Cristina Penaranda

Central Role of Defective Interleukin-2 Production in the Triggering of Islet Autoimmune Destruction

The dynamics of CD4(+) effector T cells (Teff cells) and CD4(+)Foxp3(+) regulatory T cells (Treg cells) during diabetes progression in nonobese diabetic mice was investigated to determine whether an imbalance of Treg cells and Teff cells contributes to the development of type 1 diabetes. Our results demonstrated a progressive decrease in the Treg cell:Teff cell ratio in inflamed islets but not in pancreatic lymph nodes. Intra-islet Treg cells expressed reduced amounts of CD25 and Bcl-2, suggesting that their decline was due to increased apoptosis. Additionally, administration of low-dose interleukin-2 (IL-2) promoted Treg cell survival and protected mice from developing diabetes. Together, these results suggest intra-islet Treg cell dysfunction secondary to defective IL-2 production is a root cause of the progressive breakdown of self-tolerance and the development of diabetes in nonobese diabetic mice.

Intrinsic and extrinsic control of peripheral T-cell tolerance by costimulatory molecules of the CD28/B7 family

Summary:  Positive and negative costimulation by members of the CD28 family is critical for the development of productive immune responses against foreign pathogens and their proper termination to prevent inflammation‐induced tissue damage. In addition, costimulatory signals are critical for the establishment and maintenance of peripheral tolerance. This paradigm has been established in many animal models and has led to the development of immunotherapies targeting costimulation pathways for the treatment of cancer, autoimmune disease, and allograft rejection. During the last decade, the complexity of the biology of costimulatory pathways has greatly increased due to the realization that costimulation does not affect only effector T cells but also influences regulatory T cells and antigen‐presenting cells. Thus, costimulation controls T‐cell tolerance through both intrinsic and extrinsic pathways. In this review, we discuss the influence of costimulation on intrinsic and extrinsic pathways of peripheral tolerance, with emphasis on members of the CD28 family, CD28, cytotoxic T‐lymphocyte antigen‐4 (CTLA‐4), and programmed death‐1 (PD‐1), as well as the downstream cytokine interleukin‐1 (IL‐2).

T-bet is required for optimal production of IFN-γ and antigen-specific T cell activation by dendritic cells

IFN-γ is well known as the signature cytokine of CD4+ T helper 1, CD8+, and natural killer cells, but recent studies demonstrate that antigen-presenting cells, in particular dendritic cells (DCs), are another potent source for this proinflammatory cytokine. T-bet, a transcription factor that controls IFN-γ expression in CD4+ T cells, was reported recently to be expressed in human monocytes and myeloid DCs. In this study we investigate the role of T-bet in this important cell type. The development, differentiation, and activation of bone marrow and splenic DCs were unimpaired in mice lacking T-bet. However, T-bet was essential for the optimal production of IFN-γ by both CD8α+ and CD8α- DCs. T-bet-deficient DCs were significantly impaired in their capacity to secrete IFN-γ after both stimulation with IL-12 alone or in combination with IL-18. Further, T-bet-/- DCs were impaired in their ability to activate the T helper 1 program of adoptively transferred antigen-specific T cells in vivo. The rapid up-regulation of T-bet by IFN-γ in DCs coupled with a function for DC-derived IFN-γ in T cell activation may constitute a positive feedback loop to maximize type 1 immunity.

Production of α-Galactosylceramide by a Prominent Member of the Human Gut Microbiota

A common human gut bacterium, Bacteroides fragilis, produces a sphingolipid ligand for the conserved host receptor CD1d and can modulate natural killer T cell activity.

Anti-CD3 Therapy Promotes Tolerance by Selectively Depleting Pathogenic Cells while Preserving Regulatory T Cells

Monoclonal anti-CD3 Abs have been used clinically for two decades to reverse steroid-resistant acute graft rejection. In autoimmune diabetes, short course treatment with FcR-nonbinding (FNB) anti-CD3 mAb in mice with recent onset of diabetes induces long-term disease remission. Induction of tolerogenic regulatory T cells (Tregs) has been implicated to be one of the mechanisms of action by FNB anti-CD3 mAb in these settings. In this study, we examined the effect of FNB anti-CD3 mAb treatment on the homeostasis of naive, effector, and regulatory T cells in vivo. Anti-CD3 treatment induced a transient systemic rise in the percentage but not absolute number of CD4+Foxp3+ Tregs due to selective depletion of CD4+Foxp3− conventional T cells. T cell depletion induced by FNB anti-CD3 mAb was independent of the proapoptotic proteins Fas, caspase-3, and Bim and was not inhibited by overexpression of the anti-apoptotic protein, Bcl-2. Tregs were not preferentially expanded and we found no evidence of conversion of conventional T cells into Tregs, suggesting that the pre-existing Tregs are resistant to anti-CD3–induced cell death. Interestingly, expression of the transcription factor Helios, which is expressed by thymus-derived natural Tregs, was increased in Tregs after FNB anti-CD3 mAb treatment, suggesting that the anti-CD3 treatment can alter, and potentially stabilize, Treg function. Taken together, the results suggest that FNB anti-CD3 therapy promotes tolerance by restoring the balance between pathogenic and regulatory T cells.

IL-7 receptor blockade reverses autoimmune diabetes by promoting inhibition of effector/memory T cells

To protect the organism against autoimmunity, self-reactive effector/memory T cells (TE/M) are controlled by cell-intrinsic and -extrinsic regulatory mechanisms. However, how some TE/M cells escape regulation and cause autoimmune disease is currently not understood. Here we show that blocking IL-7 receptor-α (IL-7Rα) with monoclonal antibodies in nonobese diabetic (NOD) mice prevented autoimmune diabetes and, importantly, reversed disease in new-onset diabetic mice. Surprisingly, IL-7–deprived diabetogenic TE/M cells remained present in the treated animals but showed increased expression of the inhibitory receptor Programmed Death 1 (PD-1) and reduced IFN-γ production. Conversely, IL-7 suppressed PD-1 expression on activated T cells in vitro. Adoptive transfer experiments revealed that TE/M cells from anti–IL-7Rα–treated mice had lost their pathogenic potential, indicating that absence of IL-7 signals induces cell-intrinsic tolerance. In addition to this mechanism, IL-7Rα blockade altered the balance of regulatory T cells and TE/M cells, hence promoting cell-extrinsic regulation and further increasing the threshold for diabetogenic T-cell activation. Our data demonstrate that IL-7 contributes to the pathogenesis of autoimmune diabetes by enabling TE/M cells to remain in a functionally competent state and suggest IL-7Rα blockade as a therapy for established T-cell–dependent autoimmune diseases.

Diarylureas are small-molecule inhibitors of insulin-like growth factor I receptor signaling and breast cancer cell growth

In breast and certain other cancers, receptor tyrosine kinases, including the insulin-like growth factor I receptor (IGF-IR), play an important role in promoting the oncogenic process. The IGF-IR is therefore an important target for developing new anti–breast cancer therapies. An initial screening of a chemical library against the IGF-IR in breast cancer cells identified a diaryl urea compound as a potent inhibitor of IGF-IR signaling. This class of compounds has not been studied as inhibitors of the IGF-IR. We studied the effectiveness of one diaryl urea compound, PQ401, at antagonizing IGF-IR signaling and inhibiting breast cancer cell growth in culture and in vivo. PQ401 inhibited autophosphorylation of the IGF-IR in cultured human MCF-7 cells with an IC50 of 12 μmol/L and autophosphorylation of the isolated kinase domain of the IGF-IR with an IC50 <1 μmol/L. In addition, PQ401 inhibited the growth of cultured breast cancer cells in serum at 10 μmol/L. PQ401 was even more effective at inhibiting IGF-I-stimulated growth of MCF-7 cells (IC50, 6 μmol/L). Treatment of MCF-7 cells with PQ401 was associated with a decrease in IGF-I-mediated signaling through the Akt antiapoptotic pathway. Twenty-four hours of treatment with 15 μmol/L PQ401 induced caspase-mediated apoptosis. In vivo, treatment with PQ401 (i.p. injection thrice a week) reduced the growth rate of MCNeuA cells implanted into mice. These studies indicate that diaryl urea compounds are potential new agents to test in the treatment of breast and other IGF-I-sensitive cancers. [Mol Cancer Ther 2006;5(4):1079–86]

Prevention of diabetes by FTY720-mediated stabilization of peri-islet tertiary lymphoid organs

OBJECTIVE The nonobese diabetic (NOD) mouse is a well-established mouse model of spontaneous type 1 diabetes, which is characterized by an autoimmune destruction of the insulin-secreting pancreatic β-cells. In this study, we address the role of tertiary lymphoid organs (TLOs) that form in the pancreas of NOD mice during disease progression. METHODS We developed a model designed to “lock” lymphocytes in the pancreatic lymph node (PLN) and pancreas by the use of FTY720, which blocks the exit of lymphocytes from lymph nodes. A combination of flow cytometry, immunofluorescence, and analysis of clinical scores was used to study the effects of long-term FTY720 treatment on TLO development and development of diabetes. RESULTS Continuous treatment of NOD mice with FTY720 prevented diabetes development even at a time of significant insulitis. Treatment withdrawal led to accelerated disease independent of the PLN. Interestingly, naive T-cells trafficked to and proliferated in the TLOs. In addition, morphological changes were observed that occurred during the development of the disease. Remarkably, although the infiltrates are not organized into T/B-cell compartments in 8-week-old mice, by 20 weeks of age, and in age-matched mice undergoing FTY720 treatment, the infiltrates showed a high degree of organization. However, in naturally and FTY720-induced diabetic mice, T/B-cell compartmentalization was lost. CONCLUSION Our data show that TLOs are established during diabetes development and suggest that islet destruction is due to a loss of TLO integrity, which may be prevented by FTY720 treatment.

Aberrant innate immune activation following tissue injury impairs pancreatic regeneration.

Normal tissue architecture is disrupted following injury, as resident tissue cells become damaged and immune cells are recruited to the site of injury. While injury and inflammation are critical to tissue remodeling, the inability to resolve this response can lead to the destructive complications of chronic inflammation. In the pancreas, acinar cells of the exocrine compartment respond to injury by transiently adopting characteristics of progenitor cells present during embryonic development. This process of de-differentiation creates a window where a mature and stable cell gains flexibility and is potentially permissive to changes in cellular fate. How de-differentiation can turn an acinar cell into another cell type (such as a pancreatic β-cell), or a cell with cancerous potential (as in cases of deregulated Kras activity) is of interest to both the regenerative medicine and cancer communities. While it is known that inflammation and acinar de-differentiation increase following pancreatic injury, it remains unclear which immune cells are involved in this process. We used a combination of genetically modified mice, immunological blockade and cellular characterization to identify the immune cells that impact pancreatic regeneration in an in vivo model of pancreatitis. We identified the innate inflammatory response of macrophages and neutrophils as regulators of pancreatic regeneration. Under normal conditions, mild innate inflammation prompts a transient de-differentiation of acinar cells that readily dissipates to allow normal regeneration. However, non-resolving inflammation developed when elevated pancreatic levels of neutrophils producing interferon-γ increased iNOS levels and the pro-inflammatory response of macrophages. Pancreatic injury improved following in vivo macrophage depletion, iNOS inhibition as well as suppression of iNOS levels in macrophages via interferon-γ blockade, supporting the impairment in regeneration and the development of chronic inflammation arises from aberrant activation of the innate inflammatory response. Collectively these studies identify targetable inflammatory factors that can be used to influence the development of non-resolving inflammation and pancreatic regeneration following injury.

Is Antigen Specificity of Autoreactive T Cells the Key to Islet Entry

It has been widely hypothesized that pancreatic islet infiltrates include both islet-antigen-specific and nonspecific T cells. In this issue of Immunity, Lennon et al. (2009) demonstrate that islet-antigen specificity is required for accumulation in the islets.