Their T Cell Receptor Research Articles

Chromium-51 (51Cr) Release Assay to Assess Human T Cells for Functional Avidity and Tumor Cell Recognition

Cytotoxic CD8+ T cells are able to specifically recognize and kill target cells through specific interaction between their T cell receptors (TCRs) and small immunogenic peptides (antigens) presented by major histocompatibility complex (MHC) molecules. The antigen recognition capacity and in vitro lytic activity of antigen-specific cytotoxic T cells can be assessed functionally in the so-called chromium 51 (51Cr) release assay, which was developed almost 50 years ago in our institution (Brunner et al., 1968). Radioactively-labelled cells deficient for endogenous antigen presentation [e.g., transporter for antigen presentation (TAP)-deficient T2 cells] and stably transfected with the MHC of interest (e.g., HLA-A2+) are typically used as targets during this 4h assay. Alternatively, 51Cr-labelled virus-infected or tumor cell lines presenting immunogenic antigens endogenously can serve as target cells (e.g., for the assessment of tumor recognition).In a peptide titration assay (section A), radioactively labelled target cells are pulsed with a serial dilution of the antigenic peptide and incubated at an effector (e.g., a CD8+ T cell clone) to target (51Cr -T2 cells) ratio (E:T) of 10:1 in a 96-well V-bottom plate for 4 h at 37 °C. In a tumor killing assay (section B), cytotoxic CD8+ effector cells are incubated at different ratios with the 51Cr-labelled target cell line (typically at E:T ratios of 30:1, 10:1, 3:1 and 1:1) in the presence or absence of the specific antigenic peptide (1 μM) and incubated for 4 h at 37 °C. At the end of the test, the amount of radioactivity release from the lysed target cells is determined in the supernatant using a liquid scintillation counter. The percentage of specific lysis, as well as the EC50 (i.e., 50% of maximal killing) and EMax values are then calculated, providing quantitative information about the antigen-specific functional avidity (i.e., the relative efficiency of T cell function based on antigen recognition via a defined TCR and maximal killing capacity of the analyzed T cells).

Editorial: CD1- and MR1-Restricted T Cells in Antimicrobial Immunity

The main function of the immune system is to protect the host against microbial pathogens and their deleterious products. Innate defense mechanisms quickly eliminate infectious intruders or keep them in check until highly specific adaptive responses that also give rise to immunological memory are launched. Major histocompatibility complex (MHC)-restricted T cells are key players of adaptive immunity. The remarkable diversity of their T cell receptors (TCRs) allows for specific recognition of peptides derived from virtually all protein antigens (Ags) including those harbored or even modified by the most vicious pathogens encountered over one’s lifetime. Conventional T cells sense and respond to pathogen-derived peptides complexed with polymorphic MHC molecules. This is called the rule of MHC restriction (1).

Identifying Individual T Cell Receptors of Optimal Avidity for Tumor Antigens.

Cytotoxic T cells recognize, via their T cell receptors (TCRs), small antigenic peptides presented by the major histocompatibility complex (pMHC) on the surface of professional antigen-presenting cells and infected or malignant cells. The efficiency of T cell triggering critically depends on TCR binding to cognate pMHC, i.e., the TCR–pMHC structural avidity. The binding and kinetic attributes of this interaction are key parameters for protective T cell-mediated immunity, with stronger TCR–pMHC interactions conferring superior T cell activation and responsiveness than weaker ones. However, high-avidity TCRs are not always available, particularly among self/tumor antigen-specific T cells, most of which are eliminated by central and peripheral deletion mechanisms. Consequently, systematic assessment of T cell avidity can greatly help distinguishing protective from non-protective T cells. Here, we review novel strategies to assess TCR–pMHC interaction kinetics, enabling the identification of the functionally most-relevant T cells. We also discuss the significance of these technologies in determining which cells within a naturally occurring polyclonal tumor-specific T cell response would offer the best clinical benefit for use in adoptive therapies, with or without T cell engineering.

Immunological Aspects in Oncology--Circulating γδ T Cells

γδ T cells present a minor population of the T cell family which basically differs in construction of their T cell receptor (TCR). Thanks to the features of γδ TCR, these cells can acquire unique effector functions and play a specific role (not only) in antitumor immune response. In this article, we describe the basic characteristics of this cell population and their connection to cancer. In the experimental part we performed exploratory analysis of circulating γδ T cells in reference population and comparison with melanoma and breast carcinoma patients. The median percentage of γδ T cells from all lymphocytes was 2.9% (interquartile range-IQR 1.7-4%). The median absolute numbers of γδ cells per liter of blood was 5.05×10(7) (IQR 2.9-7.84×10(7)). The median percentage of γδ cells between all CD3 T cells was 3.9% (IQR 2.3-5.6%). No correlation between γδ T cells levels and gender or age was observed in reference population. Detailed immunophenotyping was also conducted describing representation of memory subsets (using CD45RO and CD27 markers) and presence of surface markers HLADr, CD69, CD25, CD28, CCR7, CTLA 4, ICOS, PD 1L and PD 1 between γδ T cells of the controls and breast carcinoma patients. From this analysis, it is evident that γδ T cells do not represent a uniform population but they differ in surface markers as well as in their effector functions.

The Extended Family of CD1d-Restricted NKT Cells: Sifting through a Mixed Bag of TCRs, Antigens, and Functions.

Natural killer T (NKT) cells comprise a family of specialized T cells that recognize lipid antigens presented by CD1d. Based on their T cell receptor (TCR) usage and antigen specificities, CD1d-restricted NKT cells have been divided into two main subsets: type I NKT cells that use a canonical invariant TCR α-chain and recognize α-galactosylceramide (α-GalCer), and type II NKT cells that use a more diverse αβ TCR repertoire and do not recognize α-GalCer. In addition, α-GalCer-reactive NKT cells that use non-canonical αβ TCRs and CD1d-restricted T cells that use γδ or δ/αβ TCRs have recently been identified, revealing further diversity among CD1d-restricted T cells. Importantly, in addition to their distinct antigen specificities, functional differences are beginning to emerge between the different members of the CD1d-restricted T cell family. In this review, while using type I NKT cells as comparison, we will focus on type II NKT cells and the other non-invariant CD1d-restricted T cell subsets, and discuss our current understanding of the antigens they recognize, the formation of stimulatory CD1d/antigen complexes, the modes of TCR-mediated antigen recognition, and the mechanisms and consequences of their activation that underlie their function in antimicrobial responses, anti-tumor immunity, and autoimmunity.

Azacitidine improves the T-cell repertoire in patients with myelodysplastic syndromes and acute myeloid leukemia with multilineage dysplasia

Patients with myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) with multilineage dysplasia show several immunological abnormalities. In this clinical setting, by combining flow cytometry and CDR3 spectratyping we monitored the kinetic of the T-cell repertoire during Azacitidine treatment, in order to explore its potential ability to reverse the immune derangement typical of these disorders. We firstly demonstrated by flow cytometry an increase in both CD4+ and CD8+ T-cell frequencies after starting treatment. Moreover, when monitored by spectratyping our patients showed significant changes in their T-cell receptor (TCR) CDR3 profiles, which were much more evident in helper T-cells. In fact, the frequency of BV (beta variable) subfamilies showing a skewed CDR3 profile significantly decreased from baseline to the following evaluations in CD4+ T-cells (81% vs. 70%). This pattern was even more pronounced in patients responding to Azacitidine (90% vs. 61%). Our data show that the overall derangement of the T-cell repertoire detectable in patients with MDS and AML with multilineage dysplasia gradually improves during Azacitidine treatment. These findings therefore suggest that Azacitidine could be potentially able, not only to restore the hematopoietic function, but also to reverse the immune derangement typical of these hematologic disorders.

A single amino acid residue of CDR3β alters the antigenicity and autoreactivity of human invariant natural killer T cell receptors (IRM7P.707)

Abstract Detection of human invariant natural killer T (iNKT) cells relies on staining for their T cell receptor (TCR), invariant Vα24 TCRα chain paired with semi-variant Vβ11 TCRβ chain, or α-GalCer-CD1d tetramer. It has been assumed that all Vα24+ iNKT cells are stained with similar intensity by anti-Vα24 mAbs, clones C15 and 6B11, regardless of the hypervariable Vβ11 CDR3β sequences. By analyzing a large panel of autoreactive human iNKT TCRs, we found that TCRs encoding CASR at the start of CDR3β were stained with significantly lower intensity by C15 than those encoding CASS. Substitution of S to R at the fourth CDR3β residue was sufficient to diminish staining intensity by anti-Vα24 mAbs. Interestingly, the autoreactivity was also reduced in the TCRs encoding CASR. Importantly, α-GalCer tetramer positive population of human primary T cells presented low and high intensity subsets when stained with anti-Vα24 mAbs. Vβ11 TCRβ chains were cloned from each sorted population, and the Vα24 low population contained a significantly higher frequency of Vβ11 TCRs encoding CASR compared to the Vα24 high population. Therefore, human iNKT TCRs encoding CASR may falsely be negative when stained with anti-Vα24 mAbs, which underestimate the frequency of bona fide Vα24+ iNKT cells. Our data demonstrate that the fourth CDR3β amino acid residue affects iNKT TCR autoreactivity and binding of anti-Vα24 mAbs, suggesting that the CDR3β sequence alters the structural conformation of the Vα24 TCRα chain.

Engineering T Cell Receptors for Optimal Affinities and Desired Specificities

T cells, via their T‐cell receptors (TCRs), evolved to target intracellular antigenic peptides, as cell‐surface complexes with MHC products. While the structural and biochemical characteristics of the TCR:pepMHC interaction have been well studied, there remains interest in understanding the molecular basis of peptide specificity exhibited by TCRs. Furthermore, understanding the binding properties of the TCR that can optimally mediate the activity of T cells is important, especially as adoptive T cell therapies have become more feasible. We have used various strategies to engineer the binding properties of TCRs for adoptive T‐cell therapies, either as full‐length heterodimeric TCRs or as CAR‐like signaling receptors. TCR engineering has been performed using yeast display of single‐chain TCRs in order to generate affinity‐matured variants. In addition, we recently used synthetic TCR libraries in key CDR residues to convert the specificity of a TCR from a virus peptide to a cancer peptide. This approach allows the de novo isolation of TCRs with desired specificities using completely in vitro, directed evolution approaches. Various aspects of the engineering, specificity, and activity mediated by these receptors will be presented.

Engineering T-Cell Specificity Genetically to Generate Anti-melanoma Reactivity.

Melanoma tumors are known to harbor a high number of mutations leading to the expression of neo-antigens which can be recognized by the patient adaptive immune system. In this regard, immunotherapies involving adoptive cell transfer (ACT) of tumor-specific T-cells constitute a promising approach to treat melanoma. However, these cells do not always preexist in the patient or are difficult to isolate and/or expand. Thus, as the specificity of T-lymphocytes is determined by their T-cell receptor (TCR), it is possible to convert peripheral T-cells into cancer specific lymphocytes by transducing them to express a receptor that recognizes a defined tumor epitope. To this end, retroviral vectors can be used to efficiently transduce actively dividing cells such as proliferating T cells, while being relatively safe to the user. As we show herein, this approach is powerful and can be easily implemented, paving the way to the development of advanced research tools and potent clinical immunotherapeutic strategies.

Adoptive immunotherapy for hematological malignancies using T cells gene-modified to express tumor antigen-specific receptors.

Accumulating clinical evidence suggests that adoptive T-cell immunotherapy could be a promising option for control of cancer; evident examples include the graft-vs-leukemia effect mediated by donor lymphocyte infusion (DLI) and therapeutic infusion of ex vivo-expanded tumor-infiltrating lymphocytes (TIL) for melanoma. Currently, along with advances in synthetic immunology, gene-modified T cells retargeted to defined tumor antigens have been introduced as “cellular drugs”. As the functional properties of the adoptive immune response mediated by T lymphocytes are decisively regulated by their T-cell receptors (TCRs), transfer of genes encoding target antigen-specific receptors should enable polyclonal T cells to be uniformly redirected toward cancer cells. Clinically, anticancer adoptive immunotherapy using genetically engineered T cells has an impressive track record. Notable examples include the dramatic benefit of chimeric antigen receptor (CAR) gene-modified T cells redirected towards CD19 in patients with B-cell malignancy, and the encouraging results obtained with TCR gene-modified T cells redirected towards NY-ESO-1, a cancer-testis antigen, in patients with advanced melanoma and synovial cell sarcoma. This article overviews the current status of this treatment option, and discusses challenging issues that still restrain the full effectiveness of this strategy, especially in the context of hematological malignancy.

Lentiviral Nef proteins manipulate T cells in a subset-specific manner.

The role of the accessory viral Nef protein as a multifunctional manipulator of the host cell that is required for effective replication of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) in vivo is well established. It is unknown, however, whether Nef manipulates all or just specific subsets of CD4(+) T cells, which are the main targets of virus infection and differ substantially in their state of activation and importance for a functional immune system. Here, we analyzed the effect of Nef proteins differing in their T cell receptor (TCR)-CD3 downmodulation function in HIV-infected human lymphoid aggregate cultures and peripheral blood mononuclear cells. We found that Nef efficiently downmodulates TCR-CD3 in naive and memory CD4(+) T cells and protects the latter against apoptosis. In contrast, highly proliferative CD45RA(+) CD45RO(+) CD4(+) T cells were main producers of infectious virus but largely refractory to TCR-CD3 downmodulation. Such T cell subset-specific differences were also observed for Nef-mediated modulation of CD4 but not for enhancement of virion infectivity. Our results indicate that Nef predominantly modulates surface receptors on CD4(+) T cell subsets that are not already fully permissive for viral replication. As a consequence, Nef-mediated downmodulation of TCR-CD3, which distinguishes most primate lentiviruses from HIV type 1 (HIV-1) and its vpu-containing simian precursors, may promote a selective preservation of central memory CD4(+) T cells, which are critical for the maintenance of a functional immune system. The Nef proteins of human and simian immunodeficiency viruses manipulate infected CD4(+) T cells in multiple ways to promote viral replication and immune evasion in vivo. Here, we show that some effects of Nef are subset specific. Downmodulation of CD4 and TCR-CD3 is highly effective in central memory CD4(+) T cells, and the latter Nef function protects this T cell subset against apoptosis. In contrast, highly activated/proliferating CD4(+) T cells are largely refractory to receptor downmodulation but are main producers of infectious HIV-1. Nef-mediated enhancement of virion infectivity, however, was observed in all T cell subsets examined. Our results provide new insights into how primate lentiviruses manipulate their target cells and suggest that the TCR-CD3 downmodulation function of Nef may promote a selective preservation of memory CD4(+) T cells, which are critical for immune function, but has little effect on activated/proliferating CD4(+) T cells, which are the main targets for viral replication.

CD8 T cells in innate immune responses: using STAT4-dependent but antigen-independent pathways to gamma interferon during viral infection.

ABSTRACTThe cytokine gamma interferon (IFN-γ), with antimicrobial and immunoregulatory functions, can be produced by T cells following stimulation through their T cell receptors (TCRs) for antigen. The innate cytokines type 1 IFNs and interleukin-12 (IL-12) can also stimulate IFN-γ production by natural killer (NK) but not naive T cells. High basal expression of signal transducer and activator of transcription 4 (STAT4), used by type 1 IFN and IL-12 to induce IFN-γ as well as CD25, contributes to the NK cell responses. During acute viral infections, antigen-specific CD8 T cells are stimulated to express elevated STAT4 and respond to the innate factors with IFN-γ production. Little is known about the requirements for cytokine compared to TCR stimulation. Primary infections of mice with lymphocytic choriomeningitis virus (LCMV) demonstrated that although the elicited antigen-specific CD8 T cells acquired STAT4-dependent innate cytokine responsiveness for IFN-γ and CD25 induction ex vivo, TCR stimulation induced these through STAT4-independent pathways. During secondary infections, LCMV-immune CD8 T cells had STAT4-dependent IFN-γ expression at times of innate cytokine induction but subsequently expanded through STAT4-independent pathways. At times of innate cytokine responses during infection with the antigen-distinct murine cytomegalovirus virus (MCMV), NK and LCMV-immune CD8 T cells both had activation of pSTAT4 and IFN-γ. The T cell IFN-γ response was STAT4 and IL-12 dependent, but antigen-dependent expansion was absent. By dissecting requirements for STAT4 and antigen, this work provides novel insights into the endogenous regulation of cytokine and proliferative responses and demonstrates conditioning of innate immunity by experience.

CD1d lipid-antigen recognition by the γδ TCR

The T lymphocytes repertoire is divided into two major lineages, αβ and γδ T cells, which are defined by their T cell receptor (TCR) gene-segment usage. To date, the key discoveries on human CD1d restricted T cells have focussed on the type I Natural Killer T cells (NKT) subset that express an invariant TCR α chain (Vα24Jα18) which pairs with a β chain (Vβ11). The structural basis for the recognition of CD1d-lipid antigen by type I NKT cells is also now well established [1, 2]. However, there are other subsets of NKT cells that exhibit reactivity towards lipid-antigen presenting molecules (CD1d) but that do no express the typical Vα24Jα18 TCR. We identify human NKT cell subsets that express Vδ1+ γδ TCRs that recognize CD1d presenting the lipid-antigen α-galactosylceramide (α-Galcer). Here, we describe the first crystal structure of a CD1d/γδ TCR ternary complex [3] and provide structural insights into the binding mode of a γδ TCR with CD1d-αGalcer. The γδ TCR binds orthogonally over the A' pocket of CD1d, that is in clear contrast with the typical type I parallel docking mode in which the αβ TCR is perched over the F' pocket of CD1d. The germ line-encoded CDR1δ loop dominates the contacts with the CD1d molecule while the CDR3γ loop represents the main structural determinant for the antigen specificity. These findings highlight the emergence of diverse populations of NKT TCRs that exhibit different binding mode and lipid antigen specificity.

Human peripheral invariant natural killer T are adaptive lymphocytes, whose TCR CDR3β regulates their antigen specificity and reactivity to avoid harmful autoimmune responses (BA8P.124)

Abstract Human invariant natural killer T (iNKT) cells carry a sole variable element, complementarity determining region 3β (CDR3β) in their T cell receptors (TCRs). It has been widely accepted that iNKT cells recognize foreign and self-ligands via CD1d in a pattern recognition-like innate-type manner. Here, we have created a thymically unselected human iNKT Vβ11 TCR repertoire and isolated a series of iNKT TCRs with ultra-high to low autoreactivity. We have found three distinctive CDR3β sequence motifs that dictate high iNKT TCR autoreactivity. In vitro and in vivo studies demonstrated that highly autoreactive iNKT cells carry innate-type TCRs, recognize CD1d molecules in a ligand-independent manner and evoke severe systemic autoimmune responses within a few hours upon adoptive transfer. In contrast, iNKT cells with intermediate to low autoreactivity express adaptive-type TCRs, which selectively recognize self-ligands and induce tissue-specific moderate autoimmune responses in vivo. High throughput CDR3β sequencing revealed that the frequency of highly autoreactive human iNKT cells positive for all 3 motifs was significantly reduced among iNKT cells in the periphery compared to the thymus. We conclude that intermediately and lowly autoreactive iNKT cells which prevail in the human periphery are adaptive lymphocytes and that the sole adaptive CDR3β sequences regulate the antigen specificity and reactivity of iNKT cells to avoid harmful autoimmune responses.

The antigen sensitivity of effector but not memory CD4 T cells is regulated by the pathogen-induced inflammatory milieu. (IRM6P.712)

Abstract CD4 T cells play an important role in orchestrating immune responses following recognition of antigens through their T cell receptor (TCR). As such, their sensitivity for cognate antigen is likely to be tightly regulated. Previously, we demonstrated that the antigen sensitivity of CD8 T cells was tuned by inflammatory cytokines. Whether inflammatory cytokines also tune the antigen sensitivity of CD4 T cells remains unknown. Herein, we demonstrate that the antigen sensitivity of effector CD4 T cells is tuned by the inflammatory milieu. Mechanistically, we demonstrate that, in contrast to CD8 T cells, increased antigen sensitivity is not linked to enhanced TCR signal transduction capacity. In addition, tuning of the antigen sensitivity of CD4 T cells by inflammatory cytokines is independent of their role in the polarization of these cells towards a Th1 phenotype. Further, we demonstrate that, unlike CD8 T cells, inflammatory cytokines do not regulate the antigen sensitivity of memory CD4 T cells. Taken together, these data demonstrate that while inflammatory cytokines tune the antigen sensitivity of both CD4 and CD8 T cells, they do so through distinct mechanisms. Understanding the regulation of the antigen sensitivity of T cells can yield important insight leading to potential therapeutic avenues aimed at manipulating the antigen sensitivity of T cells. These approaches may be useful to prevent chronic viral infections, allow for clearance of tumors and prevent autoimmunity.

Adoptive T-cell therapy for hematological malignancies using T cells gene-modified to express tumor antigen-specific receptors

The functional properties of the adoptive immune response mediated by effector T lymphocytes are decisively regulated by their T-cell receptors (TCRs). Transfer of genes encoding target antigen-specific receptors enables polyclonal T cells to redirect toward cancer cells and virally infected cells expressing those defined antigens. Using this technology, a large population of redirected T cells displaying uniform therapeutic properties has been produced, powerfully advancing their clinical application as "cellular drugs" for adoptive immunotherapy against cancer. Clinically, anticancer adoptive immunotherapy using these genetically engineered T cells has an impressive and proven track record. Notable examples include the dramatic benefit of chimeric antigen receptor gene-modified T cells redirected towards B-cell lineage antigen CD19 in patients with chronic lymphocytic leukemia, and the impressive outcomes in the use of TCR gene-modified T cells redirected towards NY-ESO-1, a representative cancer-testis antigen, in patients with advanced melanoma and synovial cell sarcoma. In this review, we briefly overview the current status of this treatment option in the context of hematological malignancy, and discuss a number of challenges that still pose an obstacle to the full effectiveness of this strategy.

Self-Engagement Of An NKT Cell Inhibitory Receptor During Development Alters Receptor Expression and Cellular Function

Invariant NKT (iNKT) cells have been shown to be pro-inflammatory or anti-inflammatory in many pathologic conditions including infections, cancer, autoimmune diseases and allergy. Additionally, early expansion of iNKT cells correlates with successful engraftment and low incidence of graft-versus host disease suggesting a role for iNKT cells in tolerance to allogeneic transplantation. iNKT cells recognize glycolipids bound to CD1d via their T cell receptor (TCR), but also express the inhibitory receptors for MHC class I ligands (MHC I.) Little is known regarding the importance of iNKT cell self-recognition of MHC I during development and the occurrence of autoimmunity, allergy or tolerance to in utero hematopoietic cellular transplantation (IUHCT). Given the importance of NK cell self-recognition during development, we hypothesized that, like NK cells, self-engagement of MHC I inhibitory receptors during development alters the phenotype and function of self-responsive iNKT cells. Prenatal allogeneic chimeras were established by in utero transplantation of Balb/c fetal liver light density cells at E14 into age-matched C57BL/6 fetal recipients. A kinetic evaluation of iNKT cell receptor expression and function was performed after birth. iNKT cells were evaluated for expression of activating (Ly49D) and inhibitory (Ly49A, F, G) receptors specific for the donor MHC I (H-2d.) The functional response of iNKT cell subsets was measured following in vivo activation with KRN7000, the ligand for iNKT cells. Intracellular cytokine production (IFN-gamma and IL-4) production was assessed in the alloresponsive Ly49A+ iNKT cell subset and compared to naïve controls and B10.D2 (H2d) mice. We found that a negligible fraction of iNKT cells expressed the activating Ly49D receptor in either chimera or controls (<1%.) In chimeric mice, the frequency of iNKT cells expressing Ly49A, F, or G did not change significantly. However, the levels of Ly49A expression were significantly reduced on iNKT cells from all organs tested suggesting developmental recognition of donor class I ligands had occurred. These reduced receptor levels did not appear to be due to sequestration as acid stripping did not alter the phenotype. Lastly, Ly49A+ but not Ly49A- iNKT cells in chimeric mice exhibited significantly increased production of IL-4 in response to TCR stimulation suggesting a shift toward a regulatory phenotype. Consistent with this finding, IFN-gamma levels in chimeras were minimally changed compared to controls. These findings indicate that inhibitory receptor self-engagement during development leads to: 1) alterations in receptor expression; 2) shift toward a tolerogenic phenotype in self-responsive iNKT cell phenotypes; and 3) no change in the receptor expression or function of non-responsive iNKT cell phenotypes. Further studies will directly evaluate the impact of self-recognition of iNKT cells in the pathogenesis of autoimmunity and allergy or tolerance following IUHCT. Disclosures: No relevant conflicts of interest to declare.

Costimulation blockade: current perspectives and implications for therapy.

T cells must be activated before they can elicit damage to allografts, through interaction of their T cell receptor (TCR) with peptide-MHC complex and through accessory molecules. Signaling through accessory molecules or costimulatory molecules is a critical way for the immune system to fine tune T cell activation. An emerging therapeutic strategy is to target selective molecules involved in the process of T cell activation using biologic agents, which do not impact TCR signaling, thus only manipulating the T cells, which recognize alloantigen. Costimulatory receptors and their ligands are attractive targets for this strategy and could be used both to prevent acute graft rejection as well as for maintenance immunosuppression. Therapeutic agents targeting costimulatory molecules, notably belatacept, have made the progression from the bench, through nonhuman primate studies and into the clinic. This overview describes some of the most common costimulatory molecules, their role in T cell activation, and the development of reagents, which target these pathways and their efficacy in transplantation.

Signal integration in thymocytes is crucial for thymic selection

Event Abstract Back to Event Signal integration in thymocytes is crucial for thymic selection Sahamoddin Khailaie1, Aras Toker2, Jochen Huehn2 and Michael Meyer-Hermann1, 3* 1 Department of Systems Immunology, Helmholtz Center for Infection Research, Germany 2 Department of Experimental Immunology, Helmholtz Center for Infection Research, Germany 3 Bio Center for Life Science, Technische Universität Braunschweig, Germany Thymocytes are generated, selected and mature in the thymus to create a diverse, functional and self-tolerant T cell repertoire. Selection of thymocytes relies on the level of their T cell receptor (TCR) self-reactivity. Self-reactivity of thymocytes is quantified by repeated engagement of their TCRs with a diverse repertoire of self-peptides complexed with self-MHC molecule (spMHC) and may originate from either part of the complex. The role and relative importance of MHC versus self-peptides in thymic selection is not resolved. The fact that the selected T cell repertoire is MHC-restricted, requires a good mechanistic explanation of how thymocytes are able to quantify their affinity to MHC. In order to analyze how thymocytes quantify their self-reactivity, extract their MHC affinity, and how they use this information for cell fate determination, we developed a signal integration model for thymic selection, mimicking the requirement of repeated TCR signaling for successful selection and cell maturation. In this model, a polyclonal repertoire of thymocytes sequentially interact with diverse spMHCs and integrate the affinity-dependent TCR ligation signals. The strength and dynamics of the integrated signal is taken as a reference for cell fate determination. Quantification of the integrated signal and discrimination between its sustained and transient dynamics turns out as a successful basis for extracting affinity of thymocytes to MHC, detecting the existence of cognate self-peptide, and selecting a MHC-restricted self-tolerant T cell repertoire. Regulatory T-cell differentiation versus clonal deletion of autoreactive thymocytes is discussed with this model. Keywords: Thymic selection, T cell signaling, MHC restriction, Clonal Deletion, Regulatory T cell differentiation Conference: 15th International Congress of Immunology (ICI), Milan, Italy, 22 Aug - 27 Aug, 2013. Presentation Type: Abstract Topic: Adaptive Immunity Citation: Khailaie S, Toker A, Huehn J and Meyer-Hermann M (2013). Signal integration in thymocytes is crucial for thymic selection. Front. Immunol. Conference Abstract: 15th International Congress of Immunology (ICI). doi: 10.3389/conf.fimmu.2013.02.00479 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 31 Mar 2013; Published Online: 22 Aug 2013. * Correspondence: Prof. Michael Meyer-Hermann, Department of Systems Immunology, Helmholtz Center for Infection Research, Braunschweig, Germany, mmh@theoretical-biology.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Sahamoddin Khailaie Aras Toker Jochen Huehn Michael Meyer-Hermann Google Sahamoddin Khailaie Aras Toker Jochen Huehn Michael Meyer-Hermann Google Scholar Sahamoddin Khailaie Aras Toker Jochen Huehn Michael Meyer-Hermann PubMed Sahamoddin Khailaie Aras Toker Jochen Huehn Michael Meyer-Hermann Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Cytokine-Mediated Programmed Proliferation of Virus-Specific CD8+ Memory T Cells

During infection, CD8(+) Tcells not only respond to antigenic signals through their Tcell receptor (TCR) but also incorporate inflammatory signals from cytokines produced in the local infected microenvironment. Transient TCR-mediated stimulation will result in programmed proliferation that continues despite removal of the antigenic stimulus, but it remains unclear whether brief exposure to specific cytokines will elicit similar effects. Here, we have demonstrated that brief stimulation of memory Tcells with interleukin-12 (IL-12) and interleukin-18 (IL-18) results in tightly regulated programmed proliferation, in addition to acquisition of enhanced virus-specific cytokine production and cytolytic activity. CD8(+) Tcells briefly exposed to IL-12 and IL-18 invitro showed improved antiviral activity invivo, as demonstrated by increased proliferation and reduced viremia. These results indicate that even transitory exposure to inflammatory cytokines can provide a selective advantage to infiltrating CD8(+) Tcells by triggering a developmental program that is initiated prior to direct contact with virus-infected cells.