Immune phenotyping of diverse syngeneic murine brain tumors identifies immunologically distinct types

Antitumor efficacy of intermittent low-dose erlotinib plus sulindac via MHC upregulation and remodeling of the immune cell niche

A previously reported clinical trial in familial adenomatous polyposis (FAP) patients treated with erlotinib plus sulindac (ERL + SUL) highlighted immune response/interferon-γ signaling as a key pathway. In this study, we combine intermittent low-dose ERL ± SUL treatment in the polyposis in rat colon (Pirc) model with mechanistic studies on tumor-associated immune modulation. At clinically relevant doses, short-term (16 weeks) and long-term (46 weeks) ERL ± SUL administration results in near-complete tumor suppression in Pirc colon and duodenum (p < 0.0001). We identify a low-dose threshold for significant antitumor activity in Pirc rats given SUL at 125 ppm in the diet plus ERL at 5 mg/kg body weight via twice-weekly oral gavage (SUL125 + ERL5 × 2). Longitudinal analyses show diminished expression of MHC class I and II genes in polyps larger than Grade 5, a novel finding in the Pirc model. Treatment with ERL ± SUL upregulates the corresponding MHC and immune-associated factors in a subset of Pirc colon polyps, Pirc tumor cell lines, murine colon carcinoma cells, and FAP patient-derived organoids, with Nlrc5 playing a critical role in this effect. Imaging mass cytometry reveals that SUL125 + ERL5 × 2 increases tumor-associated Cd4+ T cells by ~2.6-fold (p < 0.05), with no apparent effect on Cd8+ T cells. The treatment also increases tumor-associated Cd68+ cells (p < 0.05) and decreases Foxp3+ (p < 0.01) and Arg1+ (p < 0.05) cells. Thus, intermittent low-dose ERL + SUL treatment enhances tumor-associated MHC expression and remodels the immune cell niche toward a more permissive "helper" immune microenvironment. We conclude that early immune-interception strategies targeting interferon-γ signaling may benefit FAP patients at drug doses below the clinical standard of care.

FcRn-silencing of IL-12Fc prevents toxicity of local IL-12 therapy and prolongs survival in experimental glioblastoma

Glioblastoma remains a challenging indication for immunotherapy: the blood-brain barrier hampers accessibility for systemic treatments and the immunosuppressive microenvironment impedes immune attack. Intratumoral therapy with the proinflammatory cytokine interleukin-12 (IL-12) can revert immunosuppression but leakage into the circulation causes treatment-limiting toxicity. Here we engineer an IL-12Fc fusion cytokine with reduced binding to the neonatal Fc receptor FcRn. FcRn-silenced IL-12Fc avoids FcRn-mediated brain export, thus exhibits prolonged brain retention and reduced blood levels, which prevents toxicity. In murine glioblastoma, FcRn-silenced IL-12Fc induces more durable responses with negligible systemic cytokine exposure and boosts the efficacy of radio- and chemotherapy. It triggers anti-tumor responses independently of peripheral T cell influx or lymphopenia and leads to inflammatory polarization of the tumor microenvironment in patient-derived glioblastoma explants. FcRn-silencing of IL-12Fc may unlock the full potential of IL-12 for brain cancer therapy and could be further applied to containing the activity of other therapeutics targeting neurological diseases.

Integrating antigen capturing nanoparticles and type 1 conventional dendritic cell therapy for in situ cancer immunization

Eliciting a robust immune response against tumors is often hampered by the inadequate presence of effective antigen presenting cells and their suboptimal ability to present antigens within the immunosuppressive tumor microenvironment. Here, we report a cascade antigen relay strategy integrating antigen capturing nanoparticles (AC-NPs) and migratory type 1 conventional dendritic cells (cDC1s), named Antigen Capturing nanoparticle Transformed Dendritic Cell therapy (ACT-DC), to facilitate in situ immunization. AC-NPs are engineered to capture antigens directly from the tumor and facilitate their delivery to adoptively transferred migratory cDC1s, enhancing antigen presentation to the lymph nodes and reshaping the tumor microenvironment. Our findings suggest that ACT-DC improves in situ antigen collection, triggers a robust systemic immune response without the need for exogenous antigens, and transforms the tumor environment into a more "immune-hot" state. In multiple tumor models including colon cancer, melanoma, and glioma, ACT-DC in combination with immune checkpoint inhibitors eliminates primary tumors in 50-100% of treated mice and effectively rejects two separate tumor rechallenges. Collectively, ACT-DC could provide a broadly effective approach for in situ cancer immunization and tumor microenvironment modulation.

Repurposing Chemotherapeutics in a Hyaluronic Acid-conjugate Combination Treatment Approach for the Local Immunomodulation of the Glioblastoma Microenvironment

The immunosuppressive tumor immune microenvironment (TIME) renders glioblastoma (GBM) refractory to current chemo-immunotherapeutics. We sought to explore a novel approach for local GBM-associated TIME immunomodulation based on a synergistic combination of the repurposed chemotherapeutic drugs doxorubicin (DOX), which acts to induce immunogenic cell death (ICD) and gemcitabine (GEM), which depletes immunosuppressive myeloid-derived suppressor cells (MDSCs). We conjugated DOX and GEM to hyaluronic acid (HA) to improve efficacy, given this polymer's ability to target CD44 which are overexpressed on cancer cells. The HA-DOX and HA-GEM polymer-drug conjugates provided synergistic cytotoxic effects and maintained ICD-related properties in GBM cells compared to a combination of free drugs. HA-DOX and HA-GEM also reverted the immunosuppressive GBM-associated TIME in orthotopic GL261 tumor-bearing mice by selectively depleting MDSCs and reprogramming M2-like macrophages towards a pro-inflammatory M1-like state, resulting in controlled tumor growth. Local HA-DOX and HA-GEM delivery also increased median survival and controlled tumor growth in an immune refractory SB28-GBM orthotopic mouse GBM model. These findings highlight the potential of repurposing clinically applicable chemotherapeutics in the context of polymer-drug combination treatments for novel immunomodulation strategies in unresectable GBM, which may open new avenues for developing innovative therapies.

Targeting the glioblastoma resection margin with locoregional nanotechnologies

Surgical resection is the first stage of treatment for patients diagnosed with resectable glioblastoma and is followed by a combination of adjuvant radiotherapy and systemic single-agent chemotherapy, which is typically commenced 4-6 weeks after surgery. This delay creates an interval during which residual tumour cells residing in the resection margin can undergo uninhibited proliferation and further invasion, even immediately after surgery, thus limiting the effectiveness of adjuvant therapies. Recognition of the postsurgical resection margin and peri-marginal zones as important anatomical clinical targets and the need to rethink current strategies can galvanize opportunities for local, intraoperative approaches, while also generating a new landscape of innovative treatment modalities. In this Perspective, we discuss opportunities and challenges for developing locoregional therapeutic strategies to target the glioblastoma resection margin as well as emerging opportunities offered by nanotechnology in this clinically transformative setting. We also discuss how persistent barriers to clinical translation can be overcome to offer a potential path forward towards broader acceptability of such advanced technologies.

Deuterium metabolic imaging phenotypes mouse glioblastoma heterogeneity through glucose turnover kinetics

Glioblastomas are aggressive brain tumors with dismal prognosis. One of the main bottlenecks for developing more effective therapies for glioblastoma stems from their histologic and molecular heterogeneity, leading to distinct tumor microenvironments and disease phenotypes. Effectively characterizing these features would improve the clinical management of glioblastoma. Glucose flux rates through glycolysis and mitochondrial oxidation have been recently shown to quantitatively depict glioblastoma proliferation in mouse models (GL261 and CT2A tumors) using dynamic glucose-enhanced (DGE) deuterium spectroscopy. However, the spatial features of tumor microenvironment phenotypes remain hitherto unresolved. Here, we develop a DGE Deuterium Metabolic Imaging (DMI) approach for profiling tumor microenvironments through glucose conversion kinetics. Using a multimodal combination of tumor mouse models, novel strategies for spectroscopic imaging and noise attenuation, and histopathological correlations, we show that tumor lactate turnover mirrors phenotype differences between GL261 and CT2A mouse glioblastoma, whereas recycling of the peritumoral glutamate-glutamine pool is a potential marker of invasion capacity in pooled cohorts, linked to secondary brain lesions. These findings were validated by histopathological characterization of each tumor, including cell density and proliferation, peritumoral invasion and distant migration, and immune cell infiltration. Our study bodes well for precision neuro-oncology, highlighting the importance of mapping glucose flux rates to better understand the metabolic heterogeneity of glioblastoma and its links to disease phenotypes.

V-domain immunoglobulin suppressor of T-cell activation and programmed death receptor 1 dual checkpoint blockade enhances antitumour immunity and survival in glioblastoma

BACKGROUND AND PURPOSE

The current therapy cannot meet the needs of glioblastoma (GBM). V-domain immunoglobulin suppressor of T-cell activation (VISTA) is significantly up-regulated in GBM patients; however, its therapeutic potential in GBM is still unclear.

EXPERIMENTAL APPROACH

Flow cytometry was used to detect the expression of VISTA and the co-expression pattern of VISTA and programmed death receptor 1 (PD-1) on brain infiltrating lymphocytes of GBM mice. Monoclonal antibody therapy was used to evaluate the therapeutic effect of α-VISTA monotherapy and α-VISTA combined with α-PD-1 on GBM mice. Transcriptome analysis, flow cytometry, and immunofluorescence were used to detect changes of immune microenvironment in mouse brain tumours. Immunofluorescence and TCGA data analysis were used to further validate the combined treatment strategy on patient data.

KEY RESULTS

Compared with normal mice, the frequency of VISTA expression and co-expression of VISTA and PD-1 on tumour-infiltrating lymphocytes (TILs) in tumour-bearing mice was increased. Anti-VISTA monotherapy significantly up-regulated multiple immune stimulation-related pathways and moderately prolonged mouse survival time. Blocking the immune checkpoint VISTA and PD-1 significantly prolonged the survival time of mice and cured about 80% of the mice; CD8+ T cells played an important role in this process. In addition, we found that the expression of VISTA and PD-1 was significantly up-regulated in GBM patients by immunofluorescence, and patients with high expression of VISTA and PD-1 were associated with poor overall survival. This combination of blocking the immune checkpoint VISTA and PD-1 may achieve clinical transformation in GBM.

Intratumoral gene delivery of 4-1BBL boosts IL-12-triggered anti-glioblastoma immunity

The standard of care in high-grade gliomas has remained unchanged in the past 20 years. Efforts to replicate effective immunotherapies in non-cranial tumors have led to only modest therapeutical improvements in glioblastoma (GB). Here, we demonstrate that intratumoral administration of recombinant interleukin-12 (rIL-12) promotes local cytotoxic CD8 POS T cell accumulation and conversion into an effector-like state, resulting in a dose-dependent survival benefit in preclinical GB mouse models. This tumor-reactive CD8 T cell response is further supported by intratumoral rIL-12-sensing dendritic cells (DCs) and is accompanied by the co-stimulatory receptor 4-1BB expression on both cell types. Given that DCs and CD8 POS T cells are functionally suppressed in the tumor microenvironments of de novo and recurrent glioma patients, we tested whether anti-tumor response at the rIL-12-inflamed tumor site could be enhanced with 4-1BBL, the ligand of 4-1BB. 4-1BBL was delivered using an adeno-associated virus (AAV) vector targeting GFAP-expressing cells and resulted in prolonged survival of rIL-12 treated GB-bearing mice. This study establishes that tumor antigen-specific CD8 T cell activity can be directed using an AAV-vector-mediated gene therapy approach, effectively enhancing anti-GB immunity.

Recent advances in development and delivery of non-viral nucleic acid therapeutics for brain tumor therapy

High grade gliomas (HGG) are a group of CNS tumors refractory to currently existing therapies, which routinely leads to early recurrence and a dismal prognosis. Recent advancements in nucleic acid-based therapy using a wide variety of different molecular targets and non-viral nanocarrier systems suggest that this approach holds significant potential to meet the urgent demand for improved therapeutic options for the treatment of these tumors. This review provides a comprehensive and up-to-date overview on the current landscape and progress of preclinical and clinical developments in this rapidly evolving and exciting field of research, including optimized nanocarrier delivery systems, promising therapeutic targets and tailor-made therapeutic strategies for individualized HGG patient treatment.

Oncolytic reprogramming of tumor microenvironment shapes CD4 T-cell memory via the IL6ra-Bcl6 axis for targeted control of glioblastoma

Oncolytic viruses (OVs) emerge as a promising cancer immunotherapy. However, the temporal impact on tumor cells and the tumor microenvironment, and the nature of anti-tumor immunity post-therapy remain largely unclear. Here we report that CD4+ T cells are required for durable tumor control in syngeneic murine models of glioblastoma multiforme after treatment with an oncolytic herpes simplex virus (oHSV) engineered to express IL-12. The upregulated MHCII on residual tumor cells facilitates programmed polyfunctional CD4+ T cells for tumor control and for recall responses. Mechanistically, the proper ratio of Bcl-6 to T-bet in CD4+ T cells navigates their enhanced anti-tumor capacity, and a reciprocal IL6ra-Bcl-6 regulatory axis in a memory CD4+ T-cell subset, which requires MHCII signals from reprogrammed tumor cells, tumor-infiltrating and resident myeloid cells, is necessary for the prolonged response. These findings uncover an OV-induced tumor/myeloid-CD4+ T-cell partnership, leading to long-term anti-tumor immune memory, and improved OV therapeutic efficacy.

Divergent Crosstalk Between Microglia and T Cells in Brain Cancers: Implications for Novel Therapeutic Strategies

Background: Brain cancers represent a formidable oncological challenge characterized by their aggressive nature and resistance to conventional therapeutic interventions. The tumor microenvironment has emerged as a critical determinant of tumor progression and treatment efficacy. Within this complex ecosystem, microglia and macrophages play fundamental roles, forming intricate networks with peripheral immune cell populations, particularly T cells. The precise mechanisms underlying microglial interactions with T cells and their contributions to immunosuppression remain incompletely understood. Methods: This review comprehensively examines the complex cellular dialogue between microglia and T cells in two prominent brain malignancies: primary glioblastoma and secondary brain metastases. Results: Through a comprehensive review of the current scientific literature, we explore the nuanced mechanisms through which microglial-T cell interactions modulate tumor growth and immune responses. Conclusions: Our analysis seeks to unravel the cellular communication pathways that potentially underpin tumor progression, with the ultimate goal of illuminating novel therapeutic strategies for brain cancer intervention.

Immunocompetent murine glioblastoma stem-like cell models exhibiting distinct phenotypes

Background

Glioblastoma (GBM) treatment is hindered by a dearth of representative mouse GBM preclinical models in immunocompetent mice. Here, we characterized 5 murine GBM stem-like cell (mGSC) models derived from lentivirus-induced tumors in transgenic mice that are driven by the activation of the Nf1-Ras signaling pathway and inactivation of Tp53.

Methods

MGSC lines (005, RIG, NF53, C1, and C3) were cultured as spheres in serum-free stem cell media. Whole exome sequencing (WES) was employed to quantify single nucleotide polymorphisms (SNPs). Stem cell properties were characterized by stemness in vitro and tumorigenicity after intracerebral implantation in C57BL/6 mice. Tumor phenotypes and the immune microenvironment were characterized by immunohistochemistry, flow cytometry, and RNA sequencing.

Results

WES revealed a large variation in coding sequence SNPs across mGSC lines (~20-fold), likely influenced by the mixed backgrounds of the parental mice. MGSCs exhibited variable clonogenic sphere formation and CD133 expression levels. In vivo, they consistently initiated lethal malignant gliomas, with median survival ranging from 29 to 82 days, and showed strong CD44 expression and variable invasiveness. The tumor microenvironment featured an abundance of CD68+ macrophages and uniform high PD-L1+ myeloid cells, while T-cell infiltration varied among the models, with low mutation burden C1 and C3 exhibiting fewer tumor-infiltrating T cells.

Conclusions

Upon orthotopic implantation in immunocompetent mice, mGSCs generate tumors characteristic of human GBM. Despite similar strategies to generate these mGSCs, they exhibited a range of phenotypes and immune profiles in mGSC-derived orthotopic tumors. These mGSCs provide new preclinical GBM models for developing GBM immunotherapies.

Endocannabinoid Receptor 2 Function is Associated with Tumor-Associated Macrophage Accumulation and Increases in T Cell Number to Initiate a Potent Antitumor Response in a Syngeneic Murine Model of Glioblastoma

Introduction: Glioblastoma patients have a highly immunosuppressive tumor microenvironment and systemic immunosuppression that comprise a major barrier to immune checkpoint therapy. Based on the production of endocannabinoids by glioblastomas, we explored involvement of endocannabinoid receptor 2 (CB2R), encoded by the CNR2 gene, which is predominantly expressed by immune cells, in glioblastoma-related immunosuppression. Materials & Methods: Bioinformatics of human glioblastoma databases was used to correlate enzymes involved in the synthesis and degradation of endocannabinoids, as well as CB2Rs, with patient overall survival. Intrastriatal administration of luciferase-expressing, murine GL261 glioblastoma cells was used to establish in in vivo glioblastoma model for characterization of tumor growth and intratumoral immune cell infiltration, as well as provide immune cells for in vitro co-culture experiments. Involvement of CB2Rs was determined by treatment with CB2R agonist (GW405833) or CB2R antagonist (AM630). ELISA, FACS, and immunocytochemistry were used to determine perforin, granzyme B, and surface marker levels. Results: Bioinformatics of human glioblastoma databases showed high expression of CB2R and elevated endocannabinoid production correlated with poorer prognosis, and involved immune-associated pathways. AM630treatment of GL261 glioblastoma-bearing mice induced a potent antitumor response, with survival plateauing at 50% on Day 40, when all control mice (median survival 28 days) and mice treated with GW405833 (median survival 21 days) had died. Luciferase tumor imaging revealed accelerated tumor growth by GW405833 treatment, but stable or regressing tumors in AM630-treated mice. Notably, in spleens, AM630 treatment caused an 83% decrease in monocytes/macrophages, and 1.8- and 1.6-fold increases in CD8+ and CD4+ cells, respectively. Within tumors, there was a corresponding decrease in tumor-associated macrophages (TAMs) and increase in CD8+ T cells. In vitro, lymphocytes from AM630-treated mice showed greater cytotoxic function (increased percentage of perforin- and granzyme B-positive CD8+ T cells). Discussion: These results suggest that inhibition of CB2R enhances both immunosuppressive TAM infiltration and systemic T-cell suppression through CB2R activation, and that inhibition of CB2Rs can potently counter both the immunosuppressive tumor microenvironment, as well as systemic immunosuppression in glioblastoma.

Tailoring glioblastoma treatment based on longitudinal analysis of post-surgical tumor microenvironment

Glioblastoma (GBM), an incurable primary brain tumor, typically requires surgical intervention followed by chemoradiation; however, recurrences remain fatal. Our previous work demonstrated that a nanomedicine hydrogel (GemC12-LNC) delays recurrence when administered post-surgery. However, tumor debulking also triggers time-dependent immune reactions that promote recurrence at the resection cavity borders. We hypothesized that combining the hydrogel with an immunomodulatory drug could enhance therapeutic outcomes. A thorough characterization of the post-surgical microenvironment (SMe) is crucial to guide combinatorial approaches.In this study, we performed cellular resolution imaging, flow cytometry and spatial hyperplexed immunofluorescence imaging to characterize the SMe in a syngeneic mouse model of tumor resection. Owing to our dynamic approach, we observed transient opening of the blood-brain barrier (BBB) during the first week after surgery. BBB permeability post-surgery was also confirmed in GBM patients. In our murine model, we also observed changes in immune cell morphology and spatial location post-surgery over time in resected animals as well as the accumulation of reactive microglia and anti-inflammatory macrophages in recurrences compared to unresected tumors since the first steps of recurrence growth. Therefore we investigated whether starting a systemic treatment with the SMAC mimetic small molecule (GDC-0152) directly after surgery would be beneficial for enhancing microglial anti-tumoral activity and decreasing the number of anti-inflammatory macrophages around the GemC12-LNC hydrogel-loaded tumor cavity. The immunomodulatory effects of this drug combination was firstly shown in patient-derived tumoroids. Its efficacy was confirmed in vivo by survival analysis and correlated with reversal of the immune profile as well as delayed tumor recurrence.This comprehensive study identified critical time frames and immune cellular targets within the SMe, aiding in the rational design of combination therapies to delay recurrence onset. Our findings suggest that post-surgical systemic injection of GDC-0152 in combination with GemC12-LNC local treatment is a promising and innovative approach for managing GBM recurrence, with potential for future translation to human patient.

Functional profiling of murine glioma models highlights targetable immune evasion phenotypes

Cancer-intrinsic immune evasion mechanisms and pleiotropy are a barrier to cancer immunotherapy. This is apparent in certain highly fatal cancers, including high-grade gliomas and glioblastomas (GBM). In this study, we evaluated two murine syngeneic glioma models (GL261 and CT2A) as preclinical models for human GBM using functional genetic screens, single-cell transcriptomics and machine learning approaches. Through CRISPR genome-wide co-culture killing screens with various immune cells (cytotoxic T cells, natural killer cells, and macrophages), we identified three key cancer-intrinsic evasion mechanisms: NFκB signaling, autophagy/endosome machinery, and chromatin remodeling. Additional fitness screens identified dependencies in murine gliomas that partially recapitulated those seen in human GBM (e.g., UFMylation). Our single-cell analyses showed that different glioma models exhibited distinct immune infiltration patterns and recapitulated key immune gene programs observed in human GBM, including hypoxia, interferon, and TNF signaling. Moreover, in vivo orthotopic tumor engraftment was associated with phenotypic shifts and changes in proliferative capacity, with murine tumors recapitulating the intratumoral heterogeneity observed in human GBM, exhibiting propensities for developmental- and mesenchymal-like phenotypes. Notably, we observed common transcription factors and cofactors shared with human GBM, including developmental (Nfia and Tcf4), mesenchymal (Prrx1 and Wwtr1), as well as cycling-associated genes (Bub3, Cenpa, Bard1, Brca1, and Mis18bp1). Perturbation of these genes led to reciprocal phenotypic shifts suggesting intrinsic feedback mechanisms that balance in vivo cellular states. Finally, we used a machine-learning approach to identify two distinct immune evasion gene programs, one of which represents a clinically-relevant phenotype and delineates a subpopulation of stem-like glioma cells that predict response to immune checkpoint inhibition in human patients. This comprehensive characterization helps bridge the gap between murine glioma models and human GBM, providing valuable insights for future therapeutic development.

An inducible RIPK3-driven necroptotic system enhances cancer cell-based immunotherapy and ensures safety

Recent progress in cancer cell-based therapies has led to effective targeting and robust immune responses against cancer. However, the inherent safety risks of using live cancer cells necessitate the creation of an optimized safety switch without hindering the efficacy of immunotherapy. The existing safety switches typically induce tolerogenic cell death, potentially leading to an immunosuppressive tumor immune microenvironment (TIME), which is counterproductive to the goals of immunotherapy. Here, we developed and characterized an inducible receptor-interacting protein kinase 3-driven (RIPK3-driven) necroptotic system that serves a dual function of safety switch as well as inducer of immunogenic cell death, which in turn stimulates antitumor immune responses. We show that activation of the RIPK3 safety switch triggered immunogenic responses marked by an increased release of ATP and damage-associated molecular patterns (DAMPs). Compared with other existing safety switches, incorporating the RIPK3 system inhibited tumor growth, improved survival outcomes in tumor-bearing mice, and fostered long-term antitumor immunity. Moreover, the RIPK3 system reinvigorated the TIME by promoting DC maturation, polarizing the macrophages toward a M1 phenotype, and reducing the exhaustion of CD4+ and CD8+ T lymphocytes. Our study highlights the dual role of the RIPK3-driven necroptotic system in improving the safety and efficacy of cancer cell-based therapy, with broader implications for cellular therapies.

In vivo mouse models for adult brain tumors: Exploring tumorigenesis and advancing immunotherapy development

Brain tumors, particularly glioblastoma (GBM), are devastating and challenging to treat, with a low 5-year survival rate of only 6.6%. Mouse models are established to understand tumorigenesis and develop new therapeutic strategies. Large-scale genomic studies have facilitated the identification of genetic alterations driving human brain tumor development and progression. Genetically engineered mouse models (GEMMs) with clinically relevant genetic alterations are widely used to investigate tumor origin. Additionally, syngeneic implantation models, utilizing cell lines derived from GEMMs or other sources, are popular for their consistent and relatively short latency period, addressing various brain cancer research questions. In recent years, the success of immunotherapy in specific cancer types has led to a surge in cancer immunology-related research which specifically necessitates the utilization of immunocompetent mouse models. In this review, we provide a comprehensive summary of GEMMs and syngeneic mouse models for adult brain tumors, emphasizing key features such as model origin, genetic alteration background, oncogenic mechanisms, and immune-related characteristics. Our review serves as a valuable resource for the brain tumor research community, aiding in the selection of appropriate models to study cancer immunology.

Probing the glioma micro-environment: Analysis using biopsy in combination with ultra-fast cyclic immunolabeling

The interaction between gliomas and the immune system is poorly understood and thus hindering development of effective immunotherapies for glioma patients. The immune response is highly variable during tumor development, and affected by therapies such as surgery, radiation, and chemotherapy. Currently, analysis of these local changes is difficult due to poor accessibility of the tumor and high-morbidity of sampling. In this study, we developed a model for repeat-biopsy in mice to study these local immunological changes over time. Using fine needle biopsy we were able to safely and repeatedly collect cells from intracranial tumors in mice. Ultra-fast cycling technology (FAST) was used for multi-cycle immunofluorescence of retrieved cells, and provided insights in the changing immune response over time. The combination of these techniques can be utilized to study changes in the immune response in glioma or other intracranial diseases over time, and in response to treatment within the same animal.

Vaccine-based immunotherapy and related preclinical models for glioma

Glioma, the most common primary malignant tumor in the central nervous system (CNS), lacks effective treatments, and >60% of cases are glioblastoma (GBM), the most aggressive form. Despite advances in immunotherapy, GBM remains highly resistant. Approaches that target tumor antigens expedite the development of immunotherapies, including personalized tumor-specific vaccines, patient-specific target selection, dendritic cell (DC) vaccines, and chimeric antigen receptor (CAR) and T cell receptor (TCR) T cells. Recent studies show promising results in treating GBM and lower-grade glioma (LGG), fostering hope for future immunotherapy. This review discusses tumor vaccines against glioma, preclinical models in immunological research, and the role of CD4+ T cells in vaccine-induced antitumor immunity. We also summarize clinical approaches, challenges, and future research for creating more effective vaccines.

Modifying Post-Surgical Immunity: Controlled Release of TLR7/8 Agonist for Immune Mediated Clearance of Glioblastoma

Glioblastoma is an aggressive brain cancer with a dismal prognosis despite current therapeutic interventions. Tumor resection is standard-of-care for glioblastoma and has profound immunostimulatory effects. Resulting in a nadir in tumor burden, resection offers a unique opportunity to break local immune tolerance and mount an effective anti-tumor immune response. Here, we explore the effect of local and controlled release of TLR7/8 agonist from a polymer scaffold implanted at the time of tumor resection. We find that sustained release of TLR7/8 agonist leads to clearance of residual post-resection tumor, improved survival, and subsequent protection from tumor challenge in mice bearing orthotopic GL261 or CT2A gliomas. We show that scaffold therapy boosts resection-mediated disruption to the tumor microenvironment, leading to an early inflammatory innate immune response both in the brain and cervical lymph node. This is followed by an influx of activated NK cells in the brain and effector T cells in the lymph node and brain. In sum, sustained local TLR7/8 agonism within the context of tumor resection is a promising approach for glioblastoma.

SMAC mimetic drives microglia phenotype and glioblastoma immune microenvironment

Tumor-associated macrophages/microglia (TAMs) are highly plastic and heterogeneous immune cells that can be immune-supportive or tumor-supportive depending of the microenvironment. TAMs are the most abundant immune cells in glioblastoma (GB), and play a key role in immunosuppression. Therefore, TAMs reprogramming toward immune-supportive cells is a promising strategy to overcome immunosuppression. By leveraging scRNAseq human GB databases, we identified that Inhibitor of Apoptosis Proteins (IAP) were expressed by TAMs. To investigate their role in TAMs-related immunosuppression, we antagonized IAP using the central nervous system permeant SMAC mimetic GDC-0152 (SMg). On explants and cultured immune cells isolated from human GB samples, SMg modified TAMs activity. We showed that SMg treatment promoted microglia pro-apoptotic and anti-tumoral function via caspase-3 pro-inflammatory cleavage and the inhibition of tumoroids growth. Then we designed a relevant immunogenic mouse GB model to decipher the spatio-temporal densities, distribution, phenotypes and function of TAMs with or without SMg treatment. We used 3D imaging techniques, a transgenic mouse with fluorescent TAM subsets and mass cytometry. We confirmed that SMg promoted microglia activation, antigen-presenting function and tumor infiltration. In addition, we observed a remodeling of blood vessels, a decrease in anti-inflammatory macrophages and an increased level of monocytes and their mo-DC progeny. This remodeling of the TAM landscape is associated with an increase in CD8 T cell density and activation. Altogether, these results demonstrated that SMg drives the immunosuppressive basal microglia toward an active phenotype with pro-apoptotic and anti-tumoral function and modifies the GB immune landscape. This identifies IAP as targets of choice for a potential mechanism-based therapeutic strategy and SMg as a promising molecule for this application.

Mutant IDH Modulates Suppressive Myeloid Populations in Malignant Glioma

PURPOSE

Mutations in the isocitrate dehydrogenase (IDH) genes IDH1 and IDH2 have critical diagnostic and prognostic significance in diffuse gliomas. Neomorphic mutant IDH activity has been previously implicated in T-cell suppression; however, the effects of IDH mutations on intratumoral myeloid populations remain underexplored. In this study, we investigate the influence of IDH status on the myeloid compartment using human glioma specimens and preclinical models.

EXPERIMENTAL DESIGN

We performed RNA sequencing and quantitative immunofluorescence on newly diagnosed, treatment-naive IDH-mutant grade 4 astrocytoma and IDH-wild-type (IDH-WT) glioblastoma (GBM) specimens. We also generated a syngeneic murine model, comparing transcriptomic and cell-level changes in paired isogenic glioma lines that differ only in IDH mutational status.

RESULTS

Among patient samples, IDH-mutant tumors displayed an underrepresentation of suppressive myeloid transcriptional signatures, which was confirmed at the cellular level with decreased numbers of intratumoral M2-like macrophages and myeloid-derived suppressor cells. Introduction of the mutant IDH enzyme into murine glioma was sufficient to recapitulate the transcriptomic and cellular shifts observed in patient samples.

CONCLUSIONS

We provide transcriptomic and cellular evidence that mutant IDH is associated with a quantitative reduction of suppressive myeloid cells in gliomas and that introduction of the mutant enzyme is sufficient to result in corresponding cellular changes using an in vivo preclinical model. These data advance our understanding of high-grade gliomas by identifying key myeloid cell populations that are reprogrammed by mutant IDH and may be targetable through therapeutic approaches.

Pre-Clinical Models for CAR T-Cell Therapy for Glioma

Immunotherapy represents a transformative shift in cancer treatment. Among myriad immune-based approaches, chimeric antigen receptor (CAR) T-cell therapy has shown promising results in treating hematological malignancies. Despite aggressive treatment options, the prognosis for patients with malignant brain tumors remains poor. Research leveraging CAR T-cell therapy for brain tumors has surged in recent years. Pre-clinical models are crucial in evaluating the safety and efficacy of these therapies before they advance to clinical trials. However, current models recapitulate the human tumor environment to varying degrees. Novel in vitro and in vivo techniques offer the opportunity to validate CAR T-cell therapies but also have limitations. By evaluating the strengths and weaknesses of various pre-clinical glioma models, this review aims to provide a roadmap for the development and pre-clinical testing of CAR T-cell therapies for brain tumors.

ATM Kinase Small Molecule Inhibitors Prevent Radiation-Induced Apoptosis of Mouse Neurons In Vivo

ATM kinase is becoming an important therapeutic target for tumor radiosensitization. Radiation is known to cause neuro-inflammation and neurodegeneration; however, the effects of small molecule ATM inhibitors (ATMi's) and radiation on normal tissue, including healthy brain, are largely unexplored. Therefore, we examined the mouse CNS after ATMi radiosensitization with a focus on the fate of neurons. We used several approaches to assess the effects on the DNA damage response (DDR) and apoptosis of neurons using immunostaining. In vivo, a significant decrease in viable neurons and increase in degenerating neurons and apoptosis was observed in mice treated with radiation alone. On the other hand, an ATMi alone had little to no effect on neuron viability and did not induce apoptosis. Importantly, the ATMi's did not further increase radiation toxicity. In fact, multiplex immunostaining showed that a clinical candidate ATMi (AZD1390) protected mouse neurons from apoptosis by 90% at 4 h after radiation. We speculate that the lack of toxicity to neurons is due to a normal ATM-p53 response that, if blocked transiently with an ATMi, is protective. Altogether, in line with previous work using ATM knockout mice, we provide evidence that ATM kinase inhibition using small molecules does not add to neuronal radiation toxicity, and might, in fact, protect them from radiation-induced apoptosis at least in the short term.

Classical Monocytes Shuttling for Precise Delivery of Nanotherapeutics to Glioblastoma

Glioblastoma (GBM) is the most aggressive brain tumor for which current therapies have limited efficacy. Immunosuppression and difficulties in accessing tumors with therapeutic agents are major obstacles for GBM treatments. Classical monocytes (CMs) possess the strongest infiltration among myeloid cells recruited into tumors during tumorigenesis. In this study, CMs are utilized to deliver the small-molecule CUDC-907 encapsulated in nanoparticles (907-NPs@CMs) for GBM therapy. Hitchhiking on CMs enables more 907-NPs to successfully penetrate the blood-brain barrier (BBB) and reach the interior of tumors. Results demonstrate that 907-NPs@CMs significantly improve the survival rates by suppressing tumor growth and reversing the immunosuppression of tumor microenvironment (TME). Furthermore, the high delivery efficiency of CMs reduces the amount of CUDC-907 required for treatments, reducing the physiological toxicity and off-target effects caused by high doses. 907-NPs@CMs is a safe and versatile therapeutic system that provides a platform for targeted drug delivery to tumors and the ability to treat GBM through a combination of chemotherapy and immunotherapy.

Probing the glioma micro-environment: analysis using biopsy in combination with ultra-fast cyclic immunolabeling

The interaction between gliomas and the immune system is poorly understood and thus hindering development of effective immunotherapies for glioma patients. The immune response is highly variable during tumor development, and affected by therapies such as surgery, radiation, and chemotherapy. Currently, analysis of these local changes is difficult due to poor accessibility of the tumor and high-morbidity of sampling. In this study, we developed a model for repeat-biopsy in mice to study these local immunological changes over time. Using fine needle biopsy we were able to safely and repeatedly collect cells from intracranial tumors in mice. Ultra-fast cycling technology (FAST) was used for multi-cycle immunofluorescence of retrieved cells, and provided insights in the changing immune response over time. The combination of these techniques can be utilized to study changes in the immune response in glioma or other intracranial diseases over time, and in response to treatment within the same animal.

Understanding the immunosuppressive microenvironment of glioma: mechanistic insights and clinical perspectives

Glioblastoma (GBM), the predominant and primary malignant intracranial tumor, poses a formidable challenge due to its immunosuppressive microenvironment, thereby confounding conventional therapeutic interventions. Despite the established treatment regimen comprising surgical intervention, radiotherapy, temozolomide administration, and the exploration of emerging modalities such as immunotherapy and integration of medicine and engineering technology therapy, the efficacy of these approaches remains constrained, resulting in suboptimal prognostic outcomes. In recent years, intensive scrutiny of the inhibitory and immunosuppressive milieu within GBM has underscored the significance of cellular constituents of the GBM microenvironment and their interactions with malignant cells and neurons. Novel immune and targeted therapy strategies have emerged, offering promising avenues for advancing GBM treatment. One pivotal mechanism orchestrating immunosuppression in GBM involves the aggregation of myeloid-derived suppressor cells (MDSCs), glioma-associated macrophage/microglia (GAM), and regulatory T cells (Tregs). Among these, MDSCs, though constituting a minority (4-8%) of CD45+ cells in GBM, play a central component in fostering immune evasion and propelling tumor progression, angiogenesis, invasion, and metastasis. MDSCs deploy intricate immunosuppressive mechanisms that adapt to the dynamic tumor microenvironment (TME). Understanding the interplay between GBM and MDSCs provides a compelling basis for therapeutic interventions. This review seeks to elucidate the immune regulatory mechanisms inherent in the GBM microenvironment, explore existing therapeutic targets, and consolidate recent insights into MDSC induction and their contribution to GBM immunosuppression. Additionally, the review comprehensively surveys ongoing clinical trials and potential treatment strategies, envisioning a future where targeting MDSCs could reshape the immune landscape of GBM. Through the synergistic integration of immunotherapy with other therapeutic modalities, this approach can establish a multidisciplinary, multi-target paradigm, ultimately improving the prognosis and quality of life in patients with GBM.

Orthotopic and metastatic tumour models in preclinical cancer research

Mouse models of disease play a pivotal role at all stages of cancer drug development. Cell-line derived subcutaneous tumour models are predominant in early drug discovery, but there is growing recognition of the importance of the more complex orthotopic and metastatic tumour models for understanding both target biology in the correct tissue context, and the impact of the tumour microenvironment and the immune system in responses to treatment. The aim of this review is to highlight the value that orthotopic and metastatic models bring to the study of tumour biology and drug development while pointing out those models that are most likely to be encountered in the literature. Important developments in orthotopic models, such as the increasing use of early passage patient material (PDXs, organoids) and humanised mouse models are discussed, as these approaches have the potential to increase the predictive value of preclinical studies, and ultimately improve the success rate of anticancer drugs in clinical trials.

Glioblastoma extracellular vesicles modulate immune PD-L1 expression in accessory macrophages upon radiotherapy

Glioblastoma (GBM) is the most aggressive brain tumor, presenting major challenges due to limited treatment options. Standard care includes radiation therapy (RT) to curb tumor growth and alleviate symptoms, but its impact on GBM is limited. In this study, we investigated the effect of RT on immune suppression and whether extracellular vesicles (EVs) originating from GBM and taken up by the tumor microenvironment (TME) contribute to the induced therapeutic resistance. We observed that (1) ionizing radiation increases immune-suppressive markers on GBM cells, (2) macrophages exacerbate immune suppression in the TME by increasing PD-L1 in response to EVs derived from GBM cells which is further modulated by RT, and (3) RT increases CD206-positive macrophages which have the most potential in inducing a pro-oncogenic environment due to their increased uptake of tumor-derived EVs. In conclusion, RT affects GBM resistance by immuno-modulating EVs taken up by myeloid cells in the TME.

Comprehensive analysis of disulfidptosis-related genes: a prognosis model construction and tumor microenvironment characterization in clear cell renal cell carcinoma

BACKGROUND

Disulfidptosis, a form of cell death induced by abnormal intracellular accumulation of disulfides, is a newly recognized variety of cell death. Clear cell renal cell carcinoma (ccRCC) is a usual urological tumor that poses serious health risks. There are few studies of disulfidptosis-related genes (DRGs) in ccRCC so far.

METHODS

The expression, transcriptional variants, and prognostic role of DRGs were assessed. Based on DRGs, consensus unsupervised clustering analysis was performed to stratify ccRCC patients into various subtypes and constructed a DRG risk scoring model. Patients were stratified into high or low-risk groups by this model. We focused on assessing the discrepancy in prognosis, TME, chemotherapeutic susceptibility, and landscape of immune between the two risk groups. Finally, we validated the expression and explored the biological function of the risk scoring gene FLRT3 through in vitro experiments.

RESULTS

The different subtypes had significantly different gene expression, immune, and prognostic landscapes. In the two risk groups, the high-risk group had higher TME scores, more significant immune cell infiltration, and a higher probability of benefiting from immunotherapy, but had a worse prognosis. There were also remarkable differences in chemotherapeutic susceptibility between the two risk groups. In ccRCC cells, the expression of FLRT3 was shown to be lower and its overexpression caused a decrease in cell proliferation and metastatic capacity.

CONCLUSIONS

Starting from disulfidptosis, we established a new risk scoring model which can provide new ideas for doctors to forecast patient survival and determine clinical treatment plans.

Establishment and immune phenotyping of patient-derived glioblastoma models in humanized mice

Glioblastoma (GBM) is the most aggressive and common type of malignant brain tumor diagnosed in adults. Preclinical immunocompetent mouse tumor models generated using mouse tumor cells play a pivotal role in testing the therapeutic efficacy of emerging immune-based therapies for GBMs. However, the clinical translatability of such studies is limited as mouse tumor lines do not fully recapitulate GBMs seen in inpatient settings. In this study, we generated three distinct, imageable human-GBM (hGBM) models in humanized mice using patient-derived GBM cells that cover phenotypic and genetic GBM heterogeneity in primary (invasive and nodular) and recurrent tumors. We developed a pipeline to first enrich the tumor-initiating stem-like cells and then successfully established robust patient-derived GBM tumor engraftment and growth in bone marrow-liver-thymus (BLT) humanized mice. Multiplex immunofluorescence of GBM tumor sections revealed distinct phenotypic features of the patient GBM tumors, with myeloid cells dominating the immune landscape. Utilizing flow cytometry and correlative immunofluorescence, we profiled the immune microenvironment within the established human GBM tumors in the BLT mouse models and showed tumor infiltration of variable human immune cells, creating a unique immune landscape compared with lymphoid organs. These findings contribute substantially to our understanding of GBM biology within the context of the human immune system in humanized mice and lay the groundwork for further translational studies aimed at advancing therapeutic strategies for GBM.

Understanding current experimental models of glioblastoma-brain microenvironment interactions

Glioblastoma (GBM) is a common and devastating primary brain tumor, with median survival of 16-18 months after diagnosis in the setting of substantial resistance to standard-of-care and inevitable tumor recurrence. Recent work has implicated the brain microenvironment as being critical for GBM proliferation, invasion, and resistance to treatment. GBM does not operate in isolation, with neurons, astrocytes, and multiple immune populations being implicated in GBM tumor progression and invasiveness. The goal of this review article is to provide an overview of the available in vitro, ex vivo, and in vivo experimental models for assessing GBM-brain interactions, as well as discuss each model's relative strengths and limitations. Current in vitro models discussed will include 2D and 3D co-culture platforms with various cells of the brain microenvironment, as well as spheroids, whole organoids, and models of fluid dynamics, such as interstitial flow. An overview of in vitro and ex vivo organotypic GBM brain slices is also provided. Finally, we conclude with a discussion of the various in vivo rodent models of GBM, including xenografts, syngeneic grafts, and genetically-engineered models of GBM.

Antigen presentation deficiency, mesenchymal differentiation, and resistance to immunotherapy in the murine syngeneic CT2A tumor model

Background

The GL261 and CT2A syngeneic tumor lines are frequently used as immunocompetent orthotopic mouse models of human glioblastoma (huGBM) but demonstrate distinct differences in their responses to immunotherapy.

Methods

To decipher the cell-intrinsic mechanisms that drive immunotherapy resistance in CT2A-luc and to define the aspects of human cancer biology that these lines can best model, we systematically compared their characteristics using whole exome and transcriptome sequencing, and protein analysis through immunohistochemistry, Western blot, flow cytometry, immunopeptidomics, and phosphopeptidomics.

Results

The transcriptional profiles of GL261-luc2 and CT2A-luc tumors resembled those of some huGBMs, despite neither line sharing the essential genetic or histologic features of huGBM. Both models exhibited striking hypermutation, with clonal hotspot mutations in RAS genes (Kras p.G12C in GL261-luc2 and Nras p.Q61L in CT2A-luc). CT2A-luc distinctly displayed mesenchymal differentiation, upregulated angiogenesis, and multiple defects in antigen presentation machinery (e.g. Tap1 p.Y488C and Psmb8 p.A275P mutations) and interferon response pathways (e.g. copy number losses of loci including IFN genes and reduced phosphorylation of JAK/STAT pathway members). The defect in MHC class I expression could be overcome in CT2A-luc by interferon-γ treatment, which may underlie the modest efficacy of some immunotherapy combinations. Additionally, CT2A-luc demonstrated substantial baseline secretion of the CCL-2, CCL-5, and CCL-22 chemokines, which play important roles as myeloid chemoattractants.

Conclusion

Although the clinical contexts that can be modeled by GL261 and CT2A for huGBM are limited, CT2A may be an informative model of immunotherapy resistance due to its deficits in antigen presentation machinery and interferon response pathways.

Wnt inhibition alleviates resistance to immune checkpoint blockade in glioblastoma

Wnt signaling plays a critical role in the progression and treatment outcome of glioblastoma (GBM). Here, we identified WNT7b as a heretofore unknown mechanism of resistance to immune checkpoint inhibition (αPD1) in GBM patients and murine models. Acquired resistance to αPD1 was found to be associated with the upregulation of Wnt7b and β-catenin protein levels in GBM in patients and in a clinically relevant, stem-rich GBM model. Combining the porcupine inhibitor WNT974 with αPD1 prolonged the survival of GBM-bearing mice. However, this combination had a dichotomous response, with a subset of tumors showing refractoriness. WNT974 and αPD1 expanded a subset of DC3-like dendritic cells (DCs) and decreased the granulocytic myeloid-derived suppressor cells (gMDSCs) in the tumor microenvironment (TME). By contrast, monocytic MDSCs (mMDSCs) increased, while T-cell infiltration remained unchanged, suggesting potential TME-mediated resistance. Our preclinical findings warrant the testing of Wnt7b/β-catenin combined with αPD1 in GBM patients with elevated Wnt7b/β-catenin signaling.

CXCL10 and Nrf2-upregulated mesenchymal stem cells reinvigorate T lymphocytes for combating glioblastoma

BACKGROUND

Lack of tumor-infiltrating T lymphocytes and concurrent T-cell dysfunction have been identified as major contributors to glioblastoma (GBM) immunotherapy resistance. Upregulating CXCL10 in the tumor microenvironment (TME) is a promising immunotherapeutic approach that potentially increases tumor-infiltrating T cells and boosts T-cell activity but is lacking effective delivery methods.

METHODS

In this study, mesenchymal stem cells (MSCs) were transduced with a recombinant lentivirus encoding Cxcl10, Nrf2 (an anti-apoptosis gene), and a ferritin heavy chain (Fth) reporter gene in order to increase their CXCL10 secretion, TME survival, and MRI visibility. Using FTH-MRI guidance, these cells were injected into the tumor periphery of orthotopic GL261 and CT2A GBMs in mice. Combination therapy consisting of CXCL10-Nrf2-FTH-MSC transplantation together with immune checkpoint blockade (ICB) was also performed for CT2A GBMs. Thereafter, in vivo and serial MRI, survival analysis, and histology examinations were conducted to assess the treatments' efficacy and mechanism.

RESULTS

CXCL10-Nrf2-FTH-MSCs exhibit enhanced T lymphocyte recruitment, oxidative stress tolerance, and iron accumulation. Under in vivo FTH-MRI guidance and monitoring, peritumoral transplantation of CXCL10-Nrf2-FTH-MSCs remarkably inhibited orthotopic GL261 and CT2A tumor growth in C57BL6 mice and prolonged animal survival. While ICB alone demonstrated no therapeutic impact, CXCL10-Nrf2-FTH-MSC transplantation combined with ICB demonstrated an enhanced anticancer effect for CT2A GBMs compared with transplanting it alone. Histology revealed that peritumorally injected CXCL10-Nrf2-FTH-MSCs survived longer in the TME, increased CXCL10 production, and ultimately remodeled the TME by increasing CD8+ T cells, interferon-γ+ cytotoxic T lymphocytes (CTLs), GzmB+ CTLs, and Th1 cells while reducing regulatory T cells (Tregs), exhausted CD8+ and exhausted CD4+ T cells.

CONCLUSIONS

MRI-guided peritumoral administration of CXCL10 and Nrf2-overexpressed MSCs can significantly limit GBM growth by revitalizing T lymphocytes within TME. The combination application of CXCL10-Nrf2-FTH-MSC transplantation and ICB therapy presents a potentially effective approach to treating GBM.

Uniting innate and adaptive immunity in glioblastoma; an α-CTLA-4 quest

Immunotherapies have thus far led to disappointing outcomes in patients suffering from glioblastoma. Published in Immunity, Chen et al.'s recent study shows the therapeutic potential of an αCTLA-4 antibody (Ab), specifically in murine mesenchymal-like glioblastoma. αCTLA-4 Ab efficacy relied on the distinctive cooperation between CD4+ Th1 T cells and microglia, unleashing a potent antitumor response.

Preclinical Models and Technologies in Glioblastoma Research: Evolution, Current State, and Future Avenues

Glioblastoma is the most common malignant primary central nervous system tumor and one of the most debilitating cancers. The prognosis of patients with glioblastoma remains poor, and the management of this tumor, both in its primary and recurrent forms, remains suboptimal. Despite the tremendous efforts that are being put forward by the research community to discover novel efficacious therapeutic agents and modalities, no major paradigm shifts have been established in the field in the last decade. However, this does not mirror the abundance of relevant findings and discoveries made in preclinical glioblastoma research. Hence, developing and utilizing appropriate preclinical models that faithfully recapitulate the characteristics and behavior of human glioblastoma is of utmost importance. Herein, we offer a holistic picture of the evolution of preclinical models of glioblastoma. We further elaborate on the commonly used in vitro and vivo models, delving into their development, favorable characteristics, shortcomings, and areas of potential improvement, which aids researchers in designing future experiments and utilizing the most suitable models. Additionally, this review explores progress in the fields of humanized and immunotolerant mouse models, genetically engineered animal models, 3D in vitro models, and microfluidics and highlights promising avenues for the future of preclinical glioblastoma research.

Single-nucleus RNA sequencing reveals heterogenous microenvironments and specific drug response between cervical squamous cell carcinoma and adenocarcinoma

BACKGROUND

Cervical squamous cell carcinoma (CSCC) and adenocarcinoma (CAde) are two major pathological types of cervical cancer (CC), but their high-resolution heterogeneity of tumor and immune microenvironment remains elusive.

METHODS

Here, we performed single-nucleus RNA sequencing (snRNA-seq) from five CSCC and three CAde samples, and systematically outlined their specific transcriptome atlas.

FINDINGS

We found CD8+ T cells in CSCC were more cytotoxic but lower exhausted compared to those in CAde, and phagocytic MRC1+ macrophages were specifically enriched in CSCC. Interestingly, we discovered that pro-tumoral cancer-associated myofibroblasts (myoCAFs) and cancer-associated vascular-fibroblasts (vCAFs) were more abundant in CSCC, and further verified their pro-metastatic roles in vitro. Furthermore, we also identified some specific chemotherapy drugs for CSCC (Dasatinib and Doramapimod) and CAde (Pyrimethamine and Lapatinib) by revealing their heterogeneity in transcriptomic profiles of malignant epithelial cells, and further verified their specific sensitivity in cell lines and constructed CC-derived organoids. Cell-cell communication networks revealed that the pathways of NRG1-ERBB2, and FN1-ITAG3 were specific for CAde and CSCC, respectively, which may partly explain the specificities of identified chemotherapy drugs.

INTERPRETATION

Our study described the immune heterogeneity and specific cellular interactions between CSCC and CAde, which could provide insights for uncovering pathogenesis and designing personalized treatment.

FUNDINGS

National Key R&D Program of China (2021YFC2701201), National Natural Science Foundation of China (82072895, 82141106, 82103134, 81903114).

Deciphering sources of PET signals in the tumor microenvironment of glioblastoma at cellular resolution

Various cellular sources hamper interpretation of positron emission tomography (PET) biomarkers in the tumor microenvironment (TME). We developed an approach of immunomagnetic cell sorting after in vivo radiotracer injection (scRadiotracing) with three-dimensional (3D) histology to dissect the cellular allocation of PET signals in the TME. In mice with implanted glioblastoma, translocator protein (TSPO) radiotracer uptake per tumor cell was higher compared to tumor-associated microglia/macrophages (TAMs), validated by protein levels. Translation of in vitro scRadiotracing to patients with glioma immediately after tumor resection confirmed higher single-cell TSPO tracer uptake of tumor cells compared to immune cells. Across species, cellular radiotracer uptake explained the heterogeneity of individual TSPO-PET signals. In consideration of cellular tracer uptake and cell type abundance, tumor cells were the main contributor to TSPO enrichment in glioblastoma; however, proteomics identified potential PET targets highly specific for TAMs. Combining cellular tracer uptake measures with 3D histology facilitates precise allocation of PET signals and serves to validate emerging novel TAM-specific radioligands.

Of mice and lymphoid aggregates: modeling tertiary lymphoid structures in cancer

Tertiary lymphoid structures (TLS) are lymph node-like aggregates that can form in association with chronic inflammation or cancer. Mature TLS are organized into B and T cell zones, and are not encapsulated but include all cell types necessary for eliciting an adaptive immune response. TLS have been observed in various cancer types and are generally associated with a positive prognosis as well as increased sensitivity to cancer immunotherapy. However, a comprehensive understanding of the roles of TLS in eliciting anti-tumor immunity as well as the mechanisms involved in their formation and function is still lacking. Further studies in orthotopic, immunocompetent cancer models are necessary to evaluate the influence of TLS on cancer therapies, and to develop new treatments that promote their formation in cancer. Here, we review key insights obtained from functional murine studies, discuss appropriate models that can be used to study cancer-associated TLS, and suggest guidelines on how to identify TLS and distinguish them from other antigen-presenting niches.

Successes and challenges in modeling heterogeneous BRAFV600E mutated central nervous system neoplasms

Central nervous system (CNS) neoplasms are difficult to treat due to their sensitive location. Over the past two decades, the availability of patient tumor materials facilitated large scale genomic and epigenomic profiling studies, which have resulted in detailed insights into the molecular underpinnings of CNS tumorigenesis. Based on results from these studies, CNS tumors have high molecular and cellular intra-tumoral and inter-tumoral heterogeneity. CNS cancer models have yet to reflect the broad diversity of CNS tumors and patients and the lack of such faithful cancer models represents a major bottleneck to urgently needed innovations in CNS cancer treatment. Pediatric cancer model development is lagging behind adult tumor model development, which is why we focus this review on CNS tumors mutated for BRAFV600E which are more prevalent in the pediatric patient population. BRAFV600E-mutated CNS tumors exhibit high inter-tumoral heterogeneity, encompassing clinically and histopathological diverse tumor types. Moreover, BRAFV600E is the second most common alteration in pediatric low-grade CNS tumors, and low-grade tumors are notoriously difficult to recapitulate in vitro and in vivo. Although the mutation predominates in low-grade CNS tumors, when combined with other mutations, most commonly CDKN2A deletion, BRAFV600E-mutated CNS tumors are prone to develop high-grade features, and therefore BRAFV600E-mutated CNS are a paradigm for tumor progression. Here, we describe existing in vitro and in vivo models of BRAFV600E-mutated CNS tumors, including patient-derived cell lines, patient-derived xenografts, syngeneic models, and genetically engineered mouse models, along with their advantages and shortcomings. We discuss which research gaps each model might be best suited to answer, and identify those areas in model development that need to be strengthened further. We highlight areas of potential research focus that will lead to the heightened predictive capacity of preclinical studies, allow for appropriate validation, and ultimately improve the success of "bench to bedside" translational research.

CTLA-4 blockade induces a microglia-Th1 cell partnership that stimulates microglia phagocytosis and anti-tumor function in glioblastoma

The limited efficacy of immunotherapies against glioblastoma underscores the urgency of better understanding immunity in the central nervous system. We found that treatment with αCTLA-4, but not αPD-1, prolonged survival in a mouse model of mesenchymal-like glioblastoma. This effect was lost upon the depletion of CD4+ T cells but not CD8+ T cells. αCTLA-4 treatment increased frequencies of intratumoral IFNγ-producing CD4+ T cells, and IFNγ blockade negated the therapeutic impact of αCTLA-4. The anti-tumor activity of CD4+ T cells did not require tumor-intrinsic MHC-II expression but rather required conventional dendritic cells as well as MHC-II expression on microglia. CD4+ T cells interacted directly with microglia, promoting IFNγ-dependent microglia activation and phagocytosis via the AXL/MER tyrosine kinase receptors, which were necessary for tumor suppression. Thus, αCTLA-4 blockade in mesenchymal-like glioblastoma promotes a CD4+ T cell-microglia circuit wherein IFNγ triggers microglia activation and phagocytosis and microglia in turn act as antigen-presenting cells fueling the CD4+ T cell response.

Targeting the Siglec-sialic acid axis promotes antitumor immune responses in preclinical models of glioblastoma

Glioblastoma (GBM) is the most aggressive form of primary brain tumor, for which effective therapies are urgently needed. Cancer cells are capable of evading clearance by phagocytes such as microglia- and monocyte-derived cells through engaging tolerogenic programs. Here, we found that high expression of sialic acid-binding immunoglobulin-like lectin 9 (Siglec-9) correlates with reduced survival in patients with GBM. Using microglia- and monocyte-derived cell-specific knockouts of Siglec-E, the murine functional homolog of Siglec-9, together with single-cell RNA sequencing, we demonstrated that Siglec-E inhibits phagocytosis by these cells, thereby promoting immune evasion. Loss of Siglec-E on monocyte-derived cells further enhanced antigen cross-presentation and production of pro-inflammatory cytokines, which resulted in more efficient T cell priming. This bridging of innate and adaptive responses delayed tumor growth and resulted in prolonged survival in murine models of GBM. Furthermore, we showed the combinatorial activity of Siglec-E blockade and other immunotherapies demonstrating the potential for targeting Siglec-9 as a treatment for patients with GBM.

Translational Models in Glioma Immunotherapy Research

Immunotherapy is a promising therapeutic domain for the treatment of gliomas. However, clinical trials of various immunotherapeutic modalities have not yielded significant improvements in patient survival. Preclinical models for glioma research should faithfully represent clinically observed features regarding glioma behavior, mutational load, tumor interactions with stromal cells, and immunosuppressive mechanisms. In this review, we dive into the common preclinical models used in glioma immunology, discuss their advantages and disadvantages, and highlight examples of their utilization in translational research.

Anti-PD-1 and Extended Half-life IL2 Synergize for Treatment of Murine Glioblastoma Independent of Host MHC Class I Expression

Glioblastoma (GBM) is the most common malignant brain tumor in adults, responsible for approximately 225,000 deaths per year. Despite preclinical successes, most interventions have failed to extend patient survival by more than a few months. Treatment with anti-programmed cell death protein 1 (anti-PD-1) immune checkpoint blockade (ICB) monotherapy has been beneficial for malignant tumors such as melanoma and lung cancers but has yet to be effectively employed in GBM. This study aimed to determine whether supplementing anti-PD-1 ICB with engineered extended half-life IL2, a potent lymphoproliferative cytokine, could improve outcomes. This combination therapy, subsequently referred to as enhanced checkpoint blockade (ECB), delivered intraperitoneally, reliably cures approximately 50% of C57BL/6 mice bearing orthotopic GL261 gliomas and extends median survival of the treated cohort. In the CT2A model, characterized as being resistant to CBI, ECB caused a decrease in CT2A tumor volume in half of measured animals similar to what was observed in GL261-bearing mice, promoting a trending survival increase. ECB generates robust immunologic responses, features of which include secondary lymphoid organ enlargement and increased activation status of both CD4 and CD8 T cells. This immunity is durable, with long-term ECB survivors able to resist GL261 rechallenge. Through employment of depletion strategies, ECB's efficacy was shown to be independent of host MHC class I-restricted antigen presentation but reliant on CD4 T cells. These results demonstrate ECB is efficacious against the GL261 glioma model through an MHC class I-independent mechanism and supporting further investigation into IL2-supplemented ICB therapies for tumors of the central nervous system.

Oncolytic herpes simplex viruses for the treatment of glioma and targeting glioblastoma stem-like cells

Glioblastoma (GBM) is one of the most lethal cancers, having a poor prognosis and a median survival of only about 15 months with standard treatment (surgery, radiation, and chemotherapy), which has not been significantly extended in decades. GBM demonstrates remarkable cellular heterogeneity, with glioblastoma stem-like cells (GSCs) at the apex. GSCs are a subpopulation of GBM cells that possess the ability to self-renew, differentiate, initiate tumor formation, and manipulate the tumor microenvironment (TME). GSCs are no longer considered a static population of cells with specific markers but are quite flexible phenotypically and in driving tumor heterogeneity and therapeutic resistance. In light of these features, they are a critical target for successful GBM therapy. Oncolytic viruses, in particular oncolytic herpes simplex viruses (oHSVs), have many attributes for therapy and are promising agents to target GSCs. oHSVs are genetically-engineered to selectively replicate in and kill cancer cells, including GSCs, but not normal cells. Moreover, oHSV can induce anti-tumor immune responses and synergize with other therapies, such as chemotherapy, DNA repair inhibitors, and immune checkpoint inhibitors, to potentiate treatment effects and reduce GSC populations that are partly responsible for chemo- and radio-resistance. Herein, we present an overview of GSCs, activity of different oHSVs, clinical trial results, and combination strategies to enhance efficacy, including therapeutic arming of oHSV. Throughout, the therapeutic focus will be on GSCs and studies specifically targeting these cells. Recent clinical trials and approval of oHSV G47Δ in Japan for patients with recurrent glioma demonstrate the efficacy and promise of oHSV therapy.

PPRX-1701, a nanoparticle formulation of 6'-bromoindirubin acetoxime, improves delivery and shows efficacy in preclinical GBM models

Derivatives of the Chinese traditional medicine indirubin have shown potential for the treatment of cancer through a range of mechanisms. This study investigates the impact of 6'-bromoindirubin-3'-acetoxime (BiA) on immunosuppressive mechanisms in glioblastoma (GBM) and evaluates the efficacy of a BiA nanoparticle formulation, PPRX-1701, in immunocompetent mouse GBM models. Transcriptomic studies reveal that BiA downregulates immune-related genes, including indoleamine 2,3-dioxygenase 1 (IDO1), a critical enzyme in the tryptophan-kynurenine-aryl hydrocarbon receptor (Trp-Kyn-AhR) immunosuppressive pathway in tumor cells. BiA blocks interferon-γ (IFNγ)-induced IDO1 protein expression in vitro and enhances T cell-mediated tumor cell killing in GBM stem-like cell co-culture models. PPRX-1701 reaches intracranial murine GBM and significantly improves survival in immunocompetent GBM models in vivo. Our results indicate that BiA improves survival in murine GBM models via effects on important immunotherapeutic targets in GBM and that it can be delivered efficiently via PPRX-1701, a nanoparticle injectable formulation of BiA.

Piperlongumine conquers temozolomide chemoradiotherapy resistance to achieve immune cure in refractory glioblastoma via boosting oxidative stress-inflamation-CD8+-T cell immunity

BACKGROUND

The failure of novel therapies effective in preclinical animal models largely reflects the fact that current models do not really mimic the pathological/therapeutic features of glioblastoma (GBM), in which the most effective temozolomide chemoradiotherapy (RT/TMZ) regimen can only slightly extend survival. How to improve RT/TMZ efficacy remains a major challenge in clinic.

METHODS

Syngeneic G422^TN-GBM model mice were subject to RT/TMZ, surgery, piperlongumine (PL), αPD1, glutathione. Metabolomics or transcriptomics data from G422^TN-GBM and human GBM were used for gene enrichment analysis and estimation of ROS generation/scavenging balance, oxidative stress damage, inflammation and immune cell infiltration. Overall survival, bioluminescent imaging, immunohistochemistry, and immunofluorescence staining were used to examine therapeutic efficacy and mechanisms of action.

RESULTS

Here we identified that glutathione metabolism was most significantly altered in metabolomics analysis upon RT/TMZ therapies in a truly refractory and reliable mouse triple-negative GBM (G422^TN) preclinical model. Consistently, ROS generators/scavengers were highly dysregulated in both G422^TN-tumor and human GBM. The ROS-inducer PL synergized surgery/TMZ, surgery/RT/TMZ or RT/TMZ to achieve long-term survival (LTS) in G422^TN-mice, but only one LTS-mouse from RT/TMZ/PL therapy passed the rechallenging phase (immune cure). Furthermore, the immunotherapy of RT/TMZ/PL plus anti-PD-1 antibody (αPD1) doubled LTS (50%) and immune-cured (25%) mice. Glutathione completely abolished PL-synergistic effects. Mechanistically, ROS reduction was associated with RT/TMZ-resistance. PL restored ROS level (mainly via reversing Duox2/Gpx2), activated oxidative stress/inflammation/immune responses signature genes, reduced cancer cell proliferation/invasion, increased apoptosis and CD3⁺/CD4⁺/CD8⁺ T-lymphocytes in G422^TN-tumor on the basis of RT/TMZ regimen.

CONCLUSION

Our findings demonstrate that PL reverses RT/TMZ-reduced ROS and synergistically resets tumor microenvironment to cure GBM. RT/TMZ/PL or RT/TMZ/PL/αPD1 exacts effective immune cure in refractory GBM, deserving a priority for clinical trials.

Tailoring vascular phenotype through AAV therapy promotes anti-tumor immunity in glioma

Glioblastomas are aggressive brain tumors that are largely immunotherapy resistant. This is associated with immunosuppression and a dysfunctional tumor vasculature, which hinder T cell infiltration. LIGHT/TNFSF14 can induce high endothelial venules (HEVs) and tertiary lymphoid structures (TLS), suggesting that its therapeutic expression could promote T cell recruitment. Here, we use a brain endothelial cell-targeted adeno-associated viral (AAV) vector to express LIGHT in the glioma vasculature (AAV-LIGHT). We found that systemic AAV-LIGHT treatment induces tumor-associated HEVs and T cell-rich TLS, prolonging survival in αPD-1-resistant murine glioma. AAV-LIGHT treatment reduces T cell exhaustion and promotes TCF1⁺CD8⁺ stem-like T cells, which reside in TLS and intratumoral antigen-presenting niches. Tumor regression upon AAV-LIGHT therapy correlates with tumor-specific cytotoxic/memory T cell responses. Our work reveals that altering vascular phenotype through vessel-targeted expression of LIGHT promotes efficient anti-tumor T cell responses and prolongs survival in glioma. These findings have broader implications for treatment of other immunotherapy-resistant cancers.