Surface T-cell antigen receptor expression and availability for long-term antigenic signaling.
TL;DR: This review examines the dynamics of surface TCR expression and signaling capacity during thymic and effector T‐cell development and indicates that qualitatively distinct forms of the TCR exist, and their potential role in sustained antigenic signaling is also discussed.
Abstract: It is important to understand how T-cell antigen receptor (TCR) engagement and signaling are regulated throughout an immune response. This review examines the dynamics of surface TCR expression and signaling capacity during thymic and effector T-cell development. Although the TCR can undergo vast changes in surface expression, T cells remain capable of sustaining TCR engagement for long periods of time. This may be achieved by a combination of mechanisms that involve (a) controlling the quantity of surface TCR available for ligand interaction and (b) controlling the quality of surface TCR expression during T-cell activation. TCR signaling itself appears to be one of the main quantitative modulators of surface TCR expression, and it can cause both downregulation and upregulation at different times of T-cell activation. Recent studies indicate that the degree of upregulation is tunable by the strength of antigenic stimulation. There is evidence that qualitatively distinct forms of the TCR exist, and their potential role in sustained antigenic signaling is also discussed. A goal of future studies will be to better characterize these modulations in surface TCR expression and to clarify their impact on the regulation of immune responses.
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TL;DR: It is demonstrated that directing a CD19-specific CAR to the T- cell receptor α constant (TRAC) locus not only results in uniform CAR expression in human peripheral blood T cells, but also enhances T-cell potency, with edited cells vastly outperforming conventionally generated CAR T cells in a mouse model of acute lymphoblastic leukaemia.
Abstract: Chimeric antigen receptors (CARs) are synthetic receptors that redirect and reprogram T cells to mediate tumour rejection. The most successful CARs used to date are those targeting CD19 (ref. 2), which offer the prospect of complete remission in patients with chemorefractory or relapsed B-cell malignancies. CARs are typically transduced into the T cells of a patient using γ-retroviral vectors or other randomly integrating vectors, which may result in clonal expansion, oncogenic transformation, variegated transgene expression and transcriptional silencing. Recent advances in genome editing enable efficient sequence-specific interventions in human cells, including targeted gene delivery to the CCR5 and AAVS1 loci. Here we show that directing a CD19-specific CAR to the T-cell receptor α constant (TRAC) locus not only results in uniform CAR expression in human peripheral blood T cells, but also enhances T-cell potency, with edited cells vastly outperforming conventionally generated CAR T cells in a mouse model of acute lymphoblastic leukaemia. We further demonstrate that targeting the CAR to the TRAC locus averts tonic CAR signalling and establishes effective internalization and re-expression of the CAR following single or repeated exposure to antigen, delaying effector T-cell differentiation and exhaustion. These findings uncover facets of CAR immunobiology and underscore the potential of CRISPR/Cas9 genome editing to advance immunotherapies.
1,219 citations
TL;DR: Compared with wild-type CD4-type T cells, Blimp-1-deficient CD4+ T cells proliferated more and produced excess interleukin 2 and interferon-γ but reduced interLEukin 10 after T cell receptor stimulation, which emphasizes a crucial function for Blimm-1 in controlling T cell homeostasis and activation.
Abstract: The B lymphocyte-induced maturation protein 1 (Blimp-1) transcriptional repressor is required for terminal differentiation of B lymphocytes. Here we document a function for Blimp-1 in the T cell lineage. Blimp-1-deficient thymocytes showed decreased survival and Blimp-1-deficient mice had more peripheral effector T cells. Mice lacking Blimp-1 developed severe colitis as early as 6 weeks of age, and Blimp-1-deficient regulatory T cells were defective in blocking the development of colitis. Blimp-1 mRNA expression increased substantially in response to T cell receptor stimulation. Compared with wild-type CD4(+) T cells, Blimp-1-deficient CD4(+) T cells proliferated more and produced excess interleukin 2 and interferon-gamma but reduced interleukin 10 after T cell receptor stimulation. These results emphasize a crucial function for Blimp-1 in controlling T cell homeostasis and activation.
356 citations
TL;DR: A robust protocol for the full-length profiling of human and mouse IG repertoires using unique molecular identifiers introduced in the course of cDNA synthesis to control bottlenecks and to eliminate PCR and sequencing errors is presented.
Abstract: High-throughput sequencing analysis of hypermutating immunoglobulin (IG) repertoires remains a challenging task. Here we present a robust protocol for the full-length profiling of human and mouse IG repertoires. This protocol uses unique molecular identifiers (UMIs) introduced in the course of cDNA synthesis to control bottlenecks and to eliminate PCR and sequencing errors. Using asymmetric 400+100-nt paired-end Illumina sequencing and UMI-based assembly with the new version of the MIGEC software, the protocol allows up to 750-nt lengths to be sequenced in an almost error-free manner. This sequencing approach should also be applicable to various tasks beyond immune repertoire studies. In IG profiling, the achieved length of high-quality sequence covers the variable region of even the longest chains, along with the fragment of a constant region carrying information on the antibody isotype. The whole protocol, including preparation of cells and libraries, sequencing and data analysis, takes 5 to 6 d.
156 citations
TL;DR: In RA, a systemic autoimmune disease, the inflamed synovium forms a niche for specific expanded T-cell clones, especially in early disease, which suggests that, at least in RA, autoreactive T cells should be addressed specifically in the inflaming tissue, preferably in the early phase of the disease.
Abstract: OBJECTIVE: To profile quantitatively the T-cell repertoire in multiple joints and peripheral blood of patients with recent onset (early) or established rheumatoid arthritis (RA) using a novel next-generation sequencing protocol to identify potential autoreactive clones. METHODS: Synovium of patients with recent onset (early) RA ( 18 months) (n=6) was screened for T-cell clones by sequencing over 10 000 T-cell receptors (TCR) per sample. T cells from paired blood samples were analysed for comparison. From two patients synovial T cells were obtained from multiple inflamed joints. The degree of expansion of each individual clone was based on its unique CDR3 sequence frequency within a sample. Clones with a frequency of over 0.5% were considered to be highly expanded clones (HEC). RESULTS: In early RA synovium, the T-cell repertoire was dominated by 35 HEC (median, range 2-70) accounting for 56% of the TCR sequenced. The clonal dominance in the synovium was patient specific and significantly greater than in established RA (median of 11 HEC (range 5-24) in established RA synovium accounting for 9.8% of T cells; p<0.01). 34% (range 28-40%) of the most expanded T-cell clones were shared between different joints in the same patients, compared with only 4% (range 0-8%) between synovium and blood (p=0.01). CONCLUSIONS: In RA, a systemic autoimmune disease, the inflamed synovium forms a niche for specific expanded T-cell clones, especially in early disease. This suggests that, at least in RA, autoreactive T cells should be addressed specifically in the inflamed tissue, preferably in the early phase of the disease.
121 citations
TL;DR: The findings suggest that the initial antiviral response in humans is maintained in a stable fashion without signs of contraction or changes of the clonal repertoire.
Abstract: CD8+ T-cell responses against latent viruses can cover considerable portions of the CD8+ T-cell compartment for many decades, yet their initiation and maintenance remains poorly characterized in humans. A key question is whether the clonal repertoire that is raised during the initial antiviral response can be maintained over these long periods. To investigate this we combined next-generation sequencing of the T-cell receptor repertoire with tetramer-sorting to identify, quantify and longitudinally follow virus-specific clones within the CD8+ T-cell compartment. Using this approach we studied primary infections of human cytomegalovirus (hCMV) and Epstein Barr virus (EBV) in renal transplant recipients. For both viruses we found that nearly all virus-specific CD8+ T-cell clones that appeared during the early phase of infection were maintained at high frequencies during the 5-year follow-up and hardly any new anti-viral clones appeared. Both in transplant recipients and in healthy carriers the clones specific for these latent viruses were highly dominant within the CD8+ T-cell receptor Vβ repertoire. These findings suggest that the initial antiviral response in humans is maintained in a stable fashion without signs of contraction or changes of the clonal repertoire.
116 citations
Cites result from "Surface T-cell antigen receptor exp..."
...These findings are consistent with previous reports that TCR mRNA levels are stable [17]....
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References
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TL;DR: Immunological synapse formation is now shown to be an active and dynamic mechanism that allows T cells to distinguish potential antigenic ligands and was a determinative event for T cell proliferation.
Abstract: The specialized junction between a T lymphocyte and an antigen-presenting cell, the immunological synapse, consists of a central cluster of T cell receptors surrounded by a ring of adhesion molecules. Immunological synapse formation is now shown to be an active and dynamic mechanism that allows T cells to distinguish potential antigenic ligands. Initially, T cell receptor ligands were engaged in an outermost ring of the nascent synapse. Transport of these complexes into the central cluster was dependent on T cell receptor—ligand interaction kinetics. Finally, formation of a stable central cluster at the heart of the synapse was a determinative event for T cell proliferation. A critical event in the initiation of the adaptive
2,988 citations
TL;DR: Results show that the process of positive selection is exquisitely peptide specific and sensitive to extremely low ligand density and support the notion that low efficacy ligands mediate positive selection.
2,715 citations
TL;DR: It is shown that a small number of peptideMHC complexes can achieve a high TCR occupancy, because a single complex can serially engage and trigger up to ∼200 TCRs.
Abstract: T lymphocytes can recognize and be activated by a very small number of complexes of peptide with major histocompatibility complex (MHC) molecules displayed on the surface of antigen-presenting cells (APCs). The interaction between the T-cell receptor (TCR) and its ligand has low affinity and high off-rate. Both findings suggest that an extremely small number of TCRs must be engaged in interaction with APCs and raise the question of how so few receptors can transduce an activation signal. Here we show that a small number of peptide-MHC complexes can achieve a high TCR occupancy, because a single complex can serially engage and trigger up to approximately 200 TCRs. Furthermore, TCR occupancy is proportional to the T cell's biological response. Our findings suggest that the low affinity of the TCR can be instrumental in enabling a small number of antigenic complexes to be detected.
1,203 citations
"Surface T-cell antigen receptor exp..." refers background in this paper
...When Sousa and Carneiro (104) mathematically modeled the data of Valitutti et al. (95), they noticed the biphasic kinetics of TCR downregulation....
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...On the one hand, human T-cell clones (95), a murine T-cell hybridoma (106), and naı̈ve CD4þ murine T cells (8) were shown to only...
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TL;DR: A unitary requirement for T cell responses was revealed by measurement of the number of triggered TCRs, thus making T cells more sensitive to antigenic stimulation.
Abstract: The requirements for T cell activation have been reported to vary widely depending on the state of the T cell, the type of antigen-presenting cell, and the nature of the T cell receptor (TCR) ligand. A unitary requirement for T cell responses was revealed by measurement of the number of triggered TCRs. Irrespective of the nature of the triggering ligand, T cells "counted" the number of triggered TCRs and responded when a threshold of approximately 8000 TCRs was reached. The capacity to reach the activation threshold was severely compromised by a reduction in the number of TCRs. Costimulatory signals lowered the activation threshold to approximately 1500 TCRs, thus making T cells more sensitive to antigenic stimulation.
1,063 citations
"Surface T-cell antigen receptor exp..." refers background in this paper
...However, both downregulation and upregulation of surface TCR level has been documented in activated T cells (109, 133, 134), consistent with the idea that active signal transduction can affect surface TCR expression level (Table 2)....
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TL;DR: Here, recent advances in understanding of the molecular bases and physiologic roles of the mechanisms of immune homeostasis are examined and several regulatory mechanisms function to terminate responses to foreign antigens.
Abstract: The immune system responds in a regulated fashion to microbes and eliminates them, but it does not respond to self-antigens. Several regulatory mechanisms function to terminate responses to foreign antigens, returning the immune system to a basal state after the antigen has been cleared, and to maintain unresponsiveness, or tolerance, to self-antigens. Here, recent advances in understanding of the molecular bases and physiologic roles of the mechanisms of immune homeostasis are examined.
982 citations