Tumor Resection Recruits Effector T Cells and Boosts Therapeutic Efficacy of Encapsulated Stem Cells Expressing IFNβ in Glioblastomas

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.

Interleukins and interferons in mesenchymal stromal stem cell-based gene therapy of cancer

The tumor microenvironment is importantly shaped by various cytokines, where interleukins (ILs) and interferons (IFNs) shape the balance of immune activity within tumor niche and associated lymphoid organs. Their importance in activation and tuning of both innate and adaptive immune responses prompted their use in several clinical trials, albeit with limited therapeutic efficacy and risk of toxicity due to systemic administration. Increasing preclinical evidence suggests that local delivery of ILs and IFNs could significantly increase their effectiveness, while simultaneously attenuate the known side effects and issues related to their biological activity. A prominent way to achieve this is to use cell-based delivery vehicles. For this purpose, mesenchymal stromal stem cells (MSCs) are considered an almost ideal candidate. Namely, MSCs can be obtained in large quantities and from obtainable sources (e.g. umbilical cord or adipose tissue), their ex vivo expansion is relatively straightforward compared to other cell types and they possess very low immunogenicity making them suitable for allogeneic use. Importantly, MSCs have shown an intrinsic capacity to respond to tumor-directed chemotaxis. This review provides a focused and detailed discussion on MSC-based gene therapy using ILs and IFNs, engineering techniques and insights on potential future advancements.

Identification of MDK as a Hypoxia- and Epithelial-Mesenchymal Transition-Related Gene Biomarker of Glioblastoma Based on a Novel Risk Model and In Vitro Experiments

BACKGROUND

Tumor cells are commonly exposed to a hypoxic environment, which can easily induce the epithelial-mesenchymal transition (EMT) of tumor cells, further affecting tumor proliferation, invasion, metastasis, and drug resistance. However, the predictive role of hypoxia and EMT-related genes in glioblastoma (GBM) has not been investigated.

METHODS

Intersection genes were identified by weighted correlation network analysis (WGCNA) and differential expression analyses, and a risk model was further constructed by LASSO and Cox analyses. Clinical, immune infiltration, tumor mutation, drug treatment, and enrichment profiles were analyzed based on the risk model. The expression level of the MDK gene was tested using RT-PCR, immunohistochemistry, and immunofluorescence. CCK8 and EdU were employed to determine the GBM cells' capacity for proliferation while the migration and invasion ability were detected by a wound healing assay and transwell assay, respectively.

RESULTS

Based on the GBM data of the TCGA and GTEx databases, 58 intersection genes were identified, and a risk model was constructed. The model was verified in the CGGA cohort, and its accuracy was confirmed by the ROC curve (AUC = 0.807). After combining clinical subgroups, univariate and multivariate Cox regression analyses showed that risk score and age were independent risk factors for GBM patients. Furthermore, our subsequent analysis of immune infiltration, tumor mutation, and drug treatment showed that risk score and high- and low-risk groups were associated with multiple immune cells, mutated genes, and drugs. Enrichment analysis indicated that the differences between high- and low-risk groups were manifested in tumor-related pathways, including the PI3K-AKT and JAK-STAT pathways. Finally, in vivo experiments proved that the hypoxia environment promoted the expression of MDK, and MDK knockdown reduced the proliferation, migration, and EMT of GBM cells induced by hypoxia.

CONCLUSIONS

Our novel prognostic correlation model provided more potential treatment strategies for GBM patients.

Dendritic cell vaccine of gliomas: challenges from bench to bed

Gliomas account for the majority of brain malignant tumors. As the most malignant subtype of glioma, glioblastoma (GBM) is barely effectively treated by traditional therapies (surgery combined with radiochemotherapy), resulting in poor prognosis. Meanwhile, due to its "cold tumor" phenotype, GBM fails to respond to multiple immunotherapies. As its capacity to prime T cell response, dendritic cells (DCs) are essential to anti-tumor immunity. In recent years, as a therapeutic method, dendritic cell vaccine (DCV) has been immensely developed. However, there have long been obstacles that limit the use of DCV yet to be tackled. As is shown in the following review, the role of DCs in anti-tumor immunity and the inhibitory effects of tumor microenvironment (TME) on DCs are described, the previous clinical trials of DCV in the treatment of GBM are summarized, and the challenges and possible development directions of DCV are analyzed.

Immunomodulatory Mechanisms and Therapeutic Potential of Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are regarded as highly promising cells for allogeneic cell therapy, owing to their multipotent nature and ability to display potent and varied functions in different diseases. The functions of MSCs, including native immunomodulation, high self-renewal characteristic, and secretory and trophic properties, can be employed to improve the immune-modulatory functions in diseases. MSCs impact most immune cells by directly contacting and/or secreting positive microenvironmental factors to influence them. Previous studies have reported that the immunomodulatory role of MSCs is basically dependent on their secretion ability from MSCs. This review discusses the immunomodulatory capabilities of MSCs and the promising strategies to successfully improve the potential utilization of MSCs in clinical research.

Engineered cell-based therapies in ex vivo ready-made CellDex capsules have therapeutic efficacy in solid tumors

Encapsulated cell-based therapies for solid tumors have shown promising results in pre-clinical settings. However, the inability to culture encapsulated therapeutic cells prior to their transplantation has limited their translation into clinical settings. In this study, we created a wide variety of engineered therapeutic cells (ThC) loaded in micropore-forming gelatin methacryloyl (GelMA) hydrogel (CellDex) capsules that can be cultured in vitro prior to their transplantation in surgically debulked solid tumors. We show that both allogeneic and autologous engineered cells, such as stem cells (SCs), macrophages, NK cells, and T cells, proliferate within CellDex capsules and migrate out of the gel in vitro and in vivo. Furthermore, tumor cell specific therapeutic proteins and oncolytic viruses released from CellDex capsules retain and prolong their anti-tumor effects. In vivo, ThCs in pre-manufactured Celldex capsules persist long-term and track tumor cells. Moreover, chimeric antigen receptor (CAR) T cell bearing CellDex (T-CellDex) and human SC releasing therapeutic proteins (hSC-CellDex) capsules show therapeutic efficacy in metastatic and primary brain tumor resection models that mimic standard of care of tumor resection in patients. Overall, this unique approach of pre-manufactured micropore-forming CellDex capsules offers an effective off-the-shelf clinically viable strategy to treat solid tumors locally.

Bifunctional cancer cell-based vaccine concomitantly drives direct tumor killing and antitumor immunity

The administration of inactivated tumor cells is known to induce a potent antitumor immune response; however, the efficacy of such an approach is limited by its inability to kill tumor cells before inducing the immune responses. Unlike inactivated tumor cells, living tumor cells have the ability to track and target tumors. Here, we developed a bifunctional whole cancer cell-based therapeutic with direct tumor killing and immunostimulatory roles. We repurposed the tumor cells from interferon-β (IFN-β) sensitive to resistant using CRISPR-Cas9 by knocking out the IFN-β-specific receptor and subsequently engineered them to release immunomodulatory agents IFN-β and granulocyte-macrophage colony-stimulating factor. These engineered therapeutic tumor cells (ThTCs) eliminated established glioblastoma tumors in mice by inducing caspase-mediated cancer cell apoptosis, down-regulating cancer-associated fibroblast-expressed platelet-derived growth factor receptor β, and activating antitumor immune cell trafficking and antigen-specific T cell activation signaling. This mechanism-based efficacy of ThTCs translated into a survival benefit and long-term immunity in primary, recurrent, and metastatic cancer models in immunocompetent and humanized mice. The incorporation of a double kill-switch comprising herpes simplex virus-1 thymidine kinase and rapamycin-activated caspase 9 in ThTCs ensured the safety of our approach. Arming naturally neoantigen-rich tumor cells with bifunctional therapeutics represents a promising cell-based immunotherapy for solid tumors and establishes a road map toward clinical translation.

Optogenetic-controlled immunotherapeutic designer cells for post-surgical cancer immunotherapy

Surgical resection is the main treatment option for most solid tumors, yet cancer recurrence after surgical resection remains a significant challenge in cancer therapy. Recent advances in cancer immunotherapy are enabling radical cures for many tumor patients, but these technologies remain challenging to apply because of side effects related to uncontrollable immune system activation. Here, we develop far-red light-controlled immunomodulatory engineered cells (FLICs) that we load into a hydrogel scaffold, enabling the precise optogenetic control of cytokines release (IFN-β, TNF-α, and IL-12) upon illumination. Experiments with a B16F10 melanoma resection mouse model show that FLICs-loaded hydrogel implants placed at the surgical wound site achieve sustainable release of immunomodulatory cytokines, leading to prevention of tumor recurrence and increased animal survival. Moreover, the FLICs-loaded hydrogel implants elicit long-term immunological memory that prevents against tumor recurrence. Our findings illustrate that this optogenetic perioperative immunotherapy with FLICs-loaded hydrogel implants offers a safe treatment option for solid tumors based on activating host innate and adaptive immune systems to inhibit tumor recurrence after surgery. Beyond extending the optogenetics toolbox for immunotherapy, we envision that our optogenetic-controlled living cell factory platform could be deployed for other biomedical contexts requiring precision induction of bio-therapeutic dosage.

Immunotherapy by mesenchymal stromal cell delivery of oncolytic viruses for treating metastatic tumors

Oncolytic viruses (OVs) have emerged as a very promising anti-cancer therapeutic strategy in the past decades. However, despite their pre-clinical promise, many OV clinical evaluations for cancer therapy have highlighted the continued need for their improved delivery and targeting. Mesenchymal stromal cells (MSCs) have emerged as excellent candidate vehicles for the delivery of OVs due to their tumor-homing properties and low immunogenicity. MSCs can enhance OV delivery by protecting viruses from rapid clearance following administration and also by more efficiently targeting tumor sites, consequently augmenting the therapeutic potential of OVs. MSCs can function as “biological factories,” enabling OV amplification within these cells to promote tumor lysis following MSC-OV arrival at the tumor site. MSC-OVs can promote enhanced safety profiles and therapeutic effects relative to OVs alone. In this review we explore the general characteristics of MSCs as delivery tools for cancer therapeutic agents. Furthermore, we discuss the potential of OVs as immune therapeutics and highlight some of the promising applications stemming from combining MSCs to achieve enhanced delivery and anti-tumor effectiveness of OVs at different pre-clinical and clinical stages. We further provide potential pitfalls of the MSC-OV platform and the strategies under development for enhancing the efficacy of these emerging therapeutics.

The Potential of the Gut Microbiome to Reshape the Cancer Therapy Paradigm: A Review

Importance

The gut microbiome, home to the vast kingdom of diverse commensal bacteria and other microorganisms residing within the gut, was once thought to only have roles primarily centered on digestive functions. However, recent advances in sequencing technology have elucidated intricate roles of the gut microbiome in cancer development and efficacy of therapeutic response that need to be comprehensively addressed from a clinically translational angle.

Observations

This review aims to highlight the current understanding of the association of the gut microbiome with the therapeutic response to immunotherapy, chemotherapy, radiotherapy, cancer surgery, and more, while also contextualizing possible synergistic strategies with the microbiome for tackling some of the most challenging tumors. It also provides insights on contemporary methods that target the microbiota and the current progression of findings being translated from bench to bedside.

Conclusions and Relevance

Ultimately, the importance of gut bacteria in cancer therapy cannot be overstated in its potential for ushering in a new era of cancer treatments. With the understanding that the microbiome may play critical roles in the tumor microenvironment, holistic approaches that integrate microbiome-modulating treatments with biological, immune, cell-based, and surgical cancer therapies should be explored.

To Explore the Stem Cells Homing to GBM: The Rise to the Occasion

Multiple efforts are currently underway to develop targeted therapeutic deliveries to the site of glioblastoma progression. The use of carriers represents advancement in the delivery of various therapeutic agents as a new approach in neuro-oncology. Mesenchymal stem cells (MSCs) and neural stem cells (NSCs) are used because of their capability in migrating and delivering therapeutic payloads to tumors. Two of the main properties that carrier cells should possess are their ability to specifically migrate from the bloodstream and low immunogenicity. In this article, we also compared the morphological and molecular features of each type of stem cell that underlie their migration capacity to glioblastoma. Thus, the major focus of the current review is on proteins and lipid molecules that are released by GBM to attract stem cells.

Advances in local therapy for glioblastoma - taking the fight to the tumour

Despite advances in neurosurgery, chemotherapy and radiotherapy, glioblastoma remains one of the most treatment-resistant CNS malignancies, and the tumour inevitably recurs. The majority of recurrences appear in or near the resection cavity, usually within the area that received the highest dose of radiation. Many new therapies focus on combatting these local recurrences by implementing treatments directly in or near the tumour bed. In this Review, we discuss the latest developments in local therapy for glioblastoma, focusing on recent preclinical and clinical trials. The approaches that we discuss include novel intraoperative techniques, various treatments of the surgical cavity, stereotactic injections directly into the tumour, and new developments in convection-enhanced delivery and intra-arterial treatments.

Cell-Based Therapy for the Treatment of Glioblastoma: An Update from Preclinical to Clinical Studies

Glioblastoma (GB), an aggressive primary tumor of the central nervous system, represents about 60% of all adult primary brain tumors. It is notorious for its extremely low (~5%) 5-year survival rate which signals the unsatisfactory results of the standard protocol for GB therapy. This issue has become, over time, the impetus for the discipline of bringing novel therapeutics to the surface and challenging them so they can be improved. The cell-based approach in treating GB found its way to clinical trials thanks to a marvelous number of preclinical studies that probed various types of cells aiming to combat GB and increase the survival rate. In this review, we aimed to summarize and discuss the up-to-date preclinical studies that utilized stem cells or immune cells to treat GB. Likewise, we tried to summarize the most recent clinical trials using both cell categories to treat or prevent recurrence of GB in patients. As with any other therapeutics, cell-based therapy in GB is still hampered by many drawbacks. Therefore, we highlighted several novel techniques, such as the use of biomaterials, scaffolds, nanoparticles, or cells in the 3D context that may depict a promising future when combined with the cell-based approach.

Dendritic Cell Vaccination of Glioblastoma: Road to Success or Dead End

Glioblastomas (GBM) are the most frequent and aggressive malignant primary brain tumor and remains a therapeutic challenge: even after multimodal therapy, median survival of patients is only 15 months. Dendritic cell vaccination (DCV) is an active immunotherapy that aims at inducing an antitumoral immune response. Numerous DCV trials have been performed, vaccinating hundreds of GBM patients and confirming feasibility and safety. Many of these studies reported induction of an antitumoral immune response and indicated improved survival after DCV. However, two controlled randomized trials failed to detect a survival benefit. This raises the question of whether the promising concept of DCV may not hold true or whether we are not yet realizing the full potential of this therapeutic approach. Here, we discuss the results of recent vaccination trials, relevant parameters of the vaccines themselves and of their application, and possible synergies between DCV and other therapeutic approaches targeting the immunosuppressive microenvironment of GBM.

Rationally designed drug delivery systems for the local treatment of resected glioblastoma

Glioblastoma (GBM) is a particularly aggressive brain cancer associated with high recurrence and poor prognosis. The standard of care, surgical resection followed by concomitant radio- and chemotherapy, leads to low survival rates. The local delivery of active agents within the tumor resection cavity has emerged as an attractive means to initiate oncological treatment immediately post-surgery. This complementary approach bypasses the blood-brain barrier, increases the local concentration at the tumor site while reducing or avoiding systemic side effects. This review will provide a global overview on the local treatment for GBM with an emphasis on the lessons learned from past clinical trials. The main parameters to be considered to rationally design fit-of-purpose biomaterials and develop drug delivery systems for local administration in the GBM resection cavity to prevent the tumor recurrence will be described. The intracavitary local treatment of GBM should i) use materials that facilitate translation to the clinic; ii) be characterized by easy GMP effective scaling up and easy-handling application by the neurosurgeons; iii) be adaptable to fill the tumor-resected niche, mold to the resection cavity or adhere to the exposed brain parenchyma; iv) be biocompatible and possess mechanical properties compatible with the brain; v) deliver a therapeutic dose of rationally-designed or repurposed drug compound(s) into the GBM infiltrative margin. Proof of concept with high translational potential will be provided. Finally, future perspectives to facilitate the clinical translation of the local perisurgical treatment of GBM will be discussed.

Technical choices significantly alter the adaptive immune response against immunocompetent murine gliomas in a model-dependent manner

PURPOSE

Due to the recent rise in immunotherapy research to treat glioblastoma (GBM), immunocompetent mouse models have become increasingly crucial. However, the character and kinetics of the immune response against the most prevalent immunocompetent GBM models, GL261 and CT2A, have not been well studied, nor has the impact of commonly-used marker proteins and foreign antigens.

METHODS

In this study, we compared the immune response in these models using flow cytometry and immunohistochemistry as well as investigated several factors that influence the immune response, including kinetics, tumor size, and expression of commonly-used marker proteins and foreign antigens. We hypothesize that these factors influence the immune response enough to warrant consideration when studying new immunotherapeutic approaches for GBM.

RESULTS

CT2A-Luc, but not GL261-Luc2, drastically increased the number of T cells in the brain compared with wild-type controls, and significantly altered CT2A's responsiveness to anti-PD-1 antibody therapy. Additionally, a larger cell inoculum size in the GL261 model increased the T cell response's magnitude at day 28 post-injection. CT2A and GL261 models both stimulate a peak T cell immune response at day 21 post-injection.

CONCLUSIONS

Our results suggest that the impact of foreign proteins like luciferase on the intracranial immune response is dependent upon the model, with CT2A being more sensitive to added markers. In particular, luciferase expression in CT2A could lead to meaningful misinterpretations of results from immune checkpoint inhibitor (ICI) studies.

Mesenchymal stem cells in glioblastoma therapy and progression: How one cell does it all

Mesenchymal stem cells (MSCs) are among the most investigated and applied somatic stem cells in experimental therapies for the regeneration of damaged tissues. Moreover, as it was recently postulated, MSCs may demonstrate anti-tumor properties. Glioblastoma (GBM) is a grade IV central nervous system tumor with no available effective therapy and an inevitably fatal prognosis. Experimental studies utilizing MSCs in GBM treatment resulted in numerous controversies. Native MSCs were shown to exert anti-GBM activity by controlling angiogenesis, regulating cell cycle, and inducing apoptosis. They also were used as sensitizing factors and vehicles delivering various anti-cancer compounds. On the other hand, some experiments revealed significant risks related to MSC-based therapies for GBM, such as enhancement of tumor cell proliferation, invasion, and aggressiveness. The following review elaborates on all mentioned contradictory data and provides a realistic, current clinical perspective on MSCs' potential in GBM treatment.

Stem cells for the treatment of glioblastoma: a 20-year perspective

Glioblastoma, the deadliest form of primary brain tumor, remains a disease without cure. Treatment resistance is in large part attributed to limitations in the delivery and distribution of therapeutic agents. Over the last 20 years, numerous preclinical studies have demonstrated the feasibility and efficacy of stem cells as antiglioma agents, leading to the development of trials to test these therapies in the clinic. In this review we present and analyze these studies, discuss mechanisms underlying their beneficial effect and highlight experimental progress, limitations and the emergence of promising new therapeutic avenues. We hope to increase awareness of the advantages brought by stem cells for the treatment of glioblastoma and inspire further studies that will lead to accelerated implementation of effective therapies.

Glioblastoma is the deadliest and most common form of brain tumor, for which there is no cure. It is very difficult to deliver medicine to the tumor cells, because they spread out widely into the normal brain, and local blood vessels represent a barrier that most medicines cannot cross. It was shown, in many studies over the last 20 years, that stem cells are attracted toward the tumor and that they can deliver many kinds of therapeutic agents directly to brain cancer cells and shrink the tumor. In this review we analyze these studies and present new discoveries that can be used to make stem cell therapies for glioblastoma more effective to prolong the life of patients with brain tumors.

Anti-EGFR VHH-armed death receptor ligand-engineered allogeneic stem cells have therapeutic efficacy in diverse brain metastatic breast cancers

Basal-like breast cancer (BLBC) shows brain metastatic (BM) capability and overexpresses EGFR and death-receptors 4/5 (DR4/5); however, the anatomical location of BM prohibits efficient drug-delivery to these targetable markers. In this study, we developed BLBC-BM mouse models featuring different patterns of BMs and explored the versatility of estem cell (SC)-mediated bi-functional EGFR and DR4/5-targeted treatment in these models. Most BLBC lines demonstrated a high sensitivity to EGFR and DR4/5 bi-targeting therapeutic protein, E_VDR_L [anti-EGFR VHH (E_V) fused to DR ligand (DR_L)]. Functional analyses using inhibitors and CRISPR-Cas9 knockouts revealed that the E_V domain facilitated in augmenting DR4/5-DR_L binding and enhancing DR_L-induced apoptosis. E_VDR_L secreting stem cells alleviated tumor-burden and significantly increased survival in mouse models of residual-tumor after macrometastasis resection, perivascular niche micrometastasis, and leptomeningeal metastasis. This study reports mechanism based simultaneous targeting of EGFR and DR4/5 in BLBC and defines a new treatment paradigm for treatment of BM.

Immune Profiling of Syngeneic Murine and Patient GBMs for Effective Translation of Immunotherapies

Immunotherapy for brain tumors remains elusive, unlike many other cancer types for which it is one of the most promising therapeutic options. Recent studies have comprehensively profiled the immune-landscape of the highly malignant brain tumor, glioblastoma (GBM) in patients and identified novel immune-modulatory targets. However, given that pre-clinical exploration of potential novel therapeutics is primarily performed in immune-competent mice, it is vital to compare the immune-profiling data obtained from syngeneic mouse GBM models with GBM patient samples. This will pave the way for utilizing appropriate clinically relevant mouse GBM models for evaluating novel immune-therapies in pre-clinical settings. Recent brain tumor immune-profiling studies using state-of-the-art time of flight cytometry (CyTOF) analysis compared different human and mouse GBM types and reported immunological distinctions amongst these mouse models. These studies also contrast the immune phenotype of brain tumor patients with commonly used pre-clinical immune-competent mouse models. In this perspective, we provide the outcomes of very recent brain tumor immune-profiling studies and their implications on designing and translating unique, tumor-subtype specific therapeutics.

Pre-clinical tumor models of primary brain tumors: Challenges and opportunities

Primary brain tumors are a heterogeneous group of malignancies that originate in cells of the central nervous system. A variety of models tractable for preclinical studies have been developed to recapitulate human brain tumors, allowing us to understand the underlying pathobiology and explore potential treatments. However, many promising therapeutic strategies identified using preclinical models have shown limited efficacy or failed at the clinical trial stage. The inability to develop therapeutic strategies that significantly improve survival rates in patients highlight the compelling need to revisit the design of currently available animal models and explore the use of new models that allow us to bridge the gap between promising preclinical findings and clinical translation. In this review, we discuss current strategies used to model glioblastoma, the most malignant brain tumor in adults and highlight the shortcomings of specific models that must be circumvented for the development of innovative therapeutic strategies.

Radiation and immunotherapy: emerging mechanisms of synergy

Immunotherapy (IO) has become a standard treatment in patients with metastatic and locally advanced non-small cell lung cancer (NSCLC), and is now being tested in patients with early stage disease. IO agents currently in use for lung cancer target PD-1, PD-L1, and CTLA-4. While survival and tumor control have improved with IO, many patients have limited or short responses to IO. Therefore, methods to improve the systemic response to IO are needed. Radiation therapy (RT) is an integral component of lung cancer treatment, and may improve systemic response to IO by increasing antigen presentation, increasing co-stimulatory signaling, increasing T-cells recruitment, upregulating PD-L1, increasing tumor stromal lymphocyte infiltration, and altering the microenvironment. IO after definitive chemoradiation is now standard treatment in unresectable stage III NSCLC following publication of the PACIFIC clinical trial. For early stage NSCLC, IO is being investigated in conjunction with stereotactic body radiotherapy (SBRT). The benefit of adding RT to IO in patients with metastatic disease may be especially pronounced in patients with low baseline PD-L1 expression, potentially when delivered as a short course of SBRT, as supported by the PEMBRO-RT clinical trial. Current and ongoing clinical trials are evaluating the optimal radiation dose, timing, and sequencing of RT with IO.

Different T-cell subsets in glioblastoma multiforme and targeted immunotherapy

Glioblastoma multiforme (GBM) is a brain tumor with a high mortality rate. Surgical resection combined with radiotherapy and chemotherapy is the standard treatment for GBM patients, but the 5-year survival rate of patients despite this treatment is low. Immunotherapy has attracted increasing attention in recent years. As the pioneer and the main effector cells of immunotherapy, T cells play a key role in tumor immunotherapy. However, the T cells in GBM microenvironment are inhibited by the highly immunosuppressive environment of GBM, posing huge challenges to T cell-based GBM immunotherapy. This review summarizes the effects of the GBM microenvironment on the infiltration and function of different T-cell subsets and the possible strategies to overcome immunosuppression, and thus enhance the effectiveness of GBM immunotherapy.

Glioma-initiating cells at tumor edge gain signals from tumor core cells to promote their malignancy

Intratumor spatial heterogeneity facilitates therapeutic resistance in glioblastoma (GBM). Nonetheless, understanding of GBM heterogeneity is largely limited to the surgically resectable tumor core lesion while the seeds for recurrence reside in the unresectable tumor edge. In this study, stratification of GBM to core and edge demonstrates clinically relevant surgical sequelae. We establish regionally derived models of GBM edge and core that retain their spatial identity in a cell autonomous manner. Upon xenotransplantation, edge-derived cells show a higher capacity for infiltrative growth, while core cells demonstrate core lesions with greater therapy resistance. Investigation of intercellular signaling between these two tumor populations uncovers the paracrine crosstalk from tumor core that promotes malignancy and therapy resistance of edge cells. These phenotypic alterations are initiated by HDAC1 in GBM core cells which subsequently affect edge cells by secreting the soluble form of CD109 protein. Our data reveal the role of intracellular communication between regionally different populations of GBM cells in tumor recurrence.

Intratumoural spatial heterogeneity is crucial to enhance therapeutic resistance in glioblastoma. Here, the authors show a paracrine signaling mechanism where glioblastoma-initiating cells located in the tumour edge elevate their malignancy by interaction with core-located tumour cells.

Mesenchymal Stem Cell Immunomodulation: Mechanisms and Therapeutic Potential

Mesenchymal stem/stromal cells (MSCs) are multipotent cells that are emerging as the most promising means of allogeneic cell therapy. MSCs have inherent immunomodulatory characteristics, trophic activity, high invitro self-renewal ability, and can be readily engineered to enhance their immunomodulatory functions. MSCs affect the functions of most immune effector cells via direct contact with immune cells and local microenvironmental factors. Previous studies have confirmed that the immunomodulatory effects of MSCs are mainly communicated via MSC-secreted cytokines; however, apoptotic and metabolically inactivated MSCs have more recently been shown to possess immunomodulatory potential, in which regulatory T cells and monocytes play a key role. We review the immunomodulatory aspects of naïve and engineered MSCs, and discuss strategies for increasing the potential of successfully using MSCs in clinical settings.

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

Immunotherapy has emerged as a promising approach to treat cancer, however, its efficacy in highly malignant brain-tumors, glioblastomas (GBM), is limited. Here, we generate distinct imageable syngeneic mouse GBM-tumor models and utilize RNA-sequencing, CyTOF and correlative immunohistochemistry to assess immune-profiles in these models. We identify immunologically-inert and -active syngeneic-tumor types and show that inert tumors have an immune-suppressive phenotype with numerous exhausted CD8 T cells and resident macrophages; fewer eosinophils and SiglecF+ macrophages. To mimic the clinical-settings of first line of GBM-treatment, we show that tumor-resection invigorates an anti-tumor response via increasing T cells, activated microglia and SiglecF+ macrophages and decreasing resident macrophages. A comparative CyTOF analysis of resected-tumor samples from GBM-patients and mouse GBM-tumors show stark similarities in one of the mouse GBM-tumors tested. These findings guide informed choices for use of GBM models for immunotherapeutic interventions and offer a potential to facilitate immune-therapies in GBM patients.

Syngeneic mouse models for glioblastoma (GBM) cannot fully recapitulate clinical findings and response to therapy in patients. Here the authors perform a comprehensive immune profiling of different syngeneic GBM tumour models and compare it with the immune landscape of GBM patients to identify similarities and potential confounding differences.

The Role of Caspase-4 and NLRP1 in MCF7 Cell Pyroptosis Induced by hUCMSC-Secreted Factors

Mesenchymal stem cells (MSCs) are being widely investigated for the development of novel therapeutic approaches for different cancers, including breast cancer, the leading form of cancer in women. Our previous study showed that the factors secreted by human umbilical cord MSCs (hUCMSCs) induced pyroptosis in the breast cancer cell line MCF7 and our RNA sequencing studies revealed an increase in the expression of the pyroptosis-related gene caspase-4 (CASP4) and nucleotide-binding, leucine-rich repeat pyrin domain-containing protein 1 (NLRP1) in pyroptotic MCF7 cells. Cellular pyroptosis can occur via the canonical pathway (involving caspase-1 and NLRP1) or the noncanonical pathway (involving caspase-4). In this study, we first confirmed that the inflammasome complex formed by NLRP1 and ASC is involved in MCF7 cell pyroptosis induced by hUCMSC-CM. Further, we investigated the role of CASP4 and NLRP1 in MCF7 cell pyroptosis induced by hUCMSC-secreted factors using shRNA-mediated transfection of CASP4 or NLRP1 in MCF7 cells. Cytotoxicity analyses revealed that neither CASP4 knockdown nor NLRP1 knockdown could inhibit the hUCMSC-CM-induced pyroptosis in MCF7 cells. Gene and protein expression analysis showed that hUCMSC-CM induced pyroptosis mainly via the canonical pathway in CASP4 knockdown MCF7 cells but mainly via the noncanonical pathway in NLRP1 knockdown MCF7 cells. Our study provides a foundation for further studies aimed at elucidating the precise mechanism underlying hUCMSC-induced pyroptosis in breast cancer cells and aid the identification of potential therapeutic targets for breast cancer.

Polymeric Biomaterial Scaffolds for Tumoricidal Stem Cell Glioblastoma Therapy

Glioblastoma (GBM) is the most common primary brain tumor and has a poor prognosis; as such, there is an urgent need to develop innovative new therapies. Tumoricidal stem cells are an emerging therapy that has the potential to combat limitations of traditional local and systemic chemotherapeutic strategies for GBM by providing a source for high, sustained concentrations of tumoricidal agents locally to the tumor. One major roadblock for tumoricidal stem cell therapy is that the persistence of tumoricidal stem cells injected as a cell suspension into the GBM surgical resection cavity is limited. Polymeric biomaterial scaffolds have been utilized to enhance the delivery of tumoricidal stem cells in the surgical resection cavity and extend their persistence in the brain, ultimately increasing their therapeutic efficacy against GBM. In this review, we examine three main scaffold categories explored for tumoricidal stem cell therapy: microcapsules, hydrogels, and electrospun scaffolds. Furthermore, considering the significant impact of surgery on the brain and recurrent GBM, we survey a brief history of orthotopic models of GBM surgical resection.

p19Arf sensitizes B16 melanoma cells to interferon-β delivered via mesenchymal stem cells in vitro

The immune stimulatory and anti-neoplastic functions of type I interferon have long been applied for the treatment of melanoma. However, the systemic application of high levels of this recombinant protein is often met with toxicity. An approach that provides localized, yet transient, production of type I interferon may overcome this limitation. We propose that the use of mesenchymal stem cells (MSCs) as delivery vehicles for the production of interferon-β (IFNβ) may be beneficial when applied together with our cancer gene therapy approach. In our previous studies, we have shown that adenovirus-mediated gene therapy with IFNβ was especially effective in combination with p19Arf gene transfer, resulting in immunogenic cell death. Here we showed that MSCs derived from mouse adipose tissue were susceptible to transduction with adenovirus, expressed the transgene reliably, and yet were not especially sensitive to IFNβ production. MSCs used to produce IFNβ inhibited B16 mouse melanoma cells in a co-culture assay. Moreover, the presence of p19Arf in the B16 cells sensitizes them to the IFNβ produced by the MSCs. These data represent a critical demonstration of the use of MSCs as carriers of adenovirus encoding IFNβ and applied as an anti-cancer strategy in combination with p19Arf gene therapy.

Local Intracerebral Immunomodulation Using Interleukin-Expressing Mesenchymal Stem Cells in Glioblastoma

PURPOSE

Mesenchymal stem cells (MSCs) show an inherent brain tumor tropism that can be exploited for targeted delivery of therapeutic genes to invasive glioma. We assessed whether a motile MSC-based local immunomodulation is able to overcome the immunosuppressive glioblastoma microenvironment and to induce an antitumor immune response.

EXPERIMENTAL DESIGN

We genetically modified MSCs to coexpress high levels of IL12 and IL7 (MSC^IL7/12, Apceth-301). Therapeutic efficacy was assessed in two immunocompetent orthotopic C57BL/6 glioma models using GL261 and CT2A. Immunomodulatory effects were assessed by multicolor flow cytometry to profile immune activation and exhaustion of tumor-infiltrating immune cells. Diversity of the tumor-specific immune response as analyzed using T-cell receptor sequencing.

RESULTS

Intratumoral administration of MSC^IL7/12 induced significant tumor growth inhibition and remission of established intracranial tumors, as demonstrated by MR imaging. Notably, up to 50% of treated mice survived long-term. Rechallenging of survivors confirmed long-lasting tumor immunity. Local treatment with MSC^IL7/12 was well tolerated and led to a significant inversion of the CD4⁺/CD8⁺ T-cell ratio with an intricate, predominantly CD8⁺ effector T-cell-mediated antitumor response. T-cell receptor sequencing demonstrated an increased diversity of TILs in MSC^IL7/12-treated mice, indicating a broader tumor-specific immune response with subsequent oligoclonal specification during generation of long-term immunity.

CONCLUSIONS

Local MSC-based immunomodulation is able to efficiently alter the immunosuppressive microenvironment in glioblastoma. The long-lasting therapeutic effects warrant a rapid clinical translation of this concept and have led to planning of a phase I/II study of apceth-301 in recurrent glioblastoma.

Engineered stem cells targeting multiple cell surface receptors in tumors

Multiple stem cell types exhibit inherent tropism for cancer, and engineered stem cells have been used as therapeutic agents to specifically target cancer cells. Recently, stem cells have been engineered to target multiple surface receptors on tumor cells, as well as endothelial and immune cells in the tumor microenvironment. In this review, we discuss the rationales and strategies for developing multiple receptor-targeted stem cells, their mechanisms of action, and the promises and challenges they hold as cancer therapeutics.