Stable Nanoemulsions for the Delivery of Small Molecule Immune Potentiators

Optical sensor arrays designed for guided manufacture of perfluorocarbon nanoemulsions with a non-synthetic stabilizer

Hydrophobic drugs are incorporated into oil-in-water nanoemulsions (OIW) either as new formulations or repurposed for intravenous delivery. Typically, these are manufactured through stepwise processes of sonication or high-pressure homogenization (HPH). The guiding criteria for most nanoemulsion manufacture are the size and homogeneity/polydispersity of the drug-laden particles with strict requirements for clinical injectables. To date, most formulation optimization is done through trial and error with stepwise sampling during processing utilizing dynamic light scattering (DLS), light obscuration sensing (LOS) or laser particle tracking (LPT) to assess manufacturing progress. The objective of this work was to develop and implement an in-line optical turbidity/nephelometry sensor array for the longitudinal in-process monitoring of nanoemulsion manufacture. A further objective was the use of this sensor array to rapidly optimize the manufacture of a sub-120 nm oxygen carrying perfluorocarbon nanoemulsion with a non-synthetic stabilizer. During processing, samples were taken for particle size measurement and further characterization. There was a significant correlation and agreement between particle size and sensor signal as well as improved process reproducibility through sensor-guided manufacture. Given the cost associated with nanoemulsion development and scale-up manufacture, our sensor arrays could be an invaluable tool for efficient and cost-effective drug development. Sensor-guided manufacturing was used to optimize oxygen-carrying nanoemulsions. These were tested, in vitro, for their ability to improve the viability of encapsulated endocrine clusters (mouse insulinoma, Min6) and to eliminate hypoxia due to oxygen mass transfer limitations. The nanomulsions significantly improved encapsulated cluster viability and reduced hypoxia within the microcapsule environment. STATEMENT OF SIGNIFICANCE: Nanoemulsions are rapidly becoming vehicles for the controlled release delivery of both hydrophilic and hydrophobic drugs given their large surface area for exchange. As work shifts from bench to large scale manufacturing, there is a critical need for technologies that can monitor and accumulate data during processing, particularly regarding the endpoint criteria of particle size and stability. To date, no such technology has been implemented in nanoemulsion manufacture. In this paper we develop and implement an optical sensor array for in-line nanoemulsion process monitoring and then use the array to optimize the development and manufacture of novel reproducible oxygen carrying nanoemulsions lacking synthetic surfactants.

Nasal Immunization With Small Molecule Mast Cell Activators Enhance Immunity to Co-Administered Subunit Immunogens

Mast cell activators are a novel class of mucosal vaccine adjuvants. The polymeric compound, Compound 48/80 (C48/80), and cationic peptide, Mastoparan 7 (M7) are mast cell activators that provide adjuvant activity when administered by the nasal route. However, small molecule mast cell activators may be a more cost-efficient adjuvant alternative that is easily synthesized with high purity compared to M7 or C48/80. To identify novel mast cell activating compounds that could be evaluated for mucosal vaccine adjuvant activity, we employed high-throughput screening to assess over 55,000 small molecules for mast cell degranulation activity. Fifteen mast cell activating compounds were down-selected to five compounds based on in vitro immune activation activities including cytokine production and cellular cytotoxicity, synthesis feasibility, and selection for functional diversity. These small molecule mast cell activators were evaluated for in vivo adjuvant activity and induction of protective immunity against West Nile Virus infection in BALB/c mice when combined with West Nile Virus envelope domain III (EDIII) protein in a nasal vaccine. We found that three of the five mast cell activators, ST101036, ST048871, and R529877, evoked high levels of EDIII-specific antibody and conferred comparable levels of protection against WNV challenge. The level of protection provided by these small molecule mast cell activators was comparable to the protection evoked by M7 (67%) but markedly higher than the levels seen with mice immunized with EDIII alone (no adjuvant 33%). Thus, novel small molecule mast cell activators identified by high throughput screening are as efficacious as previously described mast cell activators when used as nasal vaccine adjuvants and represent next-generation mast cell activators for evaluation in mucosal vaccine studies.

Recent advances in nano/microparticle-based oral vaccines

Background

Vaccines are often recognized as one of the most cost-effective public health interventions in controlling infectious diseases. Most pathogens infiltrate the body from mucosal sites, primarily from the oral and pulmonary region and reach the systemic circulation where disease manifestation starts. Traditional needle-based vaccines are usually not capable of inducing immunity at the mucosal sites where pathogen infiltrates start, but induces systemic immunity. In contrast to needle-based vaccines, mucosally administered vaccines induce immunity at both the mucosal sites and systemically. The oral route of immunization is the most convenient way to administer the vaccines. However, due to the complicated and hostile gastrointestinal structure and environment, vaccines need to overcome major hurdles while retaining their stability and immunogenicity.

Area covered

This review will briefly discuss different barriers to oral vaccine development. It gives a brief overview of different types of nano/microparticle-based oral vaccines and discusses how physicochemical characteristics of the particles influence overall immunity after oral immunization.

Expert opinion

Formulation strategies using novel lipid and polymer-based nano/microparticle platforms retain stability and antigenicity of vaccines against the harsh gastrointestinal condition. The physicochemical properties of particles can be uniquely tailored to prolong the release of antigens, and attached ligands (M-cells and APC-ligands) can precisely target uptake by immune cells. These represent viable strategies for efficient delivery of oral vaccines.

Emerging concepts in the science of vaccine adjuvants

Adjuvants are vaccine components that enhance the magnitude, breadth and durability of the immune response. Following its introduction in the 1920s, alum remained the only adjuvant licensed for human use for the next 70 years. Since the 1990s, a further five adjuvants have been included in licensed vaccines, but the molecular mechanisms by which these adjuvants work remain only partially understood. However, a revolution in our understanding of the activation of the innate immune system through pattern recognition receptors (PRRs) is improving the mechanistic understanding of adjuvants, and recent conceptual advances highlight the notion that tissue damage, different forms of cell death, and metabolic and nutrient sensors can all modulate the innate immune system to activate adaptive immunity. Furthermore, recent advances in the use of systems biology to probe the molecular networks driving immune response to vaccines ('systems vaccinology') are revealing mechanistic insights and providing a new paradigm for the vaccine discovery and development process. Here, we review the 'known knowns' and 'known unknowns' of adjuvants, discuss these emerging concepts and highlight how our expanding knowledge about innate immunity and systems vaccinology are revitalizing the science and development of novel adjuvants for use in vaccines against COVID-19 and future pandemics.

Nanoparticles for mucosal vaccine delivery

Mucosal surfaces represent important routes of entry into the human body for the majority of pathogens, and they constitute unique sites for targeted vaccine delivery. Nanoparticle-based drug delivery systems are emerging technologies for delivering and improving the efficacy of mucosal vaccines. Recent studies have provided new insights into formulation and delivery aspects of importance for the design of safe and efficacious mucosal subunit vaccines based on nanoparticles. These include novel nanomaterials, their physicochemical properties and formulation approaches, nanoparticle interaction with immune cells in the mucosa, and mucosal immunization and delivery strategies. Here, we present recent progress in the application of nanoparticle-based approaches for mucosal vaccine delivery and discuss future research challenges and opportunities in the field.

Lyophilizable and Multifaceted Toll-like Receptor 7/8 Agonist-Loaded Nanoemulsion for the Reprogramming of Tumor Microenvironments and Enhanced Cancer Immunotherapy

The low therapeutic efficacy of current cancer immunotherapy is related to nonimmunogenic and immunosuppressive tumor microenvironments (TMEs). To overcome these limitations, both the immune priming of antitumoral lymphocytes and the reprogramming of immunosuppressive factors in TMEs are essential. Here, we suggest a nanoemulsion (NE)-based immunotherapeutic platform that can not only modulate tumor-induced suppression but also induce an effective cell-mediated immune response for T cell proliferation. Multifunctional NEs can be fabricated by integrating the efficacy of NEs as delivery systems and the multifaceted immunomodulation characteristics (i.e., immunostimulation and reprogramming of immunosuppression) of small molecule-based Toll-like receptor 7/8 agonists. Local in situ vaccination of melanoma and cervical tumor models with tumor antigens (protein and peptide) adjuvanted with NE loaded with TLR7/8 agonists [NE (TLR7/8a)] induced the recruitment and activation of innate immune cells, infiltration of lymphocytes, and polarization of tumor-associated M2 macrophages, which resulted in inhibition of tumor growth and prolonged survival in both primary and rechallenged tumor models. Antibody-depletion experiments also suggested that macrophages, type I IFN (IFN-α and IFN-β), CD8⁺ T cells, and NK1.1⁺ cells contributed to the antitumor effect of NE (TLR7/8a). The combination of antitumoral lymphocytes and reprogramming of immunosuppressive TMEs induced by NE (TLR7/8a) treatment evoked a synergistic antitumor immune response with immune checkpoint blockade therapy (anti-PD-1 and anti-PD-L1).

[Composition and mode of action of adjuvants in licensed viral vaccines]

The immunogenicity and efficacy of vaccines is largely governed by nature and the amount of antigen(s) included. Specific immune-stimulating substances, so-called adjuvants, are added to vaccine formulations to enhance and modulate the induced immune response.Adjuvants are very different in their physicochemical nature and are primarily characterized by their immune-enhancing effects. In this report, adjuvants that are components of vaccines licensed in the EU will be presented and their mode of action will be discussed.Aluminum salts have been used for almost a century as vaccine adjuvants. In recent years numerous novel immune-stimulating substances have been developed and integrated into licensed human vaccines. These novel adjuvants are not only intended to generally increase the vaccine-induced antibody titers, but are also aimed at modulating and triggering a specific immune response. The search for innovative adjuvants was considerably stimulated during development of pandemic influenza vaccines. By using squalene-containing oil-in-water adjuvants (namely AS03 and MF59), pandemic influenza vaccines were developed that were efficacious despite a significant reduction of the antigen content.The development of novel adjuvants is a highly dynamic and essential area in modern vaccine design. Some years ago, vaccines for prevention of HPV-induced cervix carcinoma and hepatitis B were licensed that contained the toll-like receptor 4 agonist 3‑O-desacyl-monophosphoryl lipid A (MPL), a detoxified LPS version, as the adjuvant. Quite recently, a herpes zoster vaccine was licensed in Europe with a combination of MPL and the saponin QS21 as adjuvant. This combination of immune enhancers is also used in the formulations of the same manufacturer's malaria and hepatitis B vaccine.