The Change of Soluble Programmed Cell Death-Ligand 1 in Glioma Patients Receiving Radiotherapy and Its Impact on Clinical Outcomes

Radiotherapy and immunology

The majority of cancer patients receive radiotherapy during the course of treatment, delivered with curative intent for local tumor control or as part of a multimodality regimen aimed at eliminating distant metastasis. A major focus of research has been DNA damage; however, in the past two decades, emphasis has shifted to the important role the immune system plays in radiotherapy-induced anti-tumor effects. Radiotherapy reprograms the tumor microenvironment, triggering DNA and RNA sensing cascades that activate innate immunity and ultimately enhance adaptive immunity. In opposition, radiotherapy also induces suppression of anti-tumor immunity, including recruitment of regulatory T cells, myeloid-derived suppressor cells, and suppressive macrophages. The balance of pro- and anti-tumor immunity is regulated in part by radiotherapy-induced chemokines and cytokines. Microbiota can also influence radiotherapy outcomes and is under clinical investigation. Blockade of the PD-1/PD-L1 axis and CTLA-4 has been extensively investigated in combination with radiotherapy; we include a review of clinical trials involving inhibition of these immune checkpoints and radiotherapy.

The effects of tumor-derived supernatants (TDS) on cancer cell progression: A review and update on carcinogenesis and immunotherapy

Tumors can produce bioactive substances called tumor-derived supernatants (TDS) that modify the immune response in the host body. This can result in immunosuppressive effects that promote the growth and spread of cancer. During tumorigenesis, the exudation of these substances can disrupt the function of immune sentinels in the host and reinforce the support for cancer cell growth. Tumor cells produce cytokines, growth factors, and proteins, which contribute to the progression of the tumor and the formation of premetastatic niches. By understanding how cancer cells influence the host immune system through the secretion of these factors, we can gain new insights into cancer diagnosis and therapy.

PD-1/PD-L1 axis is involved in the interaction between microglial polarization and glioma

The tumor microenvironment plays a vital role in glioblastoma growth and invasion. PD-1 and PD-L1 modulate the immunity in the brain tumor microenvironment. However, the underlying mechanisms remain unclear. In the present study, in vivo and in vitro experiments were conducted to reveal the effects of PD-1/PD-L1 on the crosstalk between microglia and glioma. Results showed that glioma cells secreted PD-L1 to the peritumoral areas, particularly microglia containing highly expressed PD-1. In the early stages of glioma, microglia mainly polarized into the pro-inflammatory subtype (M1). Subsequently, the secreted PD-L1 accumulated and bound to PD-1 on microglia, facilitating their polarization toward the microglial anti-inflammatory (M2) subtype primarily via the STAT3 signaling pathway. The role of PD-1/PD-L1 in M2 polarization of microglia was partially due to PD-1/PD-L1 depletion or application of BMS-1166, a novel inhibitor of PD-1/PD-L1. Consistently, co-culturing with microglia promoted glioma cell growth and invasion, and blocking PD-1/PD-L1 significantly suppressed these processes. Our findings reveal that the PD-1/PD-L1 axis engages in the microglial M2 polarization in the glioma microenvironment and promotes tumor growth and invasion.

Interaction between PD-L1 and soluble VEGFR1 in glioblastoma-educated macrophages

PURPOSE

The combined application of immune checkpoint inhibitors (ICIs) and anti-angiogenesis therapy has shown synergistic effects on glioblastoma (GBM). As important resources of PD-L1 in the tumor microenvironment (TME), tumor-associated macrophages (TAMs) have significant impact of the efficiency of ICIs. However, the effects of anti-angiogenesis agents on immune checkpoints expression are not fully understood.

METHOD

GBM-educated macrophages were generated from circulating monocytes of healthy controls and GBM patients under the education of GBM cell line. Surface expression of PD-L1 and VEGFR1 on GBM-educated macrophages was analyzed. VEGFR1 NAb and soluble VEGFR1 (sVEGFR1) were added and their effects on PD-L1 expression on TAMs was investigated. Serum soluble PD-L1 (sPD-L1) and sVEGFR1 levels in GBM patients were measured and their correlation was analyzed.

RESULT

The expression intensity of PD-L1 on GBM-educated macrophages was higher and its up-regulation partially depends on VEGFR1 signaling pathway. GBM-educated macrophages secreted less levels of soluble VEGFR1 (sVEGFR1), and exogenous sVEGFR1 down-regulated PD-L1 expression intensity. PD-L1 blockade promoted the secretion of sVEGFR1. Finally, sVEGFR1 and sPD-L1 in serum of GBM patients were overexpressed, and a positive correlation was found.

CONCLUSION

These findings reveal the interaction between PD-L1 and VEGFR1 signaling pathway in GBM-educated macrophages. VEGFR1 is involved with PD-L1 overexpression, which can be impeded by autocrine regulation of sVEGFR1. sVEGFR1 secretion by GBM-educated macrophages can be promoted by PD-L1 blockade. Taken together, these findings provide evidences for the combined application of ICIs and anti-angiogenesis therapies in the treatment of GBM.

Rescuing Cancer Immunity by Plasma Exchange in Metastatic Melanoma (ReCIPE-M1): protocol for a single-institution, open-label safety trial of plasma exchange to clear sPD-L1 for immunotherapy

BACKGROUND

Patients with metastatic melanoma rely on PD-(L)1 immunotherapy, but only one-third of patients experience treatment response and all initial responders eventually develop resistance. Tumour-derived extracellular vesicles expressing Programmed death ligand 1 (evPD-L1) and soluble Programmed death ligand 1 (sPD-L1) in peripheral blood of patients with melanoma limit PD-(L)1 immunotherapy and correlate with poor survival. Therapeutic plasma exchange (TPE) removes immunosuppressive evPD-L1 and sPD-L1. We hypothesise that TPE may rescue and restore antimelanoma immunity.

METHODS

In this two-arm study, 60 patients with metastatic melanoma progressing on checkpoint inhibition will be accrued. All patients will undergo radiotherapy on days 1-5 (at least one measurable lesion will not be irradiated) and ongoing checkpoint inhibition on day 8 and every 2-3 weeks per standard of care. Patients with baseline sPD-L1 level of ≥1.7 ng/mL and adequate clinical capacity will be enrolled in the TPE intervention arm and will undergo TPE on days 5-7, in addition to standard of care radiotherapy and immunotherapy. Other patients will remain in the standard of care arm.The primary endpoint of the study is to evaluate safety. Secondary endpoints include kinetics of sPD-L1 and evPD-L1 and clinical response by RECIST (Response Evaluation Criteria in Solid Tumors) criteria. Study registered at ClinicalTrials.gov (NCT04581382).

ETHICS AND DISSEMINATION

This trial has been approved by the Mayo Clinic Institutional Review Board. It will assess the safety and feasibility of TPE in improving outcomes for PD-(L)1 inhibitor immunotherapy in melanoma. Data will be maintained on a secure database with deidentified patient information. Data will be shared on publication in a peer-reviewed journal without the aid of professional writers. If successful, this trial will lay the ground for phase II studies that will include cancer treated with PD-(L)1 inhibitors which may benefit from TPE such as renal, bladder and lung cancers.

TRIAL REGISTRATION NUMBER

NCT04581382.

Biological Characteristics and Clinical Significance of Soluble PD-1/PD-L1 and Exosomal PD-L1 in Cancer

The immune checkpoint pathway consisting of the cell membrane-bound molecule programmed death protein 1 (PD-1) and its ligand PD-L1 has been found to mediate negative regulatory signals that effectively inhibit T-cell proliferation and function and impair antitumor immune responses. Considerable evidence suggests that the PD-1/PD-L1 pathway is responsible for tumor immune tolerance and immune escape. Blockage of this pathway has been found to reverse T lymphocyte depletion and restore antitumor immunity. Antagonists targeting this pathway have shown significant clinical activity in specific cancer types. Although originally identified as membrane-type molecules, several other forms of PD-1/PD-L1 have been detected in the blood of cancer patients, including soluble PD-1/PD-L1 (sPD-1/sPD-L1) and exosomal PD-L1 (exoPD-L1), increasing the composition and functional complications of the PD-1/PD-L1 signaling pathway. For example, sPD-1 has been shown to block the PD-1/PD-L immunosuppressive pathway by binding to PD-L1 and PD-L2, whereas the role of sPD-L1 and its mechanism of action in cancer remain unclear. In addition, many studies have investigated the roles of exoPD-L1 in immunosuppression, as a biomarker for tumor progression and as a predictive biomarker for response to immunotherapy. This review describes the molecular mechanisms underlying the generation of sPD-1/sPD-L1 and exoPD-L1, along with their biological activities and methods of detection. In addition, this review discusses the clinical importance of sPD-1/sPD-L1 and exoPD-L1 in cancer, including their predictive and prognostic roles and the effects of treatments that target these molecules.

Prognostic prospect of soluble programmed cell death ligand-1 in cancer management

Aggressive tissue biopsy is commonly unavoidable in the management of most suspected tumor cases to conclusively verify the presence of cancerous cells through histological assessment. The extracted tissue is also immunostained for detection of antigens (tissue tumor markers) of potential prognostic or therapeutic importance to assist in treatment decision. Although liquid biopsies can be a powerful tool for monitoring treatment response, they are still excluded from standard cancer diagnostics, and their utility is still being debated in the scientific community. With a myriad of soluble tissue tumor markers now being discovered, liquid biopsies could completely change the current paradigms of cancer management. Recently, soluble programmed cell death ligand-1 (sPD-L1), which is found in the peripheral blood, i.e. serum and plasma, has shown potential as a pre-therapeutic predictive marker as well as a prognostic biomarker to monitor treatment efficacy. Thus, this review focuses on the emergence of sPD-L1 and promising technologies for its detection in order to support liquid biopsies for future cancer management.

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.

Programmed Death-Ligand 1 as a Regulator of Tumor Progression and Metastasis

Programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) immune checkpoint has long been implicated in modeling antitumor immunity; PD-1/PD-L1 axis inhibitors exert their antitumor effects by relieving PD-L1-mediated suppression on tumor-infiltrating T lymphocytes. However, recent studies have unveiled a distinct, tumor-intrinsic, potential role for PD-L1. In this review, we focus on tumor-intrinsic PD-L1 signaling and delve into preclinical evidence linking PD-L1 protein expression with features of epithelial-to-mesenchymal transition program, cancer stemness and known oncogenic pathways. We further summarize data from studies supporting the prognostic significance of PD-L1 in different tumor types. We show that PD-L1 may indeed have oncogenic potential and act as a regulator of tumor progression and metastasis.