Search

Purpose Gliomas are the most common primary tumors of the central nervous system and are categorized by the World Health Organization into either low-grade (grades 1 and 2) or high-grade (grades 3 and 4) gliomas. A subset of patients with glioma may experience no tumor-related symptoms and be incidentally diagnosed. These incidental low-grade gliomas (iLGG) maintain controversial treatment course despite scientific advancements. Here we highlight the recent advancements in classification, neuroimaging, and surgical management of these tumors. Methods A review of the literature was performed. The authors created five subtopics of focus: histological criteria, diagnostic imaging, surgical advancements, correlation of surgical resection and survival outcomes, and clinical implications. Conclusions Alternating studies suggest that these tumors may experience higher mutational rates than their counterparts. Significant progress in management of gliomas, regardless of the grade, has been made through modern neurosurgical treatment modalities, diagnostic neuroimaging, and a better understanding of the genetic composition of these tumors. An optimal treatment approach for patients with newly diagnosed iLGG remains ill-defined despite multiple studies arguing in favor of safe maximal resection. Our review emphasizes the not so benign nature of incidental low grade glioma and further supports the need for future studies to evaluate survival outcomes following surgical resection.

Supplementary Figure 3 has the top 25 TCR clones from tumor biopsies at pre-treatment and the frequency of these clones in the blood.

TCR Sequencing data of each patient

Although immunotherapeutic strategies are emerging as adjunctive treatments for cancer, sensitive methods of monitoring the immune response after treatment remain to be established. We used a novel next-generation sequencing approach to determine whether quantitative assessments of tumor-infiltrating lymphocyte (TIL) content and the degree of overlap of T-cell receptor (TCR) sequences in brain tumors and peripheral blood were predictors of immune response and overall survival in glioblastoma patients treated with autologous tumor lysate–pulsed dendritic cell immunotherapy. A statistically significant correlation was found between a higher estimated TIL content and increased time to progression and overall survival. In addition, we were able to assess the proportion of shared TCR sequences between tumor and peripheral blood at time points before and after therapy, and found the level of TCR overlap to correlate with survival outcomes. Higher degrees of overlap, or the development of an increased overlap following immunotherapy, was correlated with improved clinical outcome, and may provide insights into the successful, antigen-specific immune response. Cancer Immunol Res; 4(5); 412–8. ©2016 AACR.

Clinical patient characteristics

Cox Proportional Hazard table of the Estimated TIL content and patient survival

Supplementary Figure 1 shows representative IHC staining of TIL to confirm that these T cells are found in the parenchyma of the tumor and not tumor blood vessels.

INTRODUCTION Sodium MRI has been recently explored in brain tumors to potentially reveal complementary information with proton MRI about the tumor microenvironment. However, there remains limited investigation combining sodium and quantitative proton MRI techniques. This pilot study explored the associations of sodium MRI with diffusion-, pH-, and hypoxia-weighted MRI biomarkers in gliomas. METHODS Eleven patients with gliomas (n=8 IDH-wild-type; n=3 IDH-mutant) who obtained sodium, anatomical, diffusion-, pH-, and hypoxia-weighted MRI were studied. All images were obtained on a 3T Siemens Prisma with a dedicated multi-nuclear head coil. Regions-of-interest were segmented on the contrast-enhancing (CE) (n=10), FLAIR (n=11), and necrotic regions (n=9). Sodium values were normalized to the mean values of the eyes. Median sodium, apparent diffusion coefficient (ADC), ADC(L) from bimodal histogram analyses, MTRasym (acidity), and R2’ (hypoxia) values were obtained. RESULTS There was increased sodium in necrosis compared to FLAIR regions (mean difference=0.24; P/i>< 0.05) and compared to CE regions (mean difference=0.17; P/i>=0.07). There were significant positive correlations between sodium and ADC in CE (R=0.94; P/i>< 0.0001) and FLAIR regions (ρ=0.77; P/i>< 0.01), but not in necrosis (R=0.44; P/i>=0.24). There was also a significant positive correlation with ADC(L) in CE regions (R=0.90; P< 0.001) but not in FLAIR regions (ρ=0.50; P/i>=0.12). Furthermore, there was a significant positive correlation between sodium and MTRasym in necrosis (R=0.74; P/i>< 0.05) and a positive trend in CE regions (R=0.55; P=0.10). There was also a negative trend between sodium and R2’ in FLAIR regions (ρ=-0.58; P/i>=0.11). CONCLUSIONS Because ADC and ADC(L) are inversely related to cell density, increased sodium in gliomas may reflect increased extracellular space stemming from lower cell density, as sodium concentration is higher extracellularly. Positive associations between sodium and acidity as well as negative associations between sodium and hypoxia may reflect alterations in coupled sodium-pH and sodium-hypoxia homeostasis in gliomas.

INTRODUCTION New York-esophageal squamous cell carcinoma (NY-ESO-1) specific adoptive T-cell immunotherapy is an appealing strategy for the treatment of gliomas because it elicits a strong antibody and T-cell response and is downregulated in most normal adult tissues which produces an effective and specific antitumor response. However, NY-ESO-1 is often poorly expressed in GBM, presumably through promoter methylation. Neither the prevalence of NY-ESO-1 downregulation in glioblastoma (GBM) patient tumors nor the presumed mechanism of downregulation by promoter methylation have been formally established. METHODS We characterized baseline CpG methylation of NY-ESO-1 in patient GBM samples using bisulfite sequencing. We induced NY-ESO-1 expression in vitro in human GBM cell lines (U251) and patient-derived gliomaspheres using the demethylating agent decitabine (DAC). We investigated the epigenetic response of DAC treated GBM cell lines with bisulfite sequencing and NY-ESO-1 expression with quantitative real time PCR. Lastly, we performed single cell RNA sequencing on DAC treated and untreated U251 and PGDSC to evaluate tumor subpopulations that upregulate NY-ESO-1 and co-expressed cancer testis antigens after DAC treatment. RESULTS NY-ESO-1 expression is associated with promoter methylation in the majority of GBM. Prolonged low dose of DAC explicitly demethylated the promoter region of NY-ESO-1 and resulted in robust mRNA expression. DAC treatment co-expresses NY-ESO-1 with other cancer testis antigens CTAG2 and MAGEA4 as demonstrated by single cell RNA sequencing. CONCLUSION These results reveal a feasible strategy of cancer testis antigen promoter demethylation which creates an inducible tumor antigen for immunotherapeutic targeting. We speculate that DAC induced upregulation of NY-ESO-1 and co-expressed cancer testis antigens renders tumor recognition by NY-ESO-1 specific T cells.

Neoadjuvant drug administration provides a window of opportunity for developing novel therapies. Specifically, neoadjuvant pembrolizumab (PD1 checkpoint inhibitor) has the potential for improving understanding of immunomodulatory effects on the tumor microenvironment and for treating recurrent GBM. It is known that a functional immune deficit exists within the tumor T-lymphocyte compartment. As pembrolizumab promotes lymphocyte infiltration, it may contribute to antitumor effects in the neoadjuvant setting. Our previous randomized clinical trial (RCT) suggested that neoadjuvant pembrolizumab improved survival for recurrent GBM patients with 1-2 relapses. Here, we sought to extend our original findings and analyze the role of off-label neoadjuvant pembrolizumab in patients with multiple recurrences. We identified a retrospective 22-patient cohort at UCLA. Every patient had a GBM tissue diagnosis, received standard treatment, and had one to five recurrences. Each received off-label neoadjuvant pembrolizumab and surgical resection within 7-21 days. Progression-free (PFS) and overall survival (OS) for our cohort of neoadjuvant-treated patients were calculated as days from surgical resection and compared to historical control data from the original RCT (n = 15 neoadjuvant, 15 adjuvant). Results show that administration of neoadjuvant pembrolizumab in our cohort significantly increased median PFS compared to our historical adjuvant control (114 vs 75 days, p = 0.03). The OS of our neoadjuvant cohort was 294 days as compared to 192 days in the historical control. Both PFS and OS in our neoadjuvant cohort were not statistically different than the historical neoadjuvant cohort (PFSp = 0.08, OSp = 0.13). Since our cohort was not limited to initial recurrences, this data suggests that patients with more advanced recurrences could also benefit from neo-adjuvant therapy. Ongoing work will evaluate the microenvironmental genetic signature induced by pembrolizumab and assess pre-surgical tumor volume so that adequate comparisons can be made with other trials. We believe this promising finding offers novel therapeutic options for those patients with multiple recurrences.

Amine-weighted chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) is particularly valuable as an amine- and pH-sensitive imaging technique in brain tumors, targeting the intrinsically high concentration of amino acids with exchangeable amine protons and reduced extracellular pH in brain tumors. Amine-weighted CEST MRI contrast is dependent on the glioma genotype, likely related to differences in degree of malignancy and metabolic behavior. Amine-weighted CEST MRI may provide complementary value to anatomic imaging in conventional and exploratory therapies in brain tumors, including chemoradiation, antiangiogenic therapies, and immunotherapies. Continual improvement and clinical testing of amine-weighted CEST MRI has the potential to greatly impact patients with brain tumors by understanding vulnerabilities in the tumor microenvironment that may be therapeutically exploited.

Brain tumors reside in a modified microenvironment where inflammatory processes are heavily regulated. Nevertheless, our recent study showed a significant immune infiltration in recurrent glioblastoma (rGBM) treated with neoadjuvant PD-1 checkpoint blockade therapy. In comparison to GBM, the intracranial response of brain metastases (BrM) to immunotherapy has been less well studied. To test this question, we investigated the effect of pre-surgical immune checkpoint blockade (ICB) on the immune compartments of BrM, using multiplex immunofluorescence, single-cell RNA sequencing and spatial transcriptomics on a total of 17 patients. We found that ICB naïve BrM featured an immune exclusion phenotype with accumulation of immune cells in the fibrovascular stroma, necrotic and hemorrhagic peritumoral areas. Following ICB treatment, T cells and monocyte-derived macrophages were then observed within the tumor parenchyma. Computational receptor-ligand analysis suggested that the tumor-infiltrating T cells and macrophages were highly engaged by checkpoint receptor-ligand pairing, which may drive the T cells into an advanced exhausted state. To further explore the organization and interactions between the immune, stroma and tumor cells in BrM, we utilized the sequencing-based spatial transcriptomics technology. Our spatial transcriptomics data further highlighted the distinct spatial architectures between ICB naïve and –treated BrM tumors. It also pinpointed a unique macrophage subset that are preferentially co-localized with the brain vasculature cells and confined the immune infiltrates to the perivascular space. In summary, our study revealed ICB-induced marked changes in the immune composition and spatial organization in BrM and offers insights into new combination therapies that can help improve the clinical efficacy of immunotherapy for BrM patients.

BACKGROUND In a classic DSC perfusion sequence, T1 and T2* leakage effects compete in determining the post-bolus signal, and are influenced by tissue geometry (i.e. cell density, cell size). Different DSC sequences can be variously influenced by these effects, depending on the different degree of T1 weighting and the pre-bolus administration. Multi-echo spin-and-gradient echo (SAGE) perfusion MRI enables to disentangle T2* and T1 components that contribute to the classic DSC curve, and to simultaneously compute DSC and DCE perfusion metrics. METHODS We retrospectively selected patients with: diagnosis of primary brain tumor, availability of SAGE-based DSC perfusion and DWI datasets, availability of histopathological images from targeted biopsies located within contrast-enhancing tissue. Post-processing allowed to distinguish the pure T2* component from the pure T1 component, and to perform a DCE analysis on the latter. Quantitative perfusion MRI measurements were then evaluated with respect to underlying histopathology. RESULTS Histopathological images were available for 22 targeted biopsies (across 10 patients) meeting the inclusion criteria. The following novel MRI quantitative maps were successfully computed voxelwise: ΔR2* at steady state (reflecting T2* leakage effects), ΔR1 at steady state (reflecting T1 leakage effects), transverse relaxivity at tracer equilibrium (TRATE, reflecting the combination of T2* and T1 leakage effects). In addition, Ve and ktrans were computed from the DCE analysis, and the percentage of signal recovery (PSR) was computed from the second echo of the multi-echo DSC (comparable to a classic single-echo DSC sequence). CONCLUSIONS Histopathological validation will assess the usefulness of these novel multi-echo derived quantitative maps for the non-invasive prediction of tumor microstructure. This would be particularly relevant for: 1) differential diagnosis between brain tumors with different cell size and cell density (e.g. lymphoma vs glioblastoma); 2) treatment response assessment (as pre-existing studies proved that cell shrinkage is an early event in treatment response).

OBJECTIVE Many neurosurgeons resect nonenhancing low-grade gliomas (LGGs) by using an inside-out piecemeal resection (PMR) technique. At the authors’ institution they have increasingly used a circumferential, perilesional, sulcus-guided resection (SGR) technique. This technique has not been well described and there are limited data on its effectiveness. The authors describe the SGR technique and assess the extent to which SGR correlates with extent of resection and neurological outcome. METHODS The authors identified all patients with newly diagnosed LGGs who underwent resection at their institution over a 22-year period. Demographics, presenting symptoms, intraoperative data, method of resection (SGR or PMR), volumetric imaging data, and postoperative outcomes were obtained. Univariate analyses used ANOVA and Fisher’s exact test. Multivariate analyses were performed using multivariate logistic regression. RESULTS Newly diagnosed LGGs were resected in 519 patients, 208 (40%) using an SGR technique and 311 (60%) using a PMR technique. The median extent of resection in the SGR group was 84%, compared with 77% in the PMR group (p = 0.019). In multivariate analysis, SGR was independently associated with a higher rate of complete (100%) resection (27% vs 18%) (OR 1.7, 95% CI 1.1–2.6; p = 0.03). SGR was also associated with a statistical trend toward lower rates of postoperative neurological complications (11% vs 16%, p = 0.09). A subset analysis of tumors located specifically in eloquent brain demonstrated SGR to be as safe as PMR. CONCLUSIONS The authors describe the SGR technique used to resect LGGs and show that SGR is independently associated with statistically significantly higher rates of complete resection, without an increase in neurological complications, than with PMR. SGR technique should be considered when resecting LGGs.

Current cell-based immunotherapeutic strategies attempt to produce and maintain an immune response against glioma cells by artificially stimulating the immune system using passive and/or active approaches. Cellular immunotherapy is taken to mean the administration of live immune cells that either have immune effector capabilities themselves (passive immunotherapy) or engender a downstream antitumor response (active immunotherapy). Passive cellular immunotherapy most often takes the form of the adoptive transfer of a range of cell types, whereby antitumor immune cells from a patient (or allogeneic donor) are created, activated, and/or expanded ex vivo and subsequently administered back to the patient to directly attack the neoplasm. Active cellular immunotherapy approaches for the treatment of malignant gliomas have most often taken the form of dendritic cell (DC)-based vaccines.