Orally administered antigen can reduce or exacerbate pathology in an animal model of inflammatory arthritis dependent upon the timing of administration

Currently, treatments for rheumatoid arthritis (RA) are focussed on treatment of disease symptoms rather than addressing the cause of disease, which could lead to remission and cure. Central to disease development is the induction of autoimmunity through a breach of self-tolerance. There is considerable research in RA focussed on antigens and approaches to re-establish antigen specific tolerance. A crucial step in this research is to employ appropriate animal models to test prospective antigen specific immunotherapies, preferably in the context of joint inflammation. In this short communication, we use our previously developed model of antigen specific inflammatory arthritis in which OVA-specific TcR tg T cells drive breach of tolerance to endogenous antigens to determine the impact that the timing of therapy administration has upon disease progression. Using antigen feeding to induce tolerance we demonstrate that administration prior to articular challenge results in a reduced disease score as evidenced by pathology and serum antibody responses. By contrast, feeding antigen after articular challenge had the opposite effect and resulted in the exacerbation of pathology. Although preliminary, these data suggest that the timing of antigen administration may be key to the success of tolerogenic immunotherapies. This has important implications for the timing of potential tolerogenic therapies in patients.

Emerging Role of PD-1/PD-L1 Inhibitors in Chronic Liver Diseases

Programmed cell death protein 1 (PD-1)/PD-ligand (L)1, the immune checkpoint inhibitors have emerged as a promising strategy for the treatment of various diseases including chronic liver diseases (CLDs) such as hepatitis, liver injury and hepatocellular carcinoma (HCC). The role of PD-1/PD-L1 has been widely inspected in the treatment of viral hepatitis and HCC. PD-1 is known to play a crucial role in inhibiting immunological responses and stimulates self-tolerance by regulating the T-cell activity. Further, it promotes apoptosis of antigen-specific T-cells while preventing apoptosis of Treg cells. PD-L1 is a trans-membrane protein which is recognized as a co-inhibitory factor of immunological responses. Both, PD-1 and PD-L1 function together to downregulate the proliferation of PD-1 positive cells, suppress the expression of cytokines and stimulate apoptosis. Owing to the importance of PD-1/PD-L1 signaling, this review aims to summarize the potential of PD-1/PD-L1 inhibitors in CLDs along with toxicities associated with them. We have enlisted some of the important roles of PD-1/PD-L1 in CLDs, the clinically approved products and the pipelines of drugs under clinical evaluation.

mTEC damage risks immune recovery

Whether autologous hematopoietic stem cell transplantation is free from graft-versus-host disease is controversial. Alawam et al. (2021. J. Exp. Med.https://doi.org/10.1084/jem.20211239) now demonstrate that prolonged damage in thymic medullary epithelial cells causes the failure in self-tolerance in newly generated T cells and provokes post-transplant autoimmunity.

Immune Checkpoints and Innate Lymphoid Cells—New Avenues for Cancer Immunotherapy

Immune checkpoints (IC) are broadly characterized as inhibitory pathways that tightly regulate the activation of the immune system. These molecular “brakes” are centrally involved in the maintenance of immune self-tolerance and represent a key mechanism in avoiding autoimmunity and tissue destruction. Antibody-based therapies target these inhibitory molecules on T cells to improve their cytotoxic function, with unprecedented clinical efficacies for a number of malignancies. Many of these ICs are also expressed on innate lymphoid cells (ILC), drawing interest from the field to understand their function, impact for anti-tumor immunity and potential for immunotherapy. In this review, we highlight ILC specificities at different tissue sites and their migration potential upon inflammatory challenge. We further summarize the current understanding of IC molecules on ILC and discuss potential strategies for ILC modulation as part of a greater anti-cancer armamentarium.

Loss of self-tolerance leads to altered gene expression and IMD pathway activation in Drosophila melanogaster

Immune self-tolerance is the ability of a host's immune system to recognize and avoid triggering immune responses against self-tissue. This allows the host to avoid self-directed immune damage while still responding appropriately to pathogen infection. A breakdown of self-tolerance can lead to an autoimmune state in which immune cells target healthy self-tissue, leading to inflammation and tissue damage. In order to better understand the basic biology of autoimmunity and the role of the innate immune system in maintaining self-tolerance, we have recently characterized the Drosophila melanogaster tuSz autoimmune mutant. This mutant strain can serve as a model of innate immune mediated self-tolerance, and here we identify transcripts that are deregulated in flies experiencing a loss of self-tolerance. We found that these changes include the ectopic activation of pro-inflammatory signaling through the Relish/NFκB transcription factor, alterations in transcripts encoding proteins predicted to mediate organismal metabolism, and a downregulation of transcripts linked to developmental processes. This study can provide insight into the transcriptional and physiological changes underlying self-tolerance and autoimmunity.

Regulatory T cells suppress the formation of super-effector CD8 T cells by limiting IL-2

Regulatory T cells (Tregs) are indispensable for maintaining self-tolerance by suppressing conventional T cells. On the other hand, Tregs may promote tumor growth by inhibiting anti-cancer immunity. In this study, we identified that Tregs increase the quorum of self-reactive CD8+ T cells required for the induction of experimental autoimmune diabetes. Their major suppression mechanism is limiting available IL-2, a key cytokine for activated T cells. Specifically, Tregs inhibit the formation of a previously uncharacterized subset of antigen-stimulated CD8+ T cells. Since these T cells express high levels of IL-7 receptor and cytotoxic molecules (KLRK1, GZMB), and show superior cell killing abilities, we call them super-effector T cells. The administration of agonistic IL-2 immunocomplexes phenocopies the absence of Tregs, i.e., it induces super-effector T cells, promotes autoimmunity, and enhances anti-tumor responses. Counterparts of super-effector T cells were found in the human blood, revealing them as a potential target for immunotherapy.

Single-Cell Multiomics Defines Tolerogenic Extrathymic Aire-Expressing Populations with Unique Homology to Thymic Epithelium

The Autoimmune Regulator (Aire) gene, well defined for its role in medullary thymic epithelial cells (mTECs) and immune self-tolerance, is also expressed in extrathymic Aire-expressing cells (eTACs) in the secondary lymphoid organs. eTACs have been shown to be hematopoietic antigen presenting cells (APCs) and potent inducers of immune tolerance. However, the precise identity and function of these cells remain unclear. Here, we use high-dimensional single-cell multiomics and functional approaches to define eTACs at the transcriptional, genomic, and proteomic level. We find that eTACs consist of two similar cell types: CCR7+ Aire-expressing migratory dendritic cells (AmDCs) and a unique Aire-hi population co-expressing Aire and RAR-related orphan receptor gamma-t (RORγt). The latter, which have significant transcriptional and genomic homology to migratory dendritic cells (migDCs) and mTECs, we term Janus cells (JCs). All eTACs, and JCs in particular, have a highly accessible chromatin structure and high levels of broad gene expression, including tissue-specific antigens, as well as remarkable transcriptional and genomic homology to thymic medullary epithelium. As in the thymus, Aire expression in eTACs is also dependent on RANK-RANK-ligand interactions. Furthermore, lineage-tracing shows that JCs are not precursors to the majority of AmDCs. Finally, self-antigen expression by eTACs is sufficient to mediate negative selection of T cells escaping thymic selection and can prevent autoimmune diabetes in non-obese diabetic mice. This transcriptional, genomic, and functional symmetry between a hematopoietic Aire-expressing population in the periphery and an epithelial Aire-expressing population in the thymus suggests that a core biological program may influence self-tolerance and self-representation across the spectrum of immune development.