Enolase represents a metabolic checkpoint controlling the differential exhaustion programmes of hepatitis virus-specific CD8+ T cells

OBJECTIVE

Exhausted T cells with limited effector function are enriched in chronic hepatitis B and C virus (HBV and HCV) infection. Metabolic regulation contributes to exhaustion, but it remains unclear how metabolism relates to different exhaustion states, is impacted by antiviral therapy, and if metabolic checkpoints regulate dysfunction.

DESIGN

Metabolic state, exhaustion and transcriptome of virus-specific CD8+ T cells from chronic HBV-infected (n=31) and HCV-infected patients (n=52) were determined ex vivo and during direct-acting antiviral (DAA) therapy. Metabolic flux and metabolic checkpoints were tested in vitro. Intrahepatic virus-specific CD8+ T cells were analysed by scRNA-Seq in a HBV-replicating murine in vivo model of acute and chronic infection.

RESULTS

HBV-specific (core18-27, polymerase455-463) and HCV-specific (NS31073-1081, NS31406-1415, NS5B2594-2602) CD8+ T cell responses exhibit heterogeneous metabolic profiles connected to their exhaustion states. The metabolic state was connected to the exhaustion profile rather than the aetiology of infection. Mitochondrial impairment despite intact glucose uptake was prominent in severely exhausted T cells linked to elevated liver inflammation in chronic HCV infection and in HBV polymerase455-463 -specific CD8+ T cell responses. In contrast, relative metabolic fitness was observed in HBeAg-negative HBV infection in HBV core18-27-specific responses. DAA therapy partially improved mitochondrial programmes in severely exhausted HCV-specific T cells and enriched metabolically fit precursors. We identified enolase as a metabolic checkpoint in exhausted T cells. Metabolic bypassing improved glycolysis and T cell effector function. Similarly, enolase deficiency was observed in intrahepatic HBV-specific CD8+ T cells in a murine model of chronic infection.

CONCLUSION

Metabolism of HBV-specific and HCV-specific T cells is strongly connected to their exhaustion severity. Our results highlight enolase as metabolic regulator of severely exhausted T cells. They connect differential bioenergetic fitness with distinct exhaustion subtypes and varying liver disease, with implications for therapeutic strategies.

Phosphoinositide acyl chain saturation drives CD8+ effector T cell signaling and function

How lipidome changes support CD8+ effector T (Teff) cell differentiation is not well understood. Here we show that, although naive T cells are rich in polyunsaturated phosphoinositides (PIPn with 3-4 double bonds), Teff cells have unique PIPn marked by saturated fatty acyl chains (0-2 double bonds). PIPn are precursors for second messengers. Polyunsaturated phosphatidylinositol bisphosphate (PIP2) exclusively supported signaling immediately upon T cell antigen receptor activation. In late Teff cells, activity of phospholipase C-γ1, the enzyme that cleaves PIP2 into downstream mediators, waned, and saturated PIPn became essential for sustained signaling. Saturated PIP was more rapidly converted to PIP2 with subsequent recruitment of phospholipase C-γ1, and loss of saturated PIPn impaired Teff cell fitness and function, even in cells with abundant polyunsaturated PIPn. Glucose was the substrate for de novo PIPn synthesis, and was rapidly utilized for saturated PIP2 generation. Thus, separate PIPn pools with distinct acyl chain compositions and metabolic dependencies drive important signaling events to initiate and then sustain effector function during CD8+ T cell differentiation.

OS08.2.A Three layers of neuronal-like mechanisms driving brain tumor invasion

Background

Glioblastoma are characterized by their infiltration into the whole brain. Membrane protrusions of glioma cells called tumor microtubes are subcellular structures contributing to glioma cell invasion. They are the anatomical building block to build a functional and therapy-resistant tumor cell network interconnected by tumor microtubes (TMs) that characterizes a glioblastoma cell subpopulation, while other subpopulations appear unconnected to other glioma cells. The biological role of glioblastoma cells lacking connections with each other remains unclear. Furthermore, how neurogliomal synapses influence this subpopulation is unclear.

Material and Methods

Time-lapse in vivo two-photon microscopy and single-cell RNA-sequencing are combined to characterize functional different subpopulations of glioblastoma cells. Intravital, augmented microscopy, three-dimensional calcium imaging, electrophysiology and volume electron microscopy are used to investigate the role of neuronal invasion mechanisms and the role of neurogliomal synapses for tumor microtube generation and dynamics.

Results

In-vivo imaging revealed that glioblastoma cells lacking connections to other tumor cells and astrocytes were the main subpopulation driving glioblastoma invasion invasion. These glioblastoma cells were characterised with single-cell RNA-sequencing. This revealed that this subpopulation is enriched for neuronal, neural progenitor-like, and non-mesenchymal-like cell states as previously described. Sparse regions enriched with such tumor-cell and astrocyte-unconnected, invasive glioblastoma cells evolve over time into regions with tumor-cell and astrocyte-connected, glioblastoma cell networks reflected by molecular cell state changes that are reflected in cell state changes in different regions of human glioblastoma. In addition, mechanisms of glioblastoma cell invasion resembled neuronal and neural progenitor patterns during brain development. Lastly, neuronal activity stimulated neurogliomal synapses and subsequently increased glioblastoma cell invasivieness by stimulating generation of new tumor microtubes and enhanced tumor microtube dynamics.

Conclusion

This study uncovers three novel layers of neuronal features driving glioblastoma cell invasion. We are able to connect molecular, cellular heterogeneity and functional glioblastoma cell states interlinking heterogeneity and dissemination of glioblastoma, two important hallmarks of this disease. Lastly, this study delineates a potential roadmap to clinical translation with the multidimensional characterisation of human glioblastoma.

JS08.6.A A connectivity signature for glioblastoma

Background

Tumor cell extensions called tumor microtubes (TMs) in glioma resemble neurites during neurodevelopment and connect glioma cells to a network that has considerable relevance for tumor progression and therapy resistance. The determination of interconnectivity in individual tumors has been challenging and the impact of tumor cell connectivity on patient survival remained unresolved so far.

Material and Methods

A connectivity signature was derived by single-cell RNA-sequencing (scRNA-Seq) of highly and lowly connected cells obtained from an SR101 dye transfer xenograft model of primary glioblastoma (GB). The signature was validated in different in vitro models of cell-to-cell connectivity and could be translated to GB clinical specimens.

Results

34 of 40 connectivity genes were related to neurogenesis, neural tube development or glioma progression, including the TM-network-relevant GAP43 gene. Astrocytic-like and mesenchymal-like GB cells had the highest connectivity signature scores in scRNA-Seq data of patient-derived xenografts and patient samples. In 230 human GBs, high connectivity correlated with the mesenchymal expression subtype, TP53 wildtype, and with dismal patient survival. CHI3L1 was identified and validated as a robust molecular marker of connectivity with a functional relevance.

Conclusion

The connectivity signature gives novel insights into brain tumor biology, provides a proof-of-principle that tumor cell connectivity is relevant for patients’ prognosis, and serves as a robust biomarker that can be used for future clinical trials

T-cell exhaustion and residency dynamics inform clinical outcomes in hepatocellular carcinoma

BACKGROUND & AIMS

Despite recent translation of immunotherapies into clinical practice, the immunobiology of hepatocellular carcinoma (HCC), in particular the role and clinical relevance of exhausted and liver-resident T cells remain unclear. We therefore dissected the landscape of exhausted and resident T cell responses in the peripheral blood and tumor microenvironment of patients with HCC.

METHODS

Lymphocytes were isolated from the blood, tumor and tumor-surrounding liver tissue of patients with HCC (n = 40, n = 10 treated with anti-PD-1 therapy). Phenotype, function and response to anti-PD-1 were analyzed by mass and flow cytometry ex vivo and in vitro, tissue residence was further assessed by immunohistochemistry and imaging mass cytometry. Gene signatures were analyzed in silico.

RESULTS

We identified significant enrichment of heterogeneous populations of exhausted CD8+ T cells (TEX) in the tumor microenvironment. Strong enrichment of severely exhausted CD8 T cells expressing multiple immune checkpoints in addition to PD-1 was linked to poor progression-free and overall survival. In contrast, PD-1 was also expressed on a subset of more functional and metabolically active CD103+ tissue-resident memory T cells (TRM) that expressed few additional immune checkpoints and were associated with better survival. TEX enrichment was independent of BCLC stage, alpha-fetoprotein levels or age as a variable for progression-free survival in our cohort. These findings were in line with in silico gene signature analysis of HCC tumor transcriptomes from The Cancer Genome Atlas. A higher baseline TRM/TEX ratio was associated with disease control in anti-PD-1-treated patients.

CONCLUSION

Our data provide information on the role of peripheral and intratumoral TEX-TRM dynamics in determining outcomes in patients with HCC. The dynamics between exhausted and liver-resident T cells have implications for immune-based diagnostics, rational patient selection and monitoring during HCC immunotherapies.

LAY SUMMARY

The role of the immune response in hepatocellular carcinoma (HCC) remains unclear. T cells can mediate protection against tumor cells but are frequently dysfunctional and exhausted in cancer. We found that patients with a predominance of exhausted CD8+ T cells (TEX) had poor survival compared to patients with a predominance of tissue-resident memory T cells (TRM). This correlated with the molecular profile, metabolic and functional status of these cell populations. The enrichment of TEX was independently associated with prognosis in addition to disease stage, age and tumor markers. A high TRM proportion was also associated with better outcomes following checkpoint therapy. Thus, these T-cell populations are novel biomarkers with relevance in HCC.

Improvement of functional outcome for patients with newly diagnosed grade 2 or 3 gliomas with co-deletion of 1p/19q - IMPROVE CODEL: the NOA-18 trial

Background

Given the young age of patients with CNS WHO grade 2 and 3 oligodendrogliomas and the relevant risk of neurocognitive, functional, and quality-of-life impairment with the current aggressive standard of care treatment, chemoradiation with PCV, of the tumour located in the brain optimizing care is the major challenge.

Methods

NOA-18 aims at improving qualified overall survival (qOS) for adult patients with CNS WHO grade 2 and 3 oligodendrogliomas by randomizing between standard chemoradiation with up to six six-weekly cycles with PCV and six six-weekly cycles with lomustine and temozolomide (CETEG) (n = 182 patients per group accrued over 4 years) thereby delaying radiotherapy and adding the chemoradiotherapy concept at progression after initial radiation-free chemotherapy, allowing for effective salvage treatment and delaying potentially deleterious side effects. QOS represents a new concept and is defined as OS without functional and/or cognitive and/or quality of life deterioration regardless of whether tumour progression or toxicity is the main cause. The primary objective is to show superiority of an initial CETEG treatment followed by partial brain radiotherapy (RT) plus PCV (RT-PCV) at progression over partial brain radiotherapy (RT) followed by procarbazine, lomustine, and vincristine (PCV) chemotherapy (RT-PCV) and best investigators choice (BIC) at progression for sustained qOS. An event concerning a sustained qOS is then defined as a functional and/or cognitive and/or quality of life deterioration after completion of primary therapy on two consecutive study visits with an interval of 3 months, tolerating a deviation of at most 1 month. Assessments are done with a 3-monthly MRI, assessment of the NANO scale, HRQoL, and KPS, and annual cognitive testing. Secondary objectives are evaluation and comparison of the two groups regarding secondary endpoints (short-term qOS, PFS, OS, complete and partial response rate). The trial is planned to be conducted at a minimum of 18 NOA study sites in Germany.

Discussion

qOS represents a new concept. The present NOA trial aims at showing the superiority of CETEG plus RT-PCV over RT-PCV plus BIC as determined at the level of OS without sustained functional deterioration for all patients with oligodendroglioma diagnosed according to the most recent WHO classification.

Trial registration

Clinicaltrials.govNCT05331521. EudraCT 2018–005027-16.

AB1135 RESPONSE TO SARS-COV-2 VACCINATION IN SYSTEMIC AUTOIMMUNE RHEUMATIC DISEASE DEPENDS ON IMMUNOSUPPRESSIVE REGIMEN: A MATCHED, PROSPECTIVE COHORT STUDY

Background

Vaccination efficiency has been demonstrated to be reduced in patients with systemic autoimmune rheumatic disease (SARD) compared with the general population.

Objectives

To assess the humoral response to mRNA vaccine in patients with (SARD) and the effect of immunosuppressive medication in a matched cohort study.

Methods

Patients with SARD were enrolled and matched 1:1 for gender and age with healthy control subjects (HC). Differences in the humoral response to two doses of mRNA vaccine BNT162b2 in terms of seroconversion rate and SARS-COV-2 antibody titer between the two groups and impact of treatment within SARD patients was assessed using Fisher’s exact test, Student’s t-test, Mann-Whitney test and Kruskal-Wallis test, adjusting for multiple testing.

Results

We enrolled 82 patients with SARD and 82 matched HC (Table 1). Among patients the seroconversion rate was significantly lower after the 1st dose (65% compared to 100% in HC, p<0.0001) but levelled up after the 2nd dose (94% vs. 100%). While the difference in seroconversion rate was independent of treatment regime (no disease modifying anti-rheumatic drug (DMARD), DMARD monotherapy, DMARD combination therapy), the seroconversion rate of SARD patients on mono- or combination DMARD therapy was also significantly lower as compared to those receiving no DMARD therapy (56% for monotherapy and 57% for combination therapy compared to 77% for no DMARD therapy, p=0.002 and p=0.004 respectively; Figure 1A). Seroconversion rate after the 2nd dose was significantly lower for patients on combination DMARD therapy compared to all other groups (81% compared to 95% for monotherapy, and 100% for both no DMARD therapy and HC respectively, all p<0.0001); also antibody titers after the 2nd dose were lower when comparing patients on combination DMARD therapy to all other groups (49 binding antibody units (BAU)/ml versus 1673 BAU/ml in HC, p<0.0001; 2500 BAU/ml in those on no DMARD therapy, p<0.0001; and 687 BAU/ml in those on DMARD monotherapy, p=0.0072; Figure 1B). Considering effects of individual compounds, mycophenolate mofetil in mono- or combination therapy led to lower antibody titers after the 2nd dose as compared to HC or patients receiving no DMARDs (2 BAU/ml versus 1673 BAU/ml and 2500 BAU/ml respectively, both p<0.0001).

Figure 1.

Seroconversion rate (A) and anti-SARS-Cov 2 S antibody levels (B) after the 1stand 2ndvaccination between the healthy control (HC) group and patients according to therapy

Table 1.

Study subject characteristics

SARD (n=82)HC (n=82)Age, mean (±SD)52.05 (±14.06)52.15 (±13.42)Female, n (%)65 (79%)65 (79%)Different disease entity, n (%):33 (40%) Systemic lupus erythematosus Systemic sclerosis13 (16%) Other connective tissue diseases*15 (18%) Vasculitides#17 (21%) Miscellaneous$4 (5%)Treatment groups, n (%):43 (52%) csDMARD or b/tsDMARD monotherapy csDMARD and/or b/tsDMARD combination therapy16 (20%) No therapy23 (28%)Treatment agents, n (%):13 (16%) Methotrexate Mycophenolate14 (17%) Hydroxychloroquine28 (34%) Azathioprine13 (10%) Belimumab3 (4%) Tocilizumab3 (4%) Tacrolimus2 (2%) Olumiant1 (1%)

*dermato-/polymyositis (n=4), mixed connective tissue disease (n=2), primary Sjögren’s syndrome (n=6), undifferentiated connective tissue disease (n=3)

#antineutrophil cytoplasmic antibody (ANCA) associated vasculitis (n=3), Behcet’s disease (n=1), large-vessel vasculitis (n=3), polymyalgia rheumatica (n=10)

$ adult-onset Still’s disease (n=1), immune deficiency (n=2), sarcoidosis (n=1)

b/tsDMARD: biological/targeted synthetic disease modifying antirheumatic drug; csDMARD: conventional synthetic disease modifying antirheumatic drug; HC: healthy control; n: number; SARD: systemic autoimmune rheumatic disease; SD: standard deviation;

Conclusion

Patients with SARD showed a good response after the 2nd vaccination with the mRNA vaccine. However, the choice of immunosuppressive regimen has a marked effect on both seroconversion rate and overall antibody titer.

Acknowledgements

We thank Sylvia Taxer and Zoltan Vass for their support.

Disclosure of Interests

Peter Mandl Speakers bureau: AbbVie, Janssen, Novartis, Consultant of: AbbVie, Janssen, Novartis, Grant/research support from: AbbVie, BMS, Lilly, Novartis, MSD, UCB, Selma Tobudic: None declared, Helmut Haslacher: None declared, Daniel Mrak: None declared, Thomas Nothnagl: None declared, Thomas Perkmann: None declared, Helga Radner Speakers bureau: Gilead, Merck Sharp, Pfizer, Abbvie, Consultant of: Gilead, Merck Sharp, Pfizer, Abbvie, Judith Sautner Speakers bureau: Otsuka, Novartis, Consultant of: Lilly, Astro Pharma, UCB, Abbvie, Elisabeth Simader Grant/research support from: Pfizer, Bristol-Myers Squibb, Florian Winkler: None declared, Heinz Burgmann: None declared, Daniel Aletaha Speakers bureau: Abbvie, Amgen, Lilly, Janssen, Merck, Novartis, Pfizer, Roche, Sandoz, Consultant of: Abbvie, Amgen, Lilly, Janssen, Merck, Novartis, Pfizer, Roche, Sandoz

, Grant/research support from: Abbvie, Amgen, Lilly, Novartis, Roche, SoBi, Sanofi, Stefan Winkler: None declared, Stephan Blüml Speakers bureau: Novartis, Abbvie, Consultant of: Gilead, Merck, Novartis, Abbvie

POS1243 ACCELERATED WANING OF PROTECTIVE IMMUNITY AFTER SARS-CoV-2 mRNA VACCINATION IN PATIENTS TREATED WITH BIOLOGICAL AND TARGETED SYNTHETIC DISEASE MODIFYING ANTIRHEUMATIC DRUGS

Background

Little is known about the duration of humoral antibody levels after two SARS-CoV-2 mRNA vaccinations in patients with immunosuppression. During this ongoing global epidemic, it is of essential interest to gather information about the time of protection after initial immunization in the vulnerable patients receiving either conventional synthetic disease modifying antirheumatic drugs (csDMARD) or biological/ targeted drugs (b/tsDMARDs).

Objectives

In this study we compared the antibody level development after vaccination and after six months in patients with inflammatory arthritis, inflammatory bowel disease (IBD) and healthy controls. Furthermore, we assessed factors affecting the quality and quantity of the humoral response.

Methods

We enrolled 85 healthy controls (HC), 75 patients with rheumatoid arthritis and spondyloarthritis and 41 patients suffering from IBD. Patients treated with B-cell depleting therapies were excluded from this study. Binding antibody units were measured after vaccination and 6 or more months. Neutralizing antibodies were measured after 6 months. Multivariate regression analyses analyzing factors associated with low titers after 6 months was performed.

Results

We found that patients with inflammatory arthritis or IBD showed reduced anti-SARS-CoV-2 S titers compared to HC. When we stratified for therapies, we found that patients receiving conventional synthetic disease modifying antirheumatic dugs (csDMARDs) had comparable anti-SARS-CoV-2 S titers to HC. In contrast, patients receiving biological or targeted synthetic (b/tsDMARDs) showed reduced anti-SARS-CoV-2 Igs as well as neutralizing antibody titers compared with healthy controls (HC) or patients receiving conventional synthetic (cs)DMARDs. We further show that anti-SARS-CoV-2 titers declined more rapidly in patients receiving b/tsDMARDs compared to HC, leading to a 50 percent reduction in vaccination-associated protection time in patients receiving b/tsDMARDs when compared to those receiving csDMARDs or even HC. In multivariate regression analyses, we found that in addition to the type of treatment, also age as well as corticosteroid use were associated with reduced anti-SARS-CoV-2 S titers.

Conclusion

Patients under ongoing b/tsDMARDs therapy exposed an accelerated waning of anti-SARS-CoV-2 S titers and therefore decreased immunity and protection against severe Covid-19 infections over time. These results may lead to more personalized approaches for further vaccination strategies in this group of immunosuppressed patients.

Figure 1.

A, Analysis of anti-SARS-CoV-2 S titers 6 months after the second vaccination in patients with inflammatory arthritis, inflammatory bowel disease and HC (** p ≤ 0.01; *** p ≤ 0.005, **** p ≤ 0.001). B, Determination of neutralizing antibody activity in sera of HC and patients with inflammatory arthritis receiving the indicated therapies.

Disclosure of Interests

Selma Tobudic: None declared, Elisabeth Simader Grant/research support from: Pfizer, Bristol-Myers Squibb, Thomas Deimel: None declared, Peter Mandl Speakers bureau: AbbVie, Janssen, Bristol-Myers Squibb, Merck Sharp & Dohme, Celgene, Novartis, Pfizer, Roche, Sanofi, UCB, Consultant of: Novartis, Celgene, Grant/research support from: Novartis, Celgene, Abbvie, Roche, Bristol-Myers Squibb

, Helmuth Haslacher Grant/research support from: Glock Health, BlueSky Immunotherapies and Neutrolis;, Thomas Perkmann: None declared, Lisa Schneider: None declared, Thomas Nothnagl: None declared, Helga Lechner-Radner: None declared, Florian Winkler: None declared, Heinz Burgmann Speakers bureau: Shionogi, Pfizer, MSD, Paid instructor for: Valneva, MSD, Gilead, Consultant of: from MSD, Pfizer, Takeda, Gilead, Karin Stiasny Grant/research support from: Pfizer, Gottfried Novacek: None declared, Walter Reinisch: None declared, Daniel Aletaha Speakers bureau: Abbvie, Amgen, Lilly, Novartis, Roche, SoBi, Sanofi

Merck, Pfizer, Roche, Sandoz, Stefan Winkler: None declared, Stephan Blüml Speakers bureau: Abbvie, personal fees from Novartis

P13.12 Effect of tumor treating fields on tumor microtubes in glioma

BACKGROUND

Tumor microtubes (TMs) are ultralong membrane protrusions of tumor cells in astrocytic gliomas, including glioblastomas. TMs are used as routes for brain invasion and for cells to interconnect over long distances resulting in a functional network that allows multicellular communication. This network mediates resistance against the cytotoxicity of radiation and chemotherapy. One explanation for TM network protection is a better homeostasis of calcium ions that would otherwise increase to toxic intracellular levels in response to these therapies.

Our working hypothesis is that interfering with the integrity of the glioblastoma cell network is key to a potential breakthrough in glioma therapy. Many cellular structures are polarized and composed of charged elements and are thus potential subjects to electrical forces; this might also influence the complex intercellular calcium waves (ICWs) that are characteristic for glioma networks. We were therefore interested in the effect of TTF on glioma network maintenance.

MATERIAL AND METHODS

To examine the effect of TTF on glioma TMs we have established a 2D in vitro glioma model using glioblastoma stem cells (GBSCs) grown in high-glucose medium and a 3D model using glioma tumor organoids. Both models reliably reproduce functionality and complexity of morphological features we observe in our mouse model. We analyzed the disruption of tumor network complexity and disruption of functionality by measuring intercellular calcium waves. Tumor cell death and proliferation was investigated in the 2D in vitro glioma model using the inovitroTM-System.

RESULTS

A peculiar “cricked-TM” phenotype that rarely (0.2% ±0.14) occurred under standard or control conditions was observed in TTF-treated cells (16.22% ±5.12). Cell number was reduced by 75% in two lines of GBSCs after 5 days of TTF exposure; predominantly TM-rich GBSCs (&gt; 4 TMs) were affected. This reduction in tumor cell number corresponded with an increase in cell death (0.3% ±0.09 in untreated cells; 1.4% ±0.45 at day 5 of TTF exposure). The frequency of intercellular calcium transients, a measurement for calcium wave frequency in the glioma networks, was instantly reduced after TTF exposure to 58% ±20.42 of control levels in the primary GBSC 2D culture, and to 57.78% ±12.34 in tumor organoids derived from 3 glioblastoma patients.

CONCLUSION

This data suggests a potential effect of TTF application on tumor cell networks, at least in vitro. Interestingly, particularly those glioblastoma cells that have so far been proven to be resistant to radio- and chemotherapy appeared to be affected. We will confirm the observed effects of TTFs on tumor cell calcium signaling in our in vivo chronic cranial window mouse model. We anticipate that the results of our project will provide important insights into the underlying mechanism of TTF therapy.

P10.02 Combined methods of a micropump system and a chronic cranial window allows tumor observation with multi photon laser scanning microscopy under continuous treatment

BACKGROUND

Glioblastomas are notoriously therapy resistant tumors. As opposed to other tumor entities, no major advances in therapeutic success have been made in the past decades. This has been calling for a deeper biological understanding of the tumor, its growth and resistance patterns. We have been using a xenograft glioma model, where human glioblastoma cells are implanted under chronic cranial windows and studied longitudinally over many weeks and months using multi photon laser scanning microscopy (MPLSM). To test the effect of (new) drugs, a stable and direct delivery system avoiding the blood-brain-barrier has come into our interest.

MATERIAL AND METHODS

We implanted cranial windows and fluorescently labeled human glioblastoma stem-like cells into NMRI nude mice to follow up on the tumor development in our MPLSM model. After tumor establishment, an Alzet® micropump was implanted to directly deliver agents via a catheter system continuously over 28 days directly under the cranial window onto the brain surface. Using the MPLSM technique, the continuous delivery and infusion of drugs onto the brain and into the tumor was measured over many weeks in detail using MPLSM.

RESULTS

The establishment of the combined methods allowed reliable concurrent drug delivery over 28 days bypassing the blood-brain-barrier. Individual regions and tumor cells could be measured and followed up before, and after the beginning of the treatment, as well as after the end of the pump activity. Fluorescently labelled drugs were detectable in the MPLSM and its distribution into the brain parenchyma could be quantified. After the end of the micropump activity, further MPLSM measurements offer the possibility to observe long term effects of the applied drug on the tumor.

CONCLUSION

The combination of tumor observation in the MPSLM and concurrent continuous drug delivery is a feasible and reliable method for the investigation of (novel) anti-tumor agents, especially drugs that are not blood-brain-barrier penetrant. Morphological or even functional changes of individual tumor cells can be measured under and after treatment. These techniques can be used to test new drugs targeting the tumor, its tumor microtubes and tumor cells networks, and measure the effects longitudinally.

P13.01 Neuronal activity drives distinct invasion modes of glioma cells

BACKGROUND

Gliomas are incurable brain tumors characterized by their infiltrative growth which makes them a whole-brain disease. Previously we described membrane protrusions called tumor microtubes (TMs), and glutamatergic synapses between neurons and glioma cells, as mechanisms contributing to glioma cell invasion and tumor progression. However, the interrelation of the two, and the exact mechanisms of glioma cell dynamics over time was unknown. Therefore, we investigate neuronal synaptic input on TM-associated glioma cell motility.

MATERIAL AND METHODS

Here we established a novel workflow for analyzing single glioma cell dynamics over several hours with in-vivo two-photon microscopy. First, a membranous fluorescent marking of patient-derived glioma cells was established to reliably track membrane changes. Secondly, augmented microscopy based on deep- and machine-learning algorithms was used to track glioma cells. Neuronal activity was manipulated with different doses of isoflurane anesthesia, and used to study its effects on glioma cell dynamics.

RESULTS

This novel method revealed that motility of glioma cells can be described by the displacement of whole glioma cell somata (somatokinesis) and TM dynamics. TM motility in turn could be sub-categorized into protrusion, retraction and branching. Next, we describe three different invasion modes, all with similarities to different cell types involved in CNS development. Lastly, the effects of neuronal activity on glioma cell invasion were investigated. With the application of high anesthesia and subsequently reduced neuronal activity, TM turnover, branching events and as a result glioma cell invasion were inhibited, but in a heterogeneous manner.

CONCLUSION

The novel workflow allowed to comprehensively characterize glioma cell invasion over several hours. Its application demonstrates novel, hitherto unknown cellular mechanisms of glioma cell invasion, and provides a link between TM biology and neuron-glioma communication. Finally, neuronal input drives distinct subtypes of glioma cell motility patterns.All in all, this work presents an important first step in understanding mechanisms that lead to the whole- brain colonization of glioma cells making these brain tumors incurable. A further characterization of the exact molecular mechanisms that drive neuronal activity-dependent glioma cell motility is warranted.

Acetate Promotes T Cell Effector Function during Glucose Restriction

Competition for nutrients like glucose can metabolically restrict T cells and contribute to their hyporesponsiveness during cancer. Metabolic adaptation to the surrounding microenvironment is therefore key for maintaining appropriate cell function. For instance, cancer cells use acetate as a substrate alternative to glucose to fuel metabolism and growth. Here, we show that acetate rescues effector function in glucose-restricted CD8⁺ T cells. Mechanistically, acetate promotes histone acetylation and chromatin accessibility and enhances IFN-γ gene transcription and cytokine production in an acetyl-CoA synthetase (ACSS)-dependent manner. Ex vivo acetate treatment increases IFN-γ production by exhausted T cells, whereas reducing ACSS expression in T cells impairs IFN-γ production by tumor-infiltrating lymphocytes and tumor clearance. Thus, hyporesponsive T cells can be epigenetically remodeled and reactivated by acetate, suggesting that pathways regulating the use of substrates alternative to glucose could be therapeutically targeted to promote T cell function during cancer.

Use of Mass Cytometry to Profile Human T Cell Exhaustion

Mass cytometry has become an important technique for the deep analysis of single cell protein expression required for precision systems immunology. The ability to profile more than 40 markers per cell is particularly relevant for the differentiation of cell types for which low parametric characterization has proven difficult, such as exhausted CD8⁺ T cells (T_EX). T_EX with limited effector function accumulate in many chronic infections and cancers and are subject to inhibitory signaling mediated by several immune checkpoints (e.g., PD-1). Of note, T_EX represent considerable targets for immune-stimulatory therapies and are beginning to be recognized as a major correlate of successful checkpoint blockade approaches targeting the PD-1 pathway. T_EX exhibit substantial functional, transcriptomic and epigenomic differences compared to canonical functional T cell subsets [such as naïve (T_N), effector (T_EFF) and memory T cells (T_MEM)]. However, phenotypic distinction of T_EX from T_EFF and T_MEM can often be challenging since many molecules expressed by T_EX can also be expressed by effector and memory T cell populations. Moreover, significant heterogeneity of T_EX has been described, such as subpopulations of exhausted T cells with progenitor-progeny relationships or populations with different degrees of exhaustion or homeostatic potential that may directly inform about disease progression. In addition, T_EX subsets have essential clinical implications as they differentially respond to antiviral and checkpoint therapies. The precise assessment of T_EX thus requires a high-parametric analysis that accounts for differences to canonical T cell populations as well as for T_EX subset heterogeneity. In this review, we discuss how mass cytometry can be used to reveal the role of T_EX subsets in humans by combining exhaustion-directed phenotyping with functional profiling. Mass cytometry analysis of human T_EX populations is instrumental to gain a better understanding of T_EX in chronic infections and cancer. It has important implications for immune monitoring in therapeutic settings aiming to boost T cell immunity, such as during cancer immunotherapy.

Development of Reference Materials for Paralytic Shellfish Poisoning Toxins

A project was undertaken to develop mussel reference materials that were certified for their mass fractions of saxitoxin and decarbamoyl-saxitoxin. Fifteen laboratories from various European countries participated. Three of these had major responsibility for substantial parts of the work and overall coordination of the project. The project involved 4 main activities: (1) procurement and characterization of calibrants; (2) improvement of analytical methodology; (3) preparation of reference materials, including homogeneity and stability studies; (4) 2 interlaboratory studies and a certification exercise. The joint activities resulted in 3 homogeneous and stable reference materials: 2 lyophilized mussel materials with and without naturally incurred paralytic shellfish poisoning (PSP) toxins, and a saxitoxin enrichment solution. The reference materials were certified with respect to their saxitoxin and decarbamoyl-saxitoxin content. The lyophilized mussel material with PSP toxins (CRM 542) contained &lt;0.07 mg saxitoxin·2HCl/kg and 1.59 ± 0.20 mg decarbamoyl-saxitoxin·2HCl/kg. The lyophilized mussel material without PSP toxins (CRM 543) contained &lt;0.07 mg saxitoxin·2HCl/kg and &lt;0.04 mg decarbamoyl-saxitoxin·2HCl/kg. The certified value of the saxitoxin mass fraction in the saxitoxin enrichment solution (CRM 663) was 9.8 ± 1.2 μg/g.

P11.29 Development of ex vivo models for deeper insights into the biology and therapeutic targeting of tumor microtube networks in gliomas

BACKGROUND

The formation of multicellular networks via thin cellular protrusions named tumor microtubes (TMs) emerged as a novel mechanism of therapy resistance in malignant glioma. TMs are also involved in tumor cell invasion and growth. Within these tumor cell networks, connected tumor cells communicate via intercellular calcium waves (ICWs). Only few molecular drivers of TMs (Gap43, Ttyh1, Connexin 43) have been identified until now. Furthermore, the molecular mechanisms underlying ICWs as well as their specific biological role in glioma remains to be elucidated. A better understanding of the biology and the identification of molecular key drivers is essential for the development of drugs targeting TM formation and function.

MATERIAL AND METHODS

For this purpose, we have developed novel ex vivo models that not only provide insights into TM biology but further allow medium throughput drug screening. As classical response parameters such as the inhibition of cell growth or cytotoxicity do not necessarily correlate with effects on TM formation or function, a morphometrical approach employing laser scanning microscopy and machine-learning based image analysis tools is used. The application of fluorescent probes and genetic fluorescent reporter systems provides novel longitudinal insights into cytoskeletal dynamics, the role and exchange of organelles such as mitochondria, mechanisms of homeostasis within tumor cell networks (e.g. redox homeostasis) and ICWs in live cells. In addition to 2D glioma cell and co-culture models we have developed a fully human and mature brain organoid model. Here, complex 3D tumor cell networks corresponding to the morphology and exhibiting calcium communication patterns observed in our mouse model can be established and studied ex vivo. Furthermore, with these models not only the role of the brain microenvironment on TM formation but also direct interactions of glioma cells with neurons and glial cells as well as drug effects such as cytotoxicity on these brain cells can be investigated ex vivo.

CONCLUSION

In summary, novel tumor models enable further insights into TM biology and hence provide the basis for development of TM- and network disrupting drugs. First results of this screening opportunity will be presented.

P11.07 LAPTM5 functions as a tumor suppressor via CD40 - NFêB pathway inhibition and represents a potential biomarker for temozolomide sensitivity in CD40 proficient glioblastoma

BACKGROUND

Glioma therapy is challenged by the invasive nature of glioma resulting in tumor recurrence and treatment resistance. Lysosomal protein transmembrane 5 (LAPTM5) was identified to inhibit invasion by screening for invasion-associated genes in glioma. The aim of this study was to decipher the function of LAPTM5 in glioblastoma and its interaction with the CD40 receptor which was shown to be highly expressed in up to 40% of glioblastoma.

METHODS

LAPTM5 expression was correlated with clinical outcome of glioma patients. Knockdown of LAPTM5 was performed in different glioma cell lines to analyze the impact on clonogenicity, invasiveness, sensitivity to temozolomide chemotherapy and tumorigenicity in-vitro and in-vivo in a subcutaneous xenograft mouse model. Expression array was used to elucidate the underlying pathways. CD40 knockdown and overexpression was induced to prove the crosstalk of LAPTM5 and CD40.

RESULTS

LAPTM5 expression correlated with better overall survival in high grade glioma patients and acted as a tumor suppressor in CD40 positive glioblastoma cells. LAPTM5 inhibited CD40-mediated NFκB activation resulting in anti-invasive, anti-clonogenic and temozolomide sensitizing effects in-vitro and in-vivo. Vice-versa, knockdown of LAPTM5 enhanced tumorigenicity by activation of the NFκB pathway which was overcome by NFκB inhibition. Importantly, CD40 expression was required for LAPTM5-mediated tumor suppressive activity.

CONCLUSION

LAPTM5 conveyed tumor suppressive and temozolomide sensitizing effects in CD40-positive glioblastoma by inhibition of CD40-mediated NFκB activation and thereby might provide a reasonable biomarker for sensitivity to temozolomide in CD40-positive glioblastoma.