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Major future challenges in the field of allo-HCT include a better control of acute and chronic steroid-refractory graft-versus-host disease (SR-aGVHD, SR-cGVHD), more efficient treatment of relapse of the hematological malignancy, and overcoming poor immune reconstitution.

Myeloid-derived suppressor cells (MDSCs) can subdue inflammation. In mice with acute graft-versus-host disease (GVHD), donor MDSC infusion enhances survival that is only partial and transient because of MDSC inflammasome activation early posttransfer, resulting in differentiation and loss of suppressor function. Here we demonstrate that conditioning regimen-induced adenosine triphosphate (ATP) release is a primary driver of MDSC dysfunction through ATP receptor (P2x7R) engagement and NLR pyrin family domain 3 (NLRP3) inflammasome activation. P2x7R or NLRP3 knockout (KO) donor MDSCs provided significantly higher survival than wild-type (WT) MDSCs. Although in vivo pharmacologic targeting of NLRP3 or P2x7R promoted recipient survival, indicating in vivo biologic effects, no synergistic survival advantage was seen when combined with MDSCs. Because activated inflammasomes release mature interleukin-1�� (IL-1��), we expected that IL-1�� KO donor MDSCs would be superior in subverting GVHD, but such MDSCs proved inferior relative to WT. IL-1�� release and IL-1 receptor expression was required for optimal MDSC function, and exogenous IL-1�� added to suppression assays that included MDSCs increased suppressor potency. These data indicate that prolonged systemic NLRP3 inflammasome inhibition and decreased IL-1�� could diminish survival in GVHD. However, loss of inflammasome activation and IL-1�� release restricted to MDSCs rather than systemic inhibition allowed non-MDSC IL-1�� signaling, improving survival. Extracellular ATP catalysis with peritransplant apyrase administered into the peritoneum, the ATP release site, synergized with WT MDSCs, as did regulatory T-cell infusion, which we showed reduced but did not eliminate MDSC inflammasome activation, as assessed with a novel inflammasome reporter strain. These findings will inform future clinical using MDSCs to decrease alloresponses in inflammatory environments.

During the past decade, progress in basic immunology and applied tumor immunology has been impressive. The better understanding of the complexities of the immune system has direct implication for the immune biology of hematopoietic stem cell transplantation (HSCT), a major immunotherapeutic intervention. Major discoveries of the immunobiology of HSCT have been made in preclinical models and to a lesser extent in correlative clinical studies, which have resulted in the clinical testing of new agents and approaches to overcome obstacles that have limited the widespread application of HSCT. In this overview, we summarize some of the major advances in the field, the translation of these from the bench to the bedside, and discuss preclinical approaches that are in the progress of being translated into a clinical application.

Background: Acute graft-versus-host disease (aGVHD) is a potentially fatal complication of allogeneic hematopoietic cell transplantation that fails to improve with intense immunosuppression in some patients. We hypothesized that urinary-derived human chorionic gonadotropin [uhCG] could help facilitate resolution of life-threatening aGVHD when added as supportive care via two potential mechanisms: immunomodulation (akin to its role in pregnancy) and supplementation of epidermal growth factor (EGF, to aid in epithelial repair). Methods: In phase I, 26 participants received subcutaneous injections of uhCG in addition to standard immunosuppression (13 initial therapy for Minnesota high risk aGVHD and 13 receiving 2nd line therapy). Participants underwent serial blood testing for biomarkers of hormone response, immune modulation, and aGVHD activity on study. Findings: UhCG was well tolerated, with no dose-limiting toxicities. Sixty-two percent of patients in the high-risk cohort and 54% of patients in the 2nd line cohort had a complete response at study day 28. Plasma EGF was elevated 6-fold (from 4 to 24 pg/ml, p=0.02) at 6 hours post-dose in the high risk cohort, in contrast to no peak in plasma EGF in the more severe 2nd line cohort. After 1 week of uhCG, patients demonstrated a 2-fold increase in regulatory T cell to conventional T cell ratio, suggesting immune modulation despite high dose steroids. Responding patients showed significantly lower plasma amphiregulin and higher plasma butyrate at study completion, suggesting improvement in mucosal damage over time. Interpretation: hCG is a novel, safe supportive therapy, proceeding to phase II testing at 2,000 units/m2 in high-risk aGVHD. Trial Registration: This study is registered at ClinicalTrials.gov (NCT02525029). Funding Statement: This study was funded by the BMT Fund for the Future (SGH), a Regenerative Medicine Minnesota clinical trial award (SGH), and R01 HL11879, R01 HL56067 and R37 AI34495 (BRB). SGH is a University of Minnesota Women’s Early Research Career (WERC) award recipient and conducted this study during her time as a WERC scholar. Declaration of Interests: The authors have no relevant financial conflicts of interest to disclose. SGH has provided consulting services for Incyte, Bristol Myers Squibb, Janssen, and CSL Behring. BRB receives remuneration as an advisor to Kadmon Pharmaceuticals, Inc, Five Prime Therapeutics Inc, Regeneron Pharmaceuticals, Magenta Therapeutics, BlueRock Therapeuetics and consulting services for Bristol-Myers-Squibb, Incyte, Equillium, Regimmune, Dr. Reddy, GT Biopharma and Incyte Corp; research support from Fate Therapeutics, RXi Pharmaceuticals, Alpine Immune Sciences, Inc, Abbvie Inc., Leukemia and Lymphoma Society, Childrens' Cancer Research Fund, and KidsFirst Fund, and is a co-founder of Tmunity. Ethics Approval Statement: This study was approved by the University of Minnesota Institutional Review Board, and all participants signed written, informed consent.

Regulatory T (Treg) cells control self-tolerance, inflammatory responses and tissue homeostasis. In mature Treg cells, continued expression of FOXP3 maintains lineage identity, while T cell receptor (TCR) signaling and interleukin-2 (IL-2)/STAT5 activation support the suppressive effector function of Treg cells, but how these regulators synergize to control Treg cell homeostasis and function remains unclear. Here we show that TCR-activated posttranslational modification by O-linked N-Acetylglucosamine (O-GlcNAc) stabilizes FOXP3 and activates STAT5, thus integrating these critical signaling pathways. O-GlcNAc-deficient Treg cells develop normally but display modestly reduced FOXP3 expression, strongly impaired lineage stability and effector function, and ultimately fatal autoimmunity in mice. Moreover, deficiency in protein O-GlcNAcylation attenuates IL-2/STAT5 signaling, while overexpression of a constitutively active form of STAT5 partially ameliorates Treg cell dysfunction and systemic inflammation in O-GlcNAc deficient mice. Collectively, our data demonstrate that protein O-GlcNAcylation is essential for lineage stability and effector function in Treg cells., The transcription factor Foxp3 and Stat5 modulate lineage stability and function of regulatory T (Treg) cells to promote immune homeostasis. Here the authors show that O-GlcNAcylation of Foxp3 and Stat5, mediated by O-GlcNAc transferase (OGT), is essential for Treg-mediate immune balance, with Treg-specific deficiency of OGT leading to severe autoimmunity.

Introduction Allogeneic hematopoietic stem cell transplant (Allo-HSCT) is a potentially curative treatment for malignant and non-malignant blood disorders. However, current conditioning regimens limit its use due to regimen-related mortality and morbidities. We are developing novel antibody drug conjugates (ADCs) to provide the benefit of full-intensity conditioning to remove disease-causing cells while reducing the severity of treatment-related adverse events. These ADCs are designed to deliver agents specifically to CD45+ target cells as a sole conditioning agent or as the primary conditioning agent in a reduced intensity conditioning protocol for allo-HSCT. The aim of this study was to model this approach with a tool anti-mouse CD45 ADC to determine if targeted ADCs can be used to enable allo-HSCT in mice. Methods We developed a tool anti-mouse CD45 ADC engineered to have a short half-life (T1/2 = 1.7hr) to enable HSCT. The optimal dose of tool CD45-ADC was established in a congenic autologous mouse transplant model. Next, the tool CD45-ADC was evaluated alone or in combination with low dose (0.5 Gy) total body irradiation (TBI) or T cell-depleting anti-mouse antibodies (CD4 and CD8, 0.25 mg/kg IP) in a full mismatch allo-HSCT model (Balb/c donors (H-2d, CD45.1+) into C57Bl/6 recipients (H-2b, CD45.2+)). 9 Gy TBI served as the conventional conditioning positive control. Conditioned mice were transplanted with 2 × 107 whole bone marrow cells, and peripheral blood chimerism assessed over 16 weeks. Results A single 3 mg/kg dose of the tool CD45-ADC was an effective regimen in a congenic autologous mouse transplant model, resulting in full donor chimerism comparable to conditioning with 9 Gy TBI. In a full mismatch allo-HSCT model, a single dose of CD45-ADC enabled mixed myeloid chimerism out to 3 weeks as a single agent, but the chimerism was transient. In combination with low dose TBI or T cell depleting antibodies, the tool CD45-ADC enabled >90% peripheral donor chimerism by week 4 post-transplantation, which was maintained through week 16. Multilineage reconstitution of T-, B-, and myeloid cell compartments was observed (>90% donor chimerism) and was comparable to chimerism seen in the 9 Gy TBI positive control. Treatment with a non-targeting isotype ADC was not effective (Figure 1A, 1B). Conclusion A single dose of the tool CD45-ADC is fully myeloablative and enables complete chimerism in a full mismatch allo-HSCT model with low dose TBI or supplemental T cell depletion. Future experiments will examine the use of tool CD45-ADC conditioning in HSCT as a treatment in mouse autoimmune disease models. This targeted, readily translatable approach for safer conditioning could improve the risk-benefit profile for allogenic and haploidentical HSCT and may extend the curative potential of this therapeutic modality.

Follicular regulatory T (TFR) cells have specialized roles in modulating follicular helper T (TFH) cell activation of B cells. However, the precise role of TFR cells in controlling antibody responses to foreign antigens and autoantigens in vivo is still unclear due to a lack of specific tools. A TFR cell-deleter mouse was developed that selectively deletes TFR cells, facilitating temporal studies. TFR cells were found to regulate early, but not late, germinal center (GC) responses to control antigen-specific antibody and B cell memory. Deletion of TFR cells also resulted in increased self-reactive immunoglobulin (Ig) G and IgE. The increased IgE levels led us to interrogate the role of TFR cells in house dust mite models. TFR cells were found to control TFH13 cell-induced IgE. In vivo, loss of TFR cells increased house-dust-mite-specific IgE and lung inflammation. Thus, TFR cells control IgG and IgE responses to vaccines, allergens and autoantigens, and exert critical immunoregulatory functions before GC formation.

CD4+ follicular helper T (Tfh) cells are specialized providers of T cell help to B cells and can function as pathogenic mediators of murine antibody-dependent chronic graft-versus-host disease (GvHD). Using a parent→F1 model of lupus-like chronic GvHD, in which Tfh cell and germinal center (GC) B cell differentiation occurs over 14 days, we demonstrate that absence of CD4+ T cell-expressed C5a receptor 1 (C5ar1) or pharmacological C5aR1 blockade abrogated generation/expansion of Tfh cells, GC B cells, and autoantibodies. In a Tfh cell-dependent model of chronic GvHD manifested by bronchiolitis obliterans syndrome (BOS), C5aR1 antagonism initiated in mice with established disease ameliorated BOS and abolished the associated differentiation of Tfh and GC B cells. Guided by RNA-sequencing data, mechanistic studies performed using murine and human T cells showed that C5aR1 signaling amplifies IL-6-dependent expression of the transcription factor c-MAF and the cytokine IL-21 via phosphorylating phosphokinase B (AKT) and activating the mammalian target of rapamycin (mTOR). In addition to linking C5aR1-initiated signaling to Tfh cell differentiation, our findings suggest that C5aR1 may be a useful therapeutic target for prevention and/or treatment of individuals with Tfh cell-dependent diseases, including those chronic GvHD patients who have anti-host reactive antibodies.

Soluble thrombomodulin plasma concentrations are elevated in steroid-resistant graft-versus-host disease (GVHD), implying endothelial hypofunctioning for thrombomodulin-dependent generation of activated protein C’s (APC) anticoagulant, anti-inflammatory, and antiapoptotic functions. Recombinant thrombomodulin or APC administration decreases acute GVHD, manifested by intense inflammation and tissue destruction. Here, we administered recombinant murine wild-type (WT) APC to mice with established chronic GVHD (cGVHD), a less-inflammatory autoimmune-like disease. WT APC normalized bronchiolitis obliterans–induced pulmonary dysfunction. Signaling-selective APC variants (3A-APC [APC with lysine 191-193 replaced with 3 alanines] or 5A-APC [APC with lysine 191-193 replaced with 3 alanines and arginine 229/230 replaced with 2 alanines]) with normal cytoprotective properties, but greatly reduced anticoagulant activity, provided similar results. Mechanistically, WT APC and signaling-selective variants reduced T follicular helper cells, germinal center formation, immunoglobulin, and collagen deposition. WT APC can potentially cleave protease-activated receptor 1 (PAR1) at Arg41 or Arg46, the latter causing anti-inflammatory signaling. cGVHD was reduced in recipients of T cells from WT PAR1 or mutated Gln41-PAR1 donors but not from mutated Gln46-PAR1 donors. These data implicate donor T-cell APC-induced noncanonical cleavage at Arg46-PAR1, which is known to confer cytoprotective and anti-inflammatory activities. Together, these data indicate that APC anticoagulant activity is dispensable, whereas anti-inflammatory signaling and cytoprotective cell signaling by APC are essential. Because a phase 2 ischemic stroke clinical trial did not raise any safety issues for 3A-APC treatment, our studies provide a foundational platform for testing in clinical cGVHD therapy.

Tan et al. provide novel insights into understanding how PD-1 regulates regulatory T (T reg) cells. More specifically, this study demonstrates that loss of PD-1 on T reg cells leads to enhanced T reg cell suppressor function in vitro and in vivo. These findings have clinical relevance for understanding the efficacy of PD-1– and PD-L1–mediated checkpoint blockade., Inhibitory signals through the PD-1 pathway regulate T cell activation, T cell tolerance, and T cell exhaustion. Studies of PD-1 function have focused primarily on effector T cells. Far less is known about PD-1 function in regulatory T (T reg) cells. To study the role of PD-1 in T reg cells, we generated mice that selectively lack PD-1 in T reg cells. PD-1–deficient T reg cells exhibit an activated phenotype and enhanced immunosuppressive function. The in vivo significance of the potent suppressive capacity of PD-1–deficient T reg cells is illustrated by ameliorated experimental autoimmune encephalomyelitis (EAE) and protection from diabetes in nonobese diabetic (NOD) mice lacking PD-1 selectively in T reg cells. We identified reduced signaling through the PI3K–AKT pathway as a mechanism underlying the enhanced suppressive capacity of PD-1–deficient T reg cells. Our findings demonstrate that cell-intrinsic PD-1 restraint of T reg cells is a significant mechanism by which PD-1 inhibitory signals regulate T cell tolerance and autoimmunity., Graphical Abstract

Acute graft- vs. -host disease (GVHD) is an important cause of morbidity and death after allogeneic hematopoietic cell transplantation (HCT). We identify a new approach to prevent GVHD that impairs monocyte-derived dendritic cell (moDC) alloactivation of T cells, yet preserves graft- vs.-leukemia (GVL). Exceeding endoplasmic reticulum (ER) capacity results in a spliced form of X-box binding protein-1 (XBP-1s). XBP-1s mediates ER stress and inflammatory responses. We demonstrate that siRNA targeting XBP-1 in moDCs abrogates their stimulation of allogeneic T cells. B-I09, an inositol-requiring enzyme-1α (IRE1α) inhibitor that prevents XBP-1 splicing, reduces human moDC migration, allo-stimulatory potency, and curtails moDC IL-1β, TGFβ, and p40 cytokines, suppressing Th1 and Th17 cell priming. B-I09-treated moDCs reduce responder T cell activation via calcium flux without interfering with regulatory T cell (Treg) function or GVL effects by cytotoxic T lymphocytes (CTL) and NK cells. In a human T cell mediated xenogeneic GVHD model, B-I09 inhibition of XBP-1s reduced target-organ damage and pathogenic Th1 and Th17 cells without impacting donor Tregs or anti-tumor CTL. DC XBP-1s inhibition provides an innovative strategy to prevent GVHD and retain GVL.

Amphiregulin, a weak epidermal growth factor receptor agonist, is elevated, while epidermal growth factor, a strong epidermal growth factor receptor agonist, is low in the blood of patients with severe acute graft-versus-host disease. However, the tissue expression and function of these epidermal growth factor receptor ligands in acute graft-versus-host disease target organs is unknown. We compared by immunohistochemistry expression of amphiregulin and epidermal growth factor in archived, formalin-fixed, paraffin-embedded intestinal tissues of 48 patients with biopsy-proven gastrointestinal acute graft-versus-host disease to 3 groups: (1) 10 non-hematopoietic cell transplant normal controls, (2) 11 patients with newly diagnosed ulcerative colitis (ulcerative colitis), (3) 8 patients with a clinical diagnosis of acute graft-versus-host disease despite pathologically non-diagnostic biopsies, (4) and 10 cases of cytomegalovirus colitis. We used a semi-quantitative score of 0 (absent) through 3 (strong) to describe the intensity of immunohistochemical staining. We correlated serum and tissue amphiregulin and epidermal growth factor in patients with acute graft-versus-host disease. Gastrointestinal amphiregulin was significantly lower in acute graft-versus-host disease biopsies (median score 1), ulcerative colitis (median score 1.5), and cytomegalovirus colitis (median score 1) than in normal colon (median score 2, p = 0.004, p = 0.03, p = 0.009 respectively). Amphiregulin expression in was low in 74% of acute graft-versus-host disease cases with or without significant apoptosis. Patients with acute graft-versus-host disease exhibiting the pattern of high gastrointestinal amphiregulin but low serum amphiregulin (n = 14) had the best 1-year survival at 71%, but patients with high serum amphiregulin had poorer survival (

Background Our understanding of phenotypic and functional signatures of CD8+ T cell dysfunction in acute myeloid leukemia (AML) is limited. Deciphering these deranged T cell functional states and how they are impacted by induction chemotherapy is essential for incorporation of novel immune-based strategies to restore and maintain antileukemia immunity. Methods We utilized high-dimensional immunophenotyping, gene expression, and functional studies to characterize peripheral blood and bone marrow CD8+ T cells in 72 AML patients at diagnosis and after induction chemotherapy. Results Our data suggest that multiple aspects of deranged T cell function are operative in AML at diagnosis, with exhaustion and senescence being the dominant processes. Following treatment, the phenotypic and transcriptional profile of CD8+ T cells diverged between responders and nonresponders. Response to therapy correlated with upregulation of costimulatory, and downregulation of apoptotic and inhibitory, T cell signaling pathways, indicative of restoration of T cell function. In functional studies, AML blasts directly altered CD8+ T cell viability, expansion, co-signaling and senescence marker expression. This CD8+ T cell dysfunction was in part reversible upon PD-1 blockade or OX40 costimulation in vitro. Conclusion Our findings highlight the uniqueness of AML in sculpting CD8+ T cell responses and the plasticity of their signatures upon chemotherapy response, providing a compelling rationale for integration of novel immunotherapies to augment antileukemia immunity. Funding This work was supported by the Leukemia & Lymphoma Society grant no. 6449-13; NIH grants UM1-CA186691 and R01-HL110907-01; the American Society for Blood and Marrow Transplantation New Investigator Award/Gabrielle's Angel Foundation; the Vienna Fund for Innovative Cancer Research; and by fellowships from the Wenner-Gren Foundation and the Swedish Society for Medical Research.

Allogeneic hematopoietic stem cell transplantation (allo-SCT) is potentially curative for a number of hematologic conditions, both malignant and nonmalignant. However, its success can be limited by the development of acute and chronic graft-versus-host disease (GVHD). Chronic GVHD (cGVHD) is the most common long-term complication following allo-SCT, and patients who develop this condition have significantly higher morbidity and mortality and significantly lower quality of life than patients who do not. Until recently, there were no US Food and Drug Administration (FDA)–approved therapies for cGVHD treatment. In this review article, we describe how ibrutinib was identified as potential cGVHD therapy based on preclinical cGVHD models and clinical studies in B-cell malignancies and elucidation of its mechanisms of action in cGVHD. Results from a phase 2 clinical trial that was designed based on National Institutes of Health Criteria for the grading and staging of cGVHD culminated in the FDA-approval of ibrutinib as second line therapy of steroid-refractory or steroid-resistant cGVHD. Results of ibrutinib studies in phase 3 randomized studies, for cGVHD prophylaxis and as first -line testing along with steroids will be especially important in selecting the preferred indications for ibrutinib in patients at risk for or who have developed cGVHD.

Host genetics shape the gut microbiota, and gut dysbiosis increases the risk of acute graft-versus-host disease (aGVHD). Paneth cells and microbiota have interactions that contribute to immune regulation. α-defensin-5 (HD5) and regenerating islet-derived protein 3 alpha (Reg3A) are the most abundant Paneth cell antimicrobial peptides (AMPs). We hypothesized that single nucleotide polymorphisms (SNPs) in the genes for HD5 (DEFA5) and Reg3A (REG3A) predict aGVHD risk. We analysed pre-transplant recipient peripheral blood mononuclear cell samples from randomized Blood and Marrow Transplant Clinical Trials Network (BMT CTN) studies 0201 (94 patients with bone marrow and 93 with peripheral blood grafts) and 0901 (86 patients with myeloablative and 77 with reduced-intensity conditioning; all using peripheral blood grafts). In multivariable analysis (with a SNP × graft source interaction term in CTN-0201 and a SNP × conditioning intensity term in CTN-0901), DEFA5 rs4415345 and rs4610776 were associated with altered incidence of aGVHD grade II-IV [rs4415345 G vs. C: hazard ratio (HR) 0·58, 95% confidence interval (95% CI) 0·37-0·92, P = 0·02; rs4610776 T vs. A: HR 1·53, 95% CI 1·01-2·32, P = 0·05] in CTN-0201, but not CTN-0901, suggesting a stronger effect in bone marrow allografts. REG3A SNP was not associated with aGVHD. Host genetics may influence aGVHD risk by modulating Paneth cell function.

Post-transplant biomarkers of acute graft-versus-host disease (aGVHD) and non-relapse mortality (NRM) after allogeneic hematopoietic cell transplantation (HCT) have been extensively studied. However, pre-transplant biomarkers may provide a greater window of opportunity to intervene. We measured serum biomarkers of various aspects of gut barrier physiology before HCT (median: day-7), and 7 and 28 days post-HCT in 95 consecutive allo-HCT recipients enrolled in an open-label biorespository protocol. Biomarkers included citrulline for total functional enterocyte mass, Reg3a for antibacterial activity of the gut, and intestinal fatty acid binding protein (I-FABP) for enterocyte turnover. Using sixteen healthy controls, we demonstrated that patients came to transplant with abnormal levels of all three biomarkers (P < 0.05), reflecting residual damage from prior chemotherapy. All three biomarkers initially declined from pre-HCT to day +7 (more pronounced after myeloablative vs. reduced-intensive conditioning) followed by a recovery phase and return towards pre-HCT values by day +28. A lower pre-HCT citrulline was independently associated with a higher risk of aGVHD grade II–IV (hazard ratio: 1.32, 95% confidence interval: 1.03–1.69; P = 0.02), and this association was not specific to gut GVHD. The strongest correlate of NRM was a higher level of Reg3a at day +7 (11.51 [9.43–19.99] vs. 4.20 [2.76–6.42] ng/mL in patients with vs. without NRM, respectively; P < 0.001). I-FABP did not predict transplant outcomes. In conclusion, pre-HCT serum citrulline levels identify patients at high risk for developing aGVHD. Our results suggest that pre-HCT interventions to augment the gut barrier may decrease the risk of aGVHD.

Recent studies have underscored the critical role of retinoic acid (RA) in the development of lineage-committed CD4 and CD8 T cells in vivo. We have shown that under acute graft-versus-host disease (GVHD) inflammatory conditions, RA is upregulated in the intestine and is proinflammatory, as GVHD lethality was attenuated when donor allogeneic T cells selectively expressed a dominant negative RA receptor α that blunted RA signaling. RA can function in an autocrine and paracrine fashion, and as such, the host cell lineage responsible for the production of RA metabolism and the specific RA-metabolizing enzymes that potentiate GVHD severity are unknown. In this study, we demonstrate that enhancing RA degradation in the host and to a lesser extent donor hematopoietic cells by overexpressing the RA-catabolizing enzyme CYP26A1 reduced GVHD. RA production is facilitated by retinaldehyde isoform-2 (RALDH2) preferentially expressed in dendritic cells (DCs). Conditionally deleted RA-synthesizing enzyme RALDH2 in host or to a lesser extent donor DCs reduced GVHD lethality. Improved survival in recipients with RALDH2-deleted DCs was associated with increased T cell death, impaired T effector function, increased regulatory T cell frequency, and augmented coinhibitory molecule expression on donor CD4+ T cells. In contrast, retinaldehydrogenase isoform-1 (RALDH1) is dominantly expressed in intestinal epithelial cells. Unexpectedly, conditional host intestinal epithelial cells RALDH1 deletion failed to reduce GVHD. These data demonstrate the critical role of both donor and especially host RALDH2+ DCs in driving murine GVHD and suggest RALDH2 inhibition or CYP26A1 induction as novel therapeutic strategies to prevent GVHD.

A new study reveals that leukemia stem cells (LSCs) in acute myeloid leukemia downregulate natural killer cell‐activating receptor ligands to evade immune surveillance via the transcriptional co‐factor PARP1. The inhibition of PARP1 sensitizes LSCs to immunotherapy, highlighting its potential as a therapeutic target.

Natural killer (NK) cells are capable of fighting viral infections and cancer. However, these responses are inhibited by immune suppressor cells in the tumor microenvironment. Tumor progression promotes the recruitment and generation of intratumoral regulatory T cells (Treg), associated with a poor prognosis in cancer patients. Here, we show that canonical NK cells are highly susceptible to Treg-mediated suppression, in contrast to highly resistant CD57+ FcϵRγ−NKG2C+ adaptive (CD56+CD3−) NK cells that expand in cytomegalovirus exposed individuals. Specifically, Tregs suppressed canonical but not adaptive NK-cell proliferation, IFNγ production, degranulation, and cytotoxicity. Treg-mediated suppression was associated with canonical NK-cell downregulation of TIM3, a receptor that activates NK-cell IFNγ production upon ligand engagement, and upregulation of the NK-cell inhibitory receptors PD-1 and the IL1 receptor family member, IL1R8 (SIGIRR or TIR8). Treg production of the IL1R8 ligand, IL37, contributed to the phenotypic changes and diminished function in Treg-suppressed canonical NK cells. Blocking PD-1, IL1R8, or IL37 abrogated Treg suppression of canonical NK cells while maintaining NK-cell TIM3 expression. Our data uncover new mechanisms of Treg-mediated suppression of canonical NK cells and identify that adaptive NK cells are inherently resistant to Treg suppression. Strategies to enhance the frequency of adaptive NK cells in the tumor microenvironment or to blunt Treg suppression of canonical NK cells will enhance the efficacy of NK-cell cancer immunotherapy. Cancer Immunol Res; 6(7); 766–75. ©2018 AACR.

Age-related thymic involution is characterized by a decrease in thymic epithelial cell (TEC) number and function parallel to a disruption in their spatial organization, resulting in defective thymocyte development and proliferation as well as peripheral T cell dysfunction. Deficiency of Klotho, an antiaging gene and modifier of fibroblast growth factor signaling, causes premature aging. To investigate the role of Klotho in accelerated age-dependent thymic involution, we conducted a comprehensive analysis of thymopoiesis and peripheral T cell homeostasis using Klotho-deficient (Kl/Kl) mice. At 8 wk of age, Kl/Kl mice displayed a severe reduction in the number of thymocytes (10–100-fold reduction), especially CD4 and CD8 double-positive cells, and a reduction of both cortical and medullary TECs. To address a cell-autonomous role for Klotho in TEC biology, we implanted neonatal thymi from Klotho-deficient and -sufficient mice into athymic hosts. Kl/Kl thymus grafts supported thymopoiesis equivalently to Klotho-sufficient thymus transplants, indicating that Klotho is not intrinsically essential for TEC support of thymopoiesis. Moreover, lethally irradiated hosts given Kl/Kl or wild-type bone marrow had normal thymocyte development and comparably reconstituted T cells, indicating that Klotho is not inherently essential for peripheral T cell reconstitution. Because Kl/Kl mice have higher levels of serum phosphorus, calcium, and vitamin D, we evaluated thymus function in Kl/Kl mice fed with a vitamin D–deprived diet. We observed that a vitamin D–deprived diet abrogated thymic involution and T cell lymphopenia in 8-wk-old Kl/Kl mice. Taken together, our data suggest that Klotho deficiency causes thymic involution via systemic effects that include high active vitamin D levels.

Regulatory T cells (Treg) are crucial mediators of immune control. The characteristic gene expression and suppressive function of Treg depend considerably on the stable expression and activity of the transcription factor Foxp3. While transcriptional regulation of the Foxp3 gene has been studied in depth, both the expression and function of Foxp3 are also modulated at the protein level. However, the molecular players involved in posttranslational Foxp3 regulation are just beginning to be elucidated. Here we found TRAF6-deficient Tregs were dysfunctional in vivo; mice with Treg-restricted deletion of TRAF6 were resistant to B16 melanomas and displayed enhanced anti-tumor immunity. We further determined that Foxp3 undergoes lysine-63 chain (K63) ubiquitination at lysine 262 mediated by the E3 ligase TRAF6. When deprived of TRAF6 activity or rendered insensitive to K63 ubiquitination, Foxp3 displayed aberrant, perinuclear accumulation, disrupted function. Thus, Foxp3 ubiquitination by TRAF6 ensures proper localization of Foxp3 and facilitates Foxp3’s gene-regulating activity in Tregs. These results implicate TRAF6 as a key posttranslational, Treg-stabilizing force that may be targeted in novel tolerance-breaking therapies.

Improved diagnostic and treatment methods are needed for chronic graft-versus-host disease (cGVHD), the leading cause of late nonrelapse mortality (NRM) in long-term survivors of allogenic hematopoietic cell transplantation. Validated biomarkers that facilitate disease diagnosis and classification generally are lacking in cGVHD. Here, we conducted whole serum proteomics analysis of a well-established murine multiorgan system cGVHD model. We discovered 4 upregulated proteins during cGVHD that are targetable by genetic ablation or blocking antibodies, including the RAS and JUN kinase activator, CRKL, and CXCL7, CCL8, and CCL9 chemokines. Donor T cells lacking CRK/CRKL prevented the generation of cGVHD, germinal center reactions, and macrophage infiltration seen with wild-type T cells. Whereas antibody blockade of CCL8 or CXCL7 was ineffective in treating cGVHD, CCL9 blockade reversed cGVHD clinical manifestations, histopathological changes, and immunopathological hallmarks. Mechanistically, elevated CCL9 expression was present predominantly in vascular smooth muscle cells and uniquely seen in cGVHD mice. Plasma concentrations of CCL15, the human homolog of mouse CCL9, were elevated in a previously published cohort of 211 cGVHD patients compared with controls and associated with NRM. In a cohort of 792 patients, CCL15 measured at day +100 could not predict cGVHD occurring within the next 3 months with clinically relevant sensitivity/specificity. Our findings demonstrate for the first time the utility of preclinical proteomics screening to identify potential new targets for cGVHD and specifically CCL15 as a diagnosis marker for cGVHD. These data warrant prospective biomarker validation studies.

Over the last decade, our understanding of the pathophysiology of chronic graft-versus-host disease (cGVHD) has improved considerably. In this spotlight, we discuss emerging insights into the pathophysiology of cGVHD with a focus on B cells. First, we summarize supporting evidence derived from mouse and human studies. Next, novel cGVHD therapy approaches that target B cells will be covered to provide treating physicians with an overview of the rationale behind the emerging armamentarium against cGVHD.

Chronic graft-versus-host disease (cGVHD) is a major complication of allogeneic hematopoietic cell transplantation (allo-HCT) and remains an area of unmet clinical need with few treatment options available. Notch blockade prevents acute GVHD in multiple mouse models, but the impact of Notch signaling on cGVHD remains unknown. Using genetic and antibody-mediated strategies of Notch inhibition, we investigated the role of Notch signaling in complementary mouse cGVHD models that mimic several aspects of human cGVHD in search of candidate therapeutics. In the B10.D2→BALB/c model of sclerodermatous cGVHD, Delta-like ligand 4 (Dll4)-driven Notch signaling was essential for disease development. Antibody-mediated Dll4 inhibition conferred maximum benefits when pursued early in a preventative fashion, with anti-Dll1 enhancing early protection. Notch-deficient alloantigen-specific T cells showed no early defects in proliferation or helper polarization in vivo but subsequently exhibited markedly decreased cytokine secretion and enhanced accumulation of FoxP3+ regulatory T cells. In the B6→B10.BR major histocompatibility complex-mismatched model with multi-organ system cGVHD and prominent bronchiolitis obliterans (BO), but not skin manifestations, absence of Notch signaling in T cells provided long-lasting disease protection that was replicated by systemic targeting of Dll1, Dll4, or both Notch ligands, even during established disease. Notch inhibition decreased target organ damage and germinal center formation. Moreover, decreased BO-cGVHD was observed upon inactivation of Notch1 and/or Notch2 in T cells. Systemic targeting of Notch2 alone was safe and conferred therapeutic benefits. Altogether, Notch ligands and receptors regulate key pathogenic steps in cGVHD and emerge as novel druggable targets to prevent or treat different forms of cGVHD.

We performed a Ph2 trial in adults and children to test abatacept for AGVHD prevention (‘ABA2', Clinicaltrials # NCT01743131), based on our promising preclinical and pilot patient data. ABA2 had 2 cohorts: A) HLA-mismatched (‘7/8', n = 43), a single-arm study with pre-specified CIBMTR matched analysis (vs CNI+MTX or CNI+MTX+ATG). B) HLA-matched (‘8/8', n = 142), randomized double-blind, comparing CNI+MTX+placebo vs CNI+MTX+ABA (‘ABA'). For each ABA arm, patients received 4 doses of 10mg/kg on d -1,5,14,28. ABA2 was designed as a screening Ph2 trial, with relaxed Type 1 error (0.2) and standard Type 2 error (0.2). Power analysis assumed ABA would decrease Gr 3-4 AGVHD from 30%–>10% in 7/8s and from 20%–>10% in 8/8s. Here we report top-line results for the 7/8s (median f/u = 708d, 264-1491) and 8/8s (median f/u = 369d, 180-1175). Reduced Grade 3-4 AGVHD: ABA was associated with decreased d180 Gr 3-4 AGVHD. In 7/8s, Gr 3-4 AGVHD = 2.5% in ABA (1 event/43 patients) vs 31% (CNI+MTX) and 22% (+ATG), 1 sided p = 0.001, 0.005,). In 8/8s, Gr 3-4 AGVHD = 6.85 % (5 events/73 patients) in ABA vs 14.6% (10 events) in placebo, 1 sided p = 0.068). Reduced Grade 2-4 AGVHD in 8/8s: ABA was associated with decreased d180 Gr 2-4 AGVHD. In 7/8s, Gr 2-4 AGVHD = 42% (ABA) vs 54% (CNI+MTX) and 45% (+ATG, 1 sided p = 0.098, 0.25). In 8/8s, Gr 2-4 AGVHD = 44.5% in ABA vs 62.3% in placebo (1 sided p = 0.004). Chronic GVHD: For 7/8s, 1 yr CGVHD = 38.8% (ABA) vs 43.5% (CNI+MTX) and 35.5% (+ATG, p = 0.4, 0.99). For 8/8s, follow up is still too short to adequately evaluate, and adjudication is ongoing. No Increase In Relapse: In 7/8s, relapse = 9.37% at 1 y vs 12.9% in CNI+MTX and 13.6% in +ATG (p = 0.115 and 0.085). In 8/8s, relapse = 13.8% at 1y (ABA) vs 20.5% (placebo, p = 0.7). Remarkably, in 7/8s, where median follow up=708d, there have been no further relapses reported in ABA2, with 9.37% relapse at 2 yr vs 20.63% (CNI+MTX) and 23.4% (ATG), despite matched disease risk. Statistically significant survival advantage in 7/8s: TRM: For 7/8s, 1 yr TRM = 10.5% (ABA) vs 32.7% (CNI+MTX) and 26% (+ATG, p = 0.024, 0.365). For 8/8s, TRM = 7.1% vs 14.6% at 1 yr (p = 0.5). Relapse-Free Survival (RFS): For 7/8s, RFS = 73.7% (ABA) vs 38.7% in CNI+MTX and 48.7% in +ATG (p = 0.001 and 0.027). For 8/8s, RFS = 79.1% for ABA vs 64.9% (placebo, p = 0.38). OS: For 7/8s, OS = 71% (ABA) vs 47.5% (CNI+MTX) and 58% (+ATG, p = 0.01 and 0.145). For 8/8s, OS = 83.2% (ABA) vs 76.6 (placebo, p = 0.32). Our results suggest that short-course (4 doses) ABA can safely prevent AGVHD without compromising relapse. While this was a modestly sized study (7/8s: n = 43, 8/8 n = 142), the comparative event size for 7/8s was high enough that the protective effect of ABA was highly statistically significant. For 8/8s, there was a statistically significant improvement for Gr 2-4 GVHD and a trend toward an advantage for ABA in all other parameters. These results are the first to demonstrate efficacy of in vivo T cell costimulation blockade in preventing AGVHD.

Background Achieving mixed chimerism suppresses donor T cell alloreactivity and reduces graft-versus-host disease (GVHD)-related mortality after bone marrow transplantation (BMT). Mixed hematopoietic chimerism is the only condition proven to lead to immune tolerance after transplantation. It can be achieved with protocols utilizing chemotherapeutic agents or strategies that block T cell activation or deplete host T cells. Selective irradiation of the thymus or lymphoid organs can also lead to mixed hematopoietic chimerism. After total lymphocyte irradiation (TLI), mixed chimerism is mediated by host iNKT lymphocytes and the T helper 2 (Th2) cytokine IL4 generated by those cells. IL4 signals through IL4 receptor (IL4R) and STAT6. After a toxic myeloablative pretransplant regimen, total body irradiation (TBI), intestinal immune conditioning with helminthic commensals regulates the host immune system and promotes a transient mixed chimerism. Conditioning with helminths also induces IL4 production by host cells and regulates GVHD while preserving the graft-versus-tumor effect. We hypothesize that induction of host Th2 pathway is critical for achieving mixed chimerism by intestinal immune conditioning Methods We evaluated the role of recipient Th2 signaling in the establishment of mixed chimerism in an MHC I/II major mismatch (H2b→H2d) model that utilizes TBI. Three weeks after infection with the mouse nematode, Heligmosomoides polygyrus-bakeri (Hpb), GVHD was induced by the delivery of T cell-depleted bone marrow (TCD-BM) and splenic T cells from uninfected WT C57BL/6 (MHC:H2b) donors into lethally-irradiated WT BALB/c, interleukin 4 (IL4) -/-, IL4Rα-/- and STAT6-/- recipients (MHC: H2d). Cellular composition for donor vs recipient cells, GVHD-mediated inflammation in end-organs (colon and lung), and survival of mice in each setting were assessed Results In 3 models of disruption of the Th2 pathway, we demonstrated that Th2 signaling in the host is essential for the establishment of mixed chimerism. Helminth infection promotes mixed chimerism in WT BALB/c BMT recipients; recipient T cells constitute 3-5% of peripheral population at 6 days post-BMT, whereas recipient T cells constitute Conclusions Intestinal immune conditioning with helminths promotes mixed chimerism after toxic, host cell depleting myeloablative TBI and regulates lethal GVHD following BMT. Host cell Th2 pathway is critical for achieving mixed chimerism. Helminths stimulate CTLA4 - a cellular regulatory protein known to promote mixed chimerism after BMT- in a Th2 dependent manner Disclosures Blazar: Kadmon Corporation, LLC: Consultancy, Research Funding.

Introduction Severe acute graft-versus-host disease (aGVHD) is characterized by an imbalance of circulating tissue repair factors, with elevated amphiregulin (AREG) and very low ( Patients and Methods Twenty-six patients received hCG/EGF in addition to standard aGVHD therapy (13 with Minnesota high risk aGVHD and 13 receiving 2nd line therapy). In both cohorts, patients with a complete or partial response (CR/PR) at the end of the initial dosing period were eligible to receive maintenance hCG/EGF SQ twice weekly for up to 5 weeks. Initial hCG dosing was at 500 units hCG/m2 SQ, escalating to 2,000 units hCG/m2 in cohorts of 2, with dose assignment by the continual reassessment method. We analyzed GVHD-associated plasma biomarkers during therapy. Results HCG/EGF was well tolerated, with no dose-limiting toxicities. At day 28 of study, responses for initial therapy were 8/13 CR (62%), 0/13 PR (0%), and 5/13 NR (38%), higher than institutional historical (n=269) 26% CR, 16% PR, 57% NR (Figure 1A). Responses for 2nd line therapy were 7/13 CR (54%), 1/13 PR (8%), 5/13 NR (38%), 4 of which were deaths (31%), improved relative to historical outcomes (n=85) of 18% CR, 19% PR, 63% NR (including 16% deaths, Figure 1A). In initial therapy patients, plasma EGF rose from baseline 3 pg/ml to 25.4 pg/ml at 6 hours post-hCG/EGF dose (p=0.02), while in 2nd line patients, plasma EGF never rose from baseline 5 pg/ml. Patients with a day 28 CR/PR had a 4.6-fold reduction in plasma AREG over time (Figure 1B). Conclusions HCG/EGF is a novel adjunct therapy in life-threatening aGVHD. The mechanisms of benefit may include facilitation of tissue repair with detectable increases in circulating EGF. The optimal dose and duration of hCG/EGF are under investigation, with ongoing dose escalation in patients with steroid-refractory aGVHD based upon these results. Decreasing plasma AREG may reflect successful treatment of severe aGVHD.

Daily low-dose interleukin-2 (IL-2) at a fixed dose of 1 × 106 IU/m2/day leads to preferential expansion of CD4+CD25+CD127-Foxp3+ regulatory T cells (Treg) and clinical responses in 50-60% of adult patients with steroid-refractory chronic GVHD. During fixed-dose IL-2 therapy, plasma IL-2 levels rise rapidly, but decrease over time despite continued daily administration. Lower IL-2 levels correlate with decreased Treg proliferation, possibly due to IL-2 sequestration via binding to high-affinity IL-2 receptors on Treg. We reasoned that IL-2 dose escalation at the time of anticipated fall in plasma IL-2 levels would avoid tachyphylaxis and enhance Treg expansion. We conducted a phase 1 trial of individual patient IL-2 dose escalation over 8 weeks in adult and pediatric patients with steroid-refractory cGVHD. Daily SC IL-2 was initiated at 0.67 × 106 and 0.33 × 106 IU/m2/day in the adult and pediatric cohorts, respectively. Each participant had dose escalations at weeks 2 and 4 to a maximum dose of 2 × 106 IU/m2/day in adults and 1 × 106 IU/m2/day in children. We studied 21 participants (10 adult, 11 children) with median ages of 57 (range, 33-71) and 12 years (range, 3-22) in the adult and pediatric cohorts, respectively. The cohorts did not differ in terms of time since cGVHD onset, number of organ sites involved or failed therapies prior to enrollment. Individually dose-escalated IL-2 was well tolerated in children with 1 patient requiring dose reduction for electrolyte imbalances. In the adult cohort, 1 patient withdrew for cGVHD progression, 4 required dose reduction for injection site reactions and 2 were unevaluable. At week 8, objective cGVHD responses (PR) were seen in 8 of 11 pediatric patients (73%), but in only 1 of 8 evaluable adult patients (13%). Response sites included skin (n=4), joint/fascia/muscle (n=1), lung (n=5), and GI tract (n=2). 11 pediatric and 4 adult participants with clinical benefit (PR or SD with minor response) continued extended duration IL-2 therapy. 9 pediatric patients on IL-2 therapy were able to wean steroid therapy with a median dose reduction of 67% at 6 months (Fig. 1). Children had a superior immunologic response despite lower IL-2 doses. The median Treg:Tcon ratio at week 8 was significantly higher in the pediatric cohort (0.42 vs 0.21, p = 0.02). Both cohorts had increased NK cell numbers, with no significant changes in CD4Tcon, CD8 T cell or B cells (Fig. 2). Pediatric patients had greater thymic output of naive Treg as well as a larger fraction of PD-1-expressing effector memory Treg at baseline and during IL-2 therapy (Fig. 3), which has been correlated with improved Treg expansion and survival. We show for the first time that low-dose IL-2 is safe in children with advanced steroid-refractory cGVHD and results in a high clinical response rate. In adults, dose escalation above fixed-dose MTD did not improve Treg expansion or clinical response relative to fixed daily dosing.

Introduction cGVHD is characterized by an imbalance between effector and regulatory arms of the immune system that results in over production of IL-17 and IL-21. A reduction in the regulatory T (Treg) cells limits the ability of the immune system to re-calibrate this pro-inflammatory environment. KD025 is an oral Rho kinase 2 (ROCK2) selective inhibitor. In vitro data demonstrate KD025 modulates immune homeostasis by shifting the Th17/Treg balance towards Treg. Methods 3 cohorts (C1: 200 mg QD, C2: 200 mg BID, and C3: 400 mg QD) of patients (pts) with cGVHD after 1-3 prior lines of systemic therapy were treated in 28-Day cycles until disease progression. The primary endpoint is overall response rate (ORR) (partial/complete response) per 2014 NIH criteria. Additional endpoints include duration of response (DOR), corticosteroid (CS) dose reductions, Lee Symptom Scale (LSS) score and PD. Blood samples were collected at Cycle 1 Day 1 (C1D1), C2D1, C4D1 and C6D25, and shipped at ambient temperature. PBMC were isolated and kept frozen until analysis. Intracellular expression of IL-17A and FOXP3 was determined by flow cytometry. Results Data as of 6-June-2018 for C1 and C2 are included; C3 data will be available 4Q18. 17 and 16 pts were enrolled in C1 and C2 with median age 52 years, time from cGVHD diagnosis to KD025 treatment of 19 months, and 3 prior regimens. Median duration of treatment was37 (C1) and 33 (C2) weeks. KD025 demonstrated ORR of 65% in C1 and 63% in C2. Responses were rapid (76% at first assessment at 8 weeks) and durable (≥20 weeks) in 82% (C1) and 50% (C2) of responders. Median CS dose was reduced 44% (C1) and 26% (C2). 76% and 56% of pts achieved CS dose reductions. 5/33 (15%) pts discontinued CS. 65% (C1) and 50% (C2) achieved a meaningful improvement (≥7 point reduction) in the LSS score. Common AEs were increased LFTs 42%, URI 33%, anemia 27%, nausea 24%, diarrhea 24% and fatigue 21%. Grade 3+ LFT increases were reported for 6 (18%) pts. 2 pts discontinued treatment due to AEs possibly related to KD025 (headache, diarrhea). SAEs were reported for 11/33 pts, none considered related to KD025. There was no apparent increased risk of infection. Exploratory PD analyses revealed an early increase in the percentage of CD4+ Treg cells by C2D1 with a simultaneous decrease in Th17 cells. The percentage of CD4+ Tregs continued to increase, and the Th17 cells continued to decrease through C6D25. Conclusion KD025 achieved responses with little toxicity. Responses are clinically meaningful with durability, reductions in CS doses and improvement in LSS score. PD data indicate KD025 may restore the Th17/Treg balance.

Allogeneic hematopoietic cell transplantation is often complicated by graft-versus-host disease (GVHD). We analyzed the incidences and risk factors for acute (aGVHD) and chronic GVHD (cGVHD), and their impact on disease relapse and survival, among recipients of single umbilical cord blood (sUCB, n = 295), double umbilical cord blood (dUCB, n = 416), and matched sibling donor (MSD, n = 469) allografts. The incidences of grades II to IV aGVHD and chronic GVHD among dUCB, sUCB, and MSD were 56% and 26%, 26% and 7%, 37% and 40%, respectively. Development of aGVHD had no effect on relapse, nonrelapse mortality, or overall survival among cord blood recipients, but it was associated with worse nonrelapse mortality and survival in MSD recipients. Development of cGVHD was only associated with lower relapse in dUCBT. In multivariate analysis of GVHD incidence, age > 18 years was associated with higher incidence of aGVHD and cGVHD across all cohorts. In both UCB cohorts worse HLA match and prior aGVHD were associated with higher risks of aGVHD and cGVHD, respectively. Nonmyeloablative conditioning limited the risk of aGVHD compared with myeloablative conditioning in dUCB recipients. Cyclosporine A and mycophenolate mofetil as GVHD prophylaxis lowered the risk of cGVHD, compared with steroids with cyclosporine A, among sUCB recipients. This large contemporary analysis suggests distiinct risks and consequences of GVHD for UCB and MSD recipients. Limiting the severity of aGVHD remains important in all groups. Increasing the cord blood inventory or developing strategies that reduce the cell-dose threshold and thereby increase the chance of identifying an adequately dosed, better HLA-matched sUCB unit may further limit risks of aGVHD after UCB transplantation.

Clinical application of umbilical cord blood (UCB) as a source of hematopoietic stem cells for transplantation is limited by low CD34+ cell dose, increased risk of graft failure and slow hematopoietic recovery. While the cell dose limitation is partially mitigated by using two UCB units, larger dosed single units would be preferable. We have evaluated the feasibility and safety of StemRegenin-1 (SR-1), an aryl hydrocarbon receptor antagonist that expands CD34+ cells, by placing one of the two units in expansion culture. SR-1 produced a 330-fold increase in CD34+ cells and led to engraftment in 17/17 patients at a median of 15 days for neutrophils and 49 days for platelets, significantly faster than in patients treated with unmanipulated UCB. Taken together, the marked expansion, absence of graft failure and enhanced hematopoietic recovery support testing of SR-1 expansion as a stand-alone graft and suggest it may ameliorate a limitation of UCB transplantation.

A disodium phosphonooxymethyl prodrug of the antitumor agent triptolide was prepared from the natural product in three steps (39% yield) and displayed excellent aqueous solubility at pH 7.4 (61 mg/mL) compared to the natural product (17 μg/mL). The estimated shelf life (t90) for hydrolysis of the prodrug at 4 °C and pH 7.4 was found to be two years. In a mouse model of human colon adenocarcinoma (HT-29), the prodrug administered intraperitoneally was effective in reducing or eliminating xenograft tumors at dose levels as low as 0.3 mg/kg when given daily and at 0.9 mg/kg when given less frequently. When given via intraperitoneal and oral routes at daily doses of 0.6 and 0.9 mg/kg, the prodrug was also effective and well tolerated in a mouse model of human ovarian cancer (A2780).

Hematopoietic stem cell transplantation (HSCT) recipients lacking HLA-matched related donors have increased graft-versus-host disease (GVHD) and nonrelapse mortality (NRM). Bortezomib added to reduced-intensity conditioning can offer benefit in T cell–replete HLA-mismatched HSCT and may also benefit myeloablative conditioning (MAC) transplants. We conducted a phase II trial of short-course bortezomib plus standard tacrolimus/methotrexate after busulfan/fludarabine MAC in 34 patients with predominantly myeloid malignancies. Fourteen (41%) received 8/8 HLA-matched unrelated donor (MUD) and 20 (59%) received 7/8 HLA-mismatched related/unrelated donor peripheral blood stem cell grafts. Median age was 49 years (range, 21 to 60), and median follow-up was 25 months (range, 11 to 36). The regimen was well tolerated. No dose modifications were required. Neutrophil and platelet engraftment occurred at a median of 14 (range, 10 to 33) and 17 (range, 10 to 54) days, respectively. Median 30-day donor chimerism was 99% (range, 90 to 100), and 100-day grades II to IV and III to IV acute GVHD incidence was 32% and 12% respectively. One-year chronic GVHD incidence was 50%. Two-year cumulative incidence of both NRM and relapse was 16%. Two-year progression-free and overall survival rates were 70% and 71%, respectively. Outcomes were comparable to an 8/8 MUD MAC cohort (n = 45). Immune reconstitution was robust. Bortezomib-based MAC HSCT is well tolerated, with HLA-mismatched outcomes comparable with 8/8 MUD MAC HSCT, and is suitable for randomized evaluation. (clinicaltrials.gov: NCT01323920.)

We have demonstrated that immunostimulatory therapies such as interleukin-2 (IL-2) and anti-CD40 (αCD40) can be combined to deliver synergistic anti-tumor effects. While this strategy has shown success, efficacy varies depending on a number of factors including tumor type and severe toxicities can be seen. We sought to determine whether blockade of negative regulators such as cytotoxic T lymphocyte antigen-4 (CTLA-4) could simultaneously prolong CD8(+) T cell responses and augment T cell anti-tumor effects. We devised a regimen in which anti-CTLA-4 was administered late so as to delay contraction and minimize toxicities. This late administration both enhanced and prolonged CD8 T cell activation without the need for additional IL-2. The quality of the T cell response was improved with increased frequency of effector/effector memory phenotype cells along with improved lytic ability and bystander expansion. This enhanced CD8 response translated to improved anti-tumor responses both at the primary and metastatic sites. Importantly, toxicities were not exacerbated with combination. This study provides a platform for rational design of immunotherapy combinations to maximize anti-tumor immunity while minimizing toxicities.

Myeloid-derived suppressor cells (MDSCs) are a naturally occurring immune regulatory population associated with inhibition of ongoing inflammatory responses. In vitro generation of MDSCs from bone marrow has been shown to enhance survival in an acute model of lethal graft-versus-host disease (GVHD). However, donor MDSC infusion only partially ameliorates GVHD lethality. In order to improve the potential therapeutic benefit and ultimately survival outcomes, we set out to investigate the fate of MDSCs after transfer in the setting of acute GVHD (aGVHD). MDSCs transferred to lethally irradiated recipients of allogeneic donor hematopoietic grafts are exposed to an intense inflammatory environment associated with aGVHD, which we now show directly undermines their suppressive capacity. Under a conditioning regimen and GVHD inflammatory settings, MDSCs rapidly lose suppressor function and their potential to inhibit GVHD lethality, which is associated with their induced conversion toward a mature inflammasome-activated state. We find even brief in vitro exposure to inflammasome-activating mediators negates the suppressive potential of cultured murine and human-derived MDSCs. Consistent with a role for the inflammasome, donor MDSCs deficient in the adaptor ASC (apoptosis-associated speck-like protein containing a CARD), which assembles inflammasome complexes, conferred improved survival of mice developing GVHD compared with wild-type donor MDSCs. These data suggest the use of MDSCs as a therapeutic approach for preventing GVHD and other systemic inflammatory conditions will be more effective when combined with approaches limiting in vivo MDSC inflammasome activation, empowering MDSCs to maintain their suppressive potential.

T lymphocytes are critical mediators of the adaptive immune system and have the capacity to serve as therapeutic agents in the areas of transplant and cancer immunotherapy. While T cells can be isolated and expanded from patients, T cells derived in vitro from both hematopoietic stem/progenitor cells (HSPCs) and human pluripotent stem cells (hPSCs) offer great potential advantages in generating a self-renewing source of T cells that can be readily genetically modified. T-cell differentiation in vivo is a complex process requiring tightly regulated signals; providing the correct signals in vitro to induce T-cell lineage commitment followed by their development into mature, functional, single positive T cells, is similarly complex. In this review, we discuss current methods for the in vitro derivation of T cells from murine and human HSPCs and hPSCs that use feeder-cell and feeder-cell-free systems. Furthermore, we explore their potential for adoption for use in T-cell-based therapies. Stem Cells 2015;33:3174–3180

Novel therapies for chronic graft-versus-host disease (cGVHD) are needed. Aberrant B-cell activation has been demonstrated in mice and humans with cGVHD. Having previously found that human cGVHD B cells are activated and primed for survival, we sought to further evaluate the role of the spleen tyrosine kinase (Syk) in cGVHD in multiple murine models and human peripheral blood cells. In a murine model of multiorgan system, nonsclerodermatous disease with bronchiolitis obliterans where cGVHD is dependent on antibody and germinal center (GC) B cells, we found that activation of Syk was necessary in donor B cells, but not T cells, for disease progression. Bone marrow-specific Syk deletion in vivo was effective in treating established cGVHD, as was a small-molecule inhibitor of Syk, fostamatinib, which normalized GC formation and decreased activated CD80/86(+) dendritic cells. In multiple distinct models of sclerodermatous cGVHD, clinical and pathological disease manifestations were not eliminated when mice were therapeutically treated with fostamatinib, though both clinical and immunologic effects could be observed in one of these scleroderma models. We further demonstrated that Syk inhibition was effective at inducing apoptosis of human cGVHD B cells. Together, these data demonstrate a therapeutic potential of targeting B-cell Syk signaling in cGVHD.

Death receptor 3 (DR3, TNFRSF25) is expressed by activated lymphocytes and signaling by its ligand, TL1A, enhances cytokine expression and proliferation. Recent studies show that DR3 is also present on murine type 2 innate lymphoid cells (ILC2s). Here, we show that DR3 is expressed by IL-22-producing human group 3 innate lymphoid cells (ILC3s). Stimulation of ILC3s with exogenous TL1A alone had no impact on cytokine production or proliferation. Addition of TL1A to IL-1β + IL-23 significantly enhanced the amount IL-22 produced by ILC3s as well as the percentage IL-22- and IL-8-producing cells. Addition of TL1A to IL-1β + IL-23 also augmented ILC3 proliferation. Mechanistically, this occurred through the upregulation of CD25 and responsiveness to IL-2 stimulation. The combination of TL1A, IL-1β+ IL-23, and IL-2 expanded ILC3s while IL-1β+ IL-23 did not increase proliferation above controls. After 2 weeks of expansion, ILC3s maintained their phenotype, transcription factor expression, and function (IL-22 production). These findings identify DR3 as a costimulatory molecule on ILC3s that could be exploited for ex vivo expansion and clinical use.

Although cytomegalovirus (CMV) reactivation has long been implicated in posttransplant immune dysfunction, the molecular mechanisms that drive this phenomenon remain undetermined. To address this, we combined multiparameter flow cytometric analysis and T-cell subpopulation sorting with high-throughput sequencing of the T-cell repertoire, to produce a thorough evaluation of the impact of CMV reactivation on T-cell reconstitution after unrelated-donor hematopoietic stem cell transplant. We observed that CMV reactivation drove a >50-fold specific expansion of Granzyme B(high)/CD28(low)/CD57(high)/CD8(+) effector memory T cells (Tem) and resulted in a linked contraction of all naive T cells, including CD31(+)/CD4(+) putative thymic emigrants. T-cell receptor β (TCRβ) deep sequencing revealed a striking contraction of CD8(+) Tem diversity due to CMV-specific clonal expansions in reactivating patients. In addition to querying the topography of the expanding CMV-specific T-cell clones, deep sequencing allowed us, for the first time, to exhaustively evaluate the underlying TCR repertoire. Our results reveal new evidence for significant defects in the underlying CD8 Tem TCR repertoire in patients who reactivate CMV, providing the first molecular evidence that, in addition to driving expansion of virus-specific cells, CMV reactivation has a detrimental impact on the integrity and heterogeneity of the rest of the T-cell repertoire. This trial was registered at www.clinicaltrials.gov as #NCT01012492.

Programmed death-1 (PD-1) promotes T cell tolerance. Despite therapeutically targeting this pathway for chronic infections and tumors, little is known about how different T cell subsets are affected during blockade. We examined PD-1/PD ligand 1 (PD-L1) regulation of self-antigen–specific CD4 and CD8 T cells in autoimmune-susceptible models. PD-L1 blockade increased insulin-specific effector CD4 T cells in type 1 diabetes. However, anergic islet-specific CD4 T cells were resistant to PD-L1 blockade. Additionally, PD-L1 was critical for induction, but not maintenance, of CD8 T cell intestinal tolerance. PD-L1 blockade enhanced functionality of effector T cells, whereas established tolerant or anergic T cells were not dependent on PD-1/PD-L1 signaling to remain unresponsive. This highlights the existence of Ag-experienced T cell subsets that do not rely on PD-1/PD-L1 regulation. These findings illustrate how positive treatment outcomes and autoimmunity development during PD-1/PD-L1 inhibition are linked to the differentiation state of a T cell.

© Copyright 2015, Mary Ann Liebert, Inc. Artemis is a single-stranded endonuclease, deficiency of which results in a radiation-sensitive form of severe combined immunodeficiency (SCID-A) most effectively treated by allogeneic hematopoietic stem cell (HSC) transplantation and potentially treatable by administration of genetically corrected autologous HSCs. We previously reported cytotoxicity associated with Artemis overexpression and subsequently characterized the human Artemis promoter with the intention to provide Artemis expression that is nontoxic yet sufficient to support immunodevelopment. Here we compare the human Artemis promoter (APro) with the moderate-strength human phosphoglycerate kinase (PGK) promoter and the strong human elongation factor-1α (EF1α) promoter to regulate expression of Artemis after ex vivo lentiviral transduction of HSCs in a murine model of SCID-A. Recipient animals treated with the PGK-Artemis vector exhibited moderate repopulation of their immune compartment, yet demonstrated a defective proliferative T lymphocyte response to in vitro antigen stimulation. Animals treated with the EF1α-Artemis vector displayed high levels of T lymphocytes but an absence of B lymphocytes and deficient lymphocyte function. In contrast, ex vivo transduction with the APro-Artemis vector supported effective immune reconstitution to wild-type levels, resulting in fully functional T and B lymphocyte responses. These results demonstrate the importance of regulated Artemis expression in immune reconstitution of Artemis-deficient SCID.

Members of the B7 family have been shown to be important for regulating immune responses by providing either positive or negative costimulatory signals. The function of B7-H3 has been controversial. We show that B7-H3 is upregulated in graft-versus-host disease (GVHD) target organs, including the colon, liver, and lung. Infusion of allogeneic donor T cells into B7-H3(-/-) vs wild-type (WT) recipients resulted in increased GVHD lethality associated with increased T-cell proliferation, colonic inflammatory cytokines, and destruction of epithelial barriers. Allogeneic B7-H3(-/-) vs WT donor T cells also had increased T-cell proliferation and GVHD lethality associated with increased proliferation and cytokine secretion in the spleen, intraepithelial lymphocyte inflammatory cytokines, and intestinal permeability. Both resting and activated regulatory T cells (Tregs) lack B7-H3 messenger RNA. Consistent with these data, GVHD was augmented in recipients of B7-H3(-/-) Treg-depleted grafts. In two delayed lymphocyte infusion (DLI) models, T cells lacking B7-H3 are capable of providing graft-versus-leukemia (GVL) effects. We conclude that B7-H3 is responsible for providing a negative costimulatory signal. Our studies provide support for developing and testing new therapies directed toward the B7-H3 pathway, including approaches to augment host B7-H3 early after bone marrow transplantation to prevent GVHD and to develop potent antagonistic antibodies later after transplant to facilitate DLI-mediated GVL without GVHD complications.

Low day +100 serum epidermal growth factor levels are associated with acute GvHD after allogeneic hematopoietic cell transplantation

Recent evidence has revealed that oncogenic mutations may confer immune escape. A better understanding of how an oncogenic mutation affects immunosuppressive programmed death ligand 1 (PD-L1) expression may help in developing new therapeutic strategies. We show that oncogenic JAK2 (Janus kinase 2) activity caused STAT3 (signal transducer and activator of transcription 3) and STAT5 phosphorylation, which enhanced PD-L1 promoter activity and PD-L1 protein expression in JAK2V617F-mutant cells, whereas blockade of JAK2 reduced PD-L1 expression in myeloid JAK2V617F-mutant cells. PD-L1 expression was higher on primary cells isolated from patients with JAK2V617F–myeloproliferative neoplasms (MPNs) compared to healthy individuals and declined upon JAK2 inhibition. JAK2V617F mutational burden, pSTAT3, and PD-L1 expression were highest in primary MPN patient–derived monocytes, megakaryocytes, and platelets. PD-1 (programmed death receptor 1) inhibition prolonged survival in human MPN xenograft and primary murine MPN models. This effect was dependent on T cells. Mechanistically, PD-L1 surface expression in JAK2V617F-mutant cells affected metabolism and cell cycle progression of T cells. In summary, we report that in MPN, constitutive JAK2/STAT3/STAT5 activation, mainly in monocytes, megakaryocytes, and platelets, caused PD-L1–mediated immune escape by reducing T cell activation, metabolic activity, and cell cycle progression. The susceptibility of JAK2V617F-mutant MPN to PD-1 targeting paves the way for immunomodulatory approaches relying on PD-1 inhibition.

The clinical success of chimeric antigen receptor (CAR) T cell therapy for CD19(+) B cell malignancies can be limited by acute toxicities and immunoglobulin replacement needs due to B cell aplasia from persistent CAR T cells. Life-threatening complications include cytokine release syndrome and neurologic adverse events, the exact etiologies of which are unclear. To elucidate the underlying toxicity mechanisms and test potentially safer CAR T cells, we developed a mouse model in which human CD19 (hCD19)-specific mouse CAR T cells were adoptively transferred into mice whose normal B cells express a hCD19 transgene at hemizygous levels. Compared to homozygous hCD19 transgenic mice that have ∼75% fewer circulating B cells, hemizygous mice had hCD19 frequencies and antigen density more closely simulating human B cells. Hemizygous mice given a lethal dose of hCD19 transgene-expressing lymphoma cells and treated with CAR T cells had undetectable tumor levels. Recipients experienced B cell aplasia and antigen- and dose-dependent acute toxicities mirroring patient complications. Interleukin-6 (IL-6), interferon γ (IFN-γ), and inflammatory pathway transcripts were enriched in affected tissues. As in patients, antibody-mediated neutralization of IL-6 (and IFN-γ) blunted toxicity. Apparent behavioral abnormalities associated with decreased microglial cells point to CAR-T-cell-induced neurotoxicity. This model will prove useful in testing strategies designed to improve hCD19-specific CAR T cell safety.

NK cell-based immunotherapies have been gaining traction in the clinic for treatment of cancer. IL-15 is currently being used in number of clinical trials to improve NK cell expansion and function. The objective of this study is to evaluate the effect of repetitive IL-15 exposure on NK cells. An in vitro model in which human NK cells are continuously (on on on) or intermittently (on off on) treated with IL-15 was used to explore this question. After treatment, cells were evaluated for proliferation, survival, cell cycle gene expression, function, and metabolic processes. Our data indicate that continuous treatment of NK cells with IL-15 resulted in decreased viability and a cell cycle arrest gene expression pattern. This was associated with diminished signaling, decreased function both in vitro and in vivo, and reduced tumor control. NK cells continuously treated with IL-15 also displayed a reduced mitochondrial respiration profile when compared with NK cells treated intermittently with IL-15. This profile was characterized by a decrease in the spare respiratory capacity that was dependent on fatty acid oxidation (FAO). Limiting the strength of IL-15 signaling via utilization of an mTOR inhibitor rescued NK cell functionality in the group continuously treated with IL-15. The findings presented here show that human NK cells continuously treated with IL-15 undergo a process consistent with exhaustion that is accompanied by a reduction in FAO. These findings should inform IL-15-dosing strategies in NK cell cancer immunotherapeutic settings.

Immunosuppression is a hallmark of tumor progression, and treatments that inhibit or deplete monocytic myeloid-derived suppressive cells could promote anti-tumor immunity. c-FLIP is a central regulator of caspase-8-mediated apoptosis and necroptosis. Here we show that low-dose cytotoxic chemotherapy agents cause apoptosis linked to c-FLIP down-regulation selectively in monocytes. Enforced expression of c-FLIP or viral FLIP rescues monocytes from cytotoxicity and concurrently induces potent immunosuppressive activity, in T cell cultures and in vivo models of tumor progression and immunotherapy. FLIP-transduced human blood monocytes can suppress graft versus host disease. Neither expression of FLIP in granulocytes nor expression of other anti-apoptotic genes in monocytes conferred immunosuppression, suggesting that FLIP effects on immunosuppression are specific to monocytic lineage and distinct from death inhibition. Mechanistically, FLIP controls a broad transcriptional program, partially by NF-κB activation. Therefore, modulation of FLIP in monocytes offers a means to elicit or block immunosuppressive myeloid cells., Signaling and transcriptional regulation of MDSC activity remains largely undefined. Here the authors show that monocytic MDSC immunosuppression is triggered by c-FLIP and requires NFκB, implicate this axis in cancer prognosis and response to therapy, and employ ectopic FLIP to treat immunopathology.

MicroRNAs (miRNAs) have been shown to be key modulators of post-transcriptional gene silencing in many cellular processes. In previous studies designed to understand the role of miRNAs in thymic development, we globally deleted miRNA exclusively in thymic epithelial cells (TECs), which are critical in thymic selection. This resulted in the loss of stromal cells that instruct T cell lineage commitment and affect thymocyte positive selection, required for mature T cell development. Since murine miR-181 is expressed in the thymus and miR-181 deficiency disrupts thymocyte development, we first quantified and thereby demonstrated that miR181a1 and miR181b1 are expressed in purified TECs. By generating mice with TEC targeted loss of miR-181a1 and miR-181b1 expression, we observed that neither TEC cellularity nor thymocyte number nor differentiation was adversely affected. Thus, disrupted thymopoiesis in miR-181 deficient mice was not due to miR-181 loss of expression in TECs. Importantly, in mice with restricted TEC deficiency of miR-181a1 and miR-181b1, there were similar numbers of mature T cells in the periphery in regards to frequencies, differentiation, and function as compared to controls. Moreover miR-181a1 and miR-181b1 were not required for maintenance of thymus integrity over time, as thymic involution was not accelerated in gene-targeted mice. Taken together our data indicate that miR-181a1 and miR-181b1 are dispensable for TEC differentiation, their control of thymocyte development and mature T cell export to and homeostasis within the periphery.