Survival and differentiation defects contribute to neutropenia in glucose-6-phosphatase-β (G6PC3) deficiency in a model of mouse neutrophil granulocyte differentiation

A molecular signature for the G6PC3/SLC37A2/SLC37A4 interactors in glioblastoma disease progression and in the acquisition of a brain cancer stem cell phenotype

Background

Glycogen plays an important role in glucose homeostasis and contributes to key functions related to brain cancer cell survival in glioblastoma multiforme (GBM) disease progression. Such adaptive molecular mechanism is dependent on the glycogenolytic pathway and intracellular glucose-6-phosphate (G6P) sensing by brain cancer cells residing within those highly hypoxic tumors. The involvement of components of the glucose-6-phosphatase (G6Pase) system remains however elusive.

Objective

We questioned the gene expression levels of components of the G6Pase system in GBM tissues and their functional impact in the control of the invasive and brain cancer stem cells (CSC) phenotypes.

Methods

In silico analysis of transcript levels in GBM tumor tissues was done by GEPIA. Total RNA was extracted and gene expression of G6PC1-3 as well as of SLC37A1-4 members analyzed by qPCR in four human brain cancer cell lines and from clinically annotated brain tumor cDNA arrays. Transient siRNA-mediated gene silencing was used to assess the impact of TGF-β-induced epithelial-to-mesenchymal transition (EMT) and cell chemotaxis. Three-dimensional (3D) neurosphere cultures were generated to recapitulate the brain CSC phenotype.

Results

Higher expression in G6PC3, SLC37A2, and SLC37A4 was found in GBM tumor tissues in comparison to low-grade glioma and healthy tissue. The expression of these genes was also found elevated in established human U87, U251, U118, and U138 GBM cell models compared to human HepG2 hepatoma cells. SLC37A4/G6PC3, but not SLC37A2, levels were induced in 3D CD133/SOX2-positive U87 neurospheres when compared to 2D monolayers. Silencing of SLC37A4/G6PC3 altered TGF-β-induced EMT biomarker SNAIL and cell chemotaxis.

Conclusion

Two members of the G6Pase system, G6PC3 and SLC37A4, associate with GBM disease progression and regulate the metabolic reprogramming of an invasive and CSC phenotype. Such molecular signature may support their role in cancer cell survival and chemoresistance and become future therapeutic targets.

SLGT2 Inhibitor Rescues Myelopoiesis in G6PC3 Deficiency

The energy metabolism of myeloid cells depends primarily on glycolysis. 1,5-Anhydroglucitol (1,5AG), a natural monosaccharide, is erroneously phosphorylated by glucose-phosphorylating enzymes to produce 1,5-anhydroglucitol-6-phosphate (1,5AG6P), a powerful inhibitor of hexokinases. The endoplasmic reticulum transporter (SLC37A4/G6PT) and the phosphatase G6PC3 cooperate to dephosphorylate 1,5AG6P. Failure to eliminate 1,5AG6P is the mechanism of neutrophil dysfunction and death in G6PC3-deficient mice. Sodium glucose cotransporter 2 (SLGT2) inhibitor reduces 1,5AG level in the blood and restores the neutrophil count in G6PC3-deficient mice. In the investigator-initiated study, a 30-year-old G6PC3-deficient woman with recurrent infections, distressing gastrointestinal symptoms, and multi-lineage cytopenia was treated with an SLGT2-inhibitor. A significant increase in all the hematopoietic cell lineages and substantial improvement in the quality of life was observed.

Engraftment, Fate, and Function of HoxB8-Conditional Neutrophil Progenitors in the Unconditioned Murine Host

The development and use of murine myeloid progenitor cell lines that are conditionally immortalized through expression of HoxB8 has provided a valuable tool for studies of neutrophil biology. Recent work has extended the utility of HoxB8-conditional progenitors to the in vivo setting via their transplantation into irradiated mice. Here, we describe the isolation of HoxB8-conditional progenitor cell lines that are unique in their ability to engraft in the naïve host in the absence of conditioning of the hematopoietic niche. Our results indicate that HoxB8-conditional progenitors engraft in a β1 integrin-dependent manner and transiently generate donor-derived mature neutrophils. Furthermore, we show that neutrophils derived in vivo from transplanted HoxB8-conditional progenitors are mobilized to the periphery and recruited to sites of inflammation in a manner that depends on the C-X-C chemokine receptor 2 and β2 integrins, the same mechanisms that have been described for recruitment of endogenous primary neutrophils. Together, our studies advance the understanding of HoxB8-conditional neutrophil progenitors and describe an innovative tool that, by virtue of its ability to engraft in the naïve host, will facilitate mechanistic in vivo experimentation on neutrophils.

Chronic neutropenia: how best to assess severity and approach management?

INTRODUCTION

Neutropenia is a relatively common finding in medical practice and the medical approach requires a gradual and pertinent diagnostic procedure as well as adapted management.

AREAS COVERED

The area of chronic neutropenia remains fragmented between diverse diseases or situations. Here physicians involved in different aspects of chronic neutropenia gather both the data from medical literature till the end of May 2021 and their experience to offer a global approach for the diagnosis of chronic neutropenia as well as their medical care.

EXPERT OPINION

In most cases, the neutropenia is transient, frequently related to a viral infection, and not harmful. However, neutropenia can be chronic (i.e. >3 months) and related to a number of etiologies, some clinically benign, such as so-called 'ethnic' neutropenia. Autoimmune neutropenia is the common form in young children, whereas idiopathic/immune neutropenia is a frequent etiology in young females. Inherited neutropenia (or congenital neutropenia) is exceptional, with approximately 30 new cases per 10⁶ births and 30 known subtypes. Such patients have a high risk of invasive bacterial infections, and oral infections. Supportive therapy, which is primarily based on daily administration of an antibiotic prophylaxis and/or treatment with granulocyte-colony stimulating factor (G-CSF), contributes to avoiding recurrent infections.

The AML-associated K313 mutation enhances C/EBPα activity by leading to C/EBPα overexpression

Mutations in the transcription factor C/EBPα are found in ~10% of all acute myeloid leukaemia (AML) cases but the contribution of these mutations to leukemogenesis is incompletely understood. We here use a mouse model of granulocyte progenitors expressing conditionally active HoxB8 to assess the cell biological and molecular activity of C/EBPα-mutations associated with human AML. Both N-terminal truncation and C-terminal AML-associated mutations of C/EBPα substantially altered differentiation of progenitors into mature neutrophils in cell culture. Closer analysis of the C/EBPα-K313-duplication showed expansion and prolonged survival of mutant C/EBPα-expressing granulocytes following adoptive transfer into mice. C/EBPα-protein containing the K313-mutation further showed strongly enhanced transcriptional activity compared with the wild-type protein at certain promoters. Analysis of differentially regulated genes in cells overexpressing C/EBPα-K313 indicates a strong correlation with genes regulated by C/EBPα. Analysis of transcription factor enrichment in the differentially regulated genes indicated a strong reliance of SPI1/PU.1, suggesting that despite reduced DNA binding, C/EBPα-K313 is active in regulating target gene expression and acts largely through a network of other transcription factors. Strikingly, the K313 mutation caused strongly elevated expression of C/EBPα-protein, which could also be seen in primary K313 mutated AML blasts, explaining the enhanced C/EBPα activity in K313-expressing cells.

Cardiac Morphology and Collagen Deposition in A Glucose-6-Phosphatase Catalytic Subunit 3 (G6PC3) Knockout Mouse model

Background

Glucose-6-phosphatase-- β (3), one of multiple isoforms of glucose-6-phosphatase, catalyzes the final step in gluconeogenesis. It is known that mutated G6P3 is associated with severe neutropenia in addition to congenital heart defects, but little is known about the histological changes in cardiac tissue as a result of mutated or deleted G6PC3⁴.

Objectives

We sought to further characterize the histological alterations caused by deleted G6PC3 and determine the role of collagen deposition, myocyte proliferation and apoptosis in these changes.

Methods

Cardiac tissue from G6PC3 knockout mice and WT mice were harvested, imbedded and stained for markers of collagen (Trichrome), proliferation (KI-67), apoptosis (caspase 3) and hematopoietic stem cells (CD34). Slides were digitally uploaded, and Leica stain quantification was calculated.

Results

We demonstrated that in G6PC3 knock out adult mice have significant differences in heart morphology including decreased left ventricular collagen, decreased cellular proliferation and increased apoptosis histologically.

Conclusions

As compared to wild type, the hearts of G6PC3 knockout mice demonstrated significantly decreased collagen globally, a crucial component for adequate strength and contractility of myocardial tissue. More investigation should be done to further explore the functional effects of such alterations via echocardiograms.

In Vivo Functions of Mouse Neutrophils Derived from HoxB8-Transduced Conditionally Immortalized Myeloid Progenitors

Although neutrophils play important roles in immunity and inflammation, their analysis is strongly hindered by their short-lived and terminally differentiated nature. Prior studies reported conditional immortalization of myeloid progenitors using retroviral expression of an estrogen-dependent fusion protein of the HoxB8 transcription factor. This approach allowed the long-term culture of mouse myeloid progenitors (HoxB8 progenitors) in estrogen-containing media, followed by differentiation toward neutrophils upon estrogen withdrawal. Although several reports confirmed the in vitro functional responsiveness of the resulting differentiated cells (HoxB8 neutrophils), little is known about their capacity to perform in vivo neutrophil functions. We have addressed this issue by an in vivo transplantation approach. In vitro-generated HoxB8 neutrophils showed a neutrophil-like phenotype and were able to perform conventional neutrophil functions, like respiratory burst, chemotaxis, and phagocytosis. The i.v. injection of HoxB8 progenitors into lethally irradiated recipients resulted in the appearance of circulating donor-derived HoxB8 neutrophils. In vivo-differentiated HoxB8 neutrophils were able to migrate to the inflamed peritoneum and to phagocytose heat-killed Candida particles. The reverse passive Arthus reaction could be induced in HoxB8 chimeras but not in irradiated, nontransplanted control animals. Repeated injection of HoxB8 progenitors also allowed us to maintain stable circulating HoxB8 neutrophil counts for several days. Injection of arthritogenic K/B×N serum triggered robust arthritis in HoxB8 chimeras, but not in irradiated, nontransplanted control mice. Taken together, our results indicate that HoxB8 progenitor-derived neutrophils are capable of performing various in vivo neutrophil functions, providing a framework for using the HoxB8 system for the in vivo analysis of neutrophil function.

Metabolic abnormalities in G6PC3-deficient human neutrophils result in severe functional defects

Severe congenital neutropenia type 4 (SCN-4) is an autosomal recessive condition in which mutations in the G6PC3 gene encoding for the catalytic 3 subunit of glucose-6-phosphatase-β result in neutropenia, neutrophil dysfunction, and other syndromic features. We report a child with SCN-4 caused by compound heterozygous mutations in G6PC3, a previously identified missense mutation in exon 6 (c.758G>A[p.R235H]), and a novel missense mutation in exon 2 (c.325G>A[p.G109S]). The patient had recurrent bacterial infections, inflammatory bowel disease, neutropenia, and intermittent thrombocytopenia. Administration of granulocyte colony-stimulating factor (G-CSF) resolved the neutropenia and allowed for detailed evaluation of human neutrophil function. Random and directed migration by the patient's neutrophils was severely diminished. Associated with this were defects in CD11b expression and F-actin assembly. Bactericidal activity at bacteria/neutrophil ratios >1:1 was also diminished and was associated with attenuated ingestion. Superoxide anion generation was <25% of control values, but phox proteins appeared quantitatively normal. Extensive metabolomics analysis at steady state and upon incubation with stable isotope-labeled tracers (U-13C-glucose, 13C,15N-glutamine, and U-13C-fructose) demonstrated dramatic impairments in early glycolysis (hexose phosphate levels), hexosemonophosphate shunt (required for the generation of the NADPH), and the total adenylate pool, which could explain the dramatic cell dysfunction displayed by the patient's neutrophils. Preliminary experiments with fructose supplementation to bypass the enzyme block demonstrated that the metabolic profile could be reversed, but was not sustained long enough for functional improvement. In human deficiency of G6PC3, metabolic defects resulting from the enzyme deficiency account for diverse neutrophil functional defects and present a major risk of infection.

Hypothesis: A Novel Neuroprotective Role for Glucose-6-phosphatase (G6PC3) in Brain-To Maintain Energy-Dependent Functions Including Cognitive Processes

The isoform of glucose-6-phosphatase in liver, G6PC1, has a major role in whole-body glucose homeostasis, whereas G6PC3 is widely distributed among organs but has poorly-understood functions. A recent, elegant analysis of neutrophil dysfunction in G6PC3-deficient patients revealed G6PC3 is a neutrophil metabolite repair enzyme that hydrolyzes 1,5-anhydroglucitol-6-phosphate, a toxic metabolite derived from a glucose analog present in food. These patients exhibit a spectrum of phenotypic characteristics and some have learning disabilities, revealing a potential linkage between cognitive processes and G6PC3 activity. Previously-debated and discounted functions for brain G6PC3 include causing an ATP-consuming futile cycle that interferes with metabolic brain imaging assays and a nutritional role involving astrocyte-neuron glucose-lactate trafficking. Detailed analysis of the anhydroglucitol literature reveals that it competes with glucose for transport into brain, is present in human cerebrospinal fluid, and is phosphorylated by hexokinase. Anhydroglucitol-6-phosphate is present in rodent brain and other organs where its accumulation can inhibit hexokinase by competition with ATP. Calculated hexokinase inhibition indicates that energetics of brain and erythrocytes would be more adversely affected by anhydroglucitol-6-phosphate accumulation than heart. These findings strongly support the paradigm-shifting hypothesis that brain G6PC3 removes a toxic metabolite, thereby maintaining brain glucose metabolism- and ATP-dependent functions, including cognitive processes.

Failure to eliminate a phosphorylated glucose analog leads to neutropenia in patients with G6PT and G6PC3 deficiency

Neutropenia presents an important clinical problem in patients with G6PC3 or G6PT deficiency, yet why neutropenia occurs is unclear. We discovered that G6PC3 and G6PT collaborate to dephosphorylate a noncanonical metabolite (1,5-anhydroglucitol-6-phosphate; 1,5AG6P) which is produced when glucose-phosphorylating enzymes erroneously act on 1,5-anhydroglucitol, a food-derived polyol present in blood. In patients or mice with G6PC3 or G6PT deficiency, 1,5AG6P accumulates and inhibits the first step of glycolysis. This is particularly detrimental in neutrophils, since their energy metabolism depends almost entirely on glycolysis. Consistent with our findings, we observed that treatment with a 1,5-anhydroglucitol-lowering drug treats neutropenia in G6PC3-deficient mice. Our findings highlight that the elimination of noncanonical side products by metabolite-repair enzymes makes an important contribution to mammalian physiology.

Neutropenia represents an important problem in patients with genetic deficiency in either the glucose-6-phosphate transporter of the endoplasmic reticulum (G6PT/SLC37A4) or G6PC3, an endoplasmic reticulum phosphatase homologous to glucose-6-phosphatase. While affected granulocytes show reduced glucose utilization, the underlying mechanism is unknown and causal therapies are lacking. Using a combination of enzymological, cell-culture, and in vivo approaches, we demonstrate that G6PT and G6PC3 collaborate to destroy 1,5-anhydroglucitol-6-phosphate (1,5AG6P), a close structural analog of glucose-6-phosphate and an inhibitor of low-K_M hexokinases, which catalyze the first step in glycolysis in most tissues. We show that 1,5AG6P is made by phosphorylation of 1,5-anhydroglucitol, a compound normally present in human plasma, by side activities of ADP-glucokinase and low-K_M hexokinases. Granulocytes from patients deficient in G6PC3 or G6PT accumulate 1,5AG6P to concentrations (∼3 mM) that strongly inhibit hexokinase activity. In a model of G6PC3-deficient mouse neutrophils, physiological concentrations of 1,5-anhydroglucitol caused massive accumulation of 1,5AG6P, a decrease in glucose utilization, and cell death. Treating G6PC3-deficient mice with an inhibitor of the kidney glucose transporter SGLT2 to lower their blood level of 1,5-anhydroglucitol restored a normal neutrophil count, while administration of 1,5-anhydroglucitol had the opposite effect. In conclusion, we show that the neutropenia in patients with G6PC3 or G6PT mutations is a metabolite-repair deficiency, caused by a failure to eliminate the nonclassical metabolite 1,5AG6P.

Characterisation of Neutropenia-Associated Neutrophil Elastase Mutations in a Murine Differentiation Model In Vitro and In Vivo

Severe congenital neutropenia (SCN) is characterised by a differentiation block in the bone marrow and low neutrophil numbers in the peripheral blood, which correlates with increased risk of bacterial infections. Several underlying gene defects have been identified in SCN patients. Mutations in the neutrophil elastase (ELANE) gene are frequently found in SCN and cyclic neutropenia. Both mislocalization and misfolding of mutant neutrophil elastase protein resulting in ER stress and subsequent induction of the unfolded protein response (UPR) have been proposed to be responsible for neutrophil survival and maturation defects. However, the detailed molecular mechanisms still remain unclear, in part due to the lack of appropriate in vitro and in vivo models. Here we used a system of neutrophil differentiation from immortalised progenitor lines by conditional expression of Hoxb8, permitting the generation of mature near-primary neutrophils in vitro and in vivo. NE-deficient Hoxb8 progenitors were reconstituted with murine and human forms of typical NE mutants representative of SCN and cyclic neutropenia, and differentiation of the cells was analysed in vitro and in vivo. ER stress induction by NE mutations could be recapitulated during neutrophil differentiation in all NE mutant-reconstituted Hoxb8 cells. Despite ER stress induction, no change in survival, maturation or function of differentiating cells expressing either murine or human NE mutants was observed. Further analysis of in vivo differentiation of Hoxb8 cells in a murine model of adoptive transfer did not reveal any defects in survival or differentiation in the mouse. Although the Hoxb8 system has been found to be useful for dissection of defects in neutrophil development, our findings indicate that the use of murine systems for analysis of NE-mutation-associated pathogenesis is complicated by differences between humans and mice in the physiology of granulopoiesis, which may go beyond possible differences in expression and activity of neutrophil elastase itself.

The anti-apoptotic Bcl-2 family protein A1/Bfl-1 regulates neutrophil survival and homeostasis and is controlled via PI3K and JAK/STAT signaling

Neutrophil granulocytes are innate effector cells of the first line of defense against pyogenic bacteria. Neutrophil lifespan is short, is prolonged by pro-inflammatory stimuli, controls functionality of the cells and can determine tissue damage. Experimental analysis of primary neutrophils is difficult because of their short lifespan and lack of possibilities of genetic manipulation. The Hoxb8 system of neutrophil differentiation from immortalized progenitor cells offers the advantage of unlimited production of neutrophils in vitro as well as easy genetic modification. We here use this system to analyze the role of the poorly characterized anti-apoptotic B-cell lymphoma protein 2 (Bcl-2) family member A1/Bfl-1 (Bcl-2-related protein A1) for survival and homeostasis of neutrophils and of neutrophil progenitors. Low constitutive mRNA and protein expression of A1 was detected, while A1 was transiently upregulated early during differentiation. Pro-inflammatory stimuli caused strong, mainly transcriptional, A1 upregulation, in contrast to posttranscriptional regulation of Mcl-1 (induced myeloid leukemia cell differentiation protein). Inhibitor studies showed that phosphoinositide-3 kinase (PI3K)/Akt and Janus kinase (JAK)/signal transducer and activator of transcription (STAT) is required for A1 expression and survival of progenitors and mature neutrophils. ShRNA-mediated constitutive A1 knockdown (KD) impaired maintenance of progenitors. ShRNA experiments further showed that A1 was required early during neutrophil differentiation as well as in mature neutrophils upon pro-inflammatory stimulation. Our data further indicate differential regulation of the two anti-apoptotic proteins A1 and Mcl-1. Relevant findings were confirmed in primary human neutrophils. Our data indicate that A1, in addition to the well-established Mcl-1, substantially contributes to neutrophil survival and homeostasis. A1 may thus be a promising target for anti-inflammatory therapy.

Understanding chronic neutropenia: life is short

The pathophysiological mechanisms underlying chronic neutropenia are extensive, varying from haematopoietic stem cell disorders resulting in defective neutrophil production, to accelerated apoptosis of neutrophil progenitors or circulating mature neutrophils. While the knowledge concerning genetic defects associated with congenital neutropenia or bone marrow failure is increasing rapidly, the functional role and consequences of these genetic alterations is often not well understood. In addition, there is a large group of diseases, including primary immunodeficiencies and metabolic diseases, in which chronic neutropenia is one of the symptoms, while there is no clear bone marrow pathology or haematopoietic stem cell dysfunction. Altogether, these disease entities illustrate the complexity of normal neutrophil development, the functional role of the (bone marrow) microenvironment and the increased propensity to undergo apoptosis, which is typical for neutrophils. The large variety of disorders associated with chronic neutropenia makes classification almost impossible and possibly not desirable, based on the clinical phenotypes. However, a better understanding of the regulation of normal myeloid differentiation and neutrophil development is of great importance in the diagnostic evaluation of unexplained chronic neutropenia. In this review we propose insights in the pathophysiology of chronic neutropenia in the context of the functional role of key players during normal neutrophil development, neutrophil release and neutrophil survival.

2-Arachidonoylglycerol enhances platelet formation from human megakaryoblasts

Platelets modulate vascular system integrity, and their loss is critical in haematological pathologies and after chemotherapy. Therefore, identification of molecules enhancing platelet production would be useful to counteract thrombocytopenia. We have previously shown that 2-arachidonoylglycerol (2-AG) acts as a true agonist of platelets, as well as it commits erythroid precursors toward the megakaryocytic lineage. Against this background, we sought to further interrogate the role of 2-AG in megakaryocyte/platelet physiology by investigating terminal differentiation, and subsequent thrombopoiesis. To this end, we used MEG-01 cells, a human megakaryoblastic cell line able to produce in vitro platelet-like particles. 2-AG increased the number of cells showing ruffled surface and enhanced surface expression of specific megakaryocyte/platelet surface antigens, typical hallmarks of terminal megakaryocytic differentiation and platelet production. Changes in cytoskeleton modeling also occurred in differentiated megakaryocytes and blebbing platelets. 2-AG acted by binding to CB1 and CB2 receptors, because specific antagonists reverted its effect. Platelets were split off from megakaryocytes and were functional: they contained the platelet-specific surface markers CD61 and CD49, whose levels increased following stimulation with a natural agonist like collagen. Given the importance of 2-AG for driving megakaryopoiesis and thrombopoiesis, not surprisingly we found that its hydrolytic enzymes were tightly controlled by classical inducers of megakaryocyte differentiation. In conclusion 2-AG, by triggering megakaryocyte maturation and platelet release, may have clinical efficacy to counteract thrombocytopenia-related diseases.

ER-stress and apoptosis: molecular mechanisms and potential relevance in infection

During ER-stress, one of the responses a cell can choose is apoptosis. Apoptosis generally is a cell's preferred response when other control mechanisms are overwhelmed. We now have a reasonably clear molecular picture what is happening once the apoptotic apparatus has been started. Unclear however are the majority of the upstream pathways that connect other signalling to apoptosis. During ER-stress, confirmed apoptosis-regulating targets are pro- and anti-apoptotic proteins of the Bcl-2-family, whose concerted action induces apoptosis. I will here discuss how mitochondrial apoptosis is triggered, how this is linked to the ER-stress response and in what way this may be relevant during microbial infections.

Neutrophil granulocytes recruited upon translocation of intestinal bacteria enhance graft-versus-host disease via tissue damage

Acute graft-versus-host disease (GVHD) considerably limits wider usage of allogeneic hematopoietic cell transplantation (allo-HCT). Antigen-presenting cells and T cells are populations customarily associated with GVHD pathogenesis. Of note, neutrophils are the largest human white blood cell population. The cells cleave chemokines and produce reactive oxygen species, thereby promoting T cell activation. Therefore, during an allogeneic immune response, neutrophils could amplify tissue damage caused by conditioning regimens. We analyzed neutrophil infiltration of the mouse ileum after allo-HCT by in vivo myeloperoxidase imaging and found that infiltration levels were dependent on the local microbial flora and were not detectable under germ-free conditions. Physical or genetic depletion of neutrophils reduced GVHD-related mortality. The contribution of neutrophils to GVHD severity required reactive oxygen species (ROS) because selective Cybb (encoding cytochrome b-245, beta polypeptide, also known as NOX2) deficiency in neutrophils impairing ROS production led to lower levels of tissue damage, GVHD-related mortality and effector phenotype T cells. Enhanced survival of Bcl-xL transgenic neutrophils increased GVHD severity. In contrast, when we transferred neutrophils lacking Toll-like receptor-2 (TLR2), TLR3, TLR4, TLR7 and TLR9, which are normally less strongly activated by translocating bacteria, into wild-type C57BL/6 mice, GVHD severity was reduced. In humans, severity of intestinal GVHD strongly correlated with levels of neutrophils present in GVHD lesions. This study describes a new potential role for neutrophils in the pathogenesis of GVHD in both mice and humans.