DRD1 signaling modulates TrkB turnover and BDNF sensitivity in direct pathway striatal medium spiny neurons

Disturbed motor control is a hallmark of Parkinson's disease (PD). Cortico-striatal synapses play a central role in motor learning and adaption, and brain-derived neurotrophic factor (BDNF) from cortico-striatal afferents modulates their plasticity via TrkB in striatal medium spiny projection neurons (SPNs). We studied the role of dopamine in modulating the sensitivity of direct pathway SPNs (dSPNs) to BDNF in cultures of fluorescence-activated cell sorting (FACS)-enriched D1-expressing SPNs and 6-hydroxydopamine (6-OHDA)-treated rats. DRD1 activation causes enhanced TrkB translocation to the cell surface and increased sensitivity for BDNF. In contrast, dopamine depletion in cultured dSPN neurons, 6-OHDA-treated rats, and postmortem brain of patients with PD reduces BDNF responsiveness and causes formation of intracellular TrkB clusters. These clusters associate with sortilin related VPS10 domain containing receptor 2 (SORCS-2) in multivesicular-like structures, which apparently protects them from lysosomal degradation. Thus, impaired TrkB processing might contribute to disturbed motor function in PD.

P11.34.A Pseudoprogression in cases of brain metastases and its neurooncological pitfalls under PD-1 inhibitor therapy in the era of personalized medicine

Background

Immunotherapy plays an increasing role in combating malignant cancers. Recently, there has been a noticeable uptick of pseudoprogression mimicking true tumor growth or even intracranial abscess. PD-1 inhibitors especially have come under scrutiny for imitating progressive diseases. Here, we summarize our departmental findings to this regard.

Material and Methods

We analyzed the clinical, intraoperative and neuropathological findings as well as perioperative radiological imaging in four cases.

Results

Four patients (three males and one female, ranged 52-74 years) underwent resection for brain metastases and were subsequently treated with radiotherapy and with PD-1 inhibitors. Within one-year post-surgery, cranial MRI-imaging showed space-occupying, contrast enhanced lesions in all four patients. In two cases FET-PETs were performed pre-operatively. They showed a significant increase in aminoacid uptake. In two cases, 5-aminolevulineacid (5-ALA) was applied pre-operatively. In one case, there was considerable 5-ALA uptake. The fourth patient presented radiological signs of an abscess and underwent emergency surgery. The neuropathological workup of all tissues in question depicted highly increased activity of lymphocytes and microglia, accompanied by necrosis. All cases were classified as pseudoprogression, which, on top, had developed supramarginally in previously healthy tissue.

Conclusion

Neurooncologists face crescent challenges in the increasing cases of pseudoprogression under/after immunotherapy. Radiological imaging doesn’t seem to be able to clearly differentiate between true and pseudoprogression. Even FET-PETs, in general a valid diagnostic tool, seem to be fooled by checkpoint inhibitors. Furthermore, pseudoprogressive tissue after PD-1 inhibitor therapy might mimic tumor tissue intra-operatively by increased 5-ALA uptake. All these characteristics increase the risk of overly aggressive resection of the suspected cancerous or infectious, but in the end pseudo-progressive tissue. Brain edema and clinical symptoms spurred by pseudoprogression may be an indication for surgery, but the risk of performing possibly unnecessary surgery based on radiological findings fooled by PD-1 inhibitors should be taken into consideration. At this point, there does not seem to be a foolproof diagnostic method to differentiate pseudo- from true progression. And there is the possibility that the pseudoprogression is happening in tissue adjacent to the previously resected lesion. Neurooncologists need to acknowledge that pseudoprogression under/after immunotherapy will become only more prevalent in the future and take this message to their patients.

P06.04.B Efficacy of Podoplanin-CAR-T Cells inex vivo Patient Derived Glioblastoma Organoids

Background

Glioblastoma (GBM) is the most prevalent malignant brain tumor in adults. Recent immunotherapeutic approaches led to promising effects both in vitro and in preclinical animal models. However, tumor heterogeneity, antigen escape mechanisms and complex interactions with the tumor microenvironment (TME) hinder their clinical breakthrough. Thus, patient derived ex vivo models are needed to test new therapeutical approaches. Genetically modified T cells expressing a chimeric antigen receptor (CAR) hold enhanced affinity for tumor associated antigens. As Podoplanin (PDPN) shows stable and increased expression in GBM, it is a suitable target antigen. When activated, CAR-T cells initiate the triad of cytokine release, T cell proliferation and target cell apoptosis. We evaluated the performance of PDPN-CAR-T cells in GBM patient derived organoids (PDO).

Material and Methods

PDOs were generated from freshly resected GBM tissue and could be cultured successfully up to several months. We assessed PDPN expression of PDOs via immunohistochemistry (IHC) prior to treatment. PDPN-CAR T cells were generated from peripheral blood mononuclear cells of healthy donors via lentiviral transduction and expansion. The transduction rate was assessed by flow cytometry prior to application. PDOs treated with untransduced T cells served as controls. PDOs were incubated with a preset number of PDPN-CAR T cells at a E:T ratio of 1:4 and were examined microscopically to register morphological disintegration after 48h. Immunofluorescence staining was conducted to detect proliferating CD4+ CART cells (CD4+/ Ki67+) after 72h and cytokine release of IFN-γ was determined via ELISA after 20h.

Results

In total, PDOs from three patients were treated with PDPN-CART cells. All of them expressed the antigen according to IHC staining. All incubated PDOs presented clear disintegration of the circular organoid shape up to total dissolving, whereas control PDOs stayed intact. CD4+ CART cells showed extensive proliferation at a mean rate of 79.8% ± 6,59% which was significant for two PDOs in comparison to control PDOs (p = 0.48, p < 0.01). PDPNCART cells exhibited significantly elevated IFN-γ release in all PDOs (p < 0.01).

Conclusion

We here describe PDPN as a promising target and proved effectiveness of PDPN-CAR-T cells in an ex vivo 3D model. Additional ex vivo models like tumor slice cultures might be crucial to evaluate effectiveness of CAR-T cell therapy. PDPN-CAR-T cells should be tested in these ex vivo as well as in vivo GBM models alone and in a combined approach with CARs targeting additional antigens in order to overcome tumor heterogeneity.

EPEN-06. Comprehensive profiling of myxopapillary ependymomas identifies a distinct molecular subtype with relapsing disease

Myxopapillary ependymoma (MPE) is a heterogeneous disease regarding histopathology and outcome. The underlying molecular biology is poorly understood, and markers that reliably predict the patients’ clinical course are unknown. We assembled a cohort of 185 tumors classified as MPE based on DNA methylation from pediatric, adolescent, and adult patients. Methylation patterns, copy number profiles, and MGMT promoter methylation were analyzed for all tumors, 106 tumors were evaluated histomorphologically, and RNA sequencing was performed for 37 cases. Based on methylation profiling, we defined two subtypes MPE-A and MPEB, and explored associations with epidemiological, clinical, pathological, and molecular characteristics of these tumors. Tumors in the methylation class MPE were histologically diagnosed as WHO grade I (59%), WHO grade II (37%), or WHO grade III tumors (4%). 75/77 analyzed tumors expressed HOXB13, which is a diagnostic feature not detected in other spinal ependymal tumors. Based on DNA methylation, our series split into two subtypes. MPE-A occurred in younger patients (median age 27 vs. 45 years, p=7.3e-05). They were enriched with WHO grade I tumors and associated with papillary morphology and MGMT promoter hypermethylation (all p<0.001). MPE-B included most tumors initially diagnosed as WHO grade II and cases with tanycytic morphology. Copy number alterations were more common in MPE-A. RNA sequencing revealed an enrichment for extracellular matrix and immune system-related signatures in MPE-A. 15/30 MPE-A could not be totally resected compared to 1/58 MPE-B (p=6.3e-08), and progression-free survival was significantly better for MPE-B (p=3.4e-06, 10-year relapse rate 33% vs. 85%). We unraveled the morphological and clinical heterogeneity of MPE by identifying two molecularly distinct subtypes. These subtypes significantly differed in progression-free survival and will likely need different protocols for surveillance and treatment.

Iron as the concert master in the pathogenic orchestra playing in sporadic Parkinson's disease

About 60 years ago, the discovery of a deficiency of dopamine in the nigro-striatal system led to a variety of symptomatic therapeutic strategies to supplement dopamine and to substantially improve the quality of life of patients with Parkinson's disease (PD). Since these seminal developments, neuropathological, neurochemical, molecular biological and genetic discoveries contributed to elucidate the pathology of PD. Oxidative stress, the consequences of reactive oxidative species, reduced antioxidative capacity including loss of glutathione, excitotoxicity, mitochondrial dysfunction, proteasomal dysfunction, apoptosis, lysosomal dysfunction, autophagy, suggested to be causal for ɑ-synuclein fibril formation and aggregation and contributing to neuroinflammation and neural cell death underlying this devastating disorder. However, there are no final conclusions about the triggered pathological mechanism(s) and the follow-up of pathological dysfunctions. Nevertheless, it is a fact, that iron, a major component of oxidative reactions, as well as neuromelanin, the major intraneuronal chelator of iron, undergo an age-dependent increase. And ageing is a major risk factor for PD. Iron is significantly increased in the substantia nigra pars compacta (SNpc) of PD. Reasons for this finding include disturbances in iron-related import and export mechanisms across the blood-brain barrier (BBB), localized opening of the BBB at the nigro-striatal tract including brain vessel pathology. Whether this pathology is of primary or secondary importance is not known. We assume that there is a better fit to the top-down hypotheses and pathogens entering the brain via the olfactory system, then to the bottom-up (gut-brain) hypothesis of PD pathology. Triggers for the bottom-up, the dual-hit and the top-down pathologies include chemicals, viruses and bacteria. If so, hepcidin, a regulator of iron absorption and its distribution into tissues, is suggested to play a major role in the pathogenesis of iron dyshomeostasis and risk for initiating and progressing ɑ-synuclein pathology. The role of glial components to the pathology of PD is still unknown. However, the dramatic loss of glutathione (GSH), which is mainly synthesized in glia, suggests dysfunction of this process, or GSH uptake into neurons. Loss of GSH and increase in SNpc iron concentration have been suggested to be early, may be even pre-symptomatic processes in the pathology of PD, despite the fact that they are progression factors. The role of glial ferritin isoforms has not been studied so far in detail in human post-mortem brain tissue and a close insight into their role in PD is called upon. In conclusion, "iron" is a major player in the pathology of PD. Selective chelation of excess iron at the site of the substantia nigra, where a dysfunction of the BBB is suggested, with peripherally acting iron chelators is suggested to contribute to the portfolio and therapeutic armamentarium of anti-Parkinson medications.

P04.17 Antigen heterogeneity in glioblastoma cell lines, patient-derived cells, and patients’ glioblastoma tissue is an obstacle for CAR-T cell therapy development

BACKGROUND

Immunotherapy targeting surface antigens, e.g. CAR-T-cell therapy has become a promising therapeutic approach for glioblastoma (GBM) treatment. Antigen heterogeneity constitutes a major obstacle not only for preclinical in vitro studies but also for clinical translation. Here, we provide information about the surface expression of the eight in GBM CAR-T-cell therapy most targeted antigens (GD2, CSPG4, CD133, CD70, HER2, Il13Rα2, EGFRvIII and EphA2) by analyzing GBM cell lines (GCL), patient-derived cells (PDCL) and patients’ tumor tissue (PT) and comparing the expression profiles.

MATERIAL AND METHODS

We measured expression of the above-mentioned antigens in 7 GCL (GaMG, U87, U373, U343, U251, U138, DKMG), 7 PDCL and PT of 9 patients by flow cytometry (FACSCanto II). After evaluation with FlowJo software (TreeStar), we scored antigen expression (0–1.0: low expression, 1.1–2.0: medium expression, 2.1–3.0: high expression) and calculated the mean expression and range.

RESULTS

GD2 showed a medium expression in GCL (x̅=1.3) but was highly expressed in PDCL (x̅=2.6) and PT (x̅=2.4). In contrast, CSPG4 displayed low expression in GCL (x̅=0.3) and PT (x̅=0.4), but medium expression in PDCL (x̅=1.9). CD133, a stem cell marker, showed low expression in GCL (x̅=0.8) and PDCL (x̅=0.4), whereas the expression in PT was medium (x̅=1.4). Both CD70 and Il13Rα2 were weakly expressed in GCL, PDCL and PT (x̅=0.2, 0.4, 0.0 and 0.5, 0.6, 0.4, respectively). HER2 displayed medium expression in GCL (x̅=1.4) and PDCL (x̅=1.4) and low expression in PT (x̅=0.6). For EGFRvIII medium expression was detectable in all three entities (x̅=1.4, 1.1 and 1.1). EphA2 was mildly expressed in GCL (x̅=0.1), medium expressed in PT (x̅=2.0) and highly expressed in PDCL (x̅=2.6). Overall, there was high variability of antigen surface expression even within each of the groups.

CONCLUSION

GCL, PDCL and PT display heterogenic antigen surface expression with high variability within each group, thereby complicating clinical translation of in vitro results obtained using cell lines. This aspect should be taken into account in GBM target antigen research.

Abstract 3146: Heterogeneity of the antigen-expression pattern in primary and recurrent glioblastoma patients

Introduction: Immunotherapy leads to promising results in the treatment of glioblastoma (GBM) patients. Recent clinical trials revealed a survival benefit of patients treated with monospecific CAR-T-cells. However, antigen escape mechanisms due to heterogeneous surface expression of target antigens still constitute a critical hurdle in the immunotherapeutic treatment of GBM and are a major reason for non-response or relapse. Therefore, we aim to characterize GBM's heterogeneity, the intratumoral distribution and changes of surface antigens in relapse.

Methods: We performed immunohistochemical staining of the ten in vitro and in vivo most targeted antigens in CAR-T cell therapy (HER2, EGFRvIII, CD70, B7H3, Il13Rα2, NY-ESO1, GD2, CD133, CSPG4 and EphA2). We analyzed 35 patients, who underwent surgery for primary (PT) as well as recurrent GBM (RL). To address intrapersonal heterogeneity, we examined five fields of view per slide. As controls, we stained cerebral, cerebellar and brain stem slides of three healthy specimens. We quantified the percentage of low, medium and high antigen expressing cells on each slide by applying a specialized macro in ImageJ. We further weighted this expression score by multiplication with 1 (low), 2 (medium) or 3 (high expression). Finally, we calculated the median expression values of all tumors combined for each antigen.

Summary: Median values of EGFRvIII (PT: 0.14; RL: 0.73), HER2 (PT: 0.67; RL: 4.00) and NY-ESO1 (PT: 0.00; RL: 0.16) expression were very low. Antigen expression of CSPG4 (PT: 4.67; RL: 2.78), Il13Rα2 (PT: 3.84; RL: 2.78), GD2 (PT: 7.50; RL: 27.03) and B7H3 (PT: 8.81; RL: 16.62) was mild. CD133 (PT: 52.16; RL: 56.13), CD70 (PT: 19.18; RL: 25.02) and EphA2 (PT: 60.65; RL: 55.46) showed moderate antigen expression. None of the evaluated antigens displayed high expression. Median values of HER2 (p=0.005, Cohen's r=0.48), EGFRvIII (p=0.042, Cohen's r=0.344), and GD2 (p=0.013, Cohen's r=0.42) were significantly increased in RL compared to PT. We found significant intrapersonal expression differences for each antigen. However, none of the healthy brain tissue specimens expressed any of the ten antigens.

Conclusions: Inter- and intrapersonal heterogeneity constitutes a major obstacle for the implementation of GBM immune therapies which avoid antigen escape mechanisms.

Citation Format: Vera Dufner, Moritz Meyer-Hofmann, Jonas Feldheim, Katja Maurus, Camelia Monoranu, Thomas Nerreter, Michael Hudecek, Carsten Hagemann, Ralf-Ingo Ernestus, Mario Löhr. Heterogeneity of the antigen-expression pattern in primary and recurrent glioblastoma patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3146.

IMMU-10. INTERIM ANALYSIS OF THE HIT-HGG REZ IMMUNVAC STUDY - DENDRITIC CELL VACCINATION WITH PARTIAL TREG DEPLETION IN CHILDREN, ADOLESCENTS, AND ADULTS WITH RELAPSED HIGH-GRADE GLIOMAS

Efficacy of therapeutic dendritic cell vaccines (DCV) can be limited by immunosuppressive mechanisms in the micromilieu of high-grade gliomas. In the HIT-HGG-Rez Immunovac trial (Eudra-CT 2013-000419-26), we investigate whether a reduction of Treg with metronomic cyclophosphamide (metrCyc) might be a feasible option to improve vaccine efficacy. 10 pediatric (mean age 11.4±4.2y) and 5 adult patients (mean age 39.5±19.9y) with relapsed glioblastoma were treated according to the HIT-HGG-Rez Immunovac protocol so far. 2 children were treated within the trial, the other 13 in the pilot phase. Patients received upfront oral metrCyc for 2–4 weeks. After reoperation and monocyte-apheresis, patients received 4 weekly intradermal doses of autologous, TNFa/IL-1ß matured DCs pulsed with tumor lysate in imiquimod-prepared skin. Thereafter, tumor lysate boosts were given. All patients received at least 5 vaccines (4xDCs, 1xlysate boosts). MetrCyc was well tolerated and led to a reduction in Treg-frequency of 35.6±17.8% followed by a rebound after cessation of metrCyc. Importantly, 13/14 analyzed patients showed a positive IFNg-T-cell response against autologous tumor lysate with a tendency to decrease over time. 6-month overall survival was 100%, compared to 65% in a historical control. Mean PFS and OS were 5.7 and 21.1 months with no difference between adults and children. We conclude that DCV in combination with partial Treg depletion is feasible, safe, and related with a high rate of tumor-specific IFNg-responses. As the clinically and immunologically beneficial effects seem to diminish over time, we aim to combine our approach with checkpoint inhibition in the next amendment.

Chronophin regulates active vitamin B6 levels and transcriptomic features of glioblastoma cell lines cultured under non-adherent, serum-free conditions

BACKGROUND

The phosphatase chronophin (CIN/PDXP) has been shown to be an important regulator of glioma cell migration and invasion. It has two known substrates: p-Ser3-cofilin, the phosphorylated form of the actin binding protein cofilin, and pyridoxal 5'-phosphate, the active form of vitamin B6. Phosphoregulation of cofilin, among other functions, plays an important role in cell migration, whereas active vitamin B6 is a cofactor for more than one hundred enzymatic reactions. The role of CIN has yet only been examined in glioblastoma cell line models derived under serum culture conditions.

RESULTS

We found that CIN is highly expressed in cells cultured under non-adherent, serum-free conditions that are thought to better mimic the in vivo situation. Furthermore, the substrates of CIN, p-Ser3-cofilin and active vitamin B6, were significantly reduced as compared to cell lines cultured in serum-containing medium. To further examine its molecular role we stably knocked down the CIN protein with two different shRNA hairpins in the glioblastoma cell lines NCH421k and NCH644. Both cell lines did not show any significant alterations in proliferation but expression of differentiation markers (such as GFAP or TUBB3) was increased in the knockdown cell lines. In addition, colony formation was significantly impaired in NCH644. Of note, in both cell lines CIN knockdown increased active vitamin B6 levels with vitamin B6 being known to be important for S-adenosylmethionine biosynthesis. Nevertheless, global histone and DNA methylation remained unaltered as was chemoresistance towards temozolomide. To further elucidate the role of phosphocofilin in glioblastoma cells we applied inhibitors for ROCK1/2 and LIMK1/2 to our model. LIMK- and ROCK-inhibitor treatment alone was not toxic for glioblastoma cells. However, it had profound, but antagonistic effects in NCH421k and NCH644 under chemotherapy.

CONCLUSION

In non-adherent glioblastoma cell lines cultured in serum-free medium, chronophin knockdown induces phenotypic changes, e.g. in colony formation and transcription, but these are highly dependent on the cellular background. The same is true for phenotypes observed after treatment with inhibitors for kinases regulating cofilin phosphorylation (ROCKs and LIMKs). Targeting the cofilin phosphorylation pathway might therefore not be a straightforward therapeutic option in glioblastoma.

Lewy Bodies: A Spectator or Salient Killer?

Lewy bodies (LBs) are characteristic hallmarks of Parkinson's disease (PD). However, their role in the pathology of PD is not established yet. Are they primary events in the neurodegenerative process or only secondary phenomena? Are they signs of protecting neurons from toxicity or are they toxic per se? How are they are formed? Are LBs targets for therapeutic strategies? Addressing these questions may be of pivotal importance to unravel the basic mechanisms of neurodegeneration in PD. On the basis of current evidence, we intend to elucidate the possible role of LBs as triggers and/or markers of disease progression in PD. We present evidence for the morphogenesis of brain stem and cortical LBs, the role in neuronal cell death mechanisms, which seem to be correlated with the adhesion of LBs to and finally disruption of their inner neuronal membrane. Taken as such, LBs would be salient killers of nerve cells. However, they may also play a neuroprotective role in the early phases of neuronal pathology (LBs as a spectator), yet harmful to neuronal stability in later stages of LB development. Generation of LB pathology in the periphery (early subclinical Braak stage) might be due to reactive oxygen species (ROS) due to (chronic) bacteria-induced and/or otherwise intestinal inflammation, both leading to alpha-synuclein structural changes, oligomerization, seeding and propagation in a prion-like mechanism. If so, LB generation is a secondary process following ROS/inflammation pathology. Therapeutic implication based on LB pathology include drug development to inhibit protein misfolding, templating and transmission or vaccination against LBs, neuron regeneration strategies, anti-inflammatory and anti-biotic drugs as well as nutritional specialities to prevent intestine intoxications. In conclusion, evidence suggests LBs to be secondary hallmarks of PD pathology, induced by ROS/inflammation or other pathological triggers able to modify protein (alpha-synuclein) steric/chemical properties. Therapeutic strategies based on LB pathologies are devoted to reduce neuron cell death mechanisms in their time course and severity.

Abstract A045: Dendritic cell vaccination with partial Treg depletion in relapsed glioblastoma – results from the pilot phase of the HIT-HGG Rez Immunvac study

Efficacy of therapeutic dendritic cell vaccines (DCV) can be limited by immunosuppressive mechanisms such as regulatory T cells (Treg) overrepesented in the micromilieu of the tumor. Here, we investigated whether a reduction of Treg with metronomic cyclophosphamide (metrCyc) might be a feasible option to improve vaccine efficacy. 7 patients with replased glioblastoma were treated in the pilot phase of the HIT-HGG Rez Immunovac study (5 pediatric, 2 adult patients). After reoperation and monocyte-apheresis, patients received 4 weekly doses of autologous, TNFa/IL-1ß matured DCs pulsed with tumor lysate. Thereafter 4 monthy, and subsequently threemonthly boosts with tumor lysate were given. The intradermal injection site was prepared with topical imiquimod. Additionally, patients were pretreated with oral metrCyc 2-4 weeks before the first vaccination. MetrCyc was well tolerated with one mild and transient leukopenia in a patient, who received a parallel re-irradiation boost. All patients received at least 7 vaccines (4xDCs, 3xlysate boosts). Treg frequency decreased by 32%, but returned to normal levels after cessation of metrCyc. Importantly, 6/6 analyzed patients showed a positive (>1.5fold increase) IFNg-response of varying magnitude and duration towards the autologous tumor lysate in a IFNg-PCR assay. Furthermore, we observed an increase in VLA4+ T-cells induced by the vaccine, both in the CD4 as well as the CD8 compartment. So far, all patients relapsed after a mean of 4.8 months, however, overall survival is currently 15.2 months with 4/7 patients being still alive after a median follow-up of 21 months (range 12-27 months). One patient is disease-free after reoperation and continuation of vaccination for 26 months now. 6-month overall survival was 86%. We conclude that DC vaccination in combination with partial Treg depletion with metrCyc is feasible, safe, and possibly related with a higher than expected frequency of positive IFNg-responses towards tumor tissue. These pilot data warrant verification in the full HIT-HGG Rez Immunovac trial (Eudra-CT 2013-000419-26), which will start to recruit patients soon.

Citation Format: Matthias Eyrich, Jürgen Krauss, Mario Löhr, Antje Technau, Johannes Rachor, Camelia Monoranu, Monika Warmuth-Metz, Matthias Wölfl, Christof Kramm, Paul Gerhardt Schlegel. Dendritic cell vaccination with partial Treg depletion in relapsed glioblastoma – results from the pilot phase of the HIT-HGG Rez Immunvac study. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A045.

Recurrent somatic alterations of FGFR1 and NTRK2 in pilocytic astrocytoma

Pilocytic astrocytoma, the most common childhood brain tumor, is typically associated with mitogen-activated protein kinase (MAPK) pathway alterations. Surgically inaccessible midline tumors are therapeutically challenging, showing sustained tendency for progression and often becoming a chronic disease with substantial morbidities. Here we describe whole-genome sequencing of 96 pilocytic astrocytomas, with matched RNA sequencing (n = 73), conducted by the International Cancer Genome Consortium (ICGC) PedBrain Tumor Project. We identified recurrent activating mutations in FGFR1 and PTPN11 and new NTRK2 fusion genes in non-cerebellar tumors. New BRAF-activating changes were also observed. MAPK pathway alterations affected all tumors analyzed, with no other significant mutations identified, indicating that pilocytic astrocytoma is predominantly a single-pathway disease. Notably, we identified the same FGFR1 mutations in a subset of H3F3A-mutated pediatric glioblastoma with additional alterations in the NF1 gene. Our findings thus identify new potential therapeutic targets in distinct subsets of pilocytic astrocytoma and childhood glioblastoma.

Hotspot mutations in H3F3A and IDH1 define distinct epigenetic and biological subgroups of glioblastoma

Glioblastoma (GBM) is a brain tumor that carries a dismal prognosis and displays considerable heterogeneity. We have recently identified recurrent H3F3A mutations affecting two critical amino acids (K27 and G34) of histone H3.3 in one-third of pediatric GBM. Here, we show that each H3F3A mutation defines an epigenetic subgroup of GBM with a distinct global methylation pattern, and that they are mutually exclusive with IDH1 mutations, which characterize a third mutation-defined subgroup. Three further epigenetic subgroups were enriched for hallmark genetic events of adult GBM and/or established transcriptomic signatures. We also demonstrate that the two H3F3A mutations give rise to GBMs in separate anatomic compartments, with differential regulation of transcription factors OLIG1, OLIG2, and FOXG1, possibly reflecting different cellular origins.

Dissecting the genomic complexity underlying medulloblastoma

Medulloblastoma is an aggressively growing tumour, arising in the cerebellum or medulla/brain stem. It is the most common malignant brain tumour in children, and shows tremendous biological and clinical heterogeneity. Despite recent treatment advances, approximately 40% of children experience tumour recurrence, and 30% will die from their disease. Those who survive often have a significantly reduced quality of life. Four tumour subgroups with distinct clinical, biological and genetic profiles are currently identified. WNT tumours, showing activated wingless pathway signalling, carry a favourable prognosis under current treatment regimens. SHH tumours show hedgehog pathway activation, and have an intermediate prognosis. Group 3 and 4 tumours are molecularly less well characterized, and also present the greatest clinical challenges. The full repertoire of genetic events driving this distinction, however, remains unclear. Here we describe an integrative deep-sequencing analysis of 125 tumour-normal pairs, conducted as part of the International Cancer Genome Consortium (ICGC) PedBrain Tumor Project. Tetraploidy was identified as a frequent early event in Group 3 and 4 tumours, and a positive correlation between patient age and mutation rate was observed. Several recurrent mutations were identified, both in known medulloblastoma-related genes (CTNNB1, PTCH1, MLL2, SMARCA4) and in genes not previously linked to this tumour (DDX3X, CTDNEP1, KDM6A, TBR1), often in subgroup-specific patterns. RNA sequencing confirmed these alterations, and revealed the expression of what are, to our knowledge, the first medulloblastoma fusion genes identified. Chromatin modifiers were frequently altered across all subgroups. These findings enhance our understanding of the genomic complexity and heterogeneity underlying medulloblastoma, and provide several potential targets for new therapeutics, especially for Group 3 and 4 patients.

The need to unify neuropathological assessments of vascular alterations in the ageing brain: multicentre survey by the BrainNet Europe consortium

Here, we summarise the results after carrying out a large survey regarding the assessment of vascular alterations, both vessel changes and vascular lesions in an inter-laboratory setting. In total, 32 neuropathologists from 22 centres, most being members of BrainNet Europe (BNE), participated by filling out a questionnaire with emphasis on assessment of common vascular alterations seen in the brains of aged subjects. A certain level of harmonisation has been reached among BNE members regarding sectioning of the brain, harvesting of brain tissue for histology and staining used when compared to the survey carried out in 2006 by Pantoni and colleagues. The most significant variability was seen regarding the assessment of severity and of clinical significance of vascular alterations. Two strategies have recently been recommended regarding the assessment of vascular alterations in aged and demented subjects. The National Institute on Aging - Alzheimer's Association (NIA-AA) recommends the assessment of hippocampal sclerosis, vascular brain injury and microvascular lesions in 12 regions. Although this strategy will be easy to follow, the recommendations do not inform how the load of observed alterations should be assessed and when the observed lesions are of significance. Deramecourt and his colleagues recommend an assessment and semiquantitative grading of various pathologies in 4 brain regions. This strategy yielded a total score of 0 to 20 as an estimate of pathology load. It is, however, not clear which score is considered to be of clinical significance. Furthermore, in several BNE trials the semiquantitative assessment has yielded poor agreement rates; an observation that might negatively influence the strategy proposed by Deramecourt and his colleagues. In line with NIA-AA, a dichotomised approach of easily recognisable lesions in a standardised set of brain regions harvested for neuropathological assessment and applying reproducible sampling and staining strategies is recommended by BNE. However, a simple strategy regarding assessment of load of alteration is urgently needed to yield reproducible, and at the same time, comparable results between centres.

Staging/typing of Lewy body related alpha-synuclein pathology: a study of the BrainNet Europe Consortium

When 22 members of the BrainNet Europe (BNE) consortium assessed 31 cases with alpha-synuclein (alphaS) immunoreactive (IR) pathology applying the consensus protocol described by McKeith and colleagues in 2005, the inter-observer agreement was 80%, being lowest in the limbic category (73%). When applying the staging protocol described by Braak and colleagues in 2003, agreement was only 65%, and in some cases as low as 36%. When modifications of these strategies, i.e., McKeith's protocol by Leverenz and colleagues from 2009, Braak's staging by Müller and colleagues from 2005 were applied then the agreement increased to 78 and 82%, respectively. In both of these modifications, a reduced number of anatomical regions/blocks are assessed and still in a substantial number of cases, the inter-observer agreement differed significantly. Over 80% agreement in both typing and staging of alphaS pathology could be achieved when applying a new protocol, jointly designed by the BNE consortium. The BNE-protocol assessing alphaS-IR lesions in nine blocks offered advantages over the previous modified protocols because the agreement between the 22 observers was over 80% in most cases. Furthermore, in the BNE-protocol, the alphaS pathology is assessed as being present or absent and thus the quality of staining and the assessment of the severity of alphaS-IR pathology do not alter the inter-observer agreement, contrary to other assessment strategies. To reach these high agreement rates an entity of amygdala-predominant category was incorporated. In conclusion, here we report a protocol for assessing alphaS pathology that can achieve a high inter-observer agreement for both the assignment to brainstem, limbic, neocortical and amygdala-predominant categories of synucleinopathy and the Braak stages.

Staging of neurofibrillary pathology in Alzheimer's disease: a study of the BrainNet Europe Consortium

It has been recognized that molecular classifications will form the basis for neuropathological diagnostic work in the future. Consequently, in order to reach a diagnosis of Alzheimer's disease (AD), the presence of hyperphosphorylated tau (HP‐tau) and β‐amyloid protein in brain tissue must be unequivocal. In addition, the stepwise progression of pathology needs to be assessed. This paper deals exclusively with the regional assessment of AD‐related HP‐tau pathology. The objective was to provide straightforward instructions to aid in the assessment of AD‐related immunohistochemically (IHC) detected HP‐tau pathology and to test the concordance of assessments made by 25 independent evaluators. The assessment of progression in 7‐µm‐thick sections was based on assessment of IHC labeled HP‐tau immunoreactive neuropil threads (NTs). Our results indicate that good agreement can be reached when the lesions are substantial, i.e., the lesions have reached isocortical structures (stage V–VI absolute agreement 91%), whereas when only mild subtle lesions were present the agreement was poorer (I–II absolute agreement 50%). Thus, in a research setting when the extent of lesions is mild, it is strongly recommended that the assessment of lesions should be carried out by at least two independent observers.