TUNABLE COMPLEMENT ACTIVATION BY PARTICLES WITH VARIABLE SIZE AND Fc DENSITY

Nanometer- and angstrom-scale characteristics that modulate complement responses to nanoparticles

The contribution of the complement system to non-specific host defence and maintenance of homeostasis is well appreciated. Many particulate systems trigger complement activation but the underlying mechanisms are still poorly understood. Activation of the complement cascade could lead to particle opsonisation by the cleavage products of the third complement protein and might promote inflammatory reactions. Antibody binding in a controlled manner and/or sensing of particles by the complement pattern-recognition molecules such as C1q and mannose-binding lectin can trigger complement activation. Particle curvature and spacing arrangement/periodicity of surface functional groups/ligands are two important parameters that modulate complement responses through multivalent engagement with and conformational regulation of surface-bound antibodies and complement pattern-recognition molecules. Thus, a better fundamental understanding of nanometer- and angstrom-scale parameters that modulate particle interaction with antibodies and complement proteins could portend new possibilities for engineering of particulate drug carriers and biomedical platforms with tuneable complement responses and is discussed here.

Nanoparticle entry into cells; the cell biology weak link

Nanoparticles (NP) are attractive options for the therapeutic delivery of active pharmaceutical drugs, proteins and nucleic acids into cells, tissues and organs. Research into the development and application of NP most often starts with a diverse group of scientists, including chemists, bioengineers and material and pharmaceutical scientists, who design, fabricate and characterize NP in vitro (Stage 1). The next step (Stage 2) generally investigates cell toxicity as well as the processes by which NP bind, are internalized and deliver their cargo to appropriate model tissue culture cells. Subsequently, in Stage 3, selected NP are tested in animal systems, mostly mouse. Whereas the chemistry-based development and analysis in Stage 1 is increasingly sophisticated, the investigations in Stage 2 are not what could be regarded as 'state-of-the-art' for the cell biology field and the quality of research into NP interactions with cells is often sub-standard. In this review we describe our current understanding of the mechanisms by which particles gain entry into mammalian cells via endocytosis. We summarize the most important areas for concern, highlight some of the most common mis-conceptions, and identify areas where NP scientists could engage with trained cell biologists. Our survey of the different mechanisms of uptake into cells makes us suspect that claims for roles for caveolae, as well as macropinocytosis, in NP uptake into cells have been exaggerated, whereas phagocytosis has been under-appreciated.

Tuning Antibody Presentation to Enhance T-Cell Activation for Downstream Cytotoxicity

Cytotoxic effector cells are an integral component of the immune response against pathogens and diseases such as cancer and thus of great interest to researchers who wish to enhance the native immune response. Although researchers routinely use particles to stimulate cytotoxic T cells, few studies have comprehensively investigated: (1) beyond initial activation responses (i.e., proliferation and CD25/CD69 expression) to downstream cancer-killing effects and (2) how to drive cytotoxic T-cell responses by adjusting biomolecular and physical properties of particles. In this study, we designed particles displaying an anti-CD3 antibody to activate cytotoxic T cells and study their downstream cytotoxic effects. We evaluated the effect of antibody immobilization, particle size, molecular surface density of an anti-CD3 antibody, and the inclusion of an anti-CD28 antibody on cytolytic granule release by T cells. We found that immobilizing the anti-CD3 antibody onto smaller nanoparticles elicited increased T-cell activation products for an equivalent delivery of the anti-CD3 antibody. We further established that the mechanism behind increased cancer cell death was associated with the proximity of T cells to cancer cells. Functionalizing particles additionally with the anti-CD28 antibody at an optimized antibody density caused increased T-cell proliferation and T-cell binding but we observed no effective increase in cytotoxicity. Meaningfully, our results are discussed within the context of commercially available and widely used anti-CD3/28 Dynabeads. These results showed that T-cell activation and cytotoxicity can be optimized with a molecular presentation on smaller particles and thus, offer exciting new possibilities to engineer T-cell activation responses for effective outcomes.

Bifunctional Janus Particles as Multivalent Synthetic Nanoparticle Antibodies (SNAbs) for Selective Depletion of Target Cells

Monoclonal antibodies (mAb) have had a transformative impact on treating cancers and immune disorders. However, their use is limited by high development time and monetary cost, manufacturing complexities, suboptimal pharmacokinetics, and availability of disease-specific targets. To address some of these challenges, we developed an entirely synthetic, multivalent, Janus nanotherapeutic platform, called Synthetic Nanoparticle Antibodies (SNAbs). SNAbs, with phage-display-identified cell-targeting ligands on one "face" and Fc-mimicking ligands on the opposite "face", were synthesized using a custom, multistep, solid-phase chemistry method. SNAbs efficiently targeted and depleted myeloid-derived immune-suppressor cells (MDSCs) from mouse-tumor and rat-trauma models, ex vivo. Systemic injection of MDSC-targeting SNAbs efficiently depleted circulating MDSCs in a mouse triple-negative breast cancer model, enabling enhanced T cell and Natural Killer cell infiltration into tumors. Our results demonstrate that SNAbs are a versatile and effective functional alternative to mAbs, with advantages of a plug-and-play, cell-free manufacturing process, and high-throughput screening (HTS)-enabled library of potential targeting ligands.

Autoantibodies specific for C1q, C3b, β2-glycoprotein 1 and annexins may amplify complement activity and reduce apoptosis-mediated immune suppression

Neoplastic cells hijack cell death pathways to evade the immune response. Phosphatidylserine, a marker of apoptotic cells, and its highly conserved bridging proteins, annexins and β2-glycoprotein I, facilitate the efficient removal of apoptotic and necrotic cells via tumor-associated phagocytes in a process called efferocytosis. Efferocytosis results in the clearance of dead and dying cells and local immune suppression. Neoplastic cells also have an increased capacity to activate complement. Complement may facilitate the silent removal of tumor cells and has a dual role in promoting and inhibiting tumor growth. Here I hypothesize that immune response-generating IgG autoantibodies that recognize opsonizing fragments C1q, C3b, and phosphatidylserine-binding proteins (annexins, β2-glycoprotein I) may reduce tumor growth. I propose that these autoantibodies induce a pro-inflammatory, cytotoxic tumor microenvironment. Further, I predict that autoantibodies can drive neoplastic cell phagocytosis in an Fc receptor-dependent manner and recruit additional complement, resulting in immune-stimulatory effects. Excessive complement activation and antibody-dependent cytotoxicity may stimulate anti-tumor responses, including damage to tumor vasculature. Here I provide insights that may aid the development of more effective therapeutic modalities to control cancer. Such therapeutic approaches should kill neoplastic cells and target their interaction with host immune cells. Thereby the pro-tumorigenic effect of dead cancer cells could be limited while inducing the anti-tumor potential of tumor-associated phagocytes.

Optimizing Flux Capacity of Dead-end Filtration Membranes by Controlling Flow with Pulse Width Modulated Periodic Backflush

Standard dead-end sample filtration is used to improve sample purity, but is limited as particle build-up fouls the filter, leading to reduced recovery. The fouling layer can be periodically cleared with backflush algorithms applied through a customized fluidic actuator using variable duty cycles, significantly improving particulate recovery percentage. We show a Pulse Width Modulation (PWM) process can periodically backflush the filter membrane to repeatedly interrupt cake formation and reintegrate the fouling layer into the sample, improving net permeate flux per unit volume of sample by partially restoring filter flux capacity. PWM flow for 2.19 um (targeted) and 7.32 um (untargeted) polystyrene microbeads produced 18-fold higher permeate concentration, higher recovery up to 68.5%, and an 8-fold enrichment increase, compared to a uniform flow. As the duty cycle approaches 50%, the recovery percentage monotonically increases after a critical threshold. Further, we developed and validated a mathematical model to determine that fast, small-volume backflush pulses near 50% duty cycle yield higher recovery by decreasing fouling associated with the cake layer. Optimized PWM flow was then used to purify custom particles for immune activation, achieving 3-fold higher recovery percentage and providing a new route to improve purification yields for diagnostic and cellular applications.

Unintended effects of drug carriers: Big issues of small particles

Humoral and cellular host defense mechanisms including diverse phagocytes, leukocytes, and immune cells have evolved over millions of years to protect the body from microbes and other external and internal threats. These policing forces recognize engineered sub-micron drug delivery systems (DDS) as such a threat, and react accordingly. This leads to impediment of the therapeutic action, extensively studied and discussed in the literature. Here, we focus on side effects of DDS interactions with host defenses. We argue that for nanomedicine to reach its clinical potential, the field must redouble its efforts in understanding the interaction between drug delivery systems and the host defenses, so that we can engineer safer interventions with the greatest potential for clinical success.

Host- and pathogen-derived adjuvant coatings on protein nanoparticle vaccines

Nanoparticulate and molecular adjuvants have shown great efficacy in enhancing immune responses, and the immunogenic vaccines of the future will most likely contain both. To investigate the immunostimulatory effects of molecular adjuvants on nanoparticle vaccines, we have designed ovalbumin (OVA) protein nanoparticles coated with two different adjuvants-flagellin (FliC) and immunoglobulin M (IgM). These proteins, derived from Salmonella and mice, respectively, are representatives of pathogen- and host-derived molecules that can enhance immune responses. FliC-coated OVA nanoparticles, soluble FliC (sFliC) admixed with OVA nanoparticles, IgM-coated nanoparticles, and OVA-coated nanoparticles were assessed for immunogenicity in an in vivo mouse immunization study. IgM coatings on nanoparticles significantly enhanced both antibody and T cell responses, and promoted IgG2a class switching but not affinity maturation. FliC-coated nanoparticles and FliC-admixed with nanoparticles both triggered IgG2a class switching, but only FliC-coated nanoparticles enhanced antibody affinity maturation. Our findings that affinity maturation and class switching can be directed independently of one another suggest that adjuvant coatings on nanoparticles can be tailored to generate specific vaccine effector responses against different classes of pathogens.

Fc microparticles can modulate the physical extent and magnitude of complement activity

The complement system is an integral component of the humoral immune system, and describes a cascade of interacting proteins responsible for the opsonization and lysis of foreign pathogens, in addition to the recruitment of immune cells. However, complement activation is also implicated in the progression and complication of immune dysfunctions such as sepsis. Microparticle (MP) biomaterials capable of tuning the local magnitude of serum complement activation could improve complement-mediated cytotoxicity to serum-resistant bacteria or calm an overactive immune response during sepsis. We demonstrate that model Fc-functionalized microparticles can be designed to either enhance or diminish the local cytotoxic effect of complement activation in human serum. The particles were formed with either the antibody Fc domains oriented outward from the particle surface or randomly adsorbed in a non-oriented fashion. In the oriented Fc form, complement products were directly sequestered to the particle surface, including C5a, a potent anaphylatoxin that, when elevated, is associated with poor sepsis prognosis. The oriented particle also lowered the cytotoxicity of serum and thus decreased the antibiotic effect when compared to serum alone. Conversely, the non-oriented microparticles were found to sequester similar levels of C5a, but much lower levels of iC3b and TCC on the microparticle surface, thereby increasing the amount of the soluble terminal complement complex. In addition, the non-oriented microparticles extend the distance over which TCC forms and enhance serum cytotoxicity to bacteria. Together, these two types of complement-modulating particles provide the first biomaterial that can functionally modify the range of complement activation at sites distant from the particle surface. Thus, biomaterials that exploit Fc presentation provide new possibilities to functionally modulate complement activation to achieve a desired clinical result.

Materials design at the interface of nanoparticles and innate immunity

Engineered nanoparticle platforms have been developed intensely in recent years, yielding significantly broadened applications from interrogating novel biology to new therapies. Using these platforms requires improved understanding of design rules to improve our ability to control nanoparticle-immune system interactions.

Toxicity and inflammatory response in Swiss albino mice after intraperitoneal and oral administration of polyurethane nanoparticles

In this work in vivo experiments were conducted in order to characterize the biocompatibility of polyurethane nanoparticles (PU-NPs) after intraperitoneal (i.p.) and oral administration. Additionally, ex vivo assays were performed to assess human blood compatibility as well as in vitro assays to assess protein binding. Our results indicated that administration of three different concentrations of PU-NPs induced a significant increase in visceral fat accumulation after oral dosing. In addition, fat tissue of mice intraperitoneally treated with the highest concentration of nanoparticles showed diffuse mononuclear inflammatory infiltrate in the fat tissue. Histopathological assessment showed inflammatory infiltrate and hepatocyte vacuolization in the liver, inflammatory infiltration and vascular congestion in the lung and glomerular necrosis in the kidney. Hepatic enzymes related with liver function were significantly increased in both groups of mice treated with PU-NPs. The PU-NPs did not affect the human blood cells number as well as coagulation time but showed a susceptibility to bind in proteins commonly found in the blood stream. In addition, increased amounts of pro inflammatory cytokines in vivo, as well as ex vivo in human cells were observed. Further studies to establish the consequences of long-term exposure to PU-NPs are warranted.

Emerging technologies and bio-threats

Many Institutional Biosafety Committees have expanded their role beyond their original mission, described in the National Institutes of Health Guidelines for Research Involving Recombinant or Synthetic Nucleic Acid Molecules. The guidelines are derived from the 1975 Asilomar Conference on Recombinant DNA Molecules that convened to examine and address societal concerns surrounding the (then) newly emerging recombinant DNA technology. This chapter will focus on emerging biological agents and cutting-edge technologies that present challenges to evaluating and assessing the biohazard risks associated with research protocols. Highly specialized and/or cross-disciplinary knowledge may be required for committee members to be able to evaluate benefit versus risk for research proposals addressing emerging infectious agents or technologies. The importance of designing a process that will account for the full range of requirements to fulfill the societal expectations of safety, efficiency, and scientific progress is highlighted.

A Liquid-Handling Robot for Automated Attachment of Biomolecules to Microbeads

Diagnostics, drug delivery, and other biomedical industries rely on cross-linking ligands to microbead surfaces. Microbead functionalization requires multiple steps of liquid exchange, incubation, and mixing, which are laborious and time intensive. Although automated systems exist, they are expensive and cumbersome, limiting their routine use in biomedical laboratories. We present a small, bench-top robotic system that automates microparticle functionalization and streamlines sample preparation. The robot uses a programmable microcontroller to regulate liquid exchange, incubation, and mixing functions. Filters with a pore diameter smaller than the minimum bead diameter are used to prevent bead loss during liquid exchange. The robot uses three liquid reagents and processes up to 10(7) microbeads per batch. The effectiveness of microbead functionalization was compared with a manual covalent coupling process and evaluated via flow cytometry and fluorescent imaging. The mean percentages of successfully functionalized beads were 91% and 92% for the robot and manual methods, respectively, with less than 5% bead loss. Although the two methods share similar qualities, the automated approach required approximately 10 min of active labor, compared with 3 h for the manual approach. These results suggest that a low-cost, automated microbead functionalization system can streamline sample preparation with minimal operator intervention.

Properties and prospects of adjuvants in influenza vaccination - messy precipitates or blessed opportunities?

Influenza is a major challenge to healthcare systems world-wide. While prophylactic vaccination is largely efficient, long-lasting immunity has not been achieved in immunized populations, at least in part due to the challenges arising from the antigen variation between strains of influenza A virus as a consequence of genetic drift and shift. From progress in our understanding of the immune system, the mode-of-action of vaccines can be divided into the stimulation of the adaptive system through inclusion of appropriate vaccine antigens and of the innate immune system by the addition of adjuvant to the vaccine formulation. A shared property of many vaccine adjuvants is found in their nature of water-insoluble precipitates, for instance the particulate material made from aluminum salts. Previously, it was thought that embedding of vaccine antigens in these materials provided a "depot" of antigens enabling a long exposure of the immune system to the antigen. However, more recent work points to a role of particulate adjuvants in stimulating cellular parts of the innate immune system. Here, we briefly outline the infectious medicine and immune biology of influenza virus infection and procedures to provide sufficient and stably available amounts of vaccine antigen. This is followed by presentation of the many roles of adjuvants, which involve humoral factors of innate immunity, notably complement. In a perspective of the ultrastructural properties of these humoral factors, it becomes possible to rationalize why these insoluble precipitates or emulsions are such a provocation of the immune system. We propose that the biophysics of particulate material may hold opportunities that could aid the development of more efficient influenza vaccines.

Properties and prospects of adjuvants in influenza vaccination - messy precipitates or blessed opportunities?

Influenza is a major challenge to healthcare systems world-wide. While prophylactic vaccination is largely efficient, long-lasting immunity has not been achieved in immunized populations, at least in part due to the challenges arising from the antigen variation between strains of influenza A virus as a consequence of genetic drift and shift. From progress in our understanding of the immune system, the mode-of-action of vaccines can be divided into the stimulation of the adaptive system through inclusion of appropriate vaccine antigens and of the innate immune system by the addition of adjuvant to the vaccine formulation. A shared property of many vaccine adjuvants is found in their nature of water-insoluble precipitates, for instance the particulate material made from aluminum salts. Previously, it was thought that embedding of vaccine antigens in these materials provided a "depot" of antigens enabling a long exposure of the immune system to the antigen. However, more recent work points to a role of particulate adjuvants in stimulating cellular parts of the innate immune system. Here, we briefly outline the infectious medicine and immune biology of influenza virus infection and procedures to provide sufficient and stably available amounts of vaccine antigen. This is followed by presentation of the many roles of adjuvants, which involve humoral factors of innate immunity, notably complement. In a perspective of the ultrastructural properties of these humoral factors, it becomes possible to rationalize why these insoluble precipitates or emulsions are such a provocation of the immune system. We propose that the biophysics of particulate material may hold opportunities that could aid the development of more efficient influenza vaccines.