bluuebunny/crossref_metadata_2025_split huggingface dataset:
IMMU-12. TUMOR EXPRESSION OF CD83 PROMOTES IMMUNE CLEARANCE OF GLIOMA
Authors: Curry Rachel , McDonald Malcolm , Lozzi Brittney , Cervantes Alexis , Lee Zhung-Fu , Harmanci Arif , Rosenbaum Anna , He Peihao , Mohila Carrie , Deneen Benjamin , Serin-Harmanci Akdes , Rao Ganesh 
Published: November 2023

Abstract
Glioblastoma (GBM) remains deadly with minimal therapeutic improvement over the past decades. A hallmark of GBM is an immunosuppressive microenvironment, which includes anergic and suppressive T-cells. Antigen presentation is a critical component to successful activation of anti-tumor T cell responses and are dysregulated in GBM. To better understand how GBM cells modulate antigen presenting processes, we examined expression of antigen presentation genes in our single cell RNA-sequencing (scRNA-seq) cohort consisting of 18 GBM samples from 12 different human patients. Unexpectedly, we found a rare population of tumor cells with high expression of CD83, a marker of activated antigen presenting cells (APCs) that stabilizes MHC-II and CD86 expression. In an immunocompetent GFP-labeled piggyBac in utero electroporation (pB-IUE) model of GBM, we validated the existence of dually labeled CD83+GFP+ tumor cells using FACS image streaming. In vivo overexpression of CD83 (CD83OE) in tumor cells prolonged survival compared to control and CD83 knockout (CD83KO) tumors. In vitro, tumor cell lines derived from CD83OE tumors increased expansion and activation of co-cultured CD8+ T-cells whereas CD83KO tumors had a large population of immunosuppressive CD8+ T-cells. ELISAs of media from tumor cell lines revealed that CD83OE tumor cells secrete higher levels of the T cell activating cytokine, IL-2 than controls and CD83KO. scRNA-seq of pB-IUE tumors confirmed that CD83OE have increased activating cytokines compared to CD83KO and control tumors, and that CD83KO tumors had greater expression of immunosuppressive T-regulatory profiles. Intriguingly, we found that despite equal proliferative capacity of tumor cells both in vitro and in vivo conditions, CD83OE tumors were smaller, suggesting that CD83 expression by tumor cells stabilizes CD8+ T-cells to promote immune clearance of tumors. Collectively, our data suggests that enhancing tumor cell expression of antigen presenting markers such as CD83 may encourage immune-mediated clearance of GBM.
IMMU-13. DEVELOPMENT OF ADAPTIVE IMMUNE RESISTANCE IN A MURINE GLIOMA MODEL TREATED WITH DENDRITIC CELL VACCINATION AND PD-1 CHECKPOINT BLOCKADE
Authors: Herrera Gilbert , Sun Lu , Sammarco Alessandro , Kennewick Kelly , Bensinger Steven , Prins Robert 
Published: November 2023

Abstract
Immunotherapies such as immune checkpoint inhibitors and active vaccination have shown great potential in unleashing antitumor immunity for cancer treatment. However, their effectiveness in treating glioblastoma (GBM) is limited. In a preclinical glioma model, administration of both autologous tumor lysate-pulsed dendritic cell vaccination (ATL-DC) and anti-PD-1 checkpoint blockade (aPD1) significantly increased survival and enhanced intratumoral T cell activation. We hypothesize that the combination of these two treatments will substantially increase the abundance and activity of tumor-reactive cytotoxic T cells. As such, we recently started a phase I trial administering ATL-DC and neoadjuvant aPD1 to recurrent GBM patients (NCT ID: NCT04201873). To understand the local antitumor immune response in greater depth, we performed single-cell RNA sequencing analysis of the CD45+ immune compartment of explanted gliomas from twelve mice, four of which were treated with ATL-DC and aPD1 while the other eight received no treatment. We found that the combination therapy increased tumor-infiltrating T cells, monocytes and DCs. We also observed the expansion and differentiation of CD8+ effector T cells under the effect of combination therapy. These T cells exhibited a differentiation trajectory from a Tcf7+Il2ra+ early activated phenotype to a terminally exhausted state marked by high expression of Pdcd1, Tox and Tigit. Interestingly, combination therapy specifically increased a macrophage subset that overexpressed Ch25h, an interferon-stimulated gene encoding for the oxysterol lipid 25-hydroxycholesterol (25-HC). Preliminary results from in vitro studies demonstrated that 25-HC restricted T cell proliferation and tumor cell cytolysis, suggesting its immunosuppressive function. In summary, our study reveals the impact of ATL-DC + aPD1 combination therapy on the immune microenvironment of GBM and a potential maladaptive mechanism mediated by 25-HC. Future studies will seek to exploit these targets therapeutically to develop more effective GBM treatment regimens.
IMMU-23. FRUCTOSE METABOLISM IN MICROGLIA PROMOTES GLIOBLASTOMA GROWTH
Authors: Billingham Leah , Wang Si , Zilinger Kaylee , Chia TzuYi , Katz Joshua , Cervantes Gustavo Ignacio Vazquez , Wan Hanxiou , Boland Lauren , Hou David , Lee-Chang Catalina , Miska Jason 
Published: November 2023

Abstract
Glioblastoma (GBM) is the most common brain malignancy in adults and has a dismal prognosis. Advances in standard-of-care treatments for GBM have not kept pace with those for other malignancies, in part due to the inefficacy of immunotherapies in treating GBM. The tumor microenvironment (TME) of GBM is heavily populated with pro-tumorigenic tumor-associated macrophages (TAMs) and lacks robust infiltration of T cells. Given that the number of TAMs in the TME correlates with poor prognosis, understanding the mechanisms by which they thrive is essential for discovering new therapies. Bulk RNASeq data from mouse tumors indicates that the fructose transporter, SLC2A5, is highly expressed on TAMs relative to peripheral myeloid cells. Furthermore, human glioblastoma single cell RNASeq (scRNASeq) data indicates that SLC2A5 is expressed specifically on microglia, the tissue resident macrophage of the brain. To assess the necessity of SLC2A5 in microglia, we orthotopically implanted CT2A or QPP4 glioblastoma cells into wild-type mice and mice lacking SLC2A5 (SLC2A5 KO mice). We observed a significant increase in median survival in SLC2A5 KO mice compared to wild-type mice. This indicates a necessity of fructose metabolism in microglia to promote tumorigenesis. Upon ex vivo analysis of the immune compartment of the TME, we observed that microglial cells from tumors in SLC2A5 KO mice have higher expression of MHC-II and PDL1 molecules on the cell surface compared to those from wild-type mice. Additionally, the CD4:CD8 T cell ratio in tumors from SLC2A5 KO mice was lower than that in tumors from wild-type mice. These data suggest that fructose metabolism in microglia facilitates an immunosuppressive phenotype that promotes GBM progression.
IMMU-24. SALVAGE IMMUNOTHERAPIES FOR REPLICATION REPAIR DEFICIENT (RRD) HIGH-GRADE GLIOMA FAILING ANTI-PD1 MONOTHERAPY: A REPORT FROM THE INTERNATIONAL RRD CONSORTIUM
Authors: Das Anirban , Fernandez Nicholas , Levine Adrian , Bianchi Vanessa , Stengs Lucie , Edwards Melissa , Nobre Liana , Tsang Derek , Ertl-Wagner Birgit , Morgenstern Daniel , Shlien Adam , Hawkins Cynthia , Bouffet Eric , Tabori Uri , Pugh Trevor 
Published: November 2023

Abstract

BACKGROUND
Initial response to immune checkpoint inhibition (ICI) for DNA replication-repair deficient high-grade glioma (RRD-HGG) is encouraging. However, clinical/biologic implications of immune-directed approaches after failing ICI-monotherapy remain unknown.

METHODS
We performed an international study of patients managed using central review/treatment recommendations (2015-2021). Salvage after anti-PD1 failure included re-irradiation where feasible, and addition of anti-CTLA4 (ipilimumab), or a MEK-inhibitor (MEKi). Outcomes included radiological response (iRANO), toxicity, second progression-free (PFS2) and overall survival (OS2). Companion biomarkers were performed centrally.

RESULTS
Twenty among 75 patients treated on anti-PD1 monotherapy are progression-free at a median follow-up of 44.6-months. For 55 patients with relapsed/progressive tumors, continuation of ICI (n=38) resulted in median OS2 of 11.6-months (51% alive) versus 1.2-months when ICI was discontinued (n=17; no survivors, p&lt; 0.001). Addition of ipilimumab (n=24) resulted in response/stable disease in 75% with median OS2 of 12.1-months. High autoimmune toxicities (54%) were observed, particularly in constitutional mismatch-repair deficiency patients. The addition of MEKi led to response in 3/5 patients with prolonged survival. The addition of re-irradiation improved median OS2, especially in tumors with lower mutation burden (p=0.002), and those who received ipilimumab (median OS2=33-months). Several biological insights were gained. Increased CTLA4 expression explained responses to ipilimumab. Re-irradiation responses were attributed to the absence of radio-resistant indel signature (ID8). Early radiological ‘flare’ was observed in 33% on combined immunotherapy and re-radiation. MEKi responses were associated with reinvigoration of peripheral immune response. Finally, delayed, sustained responses were observed in ultra-hypermutant RRD-HGG exhibiting changes in somatic mutational spectra.

CONCLUSION
These data suggest that the continuous mutagenesis renders hypermutant RRD-HGG susceptible to checkpoint inhibitors beyond initial progression. The combination with re-irradiation and additional immune/targeted agents can maximize survival in these children and young adults. Future research should focus on biology-driven rational immunotherapy combinations that also result in lower toxicity to maximize patient benefit.
IMMU-25. ANALYSIS OF IMMUNOSUPPRESSIVE MYELOID CELLS IN THE GLIOBLASTOMA TUMOR MICROENVIRONMENT REVEALS THERAPEUTICALLY TARGETABLE IMMUNOMODULATORY SIGNALS ACROSS POPULATIONS
Authors: Asad Mohammad , Inocencio Julio , Crisman Celina , Himes Benjamin 
Published: November 2023

Abstract
Immunosuppression in glioblastoma (GBM) remains a critical and poorly understood barrier to the development of effective novel therapies. Increasing evidence points to the critical role of immunosuppressive myeloid cells in the immunosuppressive tumor microenvironment and an intriguing target for ameliorating tumor-mediated immune suppression. Efforts to characterize the myeloid milieu in the tumor microenvironment have revealed a highly heterogenous population of cells with the capacity to exert immunosuppressive effects. In order to maximize the efficacy of potential therapeutic targets, we sought to identify immune checkpoint markers expressed across a range of immunomodulatory myeloid cell populations in the tumor microenvironment of patients undergoing resection for GBM. Freshly collected ultrasonic aspirate obtained during the primary surgery for GBM resection (based on preoperative imaging and intraoperative frozen section, later confirmed on final pathology) was prepared for high dimensional flow cytometry to quantify the immune checkpoint marker expression profile of a number of described immunosuppressive myeloid cell populations, including both monocytic and granulocytic myeloid-derived suppressor cells (mMDSC and gMDSC), and CD16+ non-classical monocytes (NCM). mMDSCs expressed particularly high levels of TIGIT (53.9±19.27%), which was also highly expressed in the NCM population (25.03±5.44%). NCMs also demonstrated high levels of B7H3 expression (39.85±18.05%), which has recently been implicated as an important immune checkpoint protein in GBM. gMDSCs demonstrated a rather different expression profile, with significantly higher levels of VISTA expression than other immunomodulatory markers (p&lt; 0.05). These findings underscore the diversity of immunomodulatory signaling in the tumor-associated myeloid cell compartment, emphasizing the challenges in developing single-target immune checkpoint inhibitor therapy in GBM. Nevertheless, this data points to some common patterns of expression across major immunomodulatory cell populations that remain understudied in GBM and could herald more promising avenues of immunotherapy development.
IMMU-28. TREM2 INHIBITION REPROGRAMS MYELOID CELLS TO STIMULATE ANTI-TUMOR IMMUNITY THROUGH BOTH DIRECT AND INDIRECT MECHANISMS
Authors: Sun Rui , Han Rowland , McCornack Colin , Tabor G Travis , Hou Jinchao , Cleary Ryan , Mao Diane , Liu Qin , Schoch Kathleen , Luo Jingqin , Petti Allegra , Miller Timothy , Ulrich Jason , Holtzman David , Kim Albert 
Published: November 2023

Abstract
The prevailing view is that myeloid cells—macrophages and microglia—in the tumor microenvironment (TME) are immunosuppressive and promote glioblastoma (GBM) progression. However, myeloid cells have the functional plasticity to restrict or support tumor cell growth. TREM2 plays important roles in brain microglial function in neurodegenerative diseases, but the functional role of TREM2 in the GBM TME and whether TREM2 represents a meaningful therapeutic target remain largely unknown. To address these questions, we investigated the immune and tumor cell consequences of TREM2 inhibition by multiple orthogonal approaches—transgenic mice, antisense oligonucleotides, and blocking antibodies—in immunocompetent preclinical models (SB28, NPA C54B) and human GBM samples through bulk and single cell RNA-sequencing, flow cytometry, biochemistry, and functional assays. We found TREM2 is highly expressed in myeloid subsets, including macrophages and microglia in human and mouse GBM tumors, and that high TREM2 expression correlates with poor prognosis in GBM patients. TREM2 loss of function in human macrophages and mouse myeloid cells increased IFNγ-induced immunoactivation and proinflammatory polarization. Conditioned media from TREM2 deficient human macrophages directly killed patient-derived GBM tumor cells, and biochemical analysis identified TNF and other putative tumoricidal proteins in this conditioned media. In mouse GBM models, mice with chronic and acute Trem2 loss of function demonstrated increased tumor cell death and increased animal survival. Trem2 inhibition reprogrammed myeloid cell phenotypes and increased PD-1+CD8+ T cells in the TME. Remarkably, Trem2 deficiency enhanced the effectiveness of anti-PD-1 treatment in vivo. Trem2 inhibition suppresses tumor cell growth through direct and indirect immune cell mechanisms--by reshaping myeloid subset and T cell functions. Thus, Trem2 inhibitory strategies, in combination with immune checkpoint blockade, may represent an attractive new approach for GBM therapy.
IMMU-34. SYSTEMIC IMMUNE SUPPRESSION IN GLIOBLASTOMA IS TARGETED BY CONCURRENT VEGF AND PD-1 INHIBITION IN A DOSE-DEPENDENT MANNER: TRANSCRIPTOMIC FINDINGS THROUGH CITE-SEQ FROM A RANDOMIZED CONTROLLED TRIAL
Authors: Ozair Ahmad , Alban Tyler , Grabowski Matthew , Otvos Balint , Bayik Defne , Bamashmos Anas , Rayman Pat , Diaz Marcella , Khosla Atulya , Bellur Shreyas , McDermott Michael , Reardon David , Wen Patrick , Mohammadi Alireza , Peereboom David , Lathia Justin , Ahluwalia Manmeet 
Published: November 2023

Abstract

INTRODUCTION
Anti-PD1 blockade has had poor efficacy in recurrent glioblastoma (rGBM) across three RCTs. VEGF, a proangiogenic factor that is upregulated in rGBM, contributes to tumor-associated immunosuppression and is widely targeted through bevacizumab. Preclinical data indicate a potential dose-dependent effect of anti-VEGF therapy on immunomodulation. Hence, a combination of anti-PD-1 and anti-VEGF agents is a promising approach for rGBM, for which an RCT was conducted. This work sought to utilize a multimodal approach capturing single-cell gene and protein expression by ‘cellular indexing of transcriptomes and epitopes by sequencing’ (CITE-Seq) to interrogate the systemic immunological changes in response to concurrent VEG and PD-1 inhibition.

METHODS
Patients with rGBM were administered nivolumab (240mg IV q2weeks) plus either standard-dose bevacizumab (10mg/kg) or low-dose bevacizumab (3mg/kg) IV q2weeks, with 1:1 randomization. Stratification factors were age, performance status, extent of resection, and MGMT methylation status. Primary endpoint was overall survival (OS) at 12 months. CITE-Seq was performed on 16 patients across trial arms, both pre- and on-therapy, yielding total 32 immunological profiles. For control, CITE-seq was done on three patients receiving anti-VEGF therapy alone.

RESULTS
90 patients were enrolled with median age of 60.6 years and 45 patients per arm. Both arms had similar OS at 12 months (P=0.14). Significantly higher OS was found in posthoc analysis for patients aged ≥60 years with standard dose. Distinct immune cell populations were identified, and differential changes in myeloid-derived suppressor cells (MDSCs) found across trial arms on-therapy. Network medicine approach identified VEGF as target to reduce MDSCs, with VEGF primarily expressed by responders’ MDSCs. Differential gene expression analysis identified increased pro-inflammatory signatures in standard-dose arm.

CONCLUSIONS
Standard dose bevacizumab was associated with increased inflammatory response and reduction of immunosuppressive MDSC. These mechanistic insights potentially explain survival benefit seen with concurrent VEGF and PD-1 inhibition in elderly rGBM patients.
IMMU-38. INTRATUMORAL CORRELATION OF MULTIPLEX IMMUNOFLUORESCENCE AND89ZR-CREFMIRLIMAB BERDOXAM IMMUNOPET IN RECURRENT GBM PATIENTS TREATED WITH NEOADJUVANT ANTI-PD-1 +/- ANTI-CTLA-4 THERAPY
Authors: Markus Lauren , Sun Lu , Hugo Willy , Van den Abbeele Annick D , Wen Patrick , Prins Robert 
Published: November 2023

Abstract
Glioblastoma (GBM) is a highly aggressive brain tumor that responds poorly to checkpoint blockade inhibitors (ICIs), such as anti-PD-1. We previously reported that neoadjuvant anti-PD-1 therapy activated and recruited T cells into recurrent GBM (rGBM) tumors, but also increased immune checkpoint interactions between T cells and myeloid cells. To overcome this resistance mechanism, we are currently conducting a phase 1B clinical trial of neoadjuvant anti-PD-1 (Nivolumab, BMS) +/- anti-CTLA-4 (Ipilimumab, BMS) combination therapy for rGBM patients (NCT04606316). To evaluate the systemic and local tumor microenvironment effects of these checkpoint inhibitors, we used immuno-positron emission tomography (CD8 immunoPET, 89Zr-crefmirlimab berdoxam, ImaginAb) to track CD8+ T cells in five rGBM patients before and after neoadjuvant anti-PD-1 or combination therapy with anti-CTLA-4, and used multiplex immunofluorescence (mIF) to analyze the intratumoral immune profile of patient-matched tumors. We found that CD8 ImmunoPET imaging could detect physiologic tracer uptake in the lymph node basins and tumor bed prior to and following checkpoint blockade, suggesting a systemic immunometabolic response within the tumor after therapy. Correlation with mIF found that combination therapy (n=1) increased the density of conventional type 1 and 2 dendritic cells (cDC1: CD3-CD141+XCR1+ and cDC2: CD3-CD1c+) in the tumors, especially cDC1, compared to anti-PD-1 monotherapy (n=4) or untreated patients (n=3) (the densities of cDC1 and cDC2 cells were 163 cells/mm2 and 13.3 cells/mm2 respectively). Moreover, combination ICI therapy was associated with enhanced infiltration of CD8+ and CD4+ T cells in the tumor (28.7 cells/mm2 and 73.8 cells/mm2, respectively) with a specific increase in CD4+ T cells compared to anti-PD-1 monotherapy. In summary, preliminary results of the correlation of the longitudinal brain immunoPET imaging with the intratumoral mIF analysis in these five rGBM patients suggests distinct effects of monotherapy vs. combination neoadjuvant anti-PD-1 and anti-CTLA-4 therapy on the intratumoral immunometabolic profile of rGBM patients.
IMMU-42. PP2A-INHIBITION INDUCES STING-TYPE I-MEDIATED IMMUNOLOGIC CELL DEATH IN GBM
Authors: Mondal Isha , Das Oishika , Lu Rongze Olivia , Ho Winson 
Published: November 2023

Abstract
Glioblastoma (GBM) is one of the most lethal forms of brain cancer, and is known to be an aggressive, immunologically cold tumor, resulting in a lack of T-cell infiltration and killing. Thus increasing immune-mediated killing of GBM is a promising therapeutic method. Our group has found that Protein Phosphatase 2A (PP2A), a ubiquitous serine/threonine phosphatase that has been shown to enhance tumor immunogenicity in glioblastoma, does so by inducing immunogenic cell death. We used LB-100, a small molecule inhibitor of the catalytic subunit of PP2A, as a promising drug-therapy. CRISPR-KO of PP2A was generated in murine glioma lines GL261 and SB28. Markers of immunologic cell death, such as calreticulin, gamma-H2AX, and HMGB1 were assessed. In vitro, western blotting of SB28 and GL261 showed significantly increased expression of gamma-H2AX in PP2A-KO compared to WT. Flow-cytometry staining of SB28 and GL261 revealed a dramatic increase in calreticulin expression in PP2A-KO compared to WT. An antibody-based fluorescence assay for HMGB1 also showed dramatic increase in PP2A-KO compared to WT. All experiments were repeated by treating LB-100 for 24 hour to SB28 and GL261 WT and PP2A-KO cells, and revealed a dose-dependent increase in expression of immunogenic cell death markers. In vivo, B6 mice were injected intracranially with SB28 WT or PP2A-deficient tumor and monitored till endpoint. At the endpoint, tumors were harvested, cryosectioned, and stained for calreticulin and gamma-H2AX. Mice injected with PP2A-KO tumor survived longer than WT, and had the highest expression of both calreticulin gamma-H2AX when compared to WT tissue. In conclusion, PP2A-deficiency and inhibition via LB-100 is demonstrated to induce immunogenic cell death in tumors, thus being a promising target for immunotherapy.
IMMU-44. CIRCULATING CELL-FREE DNA DIRECTLY INHIBITS T CELL FUNCTION AND CONTRIBUTES TO PERIPHERAL IMMUNOSUPPRESSION IN EXPERIMENTAL GBM
Authors: Ayasoufi Katayoun , Wolf Delaney , Reesman Rachael , Rangel Frances , Gulbicki Lauren , Tritz Zachariah , Jin Fang , Hansen Michael , Fain Cori , Pfaller Christian , Johnson Aaron 
Published: November 2023

Abstract
Glioblastoma (GBM) is aggressive form of brain cancer that is associated with severe peripheral immunosuppression. This immunosuppression is a critical barrier to patient survival and the success of immunotherapies. Immunocompetent mice harboring intracranial gliomas present with the hallmark features of peripheral immunosuppression observed in GBM patients, including T cell lymphopenia. Using parabiosis, we determined that T cell lymphopenia can be transferred from glioma-bearing to healthy mice via circulation This led to the identification of a high molecular weight immunosuppressive factor in sera of glioma-bearing mice that inhibits T cell proliferation ex vivo. Proteomics analysis identified 119 proteins uniquely upregulated in the sera of glioma-bearing mice compared to controls. These proteins are associated with pathways involved in DNA response elements, cell death, and DNA-histone complexes which imply DNA release. Additional analysis revealed serum isolated from glioma-bearing mice harbor significantly higher concentrations of double stranded cell free DNA (cfDNA) compared to controls. Reducing DNA content using DNase partially reverses the proliferation defects observed in T cells when exposed to serum of glioma-bearing mice. This is while, addition of cfDNA purified from serum of glioma-bearing mice, but not genomic DNA, potently inhibited T cell function. These results were AIM2 independent implicating a novel pathway of cfDNA sensing in T cells. We contend that cfDNA induces immunosuppressive effects in experimental GBM. Devising strategies to reduce circulating cfDNA is therefore a therapeutic approach that could improve outcomes in GBM patients.