Abstract
Strategies to design delivery vehicles are critical in modern vaccine-adjuvant development. Nanoparticles (NPs) encapsulating antigen(s) and adjuvant(s) are promising vehicles to deliver antigen(s) and adjuvant(s) to antigen-presenting cells (APCs), allowing optimal immune responses against a specific pathogen. In this study, we developed a novel adjuvant delivery approach for induction of efficient in vivo immune responses. Polyethylenimine (PEI) was physically conjugated to poly(lactic-co-glycolic) acid (PLGA) to form PLGA/PEI NPs. This complex was encapsulated with resiquimod (R848) as toll-like receptor (TLR) 7/8 agonist, or monophosphoryl lipid A (MPLA) as TLR4 agonist and co-assembled with cytosine–phosphorothioate–guanine oligodeoxynucleotide (CpG ODN) as TLR9 agonist to form a tripartite formulation [two TLR agonists (inside and outside NPs) and PLGA/PEI NPs as delivery system]. The physicochemical characteristics, cytotoxicity and cellular uptake of these synthesized delivery vehicles were investigated. Cellular viability test revealed no pronounced cytotoxicity as well as increased cellular uptake compared to control groups in murine macrophage cells (J774 cell line). In the next step, PLGA (MPLA or R848)/PEI (CpG ODN) were co-delivered with ovalbumin (OVA) encapsulated into PLGA NPs to enhance the induction of immune responses. The immunogenicity properties of these co-delivery formulations were examined in vivo by evaluating the cytokine (IFN-γ, IL-4, and IL-1β) secretion and antibody (IgG1, IgG2a) production. Robust and efficient immune responses were achieved after in vivo administration of PLGA (MPLA or R848)/PEI (CpG ODN) co-delivered with OVA encapsulated in PLGA NPs in BALB/c mice. Our results demonstrate a rational design of using dual TLR agonists in a context-dependent manner for efficient nanoparticulate adjuvant-vaccine development.
Highlights
The recent advances in vaccine development have moved the area from traditional vaccines using whole microorganisms to subunit vaccines containing only purified or modified antigenic proteins
cytosine–phosphorothioate–guanine oligodeoxynucleotide (CpG ODN) as TLR9 agonist was physically linked to the core–shell of PLGA (MPLA) or PLGA (R848) using PEI to form a hybrid PLGA NPs containing dual Toll-like receptors (TLRs) agonists (MPLA + CpG ODN or R848 + CpG ODN)
Targeting antigens along with TLR agonists encapsulated in PLGA NPs to antigen-presenting cells (APCs) is a promising approach for generating potent Th1 polarizing immune responses that can be potentially useful in immunotherapy of cancer and intracellular pathogens [28]
Summary
The recent advances in vaccine development have moved the area from traditional vaccines using whole microorganisms to subunit vaccines containing only purified or modified antigenic proteins. Pattern recognition receptors (PRRs) are the main class of innate immunity sensors, recognizing diverse sets of pathogen-associated molecular patterns (PAMPs) and considered to be the target of novel molecular adjuvant developments. One of the major families of PRRs, Toll-like receptors (TLRs) are expressed by a variety of cells and capable of inducing innate immune responses and initiate the pathways toward effective adaptive immune responses. Most pathogens encounter with the immune system through multiple danger signals including PAMPs to stimulate multiple PRRs, resulting in a synergistic upregulation of pro-inflammatory cytokines and chemokines and subsequent activation of antigen-presenting cells (APCs). The combination of multiple PRRs agonists and proper delivery systems may be a promising strategy in any artificial immunization approach to induce effective immune responses in the context of vaccine-adjuvant development [1,2,3,4]
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