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Background Gliomas comprise the most common type of primary brain tumor, are highly invasive, and often fatal. IDH-mutated gliomas are particularly challenging to image and there is currently no clinically accepted method for identifying the extent of tumor burden in these neoplasms. This uncertainty poses a challenge to clinicians who must balance the need to treat the tumor while sparing healthy brain from iatrogenic damage. The purpose of this study was to investigate the feasibility of using resting-state blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to detect glioma-related asynchrony in vascular dynamics for distinguishing tumor from healthy brain. Methods Twenty-four stereotactically localized biopsies were obtained during open surgical resection from ten treatment-naïve patients with IDH-mutated gliomas who received standard-of-care preoperative imaging as well as echo-planar resting-state BOLD fMRI. Signal intensity for BOLD asynchrony and standard-of-care imaging was compared to cell counts of total cellularity (H&E), tumor density (IDH1 & Sox2), cellular proliferation (Ki67), and neuronal density (NeuN), for each corresponding sample. Results BOLD asynchrony was directly related to total cellularity (H&E, P = 4 × 10–5), tumor density (IDH1, P = 4 × 10–5; Sox2, P = 3 × 10–5), cellular proliferation (Ki67, P = .002), and inversely related to neuronal density (NeuN, P = 1 × 10–4). Conclusions Asynchrony in vascular dynamics, as measured by resting-state BOLD fMRI, correlates with tumor burden and provides a radiographic delineation of tumor boundaries in IDH-mutated gliomas.

Immune checkpoint inhibitors have been successful across several tumor types; however, their efficacy has been uncommon and unpredictable in glioblastomas (GBM), where

Immunotherapy for glioblastoma (GBM) is the subject of numerous clinical trials due to the potential ability of the adaptive immune response to combat this diffusely infiltrating tumor. However, rational application of immunotherapy to these tumors is challenging because of the peculiar immune privilege of the brain and the molecular heterogeneity of glioma antigens. Little is known about patient-to-patient variability in the potential to generate anti-glioma immune responses of their systemic and local T cell populations. We conducted a foundational study of the population-wide characteristics of both the peripheral blood and local, tissue-infiltrating T lymphocytes (TILs) of glioma patients using TCRseq. Through reverse transcription and pan-repertoire amplification of the TCR-alpha and -beta chains we generated TCRseq libraries from matched surgical tissue and peripheral blood cells. Using peripheral blood samples from primary GBM, low-grade glioma, and non-tumor patients (N = 14), we define new immunophenotypes using statistical metrics based on information theory - specifically, the clonality associated with antigen-binding function in the TCRs of TIL, and the antigen-binding associated divergence of the TIL population from the blood. We found that diversification of this repertoire was characteristic of high-grade tumors, and correlated strongly with the activation of specific immune and inflammatory pathways. Furthermore, we found strong correlation between usage of a subset of TCR sequences in patients' peripheral blood and the divergence of their TIL population from the peripheral repertoire. We anticipate that these immunophenotypes will be key to monitoring and predicting response to anti-glioma vaccines and immunotherapy, and understanding the immunological mechanisms determining their efficacy.

BACKGROUND: The primary treatment of GBM is surgical resection of the contrast enhancing mass, while regions of non-enhancing tumor are left behind, and inevitably gives rise to recurrence. Thus, there is therapeutic significance to understanding the cellular and molecular features of the non-enhancing margins of GBM. Advances in comparative genetic and molecular analyses have uncovered patterns of gene expression and genetic alterations in GBM, and led to the recognition of clinically significant tumor subtypes. However, most previous studies have been based on analysis of tissue that was removed during surgery without documenting the radiographic location. This has precluded the systematic study of intra-tumoral heterogeneity, and its correlation with radiographic regions. We propose a method of sequential image guided biopsies, allowing for specimen localization, intra-tumoral comparative analysis, and the systematic study of infiltrated tissue beyond the borders of contrast enhancement. METHODS: In 77 patients with GBM, multiple stereotactic-guided biopsies were obtained from radiographically distinct regions prior to resection. The radiographic localization of each biopsy was mapped using the 3D intraoperative neuro-navigation system (BrainLab). Sampled regions included areas of contrast enhancement (CE) and adjacent non-enhancing FLAIR+ (NEF+). Samples from each region were divided into pieces processed for RNA-seq and histological analyses. RESULTS: There were significant differences in the cellular density and cellular composition between the CE and NEF+ samples. The CE samples had higher cellularity than NEF+ samples, and were more likely to contain the histological hallmarks of GBM, including vascular proliferation and pseudopalisading necrosis. In contrast, the NEF+ regions showed the histological features of diffusely infiltrating glioma with neoplastic glial cells intermingled with non-neoplastic and reactive cells. RNA-seq showed that the CE and NEF+ regions also had markedly different expression patterns. Comparisons between our image guided biopsies and the TCGA data set showed that the CE regions were enriched for genes associated with the mesenchymal, classical and proneural subtypes while the NEF+ region were enriched for genes of the neural subtype. Further analysis revealed that region-specific and subtype-specific differences in expression patterns were predominantly due to differences in the cellular composition. CONCLUSIONS: Cellular composition is a major determinant of the expression patterns seen at the non-enhancing margins of GBM. The different GBM subtypes show distinct expression patterns that relate the contrast enhancing centers to the non-enhancing margins of the tumors. Understanding these patterns provides a means to infer the molecular and cellular features of glioma tissue left behind after surgery. SECONDARY CATEGORY: Tumor Biology.

Glioblastomas (GBMs) diffusely infiltrate the brain, making complete removal by surgical resection impossible. The mixture of neoplastic and non-neoplastic cells that remain after surgery form the biological context for adjuvant therapeutic intervention and recurrence. We performed RNA-Seq and histological analysis on radiographically guided biopsies taken from different regions of GBM and showed that the tissue contained within the contrast-enhancing (CE) core of tumors have different cellular and molecular compositions compared to tissue from the non-enhancing (NE) margins of tumors. Comparisons with the TCGA dataset showed that the samples from CE regions resembled the Proneural, Classical, or Mesenchymal subtypes of GBM, while the samples from the NE regions predominantly resembled the Neural subtype. Computational deconvolution of the RNA-seq data revealed that contributions from non-neoplastic brain cells significantly influence the expression pattern in the NE samples. Gene ontology showed that the cell type-specific expression patterns were functionally distinct and highly enriched in genes associated with the corresponding cell phenotypes. Comparing the RNA-Seq data from the GBM samples to that of normal brain revealed that the differentially expressed genes are distributed across multiple cell types. Notably, the patterns of cell type-specific alterations varied between the different GBM subtypes; the NE regions of Proneural tumors were enriched in oligodendrocyte progenitor genes while the NE regions of Mesenchymal GBM were enriched in astrocytic and microglial genes. These subtype-specific patterns in the molecular and cellular composition of the infiltrative margins of GBM make it possible to infer key characteristics of the tissue left behind after surgery.

Meeting abstracts Immunotherapy for glioblastoma (GBM) is the subject of numerous clinical trials, given the potential for the adaptive immune response to combat this diffusely infiltrating tumor. However, rational application of immunotherapy to these tumors is challenging because of the peculiar