Reconstitution of T-cell receptor repertoire diversity following T-cell depleted allogeneic bone marrow transplantation is related to hematopoietic chimerism

Graft-versus-host disease is associated with skewed γδ T-cell clonality after umbilical cord blood transplantation in children with nonmalignant diseases

BACKGROUND AIMS

The γδ T-cells (GDT) are a subpopulation of lymphocytes expressing a distinct T-cell receptor coded by the TRG and TRD genes. GDTs may have immunoregulatory function after stem cell transplantation (SCT), but the relationship between GDT clonality and acute graft-versus-host disease (aGVHD) is not known.

METHODS

We prospectively studied spectratype complex complexity of TCR Vγ (γ) and TCR Vδ (δ) pre-SCT and at approximately day 100 and day 180 post-SCT in a cohort of immunocompetent children receiving allogeneic umbilical cord blood SCT for nonmalignant diseases, with identical reduced-intensity conditioning and aGVHD prophylaxis.

RESULTS

We studied 13 children undergoing SCT at a median age of 0.9 years (total range 0.4-16.6). In those with grade 0-1 aGVHD (N = 10), the spectratype complexity of most γ and δ genes was not significantly different from baseline at day 100 or day 180 post-SCT, and there was balanced expression of genes at the γ and δ loci. In those with grade 3 aGVHD (N = 3), spectratype complexity was significantly below baseline at day 100 and day 180, and there was relative overexpression of δ2. CD3+ cell counts were also lower in participants with grade 3 aGVHD.

CONCLUSIONS

Recovery of a polyclonal GDT repertoire is an early part of immunological recovery after SCT. γ and δ gene expression is balanced in young children before and after SCT. Severe aGVHD is associated with GDT oligoclonality post-SCT and with skewed expression of δ2, which has not been previously reported. This association may reflect aGVHD therapy or aGVHD-associated immune dysregulation. Further studies of GDT clonality during the early post-SCT period may establish whether abnormal GDT spectratype precedes the clinical manifestations of aGVHD.

Immunopathogenic mechanisms and modulatory approaches to graft-versus-host disease prevention in acute myeloid leukaemia

Allogeneic haematopoietic stem cell transplantation (HSCT) remains the only potential cure for intermediate to high-risk acute myeloid leukaemia (AML). The therapeutic effect of HSCT is largely dependent on the powerful donor-derived immune response against recipient leukaemia cells, known as graft-versus-leukaemia effect (GvL). However, the donor-derived immune system can also cause acute or chronic damage to normal recipient organs and tissues, in a process known as graft-versus-host disease (GvHD). GvHD is a leading cause of non-relapse mortality in HSCT recipients. There are many similarities and cross talk between the immune pathways of GvL and GvHD. Studies have demonstrated that both processes require the presence of mismatched alloantigens between the donor and recipient, and activation of immune responses centered around donor T-cells, which can be further modulated by various recipient or donor factors. Dissecting GvL from GvHD to achieve more effective GvHD prevention and enhanced GvL has been the holy grail of HSCT research. In this review, we focused on the key factors that contribute to the immune responses of GvL and GvHD, the effect on GvL with different GvHD prophylactic strategies, and the potential impact of various AML relapse prevention therapy or treatments on GvHD.

Maternal dendritic cells influence fetal allograft response following murine in-utero hematopoietic stem cell transplantation

BACKGROUND

Intrauterine hematopoietic stem cell transplantation (IUT), potentially curative in congenital haematological disease, is often inhibited by deleterious immune responses to donor cells resulting in subtherapeutic donor cell chimerism (DCC). Microchimerism of maternal immune cells (MMc) trafficked into transplanted recipients across the placenta may directly influence donor-specific alloresponsiveness, limiting DCC. We hypothesized that dendritic cells (DC) among trafficked MMc influence the development of tolerogenic or immunogenic responses towards donor cells, and investigated if maternal DC-depletion reduced recipient alloresponsiveness and enhanced DCC.

METHODS

Using transgenic CD11c.DTR (C57BL/6) female mice enabled transient maternal DC-depletion with a single dose of diphtheria toxin (DT). CD11c.DTR females and BALB/c males were cross-mated, producing hybrid pups. IUT was performed at E14 following maternal DT administration 24 h prior. Bone marrow-derived mononuclear cells were transplanted, obtained from semi-allogenic BALB/c (paternal-derived; pIUT), C57BL/6 (maternal-derived; mIUT), or fully allogenic (aIUT) C3H donor mice. Recipient F1 pups were analyzed for DCC, while maternal and IUT-recipient immune cell profile and reactivity were examined via mixed lymphocyte reactivity functional assays. T- and B-cell receptor repertoire diversity in maternal and recipient cells were examined following donor cell exposure.

RESULTS

DCC was highest and MMc was lowest following pIUT. In contrast, aIUT recipients had the lowest DCC and the highest MMc. In groups that were not DC-depleted, maternal cells trafficked post-IUT displayed reduced TCR & BCR clonotype diversity, while clonotype diversity was restored when dams were DC-depleted. Additionally, recipients displayed increased expression of regulatory T-cells and immune-inhibitory proteins, with reduced proinflammatory cytokine and donor-specific antibody production. DC-depletion did not impact initial donor chimerism. Postnatal transplantation without immunosuppression of paternal donor cells did not increase DCC in pIUT recipients; however there were no donor-specific antibody production or immune cell changes.

CONCLUSIONS

Though maternal DC depletion did not improve DCC, we show for the first time that MMc influences donor-specific alloresponsiveness, possibly by expanding alloreactive clonotypes, and depleting maternal DC promotes and maintains acquired tolerance to donor cells independent of DCC, presenting a novel approach to enhancing donor cell tolerance following IUT. This may have value when planning repeat HSC transplantations to treat haemoglobinopathies.

An ISCT Stem Cell Engineering Committee Position Statement on Immune Reconstitution: the importance of predictable and modifiable milestones of immune reconstitution to transplant outcomes

Allogeneic stem cell transplantation is a potentially curative therapy for some malignant and non-malignant disease. There have been substantial advances since the approaches first introduced in the 1970s, and the development of approaches to transplant with HLA incompatible or alternative donors has improved access to transplant for those without a fully matched donor. However, success is still limited by morbidity and mortality from toxicity and imperfect disease control. Here we review our emerging understanding of how reconstitution of effective immunity after allogeneic transplant can protect from these events and improve outcomes. We provide perspective on milestones of immune reconstitution that are easily measured and modifiable.

RAG1 splicing mutation causes enhanced B cell differentiation and autoantibody production

Hypomorphic RAG1 or RAG2 mutations cause primary immunodeficiencies and can lead to autoimmunity, but the underlying mechanisms are elusive. We report here a patient carrying a c.116+2T>G homozygous splice site mutation in the first intron of RAG1, which led to aberrant splicing and greatly reduced RAG1 protein expression. B cell development was blocked at both the pro-B to pre-B transition and the pre-B to immature B cell differentiation step. The patient B cells had reduced B cell receptor repertoire diversity and decreased complementarity determining region 3 lengths. Despite B cell lymphopenia, the patient had abundant plasma cells in the BM and produced large quantities of IgM and IgG Abs, including autoantibodies. The proportion of naive B cells was reduced while the frequency of IgD^–CD27^– double-negative (DN) B cells, which quickly differentiated into Ab-secreting plasma cells upon stimulation, was greatly increased. Immune phenotype analysis of 52 patients with primary immunodeficiency revealed a strong association of the increased proportion of DN B and memory B cells with decreased number and proportion of naive B cells. These results suggest that the lymphopenic environment triggered naive B cell differentiation into DN B and memory B cells, leading to increased Ab production.

Cord blood CD8+ T-cell expansion following granulocyte transfusions eradicates refractory leukemia

The action of hematopoietic cell transplantation in controlling leukemia is principally mediated by donor T cells directed against residual recipient malignant cells. However, its utility is limited by graft-versus-host disease (GVHD), where alloreactivity is extended beyond leukemic and marrow cells. In a human/murine chimeric model, we previously showed that the preferential infiltration of cord blood (CB) CD8+ T cells eradicates an Epstein-Barr virus-driven lymphoblastoid tumor without causing xenogeneic GVHD. In the clinic, however, cord blood CD8+ T-cell reconstitution is significantly delayed, and the observation of such a robust antileukemia effect mediated by cord blood CD8+ T cells has not been reported. We describe an observation of very early T-cell expansion in 4 high-risk pediatric leukemia patients receiving third-party, pooled granulocytes after T cell-replete CB transplantation (CBT). The T-cell expansion was transient but robust, including expansion of CD8+ T cells, in contrast to the delayed CD8+ T-cell expansion ordinarily observed after T cell-replete CBT. The CD8+ T cells were polyclonal, rapidly switched to memory phenotype, and had the ability to mediate cytotoxicity. This phenomenon is reproducible, and each patient remains in long-term remission without GVHD. The results suggest that fetal-derived CB CD8+ T cells can be exploited to generate robust antileukemia effects without GVHD.

Assessment of immune-alternations and their correlations with therapeutic outcomes of transplantation of autologous Mesenchymal and Allogenic fetal stem cells in patients with type 1 diabetes: a study protocol

Introduction

Stem-cell therapy, which has recently emerged as a potentially therapeutic option for diabetes, is demonstrated to significantly alter both cellular and non-cellular elements of the immune system. In addition, it is demonstrated that allogenic stem-cells, once considered immune-privileged, can be rejected by the host immune system almost similar to any other somatic cell. To date, nonetheless, details of these intricate interactions remain obscure. The current study is designed to illuminate both aforementioned favorable and unfavorable stem cell-mediated immune reactions. Findings of this study may shed some light on how stem cells may exert their therapeutic effect in type 1 diabetes through immune system-mediated mechanisms and illuminate the partially-obscure immune-caused rejection of these cells.

Methods and analysis

For the purpose of this study, frozen whole blood samples obtained from patients with type 1 diabetes who received stem cells at the Endocrinology and Metabolism Research Institute of Tehran University of Medical Sciences in two different clinical trials will be thawed and analyzed. These clinical trials were carried out using two different sources of stem cells, namely allogenic fetal and autologous mesenchymal cells. The samples we aim to analyze were obtained from the patients before the procedure and regularly after it, one, three, six, 12, and 24 months later. For the purpose of this study, the following parameters will be measured: C-peptide levels, IDAA1c (a surrogate marker of beta cell function which is calculated as HbA1c (%) + [4 × insulin dose (units per kilogram per day)]), frequencies of islet-specific autoreactive CD8+ T cells (CTL), different lymphocyte subsets, thymic function indicators, T cell repertoire diversity (including Treg/Tconv ratios), plasma levels of several pro- and anti-inflammatory cytokines, diabetes autoantibodies, and HLA typing.

Ethics and dissemination

The stem cell transplantation clinical trials which provided the primary source of our samples were carried out at the Endocrinology and Metabolism Research Institute of Tehran University of Medical Sciences between 2008 and 2012. These series of clinical trials have secured approval of the ethics committee of Tehran University of Medical Sciences (ethical code number: E-0089) and registered on the national clinical trial registry of Islamic Republic of Iran (IRCT) with the identifier codes: IRCT138810271414N8 (for autologous mesenchymal cells) and IRCT201103171414N23 (for allogenic fetal cells). Our findings are to be presented at international scientific events, published in peer-reviewed journals, and disseminated both electronically and in print. Besides, results of the current study will be used for design and implementation of future laboratory investigations and clinical trials at the Endocrinology and Metabolism Research Institute of Tehran University of Medical Sciences.

T-cell receptor repertoire of cytomegalovirus-specific cytotoxic T-cells after allogeneic stem cell transplantation

Cytomegalovirus (CMV) infection is a major complication during allogeneic stem cell transplantation (allo-SCT). However, mechanisms of adaptive immunity that drive this remain unclear. To define early immunological responses to CMV after transplantation, we using next-generation sequencing to examine the repertoire of T-cell receptors in CD8⁺/CMV pp65 tetramer⁺ cells (CMV-CTLs) in peripheral blood samples obtained from 16 allo-SCT recipients with HLA-A*24:02 at the time of CMV reactivation. In most patients, TCR beta repertoire of CMV-CTLs was highly skewed (median Inverse Simpson's index: 1.595) and, 15 of 16 patients shared at least one TCR-beta clonotype with ≥ 2 patients. The shared TCRs were dominant in 12 patients and, two clonotypes were shared by about half of the patients. Similarity analysis showed that CDR3 sequences of shared TCRs were more similar than unshared TCRs. TCR beta repertoires of CMV-CTLs in 12 patients were also analyzed after 2-4 weeks to characterize the short-term dynamics of TCR repertoires. In ten patients, we observed persistence of prevailing clones. In the other two patients, TCR repertoires became more diverse, major clones declined, and new private clones subsequently emerged. These results provided the substantive clue to understand the immunological behavior against CMV reactivation after allo-SCT.

Age-Related Immune Profile of the T Cell Receptor Repertoire, Thymic Recent Output Function, and miRNAs

Background

T cell immunity plays a central role in the body's defense system, including maintaining homeostasis and preventing tumorigenesis and viral infection. Immune system functions degenerate with age, leading to immune senescence. Physiologically, immune senescence is characterized by a decrease in T cell receptor diversity, naive T cell deficiency, and alterations in T cell immune-related miRNAs. However, little is known about the characteristics of T cell immunosenescence in Chinese individuals.

Results

A significant decrease in the miR-17, miR-92a, and miR-181a levels in PBMCs was detected with age. The miR-92a and miR-181a levels were upregulated in CBMCs when comparing healthy individuals to group I (0~9 years), whereas miR-17 was downregulated. The sjTREC level in PBMCs was negatively correlated with age, and a sharp decrease in sjTRECs was found between groups I and II (10~19 years). Twenty-four TCR Vβ subfamilies could be detected in most samples, and most displayed polyclonality, while skewed expression of the Vβ subfamilies as well as an increased oligoclonal tendency was found with age. Similarly, the frequencies of the TCR Vγ and Vδ subfamilies decreased with age, and the alteration in clonality appeared to be stable at different ages.

Conclusion

We made the novel observation of T cell immunosenescence with age in Chinese individuals, which may provide information for immune targets to enhance the T cell immune response in immunotherapy settings for elderly patients.

T Cell Clonal Dynamics Determined by High-Resolution TCR-β Sequencing in Recipients after Allogeneic Hematopoietic Cell Transplantation

Delayed reconstitution of the immune system is a long-recognized complication after allogeneic hematopoietic cell transplantation (HCT). Specifically, loss of T cell diversity has been thought to contribute to infectious complications, graft-versus-host disease (GVHD), and disease relapse. We performed serial high-resolution next-generation sequencing of T cell receptor (TCR)-β in 99 related or unrelated donor (57 unrelated, 42 related) allogeneic HCT recipients (55 with reduced-intensity conditioning, 44 with myeloablative conditioning) during the first 3 months after HCT using the immunoSEQ Assay. We measured T cell fraction, clonality (1- Peilou's evenness) and Daley-Smith richness from recipient samples at multiple time points. In agreement with previous studies, we found that although absolute T cell numbers recover relatively quickly after HCT, T cell repertoire diversity remains diminished. Restricted diversity was associated with conditioning intensity, use of antithymocyte globulin, and donor type. Increased number of expanded clones compared to donor T cell clones at day +30 was associated with the incidence of acute GVHD (hazard ratio [HR], 1.11; P = .00005). Even after exclusion of the 12 patients who developed acute GVHD before day +30, the association between acute GVHD and increased clonal expansion at day +30 remained (HR, 1.098; P = .041), indicating that increased clonal T cell expansion preceded the development of acute GVHD. Our results highlight T cell clonal expansion as a potential novel biomarker for acute GVHD that warrants further study.

Rapid reconstitution of regulatory T-cell subsets is associated with reduced rates of acute graft-versus-host disease and absence of viremia after cord blood transplantation in children with reduced-intensity conditioning using alemtuzumab

Forkhead box P3 (FOXP3)+ regulatory T cell (Treg) reconstitution after unrelated donor umbilical cord blood transplantation in chemotherapy-naïve children is incompletely characterized. We studied 21 children with nonmalignant diseases receiving an identical alemtuzumab-containing regimen. We hypothesized that Treg recovery may be perturbed in patients not only by acute graft-versus-host disease (aGVHD) but also by viremia. Tregs and their memory and naïve subsets were serially monitored for proliferation and apoptosis along with conventional T cells (Tcon). A "reconstitution index" (RI) was calculated relative to pretransplantation values for each parameter. At 3 months post-UCBT, the RI of Tregs was faster compared with other immune components tested and was most rapid in patients free of aGVHD and viremia. There were significantly fewer Tregs in patients experiencing grade I-II aGVHD and/or viremia, leading to an imbalance between Tregs-Tcon ratios. Central and effector memory Tregs were most affected at this time point when they dominated in the circulation. Impaired Treg proliferation without increased apoptosis accounted for the reduced Treg-Tcon ratio. In patients affected with grade II aGVHD and viremia, the overall reduction in circulating Treg pool were associated with a more oligoclonal T-cell receptor β repertoire. Taken together, aGVHD and viremia can lead to defective Treg expansion homeostasis.

Standard Antithymocyte Globulin Dosing Results in Poorer Outcomes in Overexposed Patients after Ex Vivo CD34+ Selected Allogeneic Hematopoietic Cell Transplantation

Antithymocyte globulin (ATG) use mitigates the risk of graft rejection and graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation (allo-HCT), but ATG overexposure in the setting of lymphopenia negatively affects immune recovery. We hypothesized that standard empiric weight-based dosing of ATG, used to prevent graft rejection in ex vivo CD34-selected allo-HCT, may lead to serious adverse consequences on outcomes in certain patients. We evaluated 304 patients undergoing myeloablative-conditioned ex vivo CD34-selected allo-HCT with HLA-matched donors for the treatment of hematologic malignancies. Patients received rabbit ATG at a dose of 2.5 mg/kg/day i.v. on days -3 and/or -2. An ATG dosing cutoff of 450 mg was used for statistical analyses to assess the relationship between ATG and overall survival (OS). Among all patients, median total ATG dose was 360 mg (range, 130 to 510 mg); 279 (92%) received a total dose of ATG ≤450 mg, and 25 (8%) received a total dose >450 mg. On the first day of ATG administration (day -3), the median absolute lymphocyte count was .0 K/µL. For patients who received a total dose of ATG >450 mg or ≤450 mg, the incidences of acute and late-acute GVHD grade II-IV were statistically similar. At 3 years post-HCT, for patients who received a total dose of ATG >450 mg or ≤450 mg, nonrelapse mortality (NRM) rates were 35% and 18%, respectively (P = .029), disease-free survival (DFS) rates were 37% and 61%, respectively (P = .003), and OS rates were 40% and 67%, respectively (P = .001). Among all patient and HCT characteristics in multivariable analyses, receipt of a total dose of ATG >450 mg was associated with an increased risk of NRM (hazard ratio [HR], 2.9; P = .01), shorter DFS (HR, 2.0; P = .03), and inferior OS (HR, 2.1; P = .01). In summary, the use of weight-based ATG at a time of relative lymphopenia before ex vivo CD34-selected allo-HCT results in overdosing in heavier patients, leading to higher NRM and lower DFS and OS. Further pharmacokinetic investigation in this setting is critical to determining the optimal dosing strategy for ATG.

Immunological Balance Is Associated with Clinical Outcome after Autologous Hematopoietic Stem Cell Transplantation in Type 1 Diabetes

Autologous hematopoietic stem cell transplantation (AHSCT) increases C-peptide levels and induces insulin independence in patients with type 1 diabetes. This study aimed to investigate how clinical outcomes may associate with the immunological status, especially concerning the balance between immunoregulation and autoreactivity. Twenty-one type 1 diabetes patients were monitored after AHSCT and assessed every 6 months for duration of insulin independence, C-peptide levels, frequencies of islet-specific autoreactive CD8⁺ T cells (CTL), regulatory lymphocyte subsets, thymic function, and T-cell repertoire diversity. In median follow-up of 78 (range 15–106) months, all patients became insulin-independent, resuming insulin after median of 43 (range 6–100) months. Patients were retrospectively divided into short- or prolonged-remission groups, according to duration of insulin independence. For the entire follow-up, CD3⁺CD4⁺ T-cell numbers remained lower than baseline in both groups, whereas CD3⁺CD8⁺ T-cell levels did not change, resulting in a CD4/CD8 ratio inversion. Memory CTL comprehended most of T cells detected on long-term follow-up of patients after AHSCT. B cells reconstituted to baseline levels at 2–3 months post-AHSCT in both patient groups. In the prolonged-remission-group, baseline islet-specific T-cell autoreactivity persisted after transplantation, but regulatory T cell counts increased. Patients with lower frequencies of autoreactive islet-specific T cells remained insulin-free longer and presented greater C-peptide levels than those with lower frequencies of these cells. Therefore, immune monitoring identified a subgroup of patients with superior clinical outcome of AHSCT. Our study shows that improved immunoregulation may balance autoreactivity endorsing better metabolic outcomes in patients with lower frequencies of islet-specific T cells. Development of new strategies of AHSCT is necessary to increase frequency and function of T and B regulatory cells and decrease efficiently autoreactive islet-specific T and B memory cells in type 1 diabetes patients undergoing transplantation.

Matched unrelated donor transplants-State of the art in the 21st century

Hematopoietic stem cell transplantation (HSCT) is the therapy of choice in many hematological malignant and non-malignant diseases by using human leukocyte antigen (HLA)-matched siblings as stem cell source but only one third of the patients will have HLA-matched siblings. Hence, physicians rely on the availability of matched unrelated donors (URD). The possibility of finding a matched URD is now more than 70% due to continuous expansion of URD registries around the world. The use of URD in adult patients is steadily increasing and in the last 8 years has superseded the numbers of matched sibling donor transplants and has become the most commonly used stem cell source. There is also an increasing trend to use peripheral blood (PB) stem cells rather than bone marrow (BM) stem cells. Outcomes following URD transplants depend mainly upon the indication and urgency of transplant, age and comorbidities of recipients, cytomegalovirus (CMV) matching/mismatching between donor and the recipient, and degree of HLA matching. In some studies outcome of unrelated stem cell transplants in terms of treatment-related mortality (TRM), disease-free survival (DFS), and overall survival (OS) is comparable to sibling donors.

CMV reactivation drives posttransplant T-cell reconstitution and results in defects in the underlying TCRβ repertoire

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

Rapid memory T-cell reconstitution recapitulating CD45RA-depleted haploidentical transplant graft content in patients with hematologic malignancies

T-cell depletion of an HLA-haploidentical graft is often used to prevent graft-vs.-host disease (GvHD), but the procedure may lead to increased graft failure, relapse, and infections due to delayed immune recovery. We hypothesized that selective depletion of the CD45RA+ subset can effectively reduce GvHD through removal of naïve T cells, while providing improved donor immune reconstitution through adoptive transfer of CD45RA– memory T cells. Herein, we present results from the first 17 patients with poor-prognosis hematologic malignancy who received haploidentical donor transplantation with CD45RA-depleted progenitor cell grafts following a novel reduced intensity conditioning regimen without total body irradiation or serotherapy. Extensive depletion of CD45RA+ T cells and B cells, with preservation of abundant memory T cells, was consistently achieved in all 17 products. Neutrophil engraftment (median day +10) and full donor chimerism (median day +11) was rapidly achieved post-transplantation. Early T-cell reconstitution directly correlated with the CD45RA-depleted graft content. T-cell function recovered rapidly with broad TCR V_β spectra. There was no infection-related mortality in this heavily pretreated population, and no patient developed acute GvHD despite infusion of a median of >100 million per kilogram haploidentical T cells.

Targeted genome editing in human repopulating haematopoietic stem cells

Targeted genome editing by artificial nucleases has brought the goal of site-specific transgene integration and gene correction within the reach of gene therapy. However, its application to long-term repopulating Hematopoietic Stem Cells (HSCs) has remained elusive. Here we show that poor permissiveness to gene transfer and limited proficiency of the homology directed DNA repair pathway constrain gene targeting in human HSCs. By tailoring delivery platforms and culture conditions we overcame these barriers and provide stringent evidence of targeted integration in human HSCs by long-term multilineage repopulation of transplanted mice. We demonstrate the therapeutic potential of our strategy by targeting a corrective cDNA into the IL2RG gene of HSCs from healthy donors and a subject with X-linked Severe Combined Immunodeficiency (SCID-X1). Gene edited HSCs sustained normal hematopoiesis and gave rise to functional lymphoid cells that possess a selective growth advantage over those carrying disruptive IL2RG mutations. These results open new avenues for treating SCID-X1 and other diseases.

The molecular and functional characterization of clonally expanded CD8+ TCR BV T cells in eosinophilic granulomatosis with polyangiitis (EGPA)

In eosinophilic granulomatosis with polyangiitis (EGPA) clonally expanded T cells might concur in granuloma formation and vascular injury. The TCR β-variable (BV) chain repertoire and third complementarity determining region (CDR3) of peripheral CD4+ and CD8+ cells in EGPA patients and age-matched controls and the expression of cytokines and chemokine receptors were investigated. The CD8+ lymphocytes of EGPA patients showed an increased frequency of BV expansions with a skewed profile of BV CDR3 lengths, increased CCR5 and CXCR3 expression and increased INFγ and TNFα production. In two patients, the TCR CDR3 cDNA sequences of the expanded BV family were identified. The CD4+ lymphocytes of EGPA patients revealed a higher expression of CRTH2 and increased production of IL-5. In conclusion, CD4+ T cells display a Th2 profile and CD8+ T cells are clonally expanded in EGPA and have a proinflammatory phenotype, suggesting their pathogenic role in vasculitic damage.

Clinical Implications of T Cell Receptor Repertoire Analysis after Allogeneic Stem Cell Transplantation

Stem cell transplantation (SCT) constitutes a major challenge to the immune system. Long-term impairment of immunity against various common infectious stimuli leads to increased susceptibility to infectious diseases; in contrast, an immune response against the recipient may cause the devastating graft-versus-host disease (GvHD). Recovery of the immune system (both qualitative and quantitative) after SCT is perhaps the most important factor in determining the clinical outcome. Consequently, immune reconstitution has been extensively studied using different approaches, including quantitative analysis of immune cells as well as their phenotypic characterization. Analysis of diversity and clonality is an important tool in determining competence of the immune system, assuming that a broad diversity assures efficient response to different stimuli and clonal dominance reflects ongoing, potentially relevant immune responses. Detailed analysis of the immune repertoire through the flow cytometric and molecular study of the T cell receptor repertoire has been applied to gain quantitative and qualitative insights about the T cell immune competence and responsiveness. After SCT, a contraction of the T cell pool and a reduction in T cell receptor diversity is clearly associated with clinical immunodeficiency. Reconstitution of the immune system is often characterized by dominance of oligoclonal T cell populations, reflecting specific antigen-driven immune responses. Detailed characterization of T lymphocytes by T cell receptor analysis is possible, and may lead to the identification of individual clones involved in specific immune reactions, such as alloresponses in GvHD, the closely related graft-versus-leukemia effect and opportunistic viral agents such as CMV or EBV.

BCR CDR3 length distributions differ between blood and spleen and between old and young patients, and TCR distributions can be used to detect myelodysplastic syndrome

Complementarity-determining region 3 (CDR3) is the most hyper-variable region in B cell receptor (BCR) and T cell receptor (TCR) genes, and the most critical structure in antigen recognition and thereby in determining the fates of developing and responding lymphocytes. There are millions of different TCR Vβ chain or BCR heavy chain CDR3 sequences in human blood. Even now, when high-throughput sequencing becomes widely used, CDR3 length distributions (also called spectratypes) are still a much quicker and cheaper method of assessing repertoire diversity. However, distribution complexity and the large amount of information per sample (e.g. 32 distributions of the TCRα chain, and 24 of TCRβ) calls for the use of machine learning tools for full exploration. We have examined the ability of supervised machine learning, which uses computational models to find hidden patterns in predefined biological groups, to analyze CDR3 length distributions from various sources, and distinguish between experimental groups. We found that (a) splenic BCR CDR3 length distributions are characterized by low standard deviations and few local maxima, compared to peripheral blood distributions; (b) healthy elderly people's BCR CDR3 length distributions can be distinguished from those of the young; and (c) a machine learning model based on TCR CDR3 distribution features can detect myelodysplastic syndrome with approximately 93% accuracy. Overall, we demonstrate that using supervised machine learning methods can contribute to our understanding of lymphocyte repertoire diversity.

Quantification of total T-cell receptor diversity by flow cytometry and spectratyping

BACKGROUND

T-cell receptor diversity correlates with immune competency and is of particular interest in patients undergoing immune reconstitution. Spectratyping generates data about T-cell receptor CDR3 length distribution for each BV gene but is technically complex. Flow cytometry can also be used to generate data about T-cell receptor BV gene usage, but its utility has not been compared to or tested in combination with spectratyping.

RESULTS

Using flow cytometry and spectratype data, we have defined a divergence metric that quantifies the deviation from normal of T-cell receptor repertoire. We have shown that the sample size is a sensitive parameter in the predicted flow divergence values, but not in the spectratype divergence values. We have derived two ways to correct for the measurement bias using mathematical and statistical approaches and have predicted a lower bound in the number of lymphocytes needed when using the divergence as a substitute for diversity.

CONCLUSIONS

Using both flow cytometry and spectratyping of T-cells, we have defined the divergence measure as an indirect measure of T-cell receptor diversity. We have shown the dependence of the divergence measure on the sample size before it can be used to make predictions regarding the diversity of the T-cell receptor repertoire.

Quantitative assessment of T cell repertoire recovery after hematopoietic stem cell transplantation

Delayed T-cell recovery and restricted T-cell receptor (TCR) diversity after allogeneic hematopoietic stem cell transplantation (allo-HSCT) are associated with increased risks of infection and cancer relapse. Technical challenges have limited faithful measurement of TCR diversity following allo-HSCT. Here we combined 5′-RACE PCR with deep sequencing, to quantify TCR diversity in 28 allo-HSCT recipients using a single oligonucleotide pair. Analysis of duplicate blood samples confirmed that the frequency of individual TCRs was accurately determined. After 6 months, cord blood graft recipients approximated the TCR diversity of healthy individuals, whereas recipients of T-cell-depleted peripheral blood stem cell grafts had a 28-fold and 14-fold lower CD4⁺ and CD8⁺ T-cell diversity, respectively. After 12 months, these deficiencies had improved for the CD4⁺, but not the CD8⁺ T-cell compartment. Overall, this method provides unprecedented views of T-cell repertoire recovery after allo-HSCT and may identify patients at high risk of infection or relapse.

T-cell receptor repertoire usage in hematologic malignancies

Over the last few years several studies have addressed the possible influence of different immune mechanisms on the evolution of hematologic malignancies. More specifically, a fundamental role of reactive T-cells has now been demonstrated in the pathogenesis of many of these disorders as well as in the typical immunological milieu observed after stem cell transplantation in patients affected by these malignancies. In this context the study of the T-cell receptor (TCR) repertoire performed by different techniques, such as for instance flow cytometry and spectratyping, has undoubtedly provided a fundamental contribution. More recently, these seminal observations have even opened new potential therapeutic avenues based on the employment of adoptive T-cells somehow engineered toward potential neoplastic targets. This review will run through the most relevant studies which have tried to dissect the TCR repertoire usage in patients with different hematologic malignancies, especially focusing on the possible pathogenetic and therapeutic implications.

TRBV kinetics and its association with HLA disparity and aGVHD following allogeneic hematopoietic stem cell transplantation

INTRODUCTION

The relative expression of T cell receptor (TCR) beta variable (TRBV) and TCR diversity was compared between recipients receiving human leukocyte antigen (HLA)-mismatched transplants and those receiving HLA-matched transplants, using granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood stem cells and bone marrow as grafts.

METHODS

The kinetics of the relative expression of TRBV family members were analyzed using real-time quantitative PCR. Additionally, the association of TRBV clonotype with acute graft-versus-host disease (aGVHD) was determined by cloning and sequence analysis of the CDR3 region.

RESULTS

The TCR diversity in recipients receiving HLA-mismatched transplants was significantly lower than in those receiving HLA-matched transplants at 1 month and 2 months after hematopoietic stem cell transplantation (HSCT) (both P < 0.05). However, these differences disappeared 3 months after transplantation. The relative expression of TRBV27 (n = 7 recipients) at the onset of aGVHD was higher than in corresponding donors (P = 0.025), but no significant differences were observed between recipients lacking aGVHD and their donors at serial time points after HSCT.

CONCLUSION

Our results suggest that HLA disparity may affect the relative expression of TRBV in the early phase after transplantation, and TRBV27 may be associated with the onset of aGVHD.

Thymus and immune reconstitution after allogeneic hematopoietic stem cell transplantation in humans: never say never again

Assessment of the host immune status is becoming a key issue in allogeneic hematopoietic stem cell transplantation (allo-HSCT). In the long-term follow-up of these patients, severe post-transplant infections, relapse or secondary malignancies may be directly related to persistent immune defects. In allo-HSCT, T-cell differentiation of donor progenitors within the recipient thymus is required to generate naive recent T-cell emigrants (RTE). These cells account for a durable T-cell reconstitution, generating a diverse T-cell receptor (TCR) repertoire and robust response to infections. It is now possible to quantify the production of RTE by measuring thymic T-cell receptor excision circles or 'TREC' which are small circular DNA produced during the recombination of the genomic segments encoding the TCR alpha chain. Here we discuss the role of thymic function in allo-HSCT. The pre-transplant recipient thymic function correlates with clinical outcome in terms of survival and occurrence of severe infections. Post-transplant, TREC analysis showed that the thymus is a sensitive target to the allogeneic acute graft-versus-host disease (GvHD) reaction but is also prone to recovery in young adult patients. In all, thymus is a key player for the quality of immune reconstitution and clinical outcome after allo-HSCT. Thymic tissue is plastic and it is a future challenge to halt or reverse thymic GVHD therapeutically by acting at the level of T-cell progenitors generation, thymic homing and/or epithelial thymic tissue preservation.

Models and methods for analysis of lymphocyte repertoire generation, development, selection and evolution

T and B cell receptor repertoires are diversified by variable region gene rearrangement and selected based on functionality and lack of self-reactivity. Repertoires can also be defined based on phenotype and function rather than receptor specificity - such as the diversity of T helper cell subsets. Natural killer (NK) cell repertoires, in which each cell expresses a randomly chosen subset of its inhibitory receptor genes, and is educated based on self-MHC recognition by yet unknown mechanisms, are also phenotypic repertoires. Studying the generation, development and selection of lymphocyte repertoires, and their functions during immune responses, is essential for understanding the function of the immune system in healthy individuals and in immune deficient, autoimmune or cancer patients. The study of lymphocyte repertoires will enable clinical immunologists to develop better therapeutic monoclonal antibodies, vaccines, transplantation donor-recipient matching protocols, and other immune intervention strategies. The recent development of high-throughput methods for repertoire data collection - from multicolor flow cytometry through single-cell imaging to deep sequencing - presents us now, for the first time, with the ability to analyze and compare large samples of lymphocyte repertoires in health, aging and disease. The exponential growth of these datasets, however, challenges the theoretical immunology community to develop methods for data organization and analysis. Furthermore, the need to test hypotheses regarding immune function, and generate predictions regarding the outcomes of medical interventions, necessitates the development of complex mathematical and computational models, covering processes on multiple scales, from the genetic and molecular to the cellular and system scales.

Preserving the B-cell compartment favors operational tolerance in human renal transplantation

Transplanted individuals in operational tolerance (OT) maintain long-term stable graft function after completely stopping immunosuppression. Understanding the mechanisms involved in OT can provide valuable information about pathways to human transplantation tolerance. Here we report that operationally tolerant individuals display quantitative and functional preservation of the B-cell compartment in renal transplantation. OT exhibited normal numbers of circulating total B cells, naive, memory and regulatory B cells (Bregs) as well as preserved B-cell receptor repertoire, similar to healthy individuals. In addition, OT also displayed conserved capacity to activate the cluster of differentiation 40 (CD40)/signal transducer and activator of transcription 3 (STAT3) signaling pathway in Bregs, in contrast, with chronic rejection. Rather than expansion or higher activation, we show that the preservation of the B-cell compartment favors OT.

A potential role for B cells in suppressed immune responses in cord blood transplant recipients

We evaluated immune reconstitution in 58 adults who received hematopoietic stem cell transplants from allogeneic siblings (allosib), matched unrelated donors (MUD), or cord blood (CB) at 90-day intervals for one year post-transplant. CB recipients had a higher incidence of infections in the first 100 days compared to allosib and MUD recipients. The number of circulating T cells was lower in CB recipients compared to MUD recipients at 90 days and compared to allosib recipients at 180 days. Spectratype analysis of the TCR Vβ complementarity determining region 3 (CDR3) of patient lymphocytes revealed that the TCR repertoire remained poorly diversified even at 360 days in nearly all patients. In contrast, the number of circulating B cells was significantly elevated in CB recipients compared to allosib recipients throughout the first year post-transplant and compared to MUD recipients at 9-12 months. Spectratype analysis of the B cell receptor V_H CDR3 showed that the B cell repertoire was diversified in most patients by 90 days. CD5^pos B cells from assayed CB recipients expressed intracellular IL-10 early post-transplant. Our data suggest that B cells, in addition to T cells, may play a role in impaired immune responses in CB transplant patients.

The kinetics of early T and B cell immune recovery after bone marrow transplantation in RAG-2-deficient SCID patients

The kinetics of T and B cell immune recovery after bone marrow transplantation (BMT) is affected by many pre- and post-transplant factors. Because of the profoundly depleted baseline T and B cell immunity in recombination activating gene 2 (RAG-2)-deficient severe combined immunodeficiency (SCID) patients, some of these factors are eliminated, and the immune recovery after BMT can then be clearly assessed. This process was followed in ten SCID patients in parallel to their associated transplant-related complications. Early peripheral presence of T and B cells was observed in 8 and 4 patients, respectively. The latter correlated with pre-transplant conditioning therapy. Cells from these patients carried mainly signal joint DNA episomes, indicative of newly derived B and T cells. They were present before the normalization of the T cell receptor (TCR) and the B cell receptor (BCR) repertoire. Early presentation of the ordered TCR gene rearrangements after BMT occurred simultaneously, but this pattern was heterogeneous over time, suggesting different and individual thymic recovery processes. Our findings early after transplant could suggest the long-term patients' clinical outcome. Early peripheral presence of newly produced B and T lymphocytes from their production and maturation sites after BMT suggests donor stem cell origin rather than peripheral expansion, and is indicative of successful outcome. Peripheral detection of TCR excision circles and kappa-deleting recombination excision circles in RAG-2-deficient SCID post-BMT are early markers of T and B cell reconstitution, and can be used to monitor outcome and tailor specific therapy for patients undergoing BMT.

Evolution of the donor T-cell repertoire in recipients in the second decade after allogeneic stem cell transplantation

After allogeneic stem cell transplantation (SCT), T lymphocyte function is reestablished from the donor's postthymic T cells and through thymic T-cell neogenesis. The immune repertoire and its relation to that of the donor have not been characterized in detail in long-term adult SCT survivors. We studied 21 healthy patients in their second decade after a myeloablative SCT for hematologic malignancy (median follow-up, 12 years). Immune profiles were compared with donor samples cryopreserved at transplant and beyond 10 years from SCT. Only one recipient was on continuing immunosuppression. Compared with the donor at transplant, there was no significant difference in CD4, CD8, natural killer, and B-cell blood counts. However, compared with donors, recipients had significantly fewer naive T cells, lower T-cell receptor excision circle levels, fewer CD4 central memory cells, more effector CD8(+) cells, and more regulatory T cells. TCR repertoire analysis showed no significant difference in complexity of TCRVβ spectratype between recipients and donors, although spectratype profiles had diverged with both gain and loss of donor repertoire peaks in the recipient. In conclusion, long-term allogeneic SCT survivors have subtle defects in their immune profile consistent with defective thymic function but compatible with normal health. This study is registered at http://www.clinicaltrials.gov as NCT00106925.

Premature ageing of the immune system underlies immunodeficiency in ataxia telangiectasia

ATM kinase modulates pathways implicated in premature ageing and ATM genotype predicts survival, yet immunodeficiency in ataxia telangiectasia is regarded as mild and unrelated to age. We address this paradox in a molecularly characterised sequential adult cohort with classical and mild variant ataxia telangiectasia. Immunodeficiency has the characteristics of premature ageing across multiple cellular and molecular immune parameters. This immune ageing occurs without previous CMV infection. Age predicts immunodeficiency in genetically homogeneous ataxia telangiectasia, and in comparison with controls, calendar age is exceeded by immunological age defined by thymic naïve CD4+ T cell levels. Applying ataxia telangiectasia as a model of immune ageing, pneumococcal vaccine responses, characteristically deficient in physiological ageing, are predicted by thymic naïve CD4+ T cell levels. These data suggest inherited defects of DNA repair may provide valuable insight into physiological ageing. Thymic naïve CD4+ T cells may provide a biomarker for vaccine responsiveness in elderly cohorts.

Highly skewed T-cell receptor V-beta chain repertoire in the bone marrow is associated with response to immunosuppressive drug therapy in children with very severe aplastic anemia

One of the major obstacles of immunosuppressive therapy (IST) in children with severe aplastic anemia (SAA) comes from the often months-long unpredictability of bone-marrow (BM) recovery. In this prospective study in children with newly diagnosed very severe AA (n=10), who were enrolled in the therapy study SAA-BFM 94, we found a dramatically reduced diversity of both CD4+ and CD8+ BM cells, as scored by comprehensive V-beta chain T-cell receptor (TCR) analysis. Strongly skewed TCR V-beta pattern was highly predictive for good or at least partial treatment response (n=6, CD8+ complexity scoring median 35.5, range 24–73). In contrast, IST in patients with rather moderate reduction of TCR V-beta diversity (n=4, CD8+ complexity scoring median 109.5, range 82–124) always failed (P=0.0095). If confirmed in a larger series of patients, TCR V-beta repertoire in BM may help to assign children with SAA up-front either to IST or to allogeneic stem-cell transplantation.

Tregs prevent GVHD and promote immune reconstitution in HLA-haploidentical transplantation

Hastening posttransplantation immune reconstitution is a key challenge in human leukocyte antigen (HLA)-haploidentical hematopoietic stem-cell transplantation (HSCT). In experimental models of mismatched HSCT, T-regulatory cells (Tregs) when co-infused with conventional T cells (Tcons) favored posttransplantation immune reconstitution and prevented lethal graft-versus-host disease (GVHD). In the present study, we evaluated the impact of early infusion of Tregs, followed by Tcons, on GVHD prevention and immunologic reconstitution in 28 patients with high-risk hematologic malignancies who underwent HLA-haploidentical HSCT. We show for the first time in humans that adoptive transfer of Tregs prevented GVHD in the absence of any posttransplantation immunosuppression, promoted lymphoid reconstitution, improved immunity to opportunistic pathogens, and did not weaken the graft-versus-leukemia effect. This study provides evidence that Tregs are a conserved mechanism in humans.

Multiple myeloma patients at peripheral blood stem cell harvest: restricted usage of TCR beta variable families

The immune systems of multiple myeloma patients are suppressed by the disease itself, and this immunosuppression is further enhanced by standard therapies. The aim of our study was to evaluate the effects of initial chemotherapy and a peripheral blood mobilisation regimen on T-cell population diversity. Reverse transcription-polymerase chain reaction (RT-PCR) with a new set of primers, in combination with capillary electrophoresis, was established. The methodology was used to analyse the relative expression of 27 T-cell receptor beta variable gene families (BV families) in multiple myeloma patients undergoing peripheral blood stem cell harvest. We found that the overall BV family usage in these patients was restricted; the relative expression of 10 BV families was significantly depressed in patients compared to healthy donors. These findings demonstrate that the preparative regimen for autologous stem cell transplantation affects the T-cell population in terms of the restriction of its T-cell receptor diversity.

Graft-versus-leukemia antigen CML66 elicits coordinated B-cell and T-cell immunity after donor lymphocyte infusion

PURPOSE

The target antigens of graft-versus-leukemia that are tumor associated are incompletely characterized.

EXPERIMENTAL DESIGN

We examined responses developing against CML66, an immunogenic antigen preferentially expressed in myeloid progenitor cells identified from a patient with chronic myelogenous leukemia who attained long-lived remission following CD4+ donor lymphocyte infusion (DLI).

RESULTS

From this patient, CML66-reactive CD8+ T-cell clones were detected against an endogenously presented HLA-B*4403-restricted epitope (HDVDALLW). Neither CML66-specific antibody nor T-cell responses were detectable in peripheral blood before DLI. However, by 1 month after DLI, CD8+ T cells were present in peripheral blood and at 10-fold higher frequency in marrow. Subsequently, plasma antibody to CML66 developed in association with disease remission. Donor-derived CML66-reactive T cells were detected at low levels in vivo in marrow before DLI by ELISpot and by a nested PCR-based assay to detect clonotypic T-cell receptor sequences but not in blood of the patient pre-DLI nor of the graft donor.

CONCLUSIONS

CD4+ DLI results in rapid expansion of preexisting marrow-resident leukemia-specific donor CD8+ T cells, followed by a cascade of antigen-specific immune responses detectable in blood. Our single-antigen analysis thus shows that durable posttransplant tumor immunity is directed in part against nonpolymorphic overexpressed leukemia antigens that elicit coordinated cellular and humoral immunity.

Deficient innate immunity, thymopoiesis, and gene expression response to radiation in survivors of childhood acute lymphoblastic leukemia

BACKGROUND

Survivors of childhood acute lymphoblastic leukemia (ALL) are at an increased risk of developing secondary malignant neoplasms. Radiation and chemotherapy can cause mutations and cytogenetic abnormalities and induce genomic instability. Host immunity and appropriate DNA damage responses are critical inhibitors of carcinogenesis. Therefore, we sought to determine the long-term effects of ALL treatment on immune function and response to DNA damage.

METHODS

Comparative studies on 14 survivors in first complete remission and 16 siblings were conducted.

RESULTS

In comparison to siblings on the cells that were involved in adaptive immunity, the patients had either higher numbers (CD19+ B cells and CD4+CD25+ T regulatory cells) or similar numbers (alphabetaT cells and CD45RO+/RA- memory T cells) in the blood. In contrast, patients had lower numbers of all lymphocyte subsets involved in innate immunity (gammadeltaT cells and all NK subsets, including KIR2DL1+ cells, KIR2DL2/L3+ cells, and CD16+ cells), and lower natural cytotoxicity against K562 leukemia cells. Thymopoiesis was lower in patients, as demonstrated by less CD45RO-/RA+ naïve T cell and less SjTREC levels in the blood, whereas the Vbeta spectratype complexity score was similar. Array of gene expression response to low-dose radiation showed that about 70% of the probesets had a reduced response in patients. One of these genes, SCHIP-1, was also among the top-ranked single nucleotide polymorphisms (SNPs) during the whole-genome scanning by SNP microarray analysis.

CONCLUSION

ALL survivors were deficient in innate immunity, thymopoiesis, and DNA damage responses to radiation. These defects may contribute to their increased likelihood of second malignancy.

Restoration of peripheral blood T cell repertoire complexity during remission in advanced cutaneous T cell lymphoma

In advanced stages, cutaneous T cell lymphomas (CTCL) are associated with increased mortality from infections and also increased susceptibility to skin malignancies. In this study, we analyzed the complexity of the peripheral blood T cell repertoire with a sensitive b-variable (BV) complementarity-determining region 3 (CDR3) spectratyping analysis and flow cytometry in three-stage IV CTCL/Sezary syndrome patients who achieved complete clinical remission after therapy. The T cell repertoire of peripheral blood T cells before treatment was profoundly abnormal across multiple BV subfamilies. Following treatment, CDR3 spectratype patterns showed dramatic restoration of normal diversity and complexity. However, absolute CD4 counts across multiple BV families remained low for many months, even after identifiable circulating malignant T cell populations were eliminated. These data suggest that the diversity of the T cell repertoire can be recovered after successful treatment of even advanced CTCL.

Decreased T-cell receptor excision DNA circles in peripheral blood mononuclear cells among benzene-exposed workers

Benzene is a volatile aromatic hydrocarbon solvent which is widely used in many industries. The chronic exposure of humans to benzene in the workplace has been associated with blood disorders, as well as toxicity in lymphopoiesis, including aplastic anaemia and leukaemia. However, the mechanisms of benzene-induced haematotoxicity and leukaemogenesis remain unclear. In this study, we investigated the level of T-cell receptor excision DNA circles (TRECs) in peripheral blood mononuclear cells (PBMCs) in benzene-exposed workers. This would therefore be considered as a potential marker for estimates of thymic output and an evaluation of the content of naïve T-cells. It is hoped that the data will bring a comprehensive understanding on the influence of benzene exposure in the host T-cell immune function. Quantitative detection of TRECs in DNA of PBMCs from benzene-exposed workers was preformed by real-time polymerase chain reaction using the TaqMan technique. The benzene-exposed workers were divided into four groups, and 27 normal individuals were served as controls. The result indicated that the TRECs levels of all benzene-exposed groups were significantly decreased as compared with those of controls. In conclusion, the recent thymic output function and the T-cell immune function were apparently impaired in workers after benzene exposure.

Induction of tumor immunity following allogeneic stem cell transplantation

The curative potential of allogeneic hematopoietic stem cell transplantation (allo-HSCT) for many hematologic malignancies derives in large part from reconstitution of normal donor immunity and the development of a potent graft-versus-leukemia (GVL) immune response capable of rejecting tumor cell in vivo. Elucidation of the mechanisms of GVL by studies of animal models and analysis of clinical data has yielded important insights into how clinically effective tumor immunity is generated following allo-HSCT. These studies have identified NK cells and B cells as well as T cells as important mediators of the GVL response. A variety of antigenic targets of the GVL response have also been identified, and include tumor-associated antigens as well as minor histocompatibility antigens. The principles of effective GVL can now be applied to the development of novel therapies that enhance the therapeutic benefit of allogeneic HSCT while minimizing the toxicities associated with treatment. Moreover, many components of this approach that result in elimination of tumor cells following allogeneic HSCT can potentially be adapted to enhance the effectiveness of tumor immunity in the autologous setting.

Early recovery of CD4 T cell receptor diversity after "lymphoablative" conditioning and autologous CD34 cell transplantation

T cell diversity posttransplantation is thought to be severely restricted, based on T cell receptor beta-chain immunophenotyping or spectratyping. Using beta-chain sequencing, we studied CD4 T cell diversity in 2 adult patients undergoing "lymphoablative" conditioning with cyclophosphamide (Cy), total body irradiation (TBI), and antithymocyte globulin (ATG) and autologous transplantation of hematopoietic cells depleted of T cells by enrichment for CD34 cells. The indication for the transplantation was systemic sclerosis (SSc) or multiple sclerosis (MS). Pretransplantation, the estimated number of distinct beta chains (the minimum number of CD4 T cell clones) in the 2 patients was 600,000 to 700,000, similar to the number in a healthy control. This number was 200,000 to 500,000 at 1 month posttransplantation and 400,000 to 1,600,000 at 12 months posttransplantation. In conclusion, the number of T cells early after lymphoablative conditioning and autologous CD34 cell transplantation may be more diverse than previously appreciated, possibly because many T cell clones survive the conditioning or are reinfused with the graft. Thus, the therapy may not be completely T cell lymphoablative.

Immunomagnetic isolation of CD4+CD25+FoxP3+ natural T regulatory lymphocytes for clinical applications

Although CD4(+)/CD25(+) T regulatory cells (T(regs)) are a potentially powerful tool in bone marrow transplantation, a prerequisite for clinical use is a cell-separation strategy complying with good manufacturing practice guidelines. We isolated T(regs) from standard leukapheresis products using double-negative selection (anti-CD8 and anti-CD19 monoclonal antibodies) followed by positive selection (anti-CD25 monoclonal antibody). The final cell fraction (CD4(+)/CD25(+)) showed a mean purity of 93.6% +/- 1.1. Recovery efficiency was 81.52% +/- 7.4. The CD4(+)/CD25(+bright) cells were 28.4% +/- 6.8. The CD4(+)/CD25(+) fraction contained a mean of 51.9% +/- 15.1 FoxP3 cells and a mean of 18.9% +/- 11.5 CD127 cells. Increased FoxP3 and depleted CD127 mRNAs in CD4(+)CD25(+)FoxP3(+) cells were in line with flow cytometric results. In Vbeta spectratyping the complexity scores of CD4(+)/CD25(+) cells and CD4(+)/CD25(-) cells were not significantly different, indicating that T(regs) had a broad T cell receptor repertoire. The inhibition assay showed that CD4(+)/CD25(+) cells inhibited CD4(+)/CD25(-) cells in a dose-dependent manner (mean inhibition percentages: 72.4 +/- 8.9 [ratio of T responder (T(resp)) to T(regs), 1:2]; 60.8% +/- 20.5 (ratio of T(resp) to T(regs), 1:1); 25.6 +/- 19.6 (ratio of T(resp) to T(regs), 1:0.1)). Our study shows that negative/positive T(reg) selection, performed using the CliniMACS device and reagents, enriches significantly CD4(+)CD25(+)FoxP3(+) cells endowed with immunosuppressive capacities. The CD4(+)CD25(+)FoxP3(+) population is a source of natural T(reg) cells that are depleted of CD8(+) and CD4(+)/CD25(-) reacting clones which are potentially responsible for triggering graft-versus-host disease (GvHD). Cells isolated by means of this approach might be used in allogeneic haematopoietic cell transplantation to facilitate engraftment and reduce the incidence and severity of GvHD without abrogating the potential graft-versus-tumour effect.

Activated autologous T cells exert an anti-B-cell chronic lymphatic leukemia effect in vitro and in vivo

BACKGROUND AIMS

The impact of chronic lymphatic leukemia (CLL) tumor burden on the autologous immune system has already been demonstrated. This study attempted to elucidate the molecular mechanisms underlying T-cell immunologic deficiencies in CLL.

METHODS

Freshly isolated CD3(+) T cells from patients with a diagnosis of CLL and healthy donors were analyzed by gene expression profiling. Activated T cells from 20 patients with CLL were tested in vitro for cytotoxicity against mutated and unmutated autologous B cells and DAUDI, K562 and P815 cell lines. To investigate T-cell mediated cytotoxicity in vivo, we co-transplanted OKT3-activated T lymphocytes and autologous B-cell CLL (B-CLL) cells into NOD/SCID mice.

RESULTS

Gene expression profiles of peripheral blood T cells from B-CLL patients showed 25 down-regulated, and 31 up-regulated, genes that were mainly involved in cell differentiation, proliferation, survival, apoptosis, cytoskeleton formation, vesicle trafficking and T-cell activation. After culture, the T-cell count remained unchanged, CD8 cells expanded more than CD4 and a cytotoxicity index >30% was present in 5/20 patients. Cytotoxicity against B autologous leukemic cells did not correlate with B-cell mutational status. Only activated T cells exerting cytotoxicity against autologous leukemic B cells prevented CLL in a human-mouse chimera.

CONCLUSIONS

This study indicates that patients with CLL are affected by a partial immunologic defect that might be somewhat susceptible to repair. This study identifies the molecular pathways underlying T-cell deficiencies in CLL and shows that cytotoxic T-cell functions against autologous B-CLL can be rebuilt at least in part in vitro and in vivo.

Immune reconstitution and implications for immunotherapy following haematopoietic stem cell transplantation

Recovery of a fully functional immune system is a slow and often incomplete process following allogeneic stem cell transplantation. While innate immunity reconstitutes quickly, adaptive B- and especially T-cell lymphopoeisis may be compromised for years following transplantation. In large part, these immune system deficits are due to the decrease, or even absence, of thymopoiesis following transplantation. Thereby, T-cell reconstitution initially relies upon expansion of mature donor T cells; a proliferation driven by high cytokine levels and the presence of allo-reactive antigens. This peripheral mechanism of T-cell generation may have important clinical consequences. By expanding tumouricidal T cells, it may provide a venue to enhance T-cellular immunotherapy following transplantation. Alternatively, decreased thymic function may impair long-term anti-tumour immunity and increase the likelihood of graft-versus-host disease.

The immunopathology of thymic GVHD

The clinical success of allogeneic hematopoietic stem cell transplantation (HSCT) depends on the appropriate reconstitution of the host's immune system. While recovery of T-cell immunity may occur in transplant recipients via both thymus-dependent and thymus-independent pathways, the regeneration of a population of phenotypically naive T cells with a broad receptor repertoire relies entirely on the de novo generation of T-cells in the thymus. Preclinical models and clinical studies of allogeneic HSCT have identified the thymus as a target of graft-versus-host disease (GVHD), thus limiting T-cell regeneration. The present review focuses on recent insight into how GVHD affects thymic structure and function and how this knowledge may aid in the design of new strategies to improve T-cell reconstitution following allogeneic HSCT.

A novel virus carrier state to evaluate immunotherapeutic regimens: regulatory T cells modulate the pathogenicity of antiviral memory cells

Restrictions in the diversity of an adaptive immune repertoire can facilitate viral persistence. Because a host afflicted with an immune deficiency is not likely to purge a persistent infection using endogenous mechanisms, it is important to explore adoptive therapies to supplement the host with a functional immune defense. In this study, we describe a virus carrier state that results from introducing lymphocytic choriomeningitis virus (LCMV) into adult mice possessing a restricted T cell repertoire. On infection of these mice, LCMV establishes systemic persistence, and within the CNS the virus infects astrocytes (and later oligodendrocytes) rather than its traditional parenchymal target neurons. To determine whether LCMV could be purged from a novel target selection in the absence of an endogenous immune repertoire, we adoptively transferred virus-specific memory cells into adult carrier mice. The memory cells purged virus from the periphery as well as the CNS, but they induced fatalities not typically associated with adoptive immunotherapy. When the repertoire of the recipient mice was examined, a deficiency in natural regulatory T cells was noted. We therefore supplemented carrier mice with regulatory T cells and simultaneously performed adoptive immunotherapy. Cotransfer of regulatory T cells significantly reduced mortality while still permitting the antiviral memory cells to purge the persistent infection. These data indicate that regulatory T cells can be used therapeutically to lessen the pathogenicity of virus-specific immune cells in an immunodeficient host. We also propose that the novel carrier state described herein will facilitate the study of immunotherapeutic regimens.

Late onset of autoimmune hemolytic anemia and pure red cell aplasia after allogeneic hematopoietic stem cell transplantation using in vivo alemtuzumab

Hemolytic anemia and pure red cell aplasia (PRCA) after allogeneic hematopoietic stem cell transplantation (HSCT) have been reported to be mainly related to ABO-incompatibility between donor and recipient. Autoimmune hemolytic anemia (AIHA) without ABO-incompatibility has been also reported after allogeneic HSCT, especially with T-cell depletion. However, optimal management of AIHA or PRCA remains unclear. A 54-year-old male with myelodysplastic syndrome (MDS) underwent haploidentical human leukocyte antigen-mismatched HSCT using in vivo alemtuzumab and developed AIHA and PRCA simultaneously 15 months after transplantation, following the administration of cidofovir and probenecid for persistent cytomegalovirus (CMV) antigenemia and retinitis. AIHA was successfully treated with rituximab, and subsequently PRCA with cyclosporine without relapse of MDS or recurrence of CMV infection. The clinical course suggested that AIHA was mainly caused by humoral immune response, while PRCA was mainly caused by cell-mediated immune response in this patient, although these immune responses might be related to each other.