Soluble programmed death-1 (sPD-1) and programmed death ligand 1 (sPD-L1) as potential biomarkers for the diagnosis and prognosis of glioma patients

Prognostic significance of soluble PD-L1 in prostate cancer

Purpose

The aim of this study was to assess the role of sPD-L1 and sPD-1 as potential biomarkers in prostate cancer (PCa). The association of the values of these soluble proteins were correlated to the clinical data: stage of disease, Gleason score, biochemical recurrence etc. For a comprehensive study, the relationship between sPD-L1 and sPD-1 and circulating immune cells was further investigated.

Methods

A total of 88 patients with pT2 and pT3 PCa diagnosis and 41 heathy men were enrolled. Soluble sPD-L1 and sPD-1 levels were measured in plasma by ELISA method. Immunophenotyping was performed by flow cytometry analysis.

Results

Our study's findings demonstrate that PCa patients had higher levels of circulating sPD-L1 and sPD-1 comparing to healthy controls (p < 0.001). We found a statistically significant (p < 0.05) relationship between improved progression free survival and lower initial sPD-L1 values. Furthermore, patients with a lower sPD-1/sPD-L1 ratio were associated with a higher probability of disease progression (p < 0.05). Additionally, a significant (p < 0.05) association was discovered between higher Gleason scores and elevated preoperative sPD-L1 levels and between sPD-1 and advanced stage of disease (p < 0.05). A strong correlation (p < 0.05), between immunosuppressive CD4+CD25+FoxP3+ regulatory T cells and baseline sPD-L1 was observed in patients with unfavorable postoperative course of the disease, supporting the idea that these elements influence each other in cancer progression. In addition to the postoperative drop in circulating PD-L1, the inverse relationship (p < 0.05), between the percentage of M-MDSC and sPD-L1 in patients with BCR suggests that M-MDSC is not a source of sPD-L1 in PCa patients.

Conclusion

Our findings suggest the potential of sPD-L1 as a promising prognostic marker in prostate cancer.

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.

The performance and perspectives of dendritic cell vaccines modified by immune checkpoint inhibitors or stimulants

Therapeutic dendritic cell (DC) vaccines stimulate the elimination of tumor cells by the immune system. However, while antigen-specific T cell responses induced by DC vaccines are commonly observed, the clinical response rate is relatively poor, necessitating vaccine optimization. There is evidence that the suppression of DC function by immune checkpoints hinders the anti-tumor immune responses mediated by DC vaccines, ultimately leading to the immune escape of the tumor cells. The use of immune checkpoint inhibitors (ICIs) and immune checkpoint activators (ICAs) has extended the immunotherapeutic range. It is known that both inhibitory and stimulatory checkpoint molecules are expressed by most DC subsets and can thus be used to manipulate the effectiveness of DC vaccines. Such manipulation has been investigated using strategies such as chemotherapy, agonistic or antagonistic antibodies, siRNA, shRNA, CRISPR-Cas9, soluble antibodies, lentiviruses, and adenoviruses to maximize the efficacy of DC vaccines. Thus, a deeper understanding of immune checkpoints may assist in the development of improved DC vaccines. Here, we review the actions of various ICIs or ICAs shown by preclinical studies, as well as their potential application in DC vaccines. New therapeutic interventional strategies for blocking and stimulating immune checkpoint molecules in DCs are also described in detail.

IFN-γ induces PD-L1 through p38/JNK/ERK signaling pathways and counteracts the tumor promoting effect mediated by PD-L1 in Glioblastoma

Glioblastoma is the most malignant primary glioma. Conventional treatment methods that include surgery, radiotherapy, and chemotherapy have a limited curative effect on the tumor. With the deepening of molecular biology research, molecular targeted therapy has opened a new era of tumor therapy. Programmed death ligand 1 (PD-L1) has been proved to play a pivotal role in the tumor immune evasion process. Previous studies have confirmed the specific expression of PD-L1 in glioblastoma tissues and cells, but there are few studies on inflammation regulating PD-L1 in glioblastoma. In this study, real-time PCR, flow cytometry, and western blot were applied to detect PD-L1 in glioblastoma cells. Short hairpin RNA was used to knock down PD-L1 in glioblastoma cells. Cell counting kit-8 experiment and wound-healing assay were used to detect the proliferation and migration of glioblastoma cells. Here we demonstrated that PD-L1 was overexpressed in glioblastoma cells, and interferon-gamma (IFN-γ) induces PD-L1 in glioblastoma cells via activating p38/JNK/ERK signaling pathways. To summarize, PD-L1 promotes the occurrence and development of glioblastoma. IFN-γ counteracts the tumor-promoting effects mediated by PD-L1 in glioblastoma. IFN-γ regulates PD-L1 through multiple signaling pathways, but the total effect of IFN-γ-mediated inflammatory signals still need to be further explored in glioblastoma. PD-L1 enhances the proliferation and migration of glioblastoma cells by regulating CDK4, CDK6, MMP-2, and vimentin molecules. Most importantly, targeting PD-L1 can be applied in the treatment of glioblastoma. We speculate that IFN-γ may affect glioblastoma through other pathways, and we will continue to further explore the mechanisms in the future.