B Cells Influence Encephalitogenic T Cell Frequency to Myelin Oligodendrocyte Glycoprotein (MOG)38-49 during Full-length MOG Protein-Induced Demyelinating Disease.

Although T cells are encephalitogenic during demyelinating disease, B cell-depleting therapies are a successful treatment for patients with multiple sclerosis. Murine models of demyelinating disease utilizing myelin epitopes, such as myelin oligodendrocyte glycoprotein (MOG)35-55, induce a robust CD4 T cell response but mitigate the contribution of pathological B cells. This limits their efficacy for investigating how B cell depletion affects T cells.

Influenza-induced alveolar macrophages protect against death by malaria-associated acute lung injury.

Lower respiratory tract infections are common in malaria-endemic areas, and there is some evidence that co-infections between various bacteria/viruses and may affect disease prognosis. In this study, we report the novel finding that co-infection with influenza/A/X31 protects mice from death by NK65-Edinburgh, a model of severe malarial pulmonary leak which underpins malaria-associated acute lung injury (MA-ALI) and malaria-associated acute respiratory distress (MA-ARDS). Co-infected mice exhibit equivalent parasitemia as mice with malaria only, suggesting that the survival phenotype is due to differences in immune kinetics.

Cbl-b mitigates the responsiveness of naive CD8 T cells that experience extensive tonic T cell receptor signaling.

Naive T cells experience tonic T cell receptor (TCR) signaling in response to self-antigens presented by major histocompatibility complex (MHC) in secondary lymphoid organs. We investigated how relatively weak or strong tonic TCR signals influence naive CD8 T cell responses to stimulation with foreign antigens. The heterogeneous expression of Nur77-GFP, a transgenic reporter of tonic TCR signaling, in naive CD8 T cells suggests variable intensities or durations of tonic TCR signaling.

What's the Catch? The Significance of Catch Bonds in T Cell Activation.

One of the main goals in T cell biology has been to investigate how TCR recognition of peptide:MHC (pMHC) determines T cell phenotype and fate. Ag recognition is required to facilitate survival, expansion, and effector function of T cells. Historically, TCR affinity for pMHC has been used as a predictor for T cell fate and responsiveness, but there have now been several examples of nonfunctional high-affinity clones and low-affinity highly functional clones.

A single-amino acid substitution in the adaptor LAT accelerates TCR proofreading kinetics and alters T-cell selection, maintenance and function.

Mature T cells must discriminate between brief interactions with self-peptides and prolonged binding to agonists. The kinetic proofreading model posits that certain T-cell antigen receptor signaling nodes serve as molecular timers to facilitate such discrimination. However, the physiological significance of this regulatory mechanism and the pathological consequences of disrupting it are unknown.

Immunogen-Specific Strengths and Limitations of the Activation-Induced Marker Assay for Assessing Murine Antigen-Specific CD4+ T Cell Responses.

The activation-induced marker (AIM) assay is a cytokine-independent technique to identify Ag-specific T cells based on the upregulated expression of activation markers after Ag restimulation. The method offers an alternative to intracellular cytokine staining in immunological studies, in which limited cytokine production makes the cell subsets of interest difficult to detect. Studies of lymphocytes in human and nonhuman primates have used the AIM assay to detect Ag-specific CD4+ and CD8+ T cells.

Increased TCR signaling in regulatory T cells is disengaged from TCR affinity.

Foxp3+ regulatory T cells (Tregs) are capable suppressors of aberrant self-reactivity. However, TCR affinity and specificities that support Treg function, and how these compare to autoimmune T cells remain unresolved. In this study, we used antigen agnostic and epitope-focused analyses to compare TCR repertoires of regulatory and effector T cells that spontaneously infiltrate pancreatic islets of non-obese diabetic mice.

Strong Basal/Tonic TCR Signals Are Associated with Negative Regulation of Naive CD4 T Cells.

T cells experience varying intensities of tonic or basal TCR signaling in response to self-peptides presented by MHC (self-pMHC) in vivo. We analyzed four subpopulations of mouse naive CD4 cells that express different levels of Nur77-GFP and Ly6C, surrogate markers that positively and inversely correlate with the strength of tonic TCR signaling, respectively. Adoptive transfer studies suggest that relatively weak or strong Nur77-GFP intensity in thymocytes tends to be maintained in mature T cells.

Tuning T cell receptor sensitivity through catch bond engineering.

Adoptive cell therapy using engineered T cell receptors (TCRs) is a promising approach for targeting cancer antigens, but tumor-reactive TCRs are often weakly responsive to their target ligands, peptide-major histocompatibility complexes (pMHCs). Affinity-matured TCRs can enhance the efficacy of TCR-T cell therapy but can also cross-react with off-target antigens, resulting in organ immunopathology. We developed an alternative strategy to isolate TCR mutants that exhibited high activation signals coupled with low-affinity pMHC binding through the acquisition of catch bonds.

The magnitude of LFA-1/ICAM-1 forces fine-tune TCR-triggered T cell activation.

T cells defend against cancer and viral infections by rapidly scanning the surface of target cells seeking specific peptide antigens. This key process in adaptive immunity is sparked upon T cell receptor (TCR) binding of antigens within cell-cell junctions stabilized by integrin (LFA-1)/intercellular adhesion molecule-1 (ICAM-1) complexes. A long-standing question in this area is whether the forces transmitted through the LFA-1/ICAM-1 complex tune T cell signaling.

Mechanobiology of T Cell Activation: To Catch a Bond.

T cell activation is a critical event in the adaptive immune response, indispensable for cell-mediated and humoral immunity as well as for immune regulation. Recent years have witnessed an emerging trend emphasizing the essential role that physical force and mechanical properties play at the T cell interface. In this review, we integrate current knowledge of T cell antigen recognition and the different models of T cell activation from the perspective of mechanobiology, focusing on the interaction between the T cell receptor (TCR) and the peptide-major histocompatibility complex (pMHC) antigen.

Canonical T cell receptor docking on peptide-MHC is essential for T cell signaling.

T cell receptor (TCR) recognition of peptide-major histocompatibility complexes (pMHCs) is characterized by a highly conserved docking polarity. Whether this polarity is driven by recognition or signaling constraints remains unclear. Using "reversed-docking" TCRβ-variable (TRBV) 17 TCRs from the naïve mouse CD8 T cell repertoire that recognizes the H-2D-NP epitope, we demonstrate that their inability to support T cell activation and in vivo recruitment is a direct consequence of reversed docking polarity and not TCR-pMHCI binding or clustering characteristics.

MHC class II tetramers engineered for enhanced binding to CD4 improve detection of antigen-specific T cells.

The ability to identify T cells that recognize specific peptide antigens bound to major histocompatibility complex (MHC) molecules has enabled enumeration and molecular characterization of the lymphocytes responsible for cell-mediated immunity. Fluorophore-labeled peptide:MHC class I (p:MHCI) tetramers are well-established reagents for identifying antigen-specific CD8 T cells by flow cytometry, but efforts to extend the approach to CD4 T cells have been less successful, perhaps owing to lower binding strength between CD4 and MHC class II (MHCII) molecules. Here we show that p:MHCII tetramers engineered by directed evolution for enhanced CD4 binding outperform conventional tetramers for the detection of cognate T cells.

Targeting transcriptional coregulator OCA-B/Pou2af1 blocks activated autoreactive T cells in the pancreas and type 1 diabetes.

The transcriptional coregulator OCA-B promotes expression of T cell target genes in cases of repeated antigen exposure, a necessary feature of autoimmunity. We hypothesized that T cell-specific OCA-B deletion and pharmacologic OCA-B inhibition would protect mice from autoimmune diabetes. We developed an Ocab conditional allele and backcrossed it onto a diabetes-prone NOD/ShiLtJ strain background.

Relationship of 2D Affinity to T Cell Functional Outcomes.

T cells are critical for a functioning adaptive immune response and a strong correlation exists between T cell responses and T cell receptor (TCR): peptide-loaded MHC (pMHC) binding. Studies that utilize pMHC tetramer, multimers, and assays of three-dimensional (3D) affinity have provided advancements in our understanding of T cell responses across different diseases. However, these technologies focus on higher affinity and avidity T cells while missing the lower affinity responders.

An Engineered T Cell Receptor Variant Realizes the Limits of Functional Binding Modes.

T cell receptors (TCRs) orchestrate cellular immunity by recognizing peptides presented by a range of major histocompatibility complex (MHC) proteins. Naturally occurring TCRs bind the composite peptide/MHC surface, recognizing peptides that are structurally and chemically compatible with the TCR binding site. Here we describe a molecularly evolved TCR variant that binds the human class I MHC protein HLA-A2 independent of the bound peptide, achieved by a drastic perturbation of the TCR binding geometry that places the molecule far from the peptide binding groove.

Localized hydrogel delivery of dendritic cells for attenuation of multiple sclerosis in a murine model.

In multiple sclerosis (MS), abnormally activated immune cells responsive to myelin proteins result in widespread damage throughout the central nervous system (CNS) and ultimately irreversible disability. Immunomodulation by delivering dendritic cells (DCs) utilizes a potent and rapid MS disease progression driver therapeutically. Here, we investigated delivering DCs for disease severity attenuation using an experimental autoimmune encephalomyelitis preclinical MS model.

IL-21 from high-affinity CD4 T cells drives differentiation of brain-resident CD8 T cells during persistent viral infection.

Development of tissue-resident memory (T) CD8 T cells depends on CD4 T cells. In polyomavirus central nervous system infection, brain CXCR5 PD-1 CD4 T cells produce interleukin-21 (IL-21), and CD8 T cells lacking IL-21 receptors (IL21R) fail to become bT IL-21 CD4 T cells exhibit elevated T cell receptor (TCR) affinity and higher TCR density. IL21R brain CD8 T cells do not express CD103, depend on vascular CD8 T cells for maintenance, are antigen recall defective, and lack T core signature genes.

CD45RB Status of CD8 T Cell Memory Defines T Cell Receptor Affinity and Persistence.

The identity of CD45 isoforms on the T cell surface changes following the activation of naive T cells and impacts intracellular signaling. In this study, we find that the anti-viral memory CD8 T pool is unexpectedly comprised of both CD45RB and CD45RB populations. Relative to CD45RB memory T cells, CD45RB memory T cells have lower affinity and display greater clonal diversity, as well as a persistent CD27 phenotype.

A Critical Insulin TCR Contact Residue Selects High-Affinity and Pathogenic Insulin-Specific T Cells.

Type 1 diabetes is an autoimmune-mediated disease that culminates in the targeted destruction of insulin-producing β-cells. CD4 responses in NOD mice are dominated by insulin epitope B:9-23 (InsB) specificity, and mutation of the key T-cell receptor (TCR) contact residue within the epitope prevents diabetes development. However, it is not clear how insulin self-antigen controls the selection of autoimmune and regulatory T cells (Tregs).

A Hybrid Insulin Epitope Maintains High 2D Affinity for Diabetogenic T Cells in the Periphery.

β-Cell antigen recognition by autoreactive T cells is essential in type 1 diabetes (T1D) pathogenesis. Recently, insulin hybrid peptides (HIPs) were identified as strong agonists for CD4 diabetogenic T cells. Here, using BDC2.

Understanding TCR affinity, antigen specificity, and cross-reactivity to improve TCR gene-modified T cells for cancer immunotherapy.

Adoptive cell transfer (ACT) using T cell receptor (TCR) gene-modified T cells is an exciting and rapidly evolving field. Numerous preclinical and clinical studies have demonstrated various levels of feasibility, safety, and efficacy using TCR-engineered T cells to treat cancer and viral infections. Although evidence suggests their use can be effective, to what extent and how to improve these therapeutics are still matters of investigation.