GITR: a modulator of immune response and inflammation

Autoimmune therapies targeting costimulation and emerging trends in multivalent therapeutics

Proteins participating in immunological signaling have emerged as important targets for controlling the immune response. A multitude of receptor-ligand pairs that regulate signaling pathways of the immune response have been identified. In the complex milieu of immune signaling, therapeutic agents targeting mediators of cellular signaling often either activate an inflammatory immune response or induce tolerance. This review is primarily focused on therapeutics that inhibit the inflammatory immune response by targeting membrane-bound proteins regulating costimulation or mediating immune-cell adhesion. Many of these signals participate in larger, organized structures such as the immunological synapse. Receptor clustering and arrangement into organized structures is also reviewed and emerging trends implicating a potential role for multivalent therapeutics is posited.

The glucocorticoid-induced TNF receptor family-related protein (GITR) is critical to the development of acute pancreatitis in mice

BACKGROUND AND PURPOSE

Pancreatitis represents a life-threatening inflammatory condition where leucocytes, cytokines and vascular endothelium contribute to the development of the inflammatory disease. The glucocorticoid-induced tumour necrosis factor (TNF) receptor family-related protein (GITR) is a costimulatory molecule for T lymphocytes, modulates innate and adaptive immune system and has been found to participate in a variety of immune responses and inflammatory processes. Our purpose was to verify whether inhibition of GITR triggering results in a better outcome in experimental pancreatitis.

EXPERIMENTAL APPROACH

In male GITR knock-out (GITR(-/-)) and GITR(+/+) mice on Sv129 background, acute pancreatitis was induced after i.p. administration of cerulein. Other experimental groups of GITR(+/+) mice were also treated with different doses of Fc-GITR fusion protein (up to 6.25 µg·mouse⁻¹), given by implanted mini-osmotic pump. Clinical score and pro-inflammatory parameters were evaluated.

KEY RESULTS

A less acute pancreatitis was found in GITR(-/-) mice than in GITR(+/+) mice, with marked differences in oedema, neutrophil infiltration, pancreatic dysfunction and injury. Co-treatment of GITR(+/+) mice with cerulein and Fc-GITR fusion protein (6.25 µg·mouse⁻¹) decreased the inflammatory response and tissue injury, compared with treatment with cerulein alone. Inhibition of GITR triggering was found to modulate activation of nuclear factor κB as well as the production of TNF-α, interleukin-1β, inducible nitric oxide synthase, nitrotyrosine, poly-ADP-ribose, intercellular adhesion molecule-1 and P-selectin.

CONCLUSIONS AND IMPLICATIONS

The GITR-GITR ligand system is crucial to the development of acute pancreatitis in mice. Our results also suggest that the Fc-GITR fusion protein could be useful in the treatment of acute pancreatitis.

Human cytomegalovirus IE1 protein elicits a type II interferon-like host cell response that depends on activated STAT1 but not interferon-γ

Human cytomegalovirus (hCMV) is a highly prevalent pathogen that, upon primary infection, establishes life-long persistence in all infected individuals. Acute hCMV infections cause a variety of diseases in humans with developmental or acquired immune deficits. In addition, persistent hCMV infection may contribute to various chronic disease conditions even in immunologically normal people. The pathogenesis of hCMV disease has been frequently linked to inflammatory host immune responses triggered by virus-infected cells. Moreover, hCMV infection activates numerous host genes many of which encode pro-inflammatory proteins. However, little is known about the relative contributions of individual viral gene products to these changes in cellular transcription. We systematically analyzed the effects of the hCMV 72-kDa immediate-early 1 (IE1) protein, a major transcriptional activator and antagonist of type I interferon (IFN) signaling, on the human transcriptome. Following expression under conditions closely mimicking the situation during productive infection, IE1 elicits a global type II IFN-like host cell response. This response is dominated by the selective up-regulation of immune stimulatory genes normally controlled by IFN-γ and includes the synthesis and secretion of pro-inflammatory chemokines. IE1-mediated induction of IFN-stimulated genes strictly depends on tyrosine-phosphorylated signal transducer and activator of transcription 1 (STAT1) and correlates with the nuclear accumulation and sequence-specific binding of STAT1 to IFN-γ-responsive promoters. However, neither synthesis nor secretion of IFN-γ or other IFNs seems to be required for the IE1-dependent effects on cellular gene expression. Our results demonstrate that a single hCMV protein can trigger a pro-inflammatory host transcriptional response via an unexpected STAT1-dependent but IFN-independent mechanism and identify IE1 as a candidate determinant of hCMV pathogenicity.

NKT cell costimulation: experimental progress and therapeutic promise

Invariant natural killer T (iNKT) cells are innate lymphocytes with unique specificity for glycolipid antigens and remarkable immunomodulatory properties. The role of costimulatory interactions in iNKT cell responses has recently come under scrutiny. Although iNKT cells and their prototype glycolipid agonist α-galactosylceramide (α-GalCer) have shown promise in several clinical trials conducted in patients with cancer or viral diseases, current iNKT cell-based therapies are far from effective. The concomitant targeting of T cell receptors (TCRs) and costimulatory molecules on iNKT cells represents an exciting new opportunity to optimize such therapeutic approaches. Here, we review recent advances in our understanding of iNKT cell costimulation and discuss potential treatment modalities based on the responsiveness of iNKT cells to disease-tailored glycolipids and select costimulatory ligands.

Glucocorticoid-Induced TNFR family Related gene (GITR) enhances dendritic cell activity

Glucocorticoid-Induced TNFR family Related gene (GITR), a Tumor Necrosis Factor Receptor Superfamily (TNFRSF) member involved in immune/inflammatory processes, has been previously shown to regulate T cell activation. To study GITR role in antigen presenting cells, we evaluated the capability of bone marrow derived dendritic cells (BMDC) from GITR(-/-) mice to stimulate the activation of CD4(+)CD25(-) T lymphocytes. We found that GITR(-/-) BMDC are weaker stimulators of T cell proliferation than GITR(+/+) BMDC, either in syngenic or allogenic BMDC/T cell co-cultures. Expression of GITR in GITR(-/-) BMDC restored their ability to activate T cells while GITR silencing in GITR(+/+) BMDC inhibited the capability to stimulate T cells. GITR(-/-) BMDC showed a reduced production of the pro-inflammatory cytokine IL-6 and an increased production of the anti-inflammatory cytokine IL-10. Notably, co-culture of CD4(+)CD25(-) cells with GITR(-/-) BMDC originated FoxP3(+) cells, secreting IL-10 and TGF-β. Finally, in vivo injection of GITR(-/-) OVA-loaded BMDC led to a lower cell number and a lower activated cell number in draining lymph nodes than in GITR(+/+) OVA-loaded BMDC injected mice. Together, these results indicate that GITR plays a role in regulating BMDC activity.

Neutralization of tumor necrosis factor-related apoptosis-inducing ligand reduces spinal cord injury damage in mice

Spinal cord injury (SCI) is a major cause of disability, its clinical outcome depending mostly on the extent of damage in which proapoptotic cytokines have a crucial function. In particular, the inducers of apoptosis belonging to TNF receptor superfamily and their respective ligands are upregulated after SCI. In this study, the function of the proapoptotic cytokine tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in SCI-induced damage was investigated in the mouse. SCI resulted in severe trauma, characterized by prominent inflammation-related damage and apoptosis. Immunostaining for TRAIL and its receptor DR5 was found in the white and gray matter of the perilesional area, as also confirmed by western blotting experiments. Immunoneutralization of TRAIL resulted in improved functional recovery, reduced apoptotic cell number, modulation of molecules involved in the inflammatory response (FasL, TNF-alpha, IL-1beta, and MPO), and the corresponding signaling (caspase-8 and -3 activation, JNK phosphorylation, Bax, and Bcl-2 expression). As glucocorticoid-induced TNF receptor superfamily-related protein (GITR) activated by its ligand (GITRL) contributes to SCI-related inflammation, interactions between TRAIL and GITRL were investigated. SCI was associated with upregulated GITR and GITRL expression, a phenomenon prevented by anti-TRAIL treatment. Moreover, the expression of both TRAIL and DR5 was reduced in tissues from mice lacking the GITR gene (GITR(-/-)) in comparison with wild-type mice suggesting that TRAIL- and GITRL-activated pathways synergise in the development of SCI-related inflammatory damage. Characterization of new targets within such molecular systems may constitute a platform for innovative treatment of SCI.