Pere Santamaria

Visualizing regulatory T cell control of autoimmune responses in nonobese diabetic mice

The in vivo mechanism of regulatory T cell (Treg cell) function in controlling autoimmunity remains controversial. Here we have used two-photon laser-scanning microscopy to analyze lymph node priming of diabetogenic T cells and to delineate the mechanisms of Treg cell control of autoimmunity in vivo. Islet antigen–specific CD4+CD25− T helper cells (TH cells) and Treg cells swarmed and arrested in the presence of autoantigens. These TH cell activities were progressively inhibited in the presence of increasing numbers of Treg cells. There were no detectable stable associations between Treg and TH cells during active suppression. In contrast, Treg cells directly interacted with dendritic cells bearing islet antigen. Such persistent Treg cell–dendritic cell contacts preceded the inhibition of TH cell activation by dendritic cells, supporting the idea that dendritic cells are central to Treg cell function in vivo.

The Combined Effects of Tryptophan Starvation and Tryptophan Catabolites Down-Regulate T Cell Receptor ζ-Chain and Induce a Regulatory Phenotype in Naive T Cells

Tryptophan catabolism is a tolerogenic effector system in regulatory T cell function, yet the general mechanisms whereby tryptophan catabolism affects T cell responses remain unclear. We provide evidence that the short-term, combined effects of tryptophan deprivation and tryptophan catabolites result in GCN2 kinase-dependent down-regulation of the TCR ζ-chain in murine CD8+ T cells. TCR ζ down-regulation can be demonstrated in vivo and is associated with an impaired cytotoxic effector function in vitro. The longer-term effects of tryptophan catabolism include the emergence of a regulatory phenotype in naive CD4+CD25− T cells via TGF-β induction of the forkhead transcription factor Foxp3. Such converted cells appear to be CD25+, CD69−, CD45RBlow, CD62L+, CTLA-4+, BTLAlow and GITR+, and are capable of effective control of diabetogenic T cells when transferred in vivo. Thus, both tryptophan starvation and tryptophan catabolites contribute to establishing a regulatory environment affecting CD8+ as well as CD4+ T cell function, and not only is tryptophan catabolism an effector mechanism of tolerance, but it also results in GCN2-dependent generation of autoimmune-preventive regulatory T cells.

Identification of the β cell antigen targeted by a prevalent population of pathogenic CD8+ T cells in autoimmune diabetes

Type 1 diabetes is an autoimmune disease in which autoreactive T cells attack and destroy the insulin-producing pancreatic β cells. CD8+ T cells are essential for this β cell destruction, yet their specific antigenic targets are largely unknown. Here, we reveal that the autoantigen targeted by a prevalent population of pathogenic CD8+ T cells in nonobese diabetic mice is islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP). Through tetramer technology, IGRP-reactive T cells are readily detected in islets and peripheral blood directly ex vivo. The human IGRP gene maps to a diabetes susceptibility locus, suggesting that IGRP also may be an antigen for pathogenic T cells in human type 1 diabetes and, thus, a new, potential target for diagnostic and therapeutic approaches.

Progression of autoimmune diabetes driven by avidity maturation of a T-cell population

For unknown reasons, autoimmune diseases such as type 1 diabetes develop after prolonged periods of inflammation of mononuclear cells in target tissues. Here we show that progression of pancreatic islet inflammation to overt diabetes in nonobese diabetic (NOD) mice is driven by the ‘avidity maturation’ of a prevailing, pancreatic beta-cell-specific T-lymphocyte population carrying the CD8 antigen. This T-lymphocyte population recognizes two related peptides (NRP and NRP-A7) in the context of H-2K d class I molecules of the major histocompatibility complex (MHC). As pre-diabetic NOD mice age, their islet-associated CD8+ T lymphocytes contain increasing numbers of NRP-A7-reactive cells, and these cells bind NRP-A7/H-2Kd tetramers with increased specificity, increased avidity and longer half-lives. Repeated treatment of pre-diabetic NOD mice with soluble NRP-A7 peptide blunts the avidity maturation of the NRP-A7-reactive CD8+ T-cell population by selectively deleting those clonotypes expressing T-cell receptors with the highest affinity and lowest dissociation rates for peptide–MHC binding. This inhibits the local production of T cells that are cytotoxic to beta cells, and halts the progression from severe insulitis to diabetes. We conclude that avidity maturation of pathogenic T-cell populations may be the key event in the progression of benign inflammation to overt disease in autoimmunity.

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.

TRPV1+ Sensory Neurons Control β Cell Stress and Islet Inflammation in Autoimmune Diabetes

In type 1 diabetes, T cell-mediated death of pancreatic beta cells produces insulin deficiency. However, what attracts or restricts broadly autoreactive lymphocyte pools to the pancreas remains unclear. We report that TRPV1(+) pancreatic sensory neurons control islet inflammation and insulin resistance. Eliminating these neurons in diabetes-prone NOD mice prevents insulitis and diabetes, despite systemic persistence of pathogenic T cell pools. Insulin resistance and beta cell stress of prediabetic NOD mice are prevented when TRPV1(+) neurons are eliminated. TRPV1(NOD), localized to the Idd4.1 diabetes-risk locus, is a hypofunctional mutant, mediating depressed neurogenic inflammation. Delivering the neuropeptide substance P by intra-arterial injection into the NOD pancreas reverses abnormal insulin resistance, insulitis, and diabetes for weeks. Concordantly, insulin sensitivity is enhanced in trpv1(-/-) mice, whereas insulitis/diabetes-resistant NODxB6Idd4-congenic mice, carrying wild-type TRPV1, show restored TRPV1 function and insulin sensitivity. Our data uncover a fundamental role for insulin-responsive TRPV1(+) sensory neurons in beta cell function and diabetes pathoetiology.

Prediction of spontaneous autoimmune diabetes in NOD mice by quantification of autoreactive T cells in peripheral blood

Autoimmune (type 1) diabetes mellitus results from the destruction of insulin-producing pancreatic beta cells by T lymphocytes. Prediction of cell-mediated autoimmune diseases by direct detection of autoreactive T cells in peripheral blood has proved elusive, in part because of their low frequency and reduced avidity for peptide MHC ligands. This article was published online in advance of the print edition. The date of publication is available from the JCI website, http://www.jci.org.

Autoimmune islet destruction in spontaneous type 1 diabetes is not β-cell exclusive

Pancreatic islets of Langerhans are enveloped by peri-islet Schwann cells (pSC), which express glial fibrillary acidic protein (GFAP) and S100β. pSC-autoreactive T- and B-cell responses arise in 3- to 4-week-old diabetes-prone non-obese diabetic (NOD) mice, followed by progressive pSC destruction before detectable β-cell death. Humans with probable prediabetes generate similar autoreactivities, and autoantibodies in islet-cell autoantibody (lCA) –positive sera co-localize to pSC. Moreover, GFAP-specific NOD T-cell lines transferred pathogenic peri-insulitis to NOD/severe combined immunodeficient (NOD/SCID) mice, and immunotherapy with GFAP or S100β prevented diabetes. pSC survived in rat insulin promoter Iymphocytic choriomeningitis virus (rip–LCMV) glycoprotein/CD8+ T-cell receptorgp double-transgenic mice with virus-induced diabetes, suggesting that pSC death is not an obligate consequence of local inflammation and β-cell destruction. However, pSC were deleted in spontaneously diabetic NOD mice carrying the CD8+/8.3 T-cell receptor transgene, a T cell receptor commonly expressed in earliest islet infiltrates. Autoimmune targeting of pancreatic nervous system tissue elements seems to be an integral, early part of natural type 1 diabetes.