IMMU-43. IMMUNE CONTEXTURE OF ISOCITRATE DEHYDROGENASE STRATIFIED HUMAN GLIOMAS REVEALED BY SINGLE-CELL TRANSCRIPTOMICS AND ACCESSIBLE CHROMATIN

The immune cell composition of isocitrate dehydrogenase wild type (IDH-wt) glioma patients significantly differs compared to IDH-mutant (IDH-mut) yet a detailed and unbiased understanding of their transcriptomic and epigenetic landscapes remains elusive. To this end, we performed single-cell RNA-sequencing (scRNA-seq) and single-cell Assay for Transposase-Accessible Chromatin using sequencing (sc-ATAC-seq) on ~100,000 tumor-associated immune cells from seventeen IDH mutation classified primary and recurrent human gliomas and non-glioma brains (NGBs). Our analyses revealed sixty-two transcriptionally distinct myeloid and lymphoid cell states within and across glioma subtypes and we noted microglial attrition with increasing disease severity concomitant with invading monocyte-derived cells (MDCs) and lymphocytes. Specifically, certain microglial and monocyte-derived subpopulations were associated with antigen presentation gene modules, akin to cross-presenting dendritic cells. As tissue macrophages exhibit multifaceted polarization in response to microenvironmental cues, we clarify the existence of microglia/macrophage functional states beyond M1/M2 paradigms exemplified by the presence of palmitic-, oleic- acid, and glucocorticoid responsive polarized states. We identified cytotoxic T cells with poly-functional cytolytic states mostly in recurrent IDH-wt gliomas. Furthermore, ligand-receptor interactome analyses showed a preponderance of antigen presentation/phagocytosis over the checkpoint axis in IDH-wt compared to IDH-mut gliomas. Additionally, our sc-ATAC-seq analyses revealed differences in regulatory networks in NGBs, IDH-mut, and IDH-wt glioma-associated immune cells. In particular, we noted reduced microglial usage of an iron recycling SPIC transcription factor and Interferon Regulatory Factors (IRFs); IRF1 and IRF2 in IDH-wt relative to IDH-mut and NGBs. Unique features such as amplification of 11-Zinc Finger Protein accessibility were restricted to MDCs. Finally, sc-ATAC-seq profiles of CD8+ exhausted T cells from IDH-wt showed strong enhancer accessibility on CTLA-4, Layilin, and TIM-3 but no enrichment on PD1 was seen. In summary, our study provides unprecedented granular detail of transcriptionally and epigenomically defined glioma-specific immune contexture that can be exploited for immunotherapy applications.

The immune checkpoint VISTA exhibits high expression levels in human gliomas and associates with a poor prognosis

In human gliomas, anti-tumor T cell responses are inhibited through induction of local and systemic immunosuppression. Immune checkpoint blockade is proving to be a success in several types of cancers. However, many studies reported that the treatment of glioblastoma patients with anti-CTLA-4 or anti-PD-1 has no survival benefit compared to standard chemotherapy. This study aimed to investigate the expression and role of VISTA, a newly described immune checkpoint regulator, in human gliomas. mRNA expression was assessed in a total of 87 samples from glioma patients. 57 glioma tissues were taken at different grades. 20 peripheral blood mononuclear cells (PBMC) samples were taken before surgery and ten after surgery, all from the same set of patients. As for the control, ten specimens of PBMC were taken from healthy donors. Protein expression using immunohistochemistry was performed for 30 patients. The Cancer Genome Atlas (TCGA) data set, was also used to investigate VISTA expression through analysis of RNA-seq data of 667 glioma patients. In the Moroccan cohort, VISTA gene expression was significantly upregulated in glioma tissues related to PBMC of healthy donors. This high expression was specific to patient tissues since VISTA expression in PBMC was low when assessed either before or after surgery. Besides, VISTA exhibited higher expression levels in grade III/IV relative to grade I/II glioma patients. Interestingly, VISTA correlated positively with PD-1 expression. PD-1 also showed elevated expressions in higher glioma grades. The TCGA cohort corroborated these observations. Indeed, VISTA was also found to be strongly expressed in high grades. It was positively correlated with other critical immune checkpoints. Finally, increased VISTA transcript levels were associated with weak overall survival of glioma patients. Our study highlighted a correlation between high levels of VISTA expression and poor prognosis in glioma patients. VISTA might be involved in glioma progression and could be considered as a possible new therapeutic target, especially in advanced gliomas.

CLRM-13. INTRAOPERATIVE MICRODIALYSIS: GLIOMA INTELLIGENCE FROM BEHIND ENEMY LINES

INTRODUCTION Gliomas present a formidable challenge for translational progress. Heterogeneity within and between tumors may demand empirically individualized and adaptive paradigms requiring rapid mechanistic feedback. We asked if tumor-associated metabolic biomarkers from glioma extracellular fluid could impart mechanistic “intelligence” reflecting intra- and inter-tumoral heterogeneity. METHODS Five live human gliomas (2 oligos; 2 IDH-WT GBMs; 1 IDH-mutant GBM), were evaluated in situ with high molecular weight (100kDA) intraoperative microdialysis using 3 disparately placed catheters. Isotonic 3% dextran perfusate was collected in 20 min (40mL) aliquots. CSF samples (n=21) were additionally evaluated from these and other patients with diverse brain tumors. The IDH-mutant glioma-associated oncometabolite D2-hydroxyglutarate (D2-HG) was quantified with targeted Liquid Chromotography-Mass Spectrometry (LC-MS). Over 200 metabolites were further evaluated via untargeted LC-MS using the Metabolon platform. Correlation, clustering, ROC and enrichment analyses were employed to identify correlations within and between patient samples. RESULTS CSF samples from patients with IDH-mutant gliomas contained over twenty-fold higher levels of D2-HG (median 4.1 mM, range 1.6-13.2, n=7) compared to those from IDH-wild type tumors (median 0.19 mM; range 0.89-0.35, n=14). Microdialysate from IDH-mutant gliomas contained 10-953mM D2-HG, 9-63x higher than paired CSF samples. Interestingly, IDH status failed to predict the global metabolic signature of microdialysate. Microdialysate samples clustered into 2 major metabolic phenotype clusters with IDH-WT and IDH-mutant gliomas in each cluster. A superimposed metabolic signature distinguishing enhancing from non-enhancing tumor, was conserved in both patient clusters. Amino acid and carnitine metabolism predominated in microdialysate signatures. TCA cycle and Warburg-associated metabolites were differentially enriched in CSF samples after prior therapy independent of tumor burden. CONCLUSIONS Intra-operative micro-dialysis may complement currently available “intelligence” regarding the phenotype, burden, and metabolism of live human gliomas and is feasible within standard-of-care surgical procedures. Future work will evaluate utility for pharmacodynamic feedback following novel early phase candidate therapies.

P13.23 Study of migration characteristics of human glioma cells in vitro

BACKGROUND Gliomas are still one of the most aggressive human cancers, and even despite modern therapeutic approaches, the prognosis for patients with this disease is not favorable. It is known that glioma cells are capable of local invasiveness, when glioma cells migrate into healthy brain tissue. A lack of any definite markers, characterizing migrating glioma cells and allowing them to be distinguished from healthy brain cells, requires a thorough investigation. In case it would be possible to characterize invasive glioma cells, then a development of targeted therapy could be feasible. MATERIAL AND METHODS Cell cultures of human gliomas Gr II, III and IV were developed with 5 cultures for each Grade. MTT, RT-PCR, Western and Nosern blot, transcriptome analysis were applied. RESULTS Three cultures of human gliomas had a high degree of migration, within the range of 6% - 14%. These cultures were developed from gliomas of Grade III and Grade IV, and with IDH1- (minus) phenotype. Moreover, cell cultures with IDH1 + (plus) phenotype had a low migration rate within 1%. An intensity of migration correlated with the degree of malignancy, and an average rate decreased with a decrease of the Grade. Moreover, an analysis of the proliferative activity of cell cultures of human gliomas of various degrees of malignancy did not reveal a relationship with a migratory properties of cultures. A number of actively proliferating cultures did not show high migration, while cultures with medium proliferative activity could show a high level of migration. The low level of proliferation of cultures of gliomas of Grade II and I at the beginning of cultivation, in some cases, subsequently increased, but an inherent low migration activity did not change. In actively migrating cultures, a significant decrease in the expression of Sox2 and Nestin is detected. A positive correlation was found between migration abilities of human glioma cell culture cells and the marker Ki67, GFAP, Sox2, and Oct4. The difference was statistically significant by the one-sided Mann-Whitney test. CONCLUSION Conclusions: Cell cultures derived from glioma tumor tissue can be used to predict invasive properties of the tumor. High tumor invasiveness is characteristic for Grade III and Grade IV, and with IDH1- (minus) phenotype, and it also correlates with elevated expression of GFAP, Sox2 and Oct4The reported study was funded by RFBR according to the research project № 18-29-01012 and by the Ministry of Science and Higher Education of the Russian Federation, grant number 075-15-2020-809 (13.1902.21.0030).

Individualized diversity in the extracellular metabolome of live human gliomas

Gliomas present a formidable challenge for translational progress. Heterogeneity within and between tumors may demand empirically individualized insights, though relatively little is known about the biochemical milieu within which malignant cells thrive in the in vivo human glioma. We performed a pilot study of intraoperative high molecular weight microdialysis to sample the extracellular tumor environment within three locations in each of five molecularly diverse human gliomas spanning WHO grade 2 oligodendroglioma to WHO grade 4 glioblastoma (GBM). Microdialysates were subjected to targeted (D/L-2-hydroxyglutarate (2-HG)) and untargeted metabolomic analyses, enabling correlation, clustering, fold change, and enrichment analyses. IDH-mutant tumor microdialysate contained markedly higher levels of D2-HG than IDH-wild type tumors. However, IDH status was not predictive of the global metabolomic signature. Rather, two distinct metabolic phenotypes (α and β) emerged, with IDH-WT and IDH-mutant patient samples in each group. Individualized metabolic signatures of enhancing tumor versus adjacent brain were conserved across patients with glioblastoma regardless of metabolic phenotype. Untargeted metabolomic analysis additionally enabled correlative quantification of multiple peri-operatively administered drugs, illustrating regional heterogeneity of blood-brain barrier permeability. As such, acute intraoperative microdialysis affords a previously unharnessed window into individualized heterogeneous microenvironments within and between live human gliomas. Such access to the interstitial milieu of live human gliomas may provide a complementary tool for the development of individualized glioma therapies.