Emergent autoimmunity in graft-versus-host disease

Effect of allogeneic hematopoietic stem cell transplantation for chronic granulomatous disease in children: A multicentre, retrospective cohort study in China

Chronic granulomatous disease (CGD) in children is a rare primary immunodeficiency disorder that can lead to life-threatening infections and inflammatory complications. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is increasingly being used to treat severe CGD in children. We conducted a multicenter retrospective analysis of children with CGD who were treated with allo-HSCT at four pediatric hematopoietic stem cell transplant centers in China from September 2005 to December 2019. The study included a total of 171 patients (169 males and 2 females). The median age at the time of transplantation was 6.1 (0-16.4) years. Among them, 154 patients had X-linked recessive inheritance caused by CYBB gene mutations, 12 patients were autosomal recessive, 1 patient had DNAH11 and HYDIN gene mutations, and 4 patients had no gene mutations. The median follow-up period was 36.3 (1.9-79) months. All participating patients were applied to myeloablative conditioning (MAC) regimens. The rates of OS, EFS, and GEFS within three years were 87.5%, 85.3%, and 75.2%, respectively. The total graft failure and the total mortality rate were 5.3% and 11.1%. The cumulative incidence of acute GVHD was 53.8% and the incidence of chronic GVHD was 12.9%, The incidence of chronic GVHD was higher for patients who received unrelated donor cord blood stem cell transplantation (UD-CB) (P = 0.001). Chronic GVHD and coinfections are the risk factors for OS and EFS in patients with CGD after receiving allo-HSCT. UD-CB is a risk factor for EFS and the presence of pneumonia before transplantation is a risk factor for OS. In conclusion, through this study, we have demonstrated that allo-HSCT has excellent efficacy in the treatment of CGD in children, especially, RD-haplo is associated with a lower rate of graft failure incidence and mortality than the treatment modalities of other donor type. Therefore, allo-HSCT is strongly recommended when a well-matched donor is available. If a well-matched donor is not available, the HLA-mismatched donor should be carefully evaluated, and the conditioning regimen modified accordingly.

Heightened TLR7 signaling primes BCR-activated B cells in chronic graft-versus-host disease for effector functions

ABSTRACT

Chronic graft-versus-host disease (cGVHD) is a debilitating, autoimmune-like syndrome that can occur after allogeneic hematopoietic stem cell transplantation. Constitutively activated B cells contribute to ongoing alloreactivity and autoreactivity in patients with cGVHD. Excessive tissue damage that occurs after transplantation exposes B cells to nucleic acids in the extracellular environment. Recognition of endogenous nucleic acids within B cells can promote pathogenic B-cell activation. Therefore, we hypothesized that cGVHD B cells aberrantly signal through RNA and DNA sensors such as Toll-like receptor 7 (TLR7) and TLR9. We found that B cells from patients and mice with cGVHD had higher expression of TLR7 than non-cGVHD B cells. Using ex vivo assays, we found that B cells from patients with cGVHD also demonstrated increased interleukin-6 production after TLR7 stimulation with R848. Low-dose B-cell receptor (BCR) stimulation augmented B-cell responses to TLR7 activation. TLR7 hyperresponsiveness in cGVHD B cells correlated with increased expression and activation of the downstream transcription factor interferon regulatory factor 5. Because RNA-containing immune complexes can activate B cells through TLR7, we used a protein microarray to identify RNA-containing antigen targets of potential pathological relevance in cGVHD. We found that many of the unique targets of active cGVHD immunoglobulin G (IgG) were nucleic acid-binding proteins. This unbiased assay identified the autoantigen and known cGVHD target Ro-52, and we found that RNA was required for IgG binding to Ro-52. Herein, we find that BCR-activated B cells have aberrant TLR7 signaling responses that promote potential effector responses in cGVHD.

Chronic graft-versus-host disease. Part I: Epidemiology, pathogenesis, and clinical manifestations

Chronic graft-versus-host disease is a major complication of allogeneic hematopoietic cell transplantation and a leading cause of long-term morbidity, nonrelapse mortality, and impaired health-related quality of life. The skin is commonly affected and presents heterogeneously, making the role of dermatologists critical in both diagnosis and treatment. In addition, new clinical classification and grading schemes inform treatment algorithms, which now include 3 U.S. Food and Drug Administration-approved therapies, and evolving transplant techniques are changing disease epidemiology. Part I reviews the epidemiology, pathogenesis, clinical manifestations, and diagnosis of chronic graft-versus-host disease. Part II discusses disease grading and therapeutic management.

Harnessing and honing mesenchymal stem/stromal cells for the amelioration of graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation is a deterministic curative procedure for various hematologic disorders and congenital immunodeficiency. Despite its increased use, the mortality rate for patients undergoing this procedure remains high, mainly due to the perceived risk of exacerbating graft-versus-host disease (GVHD). However, even with immunosuppressive agents, some patients still develop GVHD. Advanced mesenchymal stem/stromal cell (MSC) strategies have been proposed to achieve better therapeutic outcomes, given their immunosuppressive potential. However, the efficacy and trial designs have varied among the studies, and some research findings appear contradictory due to the challenges in characterizing the in vivo effects of MSCs. This review aims to provide real insights into this clinical entity, emphasizing diagnostic, and therapeutic considerations and generating pathophysiology hypotheses to identify research avenues. The indications and timing for the clinical application of MSCs are still subject to debate.

Immunotherapy for neuroblastoma by hematopoietic cell transplantation and post-transplant immunomodulation

Neuroblastoma represents a relatively common childhood tumor that imposes therapeutic difficulties. High risk neuroblastoma patients have poor prognosis, display limited response to radiochemotherapy and may be treated by hematopoietic cell transplantation. Allogeneic and haploidentical transplants have the distinct advantage of reinstitution of immune surveillance, reinforced by antigenic barriers. The key factors favorable to ignition of potent anti-tumor reactions are transition to adaptive immunity, recovery from lymphopenia and removal of inhibitory signals that inactivate immune cells at the local and systemic levels. Post-transplant immunomodulation may further foster anti-tumor reactivity, with positive but transient impact of infusions of lymphocytes and natural killer cells both from the donor, the recipient or third party. The most promising approaches include introduction of antigen-presenting cells in early post-transplant stages and neutralization of inhibitory signals. Further studies will likely shed light on the nature and actions of suppressor factors within tumor stroma and at the systemic level.

Towards a Better Understanding of the Atypical Features of Chronic Graft-Versus-Host Disease: A Report from the 2020 National Institutes of Health Consensus Project Task Force

Alloreactive and autoimmune responses after allogeneic hematopoietic cell transplantation can occur in non-classical chronic graft-versus-host disease (chronic GVHD) tissues and organ systems or manifest in atypical ways in classical organs commonly affected by chronic GVHD. The National Institutes of Health (NIH) consensus projects were developed to improve understanding and classification of the clinical features and diagnostic criteria for chronic GVHD. While still speculative whether atypical manifestations are entirely due to chronic GVHD, these manifestations remain poorly captured by the current NIH consensus project criteria. Examples include chronic GVHD impacting the hematopoietic system as immune mediated cytopenias, endothelial dysfunction, or as atypical features in the musculoskeletal system, central and peripheral nervous system, kidneys, and serous membranes. These purported chronic GVHD features may contribute significantly to patient morbidity and mortality. Most of the atypical chronic GVHD features have received little study, particularly within multi-institutional and prospective studies, limiting our understanding of their frequency, pathogenesis, and relation to chronic GVHD. This NIH consensus project task force report provides an update on what is known and not known about the atypical manifestations of chronic GVHD, while outlining a research framework for future studies to be undertaken within the next three to seven years. We also provide provisional diagnostic criteria for each atypical manifestation, along with practical investigation strategies for clinicians managing patients with atypical chronic GVHD features.

Engineered cellular immunotherapies in cancer and beyond

This year marks the tenth anniversary of cell therapy with chimeric antigen receptor (CAR)-modified T cells for refractory leukemia. The widespread commercial approval of genetically engineered T cells for a variety of blood cancers offers hope for patients with other types of cancer, and the convergence of human genome engineering and cell therapy technology holds great potential for generation of a new class of cellular therapeutics. In this Review, we discuss the goals of cellular immunotherapy in cancer, key challenges facing the field and exciting strategies that are emerging to overcome these obstacles. Finally, we outline how developments in the cancer field are paving the way for cellular immunotherapeutics in other diseases.

Tissue-resident PSGL1loCD4+ T cells promote B cell differentiation and chronic graft-versus-host disease-associated autoimmunity

CD4+ T cell interactions with B cells play a critical role in the pathogenesis of systemic autoimmune diseases such as systemic lupus and chronic graft-versus-host disease (cGVHD). Extrafollicular CD44hiCD62LloPSGL1loCD4+ T cells (PSGL1loCD4+ T cells) are associated with the pathogenesis of lupus and cGVHD, but their causal role has not been established. With murine and humanized MHC-/-HLA-A2+DR4+ murine models of cGVHD, we showed that murine and human PSGL1loCD4+ T cells from GVHD target tissues have features of B cell helpers with upregulated expression of programmed cell death protein 1 (PD1) and inducible T cell costimulator (ICOS) and production of IL-21. They reside in nonlymphoid tissues without circulating in the blood and have features of tissue-resident memory T cells with upregulated expression of CD69. Murine PSGL1loCD4+ T cells from GVHD target tissues augmented B cell differentiation into plasma cells and production of autoantibodies via their PD1 interaction with PD-L2 on B cells. Human PSGL1loCD4+ T cells were apposed with memory B cells in the liver tissues of humanized mice and cGVHD patients. Human PSGL1loCD4+ T cells from humanized GVHD target tissues also augmented autologous memory B cell differentiation into plasma cells and antibody production in a PD1/PD-L2-dependent manner. Further preclinical studies targeting tissue-resident T cells to treat antibody-mediated features of autoimmune diseases are warranted.

Thalidomide as treatment of crohn-like disease occurred after allogeneic hematopoietic stem cell transplantation in a pediatric patient

BACKGROUND

Autoimmune diseases may occur after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and inflammatory bowel disease (IBD or Crohn disease) is rarely described. We describe a child who developed CD after allo-HSCT, successfully treated with thalidomide.

CASE REPORT

A child affected by mucopolysaccharidosis type I received two allogeneic HSCTs for rejection after the first one. After cutaneous and intestinal chronic GvHD and 6 months after HSCT, the patients developed a trilinear autoimmune cytopenia successfully treated with rituximab and sirolimus. Due to persisting intestinal symptoms, colonoscopies were performed and histological findings demonstrated a picture of CD. Based on this observation and according to the recommendations for the treatment of CD, thalidomide was started. A complete stable clinical response was obtained 8 weeks after start of thalidomide. Colonoscopy performed 4.8 years later demonstrated a complete endoscopic and histological remission of CD.

DISCUSSION

In this case, the diagnosis of CD after HSCT was based on histological findings. Indeed, repeated colonscopies were necessary for diagnosis, since both clinical and endoscopic features are often common to chronic GvHD and CD. Thalidomide was started at the dose of 1.7 mg/Kg/day, and it was well tolerated. Mild peripheral neurotoxicity occurred 5 years later but disappeared completely with the dose reduction. Currently, the patient is in complete remission from CD, despite the discontinuation of all the immunosuppressive therapies.

CONCLUSIONS

Thalidomide could represent a therapeutic option to treat CD as autoimmune disease after allogeneic HSCT.

National Institutes of Health Consensus Development Project on Criteria for Clinical Trials in Chronic Graft-versus-Host Disease: I. The 2020 Etiology and Prevention Working Group Report

Preventing chronic graft-versus-host disease (GVHD) remains challenging because the unique cellular and molecular pathways that incite chronic GVHD are poorly understood. One major point of intervention for potential prevention of chronic GVHD occurs at the time of transplantation when acute donor anti-recipient immune responses first set the events in motion that result in chronic GVHD. After transplantation, additional insults causing tissue injury can incite aberrant immune responses and loss of tolerance, further contributing to chronic GVHD. Points of intervention are actively being identified so that chronic GVHD initiation pathways can be targeted without affecting immune function. The major objective in the field is to continue basic studies and to translate what is learned about etiopathology to develop targeted prevention strategies that decrease the risk of morbid chronic GVHD without increasing the risks of cancer relapse or infection. Development of strategies to predict the risk of developing debilitating or deadly chronic GVHD is a high research priority. This working group recommends further interrogation into the mechanisms underpinning chronic GVHD development, and we highlight considerations for future trial design in prevention trials.

Graft-versus-host disease reduces lymph node display of tissue-restricted self-antigens and promotes autoimmunity

Acute graft-versus-host disease (GVHD) is initially triggered by alloreactive T cells, which damage peripheral tissues and lymphoid organs. Subsequent transition to chronic GVHD involves the emergence of autoimmunity, although the underlying mechanisms driving this process are unclear. Here, we tested the hypothesis that acute GVHD blocks peripheral tolerance of autoreactive T cells by impairing lymph node (LN) display of peripheral tissue–restricted antigens (PTAs). At the initiation of GVHD, LN fibroblastic reticular cells (FRCs) rapidly reduced expression of genes regulated by DEAF1, an autoimmune regulator-like transcription factor required for intranodal expression of PTAs. Subsequently, GVHD led to the selective elimination of the FRC population, and blocked the repair pathways required for its regeneration. We used a transgenic mouse model to show that the loss of presentation of an intestinal PTA by FRCs during GVHD resulted in the activation of autoaggressive T cells and gut injury. Finally, we show that FRCs normally expressed a unique PTA gene signature that was highly enriched for genes expressed in the target organs affected by chronic GVHD. In conclusion, acute GVHD damages and prevents repair of the FRC network, thus disabling an essential platform for purging autoreactive T cells from the repertoire.

Biomarkers for acute and chronic graft versus host disease: state of the art

INTRODUCTION

Despite significant advances in treatment and prevention, graft-versus-host disease (GVHD) still represents the main cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Thus, considerable research efforts have been made to find and validate reliable biomarkers for diagnosis, prognosis, and risk stratification of GVHD.

AREAS COVERED

In this review the most recent evidences on different types of biomarkers studied for GVHD, such as genetic, plasmatic, cellular markers, and those associated with microbiome, were summarized. A comprehensive search of peer-review literature was performed in PubMed including meta-analysis, preclinical and clinical trials, using the terms: cellular and plasma biomarkers, graft-versus-host disease, cytokines, and allogeneic hematopoietic stem cell transplantation.

EXPERT OPINION

In the near future, several validated biomarkers will be available to help clinicians in the diagnosis of GVHD, the identification of patients at high risk of GVHD development and in patients' stratification according to its severity. Then, immunosuppressive treatment could be tailored to each patient's real needs. However, more efforts are needed to achieve this goal. Although most of the proposed biomarkers currently lack validation with large-scale clinical data, their study led to improved knowledge of the biological basis of GVHD, and ultimately to implementation of GHVD treatment.

One-two punch injury to tolerance mechanisms in graft-versus-host disease

Chronic graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic cell transplantation that resembles autoimmunity, with unclear pathogenesis and few effective therapeutic options. In this issue of the JCI, Dertschnig et al. used mouse models to investigate the basis of T cell autoreactivity following GVHD. Notably, GVHD caused irreversible damage to a population of tolerogenic stromal cells that display peripheral tissue-restricted antigens in lymph nodes, which impaired their capacity to purge and suppress autoreactive T cells. Together with damage to central tolerance mechanisms in the thymus, these findings outline a critical one-two punch injury that profoundly disrupts immune tolerance in this devastating disease.

Autoimmune hemolytic anemia after allogeneic hematopoietic stem cell transplantation in adults: A southern China multicenter experience

To investigate the incidence and risk factors as well as prognosis of autoimmune hemolytic anemia (AIHA) following allogeneic hematopoietic stem cell transplantation (allo‐HSCT), a total of 1377 adult hematological malignancies at three institutions were enrolled in this study. The 3‐year cumulative incidence of AIHA was 2.2 ± 0.4%. Multivariate analysis showed that haploidentical donors (HRDs) and chronic graft vs host disease (cGVHD) were the independent risk factors for AIHA. Patients with AIHA treated initially with corticosteroids combined with cyclosporine A (CsA) had a higher complete response rate than those with corticosteroids monotherapy (66.7% vs 11.1%; P = .013). The 3‐year cumulative incidence of malignant diseases relapse was 4.4 ± 4.3% and 28.0 ± 1.3% (P = .013), treatment‐related mortality (TRM) was 8.9 ± 6.3% and 17.4 ± 1.2% (P = .431), disease‐free survival (DFS) was 56.1 ± 1.5% and 86.7 ± 7.2% (P = .011), and overall survival (OS) was 86.3 ± 7.4% and 64.1 ± 1.5% (P = .054), respectively, in the patients with AIHA and those without AIHA. Our results indicate that HRDs and cGVHD are risk factors for AIHA and corticosteroids combined with CsA are superior to corticosteroids as initial treatment for AIHA. Autoimmune hemolytic anemia does not contribute to increase TRM and could reduce the malignant diseases relapse and increase DFS.

Naive and Stem Cell Memory T Cell Subset Recovery Reveals Opposing Reconstitution Patterns in CD4 and CD8 T Cells in Chronic Graft vs. Host Disease

The success of allogeneic hematopoietic stem cell transplantation (allo-HSCT) in the treatment of hematological malignancies remains hampered by life-threatening chronic graft vs. host disease (cGVHD). Although multifactorial in nature, cGVHD has been associated with imbalances between effector and regulatory T cells (Treg). To further elucidate this issue, we performed a prospective analysis of patients undergoing unrelated donor allo-HSCT after a reduced intensity conditioning (RIC) regimen containing anti-thymocyte globulin (ATG) and the same GVHD prophylaxis, at a single institution. We studied T cell subset homeostasis over a 24-month follow-up after HSCT in a comparative analysis of patients with and without cGVHD. We also quantified naive and memory T cell subsets, proliferation and expression of the apoptosis-related proteins Bcl-2 and CD95. Finally, we assessed thymic function by T cell receptor excision circle (TREC) quantification and T cell receptor (TCR) diversity by TCRVβ spectratyping. While the total number of conventional CD4 (Tcon) and CD8 T cells was similar between patient groups, Treg were decreased in cGVHD patients. Interestingly, we also observed divergent patterns of Naive and Stem Cell Memory (SCM) subset recovery in Treg and Tcon compared to CD8. Patients with cGVHD showed impaired recovery of Naive and SCM Tcon and Treg, but significantly increased frequencies and absolute numbers of Naive and SCM were observed in the CD8 pool. Markedly increased EMRA CD8 T cells were also noted in cGVHD. Taken together, these results suggest that Naive, SCM and EMRA CD8 play a role in the emergence of cGHVD. Reduced Naive and recent thymic emigrant Tcon and Treg in cGVHD was likely due to impaired thymic output, as it was accompanied by decreased CD4 TREC and TCR diversity. On the other hand, CD8 TCR diversity was similar between patient groups. Furthermore, no correlation was observed between CD8 TREC content and Naive CD8 numbers, suggesting limited thymic production of Naive CD8 T cells in patients after transplant, especially in those developing cGVHD. The mechanisms behind the opposing patterns of CD4 and CD8 subset cell recovery in cGVHD remain elusive, but may be linked to thymic damage associated with the conditioning regimen and/or acute GVHD.

B cells in chronic graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (alloHCT) is the definitive therapy for numerous otherwise incurable hematologic malignancies and non-malignant diseases. The genetic disparity between donor and recipient both underpins therapeutic effects and confers donor immune system-mediated damage in the recipient, called graft-versus-host disease (GVHD). Chronic GVHD (cGVHD) is a major cause of late post-transplant morbidity and mortality. B cells have a substantiated role in cGVHD pathogenesis, as first demonstrated by clinical response to the anti-CD20 monoclonal antibody, rituximab. Initiation of CD20 blockade is met at times with limited therapeutic success that has been associated with altered peripheral B cell homeostasis and excess B Cell Activating Factor of the TNF family (BAFF). Increased BAFF to B cell ratios are associated with the presence of circulating, constitutively activated B cells in patients with cGVHD. These cGVHD patient B cells have increased survival capacity and signal through both BAFF-associated and B Cell Receptor (BCR) signaling pathways. Proximal BCR signaling molecules, Syk and BTK, appear to be hyper-activated in cGVHD B cells and can be targeted with small molecule inhibitors. Murine studies have confirmed roles for Syk and BTK in development of cGVHD. Emerging evidence has prompted investigation of several small molecule inhibitors in an attempt to restore B cell homeostasis and potentially target rare, pathologic B cell populations.

B-cell targeting in chronic graft-versus-host disease

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.

PD-L1 Prevents the Development of Autoimmune Heart Disease in Graft-versus-Host Disease

Effector memory T cells (T_EM) are less capable of inducing graft-versus-host disease (GVHD) compared with naive T cells (T_N). Previously, in the TS1 TCR transgenic model of GVHD, wherein TS1 CD4 cells specific for a model minor histocompatibility Ag (miHA) induce GVHD in miHA-positive recipients, we found that cell-intrinsic properties of TS1 T_EM reduced their GVHD potency relative to TS1 T_N Posttransplant, TS1 T_EM progeny expressed higher levels of PD-1 than did TS1 T_N progeny, leading us to test the hypothesis that T_EM induce less GVHD because of increased sensitivity to PD-ligands. In this study, we tested this hypothesis and found that indeed TS1 T_EM induced more severe skin and liver GVHD in the absence of PD-ligands. However, lack of PD-ligands did not result in early weight loss and colon GVHD comparable to that induced by TS1 T_N, indicating that additional pathways restrain alloreactive T_EM TS1 T_N also caused more severe GVHD without PD-ligands. The absence of PD-ligands on donor bone marrow was sufficient to augment GVHD caused by either T_EM or T_N, indicating that donor PD-ligand-expressing APCs critically regulate GVHD. In the absence of PD-ligands, both TS1 T_EM and T_N induced late-onset myocarditis. Surprisingly, this was an autoimmune manifestation, because its development required non-TS1 polyclonal CD8⁺ T cells. Myocarditis development also required donor bone marrow to be PD-ligand deficient, demonstrating the importance of donor APC regulatory function. In summary, PD-ligands suppress both miHA-directed GVHD and the development of alloimmunity-induced autoimmunity after allogeneic hematopoietic transplantation.

Antibodies targeting surface membrane antigens in patients with chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) after allogeneic hematopoietic stem cell transplant reflects a complex immune response resulting in chronic damage to multiple tissues. Previous studies indicated that donor B cells and the antibodies they produce play an important role in the development of cGVHD. To understand the pathogenic role of antibodies in cGVHD, we focused our studies on posttransplant production of immunoglobulin G antibodies targeting cell surface antigens expressed in multiple cGVHD affected tissues, due to their potential functional impact on living cells in vivo. Using plate-bound cell membrane proteins as targets, we detected a significantly higher level of antibodies reactive with these membrane antigens in patients who developed cGVHD, compared with those who did not and healthy donors. Plasma-reactive antibody levels increased significantly prior to the clinical diagnosis of cGVHD and were reduced following cGVHD therapies including prednisone, interleukin-2, or extracorporeal photophoresis. Using cell-based immunoprecipitation with plasma from cGVHD patients and mass spectrometry, we identified 43 membrane proteins targeted by these antibodies. The presence of antibodies in cGVHD patients' plasma that specifically target 6 of these proteins was validated. Antibodies reactive with these 6 antigens were more frequently detected in patients with cGVHD compared with patients without cGVHD and healthy donors. These results indicate that antibodies that target membrane antigens of living cells frequently develop in cGVHD patients and further support a role for B cells and antibodies in the development of cGVHD.

An aberrant NOTCH2-BCR signaling axis in B cells from patients with chronic GVHD

B-cell receptor (BCR)-activated B cells contribute to pathogenesis in chronic graft-versus-host disease (cGVHD), a condition manifested by both B-cell autoreactivity and immune deficiency. We hypothesized that constitutive BCR activation precluded functional B-cell maturation in cGVHD. To address this, we examined BCR-NOTCH2 synergy because NOTCH has been shown to increase BCR responsiveness in normal mouse B cells. We conducted ex vivo activation and signaling assays of 30 primary samples from hematopoietic stem cell transplantation patients with and without cGVHD. Consistent with a molecular link between pathways, we found that BCR-NOTCH activation significantly increased the proximal BCR adapter protein BLNK. BCR-NOTCH activation also enabled persistent NOTCH2 surface expression, suggesting a positive feedback loop. Specific NOTCH2 blockade eliminated NOTCH-BCR activation and significantly altered NOTCH downstream targets and B-cell maturation/effector molecules. Examination of the molecular underpinnings of this "NOTCH2-BCR axis" in cGVHD revealed imbalanced expression of the transcription factors IRF4 and IRF8, each critical to B-cell differentiation and fate. All-trans retinoic acid (ATRA) increased IRF4 expression, restored the IRF4-to-IRF8 ratio, abrogated BCR-NOTCH hyperactivation, and reduced NOTCH2 expression in cGVHD B cells without compromising viability. ATRA-treated cGVHD B cells had elevated TLR9 and PAX5, but not BLIMP1 (a gene-expression pattern associated with mature follicular B cells) and also attained increased cytosine guanine dinucleotide responsiveness. Together, we reveal a mechanistic link between NOTCH2 activation and robust BCR responses to otherwise suboptimal amounts of surrogate antigen. Our findings suggest that peripheral B cells in cGVHD patients can be pharmacologically directed from hyperactivation toward maturity.

Quo vadis chimerism?

Although immunity in multicellular organisms is efficient in dealing with alien agents, it may fail for allogeneic chimerism. Natural chimerism is widely documented in nature, distributed in at least ten phyla of protists, invertebrates and plants, vertebrates and mammals, including humans; it is an important ecological/evolutionary tool manipulating metazoans' life history portraits. Instead of purging allogeneic nascent selfish cells, a 'double edged sword' chimerism emerges, displaying environmental dictated costs and benefits for the genotypes involved. Benefits include the development of synergistic complementation, the increase of genetic variability, the assurance of mate location, improved size-dependent ecological qualities (growth rates, reproduction, survivorship, competition, environmental tolerance) and more. Costs include the threat of somatic and germ cell parasitism, developmental instability, death, diseases, autoimmunity, sexual sterility and organ malformations, which develop as well in mammalian natural chimerism, including humans. Because of its importance, medical sciences should study and harness natural chimerism properties for clinical purposes.

Treatment of Pediatric Acute Graft-versus-Host Disease-Lessons from Primary Immunodeficiency?

Allogeneic hematopoietic stem cell transplant (HSCT) is used to treat increasing numbers of malignant and non-malignant disorders. Despite significant advances in improved human leukocyte antigens-typing techniques, less toxic conditioning regimens and better supportive care, resulting in improved clinical outcomes, acute graft-versus-host disease (aGvHD) continues to be a major obstacle and, although it principally involves the skin, gastrointestinal tract, and liver, the thymus is also a primary target. An important aim following HSCT is to achieve complete and durable immunoreconstitution with a diverse T-cell receptor (TCR) repertoire to recognize a broad range of pathogens providing adequate long-term adaptive T-lymphocyte immunity, essential to reduce the risk of infection, disease relapse, and secondary malignancies. Reconstitution of adaptive T-lymphocyte immunity is a lengthy and complex process which requires a functioning and structurally intact thymus responsible for the production of new naïve T-lymphocytes with a broad TCR repertoire. Damage to the thymic microenvironment, secondary to aGvHD and the effect of corticosteroid treatment, disturbs normal signaling required for thymocyte development, resulting in impaired T-lymphopoiesis and reduced thymic export. Primary immunodeficiencies, in which failure of central or peripheral tolerance is a major feature, because of intrinsic defects in hematopoietic stem cells leading to abnormal T-lymphocyte development, or defects in thymic stroma, can give insights into critical processes important for recovery from aGvHD. Extracorporeal photopheresis is a potential alternative therapy for aGvHD, which acts in an immunomodulatory fashion, through the generation of regulatory T-lymphocytes (Tregs), alteration of cytokine patterns and modulation of dendritic cells. Promoting normal central and peripheral immune tolerance, with selective downregulation of immune stimulation, could reduce aGvHD, and enable a reduction in other immunosuppression, facilitating thymic recovery, restoration of normal T-lymphocyte ontogeny, and complete immunoreconstitution with improved clinical outcome as the ability to fight infections improves and risk of secondary malignancy or relapse diminishes.

The Biology of Chronic Graft-versus-Host Disease: A Task Force Report from the National Institutes of Health Consensus Development Project on Criteria for Clinical Trials in Chronic Graft-versus-Host Disease

Chronic graft-versus-host disease (GVHD) is the leading cause of late, nonrelapse mortality and disability in allogeneic hematopoietic cell transplantation recipients and a major obstacle to improving outcomes. The biology of chronic GVHD remains enigmatic, but understanding the underpinnings of the immunologic mechanisms responsible for the initiation and progression of disease is fundamental to developing effective prevention and treatment strategies. The goals of this task force review are as follows: This document is intended as a review of our understanding of chronic GVHD biology and therapies resulting from preclinical studies, and as a platform for developing innovative clinical strategies to prevent and treat chronic GVHD.

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

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

Pentraxin-3 levels in graft-versus-host disease during allogeneic hematopoietic stem cell transplantation

Acute and chronic graft-versus-host-diseases (aGVHD and cGVHD, respectively) are serious complications after hematopoietic stem cell transplantation (HSCT), impairing survival and quality of life. Because the underlying pathomechanism of GVHD is still poorly understood, we investigated the novel inflammatory marker Pentraxin-3 (PTX3) for its potential role in acute and chronic GVHD compared with autologous HSCT and healthy individuals. We collected plasma samples from patients undergoing autologous (n = 12) and allogeneic (n = 28) HSCT and from healthy individuals (n = 15) throughout 7 days before and up to 1 year after HSCT. PTX3 levels in patients with aGVHD were significantly higher (36.4 ± 23.6 ng/mL) than in allogeneic patients without aGVHD (10.4 ± 4.4 ng/mL, p = 0.0001), autologous controls (11.4 ± 6.7 ng/mL, p = 0.001), or healthy individuals (1.9 ± 0.6 ng/mL, p < 0.001). PTX3 levels in patients with cGVHD (13.6 ± 6.3 ng/mL) were significantly lower than in allogeneic patients without cGVHD (25.1 ± 13.8 ng/mL, p = 0.04) and higher than in autologous controls (8.9 ± 7.8 ng/mL, p = 0.07) and healthy individuals (1.9 ± 0.6 ng/mL, p < 0.001). Severity of aGVHD and cGVHD correlated with PTX3 levels. Rising PTX3 levels after HSCT indicated unfavorable outcome. We show that PTX3 levels correlate with the severity of aGVHD, cGVHD, and-with reservations-survival in patients undergoing allogeneic HSCT.

Extracoporeal photopheresis treatment of acute graft-versus-host disease following allogeneic haematopoietic stem cell transplantation

Acute graft-versus-host disease (aGvHD) continues to be a major obstacle to allogeneic haematopoietic stem cell transplantation. Thymic damage secondary to aGvHD along with corticosteroids and other non-selective T lymphocyte-suppressive agents used in the treatment of aGvHD concurrently impair thymopoiesis and negatively impact on immunoreconstitution of the adaptive immune compartment and ultimately adversely affect clinical outcome. Extracorporeal photopheresis (ECP) is an alternative therapeutic strategy that appears to act in an immunomodulatory fashion, potentially involving regulatory T lymphocytes and dendritic cells. By promoting immune tolerance and simultaneously avoiding systemic immunosuppression, ECP could reduce aGvHD and enable a reduction in other immunosuppression, allowing thymic recovery, restoration of normal T lymphopoiesis, and complete immunoreconstitution with improved clinical outcome. Although the safety and efficacy of ECP has been demonstrated, further randomised controlled studies are needed as well as elucidation of the underlying mechanisms responsible and the effect of ECP on thymic recovery.

Reprint of: B cells in chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) continues to be a common complication of allogeneic hematopoietic stem cell transplantation. Unlike acute graft-versus-host disease, which is mediated almost entirely by donor T cells, the immune pathology of cGVHD is more complex and donor B cells have also been found to play an important role. Recent studies from several laboratories have enhanced our understanding of how donor B cells contribute to this clinical syndrome and this has led to new therapeutic opportunities. Here, Dr Sarantopoulos reviews some of the important mechanisms responsible for persistent B cell activation and loss of B cell tolerance in patients with cGVHD. Dr Blazar describes recent studies in preclinical models that have identified novel B cell-directed agents that may be effective for prevention or treatment of cGVHD. Some B cell-directed therapies have already been tested in patients with cGVHD and Dr Cutler reviews the results of these studies documenting the potential efficacy of this approach. Supported by mechanistic studies in patients and preclinical models, new B cell-directed therapies for cGVHD will now be evaluated in clinical trials.

Aberrant B-cell homeostasis in chronic GVHD

Recent studies have compelled further interest in the potential pathological role of B cells in chronic graft-versus-host disease (cGVHD). In patients with cGVHD, B cells are activated and primed for survival via B-cell activating factor and B-cell receptor-associated pathways. Understanding the signaling pathways that drive immune pathology in cGVHD will facilitate the development of new strategies to selectively target aberrantly activated B cells and restore normal B-cell homeostasis after allogeneic stem cell transplantation.

Various forms of tissue damage and danger signals following hematopoietic stem-cell transplantation

Hematopoietic stem-cell transplantation (HSCT) is the most potent curative therapy for many malignant and non-malignant disorders. Unfortunately, a major complication of HSCT is graft-versus-host disease (GVHD), which is mediated by tissue damage resulting from the conditioning regimens before the transplantation and the alloreaction of dual immune components (activated donor T-cells and recipient’s antigen-presenting cells). This tissue damage leads to the release of alarmins and the triggering of pathogen-recognition receptors that activate the innate immune system and subsequently the adaptive immune system. Alarmins, which are of endogenous origin, together with the exogenous pathogen-associated molecular patterns (PAMPs) elicit similar responses of danger signals and represent the group of damage-associated molecular patterns (DAMPs). Effector cells of innate and adaptive immunity that are activated by PAMPs or alarmins can secrete other alarmins and amplify the immune responses. These complex interactions and loops between alarmins and PAMPs are particularly potent at inducing and then aggravating the GVHD reaction. In this review, we highlight the role of these tissue damaging molecules and their signaling pathways. Interestingly, some DAMPs and PAMPs are organ specific and GVHD-induced and have been shown to be interesting biomarkers. Some of these molecules may represent potential targets for novel therapeutic approaches.

B cells in chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) continues to be a common complication of allogeneic hematopoietic stem cell transplantation. Unlike acute graft-versus-host disease, which is mediated almost entirely by donor T cells, the immune pathology of cGVHD is more complex and donor B cells have also been found to play an important role. Recent studies from several laboratories have enhanced our understanding of how donor B cells contribute to this clinical syndrome and this has led to new therapeutic opportunities. Here, Dr Sarantopoulos reviews some of the important mechanisms responsible for persistent B cell activation and loss of B cell tolerance in patients with cGVHD. Dr Blazar describes recent studies in preclinical models that have identified novel B cell-directed agents that may be effective for prevention or treatment of cGVHD. Some B cell-directed therapies have already been tested in patients with cGVHD and Dr Cutler reviews the results of these studies documenting the potential efficacy of this approach. Supported by mechanistic studies in patients and preclinical models, new B cell-directed therapies for cGVHD will now be evaluated in clinical trials.

Pulmonary Manifestations of Hematological Malignancies: Focus on Pulmonary Chronic Graft-Versus Host Disease

Advances in the management of patients in terms of the diagnosis and treatment of hematologic malignancies and treatment-related complications, especially infectious complications, have increased survival time. However, more than half of the patients treated for hematologic malignancies will develop a pulmonary complication during their follow-up, infectious pneumonia remaining the most common diagnosis that should be considered first in regard to its potential severity. Otherwise, new complications that may involve different organs, including the lungs, have been increasingly reported. Currently, over a quarter of lung infiltrates occurring in the context of hematological diseases are due to noninfectious causes. Thus, lung physicians may be increasingly confronted with these lung disorders. Various noninfectious pulmonary complications have been described in the different hematological malignancies; however, these complications are most often studied in the context of allogeneic hematopoietic stem cell transplantation (HSCT). In this chapter, we will briefly review the lung diseases associated with various hematological malignancies before focusing on noninfectious pulmonary complications following allogeneic HSCT.

The allure and peril of hematopoietic stem cell transplantation: overcoming immune challenges to improve success

Since its inception in the mid-twentieth century, the complication limiting the application and utility of allogeneic hematopoietic stem cell transplantation (allo-HSCT) to treat patients with hematopoietic cancer is the development of graft-versus-host disease (GVHD). Ironically, GVHD is induced by the cells (T lymphocytes) transplanted for the purpose of eliminating the malignancy. Damage ensuing to multiple tissues, e.g., skin, GI, liver, and others including the eye, provides the challenge of regulating systemic and organ-specific GVH responses. Because the immune system is also targeted by GVHD, this both: (a) impairs reconstitution of immunity post-transplant resulting in patient susceptibility to lethal infection and (b) markedly diminishes the individual's capacity to generate anti-cancer immunity--the raison d'etre for undergoing allo-HSCT. We hypothesize that deleting alloreactive T cells ex vivo using a new strategy involving antigen stimulation and alkylation will prevent systemic GVHD thereby providing a platform for the generation of anti-tumor immunity. Relapse also remains the major complication following autologous HSCT (auto-HSCT). While GVHD does not complicate auto-HSCT, its absence removes significant grant anti-tumor responses (GVL) and raises the challenge of generating rapid and effective anti-tumor immunity early post-transplant prior to immune reconstitution. We hypothesize that effective vaccine usage to stimulate tumor-specific T cells followed by their amplification using targeted IL-2 can be effective in both the autologous and allogeneic HSCT setting. Lastly, our findings support the notion that the ocular compartment can be locally targeted to regulate visual complications of GVHD which may involve both alloreactive and self-reactive (i.e., autoimmune) responses.

Antigen-Specific Priming is Dispensable in Depletion of Apoptosis-Sensitive T Cells for GvHD Prophylaxis

Prophylactic approaches to graft versus host disease (GvHD) have employed both phenotypic reduction of T cells and selective elimination of host-primed donor T cells in vitro and in vivo. An additional approach to GvHD prophylaxis by functional depletion of apoptosis-sensitive donor T cells without host-specific sensitization ex vivo showed remarkable reduction in GHD incidence and severity. We address the role and significance of antigen-specific sensitization of donor T cells and discuss the mechanisms of functional T cell purging by apoptosis for GvHD prevention. Host-specific sensitization is dispensable because migration is antigen-independent and donor T cell sensitization is mediated by multiple and redundant mechanisms of presentation of major and minor histocompatibility complex and tissue antigens by donor and host antigen-presenting cells. Our data suggest that potential murine and human GvH effectors reside within subsets of preactivated T cells susceptible to negative regulation by apoptosis prior to encounter of and sensitization to specific antigens.

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

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

Oral complications and management strategies for patients undergoing cancer therapy

With cancer survival rate climbing up over the past three decades, quality of life for cancer patients has become an issue of major concern. Oral health plays an important part in one's overall quality of life. However, oral health status can be severely hampered by side effects of cancer therapies including surgery, chemotherapy, radiotherapy, and hematopoietic stem cell transplantation. Moreover, prevention and treatment of these complications are often overlooked in clinical practice. The present paper aims at drawing health care professionals' attention to oral complications associated with cancer therapy by giving a comprehensive review. Brief comments on contemporary cancer therapies will be given first, followed by detailed description of oral complications associated with cancer therapy. Finally, a summary of preventive strategies and treatment options for common oral complications including oral mucositis, oral infections, xerostomia, and dysgeusia will be given.

Autoimmune hematological diseases after allogeneic hematopoietic stem cell transplantation in children: an Italian multicenter experience

Autoimmune hematological diseases (AHDs) may occur after allogeneic hematopoietic stem cell transplantation (HSCT), but reports on these complications in large cohorts of pediatric patients are lacking. Between 1998 and 2011, 1574 consecutive children underwent allogeneic HSCT in 9 Italian centers. Thirty-three children (2.1%) developed AHDs: 15 autoimmune hemolytic anemia (45%), 10 immune thrombocytopenia (30%), 5 Evans' syndrome (15%), 2 pure red cell aplasia (6%), and 1 immune neutropenia (3%). The 10-year cumulative incidence of AHDs was 2.5% (95% confidence interval, 1.7 to 3.6). In a multivariate analysis, the use of alternative donor and nonmalignant disease was statistically associated with AHDs. Most patients with AHDs (64%) did not respond to steroids. Sustained complete remission was achieved in 87% of cases with the anti-CD20 monoclonal antibody (rituximab). Four patients (9%) (1 autoimmune hemolytic anemia, 1 Evans' syndrome, 2 immune thrombocytopenia) died at a median of 87 days after AHD diagnosis as a direct or indirect consequence of their disorder. Our data suggest that AHDs are a relatively rare complication occurring after HSCT that usually respond to treatment with rituximab.

Thymic damage, impaired negative selection, and development of chronic graft-versus-host disease caused by donor CD4+ and CD8+ T cells

Prevention of chronic graft-versus-host disease (cGVHD) remains a major challenge in allogeneic hematopoietic cell transplantation (HCT) owing to limited understanding of cGVHD pathogenesis and lack of appropriate animal models. In this study, we report that, in classical acute GVHD models with C57BL/6 donors and MHC-mismatched BALB/c recipients and with C3H.SW donors and MHC-matched C57BL/6 recipients, GVHD recipients surviving for >60 d after HCT developed cGVHD characterized by cutaneous fibrosis, tissue damage in the salivary gland, and the presence of serum autoantibodies. Donor CD8(+) T cells were more potent than CD4(+) T cells for inducing cGVHD. The recipient thymus and de novo-generated, donor-derived CD4(+) T cells were required for induction of cGVHD by donor CD8(+) T cells but not by donor CD4(+) T cells. Donor CD8(+) T cells preferentially damaged recipient medullary thymic epithelial cells and impaired negative selection, resulting in production of autoreactive CD4(+) T cells that perpetuated damage to the thymus and augmented the development of cGVHD. Short-term anti-CD4 mAb treatment early after HCT enabled recovery from thymic damage and prevented cGVHD. These results demonstrate that donor CD8(+) T cells cause cGVHD solely through thymic-dependent mechanisms, whereas CD4(+) T cells can cause cGVHD through either thymic-dependent or independent mechanisms.

Chemokine-mediated tissue recruitment of CXCR3+ CD4+ T cells plays a major role in the pathogenesis of chronic GVHD

Chemokines regulate the migration of hemopoietic cells and play an important role in the pathogenesis of many immune-mediated diseases. Intradermal recruitment of CD8(+) T cells by CXCL10 is a central feature of the pathogenesis of cutaneous acute GVHD (aGVHD), but very little is known about the pathogenesis of chronic GVHD (cGVHD). Serum concentrations of the 3 CXCR3-binding chemokines, CXCL9, CXCL10, and CXCL11, were found to be markedly increased in patients with active cGVHD of the skin (n = 8). An 80% decrease in CD4(+) cells expressing CXCR3 was seen in the blood of these patients (n = 5), whereas CD4(+) cells were increased in tissue biopsies and were clustered around the central arterioles of the dermis. The well-documented increase in expression of CXCL10 in aGVHD therefore diversifies in cGVHD to include additional members of the CXCR3-binding family and leads to preferential recruitment of CD4(+) T cells. These observations reveal a central role for chemokine-mediated recruitment of CXCR3(+) T cells in cGVHD.

Donor B cells in transplants augment clonal expansion and survival of pathogenic CD4+ T cells that mediate autoimmune-like chronic graft-versus-host disease

We reported that both donor CD4(+) T and B cells in transplants were required for induction of an autoimmune-like chronic graft-versus-host disease (cGVHD) in a murine model of DBA/2 donor to BALB/c recipient, but mechanisms whereby donor B cells augment cGVHD pathogenesis remain unknown. In this study, we report that, although donor B cells have little impact on acute GVHD severity, they play an important role in augmenting the persistence of tissue damage in the acute and chronic GVHD overlapping target organs (i.e., skin and lung); they also markedly augment damage in a prototypical cGVHD target organ, the salivary gland. During cGVHD pathogenesis, donor B cells are activated by donor CD4(+) T cells to upregulate MHC II and costimulatory molecules. Acting as efficient APCs, donor B cells augment donor CD4(+) T clonal expansion, autoreactivity, IL-7Rα expression, and survival. These qualitative changes markedly augment donor CD4(+) T cells' capacity in mediating autoimmune-like cGVHD, so that they mediate disease in the absence of donor B cells in secondary recipients. Therefore, a major mechanism whereby donor B cells augment cGVHD is through augmenting the clonal expansion, differentiation, and survival of pathogenic CD4(+) T cells.

Clinical applications for biomarkers of acute and chronic graft-versus-host disease

Acute and chronic graft-versus-host disease (aGVHD, cGVHD) are serious complications of allogeneic hematopoietic cell transplantation. The complex pathophysiology of these disease processes is associated with immune system activation, the release of cytokines and chemokines, and alterations in cell populations. The blood levels of specific protein and cellular levels in patients with GVHD have correlated with the development, diagnosis, and prognosis of GVHD. Here, we review the most promising biomarkers for aGVHD and cGVHD with clinical relevance. The utility of GVHD biomarkers in clinical care of allogeneic hematopoietic cell transplantation recipients needs to be proven through clinical trials, and potential approaches to trial design are discussed.

Emergence of T cells that recognize nonpolymorphic antigens during graft-versus- host disease

Chronic GVHD is a major cause of morbidity and mortality in allogeneic stem cell transplantation recipients and typically develops from antecedent acute GVHD. In contrast to acute GVHD, chronic GVHD has much broader tissue involvement and clinical manifestations that bear striking similarity to what is observed in autoimmune diseases. How autoimmunity arises out of alloimmunity has been a longstanding unresolved issue. To address this question, in the present study, we performed a comprehensive analysis of the clonotypic T-cell response using complementary murine models that simulate what occurs during the transition from acute to chronic GVHD. These studies revealed repertoire skewing and the presence of high-frequency clonotypes that had undergone significant in vivo expansion, indicating that GVHD-associated autoimmunity was characterized by antigen-driven expansion of a limited number of T-cell clones. Furthermore, we observed that T cells with identical TCRβ CDR3 nucleotide sequences were capable of recognizing donor and host antigens, providing evidence that the loss of self-tolerance during acute GVHD leads to the emergence of self-reactive donor T cells that are capable of recognizing nonpolymorphic tissue or commensally derived antigens. These data provide a mechanistic framework for how autoimmunity develops within the context of preexisting GVHD and provide additional insight into the pathophysiology of chronic GVHD.