic cells, independent of any association with GVHD. Peg-IFN alpha administration after relapse thus constitutes a logical strategy to invoke GVL effects and should be studied in a larger, multicenter cohort. This trial was registered at www.anzctr. org.au as #ACTRN12612000728831

MHC class II antigen presentation by the intestinal epithelium initiates graft-versus-host disease and is influenced by the microbiota

Graft-versus-host disease (GVHD) in the gastrointestinal (GI) tract is the principal determinant of lethality following allogeneic bone marrow transplantation (BMT). Here, we examined the mechanisms that initiate GVHD, including the relevant antigen-presenting cells. MHC class II was expressed on intestinal epithelial cells (IECs) within the ileum at steady state but was absent from the IECs of germ-free mice. IEC-specific deletion of MHC class II prevented the initiation of lethal GVHD in the GI tract. MHC class II expression on IECs was absent from mice deficient in the TLR adaptors MyD88 and TRIF and required IFNγ secretion by lamina propria lymphocytes. IFNγ responses are characteristically driven by IL-12 secretion from myeloid cells. Antibiotic-mediated depletion of the microbiota inhibited IL-12/23p40 production by ileal macrophages. IL-12/23p40 neutralization prevented MHC class II upregulation on IECs and initiation of lethal GVHD in the GI tract. Thus, MHC class II expression by IECs in the ileum initiates lethal GVHD, and blockade of IL-12/23p40 may represent a readily translatable therapeutic strategy

Flt-3L expansion of recipient CD8α+ dendritic cells deletes alloreactive donor T cells and represents an alternative to post-transplant cyclophosphamide for the prevention of GVHD

Allogeneic bone marrow transplantation (BMT) provides curative therapy for leukemia via immunological graft-versus-leukemia (GVL) effects. In practice, this must be balanced against life threatening pathology induced by graft-versus-host disease (GVHD). Recipient dendritic cells (DC) are thought to be important in the induction of GVL and GVHD.We have utilized preclinical models of allogeneic BMT to dissect the role and modulation of recipient DC in controlling donor T cell mediated GVHD and GVL.We demonstrate that recipient CD8a+ DC promote activation-induced clonal deletion of allospecific donor T cells after BMT. We compared pre-transplant fms-like tyrosine kinase-3 ligand (Flt-3L) treatment to the current clinical strategy of post-transplant cyclophosphamide (PT-Cy) therapy. Our results demonstrate superior protection from GVHD with the immunomodulatory Flt-3L approach, and similar attenuation of GVL responses with both strategies. Strikingly, Flt-3L treatment permitted maintenance of the donor polyclonal T cell pool, where PT-Cy did not.These data highlight pre-transplant Flt-3L therapy as a potent new therapeutic strategy to delete alloreactive T cells and prevent GVHD, which appears particularly well suited to haploidentical BMT where the control of infection and the prevention of GVHD are paramount

Acute graft-versus-host disease is regulated by an IL-17-sensitive microbiome

Donor T-cell-derived interleukin-17A(IL-17A) can mediate late-immunopathology in graft-versus-host disease (GVHD), however protective roles remain unclear. Using multiple cytokine and cytokine receptor subunit knockout mice, we demonstrate that stem cell transplant recipients lacking the ability to generate or signal IL-17 develop intestinal hyper-acute GVHD. This protective effect is restricted to the molecular interaction of IL-17A and/or IL-17F with the IL-17 receptor A/C (IL-17RA/C). The protection from GVHD afforded by IL-17A required secretion from, and signaling in, both hematopoietic and nonhematopoietic host tissue. Given the intestinal-specificity of the disease in these animals, we cohoused wild-type (WT) with IL-17RA and IL-17RC-deficient mice, which dramatically enhanced the susceptibility of WT mice to acute GVHD. Furthermore, the gut microbiome of WT mice shifted toward that of the IL-17RA/C mice during cohousing prior to transplant, confirming that an IL-17-sensitive gut microbiota controls susceptibility to acuteGVHD. Finally, induced IL-17A depletion peritransplant also enhancedacuteGVHD, consistent with an additional protective role for this cytokine independent of effects on dysbiosis