Reorienting our view of particle-based adjuvants for subunit vaccines

A highly immunogenic vaccine platform against encapsulated pathogens using chimeric probiotic Escherichia coli membrane vesicles

Vaccines against infectious diseases should elicit potent and long-lasting immunity, ideally even in those with age-related decline in immune response. Here we report a rational polysaccharide vaccine platform using probiotic Escherichia coli-derived membrane vesicles (MVs). First, we constructed a probiotic E. coli clone harboring the genetic locus responsible for biogenesis of serotype 14 pneumococcal capsular polysaccharides (CPS14) as a model antigen. CPS14 was found to be polymerized and mainly localized on the outer membrane of the E. coli cells. The glycine-induced MVs displayed the exogenous CPS14 at high density on the outermost surface, on which the CPS14 moiety was covalently tethered to a lipid A-core oligosaccharide anchor. In in vivo immunization experiments, CPS14⁺MVs, but not a mixture of free CPS14 and empty MVs, strongly elicited IgG class-switch recombination with a Th1/Th2-balanced IgG subclass distribution without any adjuvant. In addition, CPS14⁺MVs were structurally stable with heat treatment and immunization with the heat-treated MVs-elicited CPS14-specific antibody responses in mouse serum to levels comparable to those of non-treated CPS14⁺MVs. Notably, the immunogenicity of CPS14⁺MVs was significantly stronger than those of two currently licensed vaccines against pneumococci. The CPS14⁺MV-elicited humoral immune responses persisted for 1 year in both blood and lung. Furthermore, the CPS14⁺MV vaccine was widely efficacious in mice of different ages. Even in aged mice, vaccination resulted in robust production of CPS14-specific IgG that bound to the pneumococcal cell surface. Taken together, the present probiotic E. coli MVs-based vaccine platform offers a promising, generalizable solution against encapsulated pathogens.

Self-assembling synthetic nanoadjuvant scaffolds cross-link B cell receptors and represent new platform technology for therapeutic antibody production

Host antibody responses are pivotal for providing protection against infectious agents. We have pioneered a new class of self-assembling micelles based on pentablock copolymers that enhance antibody responses while providing a low inflammatory environment compared to traditional adjuvants. This type of "just-right" immune response is critical in the rational design of vaccines for older adults. Here, we report on the mechanism of enhancement of antibody responses by pentablock copolymer micelles, which act as scaffolds for antigen presentation to B cells and cross-link B cell receptors, unlike other micelle-forming synthetic block copolymers. We exploited this unique mechanism and developed these scaffolds as a platform technology to produce antibodies in vitro. We show that this novel approach can be used to generate laboratory-scale quantities of therapeutic antibodies against multiple antigens, including those associated with SARS-CoV-2 and Yersinia pestis, further expanding the value of these nanomaterials to rapidly develop countermeasures against infectious diseases.

Toxoid Vaccination against Bacterial Infection Using Cell Membrane-Coated Nanoparticles

As nanoparticles exhibit unique properties attractive for vaccine development, they have been progressively implemented as antigen delivery platforms and immune potentiators. Recently, cell membrane-coated nanoparticles have provided a novel approach for intercepting and neutralizing bacterial toxins by leveraging their natural affinity to cellular membranes. Such toxin-nanoparticle assemblies, termed nanotoxoids, allow rapid loading of different types of toxins and have been investigated for their ability to effectively confer protection against bacterial infection. This topical review will cover the current progress in antibacterial vaccine nanoformulations and highlight the nanotoxoid platform as a novel class of nanoparticulate vaccine. We aim to provide insights into the potential of nanotoxoids as a platform that is facile to implement and can be broadly applied to help address the rising threat of super pathogens.

Nano-therapeutics: A revolution in infection control in post antibiotic era

With the arrival of antibiotics 70 years ago, meant a paradigm shift in overcoming infectious diseases. For decades, drugs have been used to treat different infections. However, with time bacteria have become resistant to multiple antibiotics, making some diseases difficult to fight. Nanoparticles (NPs) as antibacterial agents appear to have potential to overcome such problems and to revolutionize the diagnosis and treatment of bacterial infections. Therefore, there is significant interest in the use of NPs to treat variety of infections, particularly caused by multidrug-resistant (MDR) strains. This review begins with illustration of types of NPs followed by the literature of current research addressing mechanisms of NPs antibacterial activity, steps involved in NP mediated drug delivery as well as areas where NPs use has potential to improve the treatment, like NP enabled vaccination. Besides, recently emerged innovative NP platforms have been highlighted and their progress made in each area has been reviewed.

Nanoparticle Vaccines Adopting Virus-like Features for Enhanced Immune Potentiation

Synthetic nanoparticles play an increasingly significant role in vaccine design and development as many nanoparticle vaccines show improved safety and efficacy over conventional formulations. These nanoformulations are structurally similar to viruses, which are nanoscale pathogenic organisms that have served as a key selective pressure driving the evolution of our immune system. As a result, mechanisms behind the benefits of nanoparticle vaccines can often find analogue to the interaction dynamics between the immune system and viruses. This review covers the advances in vaccine nanotechnology with a perspective on the advantages of virus mimicry towards immune potentiation. It provides an overview to the different types of nanomaterials utilized for nanoparticle vaccine development, including functionalization strategies that bestow nanoparticles with virus-like features. As understanding of human immunity and vaccine mechanisms continue to evolve, recognizing the fundamental semblance between synthetic nanoparticles and viruses may offer an explanation for the superiority of nanoparticle vaccines over conventional vaccines and may spur new design rationales for future vaccine research. These nanoformulations are poised to provide solutions towards pressing and emerging human diseases.

Cell Membrane-Coated Nanoparticles As an Emerging Antibacterial Vaccine Platform

Nanoparticles have demonstrated unique advantages in enhancing immunotherapy potency and have drawn increasing interest in developing safe and effective vaccine formulations. Recent technological advancement has led to the discovery and development of cell membrane-coated nanoparticles, which combine the rich functionalities of cellular membranes and the engineering flexibility of synthetic nanomaterials. This new class of biomimetic nanoparticles has inspired novel vaccine design strategies with strong potential for modulating antibacterial immunity. This article will review recent progress on using cell membrane-coated nanoparticles for antibacterial vaccination. Specifically, two major development strategies will be discussed, namely (i) vaccination against virulence factors through bacterial toxin sequestration; and (ii) vaccination against pathogens through mimicking bacterial antigen presentation.

Nanoparticle approaches against bacterial infections

Despite the wide success of antibiotics, the treatment of bacterial infections still faces significant challenges, particularly the emergence of antibiotic resistance. As a result, nanoparticle drug delivery platforms including liposomes, polymeric nanoparticles, dendrimers, and various inorganic nanoparticles have been increasingly exploited to enhance the therapeutic effectiveness of existing antibiotics. This review focuses on areas where nanoparticle approaches hold significant potential to advance the treatment of bacterial infections. These areas include targeted antibiotic delivery, environmentally responsive antibiotic delivery, combinatorial antibiotic delivery, nanoparticle-enabled antibacterial vaccination, and nanoparticle-based bacterial detection. In each area we highlight the innovative antimicrobial nanoparticle platforms and review their progress made against bacterial infections.

Nanocarrier-based immunotherapy in cancer management and research

Research in cancer immunotherapy has gained momentum in the last two decades, with many studies and clinical trials showing positive therapeutic outcomes. Immunotherapy can elicit not only a strong anticancer immune response which could even control metastases, but could also induce immunological memory, resulting in long-lasting protection in the prophylactic setting and protection against possible recurrence. Nanocarriers offer an attractive means for delivery of a multitude of therapeutic immunomodulators which are readily taken up by immune cells and can initiate a particular arm of an immunostimulatory cascade leading to tumor cell killing. This review focuses on recent advances in nanocarrier-mediated immunotherapy for the treatment of cancer. Both in vitro and in vivo studies as well as clinical progress are discussed in various sections. Description of the specific role of nanoparticle technology in immunotherapy highlights the way particles can be tailor-made in terms of size, structure, payload, and surface properties for active targeting to antigen-presenting cells and/or enhanced accumulation in the solid tumor.

Working together: interactions between vaccine antigens and adjuvants

The development of vaccines containing adjuvants has the potential to enhance antibody and cellular immune responses, broaden protective immunity against heterogeneous pathogen strains, enable antigen dose sparing, and facilitate efficacy in immunocompromised populations. Nevertheless, the structural interplay between antigen and adjuvant components is often not taken into account in the published literature. Interactions between antigen and adjuvant formulations should be well characterized to enable optimum vaccine stability and efficacy. This review focuses on the importance of characterizing antigen-adjuvant interactions by summarizing findings involving widely used adjuvant formulation platforms, such as aluminum salts, emulsions, lipid vesicles, and polymer-based particles. Emphasis is placed on the physicochemical basis of antigen-adjuvant associations and the appropriate analytical tools for their characterization, as well as discussing the effects of these interactions on vaccine potency.

Porous silicon advances in drug delivery and immunotherapy

Biomedical applications of porous silicon include drug delivery, imaging, diagnostics and immunotherapy. This review summarizes new silicon particle fabrication techniques, dynamics of cellular transport, advances in the multistage vector approach to drug delivery, and the use of porous silicon as immune adjuvants. Recent findings support superior therapeutic efficacy of the multistage vector approach over single particle drug delivery systems in mouse models of ovarian and breast cancer. With respect to vaccine development, multivalent presentation of pathogen-associated molecular patterns on the particle surface creates powerful platforms for immunotherapy, with the porous matrix able to carry both antigens and immune modulators.

Particle platforms for cancer immunotherapy

Elevated understanding and respect for the relevance of the immune system in cancer development and therapy has led to increased development of immunotherapeutic regimens that target existing cancer cells and provide long-term immune surveillance and protection from cancer recurrence. This review discusses using particles as immune adjuvants to create vaccines and to augment the anticancer effects of conventional chemotherapeutics. Several particle prototypes are presented, including liposomes, polymer nanoparticles, and porous silicon microparticles, the latter existing as either single- or multiparticle platforms. The benefits of using particles include immune-cell targeting, codelivery of antigens and immunomodulatory agents, and sustained release of the therapeutic payload. Nanotherapeutic-based activation of the immune system is dependent on both intrinsic particle characteristics and on the immunomodulatory cargo, which may include danger signals known as pathogen-associated molecular patterns and cytokines for effector-cell activation.

Vaccine design: emerging concepts and renewed optimism

Arguably, vaccination represents the single most effective medical intervention ever developed. Yet, vaccines have failed to provide any or adequate protection against some of the most significant global diseases. The pathogens responsible for these vaccine-recalcitrant diseases have properties that allow them to evade immune surveillance and misdirect or eliminate the immune response. However, genomic and systems biology tools, novel adjuvants and delivery systems, and refined molecular insight into protective immunity have started to redefine the landscape, and results from recent efficacy trials of HIV and malaria vaccines have instilled hope that another golden age of vaccines may be on the horizon.