Potent Immune Stimulation from Nanoparticle Carriers Relies on the Interplay of Adjuvant Surface Density and Adjuvant Mass Distribution

A multifunctional ATP-generating system by reduced graphene oxide-based scaffold repairs neuronal injury by improving mitochondrial function and restoring bioelectricity conduction

Peripheral nerve injury usually impairs neurological functions. The excessive oxidative stress and disrupted bioelectrical conduction gives rise to a hostile microenvironment and impedes nerve regeneration. Therefore, it is of urgent need to develop tissue engineering products which help alleviate the oxidative insults and restore bioelectrical signals. Melatonin (MLT) is an important endogenous hormone that diminishes the accumulation of reactive oxygen species. Reduced graphene oxide (RGO) possesses the excellent electrical conductivity and biocompatibility. In this study, a multilayered MLT/RGO/Polycaprolactone (PCL) composite scaffold was fabricated with beaded nanostructures to improve cell attachment and proliferation. It also exhibited stable mechanical properties by high elastic modulus and guaranteed structural integrity for nerve regeneration. The live/dead cell staining and cell counting kit assay were performed to evaluate the toxicity of the scaffold. JC-1 staining was carried out to assess the mitochondrial potential. The composite scaffold provided a biocompatible interface for cell viability and improved ATP production for energy supply. The scaffold improved the sensory and locomotor function recovery by walking track analysis and electrophysiological evaluation, reduced Schwann cell apoptosis and increased its proliferation. It further stimulated myelination and axonal outgrowth by enhancing S100β, myelin basic protein, β3-tubulin, and GAP43 levels. The findings demonstrated functional and morphological recovery by this biomimetic scaffold and indicated its potential for translational application.

Bimodal Targeting of Human Leukocytes by Fc- and CpG-Decorated Polymersomes to Tune Immune Induction

The use of well-defined nanovesicles composed of amphiphilic block copolymers (polymersomes) for delivery of adjuvants and antigens is a promising strategy for vaccine development. However, the potency of nanoparticle vaccines depends on efficient interaction with and activation of cells involved in antigen presentation, which can be achieved by targeting cellular receptors. Here, we showed that the Fc fragment display on the polymersome surface resulted in markedly improved interactions with granulocytes, monocytes, and NK cells, while for “naked” polymersomes, virtually no binding to leukocytes was observed. Moreover, CpG-decorated polymersomes were found to also interact with T and/or B cells. Interestingly, whole blood stimulations with Fc fragment and CpG-decorated polymersomes induced interleukin (IL)-6, IL-8, and TNF-α production, while naked polymersomes did not induce any cytokine production. In conclusion, specific immune induction by polymersomes can be controlled using bimodal targeting of different immune receptors, which is an essential feature for targeted vaccine delivery.

Phage display as a tool for vaccine and immunotherapy development

Bacteriophages, or phages, are viruses that specifically infect bacteria and coopt the cellular machinery to create more phage proteins, eventually resulting in the release of new phage particles. Phages are heavily utilized in bioengineering for applications ranging from tissue engineering scaffolds to immune signal delivery. Of specific interest to vaccines and immunotherapies, phages have demonstrated an ability to activate both the innate and adaptive immune systems. The genome of these viral particles can be harnessed for DNA vaccination, or the surface proteins can be exploited for antigen display. More specifically, genes that encode an antigen of interest can be spliced into the phage genome, allowing antigenic proteins or peptides to be displayed by fusion to phage capsid proteins. Phages therefore present antigens to immune cells in a highly ordered and repetitive manner. This review discusses the use of phage with adjuvanting activity as antigen delivery vehicles for vaccination against infectious disease and cancer.

Nucleic acids presenting polymer nanomaterials as vaccine adjuvants

Most vaccines developed today include only the antigens that best stimulate the immune system rather than the entire virus or microbe, which makes vaccine production and use safer and easier, though they lack potency to induce acceptable immunity and long-term protection. The incorporation of additional immune stimulating components, named adjuvants, is required to generate a strong protective immune response. Nucleic acids (DNA and RNA) and their synthetic analogs are promising candidates as vaccine adjuvants activating Toll-like receptors (TLRs). Additionally, in the last few years several nanocarriers have emerged as platforms for targeted co-delivery of antigens and adjuvants. In this review, we focus on the recent developments in polymer nanomaterials presenting nucleic acids as vaccine adjuvants. We aim to compare the effectiveness of the various classes of polymers in immune modulating materials (nanoparticles, dendrimers, single-chain particles, nanogels, polymersomes and DNA-based architectures). In particular, we address the critical role of parameters such as size, shape, complexation and release of TLR ligands, cellular uptake, stability, toxicity and potential importance of spatial control in ligand presentation.

PEGylation of model drug carriers enhances phagocytosis by primary human neutrophils

Targeted drug carriers are attractive for the delivery of therapeutics directly to the site of a disease, reducing systemic side effects and enhancing the efficacy of therapeutic molecules. However, the use of particulate carriers for drug delivery comes with its own set of challenges and barriers. Among these, a great deal of research effort has focused on protecting carriers from clearance by phagocytes via altering carrier surface chemistry, mostly with the use of polyethylene glycol (PEG) chain coatings. However, few papers have explored the effects of PEGylation on uptake by freshly-obtained primary human phagocytes in physiological conditions. In this work, we investigate the effect of PEGylation on particle uptake by primary human neutrophils in vitro and compare these effects to several cell lines and other model phagocytic cells systems. We find that human neutrophils in whole blood preferentially phagocytose PEGylated particles (e.g., ∼40% particle positive neutrophils for PEGylated versus ∼20% for carboxylated polystyrene microspheres) and that this effect is linked to factors present in human plasma. Model phagocytes internalized PEGylated particles less efficiently or equivalently to carboxylated particles in culture medium but preferentially phagocytosed PEGylated particles in the human plasma (e.g., ∼86% versus ∼63% PEGylated versus carboxylated particle positive cells, respectively). These findings have significant implications for the efficacy of PEGylation in designing long-circulating drug carriers, as well as the need for thorough characterization of drug carrier platforms in a wide array of in vitro and in vivo assays.

STATEMENT OF SIGNIFICANCE

The work in this manuscript is highly significant to the field of drug delivery, as it explores in-depth the effects of polyethylene glycol (PEG) coatings, which are frequently used to prevent phagocytic clearance of particulate drug carriers, on the phagocytosis of such carriers by neutrophils, the most abundant leukocyte in blood circulation. Surprisingly, we find that PEGylation enhances uptake by primary human neutrophils, specifically in the presence of human plasma. This result suggests that PEGylation may not confer the benefits in humans once thought, and may help to explain why PEG has not become the "magic bullet" it was once thought to be in the field of particulate drug delivery.

Neutrophil-Particle Interactions in Blood Circulation Drive Particle Clearance and Alter Neutrophil Responses in Acute Inflammation

Although nano- and microparticle therapeutics have been studied for a range of drug delivery applications, the presence of these particles in blood flow may have considerable and understudied consequences to circulating leukocytes, especially neutrophils, which are the largest human leukocyte population. The objective of this work was to establish if particulate drug carriers in circulation interfere with normal neutrophil adhesion and migration. Circulating blood neutrophils in vivo were found to be capable of rapidly binding and sequestering injected carboxylate-modified particles of both 2 and 0.5 μm diameter within the bloodstream. These neutrophil-particle associations within the vasculature were found to suppress neutrophil interactions with an inflamed mesentery vascular wall and hindered neutrophil adhesion. Furthermore, in a model of acute lung injury, intravenously administered drug-free particles reduced normal neutrophil accumulation in the airways of C57BL/6 mice between 52% and 60% versus particle-free mice and between 93% and 98% in BALB/c mice. This suppressed neutrophil migration resulted from particle-induced neutrophil diversion to the liver. These data indicate a considerable acute interaction between injected particles and circulating neutrophils that can drive variations in neutrophil function during inflammation and implicate neutrophil involvement in the clearance process of intravenously injected particle therapeutics. Such an understanding will be critical toward both enhancing designs of drug delivery carriers and developing effective therapeutic interventions in diseases where neutrophils have been implicated.