Reciprocal differentiation and tissue-specific pathogenesis of Th1, Th2, and Th17 cells in graft-versus-host disease

Targeting Histone Deacetylases to Modulate Graft-Versus-Host Disease and Graft-Versus-Leukemia

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the main therapeutic strategy for patients with both malignant and nonmalignant disorders. The therapeutic benefits of allo-HSCT in malignant disorders are primarily derived from the graft-versus-leukemia (GvL) effect, in which T cells in the donor graft recognize and eradicate residual malignant cells. However, the same donor T cells can also recognize normal host tissues as foreign, leading to the development of graft-versus-host disease (GvHD), which is difficult to separate from GvL and is the most frequent and serious complication following allo-HSCT. Inhibition of donor T cell toxicity helps in reducing GvHD but also restricts GvL activity. Therefore, developing a novel therapeutic strategy that selectively suppresses GvHD without affecting GvL is essential. Recent studies have shown that inhibition of histone deacetylases (HDACs) not only inhibits the growth of tumor cells but also regulates the cytotoxic activity of T cells. Here, we compile the known therapeutic potential of HDAC inhibitors in preventing several stages of GvHD pathogenesis. Furthermore, we will also review the current clinical features of HDAC inhibitors in preventing and treating GvHD as well as maintaining GvL.

Bendamustine with total body irradiation conditioning yields tolerant T-cells while preserving T-cell-dependent graft-versus-leukemia

Graft-versus-host disease (GvHD) remains a significant impediment to allogeneic hematopoietic cell transplantation (HCT) success, necessitating studies focused on alleviating GvHD, while preserving the graft-versus-leukemia (GvL) effect. Based on our previous studies showing bendamustine with total body irradiation (BEN-TBI) conditioning reduces GvHD compared to the current clinical standard of care cyclophosphamide (CY)-TBI in a murine MHC-mismatched bone marrow transplantation (BMT) model, this study aimed to evaluate the role and fate of donor T-cells following BEN-TBI conditioning. We demonstrate that BEN-TBI reduces GvHD compared to CY-TBI independently of T regulatory cells (Tregs). BEN-TBI conditioned mice have a smaller proportion and less activated donor T-cells, with lower CD47 expression, early post-transplant, but no sustained phenotypic differences in T-cells. In BEN-TBI conditioned mice, donor T-cells gain tolerance specific to host MHC antigens. Though these T-cells are tolerant to host antigens, we demonstrate that BEN-TBI preserves a T-cell-dependent GvL effect. These findings indicate that BEN-TBI conditioning reduces GvHD without compromising GvL, warranting its further investigation as a potentially safer and more efficacious clinical alternative to CY-TBI.

PRMT5 regulates T cell interferon response and is a target for acute graft-versus-host disease

Acute graft-versus-host disease (aGVHD) is a T cell-mediated immunological disorder and the leading cause of nonrelapse mortality in patients who receive allogeneic hematopoietic cell transplants. Based on recent observations that protein arginine methyltransferase 5 (PRMT5) and arginine methylation are upregulated in activated memory T cells, we hypothesized that PRMT5 is involved in the pathogenesis of aGVHD. Here, we show that PRMT5 expression and enzymatic activity were upregulated in activated T cells in vitro and in T cells from mice developing aGVHD after allogeneic transplant. PRMT5 expression was also upregulated in T cells of patients who developed aGVHD after allogeneic hematopoietic cell transplant compared with those who did not develop aGVHD. PRMT5 inhibition using a selective small-molecule inhibitor (C220) substantially reduced mouse and human allogeneic T cell proliferation and inflammatory IFN-γ and IL-17 cytokine production. Administration of PRMT5 small-molecule inhibitors substantially improves survival, reducing disease incidence and clinical severity in mouse models of aGVHD without adversely affecting engraftment. Importantly, we show that PRMT5 inhibition retained the beneficial graft-versus-leukemia effect by maintaining cytotoxic CD8+ T cell responses. Mechanistically, we show that PRMT5 inhibition potently reduced STAT1 phosphorylation as well as transcription of proinflammatory genes, including interferon-stimulated genes and IL-17. Additionally, PRMT5 inhibition deregulates the cell cycle in activated T cells and disrupts signaling by affecting ERK1/2 phosphorylation. Thus, we have identified PRMT5 as a regulator of T cell responses and as a therapeutic target in aGVHD.

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.

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.

The primacy of gastrointestinal tract antigen-presenting cells in lethal graft-versus-host disease

Allogeneic stem cell transplantation is a cornerstone of curative therapy for high-risk and/or advanced hematological malignancies but remains limited by graft-versus-host disease (GVHD). GVHD is initiated by the interaction between recipient antigen-presenting cells (APCs) and donor T cells, culminating in T-cell differentiation along pathogenic type-1 and type-17 paradigms at the expense of tolerogenic regulatory T-cell patterns. Type-1 and type-17 T cells secrete cytokines (eg, granulocyte-macrophage colony-stimulating factor and interferon-γ) critical to the cytokine storm that amplifies expansion of donor APCs and their alloantigen presentation. It has become increasingly clear that pathogenic donor T-cell differentiation is initiated by both professional recipient APCs (eg, dendritic cells [DCs]) and nonprofessional APCs (eg, epithelial and mesenchymal cells), particularly within the gastrointestinal (GI) tract. In the immediate peritransplantation period, these APCs are profoundly modified by pathogen-associated molecular pattern (PAMP)/damage-associated molecular pattern (DAMP) signals derived from conditioning and intestinal microbiota. Subsequently, donor DCs in the GI tract are activated by DAMP/PAMP signals in the colon that gain access to the lamina propria once the mucosal barrier mucosa is compromised by GVHD. This results in donor DC expansion and alloantigen presentation in the colon and subsequent migration into the mesenteric lymph nodes. Here, new donor T cells are primed, expanded, differentiated, and imprinted with gut-homing integrins permissive of migration into the damaged GI tract, resulting in the lethal feed-forward cascade of GVHD. These new insights into our understanding of the cellular and molecular factors initiating GVHD, both spatially and temporally, give rise to a number of logical therapeutic targets, focusing on the inhibition of APC function in the GI tract.

Graft-versus-host disease, but not graft-versus-leukemia immunity, is mediated by GM-CSF-licensed myeloid cells

Allogeneic hematopoietic cell transplantation (allo-HCT) not only is an effective treatment for several hematologic malignancies but can also result in potentially life-threatening graft-versus-host disease (GvHD). GvHD is caused by T cells within the allograft attacking nonmalignant host tissues; however, these same T cells mediate the therapeutic graft-versus-leukemia (GvL) response. Thus, there is an urgent need to understand how to mechanistically uncouple GvL from GvHD. Using preclinical models of full and partial MHC-mismatched HCT, we here show that the granulocyte-macrophage colony-stimulating factor (GM-CSF) produced by allogeneic T cells distinguishes between the two processes. GM-CSF drives GvHD pathology by licensing donor-derived phagocytes to produce inflammatory mediators such as interleukin-1β and reactive oxygen species. In contrast, GM-CSF did not affect allogeneic T cells or their capacity to eliminate leukemic cells, retaining undiminished GvL responses. Last, tissue biopsies and peripheral blood mononuclear cells from patients with grade IV GvHD showed an elevation of GM-CSF-producing T cells, suggesting that GM-CSF neutralization has translational potential in allo-HCT.

Complement-mediated thrombotic microangiopathy as a link between endothelial damage and steroid-refractory GVHD

Transplant-associated thrombotic microangiopathy (TA-TMA), a complication of hematopoietic cell transplant (HCT), is associated with significant morbidity and mortality. The pathophysiology and overlap of TA-TMA with other posttransplant complications such as graft-versus-host disease (GVHD) is poorly understood. We retrospectively identified cases of TA-TMA among patients with grade 3/4 gastrointestinal (GI) GVHD, reviewed intestinal biopsy specimens, and performed correlative testing of biomarkers associated with TA-TMA. TA-TMA was more common in patients with steroid-refractory GVHD compared with steroid-responsive GVHD (79.3% vs 42.1%; P = .001). Among patients surviving 100 days post-HCT, 1-year survival from day 100 was significantly better for patients who had not developed TA-TMA in the first 100 days (69.5% vs 36.7%; P < .001). Only 1 of 7 proposed TA-TMA histology criteria (mucosal hemorrhage) differed significantly based on GVHD steroid response. In multivariable modeling, steroid-refractory GVHD was a risk factor for development of TA-TMA (hazard ratio, 3.09; 95% confidence interval, 1.68-5.67; P < .001). There were no differences in complement activation at GVHD onset; however, 2 to 6 weeks later, patients with TA-TMA had higher levels of BBPlus and C5b-9, markers of alternative and terminal pathway activation (BBPlus: median, 600 vs 209.3 ng/mL; P = .0045) (C5b-9: median, 425.9 vs 258.4 ng/mL; P = .029). TA-TMA is associated with poor overall survival (OS) following HCT and may be detected early by histologic findings and may be differentiated from GVHD by measurement of alternative and terminal complement pathway activation. It is unknown whether treatment of TA-TMA will improve survival in steroid-refractory GVHD.

Induction of acute graft vs. host disease in lymphopenic mice

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially life-saving treatment for refractory/relapsing hematological malignancies, blood disorders or autoimmune diseases. However, approximately 40-50% of patients undergoing allogeneic HSCT will develop a multi-organ, inflammatory disorder called acute graft vs. host disease (aGVHD). Experimental and clinical studies suggest that intestinal injury due to toxic, pre-transplant conditioning protocols (e.g. lethal irradiation and/or chemotherapy) may play a major role in the development of aGVHD. However, recent studies from our laboratory suggest that this may not be the case. The objective of this study was to quantify and compare the onset and severity of aGVHD induced by the adoptive transfer of allogeneic T cells into untreated lymphopenic mice. Four million allogeneic or syngeneic CD4⁺CD62L⁺CD25^- T cells were transferred (i.p.) into NK cell-depleted RAG1^-/- mice or RAG2^-/-IL2rγ^-/-double knock-out (DKO) mice and assessed daily for signs of aGVHD. We found that adoptive transfer of allogeneic but not syngeneic T cells into NK cell-depleted RAG1^-/- or DKO mice induced many of the clinical and histological features of aGVHD including weight loss, inflammatory cytokine production and tissue inflammation. In addition, adoptive transfer of allogeneic T cells into each recipient induced severe anemia as well as dramatic reductions in bone marrow and spleen cellularity. Taken together, we conclude that allogeneic CD4⁺ T cells are both necessary and sufficient to induce aGVHD in lymphopenic recipients in the absence of toxic, pre-transplant conditioning.

Altered donor P2X7 activity in human leukocytes correlates with P2RX7 genotype but does not affect the development of graft-versus-host disease in humanised mice

Graft-versus-host disease (GVHD) is a life-threatening consequence of allogeneic haematopoietic stem cell transplantation, a curative therapy for haematological malignancies. The ATP-gated P2X7 receptor channel is implicated in the development of GVHD. P2X7 activity on human leukocytes can be influenced by gain-of-function (GOF) and loss-of-function (LOF) single nucleotide polymorphisms (SNPs) in the P2RX7 gene. In this study, the P2RX7 gene was sequenced in 25 human donors and the P2X7 activity on subsets of peripheral blood T cells, natural killer (NK) cells and monocytes was measured using an ATP-induced dye uptake assay. GOF and LOF SNPs representing 10 of the 17 known P2RX7 haplotypes were identified, and correlated with P2X7 activity on all leukocyte subsets investigated. Notably, invariant (i) NK T cells displayed the highest P2X7 activity amongst all cell types studied. To determine if donor P2X7 activity influenced the development of GVHD, immunodeficient NOD-SCID-IL2Rγnull (NSG) mice were injected with human peripheral blood mononuclear cells isolated from donors of either GOF (hP2X7GOF mice) or LOF (hP2X7LOF mice) P2RX7 genotype. Both hP2X7GOF and hP2X7LOF mice demonstrated similar human leukocyte engraftment, and showed comparable weight loss, GVHD clinical score and overall survival. Donor P2X7 activity did not affect human leukocyte infiltration or GVHD-mediated tissue damage, or the relative expression of human P2X7 or human interferon-γ (hIFNγ) in tissues. Finally, hP2X7GOF and hP2X7LOF mice demonstrated similar concentrations of serum hIFNγ. This study demonstrates that P2X7 activity correlates with donor P2RX7 genotype on human leukocyte subsets important in GVHD development, but does not affect GVHD development in a humanised mouse model of this disease.

The IL-12 Cytokine and Receptor Family in Graft-vs.-Host Disease

Allogeneic hematopoietic cell transplantation (allo-HCT) is performed with curative intent for high- risk blood cancers and bone marrow failure syndromes; yet the development of acute and chronic graft-vs.-host disease (GVHD) remain preeminent causes of death and morbidity. The IL-12 family of cytokines is comprised of IL-12, IL-23, IL-27, IL-35, and IL-39. This family of cytokines is biologically distinct in that they are composed of functional heterodimers, which bind to cognate heterodimeric receptor chains expressed on T cells. Of these, IL-12 and IL-23 share a common β cytokine subunit, p40, as well as a receptor chain: IL-12Rβ1. IL-12 and IL-23 have been documented as proinflammatory mediators of GVHD, responsible for T helper 1 (Th1) differentiation and T helper 17 (Th17) stabilization, respectively. The role of IL-27 is less defined, seemingly immune suppressive via IL-10 secretion by Type 1 regulatory (Tr1) cells yet promoting inflammation through impairing CD4⁺ T regulatory (Treg) development and/or enhancing Th1 differentiation. More recently, IL-35 was described as a potent anti-inflammatory agent produced by regulatory B and T cells. The role of the newest member, IL-39, has been implicated in proinflammatory B cell responses but has not been explored in the context of allo-HCT. This review is directed at discussing the current literature relevant to each IL-12-family cytokine and cognate receptor engagement, as well as the consequential downstream signaling implications, during GVHD pathogenesis. Additionally, we will provide an overview of translational strategies targeting the IL-12 family cytokines, their receptors, and subsequent signal transduction to control GVHD.

Achievement of Tolerance Induction to Prevent Acute Graft-vs.-Host Disease

Acute graft-vs.-host disease (GVHD) limits the efficacy of allogeneic hematopoietic stem cell transplantation (allo-HSCT), a main therapy to treat various hematological disorders. Despite rapid progress in understanding GVHD pathogenesis, broad immunosuppressive agents are most often used to prevent and remain the first line of therapy to treat GVHD. Strategies enhancing immune tolerance in allo-HSCT would permit reductions in immunosuppressant use and their associated undesirable side effects. In this review, we discuss the mechanisms responsible for GVHD and advancement in strategies to achieve immune balance and tolerance thereby avoiding GVHD and its complications.

G-CSF-induced macrophage polarization and mobilization may prevent acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Macrophages (MΦs) are an important immune cell population that are essential for tissue homeostasis and disease pathogenesis. MΦs are now classified as either M1, which produce pro-inflammatory cytokines, or M2, which produce antiinflammatory cytokines. The impact of granulocyte colony-stimulating factor (G-CSF) on MΦs in humans is unclear. Moreover, little is known about the association between MΦ subsets in allografts and the occurrence of acute graft-versus-host disease (aGVHD) in patients who undergo allogeneic hematopoietic stem cell transplantation (allo-HSCT). In the current study, we found that the M1/M2 ratio was markedly decreased in both G-CSF-treated bone marrow (post-BM) and G-CSF-treated peripheral blood from healthy donors. Post-BM MΦs exhibited reduced migration and increased phagocytosis. Moreover, post-BM MΦs reduced the percentage of Th1 and Tc1 lineages and increased the percentage of Th2, Tc2, and Treg lineages. Patients who received BM grafts with a higher M1/M2 ratio exhibited a higher incidence of grade 2-4 aGVHD. In summary, our data indicate that G-CSF decreases the M1/M2 ratio in BM grafts from healthy donors, which may contribute to preventing the occurrence of grade 2-4 aGVHD in patients after allo-HSCT.

Targeting Sirt-1 controls GVHD by inhibiting T-cell allo-response and promoting Treg stability in mice

Graft-versus-host disease (GVHD) remains one of the major complications after allogeneic bone marrow transplantation (allo-BMT). Sirtuin-1 (Sirt-1) plays a crucial role in various biological processes including cellular senescence, metabolism, and inflammatory responses. Sirt-1 deacetylation regulates different transcription factors that are important for modulating immune responses. In the current study, we addressed the role of Sirt-1 in GVHD induction by employing Sirt-1 conditional knockout mice as well as a pharmacological Sirt-1 inhibitor. Using major histocompatibility complex (MHC)-mismatched and MHC-matched murine BMT models, we found that Sirt-1-/- T cells had a reduced ability to induce acute GVHD (aGVHD) via enhanced p53 acetylation. Sirt-1-deficient T cells also promoted induced regulatory T cell (iTreg) differentiation and inhibited interferon-γ production after allo-BMT. Sirt-1 deletion in iTregs increased Foxp3 stability and restrained iTreg conversion into pathogenic T cells. Furthermore, we found that administration with a Sirt-1 inhibitor, Ex-527, significantly improved recipient survival and clinical scores, with no signs of tumor relapse. These results indicate that Sirt-1 inhibition can attenuate GVHD while preserving the graft-versus-leukemia effect. Consistently, Sirt-1-deficient T cells also displayed a remarkably reduced ability to induce chronic GVHD (cGVHD). Mechanistic studies revealed that Sirt-1 deficiency in T cells enhanced splenic B-cell reconstitution and reduced follicular T helper cell development. Sirt-1 deficiency in T cells modulated donor B-cell responses reducing both B-cell activation and plasma cell differentiation. In addition, therapeutic Sirt-1 inhibition could both prevent cGVHD and reduce established cGVHD. In conclusion, Sirt-1 is a promising therapeutic target for the control of aGVHD and cGVHD pathogenesis and possesses high potential for clinical application.

The Role of Co-stimulatory/Co-inhibitory Signals in Graft-vs.-Host Disease

Allogeneic hematopoietic cell transplantation (allo-HCT) is an effective immunotherapeutic approach for various hematologic and immunologic ailments. Despite the beneficial impact of allo-HCT, its adverse effects cause severe health concerns. After transplantation, recognition of host cells as foreign entities by donor T cells induces graft-vs.-host disease (GVHD). Activation, proliferation and trafficking of donor T cells to target organs and tissues are critical steps in the pathogenesis of GVHD. T cell activation is a synergistic process of T cell receptor (TCR) recognition of major histocompatibility complex (MHC)-anchored antigen and co-stimulatory/co-inhibitory signaling in the presence of cytokines. Most of the currently used therapeutic regimens for GVHD are based on inhibiting the allogeneic T cell response or T-cell depletion (TCD). However, the immunosuppressive drugs and TCD hamper the therapeutic potential of allo-HCT, resulting in attenuated graft-vs.-leukemia (GVL) effect as well as increased vulnerability to infection. In view of the drawback of overbroad immunosuppression, co-stimulatory, and co-inhibitory molecules are plausible targets for selective modulation of T cell activation and function that can improve the effectiveness of allo-HCT. Therefore, this review collates existing knowledge of T cell co-stimulation and co-inhibition with current research that may have the potential to provide novel approaches to cure GVHD without sacrificing the beneficial effects of allo-HCT.

Long-term treatment with the P2X7 receptor antagonist Brilliant Blue G reduces liver inflammation in a humanized mouse model of graft-versus-host disease

Allogeneic haematopoietic stem cell transplantation (HSCT) is a frequent curative therapy for numerous haematological malignancies. However, HSCT is limited by the occurrence of graft-versus-host disease (GVHD), with current therapies restricted to general immunosuppression. Activation of the P2X7 receptor by extracellular adenosine triphosphate (ATP) causes inflammation and tissue damage in GVHD. Short-term pharmacological blockade of P2X7 has been shown to reduce clinical disease and/or reduce inflammatory markers in allogeneic and humanized mouse models of GVHD. The current study demonstrates that long-term P2X7 blockade by intra-peritoneal injection of Brilliant Blue G (BBG) thrice weekly for up to 10 weeks did not impact human (h) peripheral blood mononuclear cell (PBMC) engraftment, predominantly T cells, in blood at 3 weeks post-hPBMC injection or in spleens at end-point in humanized mice. Histological analysis demonstrated long-term BBG treatment reduced leukocyte infiltration in the livers of humanized mice. Immunohistochemical analysis demonstrated that BBG treatment reduced liver apoptosis. Long-term BBG treatment did not alter clinical disease, mRNA expression of pro-inflammatory markers in tissues or serum human interferon (IFN)-γ concentrations. Therefore, this study demonstrates that P2X7 activation plays a role in GVHD pathogenesis in the livers of humanized mice, supporting a role for this receptor in GVHD development in HSCT recipients.

In vivo administration of recombinant BTNL2-Fc fusion protein ameliorates graft-versus-host disease in mice

Although hematopoietic stem cell transplantation (HSCT) has been widely used in the treatment of many diseases, graft-versus-host disease (GVHD) remains a major complication after allogeneic HSCT. Butyrophilin-like 2 (BTNL2) protein has been reported to have the ability to inhibit T cell proliferation in vitro; its ability to inhibit T cell responses in vivo has not been determined. We show here that in vivo administration of recombinant BTNL2-IgG2a Fc (rBTNL2-Ig) fusion protein ameliorates GVHD in mice. This is related to the ability of rBTNL2-Ig to inhibit T cell proliferation, activation and Th1/Th17 cytokine production in vivo. Furthermore, rBTNL2-Ig treatment increases the generation of regulatory T cells. Our results suggest that rBTNL2-Ig has the potential to be used in the prevention and treatment of patients with GVHD.

SYK inhibitor entospletinib prevents ocular and skin GVHD in mice

Graft-versus-host disease (GVHD) is a major complication of hematopoietic stem cell transplantation (HCT). The tyrosine kinase SYK contributes to both acute and chronic GVHD development, making it an attractive target for GVHD prevention. Entospletinib (ENTO) is a second-generation highly selective SYK inhibitor with a high safety profile. Potential utility of ENTO as GVHD prophylaxis in patients was examined using a preclinical mouse model of eye and skin GVHD and ENTO-compounded chow. We found that early SYK inhibition improved blood immune cell reconstitution in GVHD mice and prolonged survival, with 60% of mice surviving to day +120 compared with 10% of mice treated with placebo. Compared with mice receiving placebo, mice receiving ENTO had dramatic improvements in clinical eye scores, alopecia scores, and skin scores. Infiltrating SYK+ cells expressing B220 or F4/80, resembling SYK+ cells found in lichenoid skin lesions of chronic GVHD patients, were abundant in the skin of placebo mice but were rare in ENTO-treated mice. Thus, ENTO given early after HCT safely prevented GVHD.

Chitinase 3-Like-1-Deficient Splenocytes Deteriorated the Pathogenesis of Acute Graft-Versus-Host Disease via Regulating Differentiation of Tfh Cells

Acute graft-versus-host disease (aGVHD) is an intractable complication in transplant patients, limiting the efficacy of this therapy. Chitinase 3-like-1 (CHI3L1), a member of the glycosyl hydrolase 18 family that lacks chitinase activity, plays a critical role in a variety of inflammatory diseases. Here, we investigated the in vitro and in vivo effects of CHI3L1 on the development of aGVHD. In this study, mixed lymphocyte reactions (MLR) in vitro showed that CHI3L1 deficiency in CD4⁺ T cell promoted the production of interferon (IFN)-γ and T follicular helper (Tfh)-related cytokines such as interleukin-6 (IL-6) and interleukin-21 (IL-21). Meanwhile, the inducible Tfh cell population increased remarkably in CHI3L1-KO CD4⁺ T cells' induction group, compared with WT group. Then, in the murine acute GVHD model, we found that CHI3L1 deficiency in donor splenocytes dramatically increased the severity of aGVHD through enhancing Tfh cell differentiation. Moreover, at mRNA and protein levels, we defined several molecules that may account for the enhanced ability of CHI3L1-KO splenocytes to migrate into target organs and produce IFN-γ and Tfh-related cytokines and chemokines, such as IL-6, IL-21, and CXCL13. Expression of inducible co-stimulator (ICOS) and B cell lymphoma 6 (Bcl6) increased in the skin, the intestine, the lung, and the liver from CHI3L1-KO splenocyte-treated aGVHD mice. Therefore, these results strongly imply that CHI3L1 levels in donor cells may be related to the risk of aGVHD and targeting CHI3L1 represents a novel therapeutic strategy for controlling aGVHD progression.

A novel model for dissecting roles of IL-17 in lung transplantation

Background

The long-term success of lung transplantation is limited by the development of chronic lung allograft dysfunction (CLAD) in which IL-17 plays an important role. Direct evidence of IL-17-mediated allograft rejection has been observed when T-bet is absent. However, lack of T-bet also leads to failure in production of IFN-γ which is required for tolerance induction and allograft acceptance, as T-bet deficiency results in IL-17-expressing CD8+ T cells mediated costimulation blockade-resistant allograft rejection. Our previous research demonstrated that additional STAT6 deficiency to T-bet deficiency resulted in Th17-dominant immune responses, and importantly, restored IFN-γ production. Here we investigated whether T-bet/STAT6 double knout-out (DKO) mice as allograft recipients could provide a useful model to study IL-17 and Th17 in lung transplantation.

Methods

Murine orthotopic allogeneic lung transplants were performed in C57BL/6 wild type (WT) or T-bet/STAT6 DKO (C57BL/6 background) mice using MHC fully mismatched BALB/c donors. Syngeneic transplants were also performed in WT C57BL/6 mice using C57BL/6 donors. At day 10, histopathologic characteristics and rejection status of transplanted grafts were assessed; graft-infiltrating cells were isolated and real-time RT-PCR was performed for IL-17, IFN-γ and IL-4 expressions.

Results

Isografts showed no apparent rejection as anticipated. Allografts of both WT and DKO recipients displayed vigorous acute rejection and expressed comparable levels of IFN-γ; while T-bet/STAT6 double deficiency resulted in much more IL-17 and less IL-4 production. Histopathologic examination demonstrated that allografts of both WT and DKO recipients have marked inflammatory cell infiltration and pulmonary parenchyma lesion. In contrast to lymphocyte-predominant inflammation observed in WT recipients, allografts of DKO recipients displayed obvious polymorphonuclear cell infiltration and severer obliterative airway inflammation. Compared to WT recipients, the ratio of graft-infiltrating CD8+ versus CD4+ T cells increased significantly with much higher numbers of neutrophils in allografts of DKO recipients.

Conclusions

T-bet/STAT6 DKO recipients of lung allografts result in IL-17-dominant transplant immunity, retain IFN-γ responses, and develop neutrophilia, obliterative airway inflammation and acute transplant rejection. Our results indicate that T-bet/STAT6 DKO mice serving as allograft recipient could be utilized as a new viable model to study the roles of IL-17 in lung transplantation.

Unraveling the Mechanisms of Cutaneous Graft-Versus-Host Disease

The skin is the most common target organ affected by graft-versus-host disease (GVHD), with severity and response to therapy representing important predictors of patient survival. Although many of the initiating events in GVHD pathogenesis have been defined, less is known about why treatment resistance occurs or why there is often a permanent failure to restore tissue homeostasis. Emerging data suggest that the unique immune microenvironment in the skin is responsible for defining location- and context-specific mechanisms of injury that are distinct from those involved in other target organs. In this review, we address recent advances in our understanding of GVHD biology in the skin and outline the new research themes that will ultimately enable design of precision therapies.

The tolerogenic role of IFN-γ

Due to its extremely pleiotropic nature, the complex effects of IFN-γ exerted both on immune and non-immune cell types still remain only partially understood. The longstanding view of IFN-γ as being a predominantly inflammatory cytokine is constantly challenged by increasing demonstrations of its direct or indirect regulatory roles. Interferon-γ can exert tolerogenic effects on both innate and adaptive immune cell types, promoting tolerance of various antigen-presenting cells, and augmenting function and differentiation of regulatory T cells, respectively. Its capacity to induce IDO-competence is not limited to immune cells but extends to other cell types such as mesenchymal stem cells, epithelial cells, and tumors. The pro-inflammatory role of IFN-γ in tumor immune surveillance can backfire by directly inducing inhibitory molecule expression, such as PDL-1, on tumor cells. With increasing knowledge regarding the role of different helper T cell subsets in certain autoimmune diseases, the once contradictory observations of disease attenuation by IFN-γ can now be explained by its opposing interplay with other effector cytokines, particularly IL-17. The paradoxically immunosuppressive role of IFN-γ is also becoming evident in the transplantation setting, and graft-versus-host-disease. In the present review, we will discuss the latest findings that help to elucidate this dual role of IFN-γ at a cellular level, and in various pathophysiological states.

Newly found arsons ignite the fire of gut GVHD

Acute graft-versus-host disease (GVHD) in the gut is common following hematopoetic cell transplantation (HCT) and is associated with high mortality. However, it remains unclear whether Th1 or Th17 CD4+ T cells can initiate acute gut GVHD. In this issue of the JCI, Ullrich and colleagues identified a subset of CD4+ T cells that express high levels of IL-7Rα and granulocyte-macrophage CSF (IL-7RαhiGM-CSF+) cells that are involved in the induction of acute gut GVHD in murine models. The IL-7RαhiGM-CSF+ effector memory cells were BATF dependent, RORγt independent, produced large amounts of GM-CSF and IFN-γ, and released little IL-17. CD4+IL-7RαhiGM-CSF+ cells were not classical Th17 cells but had more of a Th1-like phenotype, despite their dependence on BATF. This work suggests that targeting the IL-7R/BATF/GM-CSF axis has therapeutic potential for treating acute gut GVHD.

Elevated Serum Interleukin-6 Predicts Favorable Response to Immunosuppressive Therapy in Children With Aplastic Anemia

BACKGROUND

Immunosuppressive therapy (IST) is the standard treatment for aplastic anemia (AA) children who lack a sibling donor, but the clinical response rate to IST varies. Predictors of response to IST are valuable for stratifying AA patients and making clinical decisions.

METHODS

The serum interleukin (IL)-6 levels of 41 AA patients were measured at the time of diagnosis and the response rate of the patients to IST was evaluated at 3, 6, and 12 months after IST. Receiver-operator characteristic (ROC) analysis was used to calculate the predictive value of initial IL-6 levels in determining response at 6 months after IST.

RESULTS

The initial IL-6 levels were significant higher in responders than nonresponders at 6 months after IST (211.89 vs. 18.09 pg/mL; P=0.005), using 36.8 pg/mL as a threshold, there were 80% sensitivity and 81% specificity for discriminating responders and nonresponders to IST. Patients with initial high IL-6 level (>36.8 pg/mL) have favorable response rates than those with initial low IL-6 level (<36.8 pg/mL) at 3, 6, and 12 months after IST (P<0.01).

CONCLUSION

High levels of IL-6 at the time of diagnosis predict a favorable response to IST in children with AA and this may be helpful for patient's stratification and clinical decisions.

Therapeutic effects of STAT3 inhibition by nifuroxazide on murine acute graft graft-vs.-host disease: Old drug, new use

Graft-vs.-host disease (GvHD) is a major and lethal complication of allogeneic bone marrow transplantation (allo-BMT). Although great development has been made, the treatment progress of this disorder is slow. Research has illustrated that STAT3 was critical for T cell alloactivation in GvHD. In the present study, the authors hypothesized that nifuroxazide, as the STAT3 inhibitor, treatment may attenuate the development of acute GvHD (aGvHD). The results demonstrated that nifuroxazide suppressed the development of aGvHD and significantly delayed aGvHD-induced lethality. Mice receiving nifuroxazide had mostly normal-appearing skin with minimal focal ulceration, mild edema and congestion in the liver, and a less-pronounced villus injury and less inflammatory infiltrate in the small intestine. Treatment with nifuroxazide inhibited the activation of STAT3, resulting in the regulation of the CD4⁺ T cells and CD4⁺CD25⁺ T cells and reduction of interferon-γ and tumor necrosis factor-α levels. In conclusion, nifuroxazide may be efficacious for post-transplant of GvHD, providing a potent drug for use as a prophylactic or as a second-line therapy for aGvHD in clinical trials.

Obese donor mice splenocytes aggravated the pathogenesis of acute graft-versus-host disease via regulating differentiation of Tregs and CD4+ T cell induced-type I inflammation

Acute graft-versus-host disease (aGVHD) remains one of the most severe complications in organ and bone marrow transplantation, leading to much morbidity and mortality. Obesity has been associated with increased risk of development of various inflammatory diseases. Here, we investigated the in vitro and in vivo effects of obese donor splenocytes on the development of acute graft-versus-host disease (aGVHD). In this study, mixed lymphocyte reactions (MLR) in vitro showed that obese donor mouse CD4+ T cell promoted the production of interleukin-2 (IL-2), interferon (IFN)-γ and tumor necrosis factor (TNF)-α. Meanwhile, the inducible Tregs population decreased greatly in obese donor mouse CD4+ T cells' induction group, compared with normal group. Then in the murine aGVHD model, we found that obese donor splenocytes dramatically increased the severity of aGVHD through down-regulating immune tolerance while enhancing systemic and local immunity. Moreover, we showed that aGVHD induced by obese donors resulted in massive expansion of donor CD3+ T cells, release of Th1-related cytokines, interleukin-17 (IL-17) and chemokines, significant increase of Th17 cells and inhibition of CD4+CD25+Foxp3+ regulatory T cells (Tregs) and impaired suppressive ability of donor Tregs. Expression of sphingosine-1-phosphate receptor 1 (S1PR1), phosphorylated Akt, mammalian target of rapamycin (mTOR) and Raptor increased, while the phosphorylation level of SMAD3 was decreased in the skin, intestine, lung and liver from obese donor splenocytes-treated aGVHD mice. Furthermore, at mRNA and protein levels, we defined several molecules that may account for the enhanced ability of obese donor splenocytes to migrate into target organs, such as IL-2, IL-17, IFN-γ, TNF-α, CXCR3, CXCL9, CXCL10, CXCL11 and CCL3. Therefore, these results imply that obese donor cells may be related to the risk of aGVHD and helping obese donor individuals lose weight represent a compulsory clinical strategy before implementing transplantation to control aGVHD of recipients.

The P2X7 receptor antagonist Brilliant Blue G reduces serum human interferon-γ in a humanized mouse model of graft-versus-host disease

Graft-versus-host disease (GVHD) remains a major problem after allogeneic haematopoietic stem cell transplantation, a curative therapy for haematological malignancies. Previous studies have demonstrated a role for the adenosine triphosphate (ATP)-gated P2X7 receptor channel in allogeneic mouse models of GVHD. In this study, injection of human peripheral blood mononuclear cells (PBMCs) into immunodeficient non-obese diabetic-severe combined immunodeficiency-interleukin (NOD-SCID-IL)-2Rγ^null (NSG) mice established a humanized mouse model of GVHD. This model was used to study the effect of P2X7 blockade in this disease. From five weeks post-PBMC injection, humanized mice exhibited clinical signs and histopathology characteristic of GVHD. The P2X7 antagonist, Brilliant Blue G (BBG), blocked ATP-induced cation uptake into both murine and human cells in vitro. Injection of BBG (50 mg/kg) into NSG mice did not affect engraftment of human leucocytes (predominantly T cells), or the clinical score and survival of mice. In contrast, BBG injection reduced circulating human interferon (IFN)-γ significantly, which was produced by human CD4⁺ and CD8⁺ T cells. BBG also reduced human T cell infiltration and apoptosis in target organs of GVHD. In conclusion, the P2X7 antagonist BBG reduced circulating IFN-γ in a humanized mouse model of GVHD supporting a potential role for P2X7 to alter the pathology of this disease in humans.

Inhibition of acute lethal pulmonary inflammation by the IDO-AhR pathway

The lung is a prototypic organ that was evolved to reduce immunopathology during the immune response to potentially hazardous endogenous and exogenous antigens. In this study, we show that donor CD4+ T cells transiently induced expression of indoleamine 2,3-dioxygenase (IDO) in lung parenchyma in an IFN-γ-dependent manner early after allogeneic hematopoietic stem cell transplantation (HSCT). Abrogation of host IDO expression by deletion of the IDO gene or the IFN-γ gene in donor T cells or by FK506 treatment resulted in acute lethal pulmonary inflammation known as idiopathic pneumonia syndrome (IPS). Interestingly, IL-6 strongly induced IDO expression in an IFN-γ-independent manner when deacetylation of STAT3 was inhibited. Accordingly, a histone deacetylase inhibitor (HDACi) could reduce IPS in the state where IFN-γ expression was suppressed by FK506. Finally, l-kynurenine produced by lung epithelial cells and alveolar macrophages during IPS progression suppresses the inflammatory activities of lung epithelial cells and CD4+ T cells through the aryl hydrocarbon receptor pathway. Taken together, our results reveal that IDO is a critical regulator of acute pulmonary inflammation and that regulation of IDO expression by HDACi may be a therapeutic approach for IPS after HSCT.

Interleukin-6 in Allogeneic Stem Cell Transplantation: Its Possible Importance for Immunoregulation and As a Therapeutic Target

Allogeneic stem cell transplantation is associated with a high risk of treatment-related mortality mainly caused by infections and graft-versus-host disease (GVHD). GVHD is characterized by severe immune dysregulation and impaired regeneration of different tissues, i.e., epithelial barriers and the liver. The balance between pro- and anti-inflammatory cytokine influences the risk of GVHD. Interleukin-6 (IL-6) is a cytokine that previously has been associated with pro-inflammatory effects. However, more recent evidence from various autoimmune diseases (e.g., inflammatory bowel disease, rheumatoid arthritis) has shown that the IL-6 activity is more complex with important effects also on tissue homeostasis, regeneration, and metabolism. This review summarizes the current understanding of how pro-inflammatory IL-6 effects exerted during the peritransplant period shapes T-cell polarization with enhancement of Th17 differentiation and suppression of regulatory T cells, and in addition we also review and discuss the results from trials exploring non-selective IL-6 inhibition in prophylaxis and treatment of GVHD. Emerging evidence suggests that the molecular strategy for targeting of IL-6-initiated intracellular signaling is important for the effect on GVHD. It will therefore be important to further characterize the role of IL-6 in the pathogenesis of GVHD to clarify whether combined IL-6 inhibition of both trans- (i.e., binding of the soluble IL-6/IL-6 receptor complex to cell surface gp130) and cis-signaling (i.e., IL-6 ligation of the IL-6 receptor/gp130 complex) or selective inhibition of trans-signaling should be tried in the prophylaxis and/or treatment of GVHD in allotransplant patients.

Tbet is a critical modulator of FoxP3 expression in autoimmune graft-versus-host disease

CD4⁺ T-helper subsets drive autoimmune chronic graft-versus-host disease, a major complication after allogeneic bone marrow transplantation. However, it remains unclear how specific T-helper subsets contribute to chronic graft-versus-host disease. T-helper type 1 cells are one of the major disease-mediating T-cell subsets and require interferon-γ signaling and Tbet expression for their function. Regulatory T cells on the other hand can inhibit T-helper type 1 cell-mediated responses. Using an established murine model that isolates the autoimmune component of graft-versus-host disease, we hypothesized that T-helper type 1 cells would restrict FoxP3-driven regulatory T cells. Upon transfer into immune-deficient syngeneic hosts, alloreactive Tbx21^−/−CD4⁺ T cells led to marked increases in FoxP3⁺ cells and reduced clinical evidence of autoimmunity. To evaluate whether peripheral induction contributed to regulatory T-cell predominance, we adoptively transferred Tbx21^−/− T cells that consisted of fate mapping for FoxP3: recipients of flow-purified effector cells that were Foxp3⁻ and Tbx21^−/− had enhanced T-regulatory-cell predominance during autoimmune graft-versus-host disease. These data directly demonstrated that peripheral T-regulatory-cell induction was inhibited by Tbet. Finally, Tbx21^−/− T-regulatory cells cross-regulated autoimmune wild-type T-effector-cell cytokine production in vivo. The Tbet pathway therefore directly impairs T-regulatory-cell reconstitution and is consequently a feasible target in efforts to prevent autoimmune graft-versus-host disease.

PD-L1 interacts with CD80 to regulate graft-versus-leukemia activity of donor CD8+ T cells

Programmed death ligand-1 (PD-L1) interacts with programmed death-1 (PD-1) and the immunostimulatory molecule CD80 and functions as a checkpoint to regulate immune responses. The interaction of PD-L1 with CD80 alone has been shown to exacerbate the severity of graft-versus-host disease (GVHD), whereas costimulation of CD80 and PD-1 ameliorates GVHD. Here we have demonstrated that temporary depletion of donor CD4+ T cells early after hematopoietic cell transplantation effectively prevents GVHD while preserving strong graft-versus-leukemia (GVL) effects in allogeneic and xenogeneic murine GVHD models. Depletion of donor CD4+ T cells increased serum IFN-γ but reduced IL-2 concentrations, leading to upregulation of PD-L1 expression by recipient tissues and donor CD8+ T cells. In GVHD target tissues, the interactions of PD-L1 with PD-1 on donor CD8+ T cells cause anergy, exhaustion, and apoptosis, thereby preventing GVHD. In lymphoid tissues, the interactions of PD-L1 with CD80 augment CD8+ T cell expansion without increasing anergy, exhaustion, or apoptosis, resulting in strong GVL effects. These results indicate that the outcome of PD-L1-mediated signaling in CD8+ T cells depends on the presence or absence of CD4+ T cells, the nature of the interacting receptor expressed by CD8+ T cells, and the tissue environment in which the signaling occurs.

Chitinase 3-like-1 deficient donor splenocytes accentuated the pathogenesis of acute graft-versus-host diseases through regulating T cell expansion and type I inflammation

Acute graft-versus-host disease (aGVHD) is a major complication following transplantation, limiting the success of this therapy. Chitinase 3-like-1 (CHI3L1), a member of the glycosyl hydrolase 18 family, plays a critical role in bacterial infections, allergic disease and a variety of malignancies. Here, we investigated whether CHI3L1 could affect the pathogenesis of aGVHD in a mouse allo-HCT model. In this study, we show that CHI3L1 deficiency in donor T cells increased the severity of aGVHD through enhancing systemic and local inflammation. In addition, we found that aGVHD induced by CHI3L1-knockout (CHI3L1-KO) donors resulted in massive expansion of donor CD3⁺ T cells, release of Th1-related cytokines and chemokines, and significant inhibition of CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs) without changing the suppressive ability of donor Tregs remarkably. Expression of PERK1/2 and PAkt increased both in the skin and intestine from CHI3L1-KO splenocytes-treated aGVHD mice. Moreover, at mRNA and protein levels, we defined several molecules that may account for the enhanced ability of CHI3L1-KO splenocytes to migrate into target organs and produce Th1-related cytokines and chemokines, such as CXCL9, CXCL11, IFN-γ and TNF-α. Therefore, these results imply that CHI3L1 levels in donor cells may be related to the risk of aGVHD and targeting CHI3L1 may be a promising clinical strategy to control aGVHD.

Rat acute GvHD is Th1 driven and characterized by predominant donor CD4+ T-cell infiltration of skin and gut

Acute graft-versus-host disease (aGvHD) remains a significant hurdle to successful treatment of many hematological disorders. The disease is caused by infiltration of alloactivated donor T cells primarily into the gastrointestinal tract and skin. Although cytotoxic T cells mediate direct cellular damage, T helper (Th) cells differentially secrete immunoregulatory cytokines. aGvHD is thought to be initiated primarily by Th1 cells but a consensus is still lacking regarding the role of Th2 and Th17 cells. The aim of this study was to determine the contribution of distinct T-cell subsets to aGvHD in the rat. aGvHD was induced by transplanting irradiated rats with T-cell-depleted major histocompatibility complex-mismatched bone marrow, followed 2 weeks later by donor lymphocyte infusion. Near complete donor T-cell chimerism was achieved in the blood and lymphatic tissues, in contrast to mixed chimerism in the skin and gut. Skin and gut donor T cells were predominantly CD4⁺, in contrast to T cells in the blood and lymphatic tissues. Genes associated with Th1 cells were upregulated in gut, liver, lung, and skin tissues affected by aGvHD. Increased serum levels of CXCL10 and IL-18 preceded symptoms of aGvHD, accompanied by increased responsiveness to CXCL10 by blood CD4⁺ T cells. No changes in the expression of Th2- or Th17-associated genes were observed, indicating that aGvHD in this rat model is mainly Th1 driven. The rat model of aGvHD could be instrumental for further investigations of donor T-cell subsets in the skin and gut and for exploring therapeutic options to ameliorate symptoms of aGvHD.

Regulatory B cells promote graft-versus-host disease prevention and maintain graft-versus-leukemia activity following allogeneic bone marrow transplantation

Regulatory B cells (Bregs) are involved in the pathogenesis of graft-versus-host disease (GVHD). However, whether Bregs can alleviate acute GVHD without compromising graft-versus-leukemia (GVL) effects remains unclear. Here, we evaluated the role of Bregs in acute GVHD and GVL activity in both a mouse model and a clinical cohort study. In the acute GVHD mouse model, co-transplantation of Bregs prevents onset through inhibiting Th1 and Th17 differentiation and expanding regulatory T cells. In the GVL mouse model, Bregs contributed to the suppression of acute GVHD but had no adverse effect on GVL activity. In the clinical cohort study, a higher dose of Bregs in allografts was associated with a lower cumulative incidence of acute GVHD but not with increased risk of relapse. Our data demonstrate that Bregs can prevent acute GVHD and maintain GVL effects and suggest that Bregs have potential as a novel strategy for acute GVHD alleviation.

The Relationship between STR-PCR Chimerism Analysis and Chronic GvHD Following Hematopoietic Stem Cell Transplantation

Background: The study attempts to assess the relationship between chimerism analysis using polymerase chain reaction of short tandem repeat (STR) and the incidence of chronic graft versus host disease (GvHD) as well as survival. Subjects and Methods: The retrospective cohort included all patients who received allo-HSCT during 2005-2013. Data collected by day +100 were reviewed in terms of the incidence of chronic GvHD and survival. Chimerism was evaluated for whole blood, T-cell and PMN cells on days 15, 30 and 60, respectively using polymerase chain reaction of short tandem repeat (STR). Results: Forty (69%) patients developed chronic GvHD, 11 (19%) relapsed and 22 (39.7%) expired during the study. There was a significant relationship between chronic GvHD and chimerism analysis including whole blood on day 60 (p=0.001), Polymorphonuclear neutrophil (PMN) on day 60 (p=0.05), T-cell on days 15 (p=0.028), 30 (p=0.01) and 60 (p=0.004). Patients with chronic GvHD showed a long-term survival as compared with those without chronic GvHD (p=0.0013). Conclusion: Conducting continuous analysis of chimerism provides an opportunity to initiate immediate measures in order to prevent complications.

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.

Chronic graft-versus-host disease: biological insights from preclinical and clinical studies

With the increasing use of mismatched, unrelated, and granulocyte colony-stimulating factor-mobilized peripheral blood stem cell donor grafts and successful treatment of older recipients, chronic graft-versus-host disease (cGVHD) has emerged as the major cause of nonrelapse mortality and morbidity. cGVHD is characterized by lichenoid changes and fibrosis that affects a multitude of tissues, compromising organ function. Beyond steroids, effective treatment options are limited. Thus, new strategies to both prevent and treat disease are urgently required. Over the last 5 years, our understanding of cGVHD pathogenesis and basic biology, born out of a combination of mouse models and correlative clinical studies, has radically improved. We now understand that cGVHD is initiated by naive T cells, differentiating predominantly within highly inflammatory T-helper 17/T-cytotoxic 17 and T-follicular helper paradigms with consequent thymic damage and impaired donor antigen presentation in the periphery. This leads to aberrant T- and B-cell activation and differentiation, which cooperate to generate antibody-secreting cells that cause the deposition of antibodies to polymorphic recipient antigens (ie, alloantibody) or nonpolymorphic antigens common to both recipient and donor (ie, autoantibody). It is now clear that alloantibody can, in concert with colony-stimulating factor 1 (CSF-1)-dependent donor macrophages, induce a transforming growth factor β-high environment locally within target tissue that results in scleroderma and bronchiolitis obliterans, diagnostic features of cGVHD. These findings have yielded a raft of potential new therapeutics, centered on naive T-cell depletion, interleukin-17/21 inhibition, kinase inhibition, regulatory T-cell restoration, and CSF-1 inhibition. This new understanding of cGVHD finally gives hope that effective therapies are imminent for this devastating transplant complication.

Upregulation of IFN-Inducible and Damage-Response Pathways in Chronic Graft-versus-Host Disease

Although chronic graft-versus-host disease (CGVHD) is the primary nonrelapse complication of allogeneic transplantation, understanding of its pathogenesis is limited. To identify the main operant pathways across the spectrum of CGVHD, we analyzed gene expression in circulating monocytes, chosen as in situ systemic reporter cells. Microarrays identified two interrelated pathways: 1) IFN-inducible genes, and 2) innate receptors for cellular damage. Corroborating these with multiplex RNA quantitation, we found that multiple IFN-inducible genes (affecting lymphocyte trafficking, differentiation, and Ag presentation) were concurrently upregulated in CGVHD monocytes compared with normal subjects and non-CGVHD control patients. IFN-inducible chemokines were elevated in both lichenoid and sclerotic CGHVD plasma and were linked to CXCR3+ lymphocyte trafficking. Furthermore, the levels of the IFN-inducible genes CXCL10 and TNFSF13B (BAFF) were correlated at both the gene and the plasma levels, implicating IFN induction as a factor in elevated BAFF levels in CGVHD. In the second pathway, damage-/pathogen-associated molecular pattern receptor genes capable of inducing type I IFN were upregulated. Type I IFN-inducible MxA was expressed in proportion to CGVHD activity in skin, mucosa, and glands, and expression of TLR7 and DDX58 receptor genes correlated with upregulation of type I IFN-inducible genes in monocytes. Finally, in serial analyses after transplant, IFN-inducible and damage-response genes were upregulated in monocytes at CGVHD onset and declined upon therapy and resolution in both lichenoid and sclerotic CGVHD patients. This interlocking analysis of IFN-inducible genes, plasma analytes, and tissue immunohistochemistry strongly supports a unifying hypothesis of induction of IFN by innate response to cellular damage as a mechanism for initiation and persistence of CGVHD.

Conditioning with Fludarabine-Busulfan versus Busulfan-Cyclophosphamide Is Associated with Lower aGVHD and Higher Survival but More Extensive and Long Standing Bone Marrow Damage

Acute graft-versus-host disease (aGVHD) is a major complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT) and a major cause of nonrelapse mortality after allo-HSCT. A conditioning regimen plays a pivotal role in the development of aGVHD. To provide a platform for studying aGVHD and evaluating the impact of different conditioning regimens, we established a murine aGVHD model that simulates the clinical situation and can be conditioned with Busulfan-Cyclophosphamide (Bu-Cy) and Fludarabine-Busulfan (Flu-Bu). In our study, BALB/c mice were conditioned with Bu-Cy or Flu-Bu and transplanted with 2 × 10⁷ bone marrow cells and 2 × 10⁷ splenocytes from either allogeneic (C57BL/6) or syngeneic (BALB/c) donors. The allogeneic recipients conditioned with Bu-Cy had shorter survivals (P < 0.05), more severe clinical manifestations, and higher hepatic and intestinal pathology scores, associated with increased INF-γ expression and diminished IL-4 expression in serum, compared to allogeneic recipients conditioned with Flu-Bu. Moreover, higher donor-derived T-cell infiltration and severely impaired B-cell development were seen in the bone marrow of mice, exhibiting aGVHD and conditioned with Flu-Bu. Our study showed that the conditioning regimen with Bu-Cy resulted in more severe aGVHD while the Flu-Bu regimen was associated with more extensive and long standing bone marrow damage.

The Role of Animal Models in the Study of Hematopoietic Stem Cell Transplantation and GvHD: A Historical Overview

Bone marrow transplantation (BMT) is the only therapeutic option for many hematological malignancies, but its applicability is limited by life-threatening complications, such as graft-versus-host disease (GvHD). The last decades have seen great advances in the understanding of BMT and its related complications; in particular GvHD. Animal models are beneficial to study complex diseases, as they allow dissecting the contribution of single components in the development of the disease. Most of the current knowledge on the therapeutic mechanisms of BMT derives from studies in animal models. Parallel to BMT, the understanding of the pathophysiology of GvHD, as well as the development of new treatment regimens, has also been supported by studies in animal models. Pre-clinical experimentation is the basis for deep understanding and successful improvements of clinical applications. In this review, we retrace the history of BMT and GvHD by describing how the studies in animal models have paved the way to the many advances in the field. We also describe how animal models contributed to the understanding of GvHD pathophysiology and how they are fundamental for the discovery of new treatments.

Recombinant IL-7/HGFβ hybrid cytokine separates acute graft-versus-host-disease from graft-versus-tumour activity by altering donor T cell trafficking

Given that donor T cells from a transplant contribute both the desired graft-versus-tumour (GVT) effect and detrimental graft-versus-host disease (GVHD), strategies to separate GVHD and GVT activity are a major clinical goal. We have previously demonstrated that in vivo administration of a recombinant (r)IL-7/HGFβ hybrid cytokine, consisting of interleukin-7 (IL-7, IL7) and the β-chain of hepatocyte growth factor (HGFβ), significantly inhibits the growth of cancer cells in murine tumour models. The antit-umour effect of rIL-7/HGFβ is related to a marked infiltration T cells in the tumour tissues. We have also shown that GVHD was not induced in rIL-7/HGFβ-treated T cell-depleted allogeneic haematopoietic stem cell transplantation (HSCT) recipients. We show here that, in T cell-replete allogeneic HSCT murine models, rIL-7/HGFβ attenuated acute GVHD (aGVHD), while promoting GVT activity. This was related to an alteration of donor T cell trafficking, with an increased infiltration of donor T cells into tumour tissues and the lympho-haematopoietic system but decreased number of the T cells in the GVHD target organs. Therefore, rIL-7/HGFβ may offer a new tool to alleviate aGVHD while prompting GVT, and to study the molecular regulation of T cell trafficking.

Donor-Derived Regulatory T Cells Attenuate the Severity of Acute Graft-Versus-Host Disease after Cord Blood Transplantation

Allogeneic peripheral blood stem cell transplantation (allo-PBSCT) is a curative therapy for some types of hematological disorders. However, allo-PBSCT is commonly complicated with acute graft-versus-host disease (aGVHD), characterized by host tissues being attacked by the grafted donor lymphocytes due to disparities of human leukocyte antigen (HLA) between the donor and host. By contrast, cord blood transplantation (CBT) is typically associated with low-grade severity of aGVHD, but the underlying mechanisms remain unclear. Donor-derived CD4(+) alloreactive T cells (ATs) are of a specific lymphocyte subset, which can be activated by the recipient's HLA, and play a crucial role in the onset of aGVHD. In the present study, we aimed to explore the difference in the property of CD4(+) ATs between cord blood (CB) and adult peripheral blood (APB). We thus found that CB and APB CD4(+) ATs contained not only effector T cells (Teffs) that execute aGVHD, but also a distinct subset of FoxP3(+) regulatory T cells (Tregs) that may alleviate aGVHD. Importantly, CB CD4(+) ATs contained higher percentage of FoxP3(+) Tregs, compared to APB CD4(+) ATs (P < 0.001), while lower percentage of Teffs (Th1, Th2 and Th17 cells) was detected in CB CD4(+) ATs (P < 0.05, P < 0.001 and P < 0.05, respectively). Our findings suggest that FoxP3(+) Tregs in CB CD4(+) ATs may contribute to attenuating the severity of aGVHD observed after CBT.

Mesenchymal stem cells improve the outcomes of liver recipients via regulating CD4+ T helper cytokines in rats

BACKGROUND

Bone marrow mesenchymal stem cells (BMMSCs) exert immunosuppressive activities in transplantation. This study aimed to determine whether BMMSCs reduce acute rejection and improve outcomes of liver transplantation in rats.

METHODS

Orthotopic liver transplantation from Lewis to Brown Norway rats was performed, which was followed by the infusion of BMMSCs through the penile superficial dorsal vein. Normal saline infusion was used as a control. Animals were sacrificed at 0, 24, 72, or 168 hours after BMMSCs infusion. Liver grafts, and recipient serum and spleen tissues were obtained. Histopathology, apoptosis, serum liver enzymes, serum cytokines, and circulating regulatory T (Treg), Th1, Th2 and Th17 cells were assessed at each time point.

RESULTS

BMMSCs significantly attenuated acute rejection and improved the survival rate of allogeneic liver transplantation recipients. Liver enzymes and liver apoptosis were significantly alleviated. The levels of the Th1/Th2 ratio-associated cytokines such as IL-2 and IFN-gamma were significantly reduced and IL-10 was significantly increased. The levels of the Th17/Tregs axis-associated cytokines such as IL-6, IL-17, IL-23, and TNF-alpha were significantly reduced, whereas TGF-beta concentration was significantly increased. Moreover, flow cytometry analysis showed that the infusion of BMMSCs significantly increased Th2 and Treg cells and decreased Th1 and Th17 cells.

CONCLUSION

BMMSCs had immunomodulatory effects, attenuated acute rejection and improved outcomes of allogeneic liver transplantation in rats by regulating the levels of cytokines associated with Th1/Th2 and Th17/Treg ratios.

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.

Translational opportunities for targeting the Th17 axis in acute graft-vs.-host disease

Allogeneic stem cell transplantation (allo-SCT) is a curative therapy for different life-threatening malignant and non-malignant hematologic disorders. Acute graft-vs.-host disease (aGVHD) and particularly gastrointestinal aGVHD remains a major source of morbidity and mortality following allo-SCT, which limits the use of this treatment in a broader spectrum of patients. Better understanding of aGVHD pathophysiology is indispensable to identify new therapeutic targets for aGVHD prevention and therapy. Growing amount of data suggest a role for T helper (Th)17 cells in aGVHD pathophysiology. In this review, we will discuss the current knowledge in this area in animal models and in humans. We will then describe new potential treatments for aGVHD along the Th17 axis.

Antibodies from donor B cells perpetuate cutaneous chronic graft-versus-host disease in mice

Cutaneous sclerosis is one of the most common clinical manifestations of chronic graft-versus-host disease (cGVHD). Donor CD4(+) T and B cells play important roles in cGVHD pathogenesis, but the role of antibodies from donor B cells remains unclear. In the current studies, we generated immunoglobulin (Ig)H(µγ1) DBA/2 mice whose B cells have normal antigen-presentation and regulatory functions but cannot secrete antibodies. With a murine cGVHD model using DBA/2 donors and BALB/c recipients, we have shown that wild-type (WT) grafts induce persistent cGVHD with damage in the thymus, peripheral lymphoid organs, and skin, as well as cutaneous T helper 17 cell (Th17) infiltration. In contrast, IgH(µγ1) grafts induced only transient cGVHD with little damage in the thymus or peripheral lymph organs or with little cutaneous Th17 infiltration. Injections of IgG-containing sera from cGVHD recipients given WT grafts but not IgG-deficient sera from recipients given IgH(µγ1) grafts led to deposition of IgG in the thymus and skin, with resulting damage in the thymus and peripheral lymph organs, cutaneous Th17 infiltration, and perpetuation of cGVHD in recipients given IgH(µγ1) grafts. These results indicate that donor B-cell antibodies augment cutaneous cGVHD in part by damaging the thymus and increasing tissue infiltration of pathogenic Th17 cells.