Dendritic Cells Loaded with Tumor Antigens and a Dual Immunostimulatory and Anti-Interleukin 10-Specific Small Interference RNA Prime T Lymphocytes against Leukemic Cells

Ribonucleic Acid Engineering of Dendritic Cells for Therapeutic Vaccination: Ready 'N Able to Improve Clinical Outcome?

Targeting and exploiting the immune system has become a valid alternative to conventional options for treating cancer and infectious disease. Dendritic cells (DCs) take a central place given their role as key orchestrators of immunity. Therapeutic vaccination with autologous DCs aims to stimulate the patient's own immune system to specifically target his/her disease and has proven to be an effective form of immunotherapy with very little toxicity. A great amount of research in this field has concentrated on engineering these DCs through ribonucleic acid (RNA) to improve vaccine efficacy and thereby the historically low response rates. We reviewed in depth the 52 clinical trials that have been published on RNA-engineered DC vaccination, spanning from 2001 to date and reporting on 696 different vaccinated patients. While ambiguity prevents reliable quantification of effects, these trials do provide evidence that RNA-modified DC vaccination can induce objective clinical responses and survival benefit in cancer patients through stimulation of anti-cancer immunity, without significant toxicity. Succinct background knowledge of RNA engineering strategies and concise conclusions from available clinical and recent preclinical evidence will help guide future research in the larger domain of DC immunotherapy.

Harnessing the Antiviral-Type Responses Induced by Immunostimulatory siRNAs for Cancer Immunotherapy

When introduced into endosomes via cationic lipids, certain small interfering RNA (siRNA) sequences activate the interferon signaling pathways in immune cells such as dendritic cells (DCs), known as the most efficient antigen-presenting cells of the immune system. Human immature DCs produced high levels of the immune-response protein interferon-α and tumor necrosis factor- α upon incubation with siRNA/lipid formulations, resulting in their maturation and expression of co-stimulatory molecules like CD80, CD86, and CD40 on the cell surface. These molecules are used by mature DCs to co-stimulate T cells during antigen presentation in lymphoid organs. Ex vivo loading of immature DCs with DOTAP-formulated immunostimulatory siRNAs and tumor antigens has proven effective as a cancer vaccine in a rat model of acute myeloid leukemia. Here, we describe this new vaccination strategy that targets tumor cells by activating DCs and blocking the expression of immunosuppressive factors.

Unleashing the Therapeutic Potential of Dendritic and T Cell Therapies Using RNA Interference

Therapeutic dendritic cell (DC) cancer vaccines work to boost the body's immune system to fight a cancer. Although this type of immunotherapy often leads to the activation of tumor-specfic T cells, clinical responses are fairly low, arguing for the need to improve the design of DC-based vaccines. Recent studies revealed a promising strategy of combining DC vaccines with small interfering RNAs (siRNAs) targeting immunosuppressive signals such as checkpoint receptors. Similarly, incorporating checkpoint siRNA blockers in adoptive T-cell therapy to amplify cytotoxic T lymphocyte responses is now being tested in the clinic. The development of the next generation of cancer immunotherapies using siRNA technology will hopefuly benefit patients with various cancer types including those who did not respond to current therapies. This review highlights the latest advances in RNA interference technology to improve the therapeutic efficacy of DC cancer vaccines and T cell therapy.

Releasing the Immune System Brakes Using siRNAs Enhances Cancer Immunotherapy

Therapeutic dendritic cell (DC) cancer vaccines rely on the immune system to eradicate tumour cells. Although tumour antigen-specific T cell responses have been observed in most studies, clinical responses are fairly low, arguing for the need to improve the design of DC-based vaccines. The incorporation of small interfering RNAs (siRNAs) against immunosuppressive factors in the manufacturing process of DCs can turn the vaccine into potent immune stimulators. Additionally, siRNA modification of ex vivo-expanded T cells for adoptive immunotherapy enhanced their killing potency. Most of the siRNA-targeted immune inhibitory factors have been successful in that their blockade produced the strongest cytotoxic T cell responses in preclinical and clinical studies. Cancer patients treated with the siRNA-modified DC vaccines showed promising clinical benefits providing a strong rationale for further development of these immunogenic vaccine formulations. This review covers the progress in combining siRNAs with DC vaccines or T cell therapy to boost anti-tumour immunity.

Rational combination immunotherapeutic approaches for effective cancer treatment

Immunotherapy is an important mode of cancer treatment. Over the past decades, immunotherapy has improved the clinical outcome for cancer patients. However, in many cases, mutations in cancer cells, lack of selectivity, insufficiency of tumor-reactive T cells, and host immunosuppression limit the clinical benefit of immunotherapy. Combination approaches in immunotherapy may overcome these obstacles. Accumulating evidence demonstrates that combination immunotherapy is the future of cancer treatment. However, designing safe and rational combinations of immunotherapy with other treatment modalities is critical. This review will discuss the optimal immunotherapy-based combinations mainly with respect to the mechanisms of action of individual therapeutic agents that target multiple steps in evasion and progression of tumor.

Engineering better immunotherapies via RNA interference

The therapeutic potential of dendritic cell (DC) cancer vaccines has gained momentum in recent years. However, clinical data indicate that antitumor immune responses generally fail to translate into measurable tumor regression. This has been ascribed to a variety of tolerance mechanisms, one of which is the expression of immunosuppressive factors by DCs and T cells. With respect to cancer immunotherapies, these factors antagonise the ability to induce robust and sustained immunity required for tumor cell eradication. Gene silencing of immunosuppressive factors in either DCs or adoptive transferred T cells enhanced anti-tumor immune responses and significantly inhibited tumor growth. Therefore, engineered next generation of DC vaccines or adoptive T-cell therapy should include immunomodulatory siRNAs to release the "brakes" imposed by the immune system. Moreover, the combination of gene silencing, antigen targeting to DCs and cytoplasmic cargo delivery will improve clinical benefits.

Engineering therapeutic cancer vaccines that activate antitumor immunity

Vaccination represents one the most effective methods of preventing disease. Because dendritic cells (DCs) are the most efficient antigen presenting cells, exploiting their plasticity is likely to yield improved therapeutic vaccines. Herein, we applied a novel DC-based vaccine (i.e., DC loaded with leukemia antigens that have been transfected with an IL-10 siRNA capable of coordinately activating DCs via TLR7/8) in a rat model of acute myeloid leukemia. Leukemic rats treated with this new vaccine had less leukemic cell mass in their bone marrows and less extramedullar dissemination of the leukemic disease examined postmortem compared with rats given the control vaccine. Collectively, the new strategy demonstrates the possible usefulness of dual siRNAs as an immunomodulatory drug with antileukemic properties.

Challenging the future of siRNA therapeutics against cancer: the crucial role of nanotechnology

The identification of numerous deregulated signaling pathways on cancer cells and supportive stromal cells has revealed several molecular targets whose downregulation can elicit significant benefits for cancer treatment. In this respect, gene downregulation can be efficiently achieved by exploiting the RNA interference mechanism, particularly by the delivery of chemical synthesized small-interfering RNAs (siRNAs), which have the ability to mediate, in a specific manner, the degradation of any mRNA with complementary nucleotide sequence. However, several concerns regarding off-target effects and immune stimulation have been raised. Depending on their sequence, siRNAs can trigger an innate immune response, which might mediate undesirable side effects that ultimately compromise their clinical utility. This is a very relevant effect that will be discussed in the present manuscript. Moreover, the major drawback in the translation of siRNAs into the clinical practice is undoubtedly their inability to accumulate in tumor sites, particularly in organs other than the liver. In fact, upon systemic administration, owing to siRNAs physico-chemical features, they are rapidly cleared from the blood stream. Therefore, the development of a proper drug delivery system is of utmost importance. In this review, some of the latest advances on different nanotechnological platforms for siRNA delivery under clinical evaluation will be discussed. Along with this, targeting approaches towards cancer and/or endothelial cells will also be addressed, as these are some of the most promising strategies to enhance specific tumor accumulation while avoiding healthy tissues. Finally, clinical information on ongoing studies in patients with advanced solid tumors will be also provided.

Overcoming self-tolerance to tumour cells

Over the past decade, immunotherapy has emerged as a promising alternative form of cancer treatment with the potential to eradicate tumour metastasis. However, its curative potential is in general limited by peripheral tolerance mechanisms and the elimination of self-reactive T cells via thymic negative selection. Unlike infectious challenges, tumour cells arise endogenously, and therefore the majority of tumour antigens are recognized as self. Under appropriate conditions, however, tumour reacting T cells can be activated through a mechanism of molecular mimicry, which involves the recognition of cross reactive foreign antigens mimicking tumour antigens. Moreover, dendritic cells can be reprogrammed by RNA interference to present self-antigens and activate anti-tumour T cells. This review highlights some of the strategies used to break self-tolerance against solid and blood tumour cells. Also, the possibility of reprogramming DC and/or lymphocyte functions using small interfering RNAi (siRNA) is discussed.

Optimized protocols for siRNA delivery into monocytes and dendritic cells

Over the past decade, immunotherapy has emerged as a promising alternative form of cancer treatment with the potential to eradicate tumour metastasis. Unfortunately, its curative potential is in general limited by immunosuppressive proteins that negatively regulate dendritic (DC) and/or T-cell function. The recent discovery of RNA interference (RNAi) has facilitated the study of gene function in immune cells and recent data indicate that DC maturation, function, and survival can be modulated by small interfering RNAs (siRNAs) targeting genes involved in immune suppression. This chapter describes detailed protocols for introducing siRNAs into human monocytes and dendritic cells using standard electroporation techniques.