Enhanced Requirement for TNFR2 in Graft Rejection Mediated by Low-Affinity Memory CD8+ T Cells during Heterologous Immunity

Tissue-resident memory T cells in chronic liver diseases: Phenotype, development and function

Tissue-resident memory (T_RM) T cells are a unique subset of memory T cells that are critical for the first line of defense against pathogens or antigens in peripheral non-lymphoid tissues such as liver, gut, and skin. Generally, T_RM cells are well adapted to the local environment in a tissue-specific manner and typically do not circulate but persist in tissues, distinguishing them from other memory T cell lineages. There is strong evidence that liver T_RM cells provide a robust adaptive immune response to potential threats. Indeed, the potent effector function of hepatic T_RM cells makes it essential for chronic liver diseases, including viral and parasite infection, autoimmune liver diseases (AILD), nonalcoholic fatty liver disease (NAFLD), hepatocellular carcinoma (HCC) and liver transplantation. Manipulation of hepatic T_RM cells might provide novel promising strategies for precision immunotherapy of chronic liver diseases. Here, we provide insights into the phenotype of hepatic T_RM cells through surface markers, transcriptional profiles and effector functions, discuss the development of hepatic T_RM cells in terms of cellular origin and factors affecting their development, analyze the role of hepatic T_RM cells in chronic liver diseases, as well as share our perspectives on the current status of hepatic T_RM cell research.

Decreased expression of transmembrane TNFR2 in lung leukocytes subpopulations of patients with non-fibrotic hypersensitivity pneumonitis compared with the fibrotic disease

Hypersensitivity pneumonitis (HP) is an interstitial lung disease, characterized by lung inflammation (non-fibrotic HP) that may often progresses to fibrosis (Fibrotic HP). The tumor necrosis factor (TNF) and its receptors (TNFR1 and TNFR2) can be found as soluble (sol) and transmembrane (tm) forms, playing pro-inflammatory functions but also has been related to immune regulatory functions. Bronchioalveolar lavage from fibrotic and non-fibrotic HP patients was obtained, and immune cells were characterized by flow cytometry, whereas soluble proteins were analyzed by ELISA. Compare to fibrotic HP patients, HP patients with non-fibrotic disease have accumulation of pro-inflammatory CD3+ myeloid cells, cell subpopulations that have decreased tmTNFR2 expression, and low frequency of regulatory-T cells. Whereas solTNF, solTNFR2, and IL-8 are increased. These findings suggest that the TNF pathway may explain, at least partially, the differences between both HP clinical forms. The evaluation of the TNF family molecules may help to develop new therapeutic approaches.

Tissue-resident memory T cells and their biological characteristics in the recurrence of inflammatory skin disorders

The skin is the largest organ of the body. The establishment of immunological memory in the skin is a crucial component of the adaptive immune response. Once naive T cells are activated by antigen-presenting cells, a small fraction of them differentiate into precursor memory T cells. These precursor cells ultimately develop into several subsets of memory T cells, including central memory T (T_CM) cells, effector memory T (T_EM) cells, and tissue resident memory T (T_RM) cells. T_RM cells have a unique transcriptional profile, and their most striking characteristics are their long-term survival (longevity) and low migration in peripheral tissues, including the skin. Under physiological conditions, T_RM cells that reside in the skin can respond rapidly to pathogenic challenges. However, there is emerging evidence to support the vital role of T_RM cells in the recurrence of chronic inflammatory skin disorders, including psoriasis, vitiligo, and fixed drug eruption, under pathological or uncontrolled conditions. Clarifying and characterizing the mechanisms that are involved in skin T_RM cells will help provide promising strategies for reducing the frequency and magnitude of skin inflammation recurrence. Here, we discuss recent insights into the generation, homing, retention, and survival of T_RM cells and share our perspectives on the biological characteristics of T_RM cells in the recurrence of inflammatory skin disorders.

Cheating the Hunger Games; Mechanisms Controlling Clonal Diversity of CD8 Effector and Memory Populations

Effector and memory CD8 T cells have an intrinsic difference in the way they must approach antigen; effector cells need to address the pathogen at hand and therefore favor outgrowth of only high-affinity clones. In contrast, the memory pool benefits from greater clonal diversity to recognize and eliminate pathogens with mutations in their immunogenic epitopes. Effector and memory fates are ultimately the result of the same three signals that control T cell activation; T cell receptor (TCR) engagement together with co-stimulation and cytokines. Great progress has been made in our understanding of the transcriptional programs that drive effector or memory differentiation. However, how these two different programs result from the same initial cues is still a matter of debate. An emerging image is that not only the classical three signals determine T cell differentiation, but also the ability of cells to access these signals relative to that of other activated clones. Inter-clonal competition is therefore not only a selective force, but also a mediator of CD8 T cell fate. How this is regulated on a transcriptional level, especially in the context of a selective “hunger game” based on antigen-affinity in which only cells of high-affinity are supposed to survive, is still poorly defined. In this review, we discuss recent literature that illustrates how antigen-affinity dependent inter-clonal competition shapes effector and memory populations in an environment of antigen affinity-driven selection. We argue that fine-tuning of TCR signal intensity presents an attractive target for regulating the scope of CD8 T cell vaccines.

Modulation of Regulatory T Cell Activity by TNF Receptor Type II-Targeting Pharmacological Agents

There is now compelling evidence that tumor necrosis factor (TNF)-TNF receptor type II (TNFR2) interaction plays a decisive role in the activation, expansion, and phenotypical stability of suppressive CD4⁺Foxp3⁺ regulatory T cells (Tregs). In an effort to translate this basic research finding into a therapeutic benefit, a number of agonistic or antagonistic TNFR2-targeting biological agents with the capacity to activate or inhibit Treg activity have been developed and studied. Recent studies also show that thalidomide analogs, cyclophosphamide, and other small molecules are able to act on TNFR2, resulting in the elimination of TNFR2-expressing Tregs. In contrast, pharmacological agents, such as vitamin D3 and adalimumab, were reported to induce the expansion of Tregs by promoting the interaction of transmembrane TNF (tmTNF) with TNFR2. These studies clearly show that TNFR2-targeting pharmacological agents represent an effective approach to modulating the function of Tregs and thus may be useful in the treatment of major human diseases such as autoimmune disorders, graft-versus-host disease (GVHD), and cancer. In this review, we will summarize and discuss the latest progress in the study of TNFR2-targeting pharmacological agents and their therapeutic potential based on upregulation or downregulation of Treg activity.

The Significance of Tumor Necrosis Factor Receptor Type II in CD8+ Regulatory T Cells and CD8+ Effector T Cells

Tumor necrosis factor (TNF) is a pleiotropic cytokine that has both pro-inflammatory and anti-inflammatory functions. The biological functions of TNF are mediated by two receptors, TNF receptor type I (TNFR1) and TNF receptor type II (TNFR2). TNFR1 is expressed universally on almost all cell types and has been extensively studied, whereas TNFR2 is mainly restricted to immune cells and some tumor cells and its role is far from clarified. Studies have shown that TNFR2 mediates the stimulatory activity of TNF on CD4⁺Foxp3⁺ regulatory T cells (Tregs) and CD8⁺Foxp3⁺ Tregs, and is involved in the phenotypic stability, proliferation, activation, and suppressive activity of Tregs. TNFR2 can also be expressed on CD8⁺ effector T cells (Teffs), which delivers an activation signal and cytotoxic ability to CD8⁺ Teffs during the early immune response, as well as an apoptosis signal to terminate the immune response. TNFR2-induced abolition of TNF receptor-associated factor 2 (TRAF2) degradation may play an important role in these processes. Consequently, due to the distribution of TNFR2 and its pleiotropic effects, TNFR2 appears to be critical to keeping the balance between Tregs and Teffs, and may be an efficient therapeutic target for tumor and autoimmune diseases. In this review, we summarize the biological functions of TNFR2 expressed on CD8⁺Foxp3⁺ Tregs and CD8⁺ Teffs, and highlight how TNF uses TNFR2 to coordinate the complex events that ultimately lead to efficient CD8⁺ T cell-mediated immune responses.

Evolving Approaches in the Identification of Allograft-Reactive T and B Cells in Mice and Humans

Whether a transplanted allograft is stably accepted, rejected, or achieves immunological tolerance is dependent on the frequency and function of alloreactive lymphocytes, making the identification and analysis of alloreactive T and B cells in transplant recipients critical for understanding mechanisms, and the prediction of allograft outcome. In animal models, tracking the fate of graft-reactive T and B cells allows investigators to uncover their biology and develop new therapeutic strategies to protect the graft. In the clinic, identification and quantification of graft-reactive T and B cells allows for the early diagnosis of immune reactivity and therapeutic intervention to prevent graft loss. In addition to rejection, probing of T and B cell fate in vivo provides insights into the underlying mechanisms of alloimmunity or tolerance that may lead to biomarkers predicting graft fate. In this review, we discuss existing and developing approaches to track and analyze alloreactive T and B cells in mice and humans and provide examples of discoveries made utilizing these techniques. These approaches include mixed lymphocyte reactions, trans-vivo delayed-type hypersensitivity, enzyme-linked immunospot assays, the use of antigen receptor transgenic lymphocytes, and utilization of peptide-major histocompatibility multimers, along with imaging techniques for static multiparameter analysis or dynamic in vivo tracking. Such approaches have already refined our understanding of the alloimmune response and are pointing to new ways to improve allograft outcomes in the clinic.