Dendritic cells and their emerging clinical applications

Optimization of Interleukin-10 incorporation for dendritic cells embedded in Poly(ethylene glycol) hydrogels

Translational research in biomaterials and immunoengineering is leading to the development of novel advanced therapeutics to treat diseases such as cancer, autoimmunity, and viral infections. Dendritic cells (DCs) are at the center of these therapeutics given that they bridge innate and adaptive immunity. The biomaterial system developed herein uses a hydrogel carrier to deliver immunomodulatory DCs for amelioration of autoimmunity. This biomaterial vehicle is comprised of a poly (ethylene glycol)-4 arm maleimide (PEG-4MAL) hydrogels, conjugated with the immunosuppressive cytokine, interleukin-10, IL-10, and cross-linked with a collagenase-degradable peptide sequence for the injectable delivery of immunosuppressive DCs to an anatomical disease-relevant site of the cervical lymph nodes, for intended application to treat multiple sclerosis. The amount of IL-10 incorporated in the hydrogel was optimized to be 500 ng in vitro, based on immunological endpoints. At this concentration, DCs exhibited the best viability, most immunosuppressive phenotype, and protection against proinflammatory insult as compared with hydrogel-incorporated DCs with lower IL-10 loading amounts. Additionally, the effect of the degradability of the PEG-4MAL hydrogel on the release rate of incorporated IL-10 was assessed by varying the ratio of degradable peptides: VPM (degradable) and DTT (nondegradable) and measuring the IL-10 release rates. This IL-10-conjugated hydrogel delivery system for immunosuppressive DCs is set to be assessed for in vivo functionality as the immunosuppressive cytokine provides a tolerogenic environment that keeps DCs in their immature phenotype, which consequently enhances cell viability and optimizes the system's immunomodulatory functionality.

[Development of intracellular drug delivery system using fusogenic liposomes]

Drug delivery system (DDS) research has contributed greatly toward improving chemotherapy efficacy and reducing its adverse effects through the development of approaches to optimize pharmacokinetics, such as controlled release and targeting. On the other hand, the remarkable progress of this latest life science research has altered the concept of what constitutes medical supplies. A change in this concept would allow for the consideration of medical materials that use not only conventional low molecular-weight organic compounds, but also biomacromolecules, including nucleic acids and proteins, that constitute living organisms. Although these biomacromolecular drugs are expected to demonstrate excellent efficacy based on their intrinsic bioactivity, they quickly degrade when administered in vivo and only a limited number have therefore been developed into medicines. In addition, most biomacromolecular drugs are ineffective until they are delivered to particular cells within a tissue or to particular organelles within a cell. To develop effective biomacromolecular medicines, it is necessary to introduce a DDS that is capable of ensuring internal stability as well as precise control of internal and intracellular dynamics, and to establish a new fundamental technology for DDS that can accommodate the material properties and mechanisms of action of the biomacromolecular drugs. In this context, this review introduces our approach to the design and creation of "Intracellular DDS" using fusogenic liposomes for application to gene therapy and tumor peptide vaccines. We suggest that this technology is very important for controlling the intracellular pharmacokinetics of biomacromolecular drugs.

Aging and the dendritic cell system: implications for cancer

The immune system shows a decline in responsiveness to antigens both with aging, as well as in the presence of tumors. The malfunction of the immune system with age can be attributed to developmental and functional alterations in several cell populations. Previous studies have shown defects in humoral responses and abnormalities in T cell function in aged individuals, but have not distinguished between abnormalities in antigen presentation and intrinsic T cell or B cell defects in aged individuals. Dendritic cells (DC) play a pivotal role in regulating immune responses by presenting antigens to naïve T lymphocytes, modulating Th1/Th2/Th3/Treg balance, producing numerous regulatory cytokines and chemokines, and modifying survival of immune effectors. DC are receiving increased attention due to their involvement in the immunobiology of tolerance and autoimmunity, as well as their potential role as biological adjuvants in tumor vaccines. Recent advances in the molecular and cell biology of different DC populations allow for addressing the issue of DC and aging both in rodents and humans. Since DC play a crucial role in initiating and regulating immune responses, it is reasonable to hypothesize that they are directly involved in altered antitumor immunity in aging. However, the results of studies focusing on DC in the elderly are conflicting. The present review summarizes the available human and experimental animal data on quantitative and qualitative alterations of DC in aging and discusses the potential role of the DC system in the increased incidence of cancer in the elderly.

Numerical and functional assessment of blood dendritic cells in prostate cancer patients

BACKGROUND

Prostate cancer is one of the leading causes of cancer deaths in males and there are currently no effective treatments available for metastatic disease. Although recent clinical trials using dendritic cell (DC) based immunotherapy treatments have demonstrated safety, immunological responses, and some clinical efficacy, better vaccine delivery strategies need to be developed. We have undertaken the first detailed analysis of blood DC (BDC) subsets and their function in prostate cancer patients, with a view to utilizing immunoselected BDC for immunotherapy.

METHODS

We enumerated the CD11c+CD1c+, CD11c+CD16+, and CD11c-CD123+ BDC subsets in whole blood of prostate cancer patients using a single platform TruCOUNT assay. These subsets were identified and purified using flow cytometry and immunomagnetic selection, and their functional capacity analyzed by costimulatory molecule expression, cytokine secretion, and antigen presenting ability.

RESULTS

There were no significant differences in the number or composition of these subsets compared to healthy donors and these cells could be purified with equal efficiency from both groups. The prostate cancer patients BDC had similar levels of key costimulatory molecules and cytokine expression profiles, compared to healthy donors, and these were upregulated to the same extent, in response to exogenous stimuli. BDC from both groups were capable of eliciting allogeneic proliferative responses and inducing autologous CD4+ responses to naïve and recall antigens, and antigen-specific CD8+ responses to influenza matrix protein and prostate specific antigen.

CONCLUSIONS

These results indicate that an immunoselected CD1c+ BDC preparation could provide a suitable vaccine delivery vehicle for future prostate cancer immunotherapy trials.

Vaccine strategies to treat lymphoproliferative disorders

Lymphoproliferative disorders, including follicular lymphoma (FL), multiple myeloma (MM) and chronic lymphatic leukaemia (CLL), are slowly progressive malignancies which remain incurable despite advances in therapy. Harnessing the immune system to recognise and destroy tumours is a promising new approach to treating these diseases. Dendritic cells (DC) are unique antigen-presenting cells that play a central role in the initiation and direction of immune responses. DC loaded ex vivo with tumour-associated antigens and administered as a vaccine have already shown promise in early clinical trials for a number of lymphoproliferative disorders, but the need for improvement is widely agreed. Recent advances in the understanding of basic DC biology and lessons from early clinical trials have provided exciting new insights into the generation of anti-tumour immune responses and the design of vaccine strategies. In this review we provide an overview of our current understanding of DC biology and their function in patients with lymphoproliferative disorders. We discuss the current status of clinical trials and new approaches to exploit the antigen presenting capacity of DC to design vaccines of the future.

DC preparations for therapy

This review describes and compares the different DC preparations currently under laboratory and clinical investigation as vehicles for cancer immunotherapy.

The large scale generation of dendritic cells for the immunization of patients with non-small cell lung cancer (NSCLC)

In the current study, we generated large numbers of dendritic cells (DCs) from patients with non-small cell lung cancer (NSCLC) for a vaccine trial. The DCs were generated from CD14+ cells obtained by immuno-magnetic bead column separation technique. The CD14+ cells were placed in culture in the presence of granulocyte macrophage colony stimulating factor (GMCSF) and Interleukin 4 (IL-4). At Day 7, apoptotic bodies derived from an allogeneic NSCLC line 1650-TC were added to the cultures at a DC:tumor cell ratio of 1:1. At Day 8, the DCs were harvested, washed and injected intradermally into patients. Using this protocol we have prepared DCs for 16 patients. An average of 9.3 x 10(7) DCs was injected for the priming dose and 8.2 x 10(7) DCs for the boost. Clinical evaluation of the patients and immune assessment are presented in a separate report. The current report provides evidence for the large scale production of functional DCs derived from patients with NSCLC which can be used as vaccines in clinical trials.

Biodegradable nanoparticle mediated antigen delivery to human cord blood derived dendritic cells for induction of primary T cell responses

Dendritic cells (DCs) in the peripheral tissues act as sentinels of the immune system. They detect and capture pathogens entering the body and present their antigens to T cells to trigger responses directed towards elimination of the pathogen. The induction of peripheral tolerance against self and certain foreign antigens is also believed to be mediated through DCs. The outcome of any immune response is largely controlled by the microenvironment of antigen capture, processing and presentation by DCs. The "context" of antigen delivery to DCs will directly influence the microenvironment of antigen presentation and hence the regulation of immune responses. We report here preliminary investigations describing the formulation of a pharmaceutically acceptable, biodegradable, and strategic nanoparticulate delivery system, and its application for efficient antigen loading of DCs to achieve antigen specific T cell activation. "Pathogen-mimicking" nanoparticles capable of interacting with DCs were fabricated by incorporating monophosphoryl lipid A (MPLA; toll-like receptor (TLR) 4 ligand) or CpG ODN (seq #2006; TLR9 ligand) in biodegradable copolymer, poly(D,L,-lactic-co-glycolic acid) (PLGA). The uptake of PLGA nanoparticles by human umbilical cord blood derived DCs (DCs propagated from CD34 progenitors) was conclusively demonstrated by scanning electron microscopy (SEM), fluorescence activated cell sorting (FACS) and confocal laser scanning microscopy (CLSM). Cell phenotype at day 12 of cultures was determined as immature DC using specific cell surface markers, i.e. CD11c (approximately 90%), MHC-II (approximately 70%), CD86 (approximately 20%), CD83 (approximately 5%), CD80 (approximately 40%), CD40 (approximately 40%), and CCR7 (approximately 5%). Tetanus toxoid (TT), a model antigen, was encapsulated in nanoparticles along with an immunomodulator, i.e. either MPLA or CpG ODN. DCs pulsed with various antigen formulations were co-cultured with autologous naïve T cells at various cell ratios (DC: T cells were 1:5-20). The DCs pulsed with TT and MPLA together in nanoparticles induced significantly higher T cell proliferation (P<0.05) as compared to when DCs pulsed with TT and MPLA in solution were employed. A similar trend was observed when CpG ODN was used instead of MPLA in the TT nanoparticles. This strategy of antigen delivery to DCs was then tested with a cancer vaccine candidate, a MUC1 lipopeptide. The T cell proliferation observed in the presence of nanoparticulate MUC1 and MPLA pulsed-DCs was much higher than DCs pulsed with soluble antigen (P<0.0005). These results indicate that PLGA nanoparticles mimicking certain features of pathogens are efficient delivery systems for targeting vaccine antigens to DCs and activation of potent T cell responses.

Advances in the use of dendritic cells and new adjuvants for the development of therapeutic vaccines

The recent advances in immunology and biotechnology have opened new perspectives for the development of immunotherapy strategies against cancer and infectious diseases. The understanding of the pivotal role of dendritic cells in the initiation and regulation of the immune response has led to an ensemble of preclinical studies and pilot clinical trials, which have provided some evidence on the potential advantages of using dendritic cells as cellular adjuvants for the development of therapeutic vaccines against infectious diseases and malignancies. Current research efforts are focused on the definition of optimal protocols for dendritic cell-based therapies in patients. An additional area of emerging importance in the field of immunotherapy is the identification of safe, selective, and more powerful adjuvants, capable not only of enhancing immune protection against pathogens, but also of breaking tolerance against certain tumor-associated antigens, which is the critical issue for the development of cancer vaccines. The recent recognition of the key role of certain cytokines, such as type I interferons, in linking the innate and adaptive immunity through their action on dendritic cells opens new perspectives for using these natural factors as adjuvants for the development of therapeutic vaccines. We review some of the emerging research aspects in immunotherapy, with special attention to the perspectives of using new adjuvants and dendritic cell-based vaccines for the treatment of cancer and infectious diseases.

Granulocyte/macrophage-colony stimulating factor and interleukin-4 expand and activate type-1 dendritic cells (DC1) when administered in vivo to cancer patients

Two rare populations of cells with the features of dendritic cell precursors (preDC) can be identified in human peripheral blood. PreDC1 are HLA-DR+/CD11c+ cells which mature into DC1 capable of stimulating Th1 responses. In contrast, preDC2 are HLA-DR+/CD11c-/CD123+ cells that promote Th2 responses when matured into DC2. We hypothesized that administration of GM-CSF and IL-4, growth factors for DC1, would specifically augment the number and function of circulating DC1 in vivo. Patients with advanced metastatic cancer were treated with GM-CSF (2.5 microg/kg/day) and IL-4 (4 or 6 microg/kg/day) for 7 days. Cytokine administration at the highest IL-4 dose produced an average 2.3-fold increase in preDC2 number, but a 6.5-fold increase in preDC1, resulting in an increased ratio of circulating preDC1:preDC2 from 1.4:1 pre-treatment to 4.3:1 after cytokine therapy. DC1 precursors identified after in vivo therapy were larger, more complex and expressed higher levels of HLA-DR, CD11c and CD80 than pre-treatment cells. DC1 isolated from the peripheral blood of patients receiving GM-CSF/IL-4 therapy demonstrated MLR activity comparable to that of monocyte-derived DC generated in vitro from the patients' pre-treatment blood using GM-CSF and IL-4. We conclude that systemic administration of GM-CSF and IL-4 preferentially expands and matures the preDC1 population in vivo. These effects correlate with antigen-presenting activity, providing a mechanism by which systemic GM-CSF and IL-4 might stimulate anti-tumor immunity in vivo.

Potent immune response against HIV-1 and protection from virus challenge in hu-PBL-SCID mice immunized with inactivated virus-pulsed dendritic cells generated in the presence of IFN-alpha

A major challenge of AIDS research is the development of therapeutic vaccine strategies capable of inducing the humoral and cellular arms of the immune responses against HIV-1. In this work, we evaluated the capability of DCs pulsed with aldrithiol-2-inactivated HIV-1 in inducing a protective antiviral human immune response in SCID mice reconstituted with human PBL (hu-PBL-SCID mice). Immunization of hu-PBL-SCID mice with DCs generated after exposure of monocytes to GM-CSF/IFN-alpha (IFN-DCs) and pulsed with inactivated HIV-1 resulted in a marked induction of human anti-HIV-1 antibodies, which was associated with the detection of anti-HIV neutralizing activity in the serum. This vaccination schedule also promoted the generation of a human CD8+ T cell response against HIV-1, as measured by IFN-gamma Elispot analysis. Notably, when the hu-PBL-SCID mice immunized with antigen-pulsed IFN-DCs were infected with HIV-1, inhibition of virus infection was observed as compared with control animals. These results suggest that IFN-DCs pulsed with inactivated HIV-1 can represent a valuable approach of immune intervention in HIV-1-infected patients.