CMTM6-Deficient Monocytes in ANCA-Associated Vasculitis Fail to Present the Immune Checkpoint PD-L1

ANCA-associated vasculitis and lung cancer: an immunological perspective

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a severe autoimmune disease that often involves the upper and lower respiratory tracts. In recent years, numerous studies have found a significant increase in the incidence of cancer among AAV patients, but the association between lung cancer and AAV remains inconclusive, with relatively low clinical attention. This review summarizes the current literature on the risk of lung cancer in patients with ANCA-associated vasculitis (AAV), detailing the potential mechanisms by which AAV may contribute to lung cancer, and further elucidates the inherent carcinogenic risks of immunosuppressants.There is a correlation between AAV and lung cancer, which is related to T cell senescence and damage, as well as the abnormal expression of cytokines such as IL-6 and IL-10. In AAV patients, the use of cyclophosphamide and azathioprine (AZA) alone has a clear carcinogenic risk, with frequent use of CYC potentially posing a high risk for lung cancer. Although TNF inhibitors (TNFi) combined with CYC have carcinogenic risks, there is insufficient evidence to link them directly to an increased risk of lung cancer. For patients at high risk for lung cancer, the judicious use of immunosuppressants, timely computed tomography (CT), and lung cancer screening can reduce the risk of lung cancer in AAV patients.

Exploring the Role of PD-1 in the Autoimmune Response: Insights into Its Implication in Systemic Lupus Erythematosus

Despite advances in understanding systemic lupus erythematosus (SLE), many challenges remain in unraveling the precise mechanisms behind the disease's development and progression. Recent evidence has questioned the role of programmed cell death protein 1 (PD-1) in suppressing autoreactive CD4+ T cells during autoimmune responses. Research has investigated the potential impacts of PD-1 on various CD4+ T-cell subpopulations, including T follicular helper (Tfh) cells, circulating Tfh (cTfh) cells, and T peripheral helper (Tph) cells, all of which exhibit substantial PD-1 expression and are closely related to several autoimmune disorders, including SLE. This review highlights the complex role of PD-1 in autoimmunity and emphasizes the imperative for further research to elucidate its functions during autoreactive T-cell responses. Additionally, we address the potential of PD-1 and its ligands as possible therapeutic targets in SLE.

Transmembrane Protein CMTM6 Alleviates Ocular Inflammatory Response and Improves Corneal Epithelial Barrier Function in Experimental Dry Eye

Purpose

To investigate the impact of transmembrane protein CMTM6 on the pathogenesis of dry eye disease (DED) and elucidate its potential mechanisms.

Methods

CMTM6 expression was confirmed by database analysis, real-time polymerase chain reaction (RT-PCR), western blot, and immunohistochemistry. Tear secretion was measured using the phenol red thread test. Immune cell infiltration was assessed through flow cytometry. Barrier function was evaluated by fluorescein sodium staining, immunofluorescence staining of zonula occludens 1 (ZO-1), and electric cell-substrate impedance sensing (ECIS) assessment. For silencing CMTM6 expression, siRNA and shRNA were employed, along with lentiviral vector-mediated overexpression of CMTM6. Proinflammatory cytokine levels were analyzed by RT-PCR and cytometric bead array (CBA) analysis.

Results

CMTM6 showed high expression in healthy human and mouse corneal and conjunctival epithelium but was notably reduced in DED. Notably, this downregulation was correlated with disease severity. Cmtm6-/- dry eye (DE) mice displayed reduced tear secretion, severe corneal epithelial defects, decreased conjunctival goblet cell density, and upregulated inflammatory response. Additionally, Cmtm6-/- DE mice and CMTM6 knockdown human corneal epithelial cell-transformed (HCE-T) cells showed more severe barrier disruption and reduced expression of ZO-1. Knockdown of CMTM6 in HCE-T cells increased inflammatory responses induced by hyperosmotic stress, which was significantly mitigated by CMTM6 overexpression. Moreover, the level of phospho-p65 in hyperosmolarity-stimulated HCE-T cells increased after silencing CMTM6. Nuclear factor kappa B (NF-κB) p65 inhibition (JSH-23) reversed the excessive inflammatory responses caused by hyperosmolarity in CMTM6 knockdown HCE-T cells.

Conclusions

The reduction in CMTM6 expression on the ocular surface contributes to the pathogenesis of DED. The CMTM6-NF-κB p65 signaling pathway may serve as a promising therapeutic target for DED.

Diminished PD-L1 regulation along with dysregulated T lymphocyte subsets and chemokine in ANCA-associated vasculitis

ANCA-associated vasculitis (AAV) is a life-threatening disease characterized by small vessel inflammation and pathogenic self-directed antibodies. Programmed death-ligand 1 receptor (PD-1) and programmed cell death ligand-1 (PD-L1) are immune checkpoint molecules crucial for maintaining tolerance and immune homeostasis. After checkpoint inhibition therapy, development of various autoimmune diseases and immune-related adverse events (irAEs) have been observed. Here, we investigated the immunomodulatory roles of neutrophils through the expression of immune checkpoint molecule (PD-L1), migratory molecules (CXCR2), chemotactic chemokines (CXCL5) and other important molecules (BAFF and HMGB1) in development of AAV. We also scrutinized the immune mechanism responsible for development of pauci-immune crescentic GN (PICGN). We demonstrate for the first time that the frequency of PD-L1 expressing neutrophils was significantly reduced in AAV patients compared to healthy controls and correlated negatively with disease severity (BVASv3). Further, in renal biopsy, reduced PD-L1 immune checkpoint expression provides a microenvironment that unleashes uncontrolled activated CD4 + T cells, B cells, neutrophils and macrophages and ultimately causes engulfment of immune complexes leading to PICGN. Furthermore, during remission, reduced neutrophils PD-L1 and CXCR2 expression, increased neutrophils CXCL5 expression and increased peripheral effector memory T cells and increased HMGB1 and BAFF levels in serum, demonstrate the propensity for the persistence of sub-clinical inflammation, which could explain relapse, in this group of diseases.

The role of PD-1 signaling in health and immune-related diseases

Programmed cell death 1 receptor (PD-1) and its ligands constitute an inhibitory pathway to mediate the mechanism of immune tolerance and provide immune homeostasis. Significantly, the binding partners of PD-1 and its associated ligands are diverse, which facilitates immunosuppression in cooperation with other immune checkpoint proteins. Accumulating evidence has demonstrated the important immunosuppressive role of the PD-1 axis in the tumor microenvironment and in autoimmune diseases. In addition, PD-1 blockades have been approved to treat various cancers, including solid tumors and hematological malignancies. Here, we provide a comprehensive review of the PD-1 pathway, focusing on the structure and expression of PD-1, programmed cell death 1 ligand 1 (PD-L1), and programmed cell death 1 ligand 2 (PD-L2); the diverse biological functions of PD-1 signaling in health and immune-related diseases (including tumor immunity, autoimmunity, infectious immunity, transplantation immunity, allergy and immune privilege); and immune-related adverse events related to PD-1 and PD-L1 inhibitors.

Rheumatic Immune-Related Adverse Events due to Immune Checkpoint Inhibitors—A 2023 Update

With the aging of the population, malignancies are becoming common complications in patients with rheumatoid arthritis (RA), particularly in elderly patients. Such malignancies often interfere with RA treatment. Among several therapeutic agents, immune checkpoint inhibitors (ICIs) which antagonize immunological brakes on T lymphocytes have emerged as a promising treatment option for a variety of malignancies. In parallel, evidence has accumulated that ICIs are associated with numerous immune-related adverse events (irAEs), such as hypophysitis, myocarditis, pneumonitis, and colitis. Moreover, ICIs not only exacerbate pre-existing autoimmune diseases, but also cause de novo rheumatic disease–like symptoms, such as arthritis, myositis, and vasculitis, which are currently termed rheumatic irAEs. Rheumatic irAEs differ from classical rheumatic diseases in multiple aspects, and treatment should be individualized based on the severity. Close collaboration with oncologists is critical for preventing irreversible organ damage. This review summarizes the current evidence regarding the mechanisms and management of rheumatic irAEs with focus on arthritis, myositis, and vasculitis. Based on these findings, potential therapeutic strategies against rheumatic irAEs are discussed.

Longitudinal monitoring of circulating immune cell phenotypes in anti-neutrophil cytoplasmic antibody-associated vasculitis

Anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) is a necrotizing multiorgan autoimmune disease that affects small- to medium-sized blood vessels. Despite the improvements in treatments, half of the patients with AAV still experience disease relapses. In this review, we focus on peripheral leukocyte properties and phenotypes in patients with AAV. In particular, we explore longitudinal changes in circulating immune cell phenotypes during the active phase of the disease and treatment. The numbers and phenotypes of leukocytes in peripheral blood were differs between AAV and healthy controls, AAV in active versus inactive phase, AAV in treatment responders versus non-responders, and AAV with and without severe infection. Therefore, biomarkers detected in peripheral blood immune cells may be useful for longitudinal monitoring of disease activity in AAV.

Suppression of Tumor or Host Intrinsic CMTM6 Drives Antitumor Cytotoxicity in a PD-L1-Independent Manner

CKLF-like MARVEL transmembrane domain-containing protein 6 (CMTM6) is known to be a regulator of membranal programmed death ligand 1 (PD-L1) stability and a factor associated with malignancy progression, but the effects and mechanisms of CMTM6 on tumor growth, as well as its potential as a target for therapy, are still largely unknown. Here, we show that CMTM6 expression increased with tumor progression in both patients and mice. Ablation of CMTM6 significantly reduced human and murine tumor growth in a manner dependent on T-cell immunity. Tumor CMTM6 suppression broke resistance to immune-checkpoint inhibitors and remodeled the tumor immune microenvironment, as specific antitumor cytotoxicity was enhanced and contributed primarily to tumor inhibition. Without the PD-1/PD-L1 axis, CMTM6 suppression still significantly dampened tumor growth dependent on cytotoxic cells. Furthermore, we identified that CMTM6 was widely expressed on immune cells. T-cell CMTM6 levels increased with sustained immune activation and intratumoral immune exhaustion and affected T cell-intrinsic PD-L1 levels. Host CMTM6 knockout significantly restrained tumor growth in a manner dependent on CD8+ T cells and not entirely dependent on PD-L1. Thus, we developed and evaluated the antitumor efficacy of CMTM6-targeting adeno-associated virus (AAV), which effectively mobilized antitumor immunity and could be combined with various antitumor drugs. Our findings reveal that both tumor and host CMTM6 are involved in antitumor immunity with or without the PD-1/PD-L1 axis and that gene therapy targeting CMTM6 is a promising strategy for cancer immunotherapy.

Targeting immune checkpoints in anti-neutrophil cytoplasmic antibodies associated vasculitis: the potential therapeutic targets in the future

Anti-neutrophil cytoplasmic autoantibodies (ANCA) associated vasculitis (AAV) is a necrotizing vasculitis mainly involving small blood vessels. It is demonstrated that T cells are important in the pathogenesis of AAV, including regulatory T cells (Treg) and helper T cells (Th), especially Th2, Th17, and follicular Th cells (Tfh). In addition, the exhaustion of T cells predicted the favorable prognosis of AAV. The immune checkpoints (ICs) consist of a group of co-stimulatory and co-inhibitory molecules expressed on the surface of T cells, which maintains a balance between the activation and exhaustion of T cells. CD28, inducible T-cell co-stimulator (ICOS), OX40, CD40L, glucocorticoid induced tumor necrosis factor receptor (GITR), and CD137 are the common co-stimulatory molecules, while the programmed cell death 1 (PD-1), cytotoxic T lymphocyte-associated molecule 4 (CTLA-4), T cell immunoglobulin (Ig) and mucin domain-containing protein 3 (TIM-3), B and T lymphocyte attenuator (BTLA), V-domain Ig suppressor of T cell activation (VISTA), T-cell Ig and ITIM domain (TIGIT), CD200, and lymphocyte activation gene 3 (LAG-3) belong to co-inhibitory molecules. If this balance was disrupted and the activation of T cells was increased, autoimmune diseases (AIDs) might be induced. Even in the treatment of malignant tumors, activation of T cells by immune checkpoint inhibitors (ICIs) may result in AIDs known as rheumatic immune-related adverse events (Rh-irAEs), suggesting the importance of ICs in AIDs. In this review, we summarized the features of AAV induced by immunotherapy using ICIs in patients with malignant tumors, and then reviewed the biological characteristics of different ICs. Our aim was to explore potential targets in ICs for future treatment of AAV.

Immunogenic cell death as driver of autoimmunity in granulomatosis with polyangiitis

Cell death and dysregulated clearance of dead cells play essential roles in the induction of chronic inflammatory processes and autoimmune diseases. Granulomatosis with polyangiitis (GPA), a neutrophil-driven autoimmune disorder, is characterized by necrotizing inflammation predominantly of the respiratory tract and an anti-neutrophil cytoplasmic autoantibody (ANCA)-associated systemic necrotizing vasculitis. Defective regulation of neutrophil homeostasis and cell death mechanisms have been demonstrated in GPA. Disturbed efferocytosis (i.e., phagocytosis of apoptotic neutrophils by macrophages) as well as cell death-related release of damage-associated molecular patterns (DAMP) such as high mobility group box 1 (HMGB1) contribute to chronic non-resolving inflammation in GPA. DAMP have been shown to induce innate as well as adaptive cellular responses thereby creating a prerequisite for the development of pathogenic autoimmunity. In this review, we discuss factors contributing to as well as the impact of regulated cell death (RCD) accompanied by DAMP-release as early drivers of the granulomatous tissue inflammation and autoimmune responses in GPA.

Pathogenic role of monocytes/macrophages in large vessel vasculitis

Vasculitis is an autoimmune vascular inflammation with an unknown etiology and causes vessel wall destruction. Depending on the size of the blood vessels, it is classified as large, medium, and small vessel vasculitis. A wide variety of immune cells are involved in the pathogenesis of vasculitis. Among these immune cells, monocytes and macrophages are functionally characterized by their capacity for phagocytosis, antigen presentation, and cytokine/chemokine production. After a long debate, recent technological advances have revealed the cellular origin of tissue macrophages in the vessel wall. Tissue macrophages are mainly derived from embryonic progenitor cells under homeostatic conditions, whereas bone marrow-derived circulating monocytes are recruited under inflammatory conditions, and then differentiate into macrophages in the arterial wall. Such macrophages infiltrate into an otherwise immunoprotected vascular site, digest tissue matrix with abundant proteolytic enzymes, and further recruit inflammatory cells through cytokine/chemokine production. In this way, macrophages amplify the inflammatory cascade and eventually cause tissue destruction. Recent studies have also demonstrated that monocytes/macrophages can be divided into several subpopulations based on the cell surface markers and gene expression. In this review, the subpopulations of circulating monocytes and the ontogeny of tissue macrophages in the artery are discussed. We also update the immunopathology of large vessel vasculitis, with a special focus on giant cell arteritis, and outline how monocytes/macrophages participate in the disease process of vascular inflammation. Finally, we discuss limitations of the current research and provide future research perspectives, particularly in humans. Through these processes, we explore the possibility of therapeutic strategies targeting monocytes/macrophages in vasculitis.

CMTM6 as a master regulator of PD-L1

Immune checkpoint proteins, such as programmed cell death receptor 1 (PD-1) and its ligand (PD-L1), play critical roles in the pathology of chronic inflammatory pathological conditions, particularly cancer. In addition, the activation of PD-1/PD-L1 pathway is involved in mediating resistance to certain anti-cancer chemo- and immuno-therapeutics. Unfortunately, targeting the PD-1/PD-L1 pathway by the available anti-PD-1/PD-L1 drugs can benefit only a small proportion of cancer patients. Thus, studying the factors that regulate the expression of these immune checkpoint proteins is of central importance in this context. Recent investigations have identified CMTM6 and, to a lesser extent, CMTM4, as master regulators of PD-L1 expression in various cancer cells. Understanding the mechanisms by which such proteins upregulate the expression of PD-L1 in tumor cells, and determining the potential regulators of CMTM6 expression in different types of cancers will accelerate the development of new therapeutic targets and/or lead to the enhancement of the currently available PD-1/PD-L1 blockade therapies.

The clinical and prognostic significance of CMTM6/PD-L1 in oncology

The recent discovery of CMTM6 and to a lesser extent CMTM4, two members of the chemokine-like factor (CKLF)-like MARVEL transmembrane domain-containing family, as master positive regulators of PD-L1 expression, the primary ligand of programmed cell death 1 (PD-1), on tumor and immune cells has opened new horizons for investigating the role of CMTM6/CMTM4 in different aspects of oncology including their clinical and prognostic values in different cancer types. The absence of a specific review article addressing the available results about the clinical and prognostic roles of CMTM6 alone and/or in combination with PD-L1 in cancer has encouraged us to write this paper.

CMTM6, a potential immunotherapy target

The CKLF-like MARVEL transmembrane domain-containing protein 6 (CMTM6), which binds to the programmed death ligand 1 (PD-L1) and stabilizes the expression of PD-L1 on the cell surface, has been recently discovered as a novel regulator of PD-L1 expression in cancer. PD-L1 is an immune checkpoint inhibitory molecule that can mediate the immune escape of tumor cells in various tumors and has been studied intensively in recent years. In 2017, two articles simultaneously reported that CMTM6 can stabilize the expression of PD-L1 on the plasma membrane and prevent PD-L1 from being degraded by lysosomes; therefore, CMTM6 may play an important role in tumor cell immune escape and immunosuppression. At present, there are few studies on the relationship between the expression of CMTM6 and PD-L1 in different tumors and diseases. These studies together suggested that CMTM6 may be a potential novel immunotherapy target. In this review, we briefly describe the latest research progresses of CMTM6 in various cancers and other diseases.