Dendritic cell biology and cancer therapy

Dendritic cells (DCs) are natures best antigen-presenting cells. They possess attributes that allow them to effectively fulfill the requirements for priming/activating T cells and mediating tumor-specific immune responses. In this review, emphasis is placed on those aspects of DC biology that best illustrate their usefulness in immunotherapy of cancer. Culture, maturation, and polarization conditions for human DC are discussed, as are strategies for antigen-loading of DCs and for their delivery to patients with cancer. A concise recommendation for monitoring of DC-based vaccination trails is provided.This work was presented at the first Cancer Immunology and Immunotherapy Summer School, 8–13 September 2003, Ionian Village, Bartholomeio, Peloponnese, Greece.     

Dendritic cell therapy for tolerance induction to stem cell transplants

With rapid progress in identification of a variety of adult stem cells, there is an urgent need for basic studies on immunomodulatory protocols relevant to stem cell transplantation. There are new possibilities for immunomodulation invoking the function of dendritic cells (DC) in the induction of tolerance. This paper addresses the application of DC immunotherapy for establishing and maintaining peripheral tolerance to stem cell or tissue allografts. While recent approaches target immature DC and their role in peripheral tolerance, many questions can be raised about the tolerogenic properties of those cells and the clinical feasibility of their use. Procedures published to date for preparation of DC differ significantly in terms of the source of cells and methods for culture and expansion of immature, apparently tolerogenic DC. With evidence for tolerogenicity associated with all classes or lineages of DC, the hypothesis is advanced that the tolerogenicity of DC is determined during hematopoiesis and may be best established by immunotherapy using DC progenitors. It is expected that peripheral tolerance and central or thymic-based tolerance may complement each other as two essential mechanisms for transplantation tolerance since different clinical situations may invoke the need for different procedures for tolerance induction.     

PET for diagnosis and therapy of brain tumors

Main contribution of PET in the management of brain tumors is at the therapeutic level. Specific reasons explain this role of molecular imaging in the therapeutic management of brain tumors, especially gliomas. Gliomas are by nature infiltrating neoplasms and the interface between tumor and normal brain tissue may not be accurately defined on CT and MRI. Also, gliomas are often histologically heterogeneous with anaplastic areas evolving within a low-grade tumor, and the contrast-enhancement on CT or MRI does not represent a good marker for anaplastic tissue detection. Finally, assessment of tumor residue, recurrence or progression may be altered by different signals related to inflammation or adjuvant therapies, even on contrast-enhanced CT and MRI. These limitations of the conventional neuroimaging in delineating tumor and detecting anaplastic tissue lead to potential inaccuracy in lesion targeting at different steps of the management (diagnostic, surgical, and post-therapeutic stages). Molecular information provided by PET has proved helpful to supplement morphological imaging data in this context. ¹⁸F-FDG (FDG) and amino-acid tracers such as ¹¹C-methionine (MET), provides complementary metabolic data that are independent from the anatomical MR information. These tracers help in the definition of glioma extension, in the detection of anaplastic areas and in the postoperative follow-up. Additionally, PET data have an independent prognostic value. To take advantage of PET data in glioma treatment, PET might be integrated in the planning of image-guided biopsies, radiosurgery and resection.     

Glutamate release by primary brain tumors induces epileptic activity

Epileptic seizures are a common and poorly understood comorbidity for individuals with primary brain tumors. To investigate peritumoral seizure etiology, we implanted human-derived glioma cells into severe combined immunodeficient mice. Within 14-18 d, glioma-bearing mice developed spontaneous and recurring abnormal electroencephalogram events consistent with progressive epileptic activity. Acute brain slices from these mice showed marked glutamate release from the tumor mediated by the system x(c)(-) cystine-glutamate transporter (encoded by Slc7a11). Biophysical and optical recordings showed glutamatergic epileptiform hyperexcitability that spread into adjacent brain tissue. We inhibited glutamate release from the tumor and the ensuing hyperexcitability by sulfasalazine (SAS), a US Food and Drug Administration-approved drug that blocks system x(c)(-). We found that acute administration of SAS at concentrations equivalent to those used to treat Crohn's disease in humans reduced epileptic event frequency in tumor-bearing mice compared with untreated controls. SAS should be considered as an adjuvant treatment to ameliorate peritumoral seizures associated with glioma in humans.     

Effect of hormones on primary cell cultures from pregnancy-dependent mouse mammary tumors.

No hormone combination was successful in maintaining long term primary cultures of pregnancy-dependent mammary tumors. Insulin provided the most consistent dose dependent stimulatory effect on short term proliferation as measured by 3H-TdR incorporation into DNA. Insulin in combination with corticosterone and prolactin produced the greatest stimulatory effect in most tumors. Both insulin at 5 microgram/ml and insulin, prolactin and hydrocortisone induced a partially synchronous wave of DNA synthesis in restimulated cultures. The time course of the wave of DNA synthesis was different for different hormone treatments. Insulin as 5 microgram/ml caused an earlier wave of DNA synthesis than insulin, prolactin plus corticosterone.     

Myxoma virus combined with rapamycin treatment enhances adoptive T cell therapy for murine melanoma brain tumors

Adoptive transfer of tumor-specific T cells has shown some success for treating metastatic melanoma. We evaluated a novel strategy to improve adoptive therapy by administering both T cells and oncolytic myxoma virus to mice with syngeneic B16.SIY melanoma brain tumors. Adoptive transfer of activated CD8⁺ 2C T cells that recognize SIY peptide doubled survival time, but SIY-negative tumors recurred. Myxoma virus killed B16.SIY cells in vitro, and intratumoral injection of virus led to selective and transient infection of the tumor. Virus treatment recruited innate immune cells to the tumor and induced IFNβ production in the brain, resulting in limited oncolytic effects in vivo. To counter this, we evaluated the safety and efficacy of co-administering 2C T cells, myxoma virus, and either rapamycin or neutralizing antibodies against IFNβ. Mice that received either triple combination therapy survived significantly longer with no apparent side effects, but eventually relapsed. Importantly, rapamycin treatment did not impair T cell-mediated tumor destruction, supporting the feasibility of combining adoptive immunotherapy and rapamycin-enhanced virotherapy. Myxoma virus may be a useful vector for transient delivery of therapeutic genes to a tumor to enhance T cell responses.     

Neural stem cells--a promising potential therapy for brain tumors

Brain tumors can be highly aggressive and debilitating for many patients and lead to an untimely death in just a few months. Unfortunately, due to the location of many brain tumors, therapy with ionizing radiation, chemotherapeutic agents and/or surgery has limited rewards. In addition, the probability of totally removing highly infiltrative tumors, particularly gliomas, is extremely low and rarely provides a cure. The need for directed targeting and ablation of tumors with minimal damage to nearby healthy tissue has lead to the most recent findings and uses of neural stem cells for therapeutic treatment of brain tumors. Recently, some very promising studies have demonstrated that exogenous neural stem cells have the remarkable ability to migrate very long distances towards sites of metastasis after transplantation. These studies also show that intravascular injections of neural stem cells may lead to preferential migration towards central nervous system tumors. It has also been demonstrated that genetically modified neural stem cells, engineered to produce anti-tumor molecules, upon transplantation, have the ability to migrate towards tumors and reduce tumor mass directly or through a "bystander" effect. Here we review the current literature examining the promise of utilizing genetically modified neural stem cells as vehicles for CNS tumor therapy.     

Gene therapy of experimental brain tumors using neural progenitor cells

Glioblastomas, the most frequent and malignant of primary brain tumors, have a very poor prognosis. Gene therapy of glioblastomas is limited by the short survival of viral vectors and by their difficulty in reaching glioblastoma cells infiltrating the brain parenchyma. Neural stem/progenitor cells can be engineered to produce therapeutic molecules and have the potential to overcome these limitations because they may travel along the white matter, like neoplastic cells, and engraft stably into the brain. Retrovirus-mediated transfer of the gene for interleukin-4 is an effective treatment for rat brain glioblastomas. Here, we transferred the gene for interleukin-4 into C57BL6J mouse primary neural progenitor cells and injected those cells into established syngeneic brain glioblastomas. This led to the survival of most tumor-bearing mice. We obtained similar results by implanting immortalized neural progenitor cells derived from Sprague-Dawley rats into C6 glioblastomas. We also documented by magnetic resonance imaging the progressive disappearance of large tumors, and detected 5-bromodeoxyuridine-labeled progenitor cells several weeks after the injection. These findings support a new approach for gene therapy of brain tumors, based on the grafting of neural stem cells producing therapeutic molecules.     

Gene therapy of primary T cell immunodeficiencies

Gene therapy of severe combined immunodeficiencies has been proven to be effective to provide sustained correction of the T cell immunodeficiencies. This has been achieved for 2 forms of SCID, i.e SCID-X1 (γc deficiency) and adenosine deaminase deficiency. Occurrence of gene toxicity generated by integration of first generation retroviral vectors, as observed in the SCID-X1 trials has led to replace these vectors by self inactivated (SIN) retro(or lenti) viruses that may provide equivalent efficacy with a better safety profile. Results of ongoing clinical studies in SCID as well as in other primary immunodeficiencies, such as the Wiskott Aldrich syndrome, will be thus very informative.     

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.     

Growth in short term primary cell cultures derived from pregnancy-dependent mammary tumors.

The behavior of cells in primary cultures derived from autonomous and pregnancy-dependent mouse mammary tumors was studied. Despite initial growth both dependent and autonomous mammary tumors produced only short-term primary cultures. Initial plating density had a marked effect on growth with only cultures plated at greater than or equal to 2 X 10(5) cells/cm2 showing any short-termed growth. Time lapse analysis showed that the lack of growth was due to failures of cytokinesis and increased death rate and intermitotic time in cultures plated at less than 2 X 10(5) cells/cm2. Using continuous label autoradiographic techniques, a partial synchronous wave of DNA synthesis was observed with newly plated and restimulated cultures. DNA synthesis reached a peak 24-48 hrs. after plating or restimulation and then dropped to low values for the next few days. Attempts to maintain the initial high rate of DNA synthesis or to induce another round of DNA synthesis by enriched media, increased serum concentrations, or other types of serum and plasma were at best only partially successful. Important hormones necessary for growth of mammary tissue in vivo may be necessary for sustained growth in vitro.     

Dendritic cell origins: puzzles and paradoxes.

In the present review, a series of studies on the origins of dendritic cells of mice and humans are summarized. Several subsets of mature dendritic cells found in vivo are described and these may correspond to distinct lineages. There is evidence that some dendritic cells are myeloid-derived and that others are lymphoid-derived. The different ways of generating dendritic cells are examined and an attempt to reconcile the differences seen using mouse and human culture models is made. The particular case of Langerhans cells is discussed and an historical overview of the biology of the plasmacytoid T cells, which may represent a distinct 'lymphoid-related' dendritic cell lineage, is given. It is concluded that three or four different pathways lead to the development of different subtypes of dendritic cells.     

Neural stem cell therapy for brain disease

Brain diseases, including brain tumors, neurodegenerative disorders, cerebrovascular diseases, and traumatic brain injuries, are among the major disorders influencing human health, currently with no effective therapy. Due to the low regeneration capacity of neurons, insufficient secretion of neurotrophic factors, and the aggravation of ischemia and hypoxia after nerve injury, irreversible loss of functional neurons and nerve tissue damage occurs. This damage is difficult to repair and regenerate the central nervous system after injury. Neural stem cells (NSCs) are pluripotent stem cells that only exist in the central nervous system. They have good self-renewal potential and ability to differentiate into neurons, astrocytes, and oligodendrocytes and improve the cellular microenvironment. NSC transplantation approaches have been made for various neurodegenerative disorders based on their regenerative potential. This review summarizes and discusses the characteristics of NSCs, and the advantages and effects of NSCs in the treatment of brain diseases and limitations of NSC transplantation that need to be addressed for the treatment of brain diseases in the future.     

A role for glutamate in growth and invasion of primary brain tumors

The vast majority of primary brain tumors derive from glial cells and are collectively called gliomas. While, they share some genetic mutations with other cancers, they do present with a unique biology and have developed adaptations to meet specific biological needs. Notably, glioma growth is physically restricted by the skull, and, unless normal brain cells are destroyed, tumors cannot expand. To overcome this challenge, glioma cells release glutamate which causes excitotoxic death to surrounding neurons, thereby vacating room for tumor expansion. The released glutamate also explains peritumoral seizures which are a common symptom early in the disease. Glutamate release occurs via system X^c, a cystine–glutamate exchanger that releases glutamate in exchange for cystine being imported for the synthesis of the cellular antioxidant GSH. It protects tumor cells from endogenously produced reactive oxygen and nitrogen species but also endows tumors with an enhanced resistance to radiation- and chemotherapy. Pre-clinical data demonstrates that pharmacological inhibition of system X^c causes GSH depletion which slows tumor growth and curtails tumor invasion in vivo . An Food and Drug Administration approved drug candidate is currently being introduced into clinical trials for the treatment of malignant glioma.     

Dendritic cell recovery post-lymphodepletion: a potential mechanism for anti-cancer adoptive T cell therapy and vaccination

Adoptive transfer of autologous tumor-reactive T cells holds promise as a cancer immunotherapy. In this approach, T cells are harvested from a tumor-bearing host, expanded in vitro and infused back to the same host. Conditioning of the recipient host with a lymphodepletion regimen of chemotherapy or radiotherapy before adoptive T cell transfer has been shown to substantially improve survival and anti-tumor responses of the transferred cells. These effects are further enhanced when the adoptive T cell transfer is followed by vaccination with tumor antigens in combination with a potent immune adjuvant. Although significant progress has been made toward an understanding of the reasons underlying the beneficial effects of lymphodepletion to T cell adoptive therapy, the precise mechanisms remain poorly understood. Recent studies, including ours, would indicate a more central role for antigen presenting cells, in particular dendritic cells. Unraveling the exact role of these important cells in mediation of the beneficial effects of lymphodepletion could provide novel pathways toward the rational design of more effective anti-cancer immunotherapy. This article focuses on how the frequency, phenotype, and functions of dendritic cells are altered during the lymphopenic and recovery phases post-induction of lymphodepletion, and how they affect the anti-tumor responses of adoptively transferred T cells.     

Uptake and utilization of CDP-choline in primary brain cell cultures from fetal brain

The utilization of double-labeled CDP-choline by cultured brain cells has been studied. CDP-choline is demonstrated to be rapidly hydrolysed into CMP and choline phosphate. The fragments, or their hydrolysis products, penetrate into the cells and are utilized for lipid synthesis. At short times after the isotope administration a rapid labeling of phosphatidylcholine was detected, when cells were incubated with CDP-choline. The same was not seen when cells were incubated with labeled choline. From these observations it can be inferred that either CDP-choline can penetrate the cell membrane or that some mechanism involving CDP-choline and leading to phospholipid synthesis can work at the external surface of the plasma membranes.