Production of an interleukin-10 blocking antibody by genetically engineered macrophages increases cancer cell death in human gastrointestinal tumor slice cultures

Although it can promote effector T-cell function, the summative effect of interleukin-10 (IL-10) in the tumor microenvironment (TME) appears to be suppressive; therefore, blocking this critical regulatory cytokine has therapeutic potential to enhance antitumor immune function. As macrophages efficiently localize to the TME, we hypothesized that they could be used as a delivery vehicle for drugs designed to block this pathway. To test our hypothesis, we created and evaluated genetically engineered macrophages (GEMs) that produce an IL-10-blocking antibody (αIL-10). Healthy donor human peripheral blood mononuclear cells were differentiated and transduced with a novel lentivirus (LV) encoding BT-063, a humanized αIL-10 antibody. The efficacy of αIL-10 GEMs was assessed in human gastrointestinal tumor slice culture models developed from resected specimens of pancreatic ductal adenocarcinoma primary tumors and colorectal cancer liver metastases. LV transduction led to sustained production of BT-063 by αIL-10 GEMs for at least 21 days. Transduction did not alter GEM phenotype as evaluated by flow cytometry, but αIL-10 GEMs produced measurable quantities of BT-063 in the TME that was associated with an ~5-fold higher rate of tumor cell apoptosis than control.

Hypoxia-inducible lentiviral gene expression in engineered human macrophages

Background

Human immune cells, including monocyte-derived macrophages, can be engineered to deliver proinflammatory cytokines, bispecific antibodies, and chimeric antigen receptors to support immune responses in different disease settings. When gene expression is regulated by constitutively active promoters, lentiviral payload gene expression is unregulated, and can result in potentially toxic quantities of proteins. Regulated delivery of lentivirally encoded proteins may allow localized or conditional therapeutic protein expression to support safe delivery of adoptively transferred, genetically modified cells with reduced capacity for systemic toxicities.

Methods

In this study, we engineered human macrophages to express genes regulated by hypoxia responsive elements included in the lentiviral promoter region to drive conditional lentiviral gene expression only under hypoxic conditions. We tested transduced macrophages cultured in hypoxic conditions for the transient induced expression of reporter genes and the secreted cytokine, interleukin-12. Expression of hypoxia-regulated genes was investigated both transcriptionally and translationally, and in the presence of human tumor cells in a slice culture system. Finally, hypoxia-regulated gene expression was evaluated in a subcutaneous humanized-mouse cancer model.

Results

Engineered macrophages were shown to conditionally and tranisently express lentivirally encoded gene protein products, including IL-12 in hypoxic conditions in vitro. On return to normoxic conditions, lentiviral payload expression returned to basal levels. Reporter genes under the control of hypoxia response elements were upregulated under hypoxic conditions in the presence of human colorectal carcinoma cells and in the hypoxic xenograft model of glioblastoma, suggesting utility for systemic engineered cell delivery capable of localized gene delivery in cancer.

Conclusions

Macrophages engineered to express hypoxia-regulated payloads have the potential to be administered systemically and conditionally express proteins in tissues with hypoxic conditions. In contrast to immune cells that function or survive poorly in hypoxic conditions, macrophages maintain a proinflammatory phenotype that may support continued gene and protein expression when regulated by conditional hypoxia responsive elements and naturally traffic to hypoxic microenvironments, making them ideal vehicles for therapeutic payloads to hypoxic tissues, such as solid tumors. With the ability to fine-tune delivery of potent proteins in response to endogenous microenvironments, macrophage-based cellular therapies may therefore be designed for different disease settings.

Arming Immune Cell Therapeutics with Polymeric Prodrugs

Engineered immune cells are an exciting therapeutic modality, which survey and attack tumors. Backpacking strategies exploit cell targeting capabilities for delivery of drugs to combat tumors and their immune-suppressive environments. Here, a new platform for arming cell therapeutics through dual receptor and polymeric prodrug engineering is developed. Macrophage and T cell therapeutics are engineered to express a bioorthogonal single chain variable fragment receptor. The receptor binds a fluorescein ligand that directs cell loading with ligand-tagged polymeric prodrugs, termed "drugamers." The fluorescein ligand facilitates stable binding of drugamer to engineered macrophages over 10 days with 80% surface retention. Drugamers also incorporate prodrug monomers of the phosphoinositide-3-kinase inhibitor, PI-103. The extended release of PI-103 from the drugamer sustains antiproliferative activity against a glioblastoma cell line compared to the parent drug. The versatility and modularity of this cell arming system is demonstrated by loading T cells with a second fluorescein-drugamer. This drugamer incorporates a small molecule estrogen analog, CMP8, which stabilizes a degron-tagged transgene to provide temporal regulation of protein activity in engineered T cells. These results demonstrate that this bioorthogonal receptor and drugamer system can be used to arm multiple immune cell classes with both antitumor and transgene-activating small molecule prodrugs.

Anti-PD-L1 antibody direct activation of macrophages contributes to a radiation-induced abscopal response in glioblastoma

BACKGROUND

Most glioblastomas recur near prior radiation treatment sites. Future clinical success will require achieving and optimizing an "abscopal effect," whereby unirradiated neoplastic cells outside treatment sites are recognized and attacked by the immune system. Radiation combined with anti-programmed cell death ligand 1 (PD-L1) demonstrated modest efficacy in phase II human glioblastoma clinical trials, but the mechanism and relevance of the abscopal effect during this response remain unknown.

METHODS

We modified an immune-competent, genetically driven mouse glioma model (forced platelet derived growth factor [PDGF] expression + phosphatase and tensin homolog loss) where a portion of the tumor burden is irradiated (PDGF) and another unirradiated luciferase-expressing tumor (PDGF + luciferase) is used as a readout of the abscopal effect following systemic anti-PD-L1 immunotherapy. We assessed relevance of tumor neoepitope during the abscopal response by inducing expression of epidermal growth factor receptor variant III (EGFRvIII) (PDGF + EGFRvIII). Statistical tests were two-sided.

RESULTS

Following radiation of one lesion, anti-PD-L1 immunotherapy enhanced the abscopal response to the unirradiated lesion. In PDGF-driven gliomas without tumor neoepitope (PDGF + luciferase, n = 8), the abscopal response occurred via anti-PD-L1 driven, extracellular signal-regulated kinase-mediated, bone marrow-derived macrophage phagocytosis of adjacent unirradiated tumor cells, with modest survival implications (median survival 41 days vs radiation alone 37.5 days, P = 0.03). In PDGF-driven gliomas with tumor neoepitope (PDGF + EGFRvIII, n = 8), anti-PD-L1 enhanced abscopal response was associated with macrophage and T-cell infiltration and increased survival benefit (median survival 36 days vs radiation alone 28 days, P = 0.001).

CONCLUSION

Our results indicate that anti-PD-L1 immunotherapy enhances a radiation- induced abscopal response via canonical T-cell activation and direct macrophage activation in glioblastoma.

Human macrophages engineered to secrete a bispecific T cell engager support antigen-dependent T cell responses to glioblastoma

BACKGROUND

Targeted and effective treatment options are needed for solid tumors, including glioblastoma (GBM), where survival rates with standard treatments are typically less than 2 years from diagnosis. Solid tumors pose many barriers to immunotherapies, including therapy half-life and persistence, tumor penetrance, and targeting. Therapeutics delivered systemically may not traffic to the tumor site. If cellular therapies or drugs are able to access the tumor site, or can be delivered directly within the tumor, treatments may not persist for the duration necessary to reduce or eliminate tumor burden. An approach that allows durable and titratable local therapeutic protein delivery could improve antitumor efficacy while minimizing toxicities or unwanted on-target, off-tissue effects.

METHODS

In this study, human monocyte-derived macrophages were genetically engineered to secrete a bispecific T cell engager (BiTE) specific to the mutated epidermal growth factor variant III (EGFRvIII) expressed by some GBM tumors. We investigated the ability of lentivirally modified macrophages to secrete a functional BiTE that can bind target tumor antigen and activate T cells. Secreted BiTE protein was assayed in a range of T cell functional assays in vitro and in subcutaneous and intracranial GBM xenograft models. Finally, we tested genetically engineered macrophages (GEMs) secreting BiTE and the proinflammatory cytokine interleukin (IL)-12 to amplify T cell responses in vitro and in vivo.

RESULTS

Transduced human macrophages secreted a lentivirally encoded functional EGFRvIII-targeted BiTE protein capable of inducing T cell activation, proliferation, degranulation, and killing of antigen-specific tumor cells. Furthermore, BiTE secreting macrophages reduced early tumor burden in both subcutaneous and intracranial mouse models of GBM, a response which was enhanced using macrophages that were dual transduced to secrete both the BiTE protein and single chain IL-12, preventing tumor growth in an aggressive GBM model.

CONCLUSIONS

The ability of macrophages to infiltrate and persist in solid tumor tissue could overcome many of the obstacles associated with systemic delivery of immunotherapies. We have found that human GEMs can locally and constitutively express one or more therapeutic proteins, which may help recruit T cells and transform the immunosuppressive tumor microenvironment to better support antitumor immunity.

Genetically engineered macrophages persist in solid tumors and locally deliver therapeutic proteins to activate immune responses

Background

Though currently approved immunotherapies, including chimeric antigen receptor T cells and checkpoint blockade antibodies, have been successfully used to treat hematological and some solid tumor cancers, many solid tumors remain resistant to these modes of treatment. In solid tumors, the development of effective antitumor immune responses is hampered by restricted immune cell infiltration and an immunosuppressive tumor microenvironment (TME). An immunotherapy that infiltrates and persists in the solid TME, while providing local, stable levels of therapeutic to activate or reinvigorate antitumor immunity could overcome these challenges faced by current immunotherapies.

Methods

Using lentivirus-driven engineering, we programmed human and murine macrophages to express therapeutic payloads, including Interleukin (IL)-12. In vitro coculture studies were used to evaluate the effect of genetically engineered macrophages (GEMs) secreting IL-12 on T cells and on the GEMs themselves. The effects of IL-12 GEMs on gene expression profiles within the TME and tumor burden were evaluated in syngeneic mouse models of glioblastoma and melanoma and in human tumor slices isolated from patients with advanced gastrointestinal malignancies.

Results

Here, we present a cellular immunotherapy platform using lentivirus-driven genetic engineering of human and mouse macrophages to constitutively express proteins, including secreted cytokines and full-length checkpoint antibodies, as well as cytoplasmic and surface proteins that overcomes these barriers. GEMs traffic to, persist in, and express lentiviral payloads in xenograft mouse models of glioblastoma, and express a non-signaling truncated CD19 surface protein for elimination. IL-12-secreting GEMs activated T cells and induced interferon-gamma (IFNγ) in vitro and slowed tumor growth resulting in extended survival in vivo. In a syngeneic glioblastoma model, IFNγ signaling cascades were also observed in mice treated with mouse bone-marrow-derived GEMs secreting murine IL-12. These findings were reproduced in ex vivo tumor slices comprised of intact MEs. In this setting, IL-12 GEMs induced tumor cell death, chemokines and IFNγ-stimulated genes and proteins.

Conclusions

Our data demonstrate that GEMs can precisely deliver titratable doses of therapeutic proteins to the TME to improve safety, tissue penetrance, targeted delivery and pharmacokinetics.

Characterization of the immune microenvironment of diffuse intrinsic pontine glioma: implications for development of immunotherapy

Background

Diffuse intrinsic pontine glioma (DIPG) is a uniformly fatal CNS tumor diagnosed in 300 American children per year. Radiation is the only effective treatment and extends overall survival to a median of 11 months. Due to its location in the brainstem, DIPG cannot be surgically resected. Immunotherapy has the ability to target tumor cells specifically; however, little is known about the tumor microenvironment in DIPGs. We sought to characterize infiltrating immune cells and immunosuppressive factor expression in pediatric low- and high-grade gliomas and DIPG.

Methods

Tumor microarrays were stained for infiltrating immune cells. RNA was isolated from snap-frozen tumor tissue and Nanostring analysis performed. DIPG and glioblastoma cells were co-cultured with healthy donor macrophages, T cells, or natural killer (NK) cells, and flow cytometry and cytotoxicity assays performed to characterize the phenotype and function, respectively, of the immune cells.

Results

DIPG tumors do not have increased macrophage or T-cell infiltration relative to nontumor control, nor do they overexpress immunosuppressive factors such as programmed death ligand 1 and/or transforming growth factor β1. H3.3-K27M DIPG cells do not repolarize macrophages, but are not effectively targeted by activated allogeneic T cells. NK cells lysed all DIPG cultures.

Conclusions

DIPG tumors have neither a highly immunosuppressive nor inflammatory microenvironment. Therefore, major considerations for the development of immunotherapy will be the recruitment, activation, and retention of tumor-specific effector immune cells.

Macrophages genetically engineered to secrete IL-12 induce tumor killing and immune activation in human tumor slice cultures

Cell-based immunotherapies for cancer, such as chimeric antigen receptor (CAR) T-cells, are effective against certain hematologic malignancies, but less reliably overcome the immunosuppressive tumor microenvironment (TME) of solid tumors to effectively cause cancer remission. Preclinical studies testing interleukin-12 (IL-12), an immune stimulating cytokine that activates T-cells and NK cells, as an anti-tumor agent have been promising. However, clinical trials have demonstrated that IL-12 is toxic if delivered systemically. To achieve local, low-dose delivery of IL-12, we have made genetically engineered macrophages (GEMs) to produce IL-12. In vitro, IL-12 GEMs stably produce IL-12 for at least one month. To evaluate their ability to stimulate an immune response and induce tumor cell death in an intact immune environment, we co-cultured them with tumor slices from both human colorectal cancer liver metastases and pancreatic ductal adenocarcinoma. In both tumor subtypes, the addition of IL-12 GEMs increased tumor cell death and generated an inflammatory response within the tumor slice, as evidenced by an increase in interferon-gamma and C-X-C Motif Chemokine Ligand 9 and 10, when compared to control GEMs. We demonstrate our GEM platform as a promising way to locally and sustainably deliver IL-12 to solid tumors to overcome the immunosuppressive TME.

Progress on Modulating Tumor-Associated Macrophages with Biomaterials

Tumor-associated macrophages (TAMs) are a complex and heterogeneous population of cells within the tumor microenvironment. In many tumor types, TAMs contribute toward tumor malignancy and are therefore a therapeutic target of interest. Here, three major strategies for regulating TAMs are highlighted, emphasizing the role of biomaterials in these approaches. First, systemic methods for targeting tumor-associated macrophage are summarized and limitations to both passive and active targeting approaches considered. Second, lessons learned from the significant literature on wound healing and macrophage response to implanted biomaterials are discussed with the vision of applying these principles to localized, biomaterial-based modulation of tumor-associated macrophage. Finally, the developing field of engineered macrophages, including genetic engineering and integration with biomaterials or drug delivery systems, is examined. Analysis of major challenges in the field along with exciting opportunities for the future of macrophage-based therapies in oncology are included.

Effects of tumor grade and dexamethasone on myeloid cells in patients with glioma

Efforts to reduce immunosuppression in the solid tumor microenvironment by blocking the recruitment or polarization of tumor associated macrophages (TAM), or myeloid derived suppressor cells (MDSCs), have gained momentum in recent years. Expanding our knowledge of the immune cell types, cytokines, or recruitment factors that are associated with high-grade disease, both within the tumor and in circulation, is critical to identifying novel targets for immunotherapy. Furthermore, a better understanding of how therapeutic regimens, such as Dexamethasone (Dex), chemotherapy, and radiation, impact these factors will facilitate the design of therapies that can be targeted to the appropriate populations and retain efficacy when administered in combination with standard of care regimens. Here we perform quantitative analysis of tissue microarrays made of samples taken from grades I-III astrocytoma and glioblastoma (GBM, grade IV astrocytoma) to evaluate infiltration of myeloid markers CD163, CD68, CD33, and S100A9. Serum, flow cytometric, and Nanostring analysis allowed us to further elucidate the impact of Dex treatment on systemic biomarkers, circulating cells, and functional markers within tumor tissue. We found that common myeloid markers were elevated in Dex-treated grade I astrocytoma and GBM compared to non-neoplastic brain tissue and grade II-III astrocytomas. Cell frequencies in these samples differed significantly from those in Dex-naïve patients in a pattern that depended on tumor grade. In contrast, observed changes in serum chemokines or circulating monocytes were independent of disease state and were due to Dex treatment alone. Furthermore, these changes seen in blood were often not reflected within the tumor tissue.

Conclusions: Our findings highlight the importance of considering perioperative treatment as well as disease grade when assessing novel therapeutic targets or biomarkers of disease.

An Uncoupling of Canonical Phenotypic Markers and Functional Potency of Ex Vivo-Expanded Natural Killer Cells

Recent advances in cellular therapies for patients with cancer, including checkpoint blockade and ex vivo-expanded, tumor-specific T cells, have demonstrated that targeting the immune system is a powerful approach to the elimination of tumor cells. Clinical efforts have also demonstrated limitations, however, including the potential for tumor cell antigenic drift and neoantigen formation, which promote tumor escape and recurrence, as well as rapid onset of T cell exhaustion in vivo. These findings suggest that antigen unrestricted cells, such as natural killer (NK) cells, may be beneficial for use as an alternative to or in combination with T cell based approaches. Although highly effective in lysing transformed cells, to date, few clinical trials have demonstrated antitumor function or persistence of transferred NK cells. Several recent studies describe methods to expand NK cells for adoptive transfer, although the effects of ex vivo expansion are not fully understood. We therefore explored the impact of a clinically validated 12-day expansion protocol using a K562 cell line expressing membrane-bound IL-15 and 4-1BB ligand with high-dose soluble IL-2 on the phenotype and functions of NK cells from healthy donors. Following expansions using this protocol, we found expression of surface proteins that implicate preferential expansion of NK cells that are not fully mature, as is typically associated with highly cytotoxic NK cell subsets. Despite increased expression of markers associated with functional exhaustion in T cells, we found that ex vivo-expanded NK cells retained cytokine production capacity and had enhanced tumor cell cytotoxicity. The preferential expansion of an NK cell subset that is phenotypically immature and functionally pleiotropic suggests that adoptively transferred cells may persist better in vivo when compared with previous methods using this approach. Ex vivo expansion does not quell killer immunoglobulin-like receptor diversity, allowing responsiveness to various factors in vivo that may influence activation and inhibition. Collectively, our data suggest that in addition to robust NK cell expansion that has been described using this method, expanded NK cells may represent an ideal cell therapy that is longer lived, highly potent, and responsive to an array of activating and inhibitory signals.

NKG2D ligand expression in pediatric brain tumors

Adult brain tumors establish an immunosuppressive tumor microenvironment as a modality of immune escape, with several immunotherapies designed to overcome this barrier. However, the relationship between tumor cells and immune cells in pediatric brain tumor patients is not as well-defined. In this study, we sought to determine whether the model of immune escape observed in adult brain tumors is reflected in patients with pediatric brain tumors by evaluating NKG2D ligand expression on tissue microarrays created from patients with a variety of childhood brain tumor diagnoses, and infiltration of Natural Killer and myeloid cells. We noted a disparity between mRNA and protein expression for the 8 known NKG2D ligands. Surprisingly, high-grade gliomas did not have increased NKG2D ligand expression compared to normal adjacent brain tissue, nor did they have significant myeloid or NK cell infiltration. These data suggest that pediatric brain tumors have reduced NK cell-mediated immune surveillance, and a less immunosuppressive tumor microenvironment as compared to their adult counterparts. These data indicate that therapies aimed to improve NK cell trafficking and functions in pediatric brain tumors may have a greater impact on anti-tumor immune responses and patient survival, with fewer obstacles to overcome.

Genetically Engineered Macrophages: A Potential Platform for Cancer Immunotherapy

In spite of their successes against hematologic malignancies, immunotherapeutic interventions for the treatment of patients with glioblastoma (GBM) have thus far been unsuccessful. This is in part due to the presence of a tumor microenvironment that fosters neoplastic growth and protects the tumor from destruction by the immune system. A novel genetically engineered macrophage-based platform has been developed with the potential to minimize the effects of the suppressive tumor microenvironment and improve innate and adaptive antitumor immune responses. A newly described lentiviral expression system was validated for the generation of transduced monocytes and monocyte-derived macrophages, and transgene expression was shown to be stable over the course of weeks to months, both in vitro and in a mouse xenograft model of GBM. Furthermore, the genetically engineered macrophages (GEMs) neither caused morbidity in animals nor contributed to accelerated tumor growth. The versatility of GEMs is also highlighted by showing that they can be engineered to secrete proteins that either reduce immune suppression, such as the soluble transforming growth factor beta receptor II, or promote immune cell activation, by expressing interleukin 21. There is also the potential to prevent GEM-mediated immune suppression by using the CRISPR system to knock out genes responsible for dysfunction of cytotoxic cells, including interleukin 10 and programmed death-ligand 1. Together, these results suggest that GEMs are an ideal cell type for transforming the tumor microenvironment and enhancing antitumor immunity. Importantly, it is anticipated that these findings will have broad applicability to other types of tumors with microenvironments that currently preclude successful immunotherapeutic approaches.

Developing immunotherapeutic strategies to target brain tumors

INTRODUCTION

Recent years have seen rapid growth in cancer treatments that enhance the anti-tumor activities of the immune system. Collectively known as immunotherapy, modulation of the immune system has shown success treating some hematological malignancies, but has yet to be successfully applied to the treatment of patients with brain tumors.

AREAS COVERED

This review highlights mechanistic insights from murine studies and compiled recent clinical trial data, focusing on the most aggressive brain tumor, glioblastoma (GBM). The field has recently accumulated a critical mass of data, and we discuss past treatment failures in the context of newly developed approaches now entering clinical trials. This article provides an overview of the immunotherapeutic armamentarium currently in development for the treatment of patients with GBM, who are in dire need of safe and effective therapies. Expert commentary: Themes that emerge include the importance of mitigating the effects of an immunosuppressive tumor microenvironment and the potential for innate immune cell activation to enhance cytotoxic anti-tumor activity. Consideration of these studies as a collective may inform the design of new immunotherapies, as well as the immune monitoring protocols for patients participating in clinical trials.

Heat-shock protein peptide complex-96 vaccination for recurrent glioblastoma: a phase II, single-arm trial

BACKGROUND

Outcomes for patients with recurrent glioblastoma multiforme (GBM) are poor and may be improved by immunotherapy. We investigated the safety and efficacy of an autologous heat-shock protein peptide complex-96 (HSPPC-96) vaccine for patients with recurrent GBM.

METHODS

In this open-label, single-arm, phase II study, adult patients with surgically resectable recurrent GBM were given vaccine after gross total resection. The primary endpoint was overall survival at 6 months. Secondary endpoints included overall survival, progression-free survival, safety, and immune profiling. Outcome analyses were performed in the intention-to-treat and efficacy populations.

RESULTS

Between October 3, 2007 and October 24, 2011, 41 patients underwent gross total resection of recurrent GBM and received a median of 6 doses of HSPPC-96 vaccine. Following treatment, 90.2% of patients were alive at 6 months (95% confidence interval [CI]: 75.9-96.8) and 29.3% were alive at 12 months (95% CI: 16.6-45.7). Median overall survival was 42.6 weeks (95% CI: 34.7-50.5). Twenty-seven (66%) patients were lymphopenic prior to therapy, and patients with lymphocyte counts below the cohort median demonstrated decreased overall survival (hazard ratio: 4.0; 95% CI: 1.4-11.8; P = .012). There were no treatment-related deaths. There were 37 serious (grades 3-5) adverse events reported, with 17 attributable to surgical resection and a single grade 3 constitutional event related to the vaccine.

CONCLUSION

The HSPPC-96 vaccine is safe and warrants further study of efficacy for the treatment of recurrent GBM. Significant pretreatment lymphopenia may impact the outcomes of immunotherapy and deserves additional investigation.

Spatial observation and quantification of microwave heating in materials

An electromagnetic exposure chamber was designed to safely deliver electromagnetic power in the range of microwaves between 0.8 and 4.2 GHz to a thin cylindrical materials. This instrumentation is unique because the diagnostics not only measure sample heating with a response time of 1.3 ms, but also energy transmitted and reflected. Energy absorption at different frequencies was quantified via electromagnetic heating using an infrared camera. This in situ IR imaging of the spatial distribution of temperature during microwave exposure coupled with sensors for determining transmitted and reflected energy enables novel new microwave energy experiments. Samples were exposed to a portion of both the electric and magnetic fields inside a waveguide and based on sample dimensions, the field strengths were assumed uniform across the sample. Three materials were examined: two were borosilicate, first coated with graphite paint and a second without the coating; and, the third was a compressed sample of flake graphite pressed to 69% of its bulk density. Results are in agreement with the theories of microwave heating and verify the functionality of this experimental design. This diagnostic will be important in future tests where a variety of different materials can be exposed to weak electromagnetic waves and their efficiency in coupling to the microwaves can be examined.

Gliomas promote immunosuppression through induction of B7-H1 expression in tumor-associated macrophages

PURPOSE

Gliomas are known to induce local and systemic immunosuppression, inhibiting T-cell-mediated cytotoxic responses to tumor growth. Tumor-associated macrophages are a significant component of the immune infiltrate in gliomas and may express immunosuppressive surface ligands, such as B7-H1.

EXPERIMENTAL DESIGN

Tumor and peripheral blood samples from patients with glioblastoma (GBM) were analyzed by flow cytometry to evaluate the expression of B7-H1 in circulating and tumor-infiltrating macrophages. Human monocytes from healthy patients were stimulated with conditioned media from glioma cells to evaluate B7-H1 expression. Production of interleukin (IL)-10 by stimulated monocytes was measured by ELISA, and stimulation with IL-10 alone was evaluated for the ability to induce B7-H1 expression. The effect of inhibiting IL-10 and its receptor on glioma-induced B7-H1 expression in monocytes was evaluated.

RESULTS

Circulating monocytes in patients with GBM had significantly increased expression of B7-H1 compared with healthy control patients. Tumor-associated macrophages from matched GBM tissue had even greater B7-H1 expression. Treatment of normal monocytes with glioma-conditioned media could significantly increase B7-H1 expression. Stimulation of monocytes with conditioned media resulted in substantial production of IL-10 and upregulation of the IL-10 receptor. Stimulation of monocytes with IL-10 alone could significantly increase B7-H1 expression, sufficient to induce T-cell apoptosis when cocultured with stimulated monocytes. Inhibition of IL-10 and the IL-10 receptor could knock down the effect of glioma media on B7-H1 by more than 50%.

CONCLUSIONS

Gliomas can upregulate B7-H1 expression in circulating monocytes and tumor-infiltrative macrophages through modulation of autocrine/paracrine IL-10 signaling, resulting in an immunosuppressive phenotype.

Individual patient-specific immunity against high-grade glioma after vaccination with autologous tumor derived peptides bound to the 96 KD chaperone protein

PURPOSE

Cancer immunotherapy offers hope of a highly specific nontoxic adjuvant treatment. Heat shock protein peptide complexes (HSPPCs) found in cancer cells carry tumor-specific antigenic proteins and can facilitate adaptive and innate immune responses. Here we show that peptides bound to a 96 kD chaperone protein (HSP-96) from brain tissue containing glioblastoma multiforme (GBM) can be used to safely immunize patients with recurrent GBM.

EXPERIMENTAL DESIGN

Multimodality immunomonitoring was completed on 12 patients with recurrent GBM before and after immunization with an autologous HSPPC vaccine derived from surgically resected tumor. Clinical endpoints included safety assessments and overall survival.

RESULTS

No adverse events attributable to the vaccine were found. Testing of peripheral blood leukocytes before and after vaccination revealed a significant peripheral immune response specific for the peptides bound to HSP-96, in 11 of the 12 patients treated. Brain biopsies of immune responders after vaccination revealed focal CD4, CD8, and CD56 IFNγ positive cell infiltrates, consistent with tumor site specific immune responses. Immune responders had a median survival of 47 weeks after surgery and vaccination, compared with 16 weeks for the single nonresponder.

CONCLUSIONS

These data provide the first evidence in humans of individual patient-specific immune responses against autologous tumor derived peptides bound to HSP-96.

Soluble factors secreted by glioblastoma cell lines facilitate recruitment, survival, and expansion of regulatory T cells: implications for immunotherapy

In patients with glioma, the tumor microenvironment can significantly impact pro-inflammatory immune cell functions. However, the mechanisms by which this occurs are poorly defined. Because immunosuppressive regulatory T cells (Treg) are over represented in the tumor microenvironment compared with peripheral blood, we hypothesized that the tumor may have an effect on Treg survival, migration, expansion, and/or induction of a regulatory phenotype from non-Treg conventional CD4+ T cells. We defined the impact of soluble factors produced by tumor cells on Treg from healthy patients in vitro to determine mechanisms by which gliomas influence T cell populations. We found that tumor-derived soluble factors allowed for preferential proliferation and increased chemotaxis of Treg, compared with conventional T cells, indicating that these mechanisms may contribute to the increased Treg in the tumor microenvironment. Conventional T cells also exhibited a significantly increased expression of pro-apoptotic transcripts in the presence of tumor-derived factors, indicating that survival of Treg in the tumor site is driven by exposure to soluble factors produced by the tumor. Together, these data suggest that tumor burden may induce increased Treg infiltration, proliferation, and survival, negating productive anti-tumor immune responses in patients treated with immunotherapies. Collectively, our data indicate that several mechanisms of Treg recruitment and retention in the tumor microenvironment exist and may need to be addressed to improve the specificity of immunotherapies seeking to eliminate Treg in patients with glioma.

Ubiquitin-specific protease 8 links the PTEN-Akt-AIP4 pathway to the control of FLIPS stability and TRAIL sensitivity in glioblastoma multiforme

The antiapoptotic protein FLIP(S) is a key suppressor of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in human glioblastoma multiforme (GBM) cells. We previously reported that a novel phosphatase and tensin homologue (PTEN)-Akt-atrophin-interacting protein 4 (AIP4) pathway regulates FLIP(S) ubiquitination and stability, although the means by which PTEN and Akt were linked to AIP4 activity were unclear. Here, we report that a second regulator of ubiquitin metabolism, the ubiquitin-specific protease 8 (USP8), is a downstream target of Akt, and that USP8 links Akt to AIP4 and the regulation of FLIP(S) stability and TRAIL resistance. In human GBM xenografts, levels of USP8 correlated inversely with pAkt levels, and genetic or pharmacologic manipulation of Akt regulated USP8 levels in an inverse manner. Overexpression of wild-type USP8, but not catalytically inactive USP8, increased FLIP(S) ubiquitination, decreased FLIP(S) half-life, decreased FLIP(S) steady-state levels, and decreased TRAIL resistance, whereas short interfering RNA (siRNA)-mediated suppression of USP8 levels had the opposite effect. Because high levels of the USP8 deubiquitinase correlated with high levels of FLIP(S) ubiquitination, USP8 seemed to control FLIP(S) ubiquitination through an intermediate target. Consistent with this idea, overexpression of wild-type USP8 decreased the ubiquitination of the FLIP(S) E3 ubiquitin ligase AIP4, an event previously shown to increase AIP4-FLIP(S) interaction, whereas siRNA-mediated suppression of USP8 increased AIP4 ubiquitination. Furthermore, the suppression of FLIP(S) levels by USP8 overexpression was reversed by the introduction of siRNA targeting AIP4. These results show that USP8, a downstream target of Akt, regulates the ability of AIP4 to control FLIP(S) stability and TRAIL sensitivity.

TGF-beta downregulates the activating receptor NKG2D on NK cells and CD8+ T cells in glioma patients

The activating receptor NKG2D, expressed by natural killer (NK) cells and CD8(+) T cells, has a role in the specific killing of transformed cells. We examined NKG2D expression in patients with glioblastoma multiforme and found that NKG2D was downregulated on NK cells and CD8(+) T cells. Expression of NKG2D on lymphocytes significantly increased following tumor resection and correlated with an increased ability to kill NKG2D ligand-positive tumor targets. Despite the presence of soluble NKG2D ligands in the sera of glioblastoma patients, NKG2D downregulation was primarily caused by tumor-derived tumor growth factor-beta, suggesting that blocking of this cytokine may have therapeutic benefit.

A novel PTEN-dependent link to ubiquitination controls FLIPS stability and TRAIL sensitivity in glioblastoma multiforme

Phosphatase and tensin homologue (PTEN) loss and activation of the Akt-mammalian target of rapamycin (mTOR) pathway increases mRNA translation, increases levels of the antiapoptotic protein FLIP(S), and confers resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in glioblastoma multiforme (GBM). In PTEN-deficient GBM cells, however, the FLIP(S) protein also exhibited a longer half-life than in PTEN mutant GBM cells, and this longer half-life correlated with decreased FLIP(S) polyubiquitination. FLIP(S) half-life in PTEN mutant GBM cells was reduced by exposure to an Akt inhibitor, but not to rapamycin, suggesting the existence of a previously undescribed, mTOR-independent linkage between PTEN and the ubiquitin-dependent control of protein stability. Total levels of the candidate FLIP(S) E3 ubiquitin ligase atrophin-interacting protein 4 (AIP4) were comparable in PTEN wild-type (WT) and PTEN mutant GBM cells, although in PTEN-deficient cells, AIP4 was maintained in a stable polyubiquitinated state that was less able to associate with FLIP(S) or with the FLIP(S)-containing death inducing signal complex. Small interfering RNA-mediated suppression of AIP4 levels in PTEN WT cells decreased FLIP(S) ubiquitination, prolonged FLIP(S) half-life, and increased TRAIL resistance. Similarly, the Akt activation that was previously shown to increase TRAIL resistance did not alter AIP4 levels, but increased AIP4 ubiquitination, increased FLIP(S) steady-state levels, and suppressed FLIP(S) ubiquitination. These results define the PTEN-Akt-AIP4 pathway as a key regulator of FLIP(S) ubiquitination, FLIP(S) stability, and TRAIL sensitivity and also define a novel link between PTEN and the ubiquitin-mediated control of protein stability.

Increased expression of the glioma-associated antigen ARF4L after loss of the tumor suppressor PTEN. Laboratory investigation

OBJECT

Despite recent advances in cancer immunotherapy, cellular mechanisms controlling expression of tumor-associated antigens are poorly understood. Mutations in cancer cells, such as loss of PTEN, may increase expression of tumor-associated antigens. The authors investigated the relationship between PTEN status and the expression of a glioma-associated antigen, adenosine diphosphate-ribosylation factor 4-like (ARF4L) protein.

METHODS

Human glioma cell lines with confirmed PTEN status were examined by Northern blot analysis and quantitative polymerase chain reaction. Western blot analysis was used to measure ARF4L protein levels across multiple cell lines.

RESULTS

The loss of PTEN was shown to lead to increased levels of ARF4L protein but no change in transcript levels. Cell lines with serial mutations, including activation of Ras and Akt pathways, also demonstrated increased levels of ARF4L protein, which decreased after treatment with rapamycin. The ARF4L transcript preferentially localized to the polysomal compartment after PTEN loss in glioma or activation of Akt in human astrocytes.

CONCLUSIONS

Expression of ARF4L is controlled by the activated Akt/mTOR pathway, which is a downstream effect of the loss of PTEN function. Mutations leading to oncogenesis may impact the regulation and expression of tumor specific antigens. Screening of mutation status in glioma may be helpful in selecting patients for immunotherapy trials in the future.

Differential ex vivo nitric oxide production by acutely isolated neonatal and adult microglia

Microglia are the macrophage population residing in the parenchyma of the central nervous system (CNS), and are thought to play critical roles in CNS development, homeostasis and defense against pathogens. Microglia are capable of rapidly responding to microbial pathogens through engagement of their Toll-like receptors (TLRs). We first compared the efficiency of these responses in primary microglia acutely isolated from adult and neonatal mice. While the cytokine and chemokine responses of adult microglia were generally higher than those of neonatal cells stimulated ex vivo through TLRs, the nitric oxide response of neonatal microglia was markedly enhanced relative to the adult cells. We then went on to identify culture conditions such as exposure to M-SCF or GM-CSF that markedly enhanced the nitric oxide response of microglia, particularly those from the adult CNS. Finally, we demonstrate that the differential nitric oxide response of neonatal and adult microglia is not only limited to the mouse, but also extends to rat microglia.

Loss of tumor suppressor PTEN function increases B7-H1 expression and immunoresistance in glioma

Cancer immunoresistance and immune escape may play important roles in tumor progression and pose obstacles for immunotherapy. Expression of the immunosuppressive protein B7 homolog 1 (B7-H1), also known as programmed death ligand-1 (PD-L1), is increased in many pathological conditions, including cancer. Here we show that expression of the gene encoding B7-H1 increases post transcriptionally in human glioma after loss of phosphatase and tensin homolog (PTEN) and activation of the phosphatidylinositol-3-OH kinase (PI(3)K) pathway. Tumor specimens from individuals with glioblastoma multiforme (GBM) had levels of B7-H1 protein that correlated with PTEN loss, and tumor-specific T cells lysed human glioma targets expressing wild-type PTEN more effectively than those expressing mutant PTEN. These data identify a previously unrecognized mechanism linking loss of the tumor suppressor PTEN with immunoresistance, mediated in part by B7-H1.

Effect of cholestyramine on the fecal excretion of intravenously administered cholesterol-4-14C and its degradation products in a hypercholesterolemic patient

The effect of cholestyramine on the fecal excretion of bile acids and neutral sterols was measured in a hypercholesterolemic patient on a low fat, high polyunsaturated fatty acid-containing diet after the intravenous injection of cholesterol-4-(14)C. A significant (16%) lowering of serum cholesterol concentration was accompanied by a 3.2-fold increase in fecal bile acid excretion but no change in neutral sterol output. The increased bile acid loss was adequate to account for the observed fall in serum cholesterol level. The implications of these findings were discussed.