Advancements and Technical Considerations for Extracellular Vesicle Isolation and Biomarker Identification in Glioblastoma

Extracellular vesicles (EVs) are membrane-bound particles released by all cells. Previous research has found that these microscopic vesicles contribute to intercellular signaling and communication. EVs carry a variety of cargo, including nucleic acids, proteins, metabolites, and lipids. The composition of EVs varies based on cell of origin. Therefore, EVs can serve as an important biomarker in the diagnosis and treatment of various cancers. EVs derived from glioblastoma (GBM) cells carry biomarkers, which could serve as the basis for a potential diagnostic strategy known as liquid biopsy. Multiple EV isolation techniques exist, including ultrafiltration, size exclusion chromatography, flow field-flow fractionation, sequential filtration, differential ultracentrifugation, and density-gradient ultracentrifugation. Recent and ongoing work aims to identify cellular markers to distinguish GBM-derived EVs from those released by noncancerous cells. Strategies include proteomic analysis of GBM EVs, identification of GBM-specific metabolites, and use of Food and Drug Administration-approved 5-aminolevulinic acid-an oral agent that causes fluorescence of GBM cells-to recognize GBM EVs in a patient's blood. In addition, accurately and precisely monitoring changes in EV cargo concentrations could help differentiate between pseudoprogression and GBM recurrence, thus preventing unnecessary surgical interventions.

Superinduction of immunosuppressive glioblastoma extracellular vesicles by IFN-γ through PD-L1 and IDO1

Background

Glioblastoma (GBM), the most common primary brain tumor, has a median survival of 15-16 months. Immunotherapy is promising but GBM-mediated immunosuppression remains a barrier. GBMs express the interferon-gamma (IFN-γ)-responsive immunosuppressive molecules PD-L1 and IDO1. Extracellular vesicles (EVs) have also been implicated in GBM-mediated immunosuppression, in part through PD-L1. We therefore sought to determine if GBM IFN-γ exposure increased GBM EV-mediated immunosuppression and mechanisms underlying this.

Methods

Human GBM-derived cells were cultured in the presence/absence of IFN-γ. EV’s were harvested. PD-L1, IDO1, and EV-associated protein expression was assessed. GBM EV’s (+/-IFN-γ) were cultured with healthy donor monocytes. Immunosuppressive myeloid-derived suppressor cell (MDSC) and non-classical monocyte (NCM) frequency was determined. Impact of GBM (+/-IFN-γ) EV-treated monocytes on CD3/CD28-mediated T cell proliferation was assessed. The impact of PD-L1 and IDO1 knockdown in GBM EV’s in this system was evaluated.

Results

IFN-γ exposure increased PD-L1 and IDO1 expression in GBM cells and EV’s without altering EV size or frequency. IFN-γ-exposed GBM EVs induced more MDSC and NCM differentiation in monocytes and these monocytes caused more T cell inhibition than IFN-γ-naive GBM EVs. PD-L1 and/or IDO1 knockdown in GBM cells abrogated the immunosuppressive effects of IFN-γ-exposed GBM EVs on monocytes.

Conclusions

IFN-γ exposure such as might occur during an anti-tumor immune response results in superinduction of GBM EVs’ baseline immunosuppressive effects on monocytes. These effects are mediated by increased PD-L1 and IDO1 expression in GBM EV’s. This data highlights mechanisms of GBM EV-mediated immunosuppression and identifies therapeutic targets (PD-L1, IDO1) to reverse these effects.

Plasma extracellular vesicles as a source of biomarkers in traumatic brain injury

OBJECTIVE

The objective of this study was to isolate extracellular vesicles (EVs) from plasma in a cohort of patients with traumatic brain injury (TBI) and analyze their contents for novel biomarkers that could prove useful for rapid diagnosis and classification of brain injury during initial evaluation.

METHODS

Plasma EVs were isolated by serial ultracentrifugation from patients with TBI (n = 15) and healthy controls (n = 5). Samples were obtained from the TRACK-TBI biorepository (2010–present). Size and concentration were determined by nanoparticle tracking. Glial fibrillary acidic protein (GFAP) concentration was determined in EV protein. EV RNA was isolated and deep sequencing of short noncoding RNA was performed.

RESULTS

Plasma EVs are physically similar but contained approximately 10 times more GFAP in TBI patients with altered consciousness than patients and controls with normal consciousness. Eleven highly differentially expressed microRNAs (miRNAs) were identified between these groups. Genes targeted by these miRNAs are highly associated with biologically relevant cellular pathways, including organismal injury, cellular development, and organismal development. Multiple additional coding and noncoding RNA species with potential biomarker utility were identified.

CONCLUSIONS

Isolating plasma EVs in patients with TBI is feasible. Increased GFAP concentration—a validated plasma TBI marker—in EVs from TBI patients with altered consciousness, along with differential expression of multiple miRNAs targeting TBI-relevant pathways, suggests that EVs may be a useful source of TBI biomarkers. Additional evaluation in larger patient cohorts is indicated.

The role of extracellular vesicles and PD-L1 in glioblastoma-mediated immunosuppressive monocyte induction

BACKGROUND

Immunosuppression in glioblastoma (GBM) is an obstacle to effective immunotherapy. GBM-derived immunosuppressive monocytes are central to this. Programmed cell death ligand 1 (PD-L1) is an immune checkpoint molecule, expressed by GBM cells and GBM extracellular vesicles (EVs). We sought to determine the role of EV-associated PD-L1 in the formation of immunosuppressive monocytes.

METHODS

Monocytes collected from healthy donors were conditioned with GBM-derived EVs to induce the formation of immunosuppressive monocytes, which were quantified via flow cytometry. Donor-matched T cells were subsequently co-cultured with EV-conditioned monocytes in order to assess effects on T-cell proliferation. PD-L1 constitutive overexpression or short hairpin RNA-mediated knockdown was used to determined the role of altered PD-L1 expression.

RESULTS

GBM EVs interact with both T cells and monocytes but do not directly inhibit T-cell activation. However, GBM EVs induce immunosuppressive monocytes, including myeloid-derived suppressor cells (MDSCs) and nonclassical monocytes (NCMs). MDSCs and NCMs inhibit T-cell proliferation in vitro and are found within GBM in situ. EV PD-L1 expression induces NCMs but not MDSCs, and does not affect EV-conditioned monocytes T-cell inhibition.

CONCLUSION

These findings indicate that GBM EV-mediated immunosuppression occurs through induction of immunosuppressive monocytes rather than direct T-cell inhibition and that, while PD-L1 expression is important for the induction of specific immunosuppressive monocyte populations, immunosuppressive signaling mechanisms through EVs are complex and not limited to PD-L1.

Isolation and Analysis of Plasma-Derived Exosomes in Patients With Glioma

Gliomas including glioblastoma (GBM) are the most common primary malignant brain tumors. Glioma extracellular vesicles (EVs) including exosomes have biological effects (e.g., immunosuppression) and contain tumor-specific cargo that could facilitate liquid biopsies. We aimed to develop a simple, reproducible technique to isolate plasma exosomes in glioma patients. Glioma patients' and normal donors' plasma exosomes underwent brief centrifugation to remove cells/debris followed by serial density gradient ultracentrifugation (DGU). EV size/concentration was determined by nanoparticle tracking. Protein cargo was screened by array, western blot, and ELISA. Nanoscale flow cytometry analysis quantified exosome and microvesicle populations pre- and post-DGU. One-step DGU efficiently isolates exosomes for nanoparticle tracking. Wild type isocitrate dehydrogenase glioma patients' (i.e., more aggressive tumors) plasma exosomes are smaller but higher concentration than normal donors. A second DGU efficiently concentrates exosomes for subsequent cargo analysis but results in vesicle aggregation that skews nanoparticle tracking. Cytokines and co-stimulatory molecules are readily detected but appeared globally reduced in GBM patients' exosomes. Surprisingly, immunosuppressive programmed death-ligand 1 (PD-L1) is present in both patients' and normal donors' exosomes. Nanoscale flow cytometry confirms efficient exosome (<100 nm) isolation post-DGU but also demonstrates increase in microvesicles (>100 nm) in GBM patients' plasma pre-DGU. Serial DGU efficiently isolates plasma exosomes with distinct differences between GBM patients and normal donors, suggesting utility for non-invasive biomarker assessment. Initial results suggest global immunosuppression rather than increased circulating tumor-derived immunosuppressive exosomes, though further assessment is needed. Increased glioma patients' plasma microvesicles suggest these may also be a key source for biomarkers.

CD38 promotes pristane-induced chronic inflammation and increases susceptibility to experimental lupus by an apoptosis-driven and TRPM2-dependent mechanism

In this study, we investigated the role of CD38 in a pristane-induced murine model of lupus. CD38-deficient (Cd38-/-) but not ART2-deficient (Art2-/-) mice developed less severe lupus compared to wild type (WT) mice, and their protective phenotype consisted of (i) decreased IFN-I-stimulated gene expression, (ii) decreased numbers of peritoneal CCR2hiLy6Chi inflammatory monocytes, TNF-α-producing Ly6G+ neutrophils and Ly6Clo monocytes/macrophages, (iii) decreased production of anti-single-stranded DNA and anti-nRNP autoantibodies, and (iv) ameliorated glomerulonephritis. Cd38-/- pristane-elicited peritoneal exudate cells had defective CCL2 and TNF-α secretion following TLR7 stimulation. However, Tnf-α and Cxcl12 gene expression in Cd38-/- bone marrow (BM) cells was intact, suggesting a CD38-independent TLR7/TNF-α/CXCL12 axis in the BM. Chemotactic responses of Cd38-/- Ly6Chi monocytes and Ly6G+ neutrophils were not impaired. However, Cd38-/- Ly6Chi monocytes and Ly6Clo monocytes/macrophages had defective apoptosis-mediated cell death. Importantly, mice lacking the cation channel TRPM2 (Trpm2-/-) exhibited very similar protection, with decreased numbers of PECs, and apoptotic Ly6Chi monocytes and Ly6Clo monocytes/macrophages compared to WT mice. These findings reveal a new role for CD38 in promoting aberrant inflammation and lupus-like autoimmunity via an apoptosis-driven mechanism. Furthermore, given the implications of CD38 in the activation of TRPM2, our data suggest that CD38 modulation of pristane-induced apoptosis is TRPM2-dependent.

Brain atrophy in picornavirus-infected FVB mice is dependent on the H-2Db class I molecule

Brain atrophy is a common feature of numerous neurologic diseases in which the role of neuroinflammation remains ill-defined. In this study, we evaluated the contribution of major histocompatibility complex class I molecules to brain atrophy in Theiler's murine encephalomyelitis virus (TMEV)-infected transgenic FVB mice that express the D^b class I molecule. FVB/D^b and wild-type FVB mice were evaluated for changes in neuroinflammation, virus clearance, neuropathology, and development of brain atrophy via T2-weighted MRI and subsequent 3-dimensional volumetric analysis. Significant brain atrophy and hippocampal neuronal loss were observed in TMEV-infected FVB/D^b mice, but not in wild-type FVB mice. Brain atrophy was observed at 1 mo postinfection and persisted through the 4-mo observation period. Of importance, virus-infected FVB/D^b mice elicited a strong CD8 T-cell response toward the immunodominant D^b-restricted TMEV-derived peptide, VP2_121-130, and cleared TMEV from the CNS. In addition, immunofluorescence revealed CD8 T cells near virus-infected neurons; therefore, we hypothesize that class I restricted CD8 T-cell responses promote development of brain atrophy. This model provides an opportunity to analyze the contribution of immune cells to brain atrophy in a system where persistent virus infection and demyelination are not factors in long-term neuropathology.-Huseby Kelcher, A. M., Atanga, P. A., Gamez, J. D., Cumba Garcia, L. M., Teclaw, S. J., Pavelko, K. D., Macura, S. I., Johnson. A. J. Brain atrophy in picornavirus-infected FVB mice is dependent on the H-2D^b class I molecule.

Future doctors and brain death: what is the prognosis?

OBJECTIVE

To evaluate the knowledge and the opinion of medical students at the Pontifical Catholic University of São Paulo related to the general aspects of donation, organ and tissue procurement, and basic concepts of brain death (BD).

MATERIALS AND METHODS

Questionnaires of 24 items were distributed among all students related to the concept and diagnosis of BD, personal aspects of tissue and organ donation, and general question concerning organ donation. The answers classified students as good versus bad experts of the concept and the diagnosis of BD.

RESULTS

Of a total of 580 students, 361 (62.24%) answered the questionnaire. Although the concept of BD was known to 70%, only 35% had a good knowledge of the diagnosis. One percent of the students were opposed to the organ donation and 76% of them were donors. Approximately 90% would authorize organ retrieval from their family members but 27% had never discussed organ donation with their families. Most students were interested in the general aspects of donation and organ procurement (88.36%).

CONCLUSION

The majority of the students know the concept of BD. General aspects regarding tissue and organ donation and diagnosis of BD might be improved with the continued education on the subject.