Exosomal PD-L1 derived from head and neck squamous cell carcinoma promotes immune evasion by activating the positive feedback loop of activated regulatory T cell-M2 macrophage

The positive feedback loop of activated regulatory T cells (aTregs) and M2 macrophages (M2) play a vital role in promoting the tumor immunosuppressive microenvironment of head and neck squamous cell carcinoma (HNSCC). However, the key factors regulating the positive feedback loop remain unclear. Herein, we investigated the effect of PD-L1 carried on exosomes derived from tumor cells (TEXs) on the aTreg-M2 positive feedback loop, as well as their role in mediating immunosuppression. In our study, TEXs with or without PD-L1 (TEX-PD-L1 or TEX-PD-L1KO) were treated with CD4+CD25- T cells and M0 macrophages, and the effect on the differentiation of aTregs, M2 and the aTreg-M2 positive feedback loop was assessed. TEXs carried more PD-L1 than tumor cells and not only promoted the differentiation of aTregs and M2, but also, most importantly, enhanced the positive feedback loop of aTreg-M2, which inhibited the proliferation of CD4+CD25- T cells and in turn led to tumor immune escape. Moreover, in vivo study showed that TEX-PD-L1KO could inhibit tumor growth and significantly improve the antitumor efficacy in both the peripheral and tumor microenvironments. Collectively this study revealed the role and mechanism of TEX-PD-L1 in negative immune regulation, and targeting TEX-PD-L1 may be a new idea and strategy for immunotherapy of HNSCC.

Single-cell analysis of a tumor-derived exosome signature correlates with prognosis and immunotherapy response

Background

Tumor-derived exosomes (TEXs) are involved in tumor progression and the immune modulation process and mediate intercellular communication in the tumor microenvironment. Although exosomes are considered promising liquid biomarkers for disease diagnosis, it is difficult to discriminate TEXs and to develop TEX-based predictive biomarkers.

Methods

In this study, the gene expression profiles and clinical information were collected from The Cancer Genome Atlas (TCGA) database, IMvigor210 cohorts, and six independent Gene Expression Omnibus datasets. A TEXs-associated signature named TEXscore was established to predict overall survival in multiple cancer types and in patients undergoing immune checkpoint blockade therapies.

Results

Based on exosome-associated genes, we first constructed a tumor-derived exosome signature named TEXscore using a principal component analysis algorithm. In single-cell RNA-sequencing data analysis, ascending TEXscore was associated with disease progression and poor clinical outcomes. In the TCGA Pan-Cancer cohort, TEXscore was elevated in tumor samples rather than in normal tissues, thereby serving as a reliable biomarker to distinguish cancer from non-cancer sources. Moreover, high TEXscore was associated with shorter overall survival across 12 cancer types. TEXscore showed great potential in predicting immunotherapy response in melanoma, urothelial cancer, and renal cancer. The immunosuppressive microenvironment characterized by macrophages, cancer-associated fibroblasts, and myeloid-derived suppressor cells was associated with high TEXscore in the TCGA and immunotherapy cohorts. Besides, TEXscore-associated miRNAs and gene mutations were also identified. Further experimental research will facilitate the extending of TEXscore in tumor-associated exosomes.

Conclusions

TEXscore capturing tumor-derived exosome features might be a robust biomarker for prognosis and treatment responses in independent cohorts.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03053-4.

Targeting Tumor-derived Exosomes Expressing CD73: New Opportunities in the Pathogenesis and Treatment of Cancer

Tumor-derived exosomes contain biological contents such as proteins, lipids, RNA (miRNAs, mRNAs, lncRNA), and DNA for intracellular communication. Meanwhile, studies have shown the role of exosomes in cancer progression, metastasis, and therapeutic resistance. Furthermore, tumor exosomes have received growing attention due to their potential as novel therapeutic protocols for the treatment of cancers. Adenosine nucleoside, which is a derivative of ATP, is highly elevated in the tumor microenvironment by CD39 and CD73 enzymatic activity. Recently, it is distinguished that cancer cell-derived exosomes carry CD39 and CD73 on their surface and may contribute to rising adenosine levels in the tumor microenvironment. In this review, we summarize the evidence of CD39/CD73-bearing exosomes and their role in cancer development, progression, invasion, angiogenesis, metastasis and their application in the selection of the appropriate strategy to treat different types of cancer.

Tumor-derived Exosome Promotes Metastasis via Altering its Phenotype and Inclusions

Although tumor-derived exosomes play an important role in the process of metastasis, differences in exosomes secreted by the same cells at different stages or conditions have not been noticed by most of the relevant researchers. Here we developed a lung cancer model in nude mice, and the phenotype and inclusions of exosomes secreted by early and advanced tumors were analysed. The size distribution and surface topography of these two exosomes were not significantly different, but the expression of CD63 in early tumor exosome (E-exosome) was significantly lower than that in advanced tumor exosome (A-exosome). α-SMA expression on HELF cells treated with A-exosome was significantly higher than that treated with E-exosome. The ability of A-exosome to promote the migration of A549 cells was better than E-exosome. Furthermore, small RNA sequence showed that only 3 of the 171 detected-small RNAs were expressed simultaneously in both exosomes. These findings proved that there are significant differences in inclusions and functions between the early and late exosomes of the same tumor. The study highlights the importance of exosomes in cancer metastasis, and might suggest exosomes can be used as biomarkers and therapeutic targets for cancer metastasis.

Exosomes as drug delivery vehicle and contributor of resistance to anticancer drugs

Exosomes are small membranous vesicles implicated in intercellular signalling. Through their uncanny ability to carry and deliver donor cellular cargo (biomolecules) to target cells, they exert a profound effect on the regular functioning of healthy cells and play a significant role in pathogenesis and progression of several diseases, including cancer. The composition and number of endogenously circulating exosomes frequently vary, which is often reflective of the pathophysiological status of the cell. Applicability of exosomes derived from normal cells as a drug carrier with or without modifying their intraluminal and surface components are generally tested. Conversely, exosomes also are reported to contribute to resistance towards several anti-cancer therapies. Therefore, it is necessary to carefully evaluate the role of exosomes in cancer progression, resistance and the potential use of exosomes as a delivery vehicle of cancer therapeutics. In this review, we summarize the recent advancements in the exploitation of exosomes as a drug delivery vehicle. We also discuss the role of exosomes in conferring resistance to anti-cancer therapeutics. While this review is focused on cancer, the exosome-based drug delivery and resistance is also applicable to other human diseases.

Exosome and Secretion: Action On?

Originally treated as part of a cellular waste, extracellular vesicles (EVs) are being shown to possess a vast variety of functions, of which exosome is the most studied one. Most cells, such as tumor cells, immunocytes, and fibroblasts can secrete exosomes, especially under certain stresses the amount is much higher, and the contents of exosome represent the status of the donor cells and the tumor microenvironment. As crucial transporters for cells' content exchange, much attention has been raised in the utilities of exosomes to suppress immune response, and to modify a microenvironment favorable for cancer progression. Exosomal immune checkpoints, such as programmed cell death ligand 1 (PD-L1), contribute to immunosuppression and are associated with anti-PD-1 response. Many forms of soluble immune checkpoint receptors have also been shown to influence efficacy mediated by their therapeutic antibodies. Therefore, targeting pro-tumorous exosomes may achieve antitumor effect supplementary to existing therapies. Exosome, itself natural liposome-like structure, allows it to be a potential drug delivery tool.

Oral cancer-derived exosomal NAP1 enhances cytotoxicity of natural killer cells via the IRF-3 pathway

OBJECTIVE

To examine the effects of oral cancer-derived exosomes (OCEXs) on natural killer (NK) cells and to explore the underlying mechanism.

MATERIALS AND METHODS

OCEXs were isolated from the cell culture supernatant of oral cancer (OC) cells using ultrafiltration and affinity chromatography and were identified using electron microscopy, nanoparticle tracking analysis (NTA) and immunoblotting. The effects of OCEXs on NK cells were analyzed using laser scanning confocal microscopy and several functional assays of NK cells. To explore the mechanism of their effects, antibody array, protein mass spectrometry and RNA interference were adopted.

RESULTS

The particles isolated from the OC cells were identified as exosomes with satisfactory morphology, concentration and purity. The OCEXs were internalized by NK cells and then promoted the biological functions of NK cells, including proliferation, release of perforin and granzyme M and cytotoxicity. Furthermore, OCEXs increased the expression of interferon regulatory factor 3 (IRF-3) and its phosphorylation, which drove the expression of the type I interferon (IFN) gene and the chemokine (C-X-C motif) ligand (CXCL) genes, thereby promoting the functions of NK cells. In addition, NF-κB-activating kinase-associated protein 1 (NAP1), an upstream activator of IRF-3, was enriched in OCEXs, and treatment with OCEXs increased the expression of NAP1 in NK cells. Importantly, NAP1-depleted OCEXs obtained from OC cells had a dramatically weakened influence on NK cells.

CONCLUSION

Our findings reveal a previously unrecognized function of exosomal NAP1 derived from OC cells in enhancing the cytotoxicity of NK cells via the IRF-3 pathway.