Loss of T Follicular Helper Cells in the Peripheral Blood of Patients with Chronic Graft-versus-Host Disease

Recent Advances and Research Progress in Biomarkers for Chronic Graft Versus Host Disease

Chronic graft-versus host disease (cGVHD) is a major risk for patients undergoing allogeneic hematopoietic stem cell transplantation. With the emergence of novel therapies and the increased understanding of the mechanisms underlying cGVHD, there are more options for cGVHD treatment. Regardless of improvements in treatment, diagnosis mainly depends on identification of symptoms, which makes precise treatment a challenge. Numerous biomarkers for cGVHD have been validated and have demonstrated strong associations with prognosis and response to treatment. The most common biomarkers mainly include critical types of immune cells, chemokines, cytokines, microRNAs, and autoantibodies, all of which play important roles in the development of cGVHD. Compared to traditional tools, biomarkers have several advantages, for example, they can be applied for early diagnosis, to identify cGVHD risk before onset, and predict which therapy is most likely to benefit patients. In this review, we summarize biomarkers with potential clinical value and discuss future applications.

Trafficking between clonally related peripheral T-helper cells and tissue-resident T-helper cells in chronic GVHD

Chronic graft-versus-host disease (cGVHD) is an autoimmune-like syndrome. CXCR5-PD-1hi peripheral T-helper (Tph) cells have an important pathogenic role in autoimmune diseases, but the role of Tph cells in cGVHD remains unknown. We show that in patients with cGVHD, expansion of Tph cells among blood CD4+ T cells was associated with cGVHD severity. These cells augmented memory B-cell differentiation and production of immunoglobulin G via interleukin 21 (IL-21). Tph cell expansion was also observed in a murine model of cGVHD. This Tph cell expansion in the blood is associated with the expansion of pathogenic tissue-resident T-helper (Trh) cells that form lymphoid aggregates surrounded by collagen in graft-versus-host disease (GVHD) target tissues. Adoptive transfer experiments showed that Trh cells from GVHD target tissues give rise to Tph cells in the blood, and conversely, Tph cells from the blood give rise to Trh cells in GVHD target tissues. Tph cells in the blood and Trh cells in GVHD target tissues had highly overlapping T-cell receptor α and β repertoires. Deficiency of IL-21R, B-cell lymphoma 6 (BCL6), or T-bet in donor T cells markedly reduced the proportions of Tph cells in the blood and Trh cells in GVHD target tissues and reduced T-B interaction in the lymphoid aggregates. These results indicate that clonally related pathogenic Tph cells and Trh cells traffic between the blood and cGVHD target tissues, and that IL-21R-BCL6 signaling and T-bet are required for the development and expansion of Tph and Trh cells in the pathogenesis of cGVHD.

Erythropoietin Reduces Auto- and Alloantibodies by Inhibiting T Follicular Helper Cell Differentiation

BACKGROUND

Although high-affinity IgG auto- and alloantibodies are important drivers of kidney inflammation that can result in ESKD, therapeutic approaches that effectively reduce such pathogenic antibodies remain elusive. Erythropoietin (EPO) has immunomodulatory functions, but its effects on antibody production are unknown.

METHODS

We assessed the effect and underlying mechanisms of EPO/EPO receptor (EPOR) signaling on primary and secondary, T cell-dependent and T-independent antibody formation using in vitro culture systems, murine models of organ transplantation and lupus nephritis, and mice conditionally deficient for the EPOR expressed on T cells or B cells.

RESULTS

In wild-type mice, recombinant EPO inhibited primary, T cell-dependent humoral immunity to model antigens and strong, polyclonal stimuli, but did not alter T-independent humoral immune responses. EPO also significantly impaired secondary humoral immunity in a potent allogeneic organ transplant model system. The effects required T cell, but not B cell, expression of the EPOR and resulted in diminished frequencies of germinal center (GC) B cells and T follicular helper cells (T_FH). In vitro and in vivo experiments showed that EPO directly prevented T_FH differentiation and function via a STAT5-dependent mechanism that reduces CD4⁺ T cell expression of Bcl6. In lupus models, EPO reduced T_FH, GC B cells, and autoantibody production, and abrogated autoimmune glomerulonephritis, demonstrating clinical relevance. In vitro studies verified that EPO prevents differentiation of human T_FH cells.

CONCLUSIONS

Our findings newly demonstrate that EPO inhibits T_FH-dependent antibody formation, an observation with potential implications for treating antibody-mediated diseases, including those of the kidney.

TFH cells in systemic sclerosis

Systemic sclerosis is an autoimmune disease characterized by excessive dermal fibrosis with progression to internal organs, vascular impairment and immune dysregulation evidenced by the infiltration of inflammatory cells in affected tissues and the production of auto antibodies. While the pathogenesis remains unclear, several data highlight that T and B cells deregulation is implicated in the disease pathogenesis. Over the last decade, aberrant responses of circulating T follicular helper cells, a subset of CD4 T cells which are able to localise predominantly in the B cell follicles through a high level of chemokine receptor CXCR5 expression are described in pathogenesis of several autoimmune diseases and chronic graft-versus-host-disease. In the present review, we summarized the observed alteration of number and frequency of circulating T follicular helper cells in systemic sclerosis. We described their role in aberrant B cell activation and differentiation though interleukine-21 secretion. We also clarified T follicular helper-like cells involvement in fibrogenesis in both human and mouse model. Finally, because T follicular helper cells are involved in both fibrosis and autoimmune abnormalities in systemic sclerosis patients, we presented the different strategies could be used to target T follicular helper cells in systemic sclerosis, the therapeutic trials currently being carried out and the future perspectives from other auto-immune diseases and graft-versus-host-disease models.

Expansion of circulating extrafollicular helper T-like cells in patients with chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) is a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Previous studies have shown that T follicular helper cells (Tfh) contribute to immune pathology in cGVHD, but the function of extrafollicular helper T cells during cGVHD pathogenesis remains largely unknown. In the current study, we identified circulating extrafollicular helper T-like cells (CD44^hiCD62L^loPSGL-1^loCD4⁺, c-extrafollicular Th-like) in human peripheral blood. We performed phenotypic and functional analyses of c-extrafollicular Th-like cells from 80 patients after allo-HSCT to explore the role of these cells in the development of human cGVHD. Patients with active cGVHD had significantly higher frequencies and counts of c-extrafollicular Th-like cells than those of patients without cGVHD. The expansion of c-extrafollicular Th-like cells was more significant in patients with moderate/severe cGVHD than that of patients with mild cGVHD. C-extrafollicular Th-like cells from patients with active cGVHD exhibited increased functional abilities to induce plasmablast differentiation and IgG1 secretion compared to those of patients without cGVHD. Moreover, c-extrafollicular Th-like cell levels were highly correlated with the generation of autoreactive B cells, plasmablasts and IgG1 antibodies. Our studies provide new insights into human cGVHD pathogenesis and identify c-extrafollicular Th-like cells as a key element in the development of human cGVHD.

Developing role of B cells in the pathogenesis and treatment of chronic GVHD

Chronic graft-versus-host disease (cGVHD) is a major complication affecting the long-term survival of patients after allogeneic haematopoietic stem cell transplantation. The mechanism of cGVHD is unclear, and while previous studies have primarily focused on T cells, the role of B cells in the pathogenesis of cGVHD has been less reported. However, current studies on cGVHD are increasingly focused on the important role of B cells. In this review, we will introduce the newest studies and examine the role of B cells in cGVHD in detail with respect to the following aspects: altered B cell subpopulations, aberrant B cell signalling pathways, autoantibodies and T-B cell interactions. Treatment strategies for the targeting of B cells during cGVHD will also be discussed.

C5aR1 regulates T follicular helper differentiation and chronic graft-versus-host disease bronchiolitis obliterans

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.

Extrafollicular CD4+ T-B interactions are sufficient for inducing autoimmune-like chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) is an autoimmune-like syndrome mediated by pathogenic CD4⁺ T and B cells, but the function of extrafollicular and germinal center CD4⁺ T and B interactions in cGVHD pathogenesis remains largely unknown. Here we show that extrafollicular CD4⁺ T and B interactions are sufficient for inducing cGVHD, while germinal center formation is dispensable. The pathogenesis of cGVHD is associated with the expansion of extrafollicular CD44^hiCD62^loPSGL-1^loCD4⁺ (PSGL-1^loCD4⁺) T cells. These cells express high levels of ICOS, and the blockade of ICOS/ICOSL interaction prevents their expansion and ameliorates cGVHD. Expansion of PSGL-1^loCD4⁺ T cells is also prevented by BCL6 or Stat3 deficiency in donor CD4⁺ T cells, with the induction of cGVHD ameliorated by BCL6 deficiency and completely suppressed by Stat3 deficiency in donor CD4⁺ T cells. These results support that Stat3- and BCL6-dependent extrafollicular CD4⁺ T and B interactions play critical functions in the pathogenesis of cGVHD.Chronic graft-versus-host disease (cGVHD) is mediated by specific CD4 and B cells, but the relative contribution of extrafollicular and germinal centre (GC) T-B interaction is unclear. Here the authors show that the extrafollicular expansion of a specific CD4 T subset is sufficient for inducing cGVHD while GC is dispensable.

Impact of Donor Activating KIR Genes on HSCT Outcome in C1-Ligand Negative Myeloid Disease Patients Transplanted with Unrelated Donors-A Retrospective Study

Natural Killer cells (NK) are lymphocytes with the potential to recognize and lyse cells which escaped T-cell mediated lysis due to their aberrant HLA expression profiles. Killer cell immunoglobulin-like receptors (KIR) influence NK-cell activity by mediation of activating or inhibitory signals upon interaction with HLA-C (C1, C2) ligands. Therefore, absence of ligands for donor inhibitory KIRs following hematopoietic stem cell transplantation (HSCT) may have an influence on its outcome. Previous studies showed that C1 negative patients have a decreased HSCT outcome. Our study, based on a cohort of 200 C1-negative patients, confirmed these findings for the endpoints: overall survival (OS: HR = 1.41, CI = 1.14–1.74, p = 0.0012), disease free survival (DFS: HR = 1.27, CI = 1.05–1.53, p = 0.015), treatment related mortality (TRM: HR = 1.41, CI = 1.01–1.96, p = 0.04), and relapse incidence (RI: HR = 1.33, CI = 1.01–1.75, p = 0.04) all being inferior when compared to C1-positive patients (n = 1246). Subsequent analysis showed that these findings applied for patients with myeloid malignancies but not for patients with lymphoproliferative diseases (OS: myeloid: HR = 1.51, CI = 1.15–1.99, p = 0.003; lymphoblastic: HR = 1.26, CI = 0.91–1.75, p = 0.16; DFS: myeloid: HR = 1.31, CI = 1.01–1.70, p = 0.04; lymphoblastic: HR = 1.21, CI = 0.90–1.61, p = 0.21; RI: myeloid: HR = 1.31, CI = 1.01–1.70, p = 0.04; lymphoblastic: HR = 1.21, CI = 0.90–1.61, p = 0.21). Interestingly, within the C1-negative patient group, transplantation with KIR2DS2 resulted in better OS (9/10 matched: HR = 0.24, CI = 0.08–0.67, p = 0.007) as well as DFS (9/10 matched: HR = 0,26, CI = 0.11–0.60, p = 0.002), and transplantation with KIR2DS1 positive donors was associated with a decreased RI (HR = 0.30, CI = 0.13–0.69, p = 0.005). TRM was increased when the donor was positive for KIR2DS1 (HR = 2.61, CI = 1.26–5.41, p = 0.001). Our findings suggest that inclusion of KIR2DS1/2/5 and KIR3DS1-genotyping in the unrelated donor search algorithm of C1-ligand negative patients with myeloid malignancies may prove to be of clinical relevance.

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.