Mitochondrial electron transport chain is necessary for NLRP3 inflammasome activation.

The NLRP3 inflammasome is linked to sterile and pathogen-dependent inflammation, and its dysregulation underlies many chronic diseases. Mitochondria have been implicated as regulators of the NLRP3 inflammasome through several mechanisms including generation of mitochondrial reactive oxygen species (ROS). Here, we report that mitochondrial electron transport chain (ETC) complex I, II, III and V inhibitors all prevent NLRP3 inflammasome activation. Ectopic expression of Saccharomyces cerevisiae NADH dehydrogenase (NDI1) or Ciona intestinalis alternative oxidase, which can complement the functional loss of mitochondrial complex I or III, respectively, without generation of ROS, rescued NLRP3 inflammasome activation in the absence of endogenous mitochondrial complex I or complex III function. Metabolomics revealed phosphocreatine (PCr), which can sustain ATP levels, as a common metabolite that is diminished by mitochondrial ETC inhibitors. PCr depletion decreased ATP levels and NLRP3 inflammasome activation. Thus, the mitochondrial ETC sustains NLRP3 inflammasome activation through PCr-dependent generation of ATP, but via a ROS-independent mechanism.

Combination of tucatinib and neural stem cells secreting anti-HER2 antibody prolongs survival of mice with metastatic brain cancer.

Brain metastases are a leading cause of death in patients with breast cancer. The lack of clinical trials and the presence of the blood-brain barrier limit therapeutic options. Furthermore, overexpression of the human epidermal growth factor receptor 2 (HER2) increases the incidence of breast cancer brain metastases (BCBM). HER2-targeting agents, such as the monoclonal antibodies trastuzumab and pertuzumab, improved outcomes in patients with breast cancer and extracranial metastases. However, continued BCBM progression in breast cancer patients highlighted the need for novel and effective targeted therapies against intracranial metastases. In this study, we engineered the highly migratory and brain tumor tropic human neural stem cells (NSCs) LM008 to continuously secrete high amounts of functional, stable, full-length antibodies against HER2 (anti-HER2Ab) without compromising the stemness of LM008 cells. The secreted anti-HER2Ab impaired tumor cell proliferation in vitro in HER2+ BCBM cells by inhibiting the PI3K-Akt signaling pathway and resulted in a significant benefit when injected in intracranial xenograft models. In addition, dual HER2 blockade using anti-HER2Ab LM008 NSCs and the tyrosine kinase inhibitor tucatinib significantly improved the survival of mice in a clinically relevant model of multiple HER2+ BCBM. These findings provide compelling evidence for the use of HER2Ab-secreting LM008 NSCs in combination with tucatinib as a promising therapeutic regimen for patients with HER2+ BCBM.

Repurposing autophagy regulators in brain tumors.

Malignant brain tumors, such as glioblastoma multiforme (GBM) and brain metastases, continue to be an unmet medical challenge. Despite advances in cancer diagnostics and therapeutics, tumor cell colonization in the central nervous system renders most treatment options ineffective. This is primarily due to the selective permeability of the blood-brain barrier (BBB), which hinders the crossing of targeting agents into the brain. As such, repositioning medications that demonstrate anticancer effects and possess the ability to cross the BBB can be a promising option. Antidepressants, which are BBB-permeable, have been reported to exhibit cytotoxicity against tumor cells. Autophagy, specifically, has been identified as one of the common key mediators of antidepressant's antitumor effects. In this work, we provide a comprehensive overview of US Food and Drug Administration (FDA)-approved antidepressants with reported cytotoxic activities in different tumor models, where autophagy dysregulation was demonstrated to play the main part. As such, imipramine, maprotiline, fluoxetine and escitalopram were shown to induce autophagy, whereas nortriptyline, clomipramine and paroxetine were identified as autophagy inhibitors. Sertraline and desipramine, depending on the neoplastic context, were demonstrated to either induce or inhibit autophagy. Collectively, these medications were associated with favorable therapeutic outcomes in a variety of cancer cell models, including brain tumors.

Therapeutic targeting of tumor-associated myeloid cells synergizes with radiation therapy for glioblastoma.

Tumor-associated myeloid cells (TAMCs) are key drivers of immunosuppression in the tumor microenvironment, which profoundly impedes the clinical response to immune-dependent and conventional therapeutic modalities. As a hallmark of glioblastoma (GBM), TAMCs are massively recruited to reach up to 50% of the brain tumor mass. Therefore, they have recently been recognized as an appealing therapeutic target to blunt immunosuppression in GBM with the hope of maximizing the clinical outcome of antitumor therapies. Here we report a nano-immunotherapy approach capable of actively targeting TAMCs in vivo. As we found that programmed death-ligand 1 (PD-L1) is highly expressed on glioma-associated TAMCs, we rationally designed a lipid nanoparticle (LNP) formulation surface-functionalized with an anti-PD-L1 therapeutic antibody (αPD-L1). We demonstrated that this system (αPD-L1-LNP) enabled effective and specific delivery of therapeutic payload to TAMCs. Specifically, encapsulation of dinaciclib, a cyclin-dependent kinase inhibitor, into PD-L1-targeted LNPs led to a robust depletion of TAMCs and an attenuation of their immunosuppressive functions. Importantly, the delivery efficiency of PD-L1-targeted LNPs was robustly enhanced in the context of radiation therapy (RT) owing to the RT-induced up-regulation of PD-L1 on glioma-infiltrating TAMCs. Accordingly, RT combined with our nano-immunotherapy led to dramatically extended survival of mice in 2 syngeneic glioma models, GL261 and CT2A. The high targeting efficiency of αPD-L1-LNP to human TAMCs from GBM patients further validated the clinical relevance. Thus, this study establishes a therapeutic approach with immense potential to improve the clinical response in the treatment of GBM and warrants a rapid translation into clinical practice.

Landscape of combination therapy trials in breast cancer brain metastasis.

Combination therapy has become a cornerstone in cancer treatment to potentiate therapeutic effectiveness and overcome drug resistance and metastasis. In this work, we explore combination trials in breast cancer brain metastasis (BCBM), highlighting deficiencies in trial design and underlining promising combination strategies. On October 31, 2019, we examined ClinicalTrials.gov for interventional and therapeutic clinical trials involving combination therapy for BCBM, without limiting for date or location. Information on trial characteristics was collected. Combination therapies used in trials were analyzed and explored in line with evidence from the medical literature. Sixty-five combination therapy trials were selected (n = 65), constituting less than 0.7% of all breast cancer trials. Most trials (62%) combined ≥2 chemotherapeutic agents. Chemotherapy with radiation was main-stay in 23% of trials. Trastuzumab was mostly used in combination (31%), followed by lapatinib (20%) and capecitabine (15%). Common strategies involved combining tyrosine kinase inhibitors with thymidylate synthase inhibitors (6 trials), dual HER-dimerization inhibitors (3 trials), microtubule inhibitors and tyrosine kinase inhibitors (3 trials), and HER-dimerization inhibitors and tyrosine kinase inhibitors (3 trials). The combination of tucatinib and capecitabine yielded the highest objective response rate (83%) in early phase trials. The triple combination of trastuzumab, tucatinib and capecitabine lowered the risk of disease progression or death by 52% in patients with HER2-positive BCBM. Combining therapeutic agents based on biological mechanisms is necessary to increase the effectiveness of available anti-cancer regimens. Significant survival benefit has yet to be achieved in future combination therapy trials. Enhancing drug delivery through blood-brain barrier permeable agents may potentiate the overall therapeutic outcomes.

GCN2 is essential for CD8+ T cell survival and function in murine models of malignant glioma.

Amino acid deprivation is a strategy that malignancies utilize to blunt anti-tumor T-cell immune responses. It has been proposed that amino acid insufficiency in T-cells is detected by GCN2 kinase, which through phosphorylation of EIF2α, shuts down global protein synthesis leading to T-cell arrest. The role of this amino acid stress sensor in the context of malignant brain tumors has not yet been studied, and may elucidate important insights into the mechanisms of T-cell survival in this harsh environment. Using animal models of glioblastoma and animals with deficiency in GCN2, we explored the importance of this pathway in T-cell function within brain tumors. Our results show that GCN2 deficiency limited CD8+ T-cell activation and expression of cytotoxic markers in two separate murine models of glioblastoma in vivo. Importantly, adoptive transfer of antigen-specific T-cells from GCN2 KO mice did not control tumor burden as well as wild-type CD8+ T-cells. Our in vitro and in vivo data demonstrated that reduction in amino acid availability caused GCN2 deficient CD8+ T-cells to become rapidly necrotic. Mechanistically, reduced CD8+ T-cell activation and necrosis was due to a disruption in TCR signaling, as we observed reductions in PKCθ and phoshpo-PKCθ on CD8+ T-cells from GCN2 KO mice in the absence of tryptophan. Validating these observations, treatment of wild-type CD8+ T-cells with a downstream inhibitor of GCN2 activation also triggered necrosis of CD8+ T-cells in the absence of tryptophan. In conclusion, our data demonstrate the vital importance of intact GCN2 signaling on CD8+ T-cell function and survival in glioblastoma.

Repolarization of myeloid derived suppressor cells via magnetic nanoparticles to promote radiotherapy for glioma treatment.

Although radiotherapy has been established as a major therapeutic modality for glioma, radical new avenues are critically needed to prevent inevitable tumor recurrence. Herein, we utilized a magnetic nanoparticle-based platform with cationic polymer modification to promote radiotherapy for glioma treatment. We found that the nanoplatform induced cytotoxicity to glioma cells under radiation as well as promoting significant survival benefits in both immunocompetent and aythmic mice with glioma. Utilizing the magnetic properties of the nanoparticles, we were able to ascertain that myeloid derived suppressor cells (MDSC) were taking up nanoparticles in the brain tumor. The observed efficacy was attributed to destruction of glioma cells as well as MDSCs repolarization from immunosuppressive phenotype to a pro-inflammatory phenotype, which promoted antitumor effects and synergistically promoted radio-therapeutic effects. Our nanoparticles provide a robust dual-targeting platform for glioma radiotherapy by simultaneous eradication of tumor cells and manipulation of myeloid phenotypes in the central nervous system.

Anti-GITR therapy promotes immunity against malignant glioma in a murine model.

Regulatory T cells (Tregs) are potently immunosuppressive cells that accumulate within the glioma microenvironment. The reduction in their function and/or trafficking has been previously shown to enhance survival in preclinical models of glioma. Glucocorticoid-induced TNFR-related protein (GITR) is a tumor necrosis factor superfamily receptor enriched on Tregs that has shown promise as a target for immunotherapy. An agonistic antibody against GITR has been demonstrated to inhibit Tregs in a number of models and has only been recently addressed in glioma. In this study, we examined the modality of the antibody function at the tumor site as opposed to the periphery as the blood-brain barrier prevents efficient antibody delivery to brain tumors. Mice harboring established GL261 tumors were treated with anti-GITR monotherapy and were shown to have a significant increase in overall survival (p < 0.01) when antibodies were injected directly into the glioma core, whereas peripheral antibody treatment only had a modest effect. Peripheral treatment resulted in a significant decrease in granzyme B (GrB) expression by Tregs, whereas intratumoral treatment resulted in both a decrease in GrB expression by Tregs and their selective depletion, which was largely mediated by FcγR-mediated destruction. We also discovered that anti-GITR treatment results in the enhanced survival and functionality of dendritic cells (DCs)-a previously unreported effect of this immunotherapy. In effect, this study demonstrates that the targeting of GITR is a feasible and noteworthy treatment option for glioma, but is largely dependent on the anatomical location in which the antibodies are delivered.

Myeloid cell-derived creatine in the hypoxic niche promotes glioblastoma growth.

Glioblastoma (GBM) is a malignancy dominated by the infiltration of tumor-associated myeloid cells (TAMCs). Examination of TAMC metabolic phenotypes in mouse models and patients with GBM identified the de novo creatine metabolic pathway as a hallmark of TAMCs. Multi-omics analyses revealed that TAMCs surround the hypoxic peri-necrotic regions of GBM and express the creatine metabolic enzyme glycine amidinotransferase (GATM). Conversely, GBM cells located within these same regions are uniquely specific in expressing the creatine transporter (SLC6A8). We hypothesized that TAMCs provide creatine to tumors, promoting GBM progression. Isotopic tracing demonstrated that TAMC-secreted creatine is taken up by tumor cells. Creatine supplementation protected tumors from hypoxia-induced stress, which was abrogated with genetic ablation or pharmacologic inhibition of SLC6A8. Lastly, inhibition of creatine transport using the clinically relevant compound, RGX-202-01, blunted tumor growth and enhanced radiation therapy in vivo. This work highlights that myeloid-to-tumor transfer of creatine promotes tumor growth in the hypoxic niche.

STING agonist-loaded, CD47/PD-L1-targeting nanoparticles potentiate antitumor immunity and radiotherapy for glioblastoma.

As a key component of the standard of care for glioblastoma, radiotherapy induces several immune resistance mechanisms, such as upregulation of CD47 and PD-L1. Here, leveraging these radiotherapy-elicited processes, we generate a bridging-lipid nanoparticle (B-LNP) that engages tumor-associated myeloid cells (TAMCs) to glioblastoma cells via anti-CD47/PD-L1 dual ligation. We show that the engager B-LNPs block CD47 and PD-L1 and promote TAMC phagocytic activity. To enhance subsequent T cell recruitment and antitumor responses after tumor engulfment, the B-LNP was encapsulated with diABZI, a non-nucleotidyl agonist for stimulator of interferon genes. In vivo treatment with diABZI-loaded B-LNPs induced a transcriptomic and metabolic switch in TAMCs, turning these immunosuppressive cells into antitumor effectors, which induced T cell infiltration and activation in brain tumors. In preclinical murine models, B-LNP/diABZI administration synergized with radiotherapy to promote brain tumor regression and induce immunological memory against glioma. In summary, our study describes a nanotechnology-based approach that hijacks irradiation-triggered immune checkpoint molecules to boost potent and long-lasting antitumor immunity against glioblastoma.

Metixene is an incomplete autophagy inducer in preclinical models of metastatic cancer and brain metastases.

A paucity of chemotherapeutic options for metastatic brain cancer limits patient survival and portends poor clinical outcomes. Using a CNS small-molecule inhibitor library of 320 agents known to be blood-brain barrier permeable and approved by the FDA, we interrogated breast cancer brain metastasis vulnerabilities to identify an effective agent. Metixene, an antiparkinsonian drug, was identified as a top therapeutic agent that was capable of decreasing cellular viability and inducing cell death across different metastatic breast cancer subtypes. This agent significantly reduced mammary tumor size in orthotopic xenograft assays and improved survival in an intracardiac model of multiorgan site metastases. Metixene further extended survival in mice bearing intracranial xenografts and in an intracarotid mouse model of multiple brain metastases. Functional analysis revealed that metixene induced incomplete autophagy through N-Myc downstream regulated 1 (NDRG1) phosphorylation, thereby leading to caspase-mediated apoptosis in both primary and brain-metastatic cells, regardless of cancer subtype or origin. CRISPR/Cas9 KO of NDRG1 led to autophagy completion and reversal of the metixene apoptotic effect. Metixene is a promising therapeutic agent against metastatic brain cancer, with minimal reported side effects in humans, which merits consideration for clinical translation.

B-cells Drive Response to PD-1 Blockade in Glioblastoma Upon Neutralization of TGFß-mediated Immunosuppression.

Immunotherapy has revolutionized cancer treatment but has yet to be translated into brain tumors. Studies in other solid tumors suggest a central role of B-cell immunity in driving immune-checkpoint-blockade efficacy. Using single-cell and single-nuclei transcriptomics of human glioblastoma and melanoma brain metastasis, we found that tumor-associated B-cells have high expression of checkpoint molecules, known to block B-cell-receptor downstream effector function such as plasmablast differentiation and antigen-presentation. We also identified TGFß-1/TGFß receptor-2 interaction as a crucial modulator of B-cell suppression. Treatment of glioblastoma patients with pembrolizumab induced expression of B-cell checkpoint molecules and TGFß-receptor-2. Abrogation of TGFß using different conditional knockouts expanded germinal-center-like intratumoral B-cells, enhancing immune-checkpoint-blockade efficacy. Finally, blocking αVß8 integrin (which controls the release of active TGFß) and PD-1 significantly increased B-cell-dependent animal survival and immunological memory. Our study highlights the importance of intratumoral B-cell immunity and a remodeled approach to boost the effects of immunotherapy against brain tumors.

Antigen-presenting B cells promote TCF-1+ PD1- stem-like CD8+ T-cell proliferation in glioblastoma.

Understanding the spatial relationship and functional interaction of immune cells in glioblastoma (GBM) is critical for developing new therapeutics that overcome the highly immunosuppressive tumor microenvironment. Our study showed that B and T cells form clusters within the GBM microenvironment within a 15-µm radius, suggesting that B and T cells could form immune synapses within the GBM. However, GBM-infiltrating B cells suppress the activation of CD8+ T cells. To overcome this immunosuppression, we leveraged B-cell functions by activating them with CD40 agonism, IFNγ, and BAFF to generate a potent antigen-presenting B cells named BVax. BVax had improved antigen cross-presentation potential compared to naïve B cells and were primed to use the IL15-IL15Ra mechanism to enhance T cell activation. Compared to naïve B cells, BVax could improve CD8 T cell activation and proliferation. Compared to dendritic cells (DCs), which are the current gold standard professional antigen-presenting cell, BVax promoted highly proliferative T cells in-vitro that had a stem-like memory T cell phenotype characterized by CD62L+CD44- expression, high TCF-1 expression, and low PD-1 and granzyme B expression. Adoptive transfer of BVax-activated CD8+ T cells into tumor-bearing brains led to T cell reactivation with higher TCF-1 expression and elevated granzyme B production compared to DC-activated CD8+ T cells. Adoptive transfer of BVax into an irradiated immunocompetent tumor-bearing host promoted more CD8+ T cell proliferation than adoptive transfer of DCs. Moreover, highly proliferative CD8+ T cells in the BVax group had less PD-1 expression than those highly proliferative CD8+ T cells in the DC group. The findings of this study suggest that BVax and DC could generate distinctive CD8+ T cells, which potentially serve multiple purposes in cellular vaccine development.

Activation of 4-1BBL+ B cells with CD40 agonism and IFNγ elicits potent immunity against glioblastoma.

Immunotherapy has revolutionized the treatment of many tumors. However, most glioblastoma (GBM) patients have not, so far, benefited from such successes. With the goal of exploring ways to boost anti-GBM immunity, we developed a B cell-based vaccine (BVax) that consists of 4-1BBL+ B cells activated with CD40 agonism and IFNγ stimulation. BVax migrates to key secondary lymphoid organs and is proficient at antigen cross-presentation, which promotes both the survival and the functionality of CD8+ T cells. A combination of radiation, BVax, and PD-L1 blockade conferred tumor eradication in 80% of treated tumor-bearing animals. This treatment elicited immunological memory that prevented the growth of new tumors upon subsequent reinjection in cured mice. GBM patient-derived BVax was successful in activating autologous CD8+ T cells; these T cells showed a strong ability to kill autologous glioma cells. Our study provides an efficient alternative to current immunotherapeutic approaches that can be readily translated to the clinic.

Polyamines drive myeloid cell survival by buffering intracellular pH to promote immunosuppression in glioblastoma.

Glioblastoma is characterized by the robust infiltration of immunosuppressive tumor-associated myeloid cells (TAMCs). It is not fully understood how TAMCs survive in the acidic tumor microenvironment to cause immunosuppression in glioblastoma. Metabolic and RNA-seq analysis of TAMCs revealed that the arginine-ornithine-polyamine axis is up-regulated in glioblastoma TAMCs but not in tumor-infiltrating CD8+ T cells. Active de novo synthesis of highly basic polyamines within TAMCs efficiently buffered low intracellular pH to support the survival of these immunosuppressive cells in the harsh acidic environment of solid tumors. Administration of difluoromethylornithine (DFMO), a clinically approved inhibitor of polyamine generation, enhanced animal survival in immunocompetent mice by causing a tumor-specific reduction of polyamines and decreased intracellular pH in TAMCs. DFMO combination with immunotherapy or radiotherapy further enhanced animal survival. These findings indicate that polyamines are used by glioblastoma TAMCs to maintain normal intracellular pH and cell survival and thus promote immunosuppression during tumor evolution.

Genes that Mediate Metastasis across the Blood-Brain Barrier.

Brain metastasis is an important cause of mortality in patients with cancer and represents the majority of all intracranial tumors. A key step during the metastatic journey of the cancer cell to the brain is the invasion through the blood-brain barrier (BBB). Nevertheless, the molecular mechanisms that govern this process remain unknown. The BBB has been blamed for limiting the access of therapeutic drugs to the brain, which provides a safe haven for cancer cells in the brain and confers poor prognosis for the patient. Here, we explore the genes that control the transmigration of metastatic cancer cells across the BBB, offering new targets for the development of gene and cell therapies against brain metastases.

Diagnostic Clinical Trials in Breast Cancer Brain Metastases: Barriers and Innovations.

Optimal treatment of breast cancer brain metastases (BCBM) is often hampered by limitations in diagnostic abilities. Developing innovative tools for BCBM diagnosis is vital for early detection and effective treatment. In this study we explored the advances in trial for the diagnosis of BCBM, with review of the literature. On May 8, 2019, we searched ClinicalTrials.gov for interventional and diagnostic clinical trials involving BCBM, without limiting for date or location. Information on trial characteristics, experimental interventions, results, and publications were collected and analyzed. In addition, a systematic review of the literature was conducted to explore published studies related to BCBM diagnosis. Only 9 diagnostic trials explored BCBM. Of these, 1 trial was withdrawn because of low accrual numbers. Three trials were completed; however, none had published results. Modalities in trial for BCBM diagnosis entailed magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET), PET-CT, nanobodies, and circulating tumor cells (CTCs), along with a collection of novel tracers and imaging biomarkers. MRI continues to be the diagnostic modality of choice, whereas CT is best suited for acute settings. Advances in PET and PET-CT allow the collection of metabolic and functional information related to BCBM. CTC characterization can help reflect on the molecular foundations of BCBM, whereas cell-free DNA offers new genetic material for further exploration in trials. The integration of machine learning in BCBM diagnosis seems inevitable as we continue to aim for rapid and accurate detection and better patient outcomes.

Current state of clinical trials in breast cancer brain metastases.

BACKGROUND: Breast cancer brain metastases (BCBM) are the final frontier in neuro-oncology for which more efficacious therapies are required. In this work, we explore clinical trials in BCBM, and determine the shortcomings in the development of new BCBM therapies to shed light on potential areas for enhancement. METHODS: On July 9, 2018, we searched ClinicalTrials.gov for all interventional and therapeutic clinical trials involving BCBM, without limiting for date or location. Information on trial characteristics, including phase, status, start and end dates, study design, primary endpoints, selection criteria, sample size, experimental interventions, results, and publications were collected and analyzed. RESULTS: Fifty-three trials fulfilled the selection criteria. Median trial duration across phases ranged between 3 and 6 years. More than half of the trials were conducted in the United States. Although 94% of the trials were in early phases (I-II), 20% of patients were in phase III trials. Two phase III trials were anteceded by phase II trials that were non-randomized; one reported positive results. Approximately one-third of the trials were completed, whereas 23% of trials were terminated early; mostly due to inadequate enrollment. Only 13% of all trials and 22% of completed trials had published results directly linked to their primary outcomes. CONCLUSIONS: The low number of trials and accrual numbers, the lack of diversity, and the scarcity of published results represent the main troubles in clinical BCBM research. Optimization of BCBM trials is necessary to achieve effective therapies.

HIF-1α Is a Metabolic Switch between Glycolytic-Driven Migration and Oxidative Phosphorylation-Driven Immunosuppression of Tregs in Glioblastoma.

The mechanisms by which regulatory T cells (Tregs) migrate to and function within the hypoxic tumor microenvironment are unclear. Our studies indicate that specific ablation of hypoxia-inducible factor 1α (HIF-1α) in Tregs results in enhanced CD8+ T cell suppression versus wild-type Tregs under hypoxia, due to increased pyruvate import into the mitochondria. Importantly, HIF-1α-deficient Tregs are minimally affected by the inhibition of lipid oxidation, a fuel that is critical for Treg metabolism in tumors. Under hypoxia, HIF-1α directs glucose away from mitochondria, leaving Tregs dependent on fatty acids for mitochondrial metabolism within the hypoxic tumor. Indeed, inhibition of lipid oxidation enhances the survival of mice with glioma. Interestingly, HIF-1α-deficient-Treg mice exhibit significantly enhanced animal survival in a murine model of glioma, due to their stymied migratory capacity, explaining their reduced abundance in tumor-bearing mice. Thus HIF-1α acts as a metabolic switch for Tregs between glycolytic-driven migration and oxidative phosphorylation-driven immunosuppression.

Myeloid-Derived Suppressive Cells Promote B cell-Mediated Immunosuppression via Transfer of PD-L1 in Glioblastoma.

The potent immunosuppression induced by glioblastoma (GBM) is one of the primary obstacles to finding effective immunotherapies. One hallmark of the GBM-associated immunosuppressive landscape is the massive infiltration of myeloid-derived suppressor cells (MDSC) and, to a lesser extent, regulatory T cells (Treg) within the tumor microenvironment. Here, we showed that regulatory B cells (Breg) are a prominent feature of the GBM microenvironment in both preclinical models and clinical samples. Forty percent of GBM patients (n = 60) scored positive for B-cell tumor infiltration. Human and mouse GBM-associated Bregs were characterized by immunosuppressive activity toward activated CD8+ T cells, the overexpression of inhibitory molecules PD-L1 and CD155, and production of immunosuppressive cytokines TGFß and IL10. Local delivery of B cell-depleting anti-CD20 immunotherapy improved overall survival of animals (IgG vs. anti-CD20 mean survival: 18.5 vs. 33 days, P = 0.0001), suggesting a potential role of Bregs in GBM progression. We unveiled that GBM-associated MDSCs promoted regulatory B-cell function by delivering microvesicles transporting membrane-bound PD-L1, able to be up-taken by tumoral B cells. The transfer of functional PD-L1 via microvesicles conferred Bregs the potential to suppress CD8+ T-cell activation and acquisition of an effector phenotype. This work uncovered the role of B cells in GBM physiopathology and provides a mechanism by which the GBM microenvironment controls B cell-mediated immunosuppression.See related Spotlight on p. 1902.