Paradoxical effects of IFN-gamma in graft-versus-host disease reflect promotion of lymphohematopoietic graft-versus-host reactions and inhibition of epithelial tissue injury

Molecular Pathway, Epidemiological Data and Treatment Strategies of Fungal Infection (Mycoses): A Comprehensive Review

The recent increase in fungal infections is a health crisis. This surge is directly tied to the increase in immunocompromised people caused by changes in medical practice, such as the use of harsh chemotherapy and immunosuppressive medicines. Immunosuppressive disorders such as HIV have exacerbated the situation dramatically. Subcutaneous or superficial fungal infections can harm the skin, keratinous tissues, and mucous membranes. This category includes some of the most common skin disorders that impact millions of people worldwide. Despite the fact that they are seldom fatal, they can have a catastrophic impact on a person's quality of life and, in rare situations, spread to other people or become obtrusive. The majority of fungal infections under the skin and on the surface are simply and quickly cured. An opportunistic organism that preys on a weak host or a natural intruder can both result in systemic fungal infections. Furthermore, it might be exceedingly lethal and dangerous to one's life. Dimorphic fungi may pose a hazard to healthy populations that are not exposed to endemic fungi. Increased surveillance, the availability of quick, noninvasive diagnostic tests, monitoring the emergence of antifungal medication resistance, and research on the pathophysiology, prevention, and management of fungal infections are just a few potential solutions to these new health problems. The goal of this review is to summarize the data available for fungal infections and the different therapies which are involved in their treatment. Additionally, it also summarizes the molecular and scientific data of the plants which contain anti-fungal activity. Data are acquired using Google, PubMed, Scholar, and other online sources.

Lack of IFN-γ Receptor Signaling Inhibits Graft-versus-Host Disease by Potentiating Regulatory T Cell Expansion and Conversion

IFN-γ is a pleiotropic cytokine that plays a controversial role in regulatory T cell (Treg) activity. In this study, we sought to understand how IFN-γ receptor (IFN-γR) signaling affects donor Tregs following allogeneic hematopoietic cell transplant (allo-HCT), a potentially curative therapy for leukemia. We show that IFN-γR signaling inhibits Treg expansion and conversion of conventional T cells (Tcons) to peripheral Tregs in both mice and humans. Mice receiving IFN-γR-deficient allo-HCT showed markedly reduced graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) effects, a trend associated with increased frequencies of Tregs, compared with recipients of wild-type allo-HCT. In mice receiving Treg-depleted allo-HCT, IFN-γR deficiency-induced peripheral Treg conversion was effective in preventing persistent GVHD while minimally affecting GVL effects. Thus, impairing IFN-γR signaling in Tcons may offer a promising strategy for achieving GVL effects without refractory GVHD. Similarly, in a human PBMC-induced xenogeneic GVHD model, significant inhibition of GVHD and an increase in donor Tregs were observed in mice cotransferred with human CD4 T cells that were deleted of IFN-γR1 by CRISPR/Cas9 technology, providing proof-of-concept support for using IFN-γR-deficient T cells in clinical allo-HCT.

Novel T cell/organoid culture system allows ex vivo modeling of intestinal graft-versus-host disease

Acute graft-versus-host disease (GvHD) remains the biggest clinical challenge and prognosis-determining complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Donor T cells are acceptedly key mediators of alloreactivity against host tissues and here especially the gut. In support of previous studies, we found that the intestinal intra-epithelial lymphocyte (IEL) compartment was dynamically regulated in the course of MHC class I full mismatch allo-HSCT. However, while intestinal epithelial cell (IEC) damage endangers the integrity of the intestinal barrier and is a core signature of intestinal GvHD, the question whether and to what degree IELs are contributing to IEC dysregulation is poorly understood. To study lymphoepithelial interaction, we employed a novel ex vivo T cell/organoid co-culture model system. Here, allogeneic intra-epithelial T cells were superior in inducing IEC death compared to syngeneic IEL and allogeneic non-IEL T cells. The ability to induce IEC death was predominately confined to TCRβ+ T cells and was executed in a largely IFNγ-dependent manner. Alloreactivity required a diverse T cell receptor (TCR) repertoire since IELs genetically modified to express a TCR restricted to a single, non-endogenous antigen failed to mediate IEC pathology. Interestingly, minor histocompatibility antigen (miHA) mismatch was sufficient to elicit IEL-driven IEC damage. Finally, advanced live cell imaging analyses uncovered that alloreactive IELs patrolled smaller areas within intestinal organoids compared to syngeneic controls, indicating their unique migratory properties within allogeneic IECs. Together, we provide here experimental evidence for the utility of a co-culture system to model the cellular and molecular characteristics of the crosstalk between IELs and IEC in an allogeneic setting ex vivo. In the light of the emerging concept of dysregulated immune-epithelial homeostasis as a core aspect of intestinal GvHD, this approach represents a novel experimental system to e.g. screen therapeutic strategies for their potential to normalize T cell/IEC- interaction. Hence, analyses in pre-clinical in vivo allo-HSCT model systems may be restricted to hereby positively selected, promising approaches.

AMPK Drives Both Glycolytic and Oxidative Metabolism in T Cells During Graft-versus-host Disease

Allogeneic T cells reprogram their metabolism during acute graft-versus-host disease (GVHD) in a process reliant on the cellular energy sensor AMP-activated protein kinase (AMPK). Deletion of AMPK in donor T cells limits GVHD but still preserves homeostatic reconstitution and graft-versus-leukemia (GVL) effects. In the current studies, murine T cells lacking AMPK decreased oxidative metabolism at early timepoints post-transplant and were also unable to mediate a compensatory increase in glycolysis following inhibition of the electron transport chain. Human T cells lacking AMPK gave similar results, with glycolytic compensation impaired both in vitro and following expansion in vivo in a modified model of GVHD. Immunoprecipitation of proteins from day 7 allogeneic T cells, using an antibody specific to phosphorylated AMPK targets, recovered lower levels of multiple glycolysis-related proteins including the glycolytic enzymes aldolase, enolase, pyruvate kinase M (PKM), and glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Functionally, murine T cells lacking AMPK exhibited impaired aldolase activity following anti-CD3/CD28 stimulation and a decrease in GAPDH activity on day 7 post-transplant. Importantly, these changes in glycolysis correlated with an impaired ability of AMPK KO T cells to produce significant amounts of interferon gamma (IFNγ) upon antigenic re-stimulation. Together these data highlight a significant role for AMPK in controlling oxidative and glycolytic metabolism in both murine and human T cells during GVHD and endorse further study of AMPK inhibition as a potential target for future clinical therapies.

KEY POINTS

AMPK plays a key role in driving both and oxidative and glycolytic metabolism in T cells during graft-versus-host disease (GVHD)Absence of AMPK simultaneously impairs both glycolytic enzyme activity, most notably by aldolase, and interferon gamma (IFNγ) production.

Tocilizumab increases regulatory T cells, reduces natural killer cells and delays graft-versus-host disease development in humanized mice treated with post-transplant cyclophosphamide

Graft-versus-host disease (GVHD) is a life-threatening complication following donor hematopoietic stem cell transplantation, where donor T cells damage host tissues. This study investigated the effect of tocilizumab (TOC) combined with post-transplant cyclophosphamide (PTCy) on immune cell engraftment and GVHD development in a humanized mouse model. NOD-scid-IL2Rγ^null (NSG) mice were injected intraperitoneally with 2 × 10⁷ human (h) peripheral blood mononuclear cells and cyclophosphamide (33 mg kg^-1 ) or saline on days 3 and 4, then TOC or control antibody (0.5 mg mouse^-1 ) twice weekly for 28 days. Mice were monitored for clinical signs of GVHD for either 28 or 70 days. Spleens and livers were assessed for human leukocyte subsets, and serum cytokines and tissue histology were analyzed. In the short-term model (day 28), liver and lung damage were reduced in PTCy + TOC compared with control mice. All groups showed similar splenic hCD45⁺ leukocyte engraftment (55-60%); however, PTCy + TOC mice demonstrated significantly increased (1.5-2-fold) splenic regulatory T cells. Serum human interferon gamma was significantly reduced in PTCy + TOC compared with control mice. Long-term (day 70), prolonged survival was similar in PTCy + TOC (median survival time, > 70 days) and PTCy mice (median survival time, 56 days). GVHD onset was significantly delayed in PTCy + TOC, compared with TOC or control mice. Notably, natural killer cells were reduced (77.5%) in TOC and PTCy + TOC mice. Overall, combining PTCy with TOC increases regulatory T cells and reduces clinical signs of early GVHD, but does not improve long-term survival compared with PTCy alone.

IFN-γR/STAT1 signaling in recipient hematopoietic antigen-presenting cells suppresses graft-versus-host disease

The absence of IFN-γ receptor (IFN-γR) or STAT1 signaling in donor cells has been shown to result in reduced induction of acute graft-versus-host disease (GVHD). In this study, we unexpectedly observed increased activation and expansion of donor lymphocytes in both lymphohematopoietic organs and GVHD target tissues of IFN-γR/STAT1-deficient recipient mice, leading to rapid mortality following the induction of GVHD. LPS-matured, BM-derived Ifngr1-/- Stat1-/- DCs (BMDCs) were more potent allogeneic stimulators and expressed increased levels of MHC II and costimulatory molecules. Similar effects were observed in human antigen-presenting cells (APCs) with knockdown of Stat1 by CRISPR/Cas9 and treatment with a JAK1/2 inhibitor. Furthermore, we demonstrated that the absence of IFN-γR/STAT1 signaling in hematopoietic APCs impaired the presentation of exogenous antigens, while promoting the presentation of endogenous antigens. Thus, the indirect presentation of host antigens to donor lymphocytes was defective in IFN-γR/STAT1-deficient, donor-derived APCs in fully donor chimeric mice. The differential effects of IFN-γR/STAT1 signaling on endogenous and exogenous antigen presentation could provide further insight into the roles of the IFN-γ/STAT1 signaling pathway in the pathogenesis of GVHD, organ rejection, and autoimmune diseases.

Graft-versus-host disease depletes plasmacytoid dendritic cell progenitors to impair tolerance induction

Graft-versus-host disease (GVHD) causes failed reconstitution of donor plasmacytoid dendritic cells (pDCs) that are critical for immune protection and tolerance. We used both murine and human systems to uncover the mechanisms whereby GVHD induces donor pDC defects. GVHD depleted Flt3-expressing donor multipotent progenitors (MPPs) that sustained pDCs, leading to impaired generation of pDCs. MPP loss was associated with decreased amounts of MPP-producing hematopoietic stem cells (HSCs) and oxidative stress-induced death of proliferating MPPs. Additionally, alloreactive T cells produced GM-CSF to inhibit MPP expression of Tcf4, the transcription factor essential for pDC development, subverting MPP production of pDCs. GM-CSF did not affect the maturation of pDC precursors. Notably, enhanced recovery of donor pDCs upon adoptive transfer early after allogeneic HSC transplantation repressed GVHD and restored the de novo generation of donor pDCs in recipient mice. pDCs suppressed the proliferation and expansion of activated autologous T cells via a type I IFN signaling-dependent mechanism. They also produced PD-L1 and LILRB4 to inhibit T cell production of IFN-γ. We thus demonstrate that GVHD impairs the reconstitution of tolerogenic donor pDCs by depleting DC progenitors rather than by preventing pDC maturation. MPPs are an important target to effectively bolster pDC reconstitution for controlling GVHD.

Immunomodulation for the Treatment of Fungal Infections: Opportunities and Challenges

Opportunistic fungal infections are major causes of morbidity and mortality in patients with single or multiple defects in their immunity. Antifungal agents targeting the pathogen remain the treatment of choice for fungal infections. However, antifungal agents are toxic to the host mainly due to the close evolutionary similarity of fungi and humans. Moreover, antifungal therapy is ineffective in patients with immunosuppression. For this reason, there is an increased demand to develop novel strategies to enhance immune function and augment the existing antifungal drugs. In recent times, targeting the immune system to improve impaired host immune responses becomes a reasonable approach to improve the effectiveness of antifungal drugs. In this regard, immunomodulating therapeutic agents that turn up the immune response in the fight against fungal infections hold promise for enhancing the efficacy and safety of conventional antifungal therapy. In general, immunomodulating therapies are safe with decreased risk of resistance and broad spectrum of activity. In this review, therefore, clinical evidences supporting the opportunities and challenges of immunomodulation therapies in the treatment of invasive fungal infections are included.

T cell-derived interferon-γ programs stem cell death in immune-mediated intestinal damage

Despite the importance of intestinal stem cells (ISCs) for epithelial maintenance, there is limited understanding of how immune-mediated damage affects ISCs and their niche. We found that stem cell compartment injury is a shared feature of both alloreactive and autoreactive intestinal immunopathology, reducing ISCs and impairing their recovery in T cell-mediated injury models. Although imaging revealed few T cells near the stem cell compartment in healthy mice, donor T cells infiltrating the intestinal mucosa after allogeneic bone marrow transplantation (BMT) primarily localized to the crypt region lamina propria. Further modeling with ex vivo epithelial cultures indicated ISC depletion and impaired human as well as murine organoid survival upon coculture with activated T cells, and screening of effector pathways identified interferon-γ (IFNγ) as a principal mediator of ISC compartment damage. IFNγ induced JAK1- and STAT1-dependent toxicity, initiating a proapoptotic gene expression program and stem cell death. BMT with IFNγ-deficient donor T cells, with recipients lacking the IFNγ receptor (IFNγR) specifically in the intestinal epithelium, and with pharmacologic inhibition of JAK signaling all resulted in protection of the stem cell compartment. In addition, epithelial cultures with Paneth cell-deficient organoids, IFNγR-deficient Paneth cells, IFNγR-deficient ISCs, and purified stem cell colonies all indicated direct targeting of the ISCs that was not dependent on injury to the Paneth cell niche. Dysregulated T cell activation and IFNγ production are thus potent mediators of ISC injury, and blockade of JAK/STAT signaling within target tissue stem cells can prevent this T cell-mediated pathology.

A single-nucleotide polymorphism in the human ENTPD1 gene encoding CD39 is associated with worsened graft-versus-host disease in a humanized mouse model

Regulatory T cells (Tregs) protect against graft-versus-host disease (GVHD), a life-threatening complication of allogeneic hematopoietic stem cell transplantation. The ectoenzyme CD39 is important for increasing the immunosuppressive function of Tregs. The rs10748643 (A → G) single-nucleotide polymorphism (SNP) in intron 1 of the human ENTPD1 gene is associated with increased proportions of CD39⁺ Tregs. This study aimed to determine whether the rs10748643 SNP corresponded to increased proportions of CD39⁺ Tregs in an Australian donor population, and whether this SNP influences clinical GVHD in a humanized mouse model. Donors were genotyped for the rs10748643 SNP by Sanger sequencing, and the proportion of CD39⁺ T cells in donor peripheral blood was determined by flow cytometry. Donors encoding the G allele (donors^AG/GG ) demonstrated higher proportions of CD39⁺ CD3⁺ CD4⁺ CD25⁺ CD127^lo Tregs, but not CD39⁺ CD3⁺ CD8⁺ T cells or CD39⁺ CD3⁺ CD4⁺ conventional T cells, compared with donors homozygous for the A allele (donors^AA ). NOD-SCID-IL2Rγ^null mice were injected with human peripheral blood mononuclear cells from either donors^AA (hCD39^AA mice) or donors^AG/GG (hCD39^AG/GG mice). hCD39^AG/GG mice demonstrated significantly greater weight loss and GVHD clinical scores, and significantly reduced survival, compared with hCD39^AA mice. hCD39^AG/GG mice showed significantly higher hCD4⁺ :hCD8⁺ T-cell ratios than hCD39^AA mice, but displayed similar proportions of CD3⁺ hCD4⁺ hCD25⁺ hCD127^lo Tregs and hCD39⁺ Tregs. However, the proportion of human Tregs corresponded to survival in hCD39^AA mice, but not in hCD39^AG/GG mice. This study demonstrates that donors encoding the G allele show higher percentages of CD39⁺ Tregs, but cause worsened GVHD in humanized mice compared with donors homozygous for the A allele.

Donor-derived IL-17A and IL-17F deficiency triggers Th1 allo-responses and increases gut leakage during acute GVHD

IL-17A and IL-17F cytokines are important regulators of acute graft-versus-host-disease (GVHD). However, contrary effects of these cytokines in inflammatory diseases have been reported. To investigate the effects of donor-derived IL-17A and IL-17F on GVHD, we made use of single (Il17a^-/- or Il17f^-/-) and double deficient (Il17af^-/-) allogeneic donor CD4⁺ T cells. We could demonstrate that transplantation of Il17af^-/- CD4⁺ donor T cells led to aggravated GVHD. However, this phenotype was not observed after transplantation of single, Il17a^-/- or Il17f^-/-, deficient CD4⁺ T cells, suggesting redundant effects of IL-17A and IL-17F. Moreover, Il17af^-/- cell recipients showed an increase of systemic IFNγ, indicating a heightened pro-inflammatory state, as well as infiltration of IFNγ-secreting CD4⁺ T cells in the recipients’ intestinal tract. These recipients exhibited significant gut leakage, and markedly macrophage infiltration in the gastrointestinal epithelial layer. Moreover, we saw evidence of impaired recovery of gut epithelial cells in recipients of Il17af^-/- CD4⁺ T cells. In this study, we show that IL-17A/F double deficiency of donor CD4⁺ T cells leads to accelerated GVHD and therefore highlight the importance of these cytokines. Together, IL-17 cytokines might serve as a brake to an intensified Th1 response, leading to the exacerbated gut damage in acute GVHD.

Anti-Apoptotic Molecule BCL2 Is a Therapeutic Target in Steroid-Refractory Graft-Versus-Host Disease

Graft-versus-host disease (GVHD) is the leading cause of mortality after hematopoietic stem cell transplantation and primarily affects barrier organs such as the skin. One-third of cases are refractory to steroid treatment resulting in poor outcomes and the need for novel therapies. Longitudinal analysis of T-cell transcriptomes in patients before the appearance of GVHD symptoms revealed the upregulation of anti-apoptotic regulator B-cell lymphoma 2 (BCL2) at GVHD initiation. To determine the potential of BCL2 inhibition in active GVHD, we analyzed tissues of 88 patients with acute or chronic GVHD. BCL2 RNA was elevated in multiple organs affected by GVHD and expression correlated with transplant-related mortality and steroid-refractory GVHD. BCL2-expressing lymphocytes were present in skin lesions and peripheral blood of patients with acute and chronic GVHD. Inhibition of BCL2 increased the CD4 to CD8 ratio in allogeneic T cells in vitro and induced apoptosis of T cells from patients with steroid-pretreated chronic GVHD ex vivo. In addition, the higher ratio of regulatory to nonregulatory T cells upon blockage of BCL2 could add to the anti-inflammatory effect of BCL2 blockage. Collectively, our results highlight BCL2 as an important factor for GVHD development and introduce BCL2 inhibition as previously unreported and urgently needed targeted therapy in the treatment of steroid-refractory GVHD.

Validation and evaluation of a common biomarker in human cancers sera protein detected by a monoclonal antibody UNIVmAb

OBJECTIVE

Management and diagnosis of multiple human cancers remains a challenge and search for a common biomarker is still debatable. In this manuscript we have evaluated the use of monoclonal antibody UNIVmAb, to detect the protein (H11) as a common biomarker for all cancers irrespective of the grade and origin. We have shown by both ELISA and Western Blot that the H11 protein, is a unique hyaluronan binding protein that has not been detected earlier. H11 protein was fractionated in an anion exchange column followed by cibacron blue gel exclusion chromatography. Hyaluronan binding H11 protein reacted with Monoclonal antibody UNIVmAb and b-HA inspite of b-Hyaluronan (biotinylated Hyaluronan) interaction and HA-Oligo (Hyaluronan oligosaccharides) competition from various grades of Human cancers sera.

RESULTS

ELISA, Western blot and b-Hyaluronan interactions clearly showed an over-expression of UNIVmAb reacted H11 protein in all fifty cancer's sera when compared with seventy normal sera. UNIVmAb reactive H11 protein can be used as a common biomarker. We believe, UNIVmAb detected H11 protein, is a unique hyaluronan binding protein, that can be used as a common biomarker for all cancers.

Targeting PI3Kδ function for amelioration of murine chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) is a leading cause of morbidity and mortality following allotransplant. Activated donor effector T cells can differentiate into pathogenic T helper (Th)-17 cells and germinal center (GC)-promoting T follicular helper (Tfh) cells, resulting in cGVHD. Phosphoinositide-3-kinase-δ (PI3Kδ), a lipid kinase, is critical for activated T cell survival, proliferation, differentiation, and metabolism. We demonstrate PI3Kδ activity in donor T cells that become Tfh cells is required for cGVHD in a nonsclerodermatous multiorgan system disease model that includes bronchiolitis obliterans (BO), dependent upon GC B cells, Tfhs, and counterbalanced by T follicular regulatory cells, each requiring PI3Kδ signaling for function and survival. Although B cells rely on PI3Kδ pathway signaling and GC formation is disrupted resulting in a substantial decrease in Ig production, PI3Kδ kinase-dead mutant donor bone marrow-derived GC B cells still supported BO cGVHD generation. A PI3Kδ-specific inhibitor, compound GS-649443, that has superior potency to idelalisib while maintaining selectivity, reduced cGVHD in mice with active disease. In a Th1-dependent and Th17-associated scleroderma model, GS-649443 effectively treated mice with active cGVHD. These data provide a foundation for clinical trials of US Food and Drug Administration (FDA)-approved PI3Kδ inhibitors for cGVHD therapy in patients.

Strategies for Enhancing and Preserving Anti-leukemia Effects Without Aggravating Graft-Versus-Host Disease

Allogeneic stem cell transplantation (allo-SCT) is a curable method for the treatment of hematological malignancies. In the past two decades, the establishment of haploidentical transplant modalities make “everyone has a donor” become a reality. However, graft-versus-host disease (GVHD) and relapse remain the major two causes of death either in the human leukocyte antigen (HLA)-matched transplant or haploidentical transplant settings, both of which restrict the improvement of transplant outcomes. Preclinical mice model showed that both donor-derived T cells and natural killer (NK) cells play important role in the pathogenesis of GVHD and the effects of graft-versus-leukemia (GVL). Hence, understanding the immune mechanisms of GVHD and GVL would provide potential strategies for the control of leukemia relapse without aggravating GVHD. The purpose of the current review is to summarize the biology of GVHD and GVL responses in preclinical models and to discuss potential novel therapeutic strategies to reduce the relapse rate after allo-SCT. We will also review the approaches, including optimal donor selection and, conditioning regimens, donor lymphocyte infusion, BCR/ABL-specific CTL, and chimeric antigen receptor-modified T cells, which have been successfully used in the clinic to enhance and preserve anti-leukemia activity, especially GVL effects, without aggravating GVHD or alleviate GVHD.

Cytotoxic Pathways in Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (allo-HCT) is a potentially curative treatment for hematologic malignancies, and other hematologic and immunologic diseases. Donor-derived immune cells identify and attack cancer cells in the patient producing a unique graft-vs.-tumor (GVT) effect. This beneficial response renders allo-HCT one of the most effective forms of tumor immunotherapy. However, alloreactive donor T cells can damage normal host cells thereby causing graft-vs.-host disease (GVHD), which results in substantial morbidity and mortality. To date, GVHD remains as the major obstacle for more successful application of allo-HCT. Of special significance in this context are a number of cytotoxic pathways that are involved in GVHD and GVT response as well as donor cell engraftment. In this review, we summarize progress in the investigation of these cytotoxic pathways, including Fas/Fas ligand (FasL), perforin/granzyme, and cytokine pathways. Many studies have delineated their distinct operating mechanisms and how they are involved in the complex cellular interactions amongst donor, host, tumor, and infectious pathogens. Driven by progressing elucidation of their contributions in immune reconstitution and regulation, various interventional strategies targeting these pathways have entered translational stages with aims to improve the effectiveness of allo-HCT.

Third party, umbilical cord blood derived regulatory T-cells for prevention of graft versus host disease in allogeneic hematopoietic stem cell transplantation: feasibility, safety and immune reconstitution

Incubation of umbilical cord blood (UCB) derived regulatory T-cells (Tregs) with fucosyltransferase enzyme improves their ability to home to the target tissue to prevent graft vs. host disease (GVHD). We report results of 5 patients (Double UCB Transplant, n=2; Peripheral Blood Matched Unrelated Donor Transplant, n=3) who received UCB-Tregs (Dose level = 1×106/kg), infused one day prior to the donor graft. All patients received their designated UCB-Treg dose without any infusion reaction. The ratio of conventional T-cells in donor graft was at least 10 times higher than infused UCB-Tregs (ratio range, 12-356). All patients engrafted at median of 13 days (range, 8-17 days). One patient died due to brain hemorrhage on day 45. A bi-modal increase of plasma IL-10 level occurred on day 7 and day 21 and notably, plasma IL-2 level dropped significantly in all patients at Day 7. All evaluable patients developed ≥grade II acute GVHD and at 1 year follow up, all were alive and without evidence of disease relapse. No increase in the chronic GVHD biomarkers (REG3a and Elafin) was observed at day 7. At the time of last follow up, all evaluable patients were off immune-suppression. Stage 2 of this clinical trial examining UCB-Treg at dose level= 1×107/kg is currently underway.

The impact of cytokine gene polymorphisms on the outcome of HLA matched sibling hematopoietic stem cell transplantation

Graft-versus-host disease (GVHD) is the major complication of allogeneic hematopoietic stem cell transplantation (HSCT); cytokines are recognized as important mediators in its pathogenesis. In this study we investigated the role of cytokine gene polymorphisms on HSCT outcome. A total of 106 patient and 98 donors were genotyped by polymerase chain reaction sequence specific primers (PCR-SSP) based assay for tumor necrosis factor-α-308 (TNFα -308), interleukin (IL)-6-174, IL-10-1082, -819, -592, Interferon-γ+874 (IFN-γ+874), and transforming growth factor-β1 (TGF-β1) codon10 and 25 polymorphisms. Except one in each category, all patients and donors were TNFα -308 high producers and the majority were IL-6-174 high producers (93.3% and 90.8% respectively); a pattern that would alleviate any potential biological impact. Patient's IFN-γ+874 showed significant association with the development of chronic GVHD. Patients with IFN-γ +874 high producer showed an 8 folds likelihood to develop chronic GVHD as compared to those with IFN-γ+874 low producer predicted phenotype (95% CI: 1.59-40.2, p = 0.01). Patient's TGFβ1-codon 10 and 25 high/intermediate producers showed a lower incidence of acute GVHD though it did not achieve statistical significance (p = 0.065) on account of the low frequency of this genotype in our patients and donors (11.4 and 8.2% respectively). Other factors contributing to risk of GVHD included older age for both acute and chronic (p = 0.01 and 0.02 respectively) with age 24 as the best discriminating cutoff; CD34+ cell dose for chronic GVHD (p = 0.045) with a dose of 8 × 10⁶/kg as the best discriminating cutoff; and conditioning regimen with Flu/Bu associated with the lowest incidence of acute GVHD (p = 0.003) and no impact on chronic GVHD. In conclusion the current study further indicates a potential role of some cytokine gene polymorphisms in the development of GVHD. The relative distribution of high and low producer genotypes in different ethnic groups contributes to their biological impact in different populations.

The glucocorticoid receptor in recipient cells keeps cytokine secretion in acute graft-versus-host disease at bay

Graft-versus-host disease (GvHD) is a life-threatening complication of hematopoietic stem cell transplantation (HSCT), which is caused by allogeneic T cells recognizing molecules of the recipient as foreign. Endogenous glucocorticoids (GC) released from the adrenal gland are crucial in regulating such inflammatory diseases. Here we demonstrate that genetically engineered mice, that are largely unresponsive to GC, suffer from aggravated clinical symptoms and increased mortality after HSCT, effects that could be tempered by neutralization of IL-6. Interestingly, selective ablation of the GC receptor (GR) in recipient myeloid cells resulted in fulminant disease as well. While histopathological analysis of the jejunum failed to reveal any differences between sick mice of both genotypes, systemic IL-6 and TNFα secretion was strongly increased in transplanted mice lacking the GR in myeloid cells briefly before the majority of them succumbed to the disease. Collectively, our findings reveal an important role of the GR in recipient cells in limiting the cytokine storm caused by GvHD induction.

Enhanced Immunosuppressive Properties of Human Mesenchymal Stem Cells Primed by Interferon-γ

Mesenchymal stem cells (MSCs) are of particular interest for the treatment of immune-related diseases owing to their immunosuppressive properties. In this study, we aimed to identify the effect of interferon (IFN)-γ priming on immunomodulation by MSCs and elucidate the possible mechanism underlying their properties for the clinical treatment of allogeneic conflicts. Infusion of MSCs primed with IFN-γ significantly reduced the symptoms of graft-versus-host disease (GVHD) in NOD-SCID mice, thereby increasing survival rate when compared with naïve MSC-infused mice. However, infusion of IFN-γ-primed MSCs in which indoleamine 2,3-dioxygenase (IDO) was downregulated did not elicit this effect. The IDO gene was expressed in MSCs via the IFN-γ-Janus kinase (JAK)-signal transducer and activator of transcription 1 (STAT1) pathway, and the infusion of IDO-over-expressing MSCs increased survival rate in an in vivo GVHD model, similar to infusion of IFN-γ-primed MSCs. These data indicate that IFN-γ production by activated T-cells is correlated with the induction of IDO expression in MSCs via the IFN-γ-JAK-STAT1 pathway, which in turn results in the suppression of T-cell proliferation. Our findings also suggest that cell therapy based on MSCs primed with IFN-γ can be used for the clinical treatment of allogeneic conflicts, including GVHD.

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IFN-γ priming enhances the immunosuppressive properties of human MSCs in in vitro and in vivo models.

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IFN-γ priming induces IDO expression in MSCs via the JAK/STAT1 signaling pathway, but TLR3 activation does not.

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Cell therapy using MSCs primed with IFN-γ could be highly effective in treating allogeneic diseases, including GVHD.

It is necessary to improve the function of mesenchymal stem cells (MSCs) to maximize their treatment potential beyond what is currently achieved in cell therapy studies using naïve heterogeneous MSCs. The preclinical study of a candidate cell therapy based on MSCs primed with interferon-γ as reported in this study, could lay the foundation for the use of cell therapy for the treatment of graft-versus-host disease (GVHD), and is very important for the initiation of clinical trials. Our findings also suggest that cell therapy based on functionally improved MSCs could be used for the clinical treatment of allogeneic conflicts.

PD-L1 serves as a double agent in separating GVL from GVHD

Allogeneic hematopoietic cell transplantation (HCT) represents a potentially curative treatment for a variety of hematologic malignancies due to the well-recognized graft-versus-leukemia/lymphoma (GVL) effect that is mediated by donor-derived alloreactive T cells. However, graft-versus-host disease (GVHD) is mediated by the same T cells and remains a significant clinical problem associated with substantial morbidity and mortality. In this issue of the JCI, Ni and colleagues used several murine models of GVHD to evaluate the effect of CD4+ T cell depletion on GVL versus GVHD and revealed that depletion of CD4+ T cells leads to the upregulation of PD-L1 by recipient tissues and donor CD8+ T cells. Interaction of PD-L1 with PD-1 in GVHD-targeted tissues resulted in CD8+ T cell exhaustion and apoptosis, thereby preventing GVHD, whereas PD-L1 interactions with CD80 in lymphoid tissue promoted CD8+ T cell survival and expansion, thereby enhancing the GVL response. By separating these seemingly similar alloreactive T cell responses based on the context of interaction, the results of this study may lay the groundwork for the development of effective clinical strategies to enhance GVL while minimizing GVHD following allogeneic HCT.

Targeting Cytokines in GVHD Therapy

Transplantation of donor-derived allogeneic hematopoietic cells causes increased survival in patients suffering from various blood cancers and other hematologic and immunologic diseases. However, this health benefit is limited to certain patients. One major complication is graft-versus-host disease (GVHD) that occurs when donor-derived immune cells recognize host cells/tissues as foreign and perpetrate subsequent destruction. Cytokines are a major class of effector molecules that are involved in GVHD pathogenesis. Proinflammatory cytokines released by activated immune cells including T cells lead to the onset of GVHD. T cell depletion (TCD) is an effective approach for GVHD prevention. Several immune suppressive drugs are also used to treat GVHD. However, these prophylactic and treatment strategies often lead to an immune compromised state that increases the risk for infection and cancer relapse. Considering the adverse effects of TCD and overall immune suppression, more selective managements such as approaches targeting proinflammatory cytokines have emerged as a promising strategy to control GVHD. Therefore, this work is dedicated to review recent development in the studies of cytokines and their future implication in GVHD therapy.

Programming of donor T cells using allogeneic δ-like ligand 4-positive dendritic cells to reduce GVHD in mice

Alloreactive T cells play a critical role in eliminating hematopoietic malignant cells but are also the mediators of graft-versus-host disease (GVHD), a major complication that subverts the success of allogeneic hematopoietic stem cell transplantation (HSCT). However, induction of alloreactive T cells does not necessarily lead to GVHD. Here we report the development of a cellular programming approach to render alloreactive T cells incapable of causing severe GVHD in both major histocompatibility complex (MHC)-mismatched and MHC-identical but minor histocompatibility antigen-mismatched mouse models. We established a novel platform that produced δ-like ligand 4-positive dendritic cells (Dll4(hi)DCs) from murine bone marrow using Flt3 ligand and Toll-like receptor agonists. Upon allogeneic Dll4(hi)DC stimulation, CD4(+) naïve T cells underwent effector differentiation and produced high levels of interferon γ (IFN-γ) and interleukin-17 in vitro, depending on Dll4 activation of Notch signaling. Following transfer, allogeneic Dll4(hi)DC-induced T cells were unable to mediate severe GVHD but preserved antileukemic activity, significantly improving the survival of leukemic mice undergoing allogeneic HSCT. This effect of Dll4(hi)DC-induced T cells was associated with their impaired expansion in GVHD target tissues. IFN-γ was important for Dll4(hi)DC programming to reduce GVHD toxicities of alloreactive T cells. Absence of T-cell IFN-γ led to improved survival and expansion of Dll4(hi)DC-induced CD4(+) T cells in transplant recipients and caused lethal GVHD. Our findings demonstrate that Dll4(hi)DC programming can overcome GVHD toxicity of donor T cells and produce leukemia-reactive T cells for effective immunotherapy.

Dendritic polyglycerol sulfate attenuates murine graft-versus-host disease

Graft-versus-host disease (GvHD) is a severe immune reaction commonly occurring after hematopoietic stem cell transplantation. The outcome of patients who do not respond to the currently used immunosuppressive drugs is poor, thus there is an urgent need for the evaluation of new therapies. Heparin has a well-known anti-inflammatory effect and heparin analogues with a low anticoagulant effect are interesting candidates as new anti-inflammatory drugs. We explored the therapeutic potential of dendritic polyglycerol sulfates (dPGS), a novel class of heparin derivatives, on murine acute GvHD in vivo. The therapeutic effect of dPGS on murine GvHD was more intense after intravenous application compared to subcutaneous injection. An increased survival rate and improved clinical scores were observed in mice treated with 5 mg/kg once a week. In these animals, there was a reduction in the percentage of CD4(+) and CD8(+) T cells, which are the main effectors of GvHD. In addition, dPGS treatment decreased the number of tumor necrosis factor alpha (TNFα)-producing T cells. Increasing the dose of dPGS reversed the positive effect on survival as well as the clinical score, which indicates a small therapeutic range. Here, we report for the first time that dPGS have a significant immunosuppressive in vivo effect in a mouse model of severe acute GvHD. Therefore, we propose to study dPGS as promising candidates for the development of potential new drugs in the treatment of steroid-refractory GvHD patients first in larger animals and later in humans.

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.

IFN-γ mediates graft-versus-breast cancer effects via enhancing cytotoxic T lymphocyte activity

Previous studies have demonstrated the beneficial effect of graft-versus-tumor (GVT) following hematopoietic stem cell transplantation (HSCT) on the incidence of leukemia relapse and the overall survival rate of patients with leukemia; however, detailed mechanisms underlying the effects GVT exhibits on solid tumors following allogeneic HSCT are yet to be elucidated. The aim of the present study was to investigate the immune mechanism underlying the effect of interferon (IFN)-γ on GVT following allogeneic HSCT in breast cancer therapy. An in situ breast cancer mouse model was established by injecting 5×10⁴ 4T1 cells into the mammary fat pads of BALB/c mice. The 4T1 cells were transfected with the firefly luciferase reporter gene in order to monitor the tumor progression in real time. An allogeneic HSCT model was then established by transplanting bone marrow mononuclear cells from C57BL/6 mice to the BALB/c mice. To investigate the influence of T lymphocyte proliferation following allogeneic bone marrow transplantation, the levels of CD3⁺CD8⁺ cytotoxic T lymphocytes (CTLs) and CD4⁺CD25⁺ regulatory T cells were determined. In addition, IFN-γ and granzyme B expression levels in splenic lymphocytes were analyzed using flow cytometry. Allogeneic HSCT was found to significantly promote the proliferation and cytotoxicity of CTLs and suppress the growth of breast cancer. Furthermore, the secretory levels of IFN-γ and granzyme B by T cells were elevated following allogeneic HSCT. These results indicated that alloreactive T cells increased the secretion of IFN-γ, which promoted the alloresponse of donor CTLs. In addition, the CTLs produced granzyme B, which exerted a tumor suppressive effect.

Allogeneic Th1 cells home to host bone marrow and spleen and mediate IFNγ-dependent aplasia

Bone marrow graft failure and poor graft function are frequent complications after hematopoietic stem cell transplantation and result in significant morbidity and mortality. Both conditions are associated with graft-versus-host disease (GVHD), although the mechanism remains undefined. Here we show, in 2 distinct murine models of GVHD (complete MHC- and class II-disparate) that mimic human peripheral blood stem cell transplantation, that Th1 CD4(+) cells induce bone marrow failure in allogeneic recipients. Bone marrow failure after transplantation of allogeneic naïve CD4(+) T cells was associated with increased CD4(+) Th1 cell development within bone marrow and lymphoid tissues. Using IFNγ-reporter mice, we found that Th1 cells generated during GVHD induced bone marrow failure after transfers into secondary recipients. Homing studies demonstrated that transferred Th1 cells express CXCR4, which was associated with accumulation within bone marrow and spleen. Allogeneic Th1 cells were activated by radiation-resistant host bone marrow cells and induced bone marrow failure through an IFNγ-dependent mechanism. Thus, allogeneic Th1 CD4(+) cells generated during GVHD traffic to hematopoietic sites and induce bone marrow failure via IFNγ-mediated toxicity. These results have important implications for prevention and treatment of bone marrow graft failure after hematopoietic stem cell transplantation.

Activated CD8 T cells acquire NK1.1 expression and preferentially locate in the liver in mice after allogeneic hematopoietic cell transplantation

Immune cells expressing both NK and T cell markers include CD1d-dependent NKT cells and CD1d-independent NKT-like cells. We now describe the presence of NK1.1(+)CD8(+) T cells in the liver, but not other tissues (spleen, bone marrow, thymus or peripheral blood) in mice receiving allogeneic hematopoietic cell transplantation (allo-HCT). These cells are CD1d-independent TCRαβ(+) T cells with an effector/memory CD44(hi)CD62L(-) phenotype, and do not express Ly49 receptors. Furthermore, these cells were derived from donor splenocytes, but not bone marrow cells. Depletion of CD8(+), but not NK1.1(+), cells from donor splenocytes prior to transplantation prevented the generation of NK1.1(+)CD8(+) T cells, indicating that these cells arose from donor NK1.1(-)CD8(+) splenic T cells. These results provide direct evidence that donor CD8(+) T cells can acquire NK1.1 expression upon activation in allo-HCT recipients and that these NK1.1(+)CD8(+) NKT-like cells maintain an effector/memory phenotype and persist in the recipients with preferential localization in the liver.

Donor bone marrow-derived T cells inhibit GVHD induced by donor lymphocyte infusion in established mixed allogeneic hematopoietic chimeras

Delayed administration of donor lymphocyte infusion (DLI) to established mixed chimeras has been shown to achieve anti-tumor responses without graft-vs.-host disease (GVHD). Herein we show that de novo donor BM-derived T cells that are tolerant of the recipients are important in preventing GVHD in mixed chimeras receiving delayed DLI. Mixed chimeras lacking donor BM-derived T cells developed significantly more severe GVHD than those with donor BM-derived T cells after DLI, even though both groups had comparable levels of total T cells at the time of DLI. Post-DLI depletion of donor BM-derived T cells in mixed chimeras, as late as 20 days after DLI, also provoked severe GVHD. Although both CD4 and CD8 T cells contributed to the protection, the latter were significantly more effective, suggesting that inhibition of GVHD was not mainly mediated by CD4 regulatory T cells. The lack of donor BM-derived T cells was associated with markedly increased accumulation of DLI-derived alloreactive T cells in parenchymal GVHD target tissues. Thus, donor BM-derived T cells are an important factor in determining the risk of GVHD and therefore, offer a potential therapeutic target for preventing and ameliorating GVHD in the setting of delayed DLI in established mixed chimeras.

IFN-γ production by allogeneic Foxp3+ regulatory T cells is essential for preventing experimental graft-versus-host disease

It is emerging that CD4+Foxp3+ regulatory T (Treg) cells can produce the proinflammatory cytokine IFN-γ when stimulated in a Th1 cytokine environment. In this study, we report that Foxp3+ Treg cells readily produced IFN-γ in vivo in a highly inflammatory model of graft-versus-host disease (GVHD) and during a Th1-dominated immune response to intracellular bacteria. Moreover, stimulation in vitro via TCR in the presence of IL-12 alone was sufficient to induce IFN-γ production by Treg cells in a dose-dependent manner. Transfer of donor Treg cells can prevent lethal GVHD; therefore, we used this model as a robust readout for in vivo Treg function. Interestingly, >50% of allogeneic donor, but not residual recipient Foxp3+ Treg cells produced IFN-γ after transplantation, suggesting that this cytokine production was alloantigen specific. These IFN-γ producers were stable Foxp3+ Treg cells because methylation analysis of the Foxp3 gene locus of transferred and reisolated Treg cells during GVHD showed a fully demethylated Treg-specific-demethylated region. Next, we addressed whether IFN-γ production was supporting or rather impairing the immunosuppressive function of Treg cells during GVHD. Blocking of IFN-γ with specific mAb completely abolished the beneficial effect of donor Treg cells. We could further show that only wild-type Treg cells, but not Treg cells from IFN-γ-deficient donor mice, prevented GVHD. This indicated that Treg cell-intrinsic IFN-γ production was required for their protective function. In conclusion, our data show that IFN-γ produced by Foxp3+ Treg cells has essential immune-regulatory functions that are required for prevention of experimental GVHD.

The interferon-dependent orchestration of innate and adaptive immunity after transplantation

The therapeutic GVL effect after allogeneic stem cell transplantation is limited by the development of GVHD. The ultimate aim of current research is to separate the 2 processes in a meaningful fashion. The IFNs are a pleiotropic group of cytokines that were originally recognized because of their ability to interfere with viral replication. However, it is now established that these cytokines play an important role in orchestrating both innate and adaptive immunity. Multiple studies have investigated the effects of both types I and II IFN on GVHD and GVL in preclinical transplant models. The results indicate variable effects that are dependent on the period of activity within the developing immune response, the presence and type of pretransplant conditioning and the differential mechanisms, and IFN sensitivity of immune pathology within individual target organs during GVHD. This Perspective discusses the current literature on the IFNs and their potential modulation within clinical transplantation, focusing particularly on enhancing the therapeutic GVL effects.

IFN-γ and indoleamine 2,3-dioxygenase signaling between donor dendritic cells and T cells regulates graft versus host and graft versus leukemia activity

Allogeneic hematopoietic stem cell transplantation (HSCT) can eradicate chemorefractory leukemia through the graft-versus-leukemia (GVL) activity of donor T cells. However, the clinical success of allo-HSCT is limited by the graft-versus-host disease (GVHD) activity of donor T cells. We have reported previously that donor bone marrow precursors of plasmacytoid dendritic cells (pre-pDCs) can activate donor T cells toward T-helper 1 immune polarization in murine allogeneic HSCT. To optimize the GVL activity of these activated donor T cells and limit their graft versus host activity, we engineered the cellular constituents of an allogeneic hematopoietic stem cell graft with highly purified hematopoietic stem cells, T cells, and pre-pDCs and studied their GVL and GVHD activities in a murine model of allogeneic HSCT. Transplanted donor pre-pDCs expanded in vivo for 2 weeks after transplant, and they markedly augmented the activation and GVL activity of donor T cells while attenuating their GVHD activity, leading to an improved therapeutic index. Bidirectional signaling between donor T cells and donor pDCs with IFN-γ synthesis by donor T cells inducing indoleamine 2,3-dioxygenase synthesis by donor pDCs limited GVHD by altering the balance between donor T-reg and inflammatory T cells. Manipulating the content of donor DC precursors in allogeneic HSCT is a novel method to optimize the balance between GVL and GVHD.

Role of IFN-γ in the establishment of anterior chamber-associated immune deviation (ACAID)-induced CD8+ T regulatory cells

Introduction of alloantigens into the AC induces a form of immune tolerance known as ACAID, which induces antigen-specific CD8+ Tregs, contributing to ocular immune privilege by down-regulating immune responses. Recent evidence suggests IFN-γ is needed for the suppressive function of CD8+ ACAID Tregs. This study tested the hypothesis that IFN-γ is needed for alloantigen-specific ACAID CD8+ Tregs to execute their suppressive function but is not required for the establishment of ACAID CD8+ Tregs. To address this hypothesis, ACAID was induced by injecting BALB/c spleen cells into the AC of WT C57BL/6 mice, IFN-γ(-/-) C57BL/6 mice, or anti-IFN-γ-treated WT C57BL/6 mice. LAT assays using C57BL/6 APCs as stimulators, CD4+ T cells from C57BL/6 mice previously immunized toward BALB/c alloantigens as effector cells, and IFN-γ-competent, IFN-γ(-/-), or IFN-γR(-/-) CD8+ Tregs were used to evaluate the suppressive function of CD8+ ACAID Tregs in response to IFN-γ. IFN-γ(-/-) mice or mice treated with anti-IFN-γ antibody prior to AC injection of alloantigen failed to develop ACAID. The suppressive function of IFN-γ(-/-) ACAID CD8+ Tregs was restored through the administration of exogenous IFN-γ. This suppressive responsiveness toward IFN-γ was CD8+ Treg-intrinsic, as CD8+ Tregs from IFN-γR(-/-) mice, which were primed in the AC with alloantigens, were not able to suppress alloantigen-specific DTH responses. These results indicate that IFN-γ is not needed for the induction of CD8+ ACAID Tregs but is required for ACAID Tregs to exert the suppression of allospecific DTH responses.

IFN-γ promotes graft-versus-leukemia effects without directly interacting with leukemia cells in mice after allogeneic hematopoietic cell transplantation

The ability of IFN-γ to enhance graft-versus-leukemia (GVL) activity without direct interaction with leukemia cells was examined by comparing GVL effects against IFN-γ receptor-deficient (GRKO) leukemia between wild-type (WT) and IFN-γ-deficient (GKO) allogeneic hematopoietic cell transplantation (allo-HCT). We established a primary IFN-γ-unresponsive T-cell leukemia model using virally-transduced GRKO B6 mouse bone marrow cells overexpressing Notch1. We first assessed GVL effects in lethally-irradiated B6 mice receiving CD4-depleted allo-HCT from WT or GKO BALB/c donors. Administration of CD4(+) cell-depleted allo-HCT from WT, but not GKO, BALB/c donors mediated significant GVL effects against GRKO leukemia. Similar results were obtained in pre-established allogeneic chimeras receiving delayed donor lymphocyte infusion (DLI). Although both WT and GKO DLI achieved significant anti-tumor responses, the former was markedly stronger than the latter. These data indicate that IFN-γ is capable of promoting GVL effects via mechanisms independent of its interaction with leukemia cells.

Absence of Stat1 in donor CD4⁺ T cells promotes the expansion of Tregs and reduces graft-versus-host disease in mice

STAT1 is the main signal transducer for type I and II IFNs and plays a central role in the regulation of innate and adaptive immune responses. We used Stat1-deficient mice to test the role of donor Stat1 in MHC-matched minor histocompatibility antigen-mismatched (mHA-mismatched) and fully MHC-mismatched models of bone marrow transplantation. Lack of Stat1 in donor splenocytes reduced graft-versus-host disease (GVHD) in both immunogenetic disparities, leading to substantially attenuated morbidity and mortality. Donor Stat1 deficiency resulted in reduced alloantigen-induced activation and expansion of donor T cells and correlated with the expansion of CD4+CD25+Foxp3+ Tregs in vivo. This expansion of Tregs was further confirmed by studies showing that Stat1 deficiency promoted the proliferation, while inhibiting the apoptosis, of natural Tregs, and that absence of Stat1 enhanced the induction of inducible Tregs both in vitro and in vivo. Ex vivo expanded Stat1-/- Tregs were superior to wild-type Tregs in suppressing alloantigen-driven expansion of T cells in vitro and in inhibiting the development of GVHD. These observations demonstrate that Stat1 is a regulator of Tregs and that targeting Stat1 in CD4+ T cells may facilitate in vitro and in vivo expansion of Tregs for therapeutic use.

Graft-versus-host disease is enhanced by extracellular ATP activating P2X7R

Danger signals released upon cell damage can cause excessive immune-mediated tissue destruction such as that found in acute graft-versus-host disease (GVHD), allograft rejection and systemic inflammatory response syndrome. Given that ATP is found in small concentrations in the extracellular space under physiological conditions, and its receptor P2X(7)R is expressed on several immune cell types, ATP could function as a danger signal when released from dying cells. We observed increased ATP concentrations in the peritoneal fluid after total body irradiation, and during the development of GVHD in mice and in humans. Stimulation of antigen-presenting cells (APCs) with ATP led to increased expression of CD80 and CD86 in vitro and in vivo and actuated a cascade of proinflammatory events, including signal transducer and activator of transcription-1 (STAT1) phosphorylation, interferon-γ (IFN-γ) production and donor T cell expansion, whereas regulatory T cell numbers were reduced. P2X(7)R expression increased when GVHD evolved, rendering APCs more responsive to the detrimental effects of ATP, thereby providing positive feedback signals. ATP neutralization, early P2X(7)R blockade or genetic deficiency of P2X(7)R during GVHD development improved survival without immune paralysis. These data have major implications for transplantation medicine, as pharmacological interference with danger signals that act via P2X(7)R could lead to the development of tolerance without the need for intensive immunosuppression.

Differential gene expression in acute lymphoblastic leukemia cells surviving allogeneic transplant

The effectiveness of allogeneic graft-versus-leukemia (GVL) activity in control of acute lymphoblastic leukemia is generally regarded as poor. One possible factor is dynamic adaptation of the leukemia cell to the allogeneic environment. This work tested the hypothesis that the pattern of gene expression in acute lymphoblastic leukemia cells in an allogeneic environment would differ from that in a non-allogeneic environment. Expression microarray studies were performed in murine B lineage acute lymphoblastic leukemia cells recovered from mice that had undergone allogeneic MHC-matched but minor histocompatibility antigen mismatched transplants. A limited number of genes were found to be differentially expressed in ALL cells surviving in the allogeneic environment. Functional analysis demonstrated that genes related to immune processes, antigen presentation, ubiquitination and GTPase function were significantly enriched. Several genes with known immune activities potentially relevant to leukemia survival (Ly6a/Sca-1, TRAIL and H2-T23) were examined in independent validation experiments. Increased expression in vivo in allogeneic hosts was observed, and could be mimicked in vitro with soluble supernatants of mixed lymphocyte reactions or interferon-gamma. The changes in gene expression were reversible when the leukemia cells were removed from the allogeneic environment. These findings suggest that acute lymphoblastic leukemia cells respond to cytokines present after allogeneic transplantation and that these changes may reduce the effectiveness of GVL activity.

Transplant long-surviving induced by CD40-CD40 ligand costimulation blockade is dependent on IFN-γ through its effect on CD4(+)CD25(+) regulatory T cells

BACKGROUND

IFN-γ was documented to be commonly associated with acute rejection. In the present study, we investigated the role of IFN-γ in the transplant long-surviving induced by blocking CD40-CD40 ligand (CD40-CD40L) costimulation and its mechanisms.

METHODS

IFN-γ expression in cardiac allografts and spleens from syngeneic and allogeneic recipients with or without anti-CD40L monoclonal antibody (MR-1) treatment was examined by real-time RT-PCR. The grafts survival time in Wild type (IFN-γ(+/+)) and IFN-γ deficient (IFN-γ(-/-)) recipients was investigated. Mixed lymphocyte reaction (MLR) of CD4(+) T cells and cytotoxic T lymphocyte (CTL) assay of CD8(+) T cells were also studied. FoxP3 expression in allografts and spleens from IFN-γ(+/+) or IFN-γ(-/-) recipients with MR-1 treatment was examined. Furthermore, FoxP3, IL-10 and CTLA-4 expressions and the suppressive capability of CD4(+)CD25(+) regulatory T cells were examined.

RESULTS

Rejected allografts showed significantly higher IFN-γ expression than long-surviving allografts. Allograft survival was not prolonged in nonimmunosuppressed IFN-γ(-/-) mice. Administration of MR-1 induced long-term survival in 90.1% of IFN-γ(+/+) recipients (98±6.6 days) but failed to do so in IFN-γ(-/-) group (16.2±4.0 days). IFN-γ(-/-) recipients facilitated the proliferation and CTL generation of T cells. The allografts and spleens from IFN-γ(+/+) recipients contained higher FoxP3 expression than IFN-γ(-/-) recipients. Moreover, CD4(+)CD25(+) T cells from IFN-γ(+/+) recipients displayed a higher FoxP3 and IL-10 expression and suppressive capability.

CONCLUSION

IFN-γ plays an important role in the long-surviving induced by blocking CD40-CD40L through inhibiting the function of activated T cells and increasing suppressive capability of CD4(+)CD25(+) regulatory T cells.

Subclinical GvHD in non-irradiated F1 hybrids: severe lymphoid-tissue GvHD causing prolonged immune dysfunction

GvHD is an important complication of allogeneic hematopoietic SCT. Parent-in-F1 models are frequently used to study GvHD immunobiology; the characteristics of parent-in-F1 GvHD vary between strain combinations and induction protocols. Here, we observed that a high-dose challenge of non-irradiated B6DBA2F1 and B6SJLF1 recipients with C57BL/6 splenocytes left the majority of recipients clinically healthy, while inducing progressive high-grade donor T-cell chimerism. We investigated this previously undescribed pattern of parent-in-F1 T-cell alloreactivity and studied the effect of serial parental splenocyte infusions on epithelial and lymphohematopoietic tissues. The majority of recipients of 4 weekly splenocyte infusions showed long-term survival with gradual establishment of high-grade donor chimerism and without any signs of epithelial-tissue GvHD. A minority of recipients showed BM failure type of GvHD and, respectively, graft rejection. Moreover, long-term F1 chimeras showed protracted pancytopenia, and in peripheral lymphoid tissues severe lymphopenia and near-complete eradication of APCs and dysfunction in antigen-presenting capacity in remaining APC. Hematopoiesis and lymphoid tissue composition recovered only after multilineage donor chimerism had established. In conclusion, we report on a novel type of parent-in-F1 hybrid GvHD, where a cumulative high dose of C57BL/6 parental splenocytes in non-irradiated F1 mice induces subclinical but severe hematolymphoid-tissue GvHD, causing prolonged immuno-incompetence.

Altered effector CD4+ T cell function in IL-21R-/- CD4+ T cell-mediated graft-versus-host disease

We previously showed that transplantation with IL-21R gene-deficient splenocytes resulted in less severe graft-versus-host disease (GVHD) than was observed with wild type splenocytes. In this study, we sought to find mechanism(s) explaining this observation. Recipients of donor CD4(+) T cells lacking IL-21R exhibited diminished GVHD symptoms, with reduced inflammatory cell infiltration into the liver and intestine, leading to prolonged survival. After transplantation, CD4(+) T cell numbers in the spleen were reduced, and MLR and cytokine production by CD4(+) T cells were impaired. These results suggest that IL-21 might promote GVHD through enhanced production of effector CD4(+) T cells. Moreover, we found that CD25 depletion altered neither the impaired MLR in vitro nor the ameliorated GVHD symptoms in vivo. Thus, the attenuated GVHD might be caused by an impairment of effector T cell differentiation itself, rather than by an increase in regulatory T cells and suppression of effector T cells.

Indoleamine 2,3-dioxygenase in human hematopoietic stem cell transplantation

In recent years tryptophan metabolism and its rate limiting enzyme indoleamine 2,3-dioxygenase (IDO) have attracted increasing attention for their potential to modulate immune responses including the regulation of transplantation tolerance. The focus of this review is to discuss some features of IDO activity which particularly relate to hematopoietic stem cell transplantation (HSCT). HSCT invariably involves the establishment of some degree of a donor-derived immune system in the recipient. Thus, the outstanding feature of tolerance in HSCT is that in this type of transplantation it is not rejection, which causes the most severe problems to HSCT recipients, but the reverse, graft-versus-host (GvH) directed immune responses. We will discuss the peculiar role of IDO activity and accelerated tryptophan metabolism at the interface between immune activation and immune suppression and delineate from theoretical and experimental evidence the potential significance of IDO in mediating tolerance in HSCT. Finally, we will examine therapeutic options for exploitation of IDO activity in the generation of allo-antigen-specific tolerance, i.e. avoiding allo-reactivity while maintaining immunocompetence, in HSCT.

Constitutively active Stat5b in CD4+ T cells inhibits graft-versus-host disease lethality associated with increased regulatory T-cell potency and decreased T effector cell responses

Overexpression of a constitutively active form of Stat5b (Stat5b-CA) increases regulatory T cells (Tregs). We show that Stat5b-CA transgenic (TG) CD4(+) T cells had a markedly reduced graft-versus-host disease (GVHD) capacity versus wild-type (WT) T cells. Stat5b-CA TG versus WT CD4(+) T cells had a higher proportion of Tregs, which were superior in suppressing alloresponses mediated by CD4(+)CD25(-) effector T cells (Teffs). By day 5 after transplantation, Stat5b-CA TG Tregs had expanded approximately 3-fold more than WT Tregs. Purified Stat5b-CA TG Tregs added to WT CD4(+)CD25(-) Teffs were superior on a per-cell basis for inhibiting GVHD versus WT Tregs. Surprisingly, rigorously Treg-depleted Stat5b-CA TG versus WT CD4(+)CD25(-) Teffs caused less GVHD lethality associated with diminished Teff proinflammatory and increased Th2 anti-inflammatory cytokine responses. Reduced GVHD by Stat5b-CA TG versus WT Teffs could not be explained by conversion into Tregs in day 10 posttransplantation spleen or small intestine. In addition, Stat5b-CA TG Teffs retained a graft-versus-leukemia response. These results indicate a major role for Stat5 in Treg expansion and potency along with a lesser but significant role in Teff activation and suggest a strategy of pharmacologic Stat5b up-regulation as a means of decreasing GVHD while retaining a graft-versus-leukemia effect.

IFN-gamma-receptor signaling ameliorates transplant vasculopathy through attenuation of CD8+ T-cell-mediated injury of vascular endothelial cells

Occlusive transplant vasculopathy (TV) is the major cause for chronic graft rejection. Since endothelial cells (EC) are the first graft cells encountered by activated host lymphocytes, it is important to delineate the molecular mechanisms that coordinate the interaction of EC with activated T cells. Here, the interaction of CD8(+) T cells with Ag-presenting EC in vivo was examined using a transgenic heart transplantation model with beta-galactosidase (beta-gal) expression exclusively in EC (Tie2-LacZ hearts). We found that priming with beta-gal peptide-loaded DC failed to generate a strong systemic IFN-gamma response, but elicited pronounced TV in both IFN-gamma receptor (IFNGR)-competent, and ifngr(-/-) Tie2-LacZ hearts. In contrast, stimulation of EC-specific CD8(+) T cells with beta-gal-recombinant mouse cytomegalovirus (MCMV-LacZ) in recipients of ifngr(+/+) Tie2-LacZ hearts did not precipitate significant TV. However, MCMV-LacZ infection of recipients of ifngr(-/-) Tie2-LacZ hearts led to massive activation of beta-gal-specific CD8 T cells, and led to development of fulminant TV. Further analyses revealed that the strong systemic IFN-gamma "storm" associated with MCMV infection induced upregulation of programmed death-1 ligand 1 (PD-L1) on EC, and subsequent attenuation of programmed death-1 (PD-1)-expressing EC-specific CD8(+) T cells. Thus, IFNGR signaling in ECs activates a potent peripheral negative feedback circuit that protects vascularized grafts from occlusive TV.

Dichotomous role of interferon-gamma in allogeneic bone marrow transplant

Interferon (IFN)-gamma is a pleiotropic cytokine with a central role in innate and adaptive immunity. As a potent pro-inflammatory and antitumor cytokine, IFN-gamma is conventionally thought to be responsible for driving cellular immune response. On the other hand, accumulating evidence suggests that IFN-gamma also has immunosuppressive activity. An important role for IFN-gamma in inhibiting graft-versus-host disease (GVHD) has been demonstrated in murine models, despite IFN-gamma being one of the key factors amplifying T cell activation during the process of acute GVHD (aGVHD), the major complication and cause of post-transplant mortality in allogeneic bone marrow transplantation (BMT). At the same time, IFN-gamma facilitates graft-versus-leukemia (GVL) activity. Dissociation of GVL effects from GVHD has been the ultimate goal of allogeneic BMT in the treatment of hematologic malignancies. This paradoxic role of IFN-gamma makes modulating its activity a promising strategy to maximize GVL while minimizing GVHD and improve clinical outcomes in BMT. In this review, the effects of IFN-gamma on GVHD and GVL are discussed with consideration of the mechanism of IFN-gamma action.

Inducing the tryptophan catabolic pathway, indoleamine 2,3-dioxygenase (IDO), for suppression of graft-versus-host disease (GVHD) lethality

During graft-versus-host disease (GVHD), donor T cells become activated and migrate to tissue sites. Previously, we demonstrated a crucial role for the immunosuppressive enzyme indoleamine 2,3-dioxygenase (IDO) in GVHD regulation. Here, we show that upon arrival in the colon, activated donor T cells produced interferon-gamma that up-regulated IDO, causing T-cell anergy and apoptosis. IDO induces GCN2 kinase, up-regulating a T-cell stress response implicated in IDO immunosuppression. Donor T cells did not require GCN2 kinase to respond to IDO, suggesting toxic IDO metabolites, and not tryptophan depletion, were responsible for suppression. When exogenous metabolites were administered, GVHD lethality was reduced. To determine whether IDO could be induced before transplantation for enhanced GVHD suppression, we first determined whether antigen-presenting cells (APCs) or epithelial cells were primarily responsible for IDO expression and subsequent GVHD suppression. Recipients with wild-type versus IDO(-/-) APCs had increased survival, regardless of epithelial-cell expression of IDO, suggesting that APCs were suitable targets for inducing IDO. Administration of an agonist to toll-like receptor-7/8, a receptor expressed primarily on APCs, induced IDO and reduced injury in the colon and ameliorated lethality. We conclude that IDO up-regulation may have therapeutic potential for preventing GVHD in the clinic.