InVivoMAb anti-rat CD28

Retinoic acid receptor-related-orphan-receptor-C (RORγt) is the key transcription factor that is driving the differentiation of IL-17 producing T-helper 17 (Th17) cells that are implicated in the pathology of various autoimmune and inflammatory diseases. Based on the importance of RORγt in promoting Th17-driven pathology, there is considerable interest to develop low-molecular-weight compounds with the aim of inhibiting the transcriptional activity of this nuclear hormone receptor. In this article, we describe the in vitro and in vivo pharmacology of a potent and selective small-molecular-weight RORγt inverse agonist. The compound binds to the ligand binding domain (LBD) of RORγt leading to displacement of a co-activator peptide. We show for the first time that a RORγt inverse agonist down-regulates permissive histone H3 acetylation and methylation at the IL17A and IL23R promoter regions, thereby providing insight into the transcriptional inhibition of RORγt-dependent genes. Consistent with this, the compound effectively reduced IL-17A production by polarized human T-cells and γδT-cells and attenuated transcription of RORγt target genes. The inhibitor showed good in vivo efficacy in an antigen-induced arthritis model in rats and reduced the frequencies of IL-17A producing cells in ex vivo recall assays. In summary, we demonstrate that inhibiting RORγt by a low-molecular-weight inhibitor results in efficient and selective blockade of the pro-inflammatory Th17/IL-17A pathway making it an attractive target for Th17-mediated disorders.

Retinoic-acid-orphan-receptor-C (RORC) is a master regulator of Th17 cells, which are pathogenic in several autoimmune diseases. Genetic Rorc deficiency in mice, while preventing autoimmunity, causes early lethality due to metastatic thymic T cell lymphomas. We sought to determine whether pharmacological RORC inhibition could be an effective and safe therapy for autoimmune diseases by evaluating its effects on Th17 cell functions and intrathymic T cell development. RORC inhibitors effectively inhibited Th17 differentiation and IL-17A production, and delayed-type hypersensitivity reactions. In vitro, RORC inhibitors induced apoptosis, as well as Bcl2l1 and BCL2L1 mRNA downregulation, in mouse and nonhuman primate thymocytes, respectively. Chronic, 13-week RORC inhibitor treatment in rats caused progressive thymic alterations in all analyzed rats similar to those in Rorc-deficient mice prior to T cell lymphoma development. One rat developed thymic cortical hyperplasia with preneoplastic features, including increased mitosis and reduced IKAROS expression, albeit without skewed T cell clonality. In summary, pharmacological inhibition of RORC not only blocks Th17 cell development and related cytokine production, but also recapitulates thymic aberrations seen in Rorc-deficient mice. While RORC inhibition may offer an effective therapeutic principle for Th17-mediated diseases, T cell lymphoma with chronic therapy remains an apparent risk.

Long-term survival of T lymphocytes in quiescent state is essential to maintain their cell numbers in secondary lymphoid organs. In mice and in rats, the loss of functional GTPase of the immune associated nucleotide binding protein 5 (GIMAP5) causes peripheral T lymphopenia due to spontaneous death of T cells. The underlying mechanism responsible for the disruption of quiescence in Gimap5 deficient T cells remains largely unknown. In this study, we show that loss of functional Gimap5 results in increased basal activation of mammalian target of rapamycin (mTOR), independent of protein phosphatase 2A (PP2A) or AMP-activated protein kinase (AMPK). Our results suggest that the constitutive activation of the phosphoinositide 3-kinase (PI3K) pathway may be one of the consequences of the absence of functional GIMAP5.

The cotton rat (Sigmodon hispidus) belongs to the rodent family of Cricetidae and provides a powerful model to study the pathogenesis of human respiratory viruses and measles virus. Recent studies in other rodent models have suggested a role for invariant natural killer T (iNKT) cells in antiviral immunity and vaccination against respiratory virus infections. Using new experimental tools, we provide the first evidence for a functional CD1d cell molecule (crCD1d) and iNKT T-cell receptor in cotton rats. The crCD1d cDNA sequence was identified and crCD1d transductants showed that monoclonal antibody WTH-2 stains crCD1d as efficiently as mouse or rat CD1d. The expression of crCD1d was clearly weaker for thymocytes and B cells, and higher for T cells, which is different to what is found in murine species. The antigen-presenting capacity of crCD1d was demonstrated with crCD1d-immunoglobulin dimers loaded with the glycolipid PBS57, which bound iNKT T-cell receptors. Evidence for functional cotton rat iNKT cells was provided by detection of interferon-gamma and interleukin-4 in cultures of splenocytes stimulated with PBS57 and alpha-galactosylceramide and by specific staining of about 0.2% of splenocytes with PBS57-loaded crCD1d dimers. Canonical AV14/AJ18 rearrangements were identified and found to contain multiple members of the AV14 (AV11) family. One of them was expressed and found to bind CD1d dimers. In summary, these data provide the first evidence for functional CD1d molecules and iNKT T-cell receptors in cotton rats and provide the tools to analyse them both in the cotton rat model of infectious diseases.