Peripheral CD8+ T cell tolerance is a checkpoint in both autoimmune disease and anti-cancer immunity. Despite its importance, the relationship between tolerance-induced states and other CD8+ T cell differentiation states remains unclear. Using flow cytometric phenotyping, single-cell RNA sequencing (scRNA-seq), and chromatin accessibility profiling, we demonstrated that in vivo peripheral tolerance to a self-antigen triggered a fundamentally distinct differentiation state separate from exhaustion, memory, and functional effector cells but analogous to cells defectively primed against tumors. Tolerant cells diverged early and progressively from effector cells, adopting a transcriptionally and epigenetically distinct state within 60 h of antigen encounter. Breaching tolerance required the synergistic actions of strong T cell receptor (TCR) signaling and inflammation, which cooperatively induced gene modules that enhanced protein translation. Weak TCR signaling during bystander infection failed to breach tolerance due to the uncoupling of effector gene expression from protein translation. Thus, tolerance engages a distinct differentiation trajectory enforced by protein translation defects.
Copyright © 2024 Elsevier Inc. All rights reserved.

Lymphocyte-specific protein tyrosine kinase (LCK) is essential for T cell antigen receptor (TCR)-mediated signal transduction. Here, we report two siblings homozygous for a novel LCK variant (c.1318C>T; P440S) characterized by T cell lymphopenia with skewed memory phenotype, infant-onset recurrent infections, failure to thrive, and protracted diarrhea. The patients' T cells show residual TCR signal transduction and proliferation following anti-CD3/CD28 and phytohemagglutinin (PHA) stimulation. We demonstrate in mouse models that complete (Lck-/-) versus partial (LckP440S/P440S) loss-of-function LCK causes disease with differing phenotypes. While both Lck-/- and LckP440S/P440S mice exhibit arrested thymic T cell development and profound T cell lymphopenia, only LckP440S/P440S mice show residual T cell proliferation, cytokine production, and intestinal inflammation. Furthermore, the intestinal disease in the LckP440S/P440S mice is prevented by CD4+ T cell depletion or regulatory T cell transfer. These findings demonstrate that P440S LCK spares sufficient T cell function to allow the maturation of some conventional T cells but not regulatory T cells-leading to intestinal inflammation.
© 2023 Lui et al.

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. Here we report that accelerating the normally slow phosphorylation of the linker for activation of T cells (LAT) residue Y136 by introducing an adjacent Gly135Asp alteration (LATG135D) disrupts ligand discrimination in vivo. The enhanced self-reactivity of LATG135D T cells triggers excessive thymic negative selection and promotes T-cell anergy. During Listeria infection, LATG135D T cells expand more than wild-type counterparts in response to very weak stimuli but display an imbalance between effector and memory responses. Moreover, despite their enhanced engagement of central and peripheral tolerance mechanisms, mice bearing LATG135D show features associated with autoimmunity and immunopathology. Our data reveal the importance of kinetic proofreading in balancing tolerance and immunity.
© 2023. The Author(s).

Thymic selection and peripheral activation of conventional T (Tconv) and regulatory T (Treg) cells depend on TCR signaling, whose anomalies are causative of autoimmunity. Here, we expressed in normal mice mutated ZAP-70 molecules with different affinities for the CD3 chains, or wild type ZAP-70 at graded expression levels under tetracycline-inducible control. Both manipulations reduced TCR signaling intensity to various extents and thereby rendered those normally deleted self-reactive thymocytes to become positively selected and form a highly autoimmune TCR repertoire. The signal reduction more profoundly affected Treg development and function because their TCR signaling was further attenuated by Foxp3 that physiologically repressed the expression of TCR-proximal signaling molecules, including ZAP-70, upon TCR stimulation. Consequently, the TCR signaling intensity reduced to a critical range generated pathogenic autoimmune Tconv cells and concurrently impaired Treg development/function, leading to spontaneous occurrence of autoimmune/inflammatory diseases, such as autoimmune arthritis and inflammatory bowel disease. These results provide a general model of how altered TCR signaling evokes autoimmune disease.
© 2022 Tanaka et al.

TnP is a family of patented synthetic peptides which is in a preclinical development stage with valuable potential therapeutic indication for multiple sclerosis (MS), an autoimmune demyelinating disease of the central nervous system (CNS). The use of a preclinical animal model, such as experimental autoimmune encephalomyelitis (EAE) has deepened our knowledge of the immunomodulatory functions of TnP as a drug. We have shown that TnP possesses a disease suppressive function in EAE, ameliorating disease severity by 40% and suppressing the accumulation of T helper (Th)1- and Th17-producing lymphocytes (by 55% and 60%, respectively) in CNS along with activated microglia/macrophages populations (by 33% and 50%, respectively), and also conferred a protective effect anticipating the remyelination process to day 66 compared to day 83 of untreated cuprizone-mice. Here we expanded our knowledge about its effects compared with current first-line disease-modifying therapies (DMT). We demonstrated that prophylactic treatment with TnP generated similar protection to betaseron (30%) or was more effective than glatiramer (44% versus 6%) or fingolimod (50% versus 19%) against the development of clinical symptoms. Although TnP controlled the leukocyte infiltration (87% versus 82%) into demyelinated areas of the spinal cord in the same way as betaseron and fingolimod, it was more effective (72% to 78% decrease) in the long-term control of neuronal degeneration compared to them. Also, when compared to glatiramer, TnP was more efficient in reversing leukocytes infiltration into the spinal cord (55% versus 24%), as well as induced a higher percentage of regulatory cells in spleen (2.9-fold versus 2.3-fold increase over vehicle-treated EAE mice) an in the spinal cord (8-fold versus 6-fold increase over vehicle-treated EAE mice). This specialized TnP profile for inducing immune tolerance and neuronal regeneration has significant therapeutic potential for the treatment of MS and other autoimmune diseases.
Copyright © 2022 Lima, Maleski, Bernardo, Zelli, Komegae and Lopes-Ferreira.