IFNγR signaling mediates alloreactive T-cell trafficking and GVHD

Over-salting ruins the balance of the immune menu

Regulatory components of the immune system are critical for preventing unintended activation of immune cells. Failure to prevent this unintended activation raises the risk of developing exaggerated inflammation and autoimmunity. In this issue of the JCI, Binger et al. and Hernandez et al. report that salt can play an important role in undermining regulatory mechanisms of the innate and adaptive immune systems. High salt levels interfere with alternative activation of macrophages (M2), which function in attenuating tissue inflammation and promoting wound healing. High salt also impairs Treg function by inducing IFNγ production in these cells. Together, these results provide evidence that environmental signals in the presence of high dietary salt enhance proinflammatory responses by interfering with both innate and adaptive regulatory mechanisms.

Maintenance Therapy with Decitabine after Allogeneic Stem Cell Transplantation for Acute Myelogenous Leukemia and Myelodysplastic Syndrome

Decitabine is a hypomethylating agent that irreversibly inhibits DNA methyltransferase I, inducing leukemic differentiation and re-expression of epigenetically silenced putative tumor antigens. We assessed safety and efficacy of decitabine maintenance after allogeneic transplantation for acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Decitabine maintenance may help eradicate minimal residual disease, decrease the incidence of graft-versus-host disease (GVHD), and facilitate a graft-versus-leukemia effect by enhancing the effect of T regulatory lymphocytes. Patients with AML/MDS in complete remission (CR) after allotransplantation started decitabine between day +50 and +100. We investigated 4 decitabine doses in cohorts of 4 patients: 5, 7.5, 10, and 15 mg/m(2)/day × 5 days every 6 weeks, for a maximum 8 cycles. The maximum tolerated dose (MTD) was defined as the maximum dose at which ≤ 25% of people experience dose-limiting toxicities during the first cycle of treatment. Twenty-four patients were enrolled and 22 were evaluable. All 4 dose levels were completed and no MTD was reached. Overall, decitabine maintenance was well tolerated. Grade 3 and 4 hematological toxicities were experienced by 75% of patients, including all patients treated at the highest dose level. Nine patients completed all 8 cycles and 8 of them remain in CR. Nine patients died from relapse (n = 4), infectious complications (n = 3), and GVHD (n = 2). Most occurrences of acute GVHD were mild and resolved without interruption of treatment; 1 patient died of acute gut GVHD. Decitabine maintenance did not clearly impact the rate of chronic GVHD. Although there was a trend of increased FOXP3 expression, results were not statistically significant. In conclusion, decitabine maintenance is associated with acceptable toxicities when given in the post-allotransplantation setting. Although the MTD was not reached, the dose of 10 mg/m(2) for 5 days every 6 weeks appeared to be the optimal dose rather than 15 mg/m(2), where most hematological toxicities occurred.

Pharmacologic Inhibition of JAK1/JAK2 Signaling Reduces Experimental Murine Acute GVHD While Preserving GVT Effects

PURPOSE

Immune-mediated graft-versus-tumor (GVT) effects can occur after allogeneic hematopoietic stem cell transplantation (HSCT), but GVT is tightly linked to its main complication, graft-versus-host disease (GVHD). Strategies aimed at modulating GVHD, while maintaining the GVT effect, are needed to improve the cure rate of transplant. Given the emerging role of Janus-activated kinase (JAK) signaling in lymphoproliferative and myeloproliferative diseases and its established function at dictating T-cell differentiation, we postulated that JAKs might be potential therapeutic targets through a pharmacologic approach.

EXPERIMENTAL DESIGN

We examined the effect of JAK1/JAK2 modulation by ruxolitinib in a mouse model of fully MHC mismatched bone marrow transplant comprising in vivo tumor inoculation.

RESULTS

JAK1/JAK2 inhibition by ruxolitinib improved both overall survival (P = 0.03) and acute GVHD pathologic score at target organs (P ≤ 0.001) of treated mice. In addition, treatment with ruxolitinib was associated with a preserved GVT effect, as evidenced by reduction of tumor burden (P = 0.001) and increase of survival time (P = 0.01). JAK1/JAK2 inhibition did not impair the in vivo acquisition of donor T-cell alloreactivity; this observation may account, at least in part, to the preserved GVT effect. Rather, JAK1/JAK2 inhibition of GVHD was associated with the modulation of chemokine receptor expression, which may have been one factor in the reduced infiltration of donor T cells in GVHD target organs.

CONCLUSIONS

These data provide further evidence that JAK inhibition represents a new and potentially clinically relevant approach to GVHD prevention.

Tolerance associated gene expression following allogeneic hematopoietic cell transplantation

Biologic markers of immune tolerance may facilitate tailoring of immune suppression duration after allogeneic hematopoietic cell transplantation (HCT). In a cross-sectional study, peripheral blood samples were obtained from tolerant (n = 15, median 38.5 months post-HCT) and non-tolerant (n = 17, median 39.5 post-HCT) HCT recipients and healthy control subjects (n = 10) for analysis of immune cell subsets and differential gene expression. There were no significant differences in immune subsets across groups. We identified 281 probe sets unique to the tolerant (TOL) group and 122 for non-tolerant (non-TOL). These were enriched for process networks including NK cell cytotoxicity, antigen presentation, lymphocyte proliferation, and cell cycle and apoptosis. Differential gene expression was enriched for CD56, CD66, and CD14 human lineage-specific gene expression. Differential expression of 20 probe sets between groups was sufficient to develop a classifier with > 90% accuracy, correctly classifying 14/15 TOL cases and 15/17 non-TOL cases. These data suggest that differential gene expression can be utilized to accurately classify tolerant patients following HCT. Prospective investigation of immune tolerance biologic markers is warranted.

The complex and central role of interferon-γ in graft-versus-host disease and graft-versus-tumor activity

Allogeneic hematopoietic cell transplantation (allo-HCT) is increasingly being performed to treat patients with hematologic malignancies. However, separating the beneficial graft-versus-tumor (GVT) or graft-versus-leukemia effects from graft-versus-host disease (GVHD) has been difficult and remains a significant challenge toward improving therapeutic efficacy and reducing toxicity of allo-HCT. GVHD is induced by donor T cells that also mediate potent anti-tumor responses. However, despite the largely shared effector mechanisms, extensive animal studies have demonstrated the potential of dissociating the GVT effect from GVHD. Also in many clinical cases, long-term remission was achieved following allo-HCT, without significant GVHD. A better mechanistic understanding of the immunopathophysiology of GVHD and GVT effects may potentially help to improve allo-HCT as well as maximize the benefit of GVT effects while minimizing GVHD. In this article, we review the role of IFN-γ in regulation of alloresponses following allo-HCT, with a focus on the mechanisms of how this cytokine may separate GVHD from GVT effects.

T-bet is critical for the development of acute graft-versus-host disease through controlling T cell differentiation and function

T-bet is a master regulator for IFN-γ production and Th1 differentiation. We evaluated the roles of T-bet and IFN-γ in T cell responses in acute graft-versus-host disease (GVHD) and found that T-bet(-/-) T cells induced significantly less GVHD compared with wild-type or IFN-γ(-/-) counterparts in both MHC-mismatched and MHC-matched but minor histocompatibility Ag-mismatched models driven by CD4 T cells. T-bet(-/-), but not IFN-γ(-/-), CD4 T cells had a markedly reduced ability to cause tissue damage in liver and gut. This distinct outcome is reflected by the differential gene expression on donor CD4 T cells deficient for T-bet or IFN-γ. At mRNA and protein levels, we defined several T-bet-dependent molecules that may account for the impaired ability of T-bet(-/-) T cells to migrate into target organs and to produce Th1-related cytokines. Moreover, these molecules were independent of either endogenous IFN-γ, such as CXCR3 and programmed death-1, or systematic IFN-γ, such as NKG2D, I-A(b), and granzyme B. Although both T-bet(-/-) and IFN-γ(-/-) CD4 T cells are prone to differentiate into Th17 cells, polarized Th17 cells deficient for T-bet but not for IFN-γ had a significantly reduced ability to cause GVHD. Finally, T-bet(-/-) T cells had a compromised graft-versus-leukemia effect, which could be essentially reversed by neutralization of IL-17 in the recipients. We conclude that T-bet is required for Th1 differentiation and migration, as well as for optimal function of Th17 cells. Thus, targeting T-bet or regulating its downstream effectors independent of IFN-γ may be a promising strategy to control GVHD in the clinic.

Pharmacologic blockade of JAK1/JAK2 reduces GvHD and preserves the graft-versus-leukemia effect

We have recently reported that interferon gamma receptor deficient (IFNγR-/-) allogeneic donor T cells result in significantly less graft-versus-host disease (GvHD) than wild-type (WT) T cells, while maintaining an anti-leukemia or graft-versus-leukemia (GvL) effect after allogeneic hematopoietic stem cell transplantation (allo-HSCT). We demonstrated that IFNγR signaling regulates alloreactive T cell trafficking to GvHD target organs through expression of the chemokine receptor CXCR3 in alloreactive T cells. Since IFNγR signaling is mediated via JAK1/JAK2, we tested the effect of JAK1/JAK2 inhibition on GvHD. While we demonstrated that pharmacologic blockade of JAK1/JAK2 in WT T cells using the JAK1/JAK2 inhibitor, INCB018424 (Ruxolitinib), resulted in a similar effect to IFNγR-/- T cells both in vitro (reduction of CXCR3 expression in T cells) and in vivo (mitigation of GvHD after allo-HSCT), it remains to be determined if in vivo administration of INCB018424 will result in preservation of GvL while reducing GvHD. Here, we report that INCB018424 reduces GvHD and preserves the beneficial GvL effect in two different murine MHC-mismatched allo-HSCT models and using two different murine leukemia models (lymphoid leukemia and myeloid leukemia). In addition, prolonged administration of INCB018424 further improves survival after allo-HSCT and is superior to other JAK1/JAK2 inhibitors, such as TG101348 or AZD1480. These data suggest that pharmacologic inhibition of JAK1/JAK2 might be a promising therapeutic approach to achieve the beneficial anti-leukemia effect and overcome HLA-barriers in allo-HSCT. It might also be exploited in other diseases besides GvHD, such as organ transplant rejection, chronic inflammatory diseases and autoimmune diseases.

Recent advances on cellular therapies and immune modulators for graft-versus-host disease

The efficacy of allogeneic hematopoietic stem cell transplantation is counterbalanced by the occurrence of life-threatening immune-mediated complications, such as graft-versus-host disease (GVHD), a multistep disease which is reportedly fatal to approximately 15% of transplant recipients. It is now established that T-cell-dendritic cell interactions, T-cell activation, release of proinflammatory cytokines and T-cell trafficking partake in GVHD pathogenesis. This article will focus on the most recent strategies aimed at preventing/treating GVHD by manipulating components of the innate and adaptive immune response from both the donor and the host.

Absence of STAT1 in donor-derived plasmacytoid dendritic cells results in increased STAT3 and attenuates murine GVHD

Selective targeting of non-T cells, including antigen-presenting cells (APCs), is a potential strategy to prevent graft-versus-host-disease (GVHD) but to maintain graft-versus-tumor (GVT) effects. Because type I and II interferons signal through signal transducer and activator of transcription-1 (STAT1), and contribute to activation of APCs after allogeneic bone marrow transplant (alloBMT), we examined whether the absence of STAT1 in donor APCs could prevent GVHD while preserving immune competence. Transplantation of STAT1(-/-) bone marrow (BM) prevented GVHD induced by STAT1(+/+) T cells, leading to expansion of B220(+) cells and regulatory T cells. STAT1(-/-) BM also preserved GVT activity and enhanced overall survival of tumor-challenged mice in the setting of GVHD. Furthermore, recipients of allogeneic STAT1(-/-) BM demonstrated increased CD9(-)Siglec H(hi) plasmacytoid dendritic cells (pDCs), and depletion of pDCs after STAT1(-/-) BM transplantation prevented GVHD resistance. STAT1(-/-) pDCs were found to produce decreased free radicals, IFNα, and interleukin (IL)-12, and increased IL-10. Additionally, STAT1(-/-) pDCs that were isolated after alloBMT showed increased gene expression of S100A8 and S100A9, and transplantation of S100A9(-/-) BM reduced GVHD-free survival. Finally, elevated STAT3 was found in STAT1(-/-) pDCs isolated after alloBMT. We conclude that interfering with interferon signaling in APCs such as pDCs provides a novel approach to regulate the GVHD/GVT axis.

The role of CXCR3 in DSS-induced colitis

Inflammatory bowel disease (IBD) is a group of disorders that are characterized by chronic, uncontrolled inflammation in the intestinal mucosa. Although the aetiopathogenesis is poorly understood, it is widely believed that IBD stems from a dysregulated immune response towards otherwise harmless commensal bacteria. Chemokines induce and enhance inflammation through their involvement in cellular trafficking. Reducing or limiting the influx of these proinflammatory cells has previously been demonstrated to attenuate inflammation. CXCR3, a chemokine receptor in the CXC family that binds to CXCL9, CXCL10 and CXCL11, is strongly overexpressed in the intestinal mucosa of IBD patients. We hypothesised that CXCR3 KO mice would have impaired cellular trafficking, thereby reducing the inflammatory insult by proinflammatory cell and attenuating the course of colitis. To investigate the role of CXCR3 in the progression of colitis, the development of dextran sulfate sodium (DSS)-induced colitis was investigated in CXCR3^−/− mice over 9 days. This study demonstrated attenuated DSS-induced colitis in CXCR3^−/− mice at both the macroscopic and microscopic level. Reduced colitis correlated with lower recruitment of neutrophils (p = 0.0018), as well as decreased production of IL-6 (p<0.0001), TNF (p = 0.0038), and IFN-γ (p = 0.0478). Overall, our results suggest that CXCR3 plays an important role in recruiting proinflammatory cells to the colon during colitis and that CXCR3 may be a therapeutic target to reduce the influx of proinflammatory cells in the inflamed colon.

Activity of therapeutic JAK 1/2 blockade in graft-versus-host disease

Graft-versus-host-disease (GVHD) is a severe complication of allogeneic hematopoietic cell transplantation (allo-HCT) characterized by the production of high levels of proinflammatory cytokines. Activated Janus kinases (JAKs) are required for T-effector cell responses in different inflammatory diseases, and their blockade could potently reduce acute GVHD. We observed that inhibition of JAK1/2 signaling resulted in reduced proliferation of effector T cells and suppression of proinflammatory cytokine production in response to alloantigen in mice. In vivo JAK 1/2 inhibition improved survival of mice developing acute GVHD and reduced histopathological GVHD grading, serum levels of proinflammatory cytokines, and expansion of alloreactive luc-transgenic T cells. Mechanistically, we could show that ruxolitinib impaired differentiation of CD4(+) T cells into IFN-γ- and IL17A-producing cells, and that both T-cell phenotypes are linked to GVHD. Conversely, ruxolitinib treatment in allo-HCT recipients increased FoxP3(+) regulatory T cells, which are linked to immunologic tolerance. Based on these results, we treated 6 patients with steroid-refractory GVHD with ruxolitinib. All patients responded with respect to clinical GVHD symptoms and serum levels of proinflammatory cytokines. In summary, ruxolitinib represents a novel targeted approach in GVHD by suppression of proinflammatory signaling that mediates tissue damage and by promotion of tolerogenic Treg cells.

The requirement of CD8+ T cells to initiate and augment acute cardiac inflammatory response to high blood pressure

Macrophage infiltration and activation in myocardium are hallmarks of acute cardiac inflammatory response to high blood pressure. However, the underlying mechanisms remain elusive. In this article, we report that CD8(+) T cells are required for cardiac recruitment and activation of macrophages. First, mice with CD8 gene-targeted (CD8 knockout) or CD8(+) T cells depleted by Ab showed significantly reduced cardiac inflammatory response to the elevation of blood pressure after angiotensin II (Ang II) infusion, whereas CD8 knockout mice reconstituted with CD8(+) T cells restored the sensitivity to Ang II. More importantly, CD8(+) T cells were required for macrophage infiltration in myocardium and subsequent activation to express proinflammatory cytokines and chemokines. Furthermore, macrophage activation required direct contact with activated CD8(+) T cells, but with TCR dispensable. TCR-independent activation of macrophages was further confirmed in MHC class I-restricted OVA-specific TCR transgenic mice, which showed a CD8(+) T cell activation and cardiac proinflammatory response to Ang II similar to that of wild-type mice. Finally, only myocardium-infiltrated, but not peripheral, CD8(+) T cells were specifically activated by Ang II, possibly by the cardiac IFN-γ that drove IFN-γR(+) CD8(+) T cell infiltration and activation. Thus, this work identified a TCR-independent innate nature of CD8(+) T cells that was critical in initiating the sterile immune response to acute elevation of blood pressure.

Comparative analysis of FoxP3(+) regulatory T cells in the target tissues and blood in chronic graft versus host disease

Activation and migration of regulatory T cells (Treg) into tissue is critical in control of inflammation, but has not been examined extensively in chronic graft versus host disease (cGVHD). In parallel studies of tissues and blood, we determined that FoxP3(+) T cells increased in proportion to T effectors (Teff) in tissue infiltrates in oral and cutaneous lichenoid cGVHD. These FoxP3(+) cells expressed distinguishing phenotypic and functional markers of Treg (CD3(+), CD4(+), CD27(+), ICOS(+) and CD39(+)), not found on FoxP3(-) Teff. Both Teff and FoxP3(+) Treg expressed T-bet and the chemokine receptor CXCR3, however, consistent with a common mechanism of chemokine-mediated migration into tissue. Furthermore, functional markers (ICOS and CD39) and chemokine receptors (CXCR3) were both present in a higher proportion of FoxP3(+) cells in tissues than in peripheral blood, consistent with recruitment and activation of Treg in cGVHD target tissues. Finally, the 'activated' CD45RA(-)FoxP3(hi) subset of Treg cells, which highly express functional markers, were found in comparable frequencies in cGVHD patients and normal controls, despite a significant deficit in naive 'resting' Treg. These findings are consistent with Treg capacity to upregulate functional markers and traffick into tissue in cGVHD.

JAK2 expression is associated with tumor-infiltrating lymphocytes and improved breast cancer outcomes: implications for evaluating JAK2 inhibitors

Janus kinase-2 (JAK2) supports breast cancer growth, and clinical trials testing JAK2 inhibitors are under way. In addition to the tumor epithelium, JAK2 is also expressed in other tissues including immune cells; whether the JAK2 mRNA levels in breast tumors correlate with outcomes has not been evaluated. Using a case-control design, JAK2 mRNA was measured in 223 archived breast tumors and associations with distant recurrence were evaluated by logistic regression. The frequency of correct pairwise comparisons of patient rankings based on JAK2 levels versus survival outcomes, the concordance index (CI), was evaluated using data from 2,460 patients in three cohorts. In the case-control study, increased JAK2 was associated with a decreasing risk of recurrence (multivariate P = 0.003, n = 223). Similarly, JAK2 was associated with a protective CI (<0.5) in the public cohorts: NETHERLANDS CI = 0.376, n = 295; METABRIC CI = 0.462, n = 1,981; OSLOVAL CI = 0.452, n = 184. Furthermore, JAK2 was strongly correlated with the favorable prognosis LYM metagene signature for infiltrating T cells (r = 0.5; P < 2 × 10(-16); n = 1,981) and with severe lymphocyte infiltration (P = 0.00003, n = 156). Moreover, the JAK1/2 inhibitor ruxolitinib potently inhibited the anti-CD3-dependent production of IFN-γ, a marker of the differentiation of Th cells along the tumor-inhibitory Th1 pathway. The potential for JAK2 inhibitors to interfere with the antitumor capacities of T cells should be evaluated.

Effect of epigallocatechin-3-gallate on graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is often complicated by alloreactive donor T-cell-mediated graft-versus-host disease (GvHD). The major polyphenol of green tea, epigallocatechin-3-gallate (EGCG), is an inhibitor of both DNA methyltransferase 1 (DNMT1) and signal transducer and activator of transcription 1 (STAT1), which are essential for induction of GvHD. Thus, in this report, we examine if in vivo administration of EGCG mitigates GvHD in several different animal models. While we concede that refinement of EGCG treatment might result in GvHD prevention, our results suggest that EGCG treatment might not be an effective therapy against GvHD in the clinic.