PD-1/PD-L1 axis in organ fibrosis

PD-L1 upregulation in activated fibroblasts promotes silica particle-induced pulmonary fibrosis

Silicosis is a severe interstitial lung disease resulting from prolonged exposure to silica dust in working environment, characterized by inflammation and fibrosis. This condition is closely associated with immune dysregulation, although the precise regulatory mechanisms remain elusive. Immune checkpoints (ICs) comprise receptor-ligand pairs crucial for immune cell activation and coordination of immune responses. Among these, PD-1 and its ligand PD-L1 have garnered significant attention in tumor research and have recently been implicated in the regulation of fibrotic diseases. Nonetheless, their involvement in silicosis remains unexplored. In this study, we observed a global upregulation of PD-1 and PD-L1 expression concomitant with the progression of silicosis, exhibiting cell specificity. Targeting PD-1/PD-L1 signaling mitigated silicosis in mice by modulating T cell homeostasis, macrophage polarization, and activation of fibrotic effector cells. Notably, PD-L1 expression on activated fibroblasts emerged as a pivotal driver of silicosis progression. Mechanistically, elevated PD-L1 levels in fibroblast activation fostered a positive feedback loop by binding to p-Smad2/3 and p-STAT3 proteins, thereby facilitating their nuclear translocation and augmenting protein stability, ultimately promoting fibroblast transdifferentiation. Consistently, knockdown of PD-L1 in lung fibroblasts significantly ameliorated silicosis in mice. In summary, PD-1/PD-L1 signaling mediates critical profibrotic signals during the progression of silicosis.

Expression of sPD-L1 levels in an ex vivo liver perfusion model

The programmed cell death protein 1 (PD-1) acts as a central inhibitory immune checkpoint receptor. The soluble form of its primary ligand, sPD-L1, was found to be elevated in the serum of patients with cancer, infectious diseases, and chronic inflammation. So far, the hepatic origin of sPD-L1 has received relatively little attention and is therefore the subject of this study in the context of normothermic machine perfusion (NMP) of liver grafts. sPD-L1 concentrations as well as several well-established clinically relevant laboratory parameters were determined in the perfusate of 16 donor liver grafts undergoing NMP up to 30 hours. sPD-L1 levels continuously increased during NMP and significantly correlated with markers of hepatic synthesis (cholinesterase), acute-phase proteins (von Willebrand factor, procalcitonin, antithrombin, interleukin-6, fibrinogen), and liver decay markers (gamma-glutamyltransferase, alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase). Perfusate leukocytes were in the lower reference range and decreased after 12 hours. Mean sPD-L1 levels in the perfusate correlated with donor levels of gamma-glutamyltransferase, alanine aminotransferase, creatinine, and blood urea nitrogen. Our study reveals a significant increase in the concentration of sPD-L1 following ischemia-reperfusion injury in a hepatic ex vivo model. sPD-L1 concentrations during NMP correlate with established acute-phase proteins and liver cell decay markers, suggesting that hepatic sPD-L1 synthesis or shedding increases during the acute phase and cell decay. Furthermore, sPD-L1 correlates with established liver function and synthesis parameters as well as with donor laboratory values and might therefore be a potential biomarker for the hepatic function of liver grafts.

The role of the PI3K/AKT/mTOR pathway in mediating PD-L1 upregulation during fibroblast transdifferentiation

Silicosis is a progressive interstitial lung disease characterized by diffuse pulmonary fibrosis. The transdifferentiation of lung fibroblasts into myofibroblasts is a key cellular event driving the progression of silicosis fibrosis. Recent studies have shown that PD-L1 expression is significantly upregulated in activated fibroblasts, and PD-L1 plays a crucial role in mediating fibroblast transdifferentiation. This study aims to elucidate the molecular mechanisms regulating PD-L1 expression in fibroblasts and analyze the functional significance of PD-L1 upregulation in fibroblast activity and silicosis fibrosis. In this research, an in vitro model of TGF-β1-induced NIH-3 T3 fibroblast transdifferentiation was established. Small molecule inhibitors, siRNA, and plasmids were used to interfere with the PI3K/AKT/mTOR signaling pathway and PD-L1 expression. It was found that TGF-β1 stimulation increased PD-L1 expression in fibroblasts, while blocking the PI3K/AKT/mTOR pathway inhibited this upregulation. Knockdown of PD-L1 significantly inhibited fibroblast transdifferentiation and impeded TGF-β1-induced activation of the PI3K/AKT/mTOR pathway, whereas PD-L1 overexpression had the opposite effect. Additionally, PD-L1 protein in fibroblasts undergoes ubiquitin-proteasome-mediated degradation, negatively regulating PD-L1 upregulation. In vivo, adeno-associated virus was used to specifically knockdown PD-L1 in mouse lung fibroblasts, resulting in significantly reduced lung tissue damage and fibrosis in silicosis mice. This effect was associated with the involvement of the PI3K/AKT/mTOR pathway. In summary, PD-L1 expression in fibroblasts is upregulated during transdifferentiation, a process regulated by the PI3K/AKT/mTOR pathway. Upregulated PD-L1 enhances PI3K/AKT/mTOR signaling through positive feedback, sustaining fibroblast activation. Ubiquitin-proteasome-mediated protein degradation may serve as a negative feedback mechanism maintaining PD-L1 homeostasis.

Myofibroblasts persist through immune privilege mechanisms to mediate oral submucous fibrosis: Uncovering the pathogenesis

Immune privilege is the ability to tolerate foreign antigens without eliciting an inflammatory immune response. Several mechanisms explain a structure's immune privilege status, which is regulated by innate and adaptive immune responses. The role of myofibroblasts in perpetuating fibrosis by acquiring an immune privileged phenotype against the backdrop of oral submucous fibrosis (OSF) is evolving. Myofibroblasts persist through the Fas/FasL autocrine pathway and induce apoptosis in epithelial cells, explaining the juxtaposition of apoptotic cells in areas of fibrosis. However, increased matrix stiffness, in addition to activating TGF-β, reduces Fas surface expression in myofibroblasts, increasing their resistance to apoptosis. The reciprocal amplification loop between the immune checkpoint proteins programmed death-ligand 1 (PD-L1) and TGF-β involves the YAP-TAZ and SMAD2,3 pathways and dramatically enhances profibrotic signalling. Increased matrix stiffness also enhances cMYC expression, which subsequently amplifies PD-L1 levels on myofibroblasts. The increase in PD-L1 on the myofibroblast microengineers the phenotype of CD4+ T cells homing to fibrotic areas by acting on the programmed cell death protein 1 (PD-1) receptor on the T-cell surface, converting these cells from antifibrotic cells to profibrotic cells that produce IL-17A and TGF-β. This manuscript provides mechanistic insight into how myofibroblasts avoid apoptosis in OSFs by evading the immune system. Targeting an immune-privileged phenotype in myofibroblasts with FAS-FASL pathway-dependent characteristics is an ideal strategy for reversing OSF.

PD-1 immunology in the kidneys: a growing relationship

In recent years, knowledge regarding immune regulation has expanded rapidly, and major advancements have been made in immunotherapy for immune-associated disorders, particularly cancer. The programmed cell death 1 (PD-1) pathway is a cornerstone in immune regulation. It comprises PD-1 and its ligands mediating immune tolerance mechanisms and immune homeostasis. Accumulating evidence demonstrates that the PD-1 axis has a crucial immunosuppressive role in the tumor microenvironment and autoimmune diseases. PD-1 receptors and ligands on immune cells and renal parenchymal cells aid in maintaining immunological homeostasis in the kidneys. Here, we present a comprehensive review of PD-1 immunology in various kidney disorders, including renal cell carcinoma, glomerulonephritis, kidney transplantation, renal aging, and renal immune-related adverse events secondary to PD-1 immunotherapy.

Inhibitory immune checkpoints suppress the surveillance of senescent cells promoting their accumulation with aging and in age-related diseases

The accumulation of pro-inflammatory senescent cells within tissues is a common hallmark of the aging process and many age-related diseases. This modification has been called the senescence-associated secretory phenotype (SASP) and observed in cultured cells and in cells isolated from aged tissues. Currently, there is a debate whether the accumulation of senescent cells within tissues should be attributed to increased generation of senescent cells or to a defect in their elimination from aging tissues. Emerging studies have revealed that senescent cells display an increased expression of several inhibitory immune checkpoint ligands, especially those of the programmed cell death protein-1 (PD-1) ligand-1 (PD-L1) proteins. It is known that the PD-L1 ligands, especially those of cancer cells, target the PD-1 receptor of cytotoxic CD8+ T and natural killer (NK) cells disturbing their functions, e.g., evoking a decline in their cytotoxic activity and promoting their exhaustion and even apoptosis. An increase in the level of the PD-L1 protein in senescent cells was able to suppress their immune surveillance and inhibit their elimination by cytotoxic CD8+ T and NK cells. Senescent cells are known to express ligands for several inhibitory immune checkpoint receptors, i.e., PD-1, LILRB4, NKG2A, TIM-3, and SIRPα receptors. Here, I will briefly describe those pathways and examine whether these inhibitory checkpoints could be involved in the immune evasion of senescent cells with aging and age-related diseases. It seems plausible that an enhanced inhibitory checkpoint signaling can prevent the elimination of senescent cells from tissues and thus promote the aging process.

Inorganic Nanoparticle Functionalization Strategies in Immunotherapeutic Applications

Nanotechnology has been increasingly utilized in anticancer treatment owing to its ability of engineering functional nanocarriers that enhance therapeutic effectiveness while minimizing adverse effects. Inorganic nanoparticles (INPs) are prevalent nanocarriers to be customized for a wide range of anticancer applications, including theranostics, imaging, targeted drug delivery, and therapeutics, because they are advantageous for their superior biocompatibility, unique optical properties, and capacity of being modified via versatile surface functionalization strategies. In the past decades, the high adaptation of INPs in this emerging immunotherapeutic field makes them good carrier options for tumor immunotherapy and combination immunotherapy. Tumor immunotherapy requires targeted delivery of immunomodulating therapeutics to tumor locations or immunological organs to provoke immune cells and induce tumor-specific immune response while regulating immune homeostasis, particularly switching the tumor immunosuppressive microenvironment. This review explores various INP designs and formulations, and their employment in tumor immunotherapy and combination immunotherapy. We also introduce detailed demonstrations of utilizing surface engineering tactics to create multifunctional INPs. The generated INPs demonstrate the abilities of stimulating and enhancing the immune response, specific targeting, and regulating cancer cells, immune cells, and their resident microenvironment, sometimes along with imaging and tracking capabilities, implying their potential in multitasking immunotherapy. Furthermore, we discuss the promises of INP-based combination immunotherapy in tumor treatments.

Association of MCP-4, NRTN, and PD-L1 with the risk of hepatic fibrosis: A Mendelian randomization study

Previous studies have confirmed the affiliation between specific inflammatory cytokines and Hepatic fibrosis (HF); however, contradictions remain in the causality. The study implemented a bidirectional two-sample Mendelian randomization (MR) analysis with published statistics derived from Genome-wide Association Studies (GWAS) to investigate casualties between inflammatory cytokines and HF. Additionally, MR analysis was also introduced to consider if 1400 blood metabolites act as the key mediators in this process. Single nucleotide polymorphisms (SNPs) with strong correlations to inflammatory factors were selected for multiple MR analyses in this study. The inverse variance weighted method (IVW) was chosen as the principal analysis, and the others as the supportive. Besides, sensitivity tests were involved to identify potential heterogeneity and pleiotropic level. IVW methods revealed that a relatively high level of prediction-based monocyte chemoattractant protein-4 (MCP-4) (95% CI: 1.014-3.336, P = .045), along with neurturin (NRTN) (95% CI: 1.204-4.004, P = .010), may increase the risk of HF; while programmed cell death 1 ligand 1 (PD-L1) (95% CI: 0.223-0.928, P = .030), showed a protective effect on HF. No significant statistical differences were detected on any other inflammatory cytokines, nor did the impact of HF genetic predisposition on the 91 circulating inflammatory cytokines-related characteristics.

Serum sPD-1 and sPD-L1 as predictive biomarkers for HBsAg clearance in HBeAg-negative CHB patients undergoing IFN-based therapy

BACKGROUND AND AIMS

For chronic hepatitis B (CHB) patients, there is still a need to improve hepatitis B surface antigen (HBsAg) clearance rates. This study aimed to assess the predictive effectiveness of soluble programmed cell death-1 (sPD-1) and soluble programmed cell death ligand-1 (sPD-L1) for HBsAg clearance in HBeAg-negative CHB patients undergoing peginterferon (Peg-IFN)-based antiviral treatment.

METHODS

This study encompassed 280 patients undergoing treatment with Peg-IFNα. Serum levels of sPD-1 and sPD-L1 were measured using ELISA kits at baseline, as well as at 12, 24 and 48 weeks. The primary endpoint of the study was the determination of HBsAg clearance at 48 weeks. Logistic regression analysis was employed to identify predictors of HBsAg clearance.

RESULTS

The clearance group demonstrated significantly lower serum sPD-L1 levels compared to the non-clearance group. While both groups exhibited an increase in sPD-1 levels, only the clearance group showed a rise in sPD-L1 levels. Multivariate analysis identified sPD-L1 increase at 24 weeks, and HBsAg decline at 24 weeks as predictors for HBsAg clearance at 48 weeks. The combined use of these indicators showed a predictive performance for HBsAg clearance with an AUROC of 0.907 (95% CI: 0.861-0.953, p < 0.001).

CONCLUSIONS

The study revealed an inverse relationship between the trends of sPD-1/sPD-L1 and HBsAg clearance during combined IFN and NAs treatment. Moreover, the magnitude of HBsAg reduction and sPD-L1 increase emerged as significant predictors for HBsAg clearance.

Shedding Light on the Role of Exosomal PD-L1 (ExoPD-L1) in Cancer Progression: an Update

Exosomes are the primary category of extracellular vesicles (EVs), which are lipid-bilayer vesicles with biological activity spontaneously secreted from either normal or tansformed cells. They serve a crucial role for intercellular communication and affect extracellular environment and the immune system. Tumor-derived exosomes (TEXs) enclose high levels of immunosuppressive proteins, including programmed death-ligand 1 (PD-L1). PD-L1 and its receptor PD-1 act as crucial immune checkpoint molecules, thus facilitating tumor advancement by inhibiting immune responses. PDL-1 is abundantly present on tumor cells and interacts with PD-1 on activated T cells, resulting in T cell suppression and allowing immune evasion of cancer cells. Various FDA-approved monoclonal antibodies inhibiting the PD-1/PD-L1 interaction are commonly used to treat a diverse range of tumors. Although the achieved results are significant, some individuals have a poor reaction to PD-1/PD-L1 blocking. PD-L1-enriched TEXs may mimic the impact of cell-surface PD-L1, consequently potentiating tumor resistance to PD1/PD-L1 based therapy. In light of this, a strong correlation between circulating exosomal PD-L1 levels and response rate to anti-PD-1/PD-L1 antibody treatment has been evinced. This article inspects the function of exosomal PDL-1 in developing resistance to anti-PD-1/PD-L1 therapy for opening new avenues for overcoming tumor resistance to such modalities and development of more favored combination therapy.

The expression of programmed cell death ligand 1 (PD-L1) involves in the clinicopathologic characteristics and prognostic implications of testicular germ cell tumor (TGCT): a systematic review and meta-analysis

Background

Testicular germ cell tumor (TGCT) is a type of tumor with relatively lower incidence but being more prevalent in young men. The expression of programmed cell death ligand 1 (PD-L1) serves as a potential biomarker for predicting the survival outcomes of other tumors. Some studies discovered higher prevalence of PD-L1 in TGCT patients who achieved favorable treatment outcomes, while other studies showed lower or absent expression of PD-L1 in TGCT with the better prognosis as well. Therefore, in order to address this controversy and clarify the association between the expression of PD-L1 and pathological features and prognosis of TGCT, this meta-analysis was conducted.

Methods

A comprehensive literature search was performed using following search terms: "testis", "testicle", "testicular", "cancer", "carcinoma", "tumor", "neoplasm", "programmed cell death ligand 1", "programmed death ligand 1", "PD-L1", "PDL1", "B7 homolog 1", "B7-H1", "B7H1" and "CD274". Relevant studies were retrieved according to the inclusion criteria from reputable databases including PubMed, Embase, Web of Science, Cochrane Library and China National Knowledge Infrastructure (CNKI). These studies investigated the expression of PD-L1 in both tumor cells and tumor infiltrating immune cells (TIICs) in TGCT. The overall proportion of PD-L1 positivity was assessed using R programming. Pooled hazard ratio (HR) and odds ratio (OR) with corresponding 95% confidence interval (CI) were calculated using Revman software to evaluate the involvement of PD-L1 expression in TGCT. The Newcastle-Ottawa Scale (NOS) was used to evaluate the quality assessment of included studies. Sensitivity analysis and publication bias evaluation were subsequently performed.

Results

A total of eight eligible studies compromising 1,589 patients diagnosed with TGCT were finally included in this study. PD-L1 positivity was detected in 31% and 41% of TGCT patients' tumor cells and TIICs, respectively. The pooled data demonstrated a significant association between elevated PD-L1 expression levels in TIICs and a favorable prognosis characterized by the reduced disease progression and relapse events (HR =0.21, 95% CI: 0.13-0.33). Furthermore, PD-L1+ TIICs exhibited higher prevalence rates in seminoma (OR =2.11, 95% CI: 1.57-2.84) and embryonal carcinoma (OR =6.23, 95% CI: 2.42-16.02) patients. Notably, PD-L1 expression in TIICs displayed a tendency to increase in TGCT patients with lower stages or without lymph node metastasis.

Conclusions

PD-L1 expression was observed in choriocarcinoma tumor cells, while yolk sac tumor and teratoma tumor cells exhibited lower or absent expression of PD-L1. Conversely, PD-L1 expression in TIICs was associated with seminoma and embryonal carcinoma, which was more commonly observed in TGCT patients with lower stages and better prognosis, thereby providing a theoretical foundation for the application of immunotherapy in relapsed/refractory TGCT patients.

Research Progress of Triptolide Against Fibrosis

Fibrosis leads to organ failure and death, which is the final stage of many chronic diseases. Triptolide (TPL) is a terpenoid extracted from the traditional Chinese medicine Tripterygium wilfordii Hook. F (TwHF). Triptolide and its derivatives (Omtriptolide, Minnelide, (5R)-5-hydroxytriptolide) have been proven to have a variety of pharmacological effects. This study comprehensively reviewed the antifibrotic mechanism of TPL and its derivatives, and discussed the application of advanced nanoparticles (NPs) drug delivery system in the treatment of fibrotic diseases by TPL. The results show that TPL can inhibit immune inflammatory response, relieve oxidative stress and endoplasmic reticulum stress (ERS), regulate collagen deposition and inhibit myofibroblast production to play an anti-fibrosis effect and reduce organ injury. A low dose of TPL has no obvious toxicity. Under pathological conditions, a toxic dose of TPL has a protective effect on organs. The emergence of TPL derivatives (especially Minnelide) and NPs drug delivery systems promotes the anti-fibrosis effect of TPL and reduces its toxicity, which may be the main direction of anti-fibrosis research in the future.

GBM Immunotherapy: Macrophage Impacts

BACKGROUND

Glioblastoma (GBM) is an extremely aggressive form of brain tumor with low survival rates. Current treatments such as chemotherapy, radiation, and surgery are problematic due to tumor growth, invasion, and tumor microenvironment. GBM cells are resistant to these standard treatments, and the heterogeneity of the tumor makes it difficult to find a universal approach. Progression of GBM and acquisition of resistance to therapy are due to the complex interplay between tumor cells and the TME. A significant portion of the TME consists of an inflammatory infiltrate, with microglia and macrophages being the predominant cells.

METHODS

Analysis of the literature data over a course of 5 years suggest that the tumor-associated macrophages (TAMs) are capable of releasing cytokines and growth factors that promote tumor proliferation, survival, and metastasis while inhibiting immune cell function at the same time.

RESULTS

Thus, immunosuppressive state, provided with this intensively studied kind of TME cells, is supposed to promote GBM development through TAMs modulation of tumor treatment-resistance and aggressiveness. Therefore, TAMs are an attractive therapeutic target in the treatment of glioblastoma.

CONCLUSION

This review provides a comprehensive overview of the latest research on the nature of TAMs and the development of therapeutic strategies targeting TAMs, focusing on the variety of macrophage properties, being modulated, as well as molecular targets.

Redundancy and absurd names in immunology

In this short review, examples of unnecessary multiple names of cell membrane molecules, for example, immune checkpoints and cytokines, are presented. Moreover, ridiculous or inaccurate names, such as 'Regulated on activation, normal T-cell expressed and secreted' and 'tissue factor', are discussed.

The role of the immunosuppressive PD-1/PD-L1 checkpoint pathway in the aging process and age-related diseases

The accumulation of senescent cells within tissues is a hallmark of the aging process. Senescent cells are also commonly present in many age-related diseases and in the cancer microenvironment. The escape of abnormal cells from immune surveillance indicates that there is some defect in the function of cytotoxic immune cells, e.g., CD8+ T cells and natural killer (NK) cells. Recent studies have revealed that the expression of programmed death-ligand 1 (PD-L1) protein is abundantly increased in senescent cells. An increase in the amount of PD-L1 protein protects senescent cells from clearance by the PD-1 checkpoint receptor in cytotoxic immune cells. In fact, the activation of the PD-1 receptor suppresses the cytotoxic properties of CD8+ T and NK cells, promoting a state of immunosenescence. The inhibitory PD-1/PD-L1 checkpoint pathway acts in cooperation with immunosuppressive cells; for example, activation of PD-1 receptor can enhance the differentiation of regulatory T cells (Treg), myeloid-derived suppressor cells (MDSC), and M2 macrophages, whereas the cytokines secreted by immunosuppressive cells stimulate the expression of the immunosuppressive PD-L1 protein. Interestingly, many signaling pathways known to promote cellular senescence and the aging process are crucial stimulators of the expression of PD-L1 protein, e.g., epigenetic regulation, inflammatory mediators, mTOR-related signaling, cGAS-STING pathway, and AhR signaling. It seems that the inhibitory PD-1/PD-L1 immune checkpoint axis has a crucial role in the accumulation of senescent cells and thus it promotes the aging process in tissues. Thus, the blockade of the PD-1/PD-L1 checkpoint signaling might be a potential anti-aging senolytic therapy. KEY MESSAGES: Senescent cells accumulate within tissues during aging and age-related diseases. Senescent cells are able to escape immune surveillance by cytotoxic immune cells. Expression of programmed death-ligand 1 (PD-L1) markedly increases in senescent cells. Age-related signaling stimulates the expression of PD-L1 protein in senescent cells. Inhibitory PD-1/PD-L1 checkpoint pathway suppresses clearance of senescent cells.

AMPK signaling inhibits the differentiation of myofibroblasts: impact on age-related tissue fibrosis and degeneration

Disruption of the extracellular matrix (ECM) and an accumulation of fibrotic lesions within tissues are two of the distinctive hallmarks of the aging process. Tissue fibroblasts are mesenchymal cells which display an impressive plasticity in the regulation of ECM integrity and thus on tissue homeostasis. Single-cell transcriptome studies have revealed that tissue fibroblasts exhibit a remarkable heterogeneity with aging and in age-related diseases. Excessive stress and inflammatory insults induce the differentiation of fibroblasts into myofibroblasts which are fusiform contractile cells and abundantly secrete the components of the ECM and proteolytic enzymes as well as many inflammatory mediators. Detrimental stresses can also induce the transdifferentiation of certain mesenchymal and myeloid cells into myofibroblasts. Interestingly, many age-related stresses, such as oxidative and endoplasmic reticulum stresses, ECM stiffness, inflammatory mediators, telomere shortening, and several alarmins from damaged cells are potent inducers of myofibroblast differentiation. Intriguingly, there is convincing evidence that the signaling pathways stimulated by the AMP-activated protein kinase (AMPK) are potent inhibitors of myofibroblast differentiation and accordingly AMPK signaling reduces fibrotic lesions within tissues, e.g., in age-related cardiac and pulmonary fibrosis. AMPK signaling is not only an important regulator of energy metabolism but it is also able to control cell fate determination and many functions of the immune system. It is known that AMPK signaling can delay the aging process via an integrated signaling network. AMPK signaling inhibits myofibroblast differentiation, e.g., by suppressing signaling through the TGF-β, NF-κB, STAT3, and YAP/TAZ pathways. It seems that AMPK signaling can alleviate age-related tissue fibrosis and degeneration by inhibiting the differentiation of myofibroblasts.