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  • br Introduction br In the last few decades immunotherapy


    1. Introduction
    In the last few decades, immunotherapy has attracted much atten-tion in treatment of various infectious diseases and cancers (Couzin-Frankel, 2013), in which different players of the host immune system are exploited to eliminate pathogens and cancer 256934-39-1 (Farkona et al., 2016; Khademi et al., 2018a). Among the immune system player,
    Corresponding author.
    dendritic cells (DCs), putatively known as professional antigen-pre-senting cells (APCs), are important target cells for immunotherapy. These cells start and activate antigen (Ag)-specific immune responses leading (Veglia and Gabrilovich, 2017) to a cascade of immune actions, which eventually induces immune system to attack abnormal cancer cells and biotic agents. When a specific Ag is recognized and taken up by an APC, it is first subjected to a multi-step internal processing of
    Table 1
    Physicochemical characteristics of synthetized liposomal formulations.
    Formulations Molar ratio Total lipid concentration (mM) Z-average (nm) PdIc Z-potential (mV)
    a Data are shown as mean ± standard deviation of three independent measurements.
    b Indicates significant difference as compared to other liposome formulations.
    c Polydispersity index below 0.2 is regarded as the best uniform size distribution.
    d Z-potential > +30 mV and < −30 mV is considered significantly positive and negative, respectively.
    degradation in endosome, then it is exposed on the cell membrane and introduced to other immune cell players. The resultant fragments of Ag (i.e. immunogenic epitopes) bind to major histocompatibility complex (MHC) class I and class II on DCs and then, the activated DCs bearing antigenic epitopes move through the draining lymph nodes, where they interact with CD8+ T or CD4+ T cells. Finally, the CD8+ T cells are induced to develop the ability to specifically recognize and destroy cancerous and infected cells, which is then called Ag-specific cytotoxic T lymphocytes (TCLs), (Mellman et al., 2011).
    Therefore, delivery of Ag to APCs is the essential rate-limiting step needed for an effective immune response. This it is considered as an important factor in cancer immunotherapy, which necessitates strate-gies to improve the Ag delivery. In this regard, various kinds of nano-carriers, including nanopolymers, nanogels, carbon nanomaterials, have already been utilized as promising technologies for Ag delivery in cancer immunotherapy (Khademi et al., 2018b; Khademi et al., 2018c; Park et al., 2018; Yuba, 2018). Among these systems, liposomes are more widely used as a delivery vehicle platform for Ag delivery (Yuba, 2018; Zamani et al., 2018; Zamani et al., 2019). Liposomes are bilayer spherical vesicles formed upon self-assembly of phospholipid molecules in an aqueous medium. They have exhibited multiple beneficial prop-erties suitable for drug formulation, including high biocompatibility, biodegradability, safety, high loading capacity and easy preparation, which make them one of the most popular type of nano-carriers in immunotherapies (Nikoofal-Sahlabadi et al., 2018; Schwendener, 2014; Zamani et al., 2018; Zamani et al., 2019).
    Phospholipids and cholesterol are the major backbone of liposomes offering various biological and physicochemical properties. Our re-cently published papers reported that the lipid components of liposomal formulations might act as immune stimulating agents as well as to the major immunogenic agent used in the formulation (Jafari et al., 2018; Razazan et al., 2017; Zamani et al., 2018). In this regard, the im-munogenic properties of liposomal formulations are associated with the physiochemical properties such as types of phospholipid, particle size, liposome surface charge and modifications (Tao Liang et al., 2006; Zamani et al., 2018).
    In our previous studies, we reported that some naive liposomal formulations (empty liposomes) were able to induce immune response in mouse models of tumors (Arab et al., 2018; Mansourian et al., 2014; Razazan et al., 2017; Shariat et al., 2014; Talesh et al., 2016; Zamani et al., 2018). This encouraged us to investigate the relationship of some lipid compositions with the level of induced immune response and with the type of immune reaction. For this purpose, four characteristic li-posomal formulations with various physicochemical properties were prepared without being loaded with tumor-specific antigens, and they were administered in a mice model of C26 colon carcinoma.
    2. Materials and methods
    The phospholipids used in the present study were 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-Dimyristoyl-sn-glycero-3- 
    phosphorylglycerol (DMPG), 1,2-dioleoyl-sn-glycero-3-phosphoethano-lamine (DOPE), 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) hydrogenated soya phosphatidylcholine (HSPC), methoxypolyethelene glycol (Mw 2000)-distearylphosphatidylethanolamine (mPEG2000-DSPE), 1,2-distearoyl-sn-glycero-3-(phospho-rac-(L-glycerol)) (sodium salt) (DSPG) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), which were obtained from Lipoid (Ludwigshafen, Germany). Cholesterol was purchased from Sigma–Aldrich (St. Louis, MO). All other chemical solvents and reagents were of chemical grade. C26 colon carcinoma cell line was purchased from Cell Lines Service (Eppelheim, Germany).