Suppression of Ongoing T Cell-Mediated Autoimmunity by Peptide-MHC Class II Dimer Vaccination

Tissue-specific autoimmune diseases such as type 1 diabetes (T1D) are characterized by T cell-driven pathology. Administration of autoantigenic peptides provides a strategy to selectively target the pathogenic T cell response. Indeed, treatment with β cell peptides effectively prevents T1D in NOD mice. However, the efficacy of peptide immunotherapy generally wanes as β cell autoimmunity progresses and islet inflammation increases. With the goal of enhancing the efficacy of peptide immunotherapy, soluble (s)IAg7-Ig dimers covalently linked to β cell autoantigen-derived peptides were tested for the capacity to suppress late preclinical T1D. NOD female mice with established β cell autoimmunity were vaccinated i.v. with a short course of sIAg7-Ig dimers tethered to peptides derived from glutamic acid decarboxylase (GAD)65 (sIAg7-pGAD65). Treatment with sIAg7-pGAD65 dimers and the equivalent of only ~7 μg of native peptide effectively blocked the progression of insulitis and the development of diabetes. Furthermore, suppression of T1D was dependent on β cell-specific IL-10-secreting CD4+ T cells, although the frequency of GAD65-specific FoxP3-expressing CD4+ T cells was also increased in sIAg7-pGAD65 dimer vaccinated NOD mice. These results demonstrate that MHC class II-Ig dimer vaccination is a robust approach to suppress ongoing T cell-mediated autoimmunity, and may provide a superior strategy of adjuvant-free peptide-based immunotherapy to induce immunoregulatory T cells

MerTK is required for apoptotic cell–induced T cell tolerance

Self-antigens expressed by apoptotic cells (ACs) may become targets for autoimmunity. Tolerance to these antigens is partly established by an ill-defined capacity of ACs to inhibit antigen-presenting cells such as dendritic cells (DCs). We present evidence that the receptor tyrosine kinase Mer (MerTK) has a key role in mediating AC-induced inhibition of DC activation/maturation. Pretreatment of DCs prepared from nonobese diabetic (NOD) mice with AC blocked secretion of proinflammatory cytokines, up-regulation of costimulatory molecule expression, and T cell activation. The effect of ACs on DCs was dependent on Gas6, which is a MerTK ligand. NOD DCs lacking MerTK expression (NOD.MerTKKD/KD) were resistant to AC-induced inhibition. Notably, autoimmune diabetes was exacerbated in NOD.MerTKKD/KD versus NOD mice expressing the transgenic BDC T cell receptor. In addition, β cell–specific CD4+ T cells adoptively transferred into NOD.MerTKKD/KD mice in which β cell apoptosis was induced with streptozotocin exhibited increased expansion and differentiation into type 1 T cell effectors. In both models, the lack of MerTK expression was associated with an increased frequency of activated pancreatic CD11c+CD8α+ DCs, which exhibited an enhanced T cell stimulatory capacity. These findings demonstrate that MerTK plays a critical role in regulating self-tolerance mediated between ACs, DCs, and T cells

IFN-γ receptor deficiency prevents diabetes induction by diabetogenic CD4 + T cells but not CD8 + T cells

IFN-γ is generally believed to be important in the autoimmune pathogenesis of type 1 diabetes (T1D). However, the development of spontaneous β cell autoimmunity is unaffected in NOD mice lacking expression of IFN-γ or the IFN-γ receptor (IFNγR), bringing into question the role IFN-γ has in T1D. In the current study an adoptive transfer model was employed to define the contribution of IFN-γ in CD4+ versus CD8+ T cell-mediated β cell autoimmunity. NOD.scid mice lacking expression of the IFNγR β chain (NOD.scid.IFNγRBnull) developed diabetes following transfer of β cell-specific CD8+ T cells alone. In contrast, β cell-specific CD4+ T cells alone failed to induce diabetes despite significant infiltration of the islets in NOD.scid.IFNγRBnull recipients. The lack of pathogenicity of CD4+ T cell effectors was due to the resistance of IFNγR-deficient β cells to inflammatory cytokine-induced cell death. On the other hand, CD4+ T cells indirectly promoted β cell destruction by providing help to CD8+ T cells in NOD.scid.IFNγRBnull recipients. These results demonstrate that IFN-γR may play a key role in CD4+ T cell-mediated β cell destruction

TRAF3 regulates homeostasis of CD8+ central memory T cells.

Our laboratory reported previously that TNF receptor associated factor 3 (TRAF3) is a positive regulator of TCR signaling and T cell function. In the current study, we present new findings that reveal differential roles for TRAF3 in the regulation of CD4+ and CD8(+) T cells. In response to TCR stimulation in vitro, TRAF3 has greater impact in CD4(+) T cells than in CD8+ T cells. However, T cell-specific TRAF3 deficient mice (CD4Cre TRAF3(fl°x)/(fl°x); T-TRAF3(-/-)) have a greater number of CD4(+)CD44(hi) effector/memory T cells than littermate control (LMC) mice, possibly due to an inefficient suppressive effect of TRAF3 deficient Foxp3+ regulatory T cells. In contrast, CD8(+)CD44(hi)CD62L(hi) central memory (Tcm) cells are markedly reduced in T-TRAF3(-/-) mice in comparison to LMC mice, although CD8(+)CD44(hi)CD62L(l°w) effector memory T (Tem) cells and naïve T cells (CD8(+)CD44(l°w)CD62L(hi)) do not show significant differences in number. Importantly, TRAF3-deficient Tcm cells exhibit defective homeostasis due to impaired IL-15 signaling. These results indicate that the involvement of TRAF3 in IL-15 mediated signaling to T cells plays a previously unappreciated and critical role in CD8(+) Tcm cell regulation and maintenance

Increased effector/memory CD4⁺ T cells in T-TRAF3^−/− mice.

<p>Splenocytes were stained for CD4, Foxp3, CD44 and CD62L. CD4⁺Foxp3⁻ T cells were gated for CD44 and CD62L analysis. (<b>A</b>) percentages, (<b>B</b>) numbers of naïve and (<b>C</b>) numbers of CD44^hiCD62L^l°^w effector/memory T cells are shown. Data represent 10 mice in each group. (<b>D</b>) and (<b>E</b>) Splenocytes were stimulated with PMA and ionomycin for 6 hr. Intracellular staining for cytokine production in CD4⁺ T cell subsets was performed. (<b>E</b>) Summarized data from three individual experiments. *p<0.01.</p

Reduced CD8⁺ central memory T cells in T-TRAF3^−/− mice.

<p>Splenocytes were stained for CD8, CD44 and CD62L. (<b>A</b>) Percentages of CD8⁺ naïve, Tem and Tcm cells in LMC and T-TRAF3^−/− mice. Numbers of naïve (<b>B</b>), Tem (<b>C</b>) and Tcm (<b>D</b>) cells are shown. (<b>E</b>) and (<b>F</b>) Splenocytes were stimulated with PMA and ionomycin for 6 hr. Intracellular staining for cytokine production in CD8⁺ T cell subsets was performed. (<b>F</b>) Summarized data from three individual experiments. *p<0.01.</p

Defective homeostasis of CD8⁺ Tcm cells in the absence of TRAF3.

<p>(<b>A</b>) and (<b>B</b>) Sorted CD8⁺ T cells were labeled with CFSE and stimulated with 60 ng/ml IL-15 for 72 hr. Cells were stained for CD8, CD44 and CD62L. The dilution of CFSE in different populations is shown in (<b>A</b>), and data from three experiments are summarized in (<b>B</b>). (<b>C</b>) and (<b>D</b>) Freshly isolated splenocytes were stained for CD8, CD44, CD62L and Annexin V. Different CD8⁺ T cell subsets were gated for Annexin V analysis (<b>C</b> and <b>D</b>). Data represent 6 mice per group. (<b>E</b>) and (<b>F</b>) Splenocytes cultured for 24 hr without stimulation and stained for CD8, CD44, CD62L and Annexin V. Annexin V positive cells in different CD8⁺ T cell subsets are shown (<b>E</b> and <b>F</b>). Data represent one of three individual experiments. *p<0.01.</p