*1A.Majid Eslahtalab, 2Ali Badiee Dendritic cells-based cancer vaccines: The role of lipid-based nanoparticles *1A.Majid Eslahtalab, 2Ali Badiee 1- School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran 2- Department of Pharmaceutics, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran * Email: eslahtalaba821@mums.ac.ir Introduction: The idea of preventing cancer have been alleged for at least 200 years [1]. There is great interest in developing novel therapies that can completely remove residual disease and prolong life. Interest in cancer vaccines has been exceptionally strong. Over the past two decades, the revolution in biotechnology has led to many capabilities that we did not have before and which have begun to explain the successes and failures of cancer vaccines providing new direction [2]. Figure 1. History of cancer prevention researches. Cancer vaccination strategies and approaches: Vaccination against cancer is an important modality complementing current standard therapies and may lead to long-term control of cancer. The long effort to produce a cancer vaccine has not succeeded. Nevertheless, a number of novel approaches can be pursued that include optimized antigen design, in vivo-targeted DCs vaccination and cancer vaccines used in combination with chemotherapy, monoclonal antibodies, adoptive T-cell transfer or stem cell transplantation [3]. Dendritic cells (DCs)-based vaccines: DCs are unique APC that play a pivotal role in the initiation and direction of an immune response. They link the innate and adaptive immune systems. DCs are distinguished from other APC such as B cells, macrophages and monocytes, as being the only cells capable of inducing naive T cell responses [4]. Figure 2. The antigen can be directly linked to the targeting moiety and be administered in combination with maturation stimuli (a). Alternatively, the maturation stimuli, for example, Toll-like receptor (TLR) ligands, can be introduced in the targeting construct itself (b). Antigen might be packaged within a microparticle, for example, a liposome, carrying targeting moieties on its surface (c). Owing to the acidic pH of late endosomes, these fusogenic peptides undergo a conformational change, resulting in leakage and possibly fusion of the liposomal and endosomal membranes, promoting cytosolic delivery of liposomal content. Subsequent to delivery of protein and peptides into the cytoplasm, the immunoproteasome digests the proteins into peptides. Epitopes exclusively generated by the standard proteasome need to be incorporated into the vaccine as peptide antigens. These peptides, enter the endoplasmic reticulum through transporter associated with antigen processing (TAP), are loaded onto MHC class I molecules and presented to CD8+ T cells [5]. Ex vivo and In vivo targeting to DCs: In ex vivo method, DCs-based cancer vaccine requires fully mature DCs for effective induction of functionally specific T cells against tumors as shown in Fig. 4. In vivo targeting of antigens to DCs represents a promising approach for DCs-based vaccination, as it can bypass the laborious and expensive ex vivo antigen loading and more importantly, in vivo DCs-targeted vaccination was reported to be more efficient in eliciting an anti-tumor immune response [3]. Figure 3. Ex vivo tergeting to DCs. Figure 4. In vivo targeting to DCs: (A) Irradiated tumor cells transduced with a viral gene transfer vector encoding a cytokine such as GM-CSF attract DCs. (B) This part explains ex vivo Targeting to DCs: DCs can be directly loaded by incubation with tumor protein lysates or peptides with sequences based on expressed tumor antigens, or by viral gene transfer vectors expressing TAAs. (C) TAAs can be locally supplied to DCs by the direct injection of peptides, viral gene expression vectors, or naked DNA expression plasmids. DCs migrate to secondary lymphoid tissues where they present the antigen epitopes to T cells to generate an antitumor cytolytic T cell response [6]. Nanoparticulate delivery systems: Particulate delivery system (e. g., emulsions, microparticles, ISCOMs, liposomes, virosomes, and virus-like particles) have comparable dimensions to the pathogens that the immune system evolved to combat and are efficiently taken up by APC and function mainly to deliver associated antigen into these key cells. They can also act as a depot from which the encapsulated antigen is gradually released. Therefore, these agents have been used as vaccine-delivery systems. In addition, formulating potent immunostimulatory adjuvants into delivery systems may limit adverse events, through restricting the systemic circulation of the adjuvant. Targeted delivery of adjuvants and antigens to specific cell types or tissues may reduce potential toxic effects and help to achieve a specific desired response [7]. These systems are divided to two major categories as described below; Polymer-based particles: A variety of polymers exist from which nanoparticles for drug delivery can be synthesized. The most commonly studied polymers are poly (D, L-lactide-co-glycolide) (PLG) and polylactide (PLA). These biodegradable, biocompatible polymers have been approved for use in humans and have been extensively studied for use in the formulation of vaccine antigens [8]. Lipid-based particles: These are versatile delivery systems that can be customized towards specific vaccine targets by varying their composition. Being natural constituents of biomembranes, lipids are attractive components of adjuvant systems in being biodegradable, biocompatible and affordable [9].   Liposome: Liposomes are spherical entities composed of a phospholipid bilayer shell with an aqueous core. There are mainly three types of liposomes; MLV (multilamillar vesicles), SUV (small unilamillar vesicles), and LUV (large unilamillar vesicles) and depends on their types, the size varys between 40 nm and ~ 2 µm [8]. Immunoliposome: Targeted liposomes have targeting ligands or affinity moieties attached to the surface of the liposomes. The targeting ligands may be antibodies or fragments thereof, in which case the liposomes are referred to as immunoliposomes [10]. Virosome: unilamellar phospholipid bilayer vesicle with a mean diameter of 150 nm. Virosomes are not able to replicate but are pure fusion-active vesicles. In contrast to liposomes, virosomes contain functional viral envelope glycoproteins [8]. Virus-like particles (VLPs): These consist of proteins that form a virus outer shell and the surface proteins, without the RNA required for replication [8]. Immunostimulating complexes (ISCOM): Vaccine delivery vehicle with potent adjuvant activity. These are ~40 nm cage-like particles produced by combining a protein antigen, cholesterol, phospholipid and the saponin adjuvant Quil A [8]. Proteosomes: These are hydrophobic, membranous, multimolecular preparations of meningococcal outer membrane proteins(OMPs) that are also B cell mitogens [11]. Cholesterol-bearing hydrophobized pullulan nanoparticles (CHP):These are a newly developed antigen delivery vehicle that can be used to formulate nanoparticles, including protein antigens. CHP is composed of pullulan backbone and cholesterol branches [8]. Monophosphoryl lipid A (MPL®): This is an immunostimulating TLR-4 receptor agonist composed of detoxified lipopolysaccharide (LPS) from Salmonella minnesota R59 [8]. Solid lipid nanoparticles (SLN): Solid lipid nanoparticles (SLN) introduced in 1991 represent an alternative carrier system to traditional colloidal carriers, such as emulsions, liposomes and polymeric micro- and nanoparticles. SLN combine advantages of the traditional systems but avoid some of their major disadvantages. SLN are capable of transporting genes to the interior of the cells and enable the transport of nucleic acids — DNA or RNA — in order to be used in gene therapy [12,13]. Lipid protamine DNA (LPD): LPD particles are formed by combining cationic liposomes and polycation-condensed DNA. Upon mixing, the components rearrange to form a virus-like structure with condensed DNA inside of lipid membranes [14]. Virosome Immunoliposome Liposome VLPs Figure 5.Lipid-based nanoparticles SLN ISCOM Proteosome LPD CHP MPL Summary, conclusions and future challenges: Novel particle-based delivery vehicles are being evaluated in a variety of vaccines, including those against diseases such as cancer, malaria, AIDS, etc., in which a cellular immune response is desired. Clinical studies of various nanoparticulate immunopotentiators and antigen delivery vehicles have shown CTL responses for ISCOMs and Montanide™. Th1 responses have been elicited for MPL®. Additionally, cellular immune responses have also been generated in humans using VLPs, virosomes, and liposomes. The breadth of carriers that has shown this desirable response shows promise for the development of new and improved vaccines of a wide variety of types. We anticipate a wave of cancer vaccine approvals in the next 5–6 years, primarily due to recent advances in the clinical trials of cancer vaccines [8,15]. References: 6- Jay A. 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