Jun Yamanouchi

Interleukin-2 gene variation impairs regulatory T cell function and causes autoimmunity

Autoimmune diseases are thought to result from imbalances in normal immune physiology and regulation. Here, we show that autoimmune disease susceptibility and resistance alleles on mouse chromosome 3 (Idd3) correlate with differential expression of the key immunoregulatory cytokine interleukin-2 (IL-2). In order to test directly that an approximately twofold reduction in IL-2 underpins the Idd3-linked destabilization of immune homeostasis, we show that engineered haplodeficiency of Il2 gene expression not only reduces T cell IL-2 production by twofold but also mimics the autoimmune dysregulatory effects of the naturally occurring susceptibility alleles of Il2. Reduced IL-2 production achieved by either genetic mechanism correlates with reduced function of CD4+ CD25+ regulatory T cells, which are critical for maintaining immune homeostasis.

Reversal of Autoimmunity by Boosting Memory-like Autoregulatory T Cells

Blunting autoreactivity without compromising immunity remains an elusive goal in the treatment of autoimmunity. We show that progression to autoimmune diabetes results in the conversion of naive low-avidity autoreactive CD8(+) T cells into memory-like autoregulatory cells that can be expanded in vivo with nanoparticles coated with disease-relevant peptide-major histocompatibility complexes (pMHC-NP). Treatment of NOD mice with monospecific pMHC-NPs expanded cognate autoregulatory T cells, suppressed the recruitment of noncognate specificities, prevented disease in prediabetic mice, and restored normoglycemia in diabetic animals. pMHC-NP therapy was inconsequential in mice engineered to bear an immune system unresponsive to the corresponding epitope, owing to absence of epitope-experienced autoregulatory T cells. pMHC-NP-expanded autoregulatory T cells suppressed local presentation of autoantigens in an interferon-gamma-, indoleamine 2,3-dioxygenase-, and perforin-dependent manner. Nanoparticles coated with human diabetes-relevant pHLA complexes restored normoglycemia in a humanized model of diabetes. These observations expose a paradigm in the pathogenesis of autoimmunity amenable for therapeutic intervention.

CD40 Ligation Releases Immature Dendritic Cells from the Control of Regulatory CD4+CD25+ T Cells

We report that disruption of CD154 in nonobese diabetic (NOD) mice abrogates the helper function of CD4+CD25- T cells without impairing the regulatory activity of CD4+CD25+ T cells. Whereas CD4+ T cells from NOD mice enhanced a diabetogenic CD8+ T cell response in monoclonal TCR-transgenic NOD mice, CD4+ T cells from NOD.CD154(-/-) mice actively suppressed it. Suppression was mediated by regulatory CD4+CD25+ T cells capable of inhibiting CD8+ T cell responses induced by peptide-pulsed dendritic cells (DCs), but not peptide/MHC monomers. It involved inhibition of DC maturation, did not occur in the presence of CD154+ T-helper cells, and could be inhibited by activation of DCs with LPS, CpG DNA, or an agonistic anti-CD40 mAb. Thus, in at least some genetic backgrounds, CD154-CD40 interactions and innate stimuli release immature DCs from suppression by CD4+CD25+ T cells.

Prevention of diabetes by manipulation of anti-IGRP autoimmunity: high efficiency of a low-affinity peptide

Antigen therapy may hold great promise for the prevention of autoimmunity; however, most clinical trials have failed, suggesting that the principles guiding the choice of treatment remain ill defined. Here, we examine the antidiabetogenic properties of altered peptide ligands of CD8+ T cells recognizing an epitope of islet-specific glucose-6-phosphatase catalytic subunit–related protein (IGRP206–214), a prevalent population of autoreactive T cells in autoimmune diabetes. We show that islet-associated CD8+ T cells in nonobese diabetic mice recognize numerous IGRP epitopes, and that these cells have a role in the outcome of protocols designed to induce IGRP206–214-specific tolerance. Ligands targeting IGRP206–214-reactive T cells prevented disease, but only at doses that spared low-avidity clonotypes. Notably, near complete depletion of the IGRP206–214-reactive T-cell pool enhanced the recruitment of subdominant specificities and did not blunt diabetogenesis. Thus, peptide therapy in autoimmunity is most effective under conditions that foster occupation of the target organ lymphocyte niche by nonpathogenic, low-avidity clonotypes.

Expanding antigen-specific regulatory networks to treat autoimmunity

Regulatory T cells hold promise as targets for therapeutic intervention in autoimmunity, but approaches capable of expanding antigen-specific regulatory T cells in vivo are currently not available. Here we show that systemic delivery of nanoparticles coated with autoimmune-disease-relevant peptides bound to major histocompatibility complex class II (pMHCII) molecules triggers the generation and expansion of antigen-specific regulatory CD4+ T cell type 1 (TR1)-like cells in different mouse models, including mice humanized with lymphocytes from patients, leading to resolution of established autoimmune phenomena. Ten pMHCII-based nanomedicines show similar biological effects, regardless of genetic background, prevalence of the cognate T-cell population or MHC restriction. These nanomedicines promote the differentiation of disease-primed autoreactive T cells into TR1-like cells, which in turn suppress autoantigen-loaded antigen-presenting cells and drive the differentiation of cognate B cells into disease-suppressing regulatory B cells, without compromising systemic immunity. pMHCII-based nanomedicines thus represent a new class of drugs, potentially useful for treating a broad spectrum of autoimmune conditions in a disease-specific manner.

Developmental control of CD8+ T cell–avidity maturation in autoimmune diabetes

The progression of immune responses is generally associated with an increase in the overall avidity of antigen-specific T cell populations for peptide-MHC. This is thought to result from preferential expansion of high-avidity clonotypes at the expense of their low-avidity counterparts. Since T cell antigen-receptor genes do not mutate, it is puzzling that high-avidity clonotypes do not predominate from the outset. Here we provide a developmental basis for this phenomenon in the context of autoimmunity. We have carried out comprehensive studies of the diabetogenic CD8 T cell population that targets residues 206-214 of the beta cell antigen islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP(206-214)) and undergoes avidity maturation as disease progresses. We find that the succession of IGRP(206-214)-specific clonotypes with increasing avidities during the progression of islet inflammation to overt diabetes in nonobese diabetic mice is fueled by autoimmune inflammation but opposed by systemic tolerance. As expected, naive high-avidity IGRP(206-214)-specific T cells respond more efficiently to antigen and are significantly more diabetogenic than their intermediate- or low-avidity counterparts. However, central and peripheral tolerance selectively limit the contribution of these high-avidity T cells to the earliest stages of disease without abrogating their ability to progressively accumulate in inflamed islets and kill beta cells. These results illustrate the way in which incomplete deletion of autoreactive T cell populations of relatively high avidity can contribute to the development of pathogenic autoimmunity in the periphery.

Expansion of the Antigenic Repertoire of a Single T Cell Receptor upon T Cell Activation

Activated T cells and their naive precursors display different functional avidities for peptide/MHC, but are thought to have identical antigenic repertoires. We show that, following activation with a cognate mimotope (NRP), diabetogenic CD8+ T cells expressing a single TCR (8.3) respond vigorously to numerous peptide analogs of NRP that were unable to elicit any responses from naive 8.3-CD8+ T cells, even at high concentrations. The NRP-reactive, in vivo activated CD8+ cells arising in pancreatic islets of nonobese diabetic mice are similarly promiscuous for peptide/MHC, and paradoxically this promiscuity expands as the aviditiy of the T cell population for NRP/MHC increases with age. Thus, activation and avidity maturation of T lymphocyte populations can lead to dramatic expansions in the range of peptides that elicit functional T cell responses.

A Critical Temporal Window for Selectin-dependent CD4+ Lymphocyte Homing and Initiation of Late-Phase Inflammation in Contact Sensitivity

Contact sensitivity (CS) is an inflammatory disorder characterized by early and late phases of leukocyte recruitment. We used a noninvasive intravital microscopy technique allowing for the direct visualization of leukocyte rolling and adhesion on blood vessel endothelium. By blocking specific adhesion molecules, we elucidated the molecular mechanisms mediating early leukocyte recruitment to be E- and P-selectin and demonstrated that leukocyte recruitment in the late phase had a different adhesive profile (mainly α4-integrin). Complete blockade of E- and P-selectin within the first 2 h of leukocyte–endothelial cell interactions (but not later) eliminated selectin-independent leukocyte recruitment at 24 h. Despite the predominance of neutrophils in the early phase, specific elimination of CD4+ lymphocytes in the early phase eliminated the late response. CD4+ lymphocytes homed to skin via E- and P-selectin within the early phase and induced the late phase response. Addition of these same CD4+ lymphocytes 2 h after antigen challenge was too late for these cells to home to the skin and induce late phase responses. Our data clearly demonstrate that the antigen-challenged microenvironment is only accessible to CD4+ lymphocytes for the first 2 h, and that this process is essential for the subsequent recruitment of other leukocyte populations in late phase responses.

Cross-Priming of Diabetogenic T Cells Dissociated from CTL-Induced Shedding of β Cell Autoantigens

Cross-presentation of self Ags by APCs is key to the initiation of organ-specific autoimmunity. As MHC class I molecules are essential for the initiation of diabetes in nonobese diabetic (NOD) mice, we sought to determine whether the initial insult that allows cross-presentation of β cell autoantigens in diabetes is caused by cognate interactions between naive CD8+ T cells and β cells. Naive splenic CD8+ T cells from transgenic NOD mice expressing a diabetogenic TCR killed peptide-pulsed targets in the absence of APCs. To ascertain the role of CD8+ T cell-induced β cell lysis in the initiation of diabetes, we expressed a rat insulin promoter (RIP)-driven adenovirus E19 transgene in NOD mice. RIP-E19 expression inhibited MHC class I transport exclusively in β cells and rendered these cells resistant to lysis by CD8+ (but not CD4+) T cells, both in vitro and in vivo. Surprisingly, RIP-E19 expression impaired the accumulation of CD8+ T cells in islets and delayed the onset of islet inflammation, without affecting the timing or magnitude of T cell cross-priming in the pancreatic lymph nodes, which is the earliest known event in diabetogenesis. These results suggest that access of β cell autoantigens to the cross-presentation pathway in diabetes is T cell independent, and reveal a previously unrecognized function of MHC class I molecules on target cells in autoimmunity: local retention of disease-initiating clonotypes.

In situ recognition of autoantigen as an essential gatekeeper in autoimmune CD8+ T cell inflammation

A current paradigm states that non-antigen-specific inflammatory cues attract noncognate, bystander T cell specificities to sites of infection and autoimmune inflammation. Here we show that cues emanating from a tissue undergoing spontaneous autoimmune inflammation cannot recruit naive or activated bystander T cell specificities in the absence of local expression of cognate antigen. We monitored the recruitment of CD8+ T cells specific for the prevalent diabetogenic epitope islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)206–214 in gene-targeted nonobese diabetic (NOD) mice expressing a T cell “invisible” IGRP206–214 sequence. These mice developed islet inflammation and diabetes with normal incidence and kinetics, but their inflammatory lesions could recruit neither naive (endogenous or exogenous) nor ex vivo-activated IGRP206–214-reactive CD8+ T cells. Conversely, IGRP206–214-reactive, but not nonautoreactive CD8+ T cells rapidly homed to and accumulated in the inflamed islets of wild-type NOD mice. Our results indicate that CD8+ T cell recruitment to a site of autoimmune inflammation results from an active process that is strictly dependent on local display of cognate pMHC and suggest that CD8+ T cells contained in extralymphoid autoimmune lesions are largely autoreactive.