Specificity of T-cell alloreactivity

Regulatory B lymphocytes: development and modulation of the host immune response during disease

The role of B lymphocytes (B cells) in immunogenic responses has become increasingly important over the past decade, focusing on a new B-cell subtype: regulatory B-cells (Bregs). These Bregs have been shown to possess potent immunosuppressive activities and have identified as key players in disease control and immune tolerance. In this review, the occurrence of Breg type in various conditions, along with evidence supporting discovered functions and proposed purposes will be explored. An example of such regulatory functions includes the induction or suppression of various T lymphocyte phenotypes in response to a particular stimulus. Should Bregs prove effective in mediating immune responses, and correlate with favorable disease outcome, they may serve as a novel therapeutic to combat disease and prevent infection. However, the induction, function and stability of these cells remain unclear and further investigation is needed to better understand their role and therapeutic efficacy.

RNA sequencing identifies clonal structure of T-cell repertoires in patients with adult T-cell leukemia/lymphoma

The diversity of T-cell receptor (TCR) repertoires, as generated by somatic DNA rearrangements, is central to immune system function. High-throughput sequencing technologies now allow examination of antigen receptor repertoires at single-nucleotide and, more recently, single-cell resolution. The TCR repertoire can be altered in the context of infections, malignancies or immunological disorders. Here we examined the diversity of TCR clonality and its association with pathogenesis and prognosis in adult T-cell leukemia/lymphoma (ATL), a malignancy caused by infection with human T-cell leukemia virus type-1 (HTLV-1). We analyzed 62 sets of high-throughput RNA sequencing data from 59 samples of HTLV-1−infected individuals—asymptomatic carriers (ACs), smoldering, chronic, acute and lymphoma ATL subtypes—and three uninfected controls to evaluate TCR distribution. Based on these TCR profiles, CD4-positive cells and ACs showed polyclonal patterns, whereas ATL patients showed oligo- or monoclonal patterns (with 446 average clonotypes across samples). Expression of TCRα and TCRβ genes in the dominant clone differed among the samples. ACs, CD4-positive samples and smoldering patients showed significantly higher TCR diversity compared with chronic, acute and lymphoma subtypes. CDR3 sequence length distribution, amino acid conservation and gene usage variability for ATL patients resembled those of peripheral blood cells from ACs and healthy donors. Thus, determining monoclonal architecture and clonal diversity by RNA sequencing might be useful for prognostic purposes and for personalizing ATL diagnosis and assessment of treatments.

ESC Working Group on Cellular Biology of the Heart: position paper for Cardiovascular Research: tissue engineering strategies combined with cell therapies for cardiac repair in ischaemic heart disease and heart failure

Morbidity and mortality from ischaemic heart disease (IHD) and heart failure (HF) remain significant in Europe and are increasing worldwide. Patients with IHD or HF might benefit from novel therapeutic strategies, such as cell-based therapies. We recently discussed the therapeutic potential of cell-based therapies and provided recommendations on how to improve the therapeutic translation of these novel strategies for effective cardiac regeneration and repair. Despite major advances in optimizing these strategies with respect to cell source and delivery method, the clinical outcome of cell-based therapy remains unsatisfactory. Major obstacles are the low engraftment and survival rate of transplanted cells in the harmful microenvironment of the host tissue, and the paucity or even lack of endogenous cells with repair capacity. Therefore, new ways of delivering cells and their derivatives are required in order to empower cell-based cardiac repair and regeneration in patients with IHD or HF. Strategies using tissue engineering (TE) combine cells with matrix materials to enhance cell retention or cell delivery in the transplanted area, and have recently received much attention for this purpose. Here, we summarize knowledge on novel approaches emerging from the TE scenario. In particular, we will discuss how combinations of cell/bio-materials (e.g. hydrogels, cell sheets, prefabricated matrices, microspheres, and injectable matrices) combinations might enhance cell retention or cell delivery in the transplantation areas, thereby increase the success rate of cell therapies for IHD and HF. We will not focus on the use of classical engineering approaches, employing fully synthetic materials, because of their unsatisfactory material properties which render them not clinically applicable. The overall aim of this Position Paper from the ESC Working Group Cellular Biology of the Heart is to provide recommendations on how to proceed in research with these novel TE strategies combined with cell-based therapies to boost cardiac repair in the clinical settings of IHD and HF.

Transient increase of activated regulatory T cells early after kidney transplantation

Regulatory T cells (Tregs) are crucial in controlling allospecific immune responses. However, studies in human kidney recipients regarding the contribution of polyspecific Tregs have provided differing results and studies on alloreactive Tregs are missing completely. In this retrospective study, we specifically analyzed activated CD4⁺CD25^highFOXP3⁺GARP⁺ Tregs in 17 patients of a living donor kidney transplantation cohort longitudinally over 24 months by flow cytometry (FOXP3: forkhead box protein 3, GARP: glycoprotein A repetitions predominant). We could demonstrate that Tregs of patients with end-stage renal disease (ESRD) are already pre-activated when compared to healthy controls. Furthermore, even though total CD4⁺CD25^highFOXP3⁺ Treg numbers decreased in the first three months after transplantation, frequency of activated Tregs increased significantly representing up to 40% of all peripheral Tregs. In a cohort of living donor kidney transplantation recipients with stable graft function, frequencies of activated Tregs did not correlate with the occurrence of acute cellular rejection or chronic graft dysfunction. Our results will be important for clinical trials using adoptive Treg therapy after kidney transplantation. Adoptively transferred Tregs could be important to compensate the Treg loss at month 3, while they have to compete within the Treg niche with a large number of activated Tregs.

Comprehensive Analysis of the Activation and Proliferation Kinetics and Effector Functions of Human Lymphocytes, and Antigen Presentation Capacity of Antigen-Presenting Cells in Xenogeneic Graft-Versus-Host Disease

Xenogeneic graft-versus-host disease (GVHD) models in highly immunodeficient mice are currently being used worldwide to investigate human immune responses against foreign antigens in vivo. However, the individual roles of CD4⁺ and CD8⁺ T cells, and donor/host hematopoietic and nonhematopoietic antigen-presenting cells (APCs) in the induction and development of GVHD have not been fully investigated. In the present study, we comprehensively investigated the immune responses of human T cells and the antigen presentation capacity of donor/host hematopoietic and nonhematopoietic APCs in xenogeneic GVHD models using nonobese diabetic/Shi-scid-IL2rg^null mice. CD4⁺ T cells and, to a lesser extent, CD8⁺ T cells individually mediated potentially lethal GVHD. In addition to inflammatory cytokine production, CD4⁺ T cells also supported the activation and proliferation of CD8⁺ T cells. Using bone marrow chimeras, we demonstrated that host hematopoietic, but not nonhematopoietic, APCs play a critical role in the development of CD4⁺ T cell-mediated GVHD. During early GVHD, we detected 2 distinct populations in memory CD4⁺ T cells. One population was highly activated and proliferated in major histocompatibility complex antigen (MHC)^+/+ mice but not in MHC^-/- mice, indicating alloreactive T cells. The other population showed a less activated and slowly proliferative status regardless of host MHC expression, and was associated with higher susceptibility to apoptosis, indicating nonalloreactive T cells in homeostasis-driven proliferation. These observations are clinically relevant to donor T cell response after allogeneic hematopoietic stem cell transplantation. Our findings provide a better understanding of the immunobiology of humanized mice and support the development of novel options for the prevention and treatment for GVHD.

Alloreactive T Cell Receptor Diversity against Structurally Similar or Dissimilar HLA-DP Antigens Assessed by Deep Sequencing

T cell alloreactivity is mediated by a self-human leukocyte antigen (HLA)-restricted T cell receptor (TCR) repertoire able to recognize both structurally similar and dissimilar allogeneic HLA molecules (i.e., differing by a single or several amino acids in their peptide-binding groove). We hypothesized that thymic selection on self-HLA molecules could have an indirect impact on the size and diversity of the alloreactive response. To test this possibility, we used TCR Vβ immunophenotyping and immunosequencing technology in a model of alloreactivity between self-HLA selected T cells and allogeneic HLA-DPB1 (DPB1) differing from self-DPB1*04:02 by a single (DPB1*02:01) or several (DPB1*09:01) amino acids in the peptide-binding groove. CD4+ T cells from three different self-DPB1*04:01,*04:02 individuals were stimulated with HeLa cells stably transduced with the relevant peptide processing machinery, co-stimulatory molecules, and HLA-DP. Flow cytometric quantification of the DPB1-specific T cell response measured as upregulation of the activation marker CD137 revealed significantly lower levels of alloreactivity against DPB1*02:01 compared with DPB1*09:01 (mean CD4+CD137+ frequency 35.2 ± 9.9 vs. 61.5 ± 7.7%, respectively, p < 0.0001). These quantitative differences were, however, not reflected by differences in the breadth of the alloreactive response at the Vβ level, with both alloantigens eliciting specific responses from all TCR-Vβ specificities tested by flow cytometry, albeit with higher levels of reactivity from most Vβ specificities against DPB1*09:01. In line with these observations, TCRB-CDR3 immunosequencing showed no significant differences in mean clonality of sorted CD137+CD4+ cells alloreactive against DPB1*02:01 or DPB1*09:01 [0.39 (0.36–0.45) and 0.39 (0.30–0.46), respectively], or in the cumulative frequencies of the 10 most frequent responding clones (55–67 and 58–62%, respectively). Most of the clones alloreactive against DPB1*02:01 (68.3%) or DPB1*09:01 (75.3%) were characterized by low-abundance (i.e., they were not appreciable among the pre-culture T cells). Interestingly, however, their cumulative frequency was lower against DPB1*02:01 compared with DPB1*09:01 (mean cumulative frequency 35.3 vs. 50.6%, respectively). Our data show that, despite lower levels of alloreactivity, a similar clonal diversity can be elicited by structurally similar compared with structurally dissimilar HLA-DPB1 alloantigens and demonstrate the power of TCRB immunosequencing in unraveling subtle qualitative changes not appreciable by conventional methods.

Humanized mice in studying efficacy and mechanisms of PD-1-targeted cancer immunotherapy

Establishment of an in vivo small animal model of human tumor and human immune system interaction would enable preclinical investigations into the mechanisms underlying cancer immunotherapy. To this end, nonobese diabetic (NOD).Cg-Prkdc^scidIL2rg^tm1Wjl/Sz (null; NSG) mice were transplanted with human (h)CD34⁺ hematopoietic progenitor and stem cells, which leads to the development of human hematopoietic and immune systems [humanized NSG (HuNSG)]. HuNSG mice received human leukocyte antigen partially matched tumor implants from patient-derived xenografts [PDX; non–small cell lung cancer (NSCLC), sarcoma, bladder cancer, and triple-negative breast cancer (TNBC)] or from a TNBC cell line-derived xenograft (CDX). Tumor growth curves were similar in HuNSG compared with nonhuman immune-engrafted NSG mice. Treatment with pembrolizumab, which targets programmed cell death protein 1, produced significant growth inhibition in both CDX and PDX tumors in HuNSG but not in NSG mice. Finally, inhibition of tumor growth was dependent on hCD8⁺ T cells, as demonstrated by antibody-mediated depletion. Thus, tumor-bearing HuNSG mice may represent an important, new model for preclinical immunotherapy research.—Wang, M., Yao, L.-C., Cheng, M., Cai, D., Martinek, J., Pan, C.-X., Shi, W., Ma, A.-H., De Vere White, R. W., Airhart, S., Liu, E. T., Banchereau, J., Brehm, M. A., Greiner, D. L., Shultz, L. D., Palucka, K., Keck, J. G. Humanized mice in studying efficacy and mechanisms of PD-1-targeted cancer immunotherapy.

Acute rejection

Despite induction immunosuppression and the use of aggressive maintenance immunosuppressive regimens, acute allograft rejection following lung transplantation is still a problem with important diagnostic and therapeutic challenges. As well as causing early graft loss and mortality, acute rejection also initiates the chronic alloimmune responses and airway-centred inflammation that predispose to bronchiolitis obliterans syndrome (BOS), also known as chronic lung allograft dysfunction (CLAD), which is a major source of morbidity and mortality after lung transplantation. Cellular responses to human leukocyte antigens (HLAs) on the allograft have traditionally been considered the main mechanism of acute rejection, but the influence of humoral immunity is increasingly recognised. As with other several other solid organ transplants, antibody-mediated rejection (AMR) is now a well-accepted and distinct clinical entity in lung transplantation. While acute cellular rejection (ACR) has defined histopathological criteria, transbronchial biopsy is less useful in AMR and its diagnosis is complicated by challenges in the measurement of antibodies directed against donor HLA, and a determination of their significance. Increasing awareness of the importance of non-HLA antigens further clouds this issue. Here, we review the pathophysiology, diagnosis, clinical presentation and treatment of ACR and AMR in lung transplantation, and discuss future potential biomarkers of both processes that may forward our understanding of these conditions.

Emerging Concepts in TCR Specificity: Rationalizing and (Maybe) Predicting Outcomes

T cell specificity emerges from a myriad of processes, ranging from the biological pathways that control T cell signaling to the structural and physical mechanisms that influence how TCRs bind peptides and MHC proteins. Of these processes, the binding specificity of the TCR is a key component. However, TCR specificity is enigmatic: TCRs are at once specific but also cross-reactive. Although long appreciated, this duality continues to puzzle immunologists and has implications for the development of TCR-based therapeutics. In this review, we discuss TCR specificity, emphasizing results that have emerged from structural and physical studies of TCR binding. We show how the TCR specificity/cross-reactivity duality can be rationalized from structural and biophysical principles. There is excellent agreement between predictions from these principles and classic predictions about the scope of TCR cross-reactivity. We demonstrate how these same principles can also explain amino acid preferences in immunogenic epitopes and highlight opportunities for structural considerations in predictive immunology.

Thymic Origins of T Cell Receptor Alloreactivity

Major histocompatibility complex (MHC) restriction is a unique feature of T cell antigen recognition. Mature T cells respond to antigenic nonself peptides bound to self-MHC molecules, but a sizeable fraction of peripheral T cells can also respond to nonself peptide-MHC (pMHC) complexes in the context of transplantation. MHC specificity of the T cell receptor (TCR) repertoire is shaped during thymic development. Two hypotheses have been proposed to explain MHC specificity of T cells. It has been suggested that MHC specificity is an intrinsic feature of TCR structure, mediated by the germline-encoded regions of the TCR sequence. In support of this model, an estimated 15% to 30% of preselection TCR repertoire is estimated to be MHC-specific. Moreover, structural studies have shown some degree of conserved binding topology for TCR-peptide MHC complexes. However, there is also evidence that MHC restriction can be imposed on the TCR repertoire during thymic development, and it has been proposed that the interaction of the Lck kinase with CD4 or CD8 coreceptors is critical for generation of MHC specificity. This review will discuss recent work on assessment of the preselection of TCR repertoire, molecular evidence for the germline encoded TCR bias for MHC, and for the coreceptor sequestration model in the context of alloreactivity and transplantation.

Modulation of let-7 miRNAs controls the differentiation of effector CD8 T cells

The differentiation of naive CD8 T cells into effector cytotoxic T lymphocytes upon antigen stimulation is necessary for successful antiviral, and antitumor immune responses. Here, using a mouse model, we describe a dual role for the let-7 microRNAs in the regulation of CD8 T cell responses, where maintenance of the naive phenotype in CD8 T cells requires high levels of let-7 expression, while generation of cytotoxic T lymphocytes depends upon T cell receptor-mediated let-7 downregulation. Decrease of let-7 expression in activated T cells enhances clonal expansion and the acquisition of effector function through derepression of the let-7 targets, including Myc and Eomesodermin. Ultimately, we have identified a novel let-7-mediated mechanism, which acts as a molecular brake controlling the magnitude of CD8 T cell responses.

DOI:http://dx.doi.org/10.7554/eLife.26398.001

Induction of a Regulatory Phenotype in CD3+ CD4+ HLA-DR+ T Cells after Allogeneic Mixed Lymphocyte Culture; Indications of Both Contact-Dependent and -Independent Activation

Although the observation of major histocompatibility complex II (MHCII) receptors on T cells is longstanding, the explanation for this occurrence remains enigmatic. Reports of an inducible, endogenous expression exist, as do studies demonstrating a protein acquisition from other cells by mechanisms including vesicle transfer. Irrespective of origin, the presence of the human MHCII isotype, human leukocyte antigen DR (HLA-DR), potentially identifies a regulatory T cell population. Using an allogeneic mixed lymphocyte culture (MLC) to induce an antigen-specific immune response, the role of antigen-presenting cells (APCs) for the presence of HLA-DR on cluster of differentiation 3(CD3)+ CD4+ T cells was evaluated. Moreover, a functional phenotype was established for these T cells. It was demonstrated that APCs were essential for HLA-DR on CD3+ CD4+ T cells. Additionally, a regulatory T cell phenotype was induced in CD3+ CD4+ HLA-DR+ responder T cells with an expression of CD25, CTLA-4, CD62L, PD-1, and TNFRII. This phenotype was induced both with and without physical T cell:APC contact, which could reveal novel indications about its functionality. To further investigate contact-independent communication, a phenotype of the small cell-derived vesicles from the MLCs was determined. Yet heterogeneous, this vesicle phenotype displayed contact-dependent differences, providing clues about their intended function in cellular communication.

Alloimmune T cells in transplantation

Alloimmune T cells are central mediators of rejection and graft-versus-host disease in both solid organ and hematopoietic stem cell transplantation. Unique among immune responses in terms of its strength and diversity, the T cell alloresponse reflects extensive genetic polymorphisms between allogeneic donors and recipients, most prominently within the major histocompatibility complex (MHC), which encodes human leukocyte antigens (HLAs) in humans. The repertoire of alloreactive T cell clones is distinct for every donor-recipient pair and includes potentially thousands of unique HLA/peptide specificities. The extraordinary magnitude of the primary alloresponse and diversity of the T cell population mediating it have presented technical challenges to its study in humans. High-throughput T cell receptor sequencing approaches have opened up new possibilities for tackling many fundamental questions about this important immunologic phenomenon.

How an alloreactive T-cell receptor achieves peptide and MHC specificity

T-cell receptor (TCR) allorecognition is often presumed to be relatively nonspecific, attributable to either a TCR focus on exposed major histocompatibility complex (MHC) polymorphisms or the degenerate recognition of allopeptides. However, paradoxically, alloreactivity can proceed with high peptide and MHC specificity. Although the underlying mechanisms remain unclear, the existence of highly specific alloreactive TCRs has led to their use as immunotherapeutics that can circumvent central tolerance and limit graft-versus-host disease. Here, we show how an alloreactive TCR achieves peptide and MHC specificity. The HCV1406 TCR was cloned from T cells that expanded when a hepatitis C virus (HCV)-infected HLA-A2^- individual received an HLA-A2⁺ liver allograft. HCV1406 was subsequently shown to recognize the HCV nonstructural protein 3 (NS3):1406-1415 epitope with high specificity when presented by HLA-A2. We show that NS3/HLA-A2 recognition by the HCV1406 TCR is critically dependent on features unique to both the allo-MHC and the NS3 epitope. We also find cooperativity between structural mimicry and a crucial peptide "hot spot" and demonstrate its role, along with the MHC, in directing the specificity of allorecognition. Our results help explain the paradox of specificity in alloreactive TCRs and have implications for their use in immunotherapy and related efforts to manipulate TCR recognition, as well as alloreactivity in general.

The Immunogenicity of HLA Class II Mismatches: The Predicted Presentation of Nonself Allo-HLA-Derived Peptide by the HLA-DR Phenotype of the Recipient Is Associated with the Formation of DSA

The identification of permissible HLA class II mismatches can prevent DSA in mismatched transplantation. The HLA-DR phenotype of recipients contributes to DSA formation by presenting allo-HLA-derived peptides to T-helper cells, which induces the differentiation of B cells into plasma cells. Comparing the binding affinity of self and nonself allo-HLA-derived peptides for recipients' HLA class II antigens may distinguish immunogenic HLA mismatches from nonimmunogenic ones. The binding affinities of allo-HLA-derived peptides to recipients' HLA-DR and HLA-DQ antigens were predicted using the NetMHCIIpan 3.1 server. HLA class II mismatches were classified based on whether they induced DSA and whether self or nonself peptide was predicted to bind with highest affinity to recipients' HLA-DR and HLA-DQ. Other mismatch characteristics (eplet, hydrophobic, electrostatic, and amino acid mismatch scores and PIRCHE-II) were evaluated. A significant association occurred between DSA formation and the predicted HLA-DR presentation of nonself peptides (P = 0.0169; accuracy = 80%; sensitivity = 88%; specificity = 63%). In contrast, mismatch characteristics did not differ significantly between mismatches that induced DSA and the ones that did not, except for PIRCHE-II (P = 0.0094). This methodology predicts DSA formation based on HLA mismatches and recipients' HLA-DR phenotype and may identify permissible HLA mismatches to help optimize HLA matching and guide donor selection.

A Paradigm Shift on the Question of B Cells in Transplantation? Recent Insights on Regulating the Alloresponse

B lymphocytes contribute to acute and chronic allograft rejection through their production of donor-specific antibodies (DSAs). In addition, B cells present allopeptides bound to self-MHC class II molecules and provide costimulation signals to T cells, which are essential to their activation and differentiation into memory T cells. On the other hand, both in laboratory rodents and patients, the concept of effector T cell regulation by B cells is gaining traction in the field of transplantation. Specifically, clinical trials using anti-CD20 monoclonal antibodies to deplete B cells and reverse DSA had a deleterious effect on rates of acute cellular rejection; a peculiar finding that calls into question a central paradigm in transplantation. Additional work in humans has characterized IL-10-producing B cells (IgM memory and transitional B cells), which suppress the proliferation and inflammatory cytokine productions of effector T cells in vitro. Understanding the mechanisms of regulating the alloresponse is critical if we are to achieve operational tolerance across transplantation. This review will focus on recent evidence in murine and human transplantation with respect to non-traditional roles for B cells in determining clinical outcomes.

Structure and Dynamics of Antigenic Peptides in Complex with TAP

The transporter associated with antigen processing (TAP) selectively translocates antigenic peptides into the endoplasmic reticulum. Loading onto major histocompatibility complex class I molecules and proofreading of these bound epitopes are orchestrated within the macromolecular peptide-loading complex, which assembles on TAP. This heterodimeric ABC-binding cassette (ABC) transport complex is therefore a major component in the adaptive immune response against virally or malignantly transformed cells. Its pivotal role predestines TAP as a target for infectious diseases and malignant disorders. The development of therapies or drugs therefore requires a detailed comprehension of structure and function of this ABC transporter, but our knowledge about various aspects is still insufficient. This review highlights recent achievements on the structure and dynamics of antigenic peptides in complex with TAP. Understanding the binding mode of antigenic peptides in the TAP complex will crucially impact rational design of inhibitors, drug development, or vaccination strategies.

Pappalysin-1 T cell receptor transgenic allo-restricted T cells kill Ewing sarcoma in vitro and in vivo

Pregnancy-associated plasma protein-A (PAPPA), also known as pappalysin, is a member of the insulin-like growth factor (IGF) family. PAPPA acts as a protease, cleaving IGF inhibitors, i.e., IGF binding proteins (IGFBPs), thereby setting free IGFs. The insulin/IGF-axis is involved in cancer in general and in Ewing sarcoma (ES) in particular. ES is a highly malignant bone tumor characterized by early metastatic spread. PAPPA is associated with various cancers. It is overexpressed and required for proliferation in ES. PAPPA also stimulates normal bone growth. We isolated HLA-A*02:01⁺/peptide-restricted T cells from A*02:01⁻ healthy donors directed against PAPPA, generated by priming with A*02:01⁺ PAPPA peptide loaded dendritic cells. After TCR identification, retrovirally TCR transduced CD8⁺ T cells were assessed for their in vitro specificity and in vivo efficacy in human ES bearing Rag2^−/−γc^−/− mice. Engraftment in mice and tumor infiltration of TCR transgenic T cells in the mice was evaluated. The TCR transgenic T cell clone PAPPA-2G6 demonstrated specific reactivity toward HLA-A*02:01⁺/PAPPA⁺ ES cell lines. We furthermore detected circulating TCR transgenic T cells in the blood in Rag2^−/−γc^−/− mice and in vivo engraftment in bone marrow. Tumor growth in mice with xenografted ES was significantly reduced after treatment with PAPPA-2G6 TCR transgenic T cells in contrast to controls. Tumors of treated mice revealed tumor-infiltrating PAPPA-2G6 TCR transgenic T cells. In summary, we demonstrate that PAPPA is a first-rate target for TCR-based immunotherapy of ES.

Genome-wide minor histocompatibility matching as related to the risk of graft-versus-host disease

The risk of acute graft-versus-host disease (GVHD) is higher after allogeneic hematopoietic cell transplantation (HCT) from unrelated donors as compared with related donors. This difference has been explained by increased recipient mismatching for major histocompatibility antigens or minor histocompatibility antigens. In the current study, we used genome-wide arrays to enumerate single nucleotide polymorphisms (SNPs) that produce graft-versus-host (GVH) amino acid coding differences between recipients and donors. We then tested the hypothesis that higher degrees of genome-wide recipient GVH mismatching correlate with higher risks of GVHD after allogeneic HCT. In HLA-genotypically matched sibling recipients, the average recipient mismatching of coding SNPs was 9.35%. Each 1% increase in genome-wide recipient mismatching was associated with an estimated 20% increase in the hazard of grades III-IV GVHD (hazard ratio [HR], 1.20; 95% confidence interval [CI], 1.05-1.37; P = .007) and an estimated 22% increase in the hazard of stage 2-4 acute gut GVHD (HR, 1.22; 95% CI, 1.02-1.45; P = .03). In HLA-A, B, C, DRB1, DQA1, DQB1, DPA1, DPB1-phenotypically matched unrelated recipients, the average recipient mismatching of coding SNPs was 17.3%. The estimated risks of GVHD-related outcomes in HLA-phenotypically matched unrelated recipients were low, relative to the large difference in genome-wide mismatching between the 2 groups. In contrast, the risks of GVHD-related outcomes were higher in HLA-DP GVH-mismatched unrelated recipients than in HLA-matched sibling recipients. Taken together, these results suggest that the increased GVHD risk after unrelated HCT is predominantly an effect of HLA-mismatching.

Minor Antigen Disparities Impede Induction of Long Lasting Chimerism and Tolerance through Bone Marrow Transplantation with Costimulation Blockade

Mixed chimerism and tolerance can be successfully induced in rodents through allogeneic bone marrow transplantation (BMT) with costimulation blockade (CB), but varying success rates have been reported with distinct models and protocols. We therefore investigated the impact of minor antigen disparities on the induction of mixed chimerism and tolerance. C57BL/6 (H2^b) mice received nonmyeloablative total body irradiation (3 Gy), costimulation blockade (anti-CD40L mAb and CTLA4Ig), and 2 × 10⁷ bone marrow cells (BMC) from either of three donor strains: Balb/c (H2^d) (MHC plus multiple minor histocompatibility antigen (mHAg) mismatched), B10.D2 (H2^d) or B10.A (H2^a) (both MHC mismatched, but mHAg matched). Macrochimerism was followed over time by flow cytometry and tolerance was tested by skin grafting. 20 of 21 recipients of B10.D2 BMC but only 13 of 18 of Balb/c BMC and 13 of 20 of B10.A BMC developed stable long-term multilineage chimerism (p < 0.05 for each donor strain versus B10.D2). Significantly superior donor skin graft survival was observed in successfully established long-term chimeras after mHAg matched BMT compared to mHAg mismatched BMT (p < 0.05). Both minor and major antigen disparities pose a substantial barrier for the induction of chimerism while the maintenance of tolerance after nonmyeloablative BMT and costimulation blockade is negatively influenced by minor antigen disparities.        

Antigen Presentation in Transplantation

Transplantation of solid organs between genetically distinct individuals leads, in the absence of immunosuppression, to T cell-dependent transplant rejection. Activation of graft-reactive T cells relies on the presentation of transplant-derived antigens (intact donor MHC molecules or processed peptides on host MHC molecules) by mature dendritic cells (DCs). This review focuses on novel insights regarding the steps for maturation and differentiation of DCs that are necessary for productive presentation of transplant antigens to host T cells. These steps include the licensing of DCs by the microbiota, their activation and maturation following recognition of allogeneic non-self, and their capture of donor cell exosomes to amplify the presentation of transplant antigens.

On the organization of human T-cell receptor loci: log-periodic distribution of T-cell receptor gene segments

The human T-cell repertoire is complex and is generated by the rearrangement of variable (V), diversity (D) and joining (J) segments on the T-cell receptor (TCR) loci. The T-cell repertoire demonstrates self-similarity in terms clonal frequencies when defined by V, D and J gene segment usage; therefore to determine whether the structural ordering of these gene segments on the TCR loci contributes to the observed clonal frequencies, the TCR loci were examined for self-similarity and periodicity in terms of gene segment organization. Logarithmic transformation of numeric sequence order demonstrated that the V and J gene segments for both T-cell receptor α (TRA) and β (TRB) loci are arranged in a self-similar manner when the spacing between the adjacent segments was considered as a function of the size of the neighbouring gene segment, with an average fractal dimension of approximately 1.5. Accounting for the gene segments occurring on helical DNA molecules with a logarithmic distribution, sine and cosine functions of the log-transformed angular coordinates of the start and stop nucleotides of successive TCR gene segments showed an ordered progression from the 5' to the 3' end of the locus, supporting a log-periodic organization. T-cell clonal frequency estimates, based on V and J segment usage, from normal stem cell donors were plotted against the V and J segment on TRB locus and demonstrated a periodic distribution. We hypothesize that this quasi-periodic variation in gene-segment representation in the T-cell clonal repertoire may be influenced by the location of the gene segments on the periodic-logarithmically scaled TCR loci. Interactions between the two strands of DNA in the double helix may influence the probability of gene segment usage by means of either constructive or destructive interference resulting from the superposition of the two helices.

sNebula, a network-based algorithm to predict binding between human leukocyte antigens and peptides

Understanding the binding between human leukocyte antigens (HLAs) and peptides is important to understand the functioning of the immune system. Since it is time-consuming and costly to measure the binding between large numbers of HLAs and peptides, computational methods including machine learning models and network approaches have been developed to predict HLA-peptide binding. However, there are several limitations for the existing methods. We developed a network-based algorithm called sNebula to address these limitations. We curated qualitative Class I HLA-peptide binding data and demonstrated the prediction performance of sNebula on this dataset using leave-one-out cross-validation and five-fold cross-validations. This algorithm can predict not only peptides of different lengths and different types of HLAs, but also the peptides or HLAs that have no existing binding data. We believe sNebula is an effective method to predict HLA-peptide binding and thus improve our understanding of the immune system.

Targeting B-cell neoplasia with T-cell receptors recognizing a CD20-derived peptide on patient-specific HLA

T cells engineered to express chimeric antigen receptors (CARs) targeted to CD19 are effective in treatment of B-lymphoid malignancies. However, CARs recognize all CD19 positive (pos) cells, and durable responses are linked to profound depletion of normal B cells. Here, we designed a strategy to specifically target patient B cells by utilizing the fact that T-cell receptors (TCRs), in contrast to CARs, are restricted by HLA. Two TCRs recognizing a peptide from CD20 (SLFLGILSV) in the context of foreign HLA-A*02:01 (CD20p/HLA-A2) were expressed as 2A-bicistronic constructs. T cells re-directed with the A23 and A94 TCR constructs efficiently recognized malignant HLA-A2(pos) B cells endogenously expressing CD20, including patient-derived follicular lymphoma and chronic lymphocytic leukemia (CLL) cells. In contrast, a wide range of HLA-A2(pos)CD20(neg) cells representing different tissue origins, and HLA-A2(neg)CD20(pos) cells, were not recognized. Cytotoxic T cells re-directed with CD20p/HLA-A2-specific TCRs or CD19 CARs responded with similar potencies to cells endogenously expressing comparable levels of CD20 and CD19. The CD20p/HLA-A2-specific TCRs recognized CD20p bound to HLA-A2 with high functional avidity. The results show that T cells expressing CD20p/HLA-A2-specific TCRs efficiently and specifically target B cells. When used in context of an HLA-haploidentical allogeneic stem cell transplantation where the donor is HLA-A2(neg) and the patient HLA-A2(pos), these T cells would selectively kill patient-derived B cells and allow reconstitution of the B-cell compartment with HLA-A2(neg) donor cells. These results should pave the way for clinical testing of T cells genetically engineered to target malignant B cells without permanent depletion of normal B cells.

The highly alloreactive nature of dual TCR T cells

PURPOSE OF REVIEW

T cells can mediate allograft rejection and graft-versus-host disease (GVHD), but are necessary for tolerance and protective immunity. Identifying T-cell populations differentially responsible for these effects has been a goal in transplant research. This review describes investigation of a small subset of T cells naturally predisposed toward alloreactivity, cells expressing two T-cell receptors (TCRs).

RECENT FINDINGS

Rare peripheral T cells express two αβTCRs. Their impact on T-cell development and function has been uncertain. Recent work demonstrates an important role for these cells in mouse models and human hematopoietic stem cell transplant patients with acute GVHD. Dual receptor T cells are preferentially activated and expanded in vitro and in vivo by allogeneic stimulation. Genetic elimination of dual TCR expression results in loss of approximately half of the alloreactive repertoire and impedes the earliest steps of GVHD.

SUMMARY

Identification of dual TCR T cells as predisposed to alloreactivity provides an opportunity to examine responses limiting transplantation. Continued investigation will reveal significant fundamental features of T-cell alloreactivity and important information about the earliest events determining allograft rejection and self-tolerance.

Transgenic antigen-specific, HLA-A*02:01-allo-restricted cytotoxic T cells recognize tumor-associated target antigen STEAP1 with high specificity

Pediatric cancers, including Ewing sarcoma (ES), are only weakly immunogenic and the tumor-patients' immune system often is devoid of effector T cells for tumor elimination. Based on expression profiling technology, targetable tumor-associated antigens (TAA) are identified and exploited for engineered T-cell therapy. Here, the specific recognition and lytic potential of transgenic allo-restricted CD8(+) T cells, directed against the ES-associated antigen 6-transmembrane epithelial antigen of the prostate 1 (STEAP1), was examined. Following repetitive STEAP1(130) peptide-driven stimulations with HLA-A*02:01(+) dendritic cells (DC), allo-restricted HLA-A*02:01(-) CD8(+) T cells were sorted with HLA-A*02:01/peptide multimers and expanded by limiting dilution. After functional analysis of suitable T cell clones via ELISpot, flow cytometry and xCELLigence assay, T cell receptors' (TCR) α- and β-chains were identified, cloned into retroviral vectors, codon optimized, transfected into HLA-A*02:01(-) primary T cell populations and tested again for specificity and lytic capacity in vitro and in a Rag2(-/-)γc(-/-) mouse model. Initially generated transgenic T cells specifically recognized STEAP1(130)-pulsed or transfected cells in the context of HLA-A*02:01 with minimal cross-reactivity as determined by specific interferon-γ (IFNγ) release, lysed cells and inhibited growth of HLA-A*02:01(+) ES lines more effectively than HLA-A*02:01(-) ES lines. In vivo tumor growth was inhibited more effectively with transgenic STEAP1(130)-specific T cells than with unspecific T cells. Our results identify TCRs capable of recognizing and inhibiting growth of STEAP1-expressing HLA-A*02:01(+) ES cells in vitro and in vivo in a highly restricted manner. As STEAP1 is overexpressed in a wide variety of cancers, we anticipate these STEAP1-specific TCRs to be potentially useful for immunotherapy of other STEAP1-expressing tumors.

Human leukocyte antigen supertype matching after myeloablative hematopoietic cell transplantation with 7/8 matched unrelated donor allografts: a report from the Center for International Blood and Marrow Transplant Research

The diversity of the human leukocyte antigen (HLA) class I and II alleles can be simplified by consolidating them into fewer supertypes based on functional or predicted structural similarities in epitope-binding grooves of HLA molecules. We studied the impact of matched and mismatched HLA-A (265 versus 429), -B (230 versus 92), -C (365 versus 349), and -DRB1 (153 versus 51) supertypes on clinical outcomes of 1934 patients with acute leukemias or myelodysplasia/myeloproliferative disorders. All patients were reported to the Center for International Blood and Marrow Transplant Research following single-allele mismatched unrelated donor myeloablative conditioning hematopoietic cell transplantation. Single mismatched alleles were categorized into six HLA-A (A01, A01A03, A01A24, A02, A03, A24), six HLA-B (B07, B08, B27, B44, B58, B62), two HLA-C (C1, C2), and five HLA-DRB1 (DR1, DR3, DR4, DR5, DR9) supertypes. Supertype B mismatch was associated with increased risk of grade II-IV acute graft-versus-host disease (hazard ratio =1.78, P=0.0025) compared to supertype B match. Supertype B07-B44 mismatch was associated with a higher incidence of both grade II-IV (hazard ratio=3.11, P=0.002) and III-IV (hazard ratio=3.15, P=0.01) acute graft-versus-host disease. No significant associations were detected between supertype-matched versus -mismatched groups at other HLA loci. These data suggest that avoiding HLA-B supertype mismatches can mitigate the risk of grade II-IV acute graft-versus-host disease in 7/8-mismatched unrelated donor hematopoietic cell transplantation when multiple HLA-B supertype-matched donors are available. Future studies are needed to define the mechanisms by which supertype mismatching affects outcomes after alternative donor hematopoietic cell transplantation.

A "hotspot" for autoimmune T cells in type 1 diabetes

The ability of a single T cell antigen receptor (TCR) to cross-react with multiple antigens allows the finite number of T cells within an organism to respond to the compendium of pathogen challenges faced during a lifetime. Effective immune surveillance, however, comes at a price. TCR cross-reactivity can allow molecular mimics to spuriously activate autoimmune T cells; it also underlies T cell rejection of organ transplants and drives graft-versus-host disease. In this issue of the JCI, Cole and colleagues provide insight into how an insulin-reactive T cell cross-reacts with pathogen-derived antigens by focusing on a limited portion of the peptides to provide a hotspot for binding. These findings dovetail with recent studies of alloreactive and autoimmune TCRs and suggest that the biochemical principles that govern conventional protein-protein interactions may allow the specificity and cross-reactivity profiles of T cells to be predicted.

Translational Implications for Off-the-shelf Immune Cells Expressing Chimeric Antigen Receptors

Chimeric antigen receptor (CAR) endows specificity to T-cells independent of human leukocyte antigen (HLA). This enables one immunoreceptor to directly target the same surface antigen on different subsets of tumor cells from multiple HLA-disparate recipients. Most approaches manufacture individualized CAR(+)T-cells from the recipient or HLA-compatible donor, which are revealing promising clinical results. This is the impetus to broaden the number of patients eligible to benefit from adoptive immunotherapy such as to infuse third-party donor derived CAR(+)T-cells. This will overcome issues associated with (i) time to manufacture T-cells, (ii) cost to generate one product for one patient, (iii) inability to generate a product from lymphopenic patients or patient's immune cells fail to complete the manufacturing process, and (iv) heterogeneity of T-cell products produced for or from individual recipients. Establishing a biobank of allogeneic genetically modified immune cells from healthy third-party donors, which are cryopreserved and validated in advance of administration, will facilitate the centralizing manufacturing and widespread distribution of CAR(+)T-cells to multiple points-of-care in a timely manner. To achieve this, it is necessary to engineer an effective strategy to avoid deleterious allogeneic immune responses leading to toxicity and rejection. We review the strategies to establish "off-the-shelf" donor-derived biobanks for human application of CAR(+)T-cells as a drug.

Bone Marrow GvHD after Allogeneic Hematopoietic Stem Cell Transplantation

The bone marrow is the origin of all hematopoietic lineages and an important homing site for memory cells of the adaptive immune system. It has recently emerged as a graft-versus-host disease (GvHD) target organ after allogeneic stem cell transplantation (alloHSCT), marked by depletion of both hematopoietic progenitors and niche-forming cells. Serious effects on the restoration of hematopoietic function and immunological memory are common, especially in patients after myeloablative conditioning therapy. Cytopenia and durable immunodeficiency caused by the depletion of hematopoietic progenitors and destruction of bone marrow niches negatively influence the outcome of alloHSCT. The complex balance between immunosuppressive and cell-depleting treatments, GvHD and immune reconstitution, as well as the desirable graft-versus-tumor (GvT) effect remains a great challenge for clinicians.

Human periodontal ligament stem cells suppress T-cell proliferation via down-regulation of non-classical major histocompatibility complex-like glycoprotein CD1b on dendritic cells

BACKGROUND AND OBJECTIVE

Periodontal ligament stem cells (PDLSCs) from the periodontal ligament tissue were recently identified as mesenchymal stem cells (MSCs). The capabilities of PDLSCs in periodontal tissue or bone regeneration have been reported, but their immunomodulatory role in T-cell immune responses via dendritic cells (DCs), known as the most potent antigen-presenting cell, has not been studied. The aim of this study is to understand the immunological function of homogeneous human STRO-1⁺ CD146⁺ PDLSCs in DC-mediated T-cell immune responses to modulate the periodontal disease process.

MATERIAL AND METHODS

We utilized highly purified (> 95%) human STRO-1⁺ CD146⁺ PDLSCs and human bone marrow mesenchymal stem cells (BMSCs). Each stem cell was co-cultured with human monocyte-derived DCs in the presence of lipopolysaccharide isolated from Porphyromonas gingivalis, a major pathogenic bacterium responsible for periodontal disease, in vitro to examine the immunological effect of each stem cell on DCs and DC-mediated T-cell proliferation.

RESULTS

We discovered that STRO-1⁺ CD146⁺ PDLSCs, as well as BMSCs, significantly decreased the level of non-classical major histocompatibility complex glycoprotein CD1b on DCs, resulting in defective T-cell proliferation, whereas most human leukocyte antigens and the co-stimulatory molecules CD80 and CD86 in/on DCs were not significantly affected by the presence of BMSCs or STRO-1⁺ CD146⁺ PDLSCs.

CONCLUSIONS

This study unveiled an immunomodulatory role of STRO-1⁺ CD146⁺ PDLSCs in negatively regulating DC-mediated T-cell immune responses, demonstrating their potential to be utilized in promising new stem cell therapies.

A long journey coming to fruition: In sight of the preselection T-cell repertoire

In addition to MHC restriction and its structural correlate the recognition of an MHC-peptide complex by the TCR, T-cell reactivity is constrained by positive and negative selection in the thymus. While mouse genetic studies have provided compelling evidence for both processes, the actual impact of selection on the mature T-cell repertoire has remained difficult to assess, in particular because it has so far not been possible to follow the intrathymic differentiation of antigen-specific T cells carrying endogenous TCR specificities. In this issue of the European Journal of Immunology, Hesnard et al. [Eur. J. Immunol. 2016. 46: 560-569] report the detection of human antigen-specific immature thymocytes, thereby opening the way to addressing these questions. Here, we discuss the implications of this technological advance.

IL-1 Receptor Signaling on Graft Parenchymal Cells Regulates Memory and De Novo Donor-Reactive CD8 T Cell Responses to Cardiac Allografts

Reperfusion of organ allografts induces a potent inflammatory response that directs rapid memory T cell, neutrophil, and macrophage graft infiltration and their activation to express functions mediating graft tissue injury. The role of cardiac allograft IL-1 receptor (IL-1R) signaling in this early inflammation and the downstream primary alloimmune response was investigated. When compared with complete MHC-mismatched wild-type cardiac allografts, IL-1R(-/-) allografts had marked decreases in endogenous memory CD8 T cell and neutrophil infiltration and expression of proinflammatory mediators at early times after transplant, whereas endogenous memory CD4 T cell and macrophage infiltration was not decreased. IL-1R(-/-) allograft recipients also had marked decreases in de novo donor-reactive CD8, but not CD4, T cell development to IFN-γ-producing cells. CD8 T cell-mediated rejection of IL-1R(-/-) cardiac allografts took 3 wk longer than wild-type allografts. Cardiac allografts from reciprocal bone marrow reconstituted IL-1R(-/-)/wild-type chimeric donors indicated that IL-1R signaling on graft nonhematopoietic-derived, but not bone marrow-derived, cells is required for the potent donor-reactive memory and primary CD8 T cell alloimmune responses observed in response to wild-type allografts. These studies implicate IL-1R-mediated signals by allograft parenchymal cells in generating the stimuli-provoking development and elicitation of optimal alloimmune responses to the grafts.

HLA mismatching as a strategy to reduce relapse after alternative donor transplantation

Human leukocyte antigen (HLA) mismatches are targets of alloreactive T cells, mediators of graft-versus-leukemia (GvL) and graft-versus-host disease (GvHD) after alternative donor transplantation. Exploitation of HLA mismatching in order to reduce relapse is hampered by necessary interventions aimed at controlling GvHD on the one hand, and by the possibility of immune escape through selective loss of mismatched HLA in relapsing leukemia on the other. Retrospective studies reporting the impact of HLA mismatches on post-transplant relapse need to be interpreted with caution, due to many confounding factors, including disease and use of T-cell depletion, and to be constantly updated to the rapidly changing clinical protocols. Current evidence suggests similar relapse rates for 8/8, 7/8 HLA-matched unrelated, T-cell-replete haploidentical and umbilical cord blood transplantation; however, investigations of locus-specific effects are still scarce in the latter two settings. In unrelated transplantation, a specific role for mismatches at HLA-C and HLA-DPB1, and therein of permissive mismatches defined on the basis of T-cell alloreactivity and/or expression levels, in reducing relapse has been demonstrated in independent studies. This observation suggests new approaches to utilize HLA matching in unrelated donor searches, and the need for further research in the field.

Xenotransplantation of Human Cardiomyocyte Progenitor Cells Does Not Improve Cardiac Function in a Porcine Model of Chronic Ischemic Heart Failure. Results from a Randomized, Blinded, Placebo Controlled Trial

BACKGROUND

Recently cardiomyocyte progenitor cells (CMPCs) were successfully isolated from fetal and adult human hearts. Direct intramyocardial injection of human CMPCs (hCMPCs) in experimental mouse models of acute myocardial infarction significantly improved cardiac function compared to controls.

AIM

Here, our aim was to investigate whether xenotransplantation via intracoronary infusion of fetal hCMPCs in a pig model of chronic myocardial infarction is safe and efficacious, in view of translation purposes.

METHODS & RESULTS

We performed a randomized, blinded, placebo controlled trial. Four weeks after ischemia/reperfusion injury by 90 minutes of percutaneous left anterior descending artery occlusion, pigs (n = 16, 68.5 ± 5.4 kg) received intracoronary infusion of 10 million fetal hCMPCs or placebo. All animals were immunosuppressed by cyclosporin (CsA). Four weeks after infusion, endpoint analysis by MRI displayed no difference in left ventricular ejection fraction, left ventricular end diastolic and left ventricular end systolic volumes between both groups. Serial pressure volume (PV-)loop and echocardiography showed no differences in functional parameters between groups at any timepoint. Infarct size at follow-up, measured by late gadolinium enhancement MRI showed no difference between groups. Intracoronary pressure and flow measurements showed no signs of coronary obstruction 30 minutes after cell infusion. No premature death occurred in cell treated animals.

CONCLUSION

Xenotransplantation via intracoronary infusion of hCMPCs is feasible and safe, but not associated with improved left ventricular performance and infarct size compared to placebo in a porcine model of chronic myocardial infarction.

Matched Peptides: Tuning Matched Molecular Pair Analysis for Biopharmaceutical Applications

Biopharmaceuticals hold great promise for the future of drug discovery. Nevertheless, rational drug design strategies are mainly focused on the discovery of small synthetic molecules. Herein we present matched peptides, an innovative analysis technique for biological data related to peptide and protein sequences. It represents an extension of matched molecular pair analysis toward macromolecular sequence data and allows quantitative predictions of the effect of single amino acid substitutions on the basis of statistical data on known transformations. We demonstrate the application of matched peptides to a data set of major histocompatibility complex class II peptide ligands and discuss the trends captured with respect to classical quantitative structure–activity relationship approaches as well as structural aspects of the investigated protein–peptide interface. We expect our novel readily interpretable tool at the interface of cheminformatics and bioinformatics to support the rational design of biopharmaceuticals and give directions for further development of the presented methodology.

Tolerance induction using nanoparticles bearing HY peptides in bone marrow transplantation

Allogeneic cell therapies have either proven effective or have great potential in numerous applications, though the required systemic, life-long immunosuppression presents significant health risks. Inducing tolerance to allogeneic cells offers the potential to reduce or eliminate chronic immunosuppression. Herein, we investigated antigen-loaded nanoparticles for their ability to promote transplant tolerance in the minor histocompatibility antigen sex-mismatched C57BL/6 model of bone marrow transplantation. In this model, the peptide antigens Dby and Uty mediate rejection of male bone marrow transplants by female CD4+ and CD8+ T cells, respectively, and we investigated the action of nanoparticles on these T cell subsets. Antigens were coupled to or encapsulated within poly(lactide-co-glycolide) (PLG) nanoparticles with an approximate diameter of 500 nm. Delivery of the CD4-encoded Dby epitope either coupled to or encapsulated within PLG particles prevented transplant rejection, promoted donor-host chimerism, and suppressed proliferative and IFN-γ responses in tolerized recipients. Nanoparticles modified with the Uty peptide did not induce tolerance. The dosing regimen was investigated with Dby coupled particles, and a single dose delivered the day after bone marrow transplant was sufficient for tolerance induction. The engraftment of cells was significantly affected by PD-1/PDL-1 costimluation, as blockade of PD-1 reduced engraftment by ∼50%. In contrast, blockade of regulatory T cells did not impact the level of chimerism. The delivery of antigen on PLG nanoparticles promoted long-term engraftment of bone marrow in a model with a minor antigen mismatch in the absence of immunosuppression, and this represents a promising platform for developing a translatable, donor-specific tolerance strategy.

T-cell receptor gene therapy--ready to go viral?

T lymphocytes can be redirected to recognize a tumor target and harnessed to combat cancer by genetic introduction of T-cell receptors of a defined specificity. This approach has recently mediated encouraging clinical responses in patients with cancers previously regarded as incurable. However, despite the great promise, T-cell receptor gene therapy still faces a multitude of obstacles. Identification of epitopes that enable effective targeting of all the cells in a heterogeneous tumor while sparing normal tissues remains perhaps the most demanding challenge. Experience from clinical trials has revealed the dangers associated with T-cell receptor gene therapy and highlighted the need for reliable preclinical methods to identify potentially hazardous recognition of both intended and unintended epitopes in healthy tissues. Procedures for manufacturing large and highly potent T-cell populations can be optimized to enhance their antitumor efficacy. Here, we review the current knowledge gained from preclinical models and clinical trials using adoptive transfer of T-cell receptor-engineered T lymphocytes, discuss the major challenges involved and highlight potential strategies to increase the safety and efficacy to make T-cell receptor gene therapy a standard-of-care for large patient groups.

Machine Learning Methods for Predicting HLA-Peptide Binding Activity

As major histocompatibility complexes in humans, the human leukocyte antigens (HLAs) have important functions to present antigen peptides onto T-cell receptors for immunological recognition and responses. Interpreting and predicting HLA–peptide binding are important to study T-cell epitopes, immune reactions, and the mechanisms of adverse drug reactions. We review different types of machine learning methods and tools that have been used for HLA–peptide binding prediction. We also summarize the descriptors based on which the HLA–peptide binding prediction models have been constructed and discuss the limitation and challenges of the current methods. Lastly, we give a future perspective on the HLA–peptide binding prediction method based on network analysis.

Identification of a naturally processed HLA-Cw7-binding peptide that cross-reacts with HLA-A24-restricted ovarian cancer-specific CTLs

Here, we describe an human leukocyte antigen (HLA)-A*24:02-restricted cytotoxic T-lymphocyte (CTL) clone, 1G3, established from naïve CD8(+) T-lymphocytes obtained from a healthy donor stimulated with HLA-modified TOV21G, an ovarian cancer cell line. The 1G3 clone responds not only to ovarian cancer cells in the context of HLA-A*24:02 but also to allogeneic HLA-Cw*07:02 molecules through cross-reactive T-cell receptor recognition. Expression screening using a complementary DNA library constructed from TOV21G messenger RNA revealed that this alloreactivity was mediated through the nine-mer peptide VRTPYTMSY, derived from RNA-binding motif protein 4. To our knowledge, this study presents the first example of the allorecognition of an HLA-Cw molecule by HLA-A-restricted T-cells, thereby revealing a naturally processed epitope peptide. These findings provide the structural bases for the allorecognition of human T-cells. In addition, this study suggests that unexpected alloresponses occur in certain HLA combinations, and further study is needed to understand the mechanisms of alloreactivity for better prediction of alloresponses in clinical settings.

Self-recognition drives the preferential accumulation of promiscuous CD4(+) T-cells in aged mice

T-cell recognition of self and foreign peptide antigens presented in major histocompatibility complex molecules (pMHC) is essential for life-long immunity. How the ability of the CD4⁺ T-cell compartment to bind self- and foreign-pMHC changes over the lifespan remains a fundamental aspect of T-cell biology that is largely unexplored. We report that, while old mice (18–22 months) contain fewer CD4⁺ T-cells compared with adults (8–12 weeks), those that remain have a higher intrinsic affinity for self-pMHC, as measured by CD5 expression. Old mice also have more cells that bind individual or multiple distinct foreign-pMHCs, and the fold increase in pMHC-binding populations is directly related to their CD5 levels. These data demonstrate that the CD4⁺ T-cell compartment preferentially accumulates promiscuous constituents with age as a consequence of higher affinity T-cell receptor interactions with self-pMHC.

DOI:http://dx.doi.org/10.7554/eLife.05949.001

The immune system's T cells help the body to recognize and destroy harmful pathogens, such as viruses and bacteria. T cells ‘remember’ immunity-inducing fragments, called antigens, from the pathogens they have encountered. This memory then allows the immune system to quickly fend off infections if those pathogens, or even related pathogens, invade again. Vaccines exploit the ability to form immunological memory by exposing the body to harmless forms of the pathogen, or even just particular antigens from it. This allows the T cells to learn how to identify the pathogen without any risk of illness.

Vaccines have been extremely successful and have helped to virtually eliminate some diseases. However, for reasons that are unclear, the immune systems of older adults become less functional, so vaccines often lose their effectiveness. Paradoxically, as people age T cells become more likely to attack the body's cells, causing autoimmune diseases like arthritis. Understanding what happens to aging T cells to cause these immune changes may help scientists design vaccines that remain effective as people age.

Little is known about what happens to a particular type of T cell—the CD4⁺ T cells—as people age, even though this population plays a critical role in providing other immune cells with detailed instructions on when and how to fight a pathogen. Now, Deshpande et al. show that CD4⁺ T cells undergo a remarkable set of changes in aging mice. Mice that are nearing the end of their natural lifespan have fewer CD4⁺ T cells than younger mice. However, those CD4⁺ T cells that remain are more likely than CD4⁺ T cells from younger mice to be able to recognize multiple antigens. This increase in the proportion of multitasking CD4⁺ T cells corresponds with an increased tendency of these cells to bind to the body's own cells. If similar changes occur in older people, this may help explain some age-related autoimmune diseases. Yet, the relationship between the increase in multitasking CD4⁺ T cells and the decrease in immune function with aging remains to be fully explored.

The challenge for scientists now is to determine how these age-related changes in CD4⁺ T cells affect immune responses to vaccines or pathogens in older individuals. One implication of this work is that CD4⁺ T cell responses may be too robust and out of balance with other arms of the immune system. This could even lead to conditions such as autoimmunity. Alternatively, while there may be more CD4⁺ T cells that can multitask by recognizing multiple antigens, their ability to respond appropriately to infections or vaccinations may be diminished. What is clear from the work of Deshpande et al. is that the rules that have been defined for immunity in adults change with aging. The rules that govern immunity in the elderly must be more clearly defined to realize the goal of designing immunotherapies, such as vaccines, that provide protection throughout the lifespan.

DOI:http://dx.doi.org/10.7554/eLife.05949.002

Association between a gain-of-function variant of PTPN22 and rejection in liver transplantation

BACKGROUND

The protein tyrosine phosphatase nonreceptor 22 gene (PTPN22) encodes a strong T-cell regulator called lymphoid protein tyrosine phosphatase. Previously, PTPN22 was described as a susceptibility gene for autoimmunity because it contains single nucleotide polymorphisms (SNPs) associated with several autoimmune diseases. One SNP (rs2476601; 1858G>A) has emerged as a particularly potent risk factor for autoimmunity. We address the question whether PTPN22 polymorphisms are also associated with acute rejection after liver transplantation.

METHODS

We investigated the influence of six PTPN22 SNPs on the susceptibility to acute liver allograft rejection. Consequently, we carried out a retrospective study genotyping 345 German liver recipients at six SNP loci, which include rs2488457 (-1123G>C), rs33996649 (788C>T), rs2476601 (1858G>A), rs1310182 (-852A>G), rs1217388 (-2200G>A), rs3789604 (64434T>G). Our study enrolled 165 recipients who did not develop rejection, 123 who showed one rejection episode, and 57 patients who suffered from multiple acute rejections after transplantation.

RESULTS

The 1858A allele containing genotypes (GA+AA) and the 1858A allele had a significantly higher frequency in the group of patients with multiple rejection episodes (35.1% and 18.4%) compared to rejection-free patients (15.8% and 7.9%; P=0.022 and 0.023). In contrast, we could not detect any association between rejection and the other tested SNPs. Additionally, we identified one haplotype contributing to risk of multiple rejections, however, exhibiting no stronger impact than the 1858A allele alone.

CONCLUSION

We conclude that the 1858G>A SNP may confer susceptibility to multiple acute liver transplant rejections in the German population.

Tempering allorecognition to induce transplant tolerance with chemically modified apoptotic donor cells

The development of organ transplantation as a therapy for end-stage organ failure is among the most significant achievements of 20th century medicine, but chronic rejection remains a barrier to achieving long-term success. Current therapeutic regimens consist of immunosuppressive drugs that are efficient at delaying rejection but are associated with significant risks such as opportunistic infections, toxicity, and malignancy. Thus, the induction of specific immune tolerance to transplant antigens is the coveted aim of researchers. The use of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (ECDI)-treated, autoantigen-coupled syngeneic leukocytes has been developed as a specific immunotherapy in preclinical models of autoimmunity and is currently in a phase II clinical trial for the treatment of multiple sclerosis. In this review, we discuss the use of allogeneic ECDI-treated apoptotic donor leukocytes (allo-ECDI-SP) as a strategy for inducing antigen-specific tolerance in allogeneic transplantation. Allo-ECDI-SP therapy induces long-term systemic immune tolerance to transplant antigens by subverting alloimmune recognition and exploiting apoptotic cell uptake pathways to recapitulate innate mechanisms of peripheral tolerance. Lastly, we discuss potential indications and challenges for transitioning allo-ECDI-SP therapy into clinical practice.

Cellular and molecular targeting for nanotherapeutics in transplantation tolerance

The induction of donor-specific tolerance to transplanted cells and organs, while preserving immune function as a whole, remains a highly sought after and elusive strategy for overcoming transplant rejection. Tolerance necessitates modulating a diverse array of cell types that recognize and respond to alloantigens, including antigen presenting cells and T lymphocytes. Nanotherapeutic strategies that employ cellular and biomaterial engineering represent an emerging technology geared towards the goal of inducing transplant tolerance. Nanocarriers offer a platform for delivering antigens of interest to specific cell types in order to achieve tolerogenic antigen presentation. Furthermore, the technologies also provide an opportunity for local immunomodulation at the graft site. Nanocarriers delivering a combination of antigens and immunomodulating agents, such as rapamycin, provide a unique technology platform with the potential to enhance outcomes for the induction of transplant tolerance.

Generation of human memory stem T cells after haploidentical T-replete hematopoietic stem cell transplantation

Memory stem T cells (TSCM) have been proposed as key determinants of immunologic memory. However, their exact contribution to a mounting immune response, as well as the mechanisms and timing of their in vivo generation, are poorly understood. We longitudinally tracked TSCM dynamics in patients undergoing haploidentical hematopoietic stem cell transplantation (HSCT), thereby providing novel hints on the contribution of this subset to posttransplant immune reconstitution in humans. We found that donor-derived TSCM are highly enriched early after HSCT. We showed at the antigen-specific and clonal level that TSCM lymphocytes can differentiate directly from naive precursors infused within the graft and that the extent of TSCM generation might correlate with interleukin 7 serum levels. In vivo fate mapping through T-cell receptor sequencing allowed defining the in vivo differentiation landscapes of human naive T cells, supporting the notion that progenies of single naive cells embrace disparate fates in vivo and highlighting TSCM as relevant novel players in the diversification of immunological memory after allogeneic HSCT.