Mechanisms of action of antithymocyte globulin: T-cell depletion and beyond

Immunosuppressive therapy in myelodysplastic syndromes: a borrowed therapy in search of the right place

INTRODUCTION

Myelodysplastic syndromes (MDS) encompass a heterogenous collection of clonal hematopoietic stem cell disorders defined by dysregulated hematopoiesis, peripheral cytopenias, and a risk of leukemic progression. Increasing data support the role of innate and adaptive immune pathways in the pathogenesis and disease course of MDS. The role of immunosuppressive therapy has an established role in the treatment of other hematologic diseases, such as aplastic anemia whose pathogenesis is postulated to reflect that of MDS with regards to many aspects of immune activation. Areas covered: This paper discusses the current understanding of immune dysregulation as it pertains to MDS, the clinical experience with immunosuppressive therapy in the management of MDS, as well as future prospects which will likely improve therapeutic options and outcomes for patients with MDS. Expert commentary: Though limited by paucity of high quality data, immunomodulatory and immunosuppressive therapies for the treatment of MDS have shown meaningful clinical activity in selected patients. Continued clarification of the immune pathways that are dysregulated in MDS and establishing predictors for clinical benefit of immunosuppressive therapy are vital to improve the use and outcomes with these therapies.

Effect of Antihuman T Lymphocyte Globulin on Immune Recovery after Myeloablative Allogeneic Stem Cell Transplantation with Matched Unrelated Donors: Analysis of Immune Reconstitution in a Double-Blind Randomized Controlled Trial

We recently conducted a randomized double-blind study in which we demonstrated that moderate/severe chronic graft-versus-host disease (cGVHD) but not cGVHD-free survival was reduced in patients receiving anti-T lymphocyte globulin (ATLG) versus placebo. In a companion study we performed immunophenotypic analysis to determine the impact of ATLG on immune reconstitution (IR) and to correlate IR with clinical outcomes. The randomized study (n = 254) included patients (aged 18 to 65 years) who underwent myeloablative transplants for acute myeloid leukemia, myelodysplastic syndrome, or acute lymphoblastic leukemia from HLA-matched unrelated donors. Ninety-one patients consented for the companion IR study (ATLG = 44, placebo = 47). Blood samples were collected on days 30, 100, 180, and 360 after hematopoietic cell transplantation (HCT), and multiparameter flow cytometry was performed in a blinded fashion. Reconstitution of CD3⁺ and CD4⁺ T cells was delayed up to 6 months post-HCT in the ATLG arm, whereas absolute regulatory T cell (Treg) (CD4⁺25⁺127-) numbers were lower only in the first 100 days. Analysis of the CD4⁺ Treg and conventional T cells (Tconv) (CD4⁺25^-127⁺) compartments showed a profound absence of naive Tregs and Tconv in the first 100 days post-HCT, with very slow recovery for 1 year. B cell and natural killer cell recovery were similar in each arm. Higher absolute counts of CD3⁺, CD4⁺, CD8⁺ T, Tregs, and Tconv were associated with improved overall survival, progression-free survival, and nonrelapse mortality but not moderate/severe cGVHD. Although ATLG delays CD3⁺ and CD4⁺ T cell recovery post-transplant, it has a relative Treg sparing effect after the early post-HCT period, with possible implications for protection from cGVHD. ATLG severely compromises the generation of naive CD4⁺ cells (Treg and Tconv), potentially affecting the diversity of the TCR repertoire and T cell responses against malignancy and infection.

Posttransplant Immune Activation: Innocent Bystander or Insidious Culprit of Posttransplant Accelerated Atherosclerosis

Cardiovascular disease is a major cause of morbidity, disability, and mortality in kidney transplant patients. Cumulative reports indicate that the excessive risk of cardiovascular events is not entirely explained by the increased prevalence of traditional cardiovascular risk factors. Atherosclerosis is a chronic inflammatory disease, and it has been postulated that posttransplant immune disturbances may explain the gap between the predicted and observed risks of cardiovascular events. Although concordant data suggest that innate immunity contributes to the posttransplant accelerated atherosclerosis, only few arguments plead for a role of adaptive immunity. We report and discuss here consistent data demonstrating that CD8⁺ T cell activation is a frequent posttransplant immune feature that may have pro-atherogenic effects. Expansion of exhausted/activated CD8⁺ T cells in kidney transplant recipients is stimulated by several factors including cytomegalovirus infections, lymphodepletive therapy (e.g., antithymocyte globulins), chronic allogeneic stimulation, and a past history of renal insufficiency. This is observed in the setting of decreased thymic activity, a process also found in elderly individuals and reflecting accelerated immune senescence.

Idiopathic severe aplastic anemia with a delayed response to immunosuppressive therapy: a case report

Bone marrow transplantation is the definitive treatment of severe aplastic anemia; however, with the absence of this option, combined immunosuppressive therapy with antithymocyte globulin (ATG) and cyclosporine A is used as a first‐line therapy. This case report highlights the possible delay in response to ATG protocol in treating aplastic anemia.

Autologous Hematopoietic Stem Cell Transplantation for Antiphospholipid Syndrome: Case Report and Review of the Literature

Refractory antiphospholipid syndrome represents a challenge for preventing thrombosis that may occur despite adequate anticoagulation and immunomodulation therapy. Here, we report a 35-year-old male patient who presented with variable venous thromboembolic events. Autologous hematopoietic stem cell transplant was performed after conditioning with cyclophosphamide and antithymocyte globulin. Five years after transplant, the treatment continued to show a successful outcome in preventing new thrombotic events. Autologous hematopoietic stem cell transplant represents a chance for cure from antiphospholipid syndrome despite the paucity of reported data so far.

Anti-thymocyte globulin improves survival free from relapse and graft-versus-host disease after allogeneic peripheral blood stem cell transplantation in patients with Philadelphia-negative acute lymphoblastic leukemia: An analysis by the Acute Leukemia Working Party of the EBMT

BACKGROUND

Mobilized peripheral blood stem cells are currently the predominant source of grafts for allogeneic transplantation (allogeneic peripheral blood stem cell transplantation [allo-PBSCT]), although, in comparison with bone marrow, their use is associated with an increased risk of chronic graft-versus-host disease (cGVHD). Attempts to reduce the incidence of cGVHD include the addition of anti-thymocyte globulin (ATG) to the pretransplant conditioning regimen.

METHODS

The goal of this retrospective study was to analyze the effect of ATG on allo-PBSCT outcomes for adults with Philadelphia-negative acute lymphoblastic leukemia (Ph-neg ALL). The primary endpoint was survival free from relapse, grade 3 to 4 acute graft-versus-host disease (aGVHD), and cGVHD (ie, graft-versus-host disease-free/relapse-free survival [GRFS]). Nine-hundred twenty-four patients who underwent unmanipulated allo-PBSCT in their first complete remission between 2007 and 2016 were included. ATG was used in 97 of the 494 transplants from matched sibling donors (20%) and in 307 of the 430 transplants from human leukocyte antigen-matched (8 of 8 loci) unrelated donors (71%).

RESULTS

The use of ATG was an independent factor for an improved chance of GRFS (hazard ratio [HR], 0.70; P = .0009). Furthermore, it was associated with a reduced risk of both grade 2 to 4 (HR, 0.66; P = .005) and grade 3 to 4 aGVHD (HR, 0.58; P = .03). Similarly, its addition reduced the incidence of both total (HR, 0.45; P < 10^-5 ) and extensive cGVHD (HR, 0.30; P < 10^-5 ) as well as nonrelapse mortality (HR, 0.58; P = .01). No significant effect was found with respect to leukemia-free or overall survival. However, an increased risk of relapse was noted for those who received ATG (HR, 1.40; P = .04).

CONCLUSIONS

Patients with Ph-neg ALL treated with allo-PBSCT benefit from the use of ATG in terms of improved GRFS. Its use may, therefore, be considered in this setting. Cancer 2018;124:2523-33. © 2018 American Cancer Society.

Poor Patient and Graft Outcome After Induction Treatment by Antithymocyte Globulin in Recipients of a Kidney Graft After Nonrenal Organ Transplantation

Background

End-stage renal failure occurs in a substantial number of patients having received a nonrenal transplantation (NRT), for whom a kidney transplantation is needed. The medical strategy regarding the use of immunosuppression (IS) for a kidney graft in patients after an NRT is not well established. The prekidney grafts long-term IS advocates for a mild induction, such as using anti-IL-2R antibodies, whereas addition of new incompatibilities and anti-HLA preimmunization may suggest using stronger IS such as induction by polyclonal antithymocyte globulins (ATG).

Methods

We performed Cox multivariate and propensity score analysis of our validated transplant database to study the impact of the type of induction therapy on kidney graft survival of recipients of a kidney graft after NRT.

Results

We report here that kidney transplantation after NRT treated with an ATG induction has a poorer outcome (kidney and recipient survival) than that with an anti-IL-2R induction. After accounting for potential baseline differences with a multivariate Cox model, or by adjusting on a propensity score, we found that despite patients having received ATG cumulate more risk factors, ATG appears independently involved. As animal-derived biotherapeutics induce antiglycan antibodies and particularly anti-N-glycolylneuraminic acid (Neu5Gc) IgGs which may activate endothelial cells in patients and grafts, we also investigated the magnitude and the nature of the anti-Neu5Gc elicited by the induction and showed that induction was associated with a shift in anti-Neu5Gc IgG repertoire. Possible reasons and mechanisms of a deleterious ATG usage in these patients are discussed.

Conclusions

Our study suggests that ATG induction after a kidney transplantation in recipients already under maintenance IS for a NRT should be used cautiously.

Anti-thymocyte globulins in kidney transplantation: focus on current indications and long-term immunological side effects

Antithymocyte globulins (ATGs) are part of the immunosuppression arsenal currently used by clinicians to prevent or treat acute rejection in solid organ transplantation. ATG is a mixture of non-specific anti-lymphocyte immunoglobulins targeting not only T cell subsets but also several other immune and non-immune cells, rendering its precise immunoglobulin composition difficult to appreciate or to compare from one preparation to another. Furthermore, several mechanisms of action have been described. Taken together, this probably explains the efficacy and the side effects associated with this drug. Recent data suggest a long-term negative impact on allograft and patient outcomes, pointing out the need to better characterize the potential toxicity and the benefit-risk balance associated to this immunosuppressive therapy within large clinical trials.

The putative anti-leukemic effects of anti-thymocyte globulins in patients with CD7-positive acute myeloid leukemia

Polyclonal anti-thymocyte globulins (ATGs) are widely used in allogeneic stem cell transplantation (allo-SCT) for GvHD prophylaxis. ATGs exerted anti-tumor effects in in vitro experiments, but in vivo studies are lacking. We experienced a case of relapsed AML with cells positive for CD7 who underwent haploidentical SCT and unexpectedly achieved a significant reduction of AML cells in the peripheral blood after receiving ATGs before the administration of other drugs in the conditioning regimen. This patient achieved long-term survival after haploidentical SCT. To assess the impact of ATGs on clinical outcomes in patients with AML, we performed a retrospective analysis of allo-SCT for relapsed/refractory AML and divided 132 patients into four groups according to the expression of CD7 in AML cells and use of ATGs as part of the conditioning regimen, as follows: CD7-positive ATG group (n = 15), CD7-positive no-ATG group (n = 32), CD7-negative ATG group (n = 19), and CD7-negative no-ATG group (n = 66). The overall survival rates in the CD7-positive ATG group were significantly higher than those in the CD7-positive no-ATG group, whereas these rates did not differ statistically between the CD7-negative ATG and CD7-negative no-ATG groups. Our results indicate a possible anti-leukemic effect of ATGs against CD7-positive AML in humans.

Reactivation of Hemophagocytic Lymphohistiocytosis Triggered by Antithymocyte Globulin

A 16-year-old boy with Epstein-Barr virus-associated hemophagocytic lymphohistiocytosis (HLH) underwent allogeneic hematopoietic stem cell transplantation after conditioning with fludarabine, melphalan, total body irradiation, and rabbit antithymocyte globulin (ATG). A severe, persistent infusion reaction occurred after the initial administration of ATG. Investigations showed a rapid increase in the levels of liver enzymes and ferritin, and the reactivation of HLH was confirmed by marked hemophagocytosis in the bone marrow. Treatment with pulse glucocorticoid therapy resulted in the improvement of HLH. This is the first case of HLH reactivation triggered by ATG. Physicians should therefore be cautious of HLH reactivation, especially when a severe and prolonged infusion reaction occurs.

Allogenic peripheral stem cell transplantation from HLA-matched related donors for adult sickle cell disease: remarkable outcomes from a single-center trial

Adult patients with sickle cell disease (SCD) are highly susceptible to stem cell transplant complications, including drug toxicity, graft versus host disease (GVHD), and graft rejection due to SCD-related tissue damage, endothelial activation, and inflammation. The scarcity of compatible stem cells for transplantation further limits treatment options, with only 43 cases of adult allogeneic peripheral blood stem cell transplantation (allo-PSCT) from human leukocyte antigen (HLA)-identical sibling donors reported in the international registry for the period 1986-2013. Herein we report remarkable outcomes in a cohort of adult SCD patients who underwent allo-PSCT using a fludarabine (Flu), busulfan (Bu), and anti-T-cell lymphocyte globulin (ATG)-based conditioning regimen in combination with very low dose total body irradiation (TBI), followed by post-transplant cyclophosphamide (Cy) and sirolimus as GVHD prophylaxis. We performed a single-center, retrospective study consisting of 20 consecutive patients (mean age 33.4 years) who underwent allo-PSCT from HLA-matched related donors with a conditioning regimen of Flu 150/Bu 3.2/Cy 29/ATG 30 (Fresenius)/TBI 200 between September 2013 and September 2017. Data were validated by an independent data audit group of the affiliated JACIE-accredited transplantation center. All patients experienced a sustained donor cell engraftment. Full donor chimerism (total cell) occurred within 180 days in all patients. Mean duration of follow-up was 13.8 months (range: 0.3-50 months), with 12 (60%) patients completing 12 months. No non-relapse mortality or graft rejection occurred. Successful treatment was achieved without the presence of graft loss, grade III-IV acute GVHD, extensive chronic GVHD, or other major complications. Allo-PSCT in combination with Flu 150/Bu 3.2/Cy 29/ATG 30(Fresenius)/TBI 200- Cy/Sirolimus therapy yielded encouraging outcomes with no mortality and low incidence of GVHD. Further controlled studies will be necessary to compare transplant protocols and long-term outcomes.

Current systemic therapeutic options for advanced mycosis fungoides and Sézary syndrome

Mycosis fungoides (MF) and Sézary syndrome (SS) are the most common cutaneous T-cell lymphomas (CTCLs). Both lack curative options, and advanced-stage carries a poor prognosis. Whilst there are a number of treatments available, achieving and maintaining a durable remission remains challenging. We review current systemic treatment options as monotherapy for advanced-stage MF (IIB-IV), appraising their mechanism of action, analyzing their efficacy, and describing toxicities. Individually, reported overall response rates (ORR) vary widely in the literature and duration of responses are typically short, ranging from 7.5 to 22.4 months. Combined therapy is frequently used in an effort to boost responses, although prospective studies comparing combinations to single agent therapies are rarely conducted. While recent translational research has led to increased understanding of the immunopathogenesis of MF and SS and the development of new treatments, current standard of care therapies are not curative and have low ORR for advanced-stage disease.

Efficacy and safety of combined immunosuppressive therapy plus umbilical cord blood infusion in severe aplastic anemia patients: A cohort study

The present study aimed to evaluate the efficacy and safety of combined immunosuppressive therapy (IST) plus umbilical cord blood infusion (UCBI) in severe aplastic anemia (SAA) patients. A total of 68 patients with SAA were enrolled in the current prospective cohort study and divided into the IST (n=35; positive control) and IST+UCBI (n=33; experimental) groups according to the treatment conditions. Patients in the IST group were treated with rabbit antithymocyte globulin (r-ATG) at a dose of 2.5 mg/kg through intravenous infusion once a day for five days. This was combined with oral cyclosporine A (CsA) at a dose of 3–5 mg/kg twice a day for 2 years. Patients in the IST+UBCI group were treated with r-ATG and CsA at the same doses and frequencies as the IST group plus one UCBI 1 day after the final treatment with r-ATG. At 6 months post treatment, the complete response and overall response rate (ORR) of the IST+UCBI group were markedly higher compared with those in the IST group. Furthermore, patients in the IST+UCBI group achieved absolute neutrophil count (ANC) and platelet count responses more rapidly as compared with the IST group. However, no difference in the hemoglobin (Hb) response was identified between the two groups. In addition, SAA patients achieved responses in the ANC and platelet count more rapidly in comparison with very severe aplastic anemia (VSAA) patients, while the number of days to Hb responses were similar in the SAA and VSAA patients. Multivariate logistic regression analysis also revealed that IST+UCBI treatment was an independent predicting factor for patients achieving complete response or partial response, whereas VSAA was an independent predictor of a worse ORR. Platelet and reticulocyte were also independent predicting factors. Finally, the survival of patients was similar between the groups, and no difference in the safety of the treatment was observed. In conclusion, combined IST plus UCBI treatment may be applied as an effective and safe therapy for SAA patients.

Glycan microarray reveal induced IgGs repertoire shift against a dietary carbohydrate in response to rabbit anti-human thymocyte therapy

Humans have circulating antibodies against diverse glycans containing N-glycolylneuraminic acid (Neu5Gc) due to function-loss mutation of the CMAH gene. This xenogenic non-human carbohydrate is abundant in red meat, xenografts and biotherapeutics. Low levels of diet-derived Neu5Gc is also present on normal human endothelial cells, and together with anti-Neu5Gc antibodies could potentially mediate “xenosialitis” chronic-inflammation. Rabbit anti-human thymocyte globulin (ATG) is a drug containing polyclonal IgG glycoproteins commonly used as an immunosuppressant in human transplantation and autoimmune diseases. In type-1 diabetes patients, infusion of Neu5Gc-glycosylated ATG caused increased global anti-Neu5Gc response. Here, for the first time we explore changes in anti-Neu5Gc IgG repertoire following the immunization elicited by ATG, compared with the basal antibodies repertoire that reflect exposure to dietary-Neu5Gc. We used glycan microarrays with multiple Neu5Gc-glycans and controls to elucidate eventual differences in ATG-elicited repertoire, before/after ATG administration and track their kinetics (0, 1, 18 and 24 months). Response of all basal-pre-existing Neu5Gc-specific antibodies rapidly increased. This response peaked at one month post-ATG, with enhanced affinity, then resolved at 18–24 months. Induced-antibodies showed expanded diversity and de-novo recognition of different Neu5Gc-glycans, including endogenous glycolipids, that was further validated by affinity-purified anti-Neu5Gc antibodies from patients’ sera. These findings strongly suggest that ATG-induced anti-Neu5Gc IgGs represent a secondary exposure to this dietary carbohydrate-antigen in humans, with immune memory. Given their modified recognition patterns, ATG-evoked anti-Neu5Gc antibodies could potentially mediate biological effects different from pre-existing antibodies.

The Role of Anti-Thymocyte Globulin or Alemtuzumab-Based Serotherapy in the Prophylaxis and Management of Graft-Versus-Host Disease

Allogeneic hematopoietic stem cell transplant is an established treatment modality for hematologic and non-hematologic diseases. However, it is associated with acute and long-term sequelae which can translate into mortality. Graft-versus-host disease (GVHD) remains a glaring obstacle, especially with the advent of reduced-intensity conditioning. Serotherapy capitalizes on antibodies which target T cells and other immune cells to mitigate this effect. This article focuses on the utility of two such agents: anti-thymocyte globulin (ATG) and alemtuzumab. ATG has demonstrated benefit in prophylaxis against GVHD, especially in the chronic presentation. However, there is limited impact of ATG on overall survival and it has little utility in the treatment context. There may be an initial improvement, particularly in skin manifestations, but no substantial benefit has been elicited. Alemtuzumab has shown benefit in both prophylaxis and treatment of GVHD, but at the consequence of a more profound immunosuppressive phase, mandating aggressive viral prophylaxis. There remains heterogeneity in the doses and regimens of the agents, with no standardized protocol in place. Furthermore, it seems that once steroid-refractory GVHD has been established, there is little that can be offered to offset the ultimately dismal outcome. Here we present a systematic overview of ATG- or alemtuzumab-based serotherapy in the prophylaxis and management of GVHD.

T Cell Receptor Profiling in Type 1 Diabetes

PURPOSE OF REVIEW

The genetic susceptibility and dominant protection for type 1 diabetes (T1D) associated with human leukocyte antigen (HLA) haplotypes, along with minor risk variants, have long been thought to shape the T cell receptor (TCR) repertoire and eventual phenotype of autoreactive T cells that mediate β-cell destruction. While autoantibodies provide robust markers of disease progression, early studies tracking autoreactive T cells largely failed to achieve clinical utility.

RECENT FINDINGS

Advances in acquisition of pancreata and islets from T1D organ donors have facilitated studies of T cells isolated from the target tissues. Immunosequencing of TCR α/β-chain complementarity determining regions, along with transcriptional profiling, offers the potential to transform biomarker discovery. Herein, we review recent studies characterizing the autoreactive TCR signature in T1D, emerging technologies, and the challenges and opportunities associated with tracking TCR molecular profiles during the natural history of T1D.

Anti-Gal and Anti-Neu5Gc Responses in Nonimmunosuppressed Patients After Treatment With Rabbit Antithymocyte Polyclonal IgGs

BACKGROUND

Polyclonal antihuman thymocyte rabbit IgGs (antithymocyte globulin [ATG]) are popular immunosuppressive drugs used to prevent or treat organ or bone-marrow allograft rejection, graft versus host disease, and autoimmune diseases. However, animal-derived glycoproteins are also strongly immunogenic and rabbit ATG induces serum sickness disease in almost all patients without additional immunosuppressive drugs, as seen in the Study of Thymoglobulin to arrest Type 1 Diabetes (START) trial of ATG therapy in new-onset type 1 diabetes.

METHODS

Using enzyme-linked immunosorbent assay, we analyzed serial sera from the START study to decipher the various anti-ATG specificities developed by the patients in this study: antitotal ATG, but also antigalactose-α1-3-galactose (Gal) and anti-Neu5Gc antibodies, 2 xenocarbohydrate epitopes present on rabbit IgG glycans and lacking in humans.

RESULTS

We show that diabetic patients have substantial levels of preexisting antibodies of the 3 specificities, before infusion, but of similar levels as healthy individuals. ATG treatment resulted in highly significant increases of both IgM (for anti-ATG and anti-Neu5Gc) and IgG (for anti-ATG, -Gal, and -Neu5Gc), peaking at 1 month and still detectable 1 year postinfusion.

CONCLUSIONS

Treatment with rabbit polyclonal IgGs in the absence of additional immunosuppression results in a vigorous response against Gal and Neu5Gc epitopes, contributing to an inflammatory environment that may compromise the efficacy of ATG therapy. The results also suggest using IgGs lacking these major xenoantigens may improve safety and efficacy of ATG treatment.

Characterization of the interactions of rabbit neonatal Fc receptor (FcRn) with rabbit and human IgG isotypes

Despite the increasing importance of rabbit as an animal model in pharmacological studies like investigating placental transfer of therapeutic IgGs, little is known about the molecular interaction of the rabbit neonatal Fc receptor (FcRn) with rabbit and human IgG molecules. We analyzed the interactions of the rabbit and human FcRn with rabbit and human IgG isotypes using surface plasmon resonance assay. Similar to FcRn of other species, rabbit FcRn functions in pH-dependent manner, as it binds IgGs at pH 6.0, but no binding occurs at pH 7.4. We also showed that rabbit FcRn binds rabbit IgG and human IgG1 with nearly identical affinity, whereas it has stronger interactions with the other human IgG isotypes. The similar affinity of rabbit IgG and human IgG1 for rabbit FcRn was confirmed by in vitro FcRn-mediated recycling assay. These data verify that rabbit is an appropriate animal model for analyzing the pharmacokinetics of human therapeutic monoclonal antibodies.

In-vivo or ex-vivo T cell depletion or both to prevent graft-versus-host disease after hematopoietic stem cell transplantation

INTRODUCTION

Hematopoietic stem cell transplantation (HSCT) represents a widely accepted therapeutic strategy for the treatment of hematologic disorders which are otherwise considered incurable. Alloreactive T cells infused with the stem cell inoculum may generate graft-versus-host disease (GVHD) representing one the most relevant obstacles to the successful outcome of patients receiving allogeneic HSCT. Areas covered: In this review, the authors provide an overview of the most recent approaches of T-cell depletion (TCD) including ex-vivo αβ+ TCD and in-vivo TCD with anti-thymocyte globulin (ATG). Expert opinion: Ex vivo depletion of donor T-cells prevents both acute and chronic GVHD without the need for any additional posttransplant immunological prophylaxis either in haploidentical HSCT and HLA matched transplants. Three prospective trials evaluating the efficacy of ATG in matched unrelated donor transplant recipients demonstrated that ATG reduces the incidence of both acute and chronic GVHD without a significant increase of relapse rate, and similar results have been reported in the setting of blood stem cell grafts from matched sibling donors.

Depletion-Resistant CD4 T Cells Enhance Thymopoiesis During Lymphopenia

Lymphoablation is routinely used in transplantation, and its success is defined by the balance of pathogenic versus protective T cells within reconstituted repertoire. While homeostatic proliferation and thymopoiesis may both cause T cell recovery during lymphopenia, the relative contributions of these mechanisms remain unclear. The goal of this study was to investigate the role of the thymus during T cell reconstitution in adult allograft recipients subjected to lymphoablative induction therapy. Compared with euthymic mice, thymectomized heart allograft recipients demonstrated severely impaired CD4 and CD8 T cell recovery and prolonged heart allograft survival after lymphoablation with murine anti-thymocyte globulin (mATG). The injection with agonistic anti-CD40 mAb or thymus transplantation only partially restored T cell reconstitution in mATG-treated thymectomized mice. After mATG depletion, residual CD4 T cells migrated into the thymus and enhanced thymopoiesis. Conversely, depletion of CD4 T cells before lymphoablation inhibited thymopoiesis at the stage of CD4^- CD8^- CD44^hi CD25⁺ immature thymocytes. This is the first demonstration that the thymus and peripheral CD4 T cells cooperate to ensure optimal T cell reconstitution after lymphoablation. Targeting thymopoiesis through manipulating functions of depletion-resistant helper T cells may thus improve therapeutic benefits and minimize the risks of lymphoablation in clinical settings.

Total Recall: Can We Reshape T Cell Memory by Lymphoablation?

Despite recent advances in immunosuppression, donor-reactive memory T cells remain a serious threat to successful organ transplantation. To alleviate damaging effects of preexisting immunologic memory, lymphoablative induction therapies are used as part of standard care in sensitized recipients. However, accumulating evidence suggests that memory T cells have advantages over their naive counterparts in surviving depletion and expanding under lymphopenic conditions. This may at least partially explain the inability of existing lymphoablative strategies to improve long-term allograft outcome in sensitized recipients, despite the well-documented decrease in the frequency of early acute rejection episodes. This minireview summarizes the insights gained from both experimental and clinical transplantation as to the effects of existing lymphoablative strategies on memory T cells and discusses the latest research developments aimed at improving the efficacy and safety of lymphoablation.

Combination Immunotherapy for Type 1 Diabetes

PURPOSE OF REVIEW

Type 1 diabetes (T1D) is an autoimmune disease marked by β-cell destruction. Immunotherapies for T1D have been investigated since the 1980s and have focused on restoration of tolerance, T cell or B cell inhibition, regulatory T cell (Treg) induction, suppression of innate immunity and inflammation, immune system reset, and islet transplantation. The purpose of this review is to provide an overview and lessons learned from single immunotherapy trials, describe recent and ongoing combination immunotherapy trials, and provide perspectives on strategies for future combination clinical interventions aimed at preserving insulin secretion in T1D.

RECENT FINDINGS

Combination immunotherapies have had mixed results in improving short-term glycemic control and insulin secretion in recent-onset T1D. A handful of studies have successfully reached their primary end-point of improved insulin secretion in recent-onset T1D. However, long-term improvements glycemic control and the restoration of insulin independence remain elusive. Future interventions should focus on strategies that combine immunomodulation with efforts to alleviate β-cell stress and address the formation of antigens that activate autoimmunity.

Impact of Thymoglobulin by Stem Cell Source (Peripheral Blood Stem Cell or Bone Marrow) After Myeloablative Stem Cell Transplantation From HLA 10/10-Matched Unrelated Donors: A Report From the Société Française de Greffe de Moelle et de Thérapie Cellulaire

BACKGROUND

The impact of antithymocyte globulin (ATG) in the setting of a myeloablative conditioning transplantation remains controversial, especially when using bone marrow (BM) as the stem cell source.

METHODS

We therefore conducted a retrospective analysis to investigate the impact of ATG in patients with acute myeloid leukemia or myelodysplastic syndrome receiving myeloablative conditioning followed by a matched 10 of 10 unrelated donor transplant from BM or peripheral blood stem cells (PBSCs). Our study included 356 patients conditioned with cyclophosphamide associated with fractionated total body irradiation or busulfan.

RESULTS

Median follow-up was 17.6 months (range, 0-156). The ATG and PBSCs were the only variables that independently decreased the cumulative incidence (CI) of chronic graft-versus-host disease (GvHD) (hazards ratio [HR], 0.4; 95% CI, 0.21-0.73; P < 0.01; and HR, 0.53; 95% CI, 0.30-0.90; P = 0.02, respectively). The ATG had no impact on overall survival, disease-free survival, relapse, and nonrelapse mortality. In the PBSC group (n = 139), ATG was associated with a lower CI of both grades III to IV acute GvHD (HR, 0.17; 95% CI, 0.03-0.91; P = 0.04), chronic GvHD (HR, 0.31; 95% CI, 0.11-0.87; P = 0.03), and GvHD-free/relapse-free survival (HR, 0.48; 95% CI, 0.29-0.80; P < 0.01), whereas these correlations were not significant in the group of patients (n = 217) receiving BM (HR, 0.36; 95% CI, 0.11-1.93; P = 0.06 for grade III-IV acute GvHD; HR, 0.49; 95% CI, 0.22-1.06; P = 0.08 for chronic GvHD; and HR, 0.69; 95% CI, 0.46-1.01; P = 0.06 for GvHD-free/relapse-free survival).

CONCLUSIONS

Although our results confirm the recommendation for ATG to be added after PBSC transplantation, no obvious benefit was identified using this approach in the setting of BM transplantation. Only prospective studies may yield definitive answers to this question.

Immune reconstitution and outcomes after conditioning with anti-thymocyte-globulin in unrelated cord blood transplantation; the good, the bad, and the ugly

Unrelated umbilical cord blood transplantation (UCBT) exhibits a low risk of graft-versus-host-disease (GvHD) and has unique potent anti-virus and anti-leukemia effects. Anti-thymocyte globulin (ATG) in the conditioning regimen for UCBT is successful in reducing graft rejection and GvHD. Nevertheless, this beneficial effect of ATG coincides with its detrimental effect on immune reconstitution. The latter directly relates to a high incidence of viral infections and leukemia relapses. ATG has been used in transplant patients for over 30 years. In recent years, the knowledge on the mechanisms of action of ATG and its implementation in the UCBT setting has increased dramatically. Important data became available showing the highly variable pharmacokinetics (PK) of ATG and its consequence on outcome measures. Here, we review the effects of ATG on immune reconstitution and subsequent outcomes after UCBT, and describe the mechanisms causing these effects. We highlight the importance of optimizing ATG exposure before and after UCBT and discuss strategies to maintain the 'good' and overcome the 'bad and ugly' effects of ATG on UCBT outcome.

Clinical utility of soluble interleukin-2 receptor in hemophagocytic syndromes: a systematic scoping review

The serum-soluble interleukin-2 receptor (sIL-2r) level is considered an important diagnostic test and disease marker in hemophagocytic syndromes/hemophagocytic lymphohistiocytosis (HPS/HLH). However, this cytokine receptor is rarely measured in clinical practice and has been excluded from recent diagnostic/classification criteria such as the HScore and macrophage activation syndrome (MAS) 16. We performed a systematic scoping review of 64 articles (1975-2016) examining the clinical utility of sIL-2r in HPS/HLH. Twenty-two articles describe sIL-2r as a sensitive diagnostic marker for HLH, but only three distinct datasets actually address sensitivity. The original HLH-2004 Guidelines reported sensitivity of 93% and specificity of 100% for sIL-2r ≥ 2400, based on a pediatric dataset (n = 152) which is published for the first time in this review. Two pediatric studies reported sensitivity of 89% for sIL-2r ≥ 2400 in diagnosis of MAS complicating juvenile idiopathic arthritis (JIA) (n = 27) and 88% for secondary HLH in acute liver failure (n = 9). Twenty articles described sIL-2r as a dynamic marker of disease activity that falls with response to treatment, and 15 described high initial sIL-2r levels >10,000 U/mL as a poor prognostic marker. The ability of sIL-2r to distinguish between subtypes of HPS/HLH was inconsistent. This review confirms the importance of soluble IL-2r as a diagnostic and disease marker in HPS/HLH, but also reveals the need for more primary data about its performance characteristics, particularly in adults. More emphasis should be made in including this simple, inexpensive test in clinical practice and studies of HPS/HLH.

Use of Anti-Thymocyte Globulin for Induction Therapy in Cardiac Transplantation: A Review

The most common causes of death after heart transplantation (HTx) include acute rejection and multi-organ failure in the early period and malignancy and cardiac allograft vasculopathy (CAV) in the late period. Polyclonal antibody preparations such as rabbit anti-thymocyte globulin (ATG) may reduce early acute rejection and the later occurrence of CAV after HTx. ATG therapy depletes T cells, modulates adhesion and cell-signaling molecules, interferes with dendritic cell function, and induces B-cell apoptosis and regulatory and natural killer T-cell expansion. Evidence from animal studies and from retrospective clinical studies in humans indicates that ATG can be used to delay calcineurin inhibitor (CNI) exposure after HTx, thus benefiting renal function, and to reduce the incidence of CAV and ischemia-reperfusion injury in the transplanted heart. ATG may reduce de novo antibody production after HTx. ATG does not appear to increase cytomegalovirus infection rates with longer prophylaxis (6-12 months). In addition, ATG may reduce the risk of lymphoproliferative disease and does not appear to confer an additive effect on acquiring lymphoma after HTx. Randomized, controlled trials may provide stronger evidence of ATG association with patient survival, graft rejection, renal protection through delayed CNI initiation, as well as other benefits. It can also help establish optimal dosing and patient criteria to maximize treatment benefits.

Do Prior Driveline Infections Increase the Risk of Infection in Heart Transplant Patients Treated With Rabbit Antithymocyte Globulin Induction Therapy?

BACKGROUND

The use of mechanical circulatory support devices (MCSDs) has been increasing over the past several years. Driveline infections (DLIs) are one of the most common complications seen in these patients; reportedly, up to 50% of patients with MCSDs can develop this complication. It is believed that the removal of the driveline results in treatment of the localized infection area. MCSD patients are also known to develop circulating antibodies. These circulating antibodies have been associated with poor outcomes after heart transplantation. The use of rabbit antithymocyte globulin (ATG) as induction therapy reportedly decreases the development of circulating antibodies; it is now commonly used in sensitized patients undergoing heart transplantation. It is unknown whether ATG induction therapy immediate posttransplant will increase the risk of infection of those MCSD patients with DLIs.

METHODS

Between 2003 and 2013, we evaluated 57 MCSD patients who subsequently underwent heart transplantation and received ATG induction therapy. Patients were divided into those with previous MCSD DLI and those without, and they were assessed for 1-year freedom from infection (specifically, sternal wound infections). One-year survival and freedom from treated rejection, both cellular and antibody mediated, were also assessed.

RESULTS

MCSD patients with DLIs who received ATG induction did not have a lower freedom from any treated infection and from sternal wound infection posttransplant compared with those MCSD patients without DLIs and not treated with ATG induction. There were also no significant differences between the 2 groups in terms of 1-year posttransplant survival and freedom from treated rejection.

CONCLUSIONS

The use of ATG induction in patients with prior DLIs did not seem to increase the risk for posttransplant infection (eg, sternal wound infection). ATG induction can therefore be safely used in this population.

In vitro immunoregulatory effects of thymoglobulin on human immune cell subpopulations

Thymoglobulin (ATG) is a polyclonal rabbit antibody against human thymocytes used as a T cell-depleting agent in organ transplantation. Its polyclonal character suggests that its effect may go far beyond just T cell depletion. The aim of this study was to further elucidate possible mechanisms underlying the suppressive activity of ATG. For in vitro studies, human peripheral blood mononuclear cells (PBMC) were incubated with ATG or control Ig for various time points. Foxp3⁺ regulatory cells (T_regs) and monocytes were phenotypically analyzed by flow cytometry and functionally tested by in vitro suppression assays. Cytokine levels were determined by quantitative RT- PCR, Multiplex or ELISA techniques. In vitro, the frequencies of Foxp3⁺ T_regs increased when human PBMC were stimulated with ATG as compared with stimulation by rabbit Ig or without stimulation. ATG-treated cells suppressed proliferation of autologous PBMC stimulated with anti-CD3 and anti-CD28 monoclonal antibodies and this suppression could be reversed by exogenous IL-2. The Foxp3⁺ expression dropped down on day 10, which suggests that it is transient. Monocytes and natural killer cells stimulated with ATG down-modulated CD16. Monocytes suppressed the proliferation of autologous PBMC. However, there were not statistically significant differences in IL-10, TNF-α and TGF-β1 secretion by monocytes stimulated with ATG or control rabbit Ig. These findings suggest that ATG has immunomodulatory effects that go beyond T cell depletion and induction of Foxp3⁺ T_regs. The induction of immunosuppressive monocytes might have a protective role in delaying transplant rejection.

Autologous hematopoietic stem cells for refractory Crohn's disease

INTRODUCTION

Autologous hematopoietic stem cells are gaining ground as an effective and safe treatment for treating severe refractory Crohn's disease (CD). Autologous hematopoietic stem cell therapy (AHSCT) induces resetting of the immune system by de novo regeneration of T-cell repertoire and repopulation of epithelial cells by bone-marrow derived cells to help patients achieve clinical and endoscopic remission. Areas covered: Herein, the authors discuss the use of AHSCT in treating patients with CD. Improvements in disease activity have been seen in patients with severe autoimmune disease and patients with severe CD who underwent AHSCT for a concomitant malignant hematological disease. Clinical and endoscopic remission has been achieved in patients treated with AHSCT for CD. The only randomized trial published to date, the ASTIC Trial, did not support further use of AHSCT to treat CD. Yet, critics of this trial have deemed AHSCT as a promising treatment for severe refractory CD. Expert opinion: Even with the promising evidence presented for HSCT for refractory CD, protocols need to be refined through the collaboration of GI and hemato-oncology professionals. The goal is to incorporate safe AHSCT and restore tolerance by delivering an effective immune 'cease fire' as a treatment option for severe refractory CD.

Association between anti-thymocyte globulin exposure and survival outcomes in adult unrelated haemopoietic cell transplantation: a multicentre, retrospective, pharmacodynamic cohort analysis

BACKGROUND

Anti-thymocyte globulin (ATG) is used to prevent graft-versus-host disease (GvHD) after allogeneic haemopoietic cell transplantation (HCT). However, ATG can also cause delayed immune reconstitution of T cells, negatively affecting survival. We studied the relation between exposure to ATG and clinical outcomes in adult patients with acute leukaemia and myelodysplastic syndrome.

METHODS

We did a retrospective, pharmacokinetic-pharmacodynamic analysis of data from patients with acute lymphoid leukaemia, acute myeloid leukaemia, or myelodysplastic syndrome receiving their first T-cell repleted allogeneic peripheral blood stem cell HCT with ATG (thymoglobulin) as part of non-myeloablative conditioning from March 1, 2004, to June 1, 2015. Patients received a cumulative intravenous dose of 8 mg/kg divided over 4 days, starting on day -8 before HCT. Active ATG concentrations were measured using a validated bioassay and pharmacokinetic exposure measures (maximum concentration, concentration at time of infusion of the graft, time to reach a concentration of 1 arbitary unit [AU] per day/mL, area under the curve [AUC], and the AUC before and after HCT) were calculated with a validated population pharmacokinetic model. The main outcome of interest was 5-year overall survival, defined as days to death from any cause or last follow-up. Other outcomes were relapse-related mortality, non-relapse mortality, event-free survival, acute and chronic GvHD, and assessment of current and optimum dosing. We used Cox proportional hazard models and Fine-Gray competing risk models for the analyses.

FINDINGS

146 patients were included. ATG exposure after HCT was shown to be the best predictor for 5-year overall survival. Optimum exposure after transplantation was determined to be 60-95 AU per day/mL. Estimated 5-year overall survival in the group who had optimum exposure (69%, 95% CI 55-86) was significantly higher than in the group who had below optimum exposure (32%, 20-51, p=0·00037; hazard ratio [HR] 2·41, 95% CI 1·15-5·06, p=0·020) and above optimum exposure (48%, 37-62, p=0·030; HR 2·11, 95% CI 1·04-4·27, p=0·038). Patients in the optimum exposure group had a greater chance of event-free survival than those in the below optimum exposure group (HR 2·54, 95% CI 1·29-5·00, p=0·007; HR for the above optimum group: 1·83, 0·97-3·47, p=0·063). Above-optimum exposure led to higher relapse-related mortality compared with optimum exposure (HR 2·66, 95% CI 1·12-6·31; p=0·027). Below optimum exposure increased non-relapse mortality compared with optimum exposure (HR 4·36, 95% CI 1·60-11·88; p=0·0040), grade 3-4 acute GvHD (3·09, 1·12-8·53; p=0·029), but not chronic GvHD (2·38, 0·93-6·08; p=0·070). Modelled dosing based on absolute lymphocyte counts led to higher optimum target attainment than did weight-based dosing.

INTERPRETATION

Exposure to ATG affects survival after HCT in adults, stressing the importance of optimum ATG dosing. Individualised dosing of ATG, based on lymphocyte counts rather than bodyweight, might improve survival chances after HCT.

FUNDING

Netherlands Organization for Health Research and Development and Queen Wilhelma Fund for Cancer Research.

Differential depletion of total T cells and regulatory T cells and prolonged allotransplant survival in CD3Ɛ humanized mice treated with polyclonal anti human thymocyte globulin

Thymoglobulin (ATG) is a polyclonal rabbit antibody against human thymocytes used as a T cell-depleting agent to prevent or treat allotransplant rejection. The aim of the present study was to investigate the effect of low dose ATG treatment exclusively on T cells using a humanized BALB/c human CD3Ɛ transgenic mouse model expressing both human and murine T cell receptors (TCR). Mice received a single intravenous (i.v.) injection of ATG. Blood and peripheral lymphoid organs were obtained after different time points. We found a significant T cell depletion in this mouse model. In addition, regulatory T cells (Tregs) proved to be less sensitive to depletion than the rest of T cells and the Treg:non-Treg ratio was therefore increased. Finally, we also investigated the effect of ATG in a heterotopic allogenic murine model of heart transplantation. Survival and transplant function were significantly prolonged in ATG-treated mice. In conclusion, we showed (a) an immunosuppressive effect of ATG in this humanized mouse model which is exclusively mediated by reactivity against human CD3Ɛ; (b) provided evidence for a relative resistance of Tregs against this regimen; and

Role of Memory T Cells in Allograft Rejection and Tolerance

Memory T cells are characterized by their low activation threshold, robust effector functions, and resistance to conventional immunosuppression and costimulation blockade. Unlike their naïve counterparts, memory T cells reside in and recirculate through peripheral non-lymphoid tissues. Alloreactive memory T cells are subdivided into different categories based on their origins, phenotypes, and functions. Recipients whose immune systems have been directly exposed to allogeneic major histocompatibility complex (MHC) molecules display high affinity alloreactive memory T cells. In the absence of any prior exposure to allogeneic MHC molecules, endogenous alloreactive memory T cells are regularly generated through microbial infections (heterologous immunity). Regardless of their origin, alloreactive memory T cells represent an essential element of the allograft rejection process and a major barrier to tolerance induction in clinical transplantation. This article describes the different subsets of alloreactive memory T cells involved in transplant rejection and examine their generation, functional properties, and mechanisms of action. In addition, we discuss strategies developed to target deleterious allospecific memory T cells in experimental animal models and clinical settings.

Targeting the Monocyte-Macrophage Lineage in Solid Organ Transplantation

There is an unmet clinical need for immunotherapeutic strategies that specifically target the active immune cells participating in the process of rejection after solid organ transplantation. The monocyte–macrophage cell lineage is increasingly recognized as a major player in acute and chronic allograft immunopathology. The dominant presence of cells of this lineage in rejecting allograft tissue is associated with worse graft function and survival. Monocytes and macrophages contribute to alloimmunity via diverse pathways: antigen processing and presentation, costimulation, pro-inflammatory cytokine production, and tissue repair. Cross talk with other recipient immune competent cells and donor endothelial cells leads to amplification of inflammation and a cytolytic response in the graft. Surprisingly, little is known about therapeutic manipulation of the function of cells of the monocyte–macrophage lineage in transplantation by immunosuppressive agents. Although not primarily designed to target monocyte–macrophage lineage cells, multiple categories of currently prescribed immunosuppressive drugs, such as mycophenolate mofetil, mammalian target of rapamycin inhibitors, and calcineurin inhibitors, do have limited inhibitory effects. These effects include diminishing the degree of cytokine production, thereby blocking costimulation and inhibiting the migration of monocytes to the site of rejection. Outside the field of transplantation, some clinical studies have shown that the monoclonal antibodies canakinumab, tocilizumab, and infliximab are effective in inhibiting monocyte functions. Indirect effects have also been shown for simvastatin, a lipid lowering drug, and bromodomain and extra-terminal motif inhibitors that reduce the cytokine production by monocytes–macrophages in patients with diabetes mellitus and rheumatoid arthritis. To date, detailed knowledge concerning the origin, the developmental requirements, and functions of diverse specialized monocyte–macrophage subsets justifies research for therapeutic manipulation. Here, we will discuss the effects of currently prescribed immunosuppressive drugs on monocyte/macrophage features and the future challenges.

Impact of Desensitization on Antiviral Immunity in HLA-Sensitized Kidney Transplant Recipients

Viral infections represent significant morbidity and mortality factors in kidney transplant recipients, with CMV, EBV, and BKV infections being most common. Desensitization (DES) with IVIg and rituximab with/without plasma exchange followed by kidney transplantation with alemtuzumab induction increased successful transplant rates in HLA-sensitized patients but may represent an increased risk for viral infections due to severe lymphocyte depletion. Here, we report on the posttransplant viral infection status in 372 DES versus 538 non-DES patients. CMV and EBV viremia were significantly lower in DES patients, while BKV viremia was similar. This trend was observed primarily in CMV sero(-), EBV sero(+), and sero(-) patients. No patient developed PTLD. The incidence of BKAN, allograft, and patient survival was similar in both groups. These viral infections were not associated with subsequent allograft rejection which occurred within 6 months after the infection. Conclusions. The IVIg + rituximab desensitization combined with alemtuzumab induction with triple immunosuppression maintenance does not increase the risk for CMV, EBV, and BKV infections. Possible factors include, in addition to posttransplant antiviral prophylaxis and PCR monitoring, presence of memory T cells and antibodies specific to CMV and likely EBV, NK cell-mediated ADCC despite lymphocyte depletion, elimination of EBV and CMV reservoirs by rituximab and alemtuzumab, and use of IVIg with antiviral properties.

Use of polyclonal/monoclonal antibody therapies in transplantation

INTRODUCTION

For over thirty years, antibody (mAb)-based therapies have been a standard component of transplant immunosuppression, and yet much remains to be learned in order for us to truly harness their therapeutic capabilities. Current mAbs used in transplant directly target and destroy graft-destructive immune cells, interrupt cytokine and costimulation-dependent T and B cell activation, and prevent down-stream complement activation. Areas covered: This review summarizes our current approaches to using antibody-based therapies to prevent and treat allograft rejection. It also provides examples of promising novel mAb therapies, and discusses the potential for future mAb development in transplantation. Expert opinion: The broad capability of antibodies, in parallel with our growing ability to synthetically modulate them, offers exciting opportunities to develop better biologic therapeutics. In order to do so, we must further our understanding about the basic biology underlying allograft rejection, and gain better appreciation of how characteristics of therapeutic antibodies affect their efficacy.

The absolute number of regulatory T cells in unmanipulated peripheral blood grafts predicts the occurrence of acute graft-versus-host disease post haplo-identical hematopoietic stem cell transplantation

CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs) have been reported to play a central role in suppressing acute graft-versus-host disease (aGVHD), but whether the Treg contents of grafts correlates with the occurrence of aGVHD post haplo-identical hematopoietic stem cell transplantation (haplo-HSCT) remains unclear. In the present study, changes in Tregs in peripheral blood (PB) were followed before and after granulocyte colony-stimulating factor (G-CSF) mobilization. In addition, functional analyses of Tregs in PB grafts and bone marrow (BM) grafts were performed. To probe the prognostic value of Tregs for aGVHD, an analysis of Tregs in haplo-identical grafts was conducted in 61 patients. Moreover, univariate and multivariate analyses of both clinical variables and cellular subsets were performed. The results showed that both the percentage Tregs of CD4⁺ T cells and absolute numbers of Tregs per 10⁶ total nucleated cells significantly increased after G-CSF administration. Additionally, Tregs in PB grafts exhibited a stronger inhibitory effect on antigen-specific T cell proliferation than did Tregs in BM grafts. Strikingly, patients receiving more Tregs in PB grafts had a lower cumulative incidence of aGVHD II-IV (36% versus 58%, P=0.046). Further, in a multivariate analysis, the number of Tregs in PB grafts was significantly associated with a lower occurrence of aGVHD II-IV (P=0.02). In contrast, the number of Tregs in BM grafts was not associated with the occurrence of aGVHD in the current study. Further analysis showed that the Treg content in grafts did not affect Treg reconstitution, infection rate, or incidence of chronic GVHD after haplo-HSCT. Moreover, no significant correlations between cell types in grafts and the survival end points or relapse rates were found in the present study. In conclusion, our results suggest that a high number of Tregs in PB grafts is associated with reduced risk of aGVHD in haplo-HSCT in our transplant setting.

B cell repertoires in HLA-sensitized kidney transplant candidates undergoing desensitization therapy

Background

Kidney transplantation is the most effective treatment for end-stage renal disease. Sensitization refers to pre-existing antibodies against human leukocyte antigen (HLA) protein and remains a major barrier to successful transplantation. Despite implementation of desensitization strategies, many candidates fail to respond. Our objective was to determine whether measuring B cell repertoires could differentiate candidates that respond to desensitization therapy.

Methods

We developed an assay based on high-throughput DNA sequencing of the variable domain of the heavy chain of immunoglobulin genes to measure changes in B cell repertoires in 19 highly HLA-sensitized kidney transplant candidates undergoing desensitization and 7 controls with low to moderate HLA sensitization levels. Responders to desensitization had a decrease of 5% points or greater in cumulated calculated panel reactive antibody (cPRA) levels, and non-responders had no decrease in cPRA.

Results

Dominant B cell clones were not observed in highly sensitized candidates, suggesting that the B cells responsible for sensitization are either not present in peripheral blood or present at comparable levels to other circulating B cells. Candidates that responded to desensitization therapy had pre-treatment repertoires composed of a larger fraction of class-switched (IgG and IgA) isotypes compared to non-responding candidates. After B cell depleting therapy, the proportion of switched isotypes increased and the mutation frequencies of the remaining non-switched isotypes (IgM and IgD) increased in both responders and non-responders, perhaps representing a shift in the repertoire towards memory B cells or plasmablasts. Conversely, after transplantation, non-switched isotypes with fewer mutations increased, suggesting a shift in the repertoire towards naïve B cells.

Conclusions

Relative abundance of different B cell isotypes is strongly perturbed by desensitization therapy and transplantation, potentially reflecting changes in the relative abundance of memory and naïve B cell compartments. Candidates that responded to therapy experienced similar changes to those that did not respond. Further studies are required to understand differences between these two groups of highly sensitized kidney transplant candidates.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-017-1118-7) contains supplementary material, which is available to authorized users.

Maintenance immunosuppressants in the management of antibody-mediated renal allograft rejection: which regimen is best?

Antibody-mediated rejection (AMR) is a pivotal cause of long-term graft failure following renal transplantation. De novo donor-specific antibody reduction is essential to prevent AMR and improve long-term graft survival in renal transplant recipients. Although the number of early AMR episodes can be successfully controlled by attenuating de novo donor-specific antibodies, the long-term outcomes are unsatisfactory. Numerous studies have focused on new strategies to reverse AMR, but the available evidence suggests that maintenance immunosuppressive agents play important roles. This article reviews data on the use of various maintenance immunosuppressive strategies in the management of AMR, with a focus on antibody-mediated kidney transplant rejection. Its aim is to help provide options benefitting long-term graft survival in renal transplant recipients.

Efficacy of antithymocyte globulin for allogeneic hematopoietic cell transplantation: a systematic review and meta-analysis

The efficacy of rabbit antithymocyte globulin (ATG) for the prevention of graft-versus-host disease (GVHD) has been evaluated in several randomized control trials, but the results show some discrepancies. Therefore, we performed a systematic review and meta-analysis covering the latest RCTs including six trials (total 845 patients). The incidence of acute and chronic GVHD was significantly lower in the ATG arms (risk ratio, 0.75 and 0.54, respectively). No significant differences were found regarding overall survival, the incidence of relapse, and non-relapse mortality; however, the incidence of cytomegalovirus and Epstein-Barr virus reactivation increased (risk ratio, 1.25 and 1.33), and neutrophil engraftment was significantly delayed (median, 2.66 days). In conclusion, rabbit ATG should be beneficial as a GVHD prophylaxis in addition to conventional regimens, with close monitoring of virus reactivation and enough attention to delayed engraftment. Studies comparing the timing and dosage of ATG are essential to determine the suitable prophylactic regimens.

Serial measurement of presepsin, procalcitonin, and C-reactive protein in the early postoperative period and the response to antithymocyte globulin administration after heart transplantation

Differentiation between systemic inflammatory response syndrome and sepsis in surgical patients is of crucial significance. Procalcitonin (PCT) and C-reactive protein (CRP) are widely used biomarkers, but PCT becomes compromised after antithymocyte globulin (ATG) administration, and CRP exhibits limited specificity. Presepsin has been suggested as an alternative biomarker of sepsis. This study aimed to demonstrate the role of presepsin in patients after heart transplantation (HTx). Plasma presepsin, PCT, and CRP were measured in 107 patients serially for up to 10 days following HTx. Time responses of biomarkers were evaluated for both noninfected (n=91) and infected (n=16) patients. Areas under the concentration curve differed in the two groups of patients for presepsin (P<.001), PCT (P<.005), and CRP (P<.001). The effect of time and infection was significant for all three biomarkers (P<.05 all). In contrast to PCT, presepsin was not influenced by ATG administration. More than 25% of noninfected patients had PCT above 42 μg/L on the first day, and the peak concentration of CRP in infected patients was reached on the third post-transplant day (median 135 mg/L). Presepsin seems to be as valuable a biomarker as PCT or CRP in the evaluation of infectious complications in patients after HTx.

Anti-thymocyte globulin as graft-versus-host disease prevention in the setting of allogeneic peripheral blood stem cell transplantation: a review from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation

Allogeneic hematopoietic stem cell transplantation is increasingly used as treatment for patients with life-threatening blood diseases. Its curative potential is largely based on immune-mediated graft-versus-leukemia effects caused by donor T cells contained in the graft. Unfortunately, donor T cells are also the cause of graft-versus-host disease. The vast majority of human leukocyte antigen-matched allogeneic hematopoietic stem cell transplants are nowadays carried out with peripheral blood stem cells as the stem cell source. In comparison with bone marrows, peripheral blood stem cells contain more hematopoietic stem/progenitor cells but also one log more T cells. Consequently, the use of peripheral blood stem cells instead of bone marrow has been associated with faster hematologic recovery and a lower risk of relapse in patients with advanced disease, but also with a higher incidence of chronic graft-versus-host disease. These observations have been the basis for several studies aimed at assessing the impact of immunoregulation with anti-thymocyte globulin on transplantation outcomes in patients given human leukocyte antigen-matched peripheral blood stem cells from related or unrelated donors. After a brief introduction on anti-thymocyte globulin, this article reviews recent studies assessing the impact of anti-thymocyte globulin on transplantation outcomes in patients given peripheral blood stem cells from human leukocyte antigen-matched related or unrelated donors as well as in recipients of grafts from human leukocyte antigen haploidentical donors.

Low-dose thymoglobulin as second-line treatment for steroid-resistant acute GvHD: an analysis of the JSHCT

A nationwide retrospective study for the clinical outcomes of 99 patients who had received thymoglobulin at a median total dose of 2.5 mg/kg (range, 0.5-18.5 mg/kg) as a second-line treatment for steroid-resistant acute GvHD was conducted. Of the 92 evaluable patients, improvement (complete or partial response) was observed in 55 patients (60%). Multivariate analysis demonstrated that male sex and grade III and IV acute GvHD were associated with a lower improvement rate, whereas thymoglobulin dose (<2.0, 2.0-3.9 and ⩾4.0 mg/kg) was NS. Factors associated with significantly higher nonrelapse mortality included higher patient age (⩾50 years), grade IV acute GvHD, no improvement of GvHD and higher dose of thymoglobulin (hazard ratio, 2.55; 95% confidence interval, 1.34-4.85; P=0.004 for 2.0-3.9 mg/kg group and 1.79; 0.91-3.55; P=0.093 for ⩾4.0 mg/kg group). Higher dose of thymoglobulin was associated with a higher incidence of bacterial infections, CMV antigenemia and any additional infection. Taken together, low-dose thymoglobulin at a median total dose of 2.5 mg/kg provides a comparable response rate to standard-dose thymoglobulin reported previously, and <2.0 mg/kg thymoglobulin is recommended in terms of the balance between efficacy and adverse effects.