Immune checkpoint inhibitors in the treatment of cancer

Bibliometric analysis: a study of the microenvironment in cervical cancer (2000-2024)

Objective

The incidence of cervical cancer has increased in recent years. The tumor microenvironment (TME) is the local biological environment involved in tumor occurrence and development. This study aimed to conduct a comprehensive analysis of the global research on the TME in cervical cancer (CC), providing a knowledge framework in this field from a holistic and systematic perspective based on a bibliometric analysis.

Methods

Studies focusing on the TME in cervical cancer were searched using the Web of Science Core Collection database. The annual output, cooperation, hotspots, research status, and development trends in this field were analyzed using bibliometric softwares (VOSviewer and CiteSpace).

Results

A total of 1,057 articles published between 2000 and 2024 were selected. The number of publications and citations has recently increased. Cooperation network analysis indicated that China holds the foremost position in research on the TME in cervical cancer with the highest volume of publications, thus exerting the greatest influence. Fudan University had the highest output. Frontiers in Oncology showed the highest degree of productivity in this field. Rofstad, Einar K. made the most article contributions and was the most co-cited author. Four clusters were obtained after a cluster analysis of the keywords: TME, cervical cancer, immunotherapy, and prognosis. Immunotherapy, human papillomavirus, and biomarkers were relatively recent keywords that attracted increasing attention from researchers.

Discussion

This bibliometric analysis provides a data-based and objective introduction to the TME of cervical cancer, and offers readers a valuable reference for future research.

Conclusions

Comprehensive research in this field was mainly distributed in the TME of cervical cancer through the analysis of keywords and documents. Sufficient evidence supports mechanism research and application exploration. Further research should explore new topics related to the TME of cervical cancer.

Fulminant Type 1 Diabetes Mellitus Leading to Diabetic Ketoacidosis and Mesenteric Ischemia With Necrosis Following Pembrolizumab Administration: A Case Report

Immune checkpoint inhibitors (ICIs), such as pembrolizumab, have revolutionized cancer therapy but can lead to severe immune-related adverse events (irAEs). We present a case of fulminant type 1 diabetes mellitus (T1DM) with diabetic ketoacidosis (DKA) and mesenteric ischemia in a 78-year-old woman with recurrent stage IIIC1 cervical cancer treated with pembrolizumab. Thirty-four days after initiating a pembrolizumab-containing regimen, she presented with vomiting, severe hyperglycemia, metabolic acidosis, and strongly positive urine ketones. Laboratory findings confirmed complete insulin deficiency, leading to a diagnosis of fulminant T1DM and DKA, requiring intensive insulin therapy. Despite treatment, her condition rapidly deteriorated, with worsening DKA, hyperglycemia, gastrointestinal bleeding, and extensive mucosal necrosis identified through endoscopy and imaging. The patient ultimately progressed to septic shock and died the same day. Fulminant T1DM is characterized by abrupt β-cell destruction and rapid DKA onset. In this case, DKA likely contributed to mesenteric ischemia, a severe vascular complication. This is the first reported case of fulminant T1DM, DKA, and mesenteric ischemia following pembrolizumab. The case underscores the importance of vigilance, early recognition, and multidisciplinary management of irAEs to prevent fatal outcomes.

The efficacy outcomes in non-small cell lung cancer patients treated with PD axis inhibitor agents - a population-based study of the Vojvodina region

Background: By 2021, the FDA approved the use of the drugs pembrolizumab and atezolizumab in the first-line treatment of patients with high positivity of programmed death ligand-1 (PD-L1) in locally advanced and metastatic non-small-cell-lung cancer (NSCLC). This approval was the result of statistically significant evidence from international, multicentric clinical studies that all reported increasing progression-free survival (PFS) and overall survival (OS) in these patients. Methods: In our study, we reported the demographic and clinical characteristics of 79 patients diagnosed with NSCLC with expression of PD-L1 ≥50% from January 2019 to December 2022 at the Institute for Pulmonary Diseases of Vojvodina, who received pembrolizumab therapy as the first-line treatment. Patients were divided according to the histological type of lung cancer as adenocarcinoma (ADC) or squamous cell carcinoma (SCC) of the lung. In 52 of the 79 patients, PFS and in 32 of them overall survival (censored OS) was shown according to the histological type of tumor, the tumor proportion score (TPS) of PDL-1 expression, and the metastatic status within the Tumor Nodes Metastasis (TNM) disease classification. Independent factors of death outcome were shown by multivariable proportional hazard regression analysis. Results: The study included 79 patients diagnosed with NSCLC with an expression of PD-L1 ≥50%, 50 (63.3%) patients with ADC, and 29 (36.7%) patients with SCC, whose 55 (69.6%) PDL-1 expression was obtained from broncho biopsy (BB). The majority of patients, 49 (62%), had a TPS PD-L1 score of 51%-79%. Median, PFS for adenocarcinoma was 22 months and censored OS was 27 months, while for squamous cell carcinoma, median PFS was 12 months, and censored OS was 21 months. M1b disease stage, which was the most common in patients, had a PFS of 16 months and a censored OS of 18 months. Conclusion: Pembrolizumab monotherapy in patients with NSCLC in the fourth stage of the disease and with the positivity of the immune checkpoint protein TPS PD-L1 above 50% represents a safe therapy that allows a satisfactory period without disease progression and overall survival with acceptable treatment complications.

Role of PARP Inhibitors in Cancer Immunotherapy: Potential Friends to Immune Activating Molecules and Foes to Immune Checkpoints

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) induce cytotoxic effects as single agents in tumors characterized by defective repair of DNA double-strand breaks deriving from BRCA1/2 mutations or other abnormalities in genes associated with homologous recombination. Preclinical studies have shown that PARPi-induced DNA damage may affect the tumor immune microenvironment and immune-mediated anti-tumor response through several mechanisms. In particular, increased DNA damage has been shown to induce the activation of type I interferon pathway and up-regulation of PD-L1 expression in cancer cells, which can both enhance sensitivity to Immune Checkpoint Inhibitors (ICIs). Despite the recent approval of ICIs for a number of advanced cancer types based on their ability to reinvigorate T-cell-mediated antitumor immune responses, a consistent percentage of treated patients fail to respond, strongly encouraging the identification of combination therapies to overcome resistance. In the present review, we analyzed both established and unexplored mechanisms that may be elicited by PARPi, supporting immune reactivation and their potential synergism with currently used ICIs. This analysis may indicate novel and possibly patient-specific immune features that might represent new pharmacological targets of PARPi, potentially leading to the identification of predictive biomarkers of response to their combination with ICIs.

Association between immune-mediated adverse events and efficacy in metastatic non-small-cell lung cancer patients treated with durvalumab and tremelimumab

PURPOSE

Immune-mediated adverse events (imAEs) may be associated with response to immune checkpoint inhibitors. We assessed the relationship between imAE development and efficacy in metastatic non-small-cell lung cancer patients treated with durvalumab (anti-programmed cell death ligand-1 [PD-L1]) alone or in combination with tremelimumab (anti-cytotoxic T-lymphocyte-associated protein 4).

METHODS

The analysis used individual patient-level data from 307 and 310 patients in the monotherapy and combination arms of MYSTIC, respectively. We evaluated the association between treatment efficacy and development of imAEs using univariate and multivariate survival analyses. Using machine learning, we built a predictive model utilizing baseline clinical and laboratory features to identify patients at risk of developing imAEs and further evaluated patient survival based on a threshold index extracted from the model.

RESULTS

Patients who developed any grade of imAE had improved overall survival versus patients without (hazard ratio [HR] 0.51; 95% confidence interval [CI]: 0.41-0.62). imAE development was associated with improved overall survival (HR 0.54; 95% CI 0.44-0.66) in a multivariate Cox proportional hazard model considering patient demographic features and baseline characteristics. Higher odds of imAE development were observed (odds ratio 3.023; 95% CI: 1.56-5.83) in responders versus non-responders in patients treated with immunotherapy. Based on baseline characteristics, the random forest classification algorithm was used to formulate a predictive model to identify patients at increased risk of developing imAEs during treatment.

CONCLUSION

Post-hoc exploratory analysis found that the efficacy of immunotherapy was improved in patients who developed on-treatment imAEs. This was independent of severity of imAEs or the need for steroid treatment, which is important in allowing patients to remain on treatment and derive optimal clinical benefit. Further research is warranted to establish the correlation between incidence of imAEs and efficacy in this patient population.

Immune checkpoint inhibitors in advanced and recurrent/metastatic cervical cancer

Cervical cancer (CC) poses a serious threat to women’s health. Although many early-stage patients have a good prognosis, there are still a lack of effective therapies for advanced and recurrent/metastatic CC. In this context, immunotherapy and immune checkpoint inhibitors (ICIs) are particularly likely to play a role in the treatment of cervical tumors in a variety of disease settings. Some promising immune checkpoints include programmed cell death 1 (PD-1), programmed death ligand 1 (PD-L1) and cytotoxic T lymphocyte antigen 4 (CTLA-4), which exert immunomodulatory effects as negative regulators of T-cell activation and suppress immune responses in cervical cancer through cancer cell immune evasion. Initial trials of ICIs for CC have shown encouraging results in terms of objective response rate (ORR), progression-free survival (PFS), and overall survival (OS), both monotherapy and combination strategies. Meanwhile, human papillomavirus, vaginal microecology and intestinal microenvironment play an important role in CC, which provides new treatment directions. This review analyzed a number of completed or ongoing clinical trials of ICIs in the treatment of advanced and recurrent/metastatic CC. And we also analyzed the important relationship between vaginal microecology and intestinal microecology with CC and their related immunotherapy prospects.

The new progress in cancer immunotherapy

The cross talk between immune and non-immune cells in the tumor microenvironment leads to immunosuppression, which promotes tumor growth and survival. Immunotherapy is an advanced treatment that boosts humoral and cellular immunity rather than using chemotherapy or radiation-based strategy associated with non-specific targets and toxic effects on normal cells. Immune checkpoint inhibitors and T cell-based immunotherapy have already exhibited significant effects against solid tumors and leukemia. Tumor cells that escape immune surveillance create a major obstacle to acquiring an effective immune response in cancer patients. Tremendous progress had been made in recent years on a wide range of innate and adaptive immune checkpoints which play a significant role to prevent tumorigenesis, and might therefore be potential targets to suppress tumor cells growth. This review aimed to summarize the underlying molecular mechanisms of existing immunotherapy approaches including T cell and NK-derived immune checkpoint therapy, as well as other intrinsic and phagocytosis checkpoints. Together, these insights will pave the way for new innate and adaptive immunomodulatory targets for the development of highly effective new therapy in the future.

Immune Checkpoint Inhibitors and Venous Thromboembolism: An Analysis of the WHO Pharmacovigilance Database

Data on venous thromboembolic events (VTEs) in patients receiving immune checkpoint inhibitors (ICIs) are scarce and conflicting. This study investigated the risk of reporting VTEs associated with ICIs in comparison with all other anticancer drugs. The World Health Organization pharmacovigilance database (VigiBase), comprising >30 million individual case safety reports, was queried. All reports on patients with cancer, involving at least one anticancer drug as a suspect or interacting drug and registered from January 1, 2008, to May 31, 2021, were included. The association between ICIs and the risk of reporting VTEs was estimated using the reporting odds ratio (ROR) as a measure of disproportionality with all other anticancer drugs as comparators. RORs were estimated as crude and adjusted RORs for age, sex, and other medications (excluding anticancer drugs) associated with risk of VTEs. Among 1,196 patients experiencing VTEs after ICI treatment, the median age was 65 years and 57.6% were men. Anti-PD-1 agents (62.5%) were the most frequently reported. ICIs were not associated with higher reporting of VTEs when compared with other anticancer drugs (crude ROR 0.63, 95% confidence interval (CI) 0.60 to 0.67 and adjusted ROR 0.70, 95% CI 0.65-0.74). No signal of disproportionate reporting was found when considering each class of ICIs. In conclusion, ICIs were not associated with higher reporting of VTEs, in comparison with all other anticancer drugs in a large-scale pharmacovigilance database. Owing to the limitations inherent to pharmacovigilance studies, prospective studies, including an adequate comparison group, are needed to assess the risk of VTEs in ICI-treated patients.

Oxidative Stress in Cancer Immunotherapy: Molecular Mechanisms and Potential Applications

Immunotherapy is an effective treatment option that revolutionizes the management of various cancers. Nevertheless, only a subset of patients receiving immunotherapy exhibit durable responses. Recently, numerous studies have shown that oxidative stress induced by reactive oxygen species (ROS) plays essential regulatory roles in the tumor immune response, thus regulating immunotherapeutic effects. Specifically, studies have revealed key roles of ROS in promoting the release of tumor-associated antigens, manipulating antigen presentation and recognition, regulating immune cell phenotypic differentiation, increasing immune cell tumor infiltration, preventing immune escape and diminishing immune suppression. In the present study, we briefly summarize the main classes of cancer immunotherapeutic strategies and discuss the interplay between oxidative stress and anticancer immunity, with an emphasis on the molecular mechanisms underlying the oxidative stress-regulated treatment response to cancer immunotherapy. Moreover, we highlight the therapeutic opportunities of manipulating oxidative stress to improve the antitumor immune response, which may improve the clinical outcome.

Look into my onco-forest - review of plant natural products with anticancer activity

Cancer is a multistage process that can be treated by numerous modalities including systemic treatment. About half of the molecules that have been approved in the last few decades count for plant derivatives. This review presents the application of tree/shrub-derived biologically active compounds as anticancer agents. Different parts of trees/shrubs - wood, bark, branches, roots, leaves, needles, fruits, flowers etc. - contain a wide variety of primary and secondary metabolites, which demonstrate anticancer properties. Special attention was paid to phenolics (phenolic acids and polyphenols, including flavonoids and non-flavonoids (tannins, lignans, stilbenes)), essential oils and their main constituents such as terpenes/terpenoids, phytosterols, alkaloids and many others. Anticancer properties of these compounds are mainly attributed to their strong antioxidant properties. In vitro experiments on various cancer cell lines revealed a cytotoxic effect of tree-derived extracts. Mechanisms of anticancer action of the extracts are also listed. Examples of drugs that successfully underwent clinical trials with well-established position in the guidelines created by oncological societies are provided. The review also focuses on directions for the future in the development of anticancer agents derived from trees/shrubs. Applying biologically active compounds derived from trees and shrubs as anticancer agents continuously seems a promising strategy in cancer systemic treatment.

[Management of persistent colitis after successful immunotherapy for non-small cell carcinoma of the lung]

Immune checkpoint inhibitors have shown remarkable efficacy as new-generation drugs in anti-tumor therapy. However, the nonspecific activation of the immune system leads to a number of adverse side effects, so-called immune-related adverse events (irAEs), including the occurrence of diarrhea and colitis in about one third of treated patients.Endoscopically and histologically, there is significant overlap of immune-mediated colitis with classic IBD, making differentiation difficult.Therapeutically, high-dose glucocorticoids are used in grade 3 (severe) to grade 4 (life-threatening) colitis, in addition to discontinuation of ICI therapy. Steroid-refractory cases (up to 42%) benefit from the TNF inhibitor infliximab. Vedolizumab, analogous to inflammatory bowel disease, represents second-line therapy for infliximab-refractory cases. Little data exist to date on the efficacy of tofacitinib in refractory cases.We describe the case and therapeutic management of severe and persistent immune-mediated colitis after successful immunochemotherapy with pembrolizumab in an 80-year-old man with metastatic non-small cell carcinoma of the lung and pre-existing colitis unclassified and other comorbidities.

Phosphoribosyl Pyrophosphate Amido Transferase: A New Prognostic Biomarker for Hepatocellular Carcinoma

Background

PPAT (phosphoribosyl pyrophosphate amido transferase) catalyzes the first committed step of de novo purine biosynthesis and is a key regulatory point in the biosynthesis of nascent purine nucleotides. However, the clinical significance and biologic role of PPAT in hepatocellular carcinoma (HCC) remain unknown.

Methods

We compared the expression of PPAT in carcinomatous and precancerous hepatocellular carcinoma tissues by immunohistochemistry in 90 cases of HCC. Correlation analysis was also made on clinical data, survival, classification, and staging.

Results

The expression of PPAT in HCC tumor tissues is significantly higher than that in adjacent normal tissues. The results of the Kaplan–Meier analysis showed that HCC patients with high PPAT expression survived shorter than those with low PPAT expression. Moreover, the expression of PPAT was significantly associated with the tumor grade (P=0.014), PD-L1 (P<0.001), and CTLA4 (P=0.003). The later grade of the tumor, the higher the expression of PPAT. In the PD-L1 high expression group, PPAT is also highly expressed.

Conclusion

Our study demonstrated that PPAT expression might be included in the process of carcinogenesis and prognosis. Hence, PPAT could be served as a new prognostic biomarker for patients of HCC.

Breast Cancer Tumor Microenvironment and Molecular Aberrations Hijack Tumoricidal Immunity

Simple Summary

Immune therapy is designed to stimulate tumoricidal effects in a variety of solid tumors including breast carcinomas. However, the emergence of resistant clones leads to treatment failure. Understanding the molecular, cellular, and microenvironmental aberrations is crucial to uncovering underlying mechanisms and developing advanced strategies for preventing or combating these resistant malignancies. This review will summarize research findings revealing various mechanisms employed to hijack innate and adaptive immune surveillance mechanisms, develop hypoxic and tumor promoting metabolism, and foster an immune tolerance microenvironment. In addition, it will highlight potential targets for therapeutic approaches.

Abstract

Breast cancer is the most common malignancy among females in western countries, where women have an overall lifetime risk of >10% for developing invasive breast carcinomas. It is not a single disease but is composed of distinct subtypes associated with different clinical outcomes and is highly heterogeneous in both the molecular and clinical aspects. Although tumor initiation is largely driven by acquired genetic alterations, recent data suggest microenvironment-mediated immune evasion may play an important role in neoplastic progression. Beyond surgical resection, radiation, and chemotherapy, additional therapeutic options include hormonal deactivation, targeted-signaling pathway treatment, DNA repair inhibition, and aberrant epigenetic reversion. Yet, the fatality rate of metastatic breast cancer remains unacceptably high, largely due to treatment resistance and metastases to brain, lung, or bone marrow where tumor bed penetration of therapeutic agents is limited. Recent studies indicate the development of immune-oncological therapy could potentially eradicate this devastating malignancy. Evidence suggests tumors express immunogenic neoantigens but the immunity towards these antigens is frequently muted. Established tumors exhibit immunological tolerance. This tolerance reflects a process of immune suppression elicited by the tumor, and it represents a critical obstacle towards successful antitumor immunotherapy. In general, immune evasive mechanisms adapted by breast cancer encompasses down-regulation of antigen presentations or recognition, lack of immune effector cells, obstruction of anti-tumor immune cell maturation, accumulation of immunosuppressive cells, production of inhibitory cytokines, chemokines or ligands/receptors, and up-regulation of immune checkpoint modulators. Together with altered metabolism and hypoxic conditions, they constitute a permissive tumor microenvironment. This article intends to discern representative incidents and to provide potential innovative therapeutic regimens to reinstate tumoricidal immunity.

Cancer Immunotherapy: Fecal Microbiota Transplantation Brings Light

OPINION STATEMENT

Immunotherapy is revolutionizing tumor treatment by activating the immune response to tumors. Among them, immunotherapy represented by immune checkpoint inhibitors is considered to be a milestone in tumor treatment. It has revolutionized the management of advanced malignant tumors by activating T cells, promoting cytotoxic signaling pathways, and killing tumor cells, effectively improving the overall survival of patients. However, resistance to immunotherapy and immune-related adverse events remain challenges for immunotherapy. It has been demonstrated in previous studies that modulating intestinal microbiota can enhance immunotherapy response and reduce complications. Currently, the more mature method for microbiota regulation is fecal microbiota transplantation, which involves transfering a donor's microbiome to the recipient in the form of capsules or fecal microbiota suspension to restore the richness of the recipient's intestinal microbiota. In terms of cancer immunotherapy, fecal microbiota transplantation in patients who fail to respond to immune checkpoint inhibitors is expected to produce better prognosis for patients.

A novel pyroptosis-related gene signature to predict outcomes in laryngeal squamous cell carcinoma

Pyroptosis, a pro-inflammatory form of programmed cell death, is associated with carcinogenesis and progression. However, there is little information concerning pyroptosis-related genes (PRGs) in laryngeal squamous cell carcinoma (LSCC). Herein, we aim to explore the prognostic value of PRGs in LSCC. The expression and clinical data of 47 PRGs in LSCC patients were obtained from The Cancer Genome Atlas. A novel prognostic PRG signature was constructed using least absolute shrinkage and selection operator analysis. Receiver operating characteristic (ROC) curves were drawn, and Kaplan-Meier survival Cox proportional hazard regression analyses were performed to measure the predictive capacity of the PRG signature. Furthermore, we constructed a six-PRG signature to divide LSCC patients into high- and low-risk groups. Patients in the high-risk group had worse overall survival than the low-risk group. The area under the time-dependent ROC curve was 0.696 for 1 year, 0.784 for 3 years, and 0.738 for 5 years. We proved that the PRGs signature was an independent predictor for LSCC. Functional enrichment analysis indicated that several immune-related pathways were significantly enriched in the low-risk group. Consistent with this, patients with low-risk scores had higher immune scores and better immunotherapeutic responses than the high-risk group. In conclusion, we established a novel PRGs signature that can predict outcome and response to immunotherapy of LSCC, pyroptosis may be a potential target for LSCC.

Characterization of m6A-Related Genes Landscape in Skin Cutaneous Melanoma to Aid Immunotherapy and Assess Prognosis

Background

Skin cutaneous melanoma (SKCM) is the most malignant tumor among skin cancers. Immunotherapy has shown a great role in the advantageous prognosis of SKCM. However, only a small percentage of people can benefit from immunotherapy. To date, there has been insufficient evidence to reveal the prognostic value of m6A in SKCM and its relationship with the infiltration of immune cells and the efficacy of immunotherapy.

Methods

Here, we synthetically analyzed 23 m6A regulators from SKCM samples collected from the TCGA and GEO databases. We defined three m6A modification patterns and constructed m6A scores using principal component analysis (PCA).

Results

We found significant differences in overall survival (OS) and immune infiltration between different m6A subclusters. Besides, m6A score was positively correlated with regulatory T-cell and helper T-cell content, which may account for the association of high m6A scores with superior prognosis. Multivariate Cox regression analysis revealed that the m6A score was an independent prognostic indicator. Moreover, patients with high m6A scores showed a better response to immunotherapy, and this result was further validated in two independent immunotherapy cohorts receiving anti-PD-1/PD-L1 therapy.

Conclusion

The findings suggested the m6A score can screen suitable candidates for immunotherapy and can predict immunotherapy response. This analysis of different m6A patterns in a large sample of SKCM expanded our understanding of TME and provided new ideas for prognostic assessment and personalized immunotherapy strategies for SKCM patients.

Glucocorticoid and PD-1 Cross-Talk: Does the Immune System Become Confused?

Programmed cell death protein 1 (PD-1) and its ligands, PD-L1/2, control T cell activation and tolerance. While PD-1 expression is induced upon T cell receptor (TCR) activation or cytokine signaling, PD-L1 is expressed on B cells, antigen presenting cells, and on non-immune tissues, including cancer cells. Importantly, PD-L1 binding inhibits T cell activation. Therefore, the modulation of PD-1/PD-L1 expression on immune cells, both circulating or in a tumor microenvironment and/or on the tumor cell surface, is one mechanism of cancer immune evasion. Therapies that target PD-1/PD-L1, blocking the T cell-cancer cell interaction, have been successful in patients with various types of cancer. Glucocorticoids (GCs) are often administered to manage the side effects of chemo- or immuno-therapy, exerting a wide range of immunosuppressive and anti-inflammatory effects. However, GCs may also have tumor-promoting effects, interfering with therapy. In this review, we examine GC signaling and how it intersects with PD-1/PD-L1 pathways, including a discussion on the potential for GC- and PD-1/PD-L1-targeted therapies to "confuse" the immune system, leading to a cancer cell advantage that counteracts anti-cancer immunotherapy. Therefore, combination therapies should be utilized with an awareness of the potential for opposing effects on the immune system.

Soluble Programmed Death Ligand-1 (sPD-L1): A Pool of Circulating Proteins Implicated in Health and Diseases

Upon T-cell receptor stimulation, the Programmed cell Death-1 receptor (PD-1) expressed on T-cells can interact with its ligand PD-L1 expressed at the surface of cancer cells or antigen-presenting cells. Monoclonal antibodies targeting PD-1 or PD-L1 are routinely used for the treatment of cancers, but their clinical efficacy varies largely across the variety of tumor types. A part of the variability is linked to the existence of several forms of PD-L1, either expressed on the plasma membrane (mPD-L1), at the surface of secreted cellular exosomes (exoPD-L1), in cell nuclei (nPD-L1), or as a circulating, soluble protein (sPD-L1). Here, we have reviewed the different origins and roles of sPD-L1 in humans to highlight the biochemical and functional heterogeneity of the soluble protein. sPD-L1 isoforms can be generated essentially by two non-exclusive processes: (i) proteolysis of m/exoPD-L1 by metalloproteases, such as metalloproteinases (MMP) and A disintegrin and metalloproteases (ADAM), which are capable of shedding membrane PD-L1 to release an active soluble form, and (ii) the alternative splicing of PD-L1 pre-mRNA, leading in some cases to the release of sPD-L1 protein isoforms lacking the transmembrane domain. The expression and secretion of sPD-L1 have been observed in a large variety of pathologies, well beyond cancer, notably in different pulmonary diseases, chronic inflammatory and autoimmune disorders, and viral diseases. The expression and role of sPD-L1 during pregnancy are also evoked. The structural heterogeneity of sPD-L1 proteins, and associated functional/cellular plurality, should be kept in mind when considering sPD-L1 as a biomarker or as a drug target. The membrane, exosomal and soluble forms of PD-L1 are all integral parts of the highly dynamic PD-1/PD-L1 signaling pathway, essential for immune-tolerance or immune-escape.