IL-6-mediated endothelial injury impairs antiviral humoral immunity after bone marrow transplantation

Endothelial function and integrity are compromised after allogeneic bone marrow transplantation (BMT), but how this affects immune responses broadly remains unknown. Using a preclinical model of CMV reactivation after BMT, we found compromised antiviral humoral responses induced by IL-6 signaling. IL-6 signaling in T cells maintained Th1 cells, resulting in sustained IFN-γ secretion, which promoted endothelial cell (EC) injury, loss of the neonatal Fc receptor (FcRn) responsible for IgG recycling, and rapid IgG loss. T cell-specific deletion of IL-6R led to persistence of recipient-derived, CMV-specific IgG and inhibited CMV reactivation. Deletion of IFN-γ in donor T cells also eliminated EC injury and FcRn loss. In a phase III clinical trial, blockade of IL-6R with tocilizumab promoted CMV-specific IgG persistence and significantly attenuated early HCMV reactivation. In sum, IL-6 invoked IFN-γ-dependent EC injury and consequent IgG loss, leading to CMV reactivation. Hence, cytokine inhibition represents a logical strategy to prevent endothelial injury, thereby preserving humoral immunity after immunotherapy.

Clinical grade multiparametric cell sorting and gene-marking of regulatory T cells

BACKGROUND AIMS

Regulatory T cells (Tregs) are the main mediators of peripheral tolerance. Treg-directed therapy has shown promising results in preclinical studies of diverse immunopathologies. At present, the clinical applicability of adoptive Treg transfer is limited by difficulties in generating Tregs at sufficient cell dose and purity.

METHODS

We developed a Good Manufacturing Practice (GMP) compliant method based on closed-system multiparametric Fluorescence-Activated Cell Sorting (FACS) to purify Tregs, which are then expanded in vitro and gene-marked with a clinical grade retroviral vector to enable in vivo fate tracking. Following small-scale optimization, we conducted four clinical-scale processing runs.

RESULTS

We showed that Tregs could be enriched to 87- 92% purity following FACS-sorting, and expanded and transduced to yield clinically relevant cell dose of 136-732×106 gene-marked cells, sufficient for a cell dose of at least 2 × 106 cells/kg. The expanded Tregs were highly demethylated in the FOXP3 Treg-specific demethylated region (TSDR), consistent with bona fide natural Tregs. They were suppressive in vitro, but a small percentage could secrete proinflammatory cytokines, including interferon-γ and interleukin-17A.

CONCLUSIONS

This study demonstrated the feasibility of isolating, expanding and gene-marking Tregs in clinical scale, thus paving the way for future phase I trials that will advance knowledge about the in vivo fate of transferred Tregs and its relationship with concomitant Treg-directed pharmacotherapy and clinical response.

CMV exposure drives long-term CD57+ CD4 memory T-cell inflation following allogeneic stem cell transplant

Donor and recipient cytomegalovirus (CMV) serostatus correlate with transplant-related mortality that is associated with reduced survival following allogeneic stem cell transplant (SCT). Prior epidemiologic studies have suggested that CMV seronegative recipients (R-) receiving a CMV-seropositive graft (D+) experience inferior outcomes compared with other serostatus combinations, an observation that appears independent of viral reactivation. We therefore investigated the hypothesis that prior donor CMV exposure irreversibly modifies immunologic function after SCT. We identified a CD4+/CD57+/CD27- T-cell subset that was differentially expressed between D+ and D- transplants and validated results with 120 patient samples. This T-cell subset represents an average of 2.9% (D-/R-), 18% (D-/R+), 12% (D+/R-), and 19.6% (D+/R+) (P < .0001) of the total CD4+ T-cell compartment and stably persists for at least several years post-SCT. Even in the absence of CMV reactivation post-SCT, D+/R- transplants displayed a significant enrichment of these cells compared with D-/R- transplants (P = .0078). These are effector memory cells (CCR7-/CD45RA+/-) that express T-bet, Eomesodermin, granzyme B, secrete Th1 cytokines, and are enriched in CMV-specific T cells. These cells are associated with decreased T-cell receptor diversity (P < .0001) and reduced proportions of major histocompatibility class (MHC) II expressing classical monocytes (P < .0001), myeloid (P = .024), and plasmacytoid dendritic cells (P = .0014). These data describe a highly expanded CD4+ T-cell population and putative mechanisms by which prior donor or recipient CMV exposure may create a lasting immunologic imprint following SCT, providing a rationale for using D- grafts for R- transplant recipients.

Infectious complications of CAR T-cell therapy: a clinical update

Chimeric antigen receptor (CAR) T-cell therapy is a revolutionary treatment modality used to treat haematological malignancies. Lymphocytes are engineered to produce CARs directed towards tumour cell antigens. Clinical trials have demonstrated impressive malignancy-related outcomes. Unfortunately, numerous off-target effects can cause toxicity-related adverse events in this population, the main being cytokine release syndrome and immune effector cell neurotoxicity syndrome. This causes significant patient morbidity and poor outcomes. Patients who receive CAR T-cell therapy are also profoundly immunosuppressed and often cytopenic, which is caused by a multitude of patient- and treatment-related factors. Thus, infection-related complications are also common in this group. Indeed, up to one third of patients will suffer a serious bacterial infection in the first 30 days after therapy. Viral respiratory tract infection appears to be the most common during the late phase and can be severe; one patient has died of influenza A infection. Fungal infection and cytomegalovirus (CMV) reactivation appear to be uncommon. Although institutional guidelines on infection-prevention strategies are available, there is a dearth of evidence to support their approach. Future research needs to target important unanswered questions that remain in this patient population in order to improve their short- and long-term outcomes.

IFN-λ therapy prevents severe gastrointestinal graft-versus-host disease

Immunopathology and intestinal stem cell (ISC) loss in the gastrointestinal (GI) tract is the prima facie manifestation of graft-versus-host disease (GVHD) and is responsible for significant mortality after allogeneic bone marrow transplantation (BMT). Approaches to prevent GVHD to date focus on immune suppression. Here, we identify interferon-λ (IFN-λ; interleukin-28 [IL-28]/IL-29) as a key protector of GI GVHD immunopathology, notably within the ISC compartment. Ifnlr1-/- mice displayed exaggerated GI GVHD and mortality independent of Paneth cells and alterations to the microbiome. Ifnlr1-/- intestinal organoid growth was significantly impaired, and targeted Ifnlr1 deficiency exhibited effects intrinsic to recipient Lgr5+ ISCs and natural killer cells. PEGylated recombinant IL-29 (PEG-rIL-29) treatment of naive mice enhanced Lgr5+ ISC numbers and organoid growth independent of both IL-22 and type I IFN and modulated proliferative and apoptosis gene sets in Lgr5+ ISCs. PEG-rIL-29 treatment improved survival, reduced GVHD severity, and enhanced epithelial proliferation and ISC-derived organoid growth after BMT. The preservation of ISC numbers in response to PEG-rIL-29 after BMT occurred both in the presence and absence of IFN-λ-signaling in recipient natural killer cells. IFN-λ is therefore an attractive and rapidly testable approach to prevent ISC loss and immunopathology during GVHD.

IL-6 dysregulation originates in dendritic cells and mediates 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 and 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 (DCs) initiates the systemic dysregulation of this cytokine. Inhibition of DC-driven classical signaling after targeted IL-6 receptor (IL-6R) deletion in T cells eliminated pathogenic donor Th17/Th22 cell differentiation and resulted in long-term survival. After engraftment, donor DCs assume the same role, maintaining classical IL-6 signaling-dependent GVHD responses. Surprisingly, cluster signaling was not active after transplantation, whereas inhibition of trans signaling with soluble gp130Fc 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 important therapeutic targets after alloSCT.

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.

Immune responses to the microbiome tune MHC class II antigen presentation by the intestinal epithelium to control gut pathology

The factors initiating pathology in the gastrointestinal (GI) tract are largely unknown. Graft-versus-host disease (GVHD) of the gastrointestinal (GI) tract is the principal determinant of lethality following allogeneic bone marrow transplantation (BMT). MHC class II-dependent GVHD is initiated by recipient alloantigens being presented to donor T cells that in turn undergo Th1 and Th17 differentiation to mediate pathology in the GI tract. Critically, the mechanisms that initiate disease, especially the relevant antigen presenting cells, remain unclear. Here, we identify the response of IL-12-secreting macrophages to the microbiome as the key driver of IFNγ secretion by mucosal type-1 innate lymphoid cells (ILC1). The latter controls MHC class II expression and antigen presentation by intestinal epithelial cells (IEC) specifically within the ileum. When these tightly regulated responses between microbiome and lamina propria lymphocytes are perturbed by inflammatory signals driven by pre-transplant conditioning, dramatic increases in antigen presentation by IEC occur in the ileum and lethal GVHD ensues. Conditional and Villin-specific deletion of MHC class II in IEC, or inhibition of IL-12 pre-transplant, completely prevent the initiation of lethal GVHD, identifying a readily translatable therapeutic strategy.

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.

Sorafenib promotes graft-versus-leukemia activity in mice and humans through IL-15 production in FLT3-ITD-mutant leukemia cells

Individuals with acute myeloid leukemia (AML) harboring an internal tandem duplication (ITD) in the gene encoding Fms-related tyrosine kinase 3 (FLT3) who relapse after allogeneic hematopoietic cell transplantation (allo-HCT) have a 1-year survival rate below 20%. We observed that sorafenib, a multitargeted tyrosine kinase inhibitor, increased IL-15 production by FLT3-ITD+ leukemia cells. This synergized with the allogeneic CD8+ T cell response, leading to long-term survival in six mouse models of FLT3-ITD+ AML. Sorafenib-related IL-15 production caused an increase in CD8+CD107a+IFN-γ+ T cells with features of longevity (high levels of Bcl-2 and reduced PD-1 levels), which eradicated leukemia in secondary recipients. Mechanistically, sorafenib reduced expression of the transcription factor ATF4, thereby blocking negative regulation of interferon regulatory factor 7 (IRF7) activation, which enhanced IL-15 transcription. Both IRF7 knockdown and ATF4 overexpression in leukemia cells antagonized sorafenib-induced IL-15 production in vitro. Human FLT3-ITD+ AML cells obtained from sorafenib responders following sorafenib therapy showed increased levels of IL-15, phosphorylated IRF7, and a transcriptionally active IRF7 chromatin state. The mitochondrial spare respiratory capacity and glycolytic capacity of CD8+ T cells increased upon sorafenib treatment in sorafenib responders but not in nonresponders. Our findings indicate that the synergism of T cells and sorafenib is mediated via reduced ATF4 expression, causing activation of the IRF7-IL-15 axis in leukemia cells and thereby leading to metabolic reprogramming of leukemia-reactive T cells in humans. Therefore, sorafenib treatment has the potential to contribute to an immune-mediated cure of FLT3-ITD-mutant AML relapse, an otherwise fatal complication after allo-HCT.

Flt-3L Expansion of Recipient CD8α+ Dendritic Cells Deletes Alloreactive Donor T Cells and Represents an Alternative to Posttransplant Cyclophosphamide for the Prevention of GVHD

Purpose: Allogeneic bone marrow transplantation (BMT) provides curative therapy for leukemia via immunologic 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.Experimental Design: We have utilized preclinical models of allogeneic BMT to dissect the role and modulation of recipient DCs in controlling donor T-cell-mediated GVHD and GVL.Results: We demonstrate that recipient CD8α⁺ DCs promote activation-induced clonal deletion of allospecific donor T cells after BMT. We compared pretransplant fms-like tyrosine kinase-3 ligand (Flt-3L) treatment to the current clinical strategy of posttransplant 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.Conclusions: 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. Clin Cancer Res; 24(7); 1604-16. ©2018 AACR.

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

Donor T cell-derived 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 (SCT) 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-17RA/C receptor. The protection from GVHD afforded by IL-17A required secretion from, and signaling in, both hematopoietic and non-hematopoietic host tissue. Given the intestinal-specificity of the disease in these animals, we hypothesized a microbiome contribution. Cohousing of WT with IL-17RA and IL-17RC deficient mice, dramatically enhanced the susceptibility of WT mice to acute GVHD. Furthermore, the gut microbiome of WT mice shifted towards that of the IL-17RA/C mice during cohousing prior to transplant, confirming that IL-17-sensitive gut microbiota controls susceptibility to acute GVHD. Finally, induced IL-17A deletion peri-transplant also enhanced acute GVHD, consistent with an additional protective role for this cytokine independent of effects on dysbiosis. Importantly, this implies that blocking IL-17 in a clinical trial could have adverse effects via dysbiosis, particularly in the early post-transplant setting and raises caution about their potential effects if used long term.

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.