Nanovaccines for malaria using Plasmodium falciparum antigen Pfs25 attached gold nanoparticles

Tiny Green Army: Fighting Malaria with Plants and Nanotechnology

Malaria poses a global threat to human health, with millions of cases and thousands of deaths each year, mainly affecting developing countries in tropical and subtropical regions. Malaria's causative agent is Plasmodium species, generally transmitted in the hematophagous act of female Anopheles sp. mosquitoes. The main approaches to fighting malaria are eliminating the parasite through drug treatments and preventing transmission with vector control. However, vector and parasite resistance to current strategies set a challenge. In response to the loss of drug efficacy and the environmental impact of pesticides, the focus shifted to the search for biocompatible products that could be antimalarial. Plant derivatives have a millennial application in traditional medicine, including the treatment of malaria, and show toxic effects towards the parasite and the mosquito, aside from being accessible and affordable. Its disadvantage lies in the type of administration because green chemical compounds rapidly degrade. The nanoformulation of these compounds can improve bioavailability, solubility, and efficacy. Thus, the nanotechnology-based development of plant products represents a relevant tool in the fight against malaria. We aim to review the effects of nanoparticles synthesized with plant extracts on Anopheles and Plasmodium while outlining the nanotechnology green synthesis and current malaria prevention strategies.

In silico description of the adsorption of cell signaling pathway proteins ovalbumin, glutathione, LC3, TLR4, ASC PYCARD, PI3K and NF-Kβ on 7.0 nm gold nanoparticles: obtaining their Lennard-Jones-like potentials through docking and molecular mechanics

The impact of vaccination on the world's population is difficult to calculate. For developing different types of vaccines, adjuvants are substances added to vaccines to increase the magnitude and durability of the immune response and the effectiveness of the vaccine. This work explores the potential use of spherical gold nanoparticles (AuNPs) as adjuvants. Thus, we employed docking techniques and molecular mechanics to describe how a AuNP 7.0 nm in diameter interacts with cell signaling pathway proteins. Initially, we used X-ray crystallization data of the proteins ovalbumin, glutathione, LC3, TLR4, ASC PYCARD, PI3K, and NF-Kβ to study the adsorption with an AuNP through molecular docking. Therefore, interaction energies were obtained for the AuNP complexes and individual proteins, as well as the AuNP and OVA complex (AuNP@OVA) with each cellular protein, respectively. Results showed that AuNPs had the highest affinity for OVA individually, followed by glutathione, ASC PYCARD domain, LC3, PI3K, NF-Kβ, and TLR4. Furthermore, when evaluating the AuNP@OVA complex, glutathione showed a greater affinity with more potent interaction energy when compared to the other studied systems.

Nanotechnology-Based Strategies in Parasitic Disease Management: From Prevention to Diagnosis and Treatment

Parasitic infections are a major global health issue causing significant mortality and morbidity. Despite substantial advances in the diagnostics and treatment of these diseases, the currently available options fall far short of expectations. From diagnosis and treatment to prevention and control, nanotechnology-based techniques show promise as an alternative approach. Nanoparticles can be designed with specific properties to target parasites and deliver antiparasitic medications and vaccines. Nanoparticles such as liposomes, nanosuspensions, polymer-based nanoparticles, and solid lipid nanoparticles have been shown to overcome limitations such as limited bioavailability, poor cellular permeability, nonspecific distribution, and rapid drug elimination from the body. These nanoparticles also serve as nanobiosensors for the early detection and treatment of these diseases. This review aims to summarize the potential applications of nanoparticles in the prevention, diagnosis, and treatment of parasitic diseases such as leishmaniasis, malaria, and trypanosomiasis. It also discusses the advantages and disadvantages of these applications and their market values and highlights the need for further research in this field.

Nanovaccines: A game changing approach in the fight against infectious diseases

The field of nanotechnology has revolutionised global attempts to prevent, treat, and eradicate infectious diseases in the foreseen future. Nanovaccines have proven to be a valuable pawn in this novel technology. Nanovaccines are made up of nanoparticles that are associated with or prepared with components that can stimulate the host's immune system. In addition to their delivery capabilities, the nanocarriers have been demonstrated to possess intrinsic adjuvant properties, working as immune cell stimulators. Thus, nanovaccines have the potential to promote rapid as well as long-lasting humoral and cellular immunity. The nanovaccines have several possible benefits, including site-specific antigen delivery, increased antigen bioavailability, and a diminished adverse effect profile. To avail these benefits, several nanoparticle-based vaccines are being developed, including virus-like particles, liposomes, polymeric nanoparticles, nanogels, lipid nanoparticles, emulsion vaccines, exomes, and inorganic nanoparticles. Inspired by their distinctive properties, researchers are working on the development of nanovaccines for a variety of applications, such as cancer immunotherapy and infectious diseases. Although a few challenges still need to be overcome, such as modulation of the nanoparticle pharmacokinetics to avoid rapid elimination from the bloodstream by the reticuloendothelial system, The future prospects of this technology are also assuring, with multiple options such as personalised vaccines, needle-free formulations, and combination nanovaccines with several promising candidates.

Emerging peptide-based nanovaccines: From design synthesis to defense against cancer and infection

Peptide-based vaccines, which form one of the most potent vaccine platforms, offer exclusive advantages over classical vaccines that use whole organisms or proteins. However, peptides alone are still poor stability and weak immunogenicity, thus need a delivery system that can overcome these shortcomings. Currently, nanotechnology has been extensively utilized to address this issue. Nanovaccines, as new formulations of vaccines using nanoparticles (NPs) as carriers or adjuvants, are undergoing development instead of conventional vaccines. Indeed, peptide-based nanovaccine is a rapidly developing field of research that is emerging out of the confluence of antigenic peptides with the nano-delivery system. In this review, we shed light on the rational design and preparation strategies based on various nanomaterials of peptide-based nanovaccines, and we spotlight progress in the development of peptide-based nanovaccines against cancer and infectious diseases. Finally, the future prospects for development of peptide-based nanovaccines are presented.

Potential of nanoformulations in malaria treatment

Malaria is caused by the protozoan Plasmodium sp and affects millions of people worldwide. Its clinical form ranges from asymptomatic to potentially fatal and severe. Current treatments include single drugs such as chloroquine, lumefantrine, primaquine, or in combination with artemisinin or its derivatives. Resistance to antimalarial drugs has increased; therefore, there is an urgent need to diversify therapeutic approaches. The disease cycle is influenced by biological, social, and anthropological factors. This longevity and complexity contributes to the records of drug resistance, where further studies and proposals for new therapeutic formulations are needed for successful treatment of malaria. Nanotechnology is promising for drug development. Preclinical formulations with antimalarial agents have shown positive results, but only a few have progressed to clinical phase. Therefore, studies focusing on the development and evaluation of antimalarial formulations should be encouraged because of their enormous therapeutic potential.

Nano toolbox in immune modulation and nanovaccines

Despite the great success of vaccines over two centuries, the conventional strategy is based on attenuated/altered microorganisms. However, this is not effective for all microbes and often fails to elicit a protective immune response, and sometimes poses unexpected safety risks. The expanding nano toolbox may overcome some of the roadblocks in vaccine development given the plethora of unique nanoparticle (NP)-based platforms that can successfully induce specific immune responses leading to exciting and novel solutions. Nanovaccines necessitate a thorough understanding of the immunostimulatory effect of these nanotools. We present a comprehensive description of strategies in which nanotools have been used to elicit an immune response and provide a perspective on how nanotechnology can lead to future personalized nanovaccines.

Current challenges and nanotechnology-based pharmaceutical strategies for the treatment and control of malaria

Malaria is one of the prevalent tropical diseases caused by the parasitic protozoan of the genus Plasmodium spp. With an estimated 228 million cases, it is a major public health concern with high incidence of morbidity and mortality worldwide. The emergence of drug-resistant parasites, inadequate vector control measures, and the non-availability of effective vaccine(s) against malaria pose a serious challenge to malaria eradication especially in underdeveloped and developing countries. Malaria treatment and control comprehensively relies on chemical compounds, which encompass various complications, including severe toxic effects, emergence of drug resistance, and high cost of therapy. To overcome the clinical failures of anti-malarial chemotherapy, a new drug development is of an immediate need. However, the drug discovery and development process is expensive and time consuming. In such a scenario, nanotechnological strategies may offer promising alternative approach for the treatment and control of malaria, with improved efficacy and safety. Nanotechnology based formulations of existing anti-malarial chemotherapeutic agents prove to exceed the limitations of existing therapies in relation to optimum therapeutic benefits, safety, and cost effectiveness, which indeed advances the patient's compliance in treatment. In this review, the shortcomings of malaria therapeutics and necessity of nanotechnological strategies for treating malaria were discussed.

Efficacy and Immune Response Elicited by Gold Nanoparticle- Based Nanovaccines against Infectious Diseases

The use of nanoparticles for developing vaccines has become a routine process for researchers and pharmaceutical companies. Gold nanoparticles (GNPs) are chemical inert, have low toxicity, and are easy to modify and functionalize, making them an attractive choice for nanovaccine development. GNPs are modified for diagnostics and detection of many pathogens. The biocompatibility and biodistribution properties of GNPs render them ideal for use in clinical settings. They have excellent immune modulatory and adjuvant properties. They have been used as the antigen carrier for the delivery system to a targeted site. Tagging them with antibodies can direct the drug or antigen-carrying GNPs to specific tissues or cells. The physicochemical properties of the GNP, together with its dynamic immune response based on its size, shape, surface charge, and optical properties, make it a suitable candidate for vaccine development. The clear outcome of modulating dendritic cells, T and B lymphocytes, which trigger cytokine release in the host, indicates GNPs' efficiency in combating pathogens. The high titer of IgG and IgA antibody subtypes and their enhanced capacity to neutralize pathogens are reported in multiple studies on GNP-based vaccine development. The major focus of this review is to illustrate the role of GNPs in developing nanovaccines against multiple infectious agents, ranging from viruses to bacteria and parasites. Although the use of GNPs has its shortcomings and a low but detectable level of toxicity, their benefits warrant investing more thought and energy into the development of novel vaccine strategies.

From Bench to the Clinic: The Path to Translation of Nanotechnology-Enabled mRNA SARS-CoV-2 Vaccines

During the last decades, the use of nanotechnology in medicine has effectively been translated to the design of drug delivery systems, nanostructured tissues, diagnostic platforms, and novel nanomaterials against several human diseases and infectious pathogens. Nanotechnology-enabled vaccines have been positioned as solutions to mitigate the pandemic outbreak caused by the novel pathogen severe acute respiratory syndrome coronavirus 2. To fast-track the development of vaccines, unprecedented industrial and academic collaborations emerged around the world, resulting in the clinical translation of effective vaccines in less than one year. In this article, we provide an overview of the path to translation from the bench to the clinic of nanotechnology-enabled messenger ribonucleic acid vaccines and examine in detail the types of delivery systems used, their mechanisms of action, obtained results during each phase of their clinical development and their regulatory approval process. We also analyze how nanotechnology is impacting global health and economy during the COVID-19 pandemic and beyond.

Formation, antimicrobial activity, and biomedical performance of plant-based nanoparticles: a review

Because many engineered nanoparticles are toxic, there is a need for methods to fabricate safe nanoparticles such as plant-based nanoparticles. Indeed, plant extracts contain flavonoids, amino acids, proteins, polysaccharides, enzymes, polyphenols, steroids, and reducing sugars that facilitate the reduction, formation, and stabilization of nanoparticles. Moreover, synthesizing nanoparticles from plant extracts is fast, safe, and cost-effective because it does not consume much energy, and non-toxic derivatives are generated. These nanoparticles have diverse and unique properties of interest for applications in many fields. Here, we review the synthesis of metal/metal oxide nanoparticles with plant extracts. These nanoparticles display antibacterial, antifungal, anticancer, and antioxidant properties. Plant-based nanoparticles are also useful for medical diagnosis and drug delivery.

Innovative vaccine platforms against infectious diseases: Under the scope of the COVID-19 pandemic

While classic vaccines have proved greatly efficacious in eliminating serious infectious diseases, innovative vaccine platforms open a new pathway to overcome dangerous pandemics via the development of safe and effective formulations. Such platforms play a key role either as antigen delivery systems or as immune-stimulators that induce both innate and adaptive immune responses. Liposomes or lipid nanoparticles, virus-like particles, nanoemulsions, polymeric or inorganic nanoparticles, as well as viral vectors, all belong to the nanoscale and are the main categories of innovative vaccines that are currently on the market or in clinical and preclinical phases. In this paper, we review the above formulations used in vaccinology and we discuss their connection with the development of safe and effective prophylactic vaccines against SARS-CoV-2.

Gold nanoparticle-based platforms for vaccine development

Since their discovery, therapeutic or prophylactic vaccines represent a promising option to prevent or cure infections and other pathologies, such as cancer or autoimmune disorders. More recently, among a number of nanomaterials, gold nanoparticles (AuNPs) have emerged as novel tools for vaccine developments, thanks to their inherent ability to tune and upregulate immune response. Moreover, owing to their features, AuNPs can exert optimal actions both as delivery systems and as adjuvants. Notwithstanding the potential huge impact in vaccinology, some challenges remain before AuNPs in vaccine formulations can be translated into the clinic. The current review provides an updated overview of the most recent and effective application of gold nanoparticles as efficient means to develop a new generation of vaccine.

Malaria transmission-blocking conjugate vaccine in ALFQ adjuvant induces durable functional immune responses in rhesus macaques

Malaria transmission-blocking vaccines candidates based on Pfs25 and Pfs230 have advanced to clinical studies. Exoprotein A (EPA) conjugate of Pfs25 in Alhydrogel^® developed functional immunity in humans, with limited durability. Pfs230 conjugated to EPA (Pfs230D1-EPA) with liposomal adjuvant AS01 is currently in clinical trials in Mali. Studies with these conjugates revealed that non-human primates are better than mice to recapitulate the human immunogenicity and functional activity. Here, we evaluated the effect of ALFQ, a liposomal adjuvant consisting of TLR4 agonist and QS21, on the immunogenicity of Pfs25-EPA and Pfs230D1-EPA in Rhesus macaques. Both conjugates generated strong antibody responses and functional activity after two vaccinations though activity declined rapidly. A third vaccination of Pfs230D1-EPA induced functional activity lasting at least 9 months. Antibody avidity increased with each vaccination and correlated strongly with functional activity. IgG subclass analysis showed induction of Th1 and Th2 subclass antibody levels that correlated with activity.

Nanovaccine: an emerging strategy

INTRODUCTION

Vaccination is so far the most effective way of eradicating infections. Rapidly emerging drug resistance against infectious diseases and chemotherapy-related toxicities in cancer warrant immediate vaccine development to save mankind. Subunit vaccines alone, however, fail to elicit sufficiently strong and long-lasting protective immunity against deadly pathogens. Nanoparticle (NP)-based delivery vehicles like microemulsions, liposomes, virosomes, nanogels, micelles and dendrimers offer promising strategies to overcome limitations of traditional vaccine adjuvants. Nanovaccines can improve targeted delivery, antigen presentation, stimulation of body's innate immunity, strong T cell response combined with safety to combat infectious diseases and cancers. Further, nanovaccines can be highly beneficial to generate effective immutherapeutic formulations against cancer.

AREAS COVERED

This review summarizes the emerging nanoparticle strategies highlighting their success and challenges in preclinical and clinical trials in infectious diseases and cancer. It provides a concise overview of current nanoparticle-based vaccines, their adjuvant potential and their cellular delivery mechanisms.

EXPERT OPINION

The nanovaccines (50-250 nm in size) are most efficient in terms of tissue targeting, prolonged circulation and preferential uptake by the professional APCs chiefly due to their small size. More rational designing, improved antigen loading, extensive functionalization and targeted delivery are some of the future goals of ideal nanovaccines.

How can we develop an effective subunit vaccine to achieve successful malaria eradication?

Malaria, a mosquito-borne infection, is the most widespread parasitic disease. Despite numerous efforts to eradicate malaria, this disease is still a health concern worldwide. Owing to insecticide-resistant vectors and drug-resistant parasites, available controlling measures are insufficient to achieve a malaria-free world. Thus, there is an urgent need for new intervention tools such as efficient malaria vaccines. Subunit vaccines are the most promising malaria vaccines under development. However, one of the major drawbacks of subunit vaccines is the lack of efficient and durable immune responses including antigen-specific antibody, CD4⁺, and CD8⁺ T-cell responses, long-lived plasma cells, memory cells, and functional antibodies for parasite neutralization or inhibition of parasite invasion. These types of responses could be induced by whole organism vaccines, but eliciting these responses with subunit vaccines has been proven to be more challenging. Consequently, subunit vaccines require several policies to overcome these challenges. In this review, we address common approaches that can improve the efficacy of subunit vaccines against malaria.

Nanovaccines against Animal Pathogens: The Latest Findings

Nowadays, safe and efficacious vaccines represent powerful and cost-effective tools for global health and economic growth. In the veterinary field, these are undoubtedly key tools for improving productivity and fighting zoonoses. However, cases of persistent infections, rapidly evolving pathogens having high variability or emerging/re-emerging pathogens for which no effective vaccines have been developed point out the continuing need for new vaccine alternatives to control outbreaks. Most licensed vaccines have been successfully used for many years now; however, they have intrinsic limitations, such as variable efficacy, adverse effects, and some shortcomings. More effective adjuvants and novel delivery systems may foster real vaccine effectiveness and timely implementation. Emerging vaccine technologies involving nanoparticles such as self-assembling proteins, virus-like particles, liposomes, virosomes, and polymeric nanoparticles offer novel, safe, and high-potential approaches to address many vaccine development-related challenges. Nanotechnology is accelerating the evolution of vaccines because nanomaterials having encapsulation ability and very advantageous properties due to their size and surface area serve as effective vehicles for antigen delivery and immunostimulatory agents. This review discusses the requirements for an effective, broad-coverage-elicited immune response, the main nanoplatforms for producing it, and the latest nanovaccine applications for fighting animal pathogens.

Iron nanoparticles as novel vaccine adjuvants

The poor immunogenicity of peptide vaccines compared to conventional ones re usually improved by applying different adjuvants. As chemical or biological substances, adjuvants are added to vaccines to enhance and prolong the immune response. According to considerable investigations over the recent years in the context of finding new adjuvants, a handful of vaccine adjuvants have been licensed for human use. Recently, engineered nanoparticles (NPs) have been introduced as novel alternatives to traditional vaccine adjuvant. Metallic nanoparticles (MeNPs) are among the most promising NPs used for vaccine adjuvant as well as the delivery system that can improve immune responses against pathogens. Iron NPs, as an important class of MeNPs, have gained increasing attention as novel vaccine adjuvants. These particles have shown acceptable results in preclinical studies. Hence, understanding the physicochemical properties of iron NPs, including size, surface properties, charge and route of administration, is of substantial importance. The aim of this review is to provide an overview of the immunomodulatory effects of iron NPs as novel adjuvants. Furthermore, physicochemical properties of these NPs were also discussed.

Advances in nanomaterial vaccine strategies to address infectious diseases impacting global health

Despite the overwhelming success of vaccines in preventing infectious diseases, there remain numerous globally devastating diseases without fully protective vaccines, particularly human immunodeficiency virus (HIV), malaria and tuberculosis. Nanotechnology approaches are being developed both to design new vaccines against these diseases as well as to facilitate their global implementation. The reasons why a given pathogen may present difficulties for vaccine design are unique and tied to the co-evolutionary history of the pathogen and humans, but there are common challenges that nanotechnology is beginning to help address. In each case, a successful vaccine will need to raise immune responses that differ from the immune responses raised by normal infection. Nanomaterials, with their defined compositions, commonly modular construction, and length scales allowing the engagement of key immune pathways, collectively facilitate the iterative design process necessary to identify such protective immune responses and achieve them reliably. Nanomaterials also provide strategies for engineering the trafficking and delivery of vaccine components to key immune cells and lymphoid tissues, and they can be highly multivalent, improving their engagement with the immune system. This Review will discuss these aspects along with recent nanomaterial advances towards vaccines against infectious disease, with a particular emphasis on HIV/AIDS, malaria and tuberculosis.

The rapid diagnosis and effective inhibition of coronavirus using spike antibody attached gold nanoparticles

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of the coronavirus disease that began in 2019 (COVID-19), has been responsible for 1.4 million deaths worldwide as of 13 November 2020. Because at the time of writing no vaccine is yet available, a rapid diagnostic assay is very urgently needed. Herein, we present the development of anti-spike antibody attached gold nanoparticles for the rapid diagnosis of specific COVID-19 viral antigen or virus via a simple colorimetric change observation within a 5 minute time period. For rapid and highly sensitive identification, surface enhanced Raman spectroscopy (SERS) was employed using 4-aminothiophenol as a reporter molecule, which is attached to the gold nanoparticle via an Au-S bond. In the presence of COVID-19 antigen or virus particles, owing to the antigen-antibody interaction, the gold nanoparticles undergo aggregation, changing color from pink to blue, which allows for the determination of the presence of antigen or virus very rapidly by the naked eye, even at concentrations of 1 nanogram (ng) per mL for COVID-19 antigen and 1000 virus particles per mL for SARS-CoV-2 spike protein pseudotyped baculovirus. Importantly, the aggregated gold nanoparticles form "hot spots" to provide very strong SERS signal enhancement from anti-spike antibody and 4-aminothiophenol attached gold nanoparticles via light-matter interactions. Finite-difference time-domain (FDTD) simulation data indicate a 4-orders-of-magnitude Raman enhancement in "hot spot" positions when gold nanoparticles form aggregates. Using a portable Raman analyzer, our reported data demonstrate that our antibody and 4-aminothiophenol attached gold nanoparticle-based SERS probe has the capability to detect COVID-19 antigen even at a concentration of 4 picograms (pg) per mL and virus at a concentration of 18 virus particles per mL within a 5 minute time period. Using HEK293T cells, which express angiotensin-converting enzyme 2 (ACE2), by which SARS-CoV-2 enters human cells, we show that anti-spike antibody attached gold nanoparticles have the capability to inhibit infection by the virus. Our reported data show that antibody attached gold nanoparticles bind to SARS-CoV-2 spike protein, thereby inhibiting the virus from binding to cell receptors, which stops virus infection and spread. It also has the capability to destroy the lipid membrane of the virus.

Biomaterials-based formulations and surfaces to combat viral infectious diseases

Rapidly growing viral infections are potent risks to public health worldwide. Accessible virus-specific antiviral vaccines and drugs are therapeutically inert to emerging viruses, such as Zika, Ebola, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Therefore, discovering ways to prevent and control viral infections is among the foremost medical challenge of our time. Recently, innovative technologies are emerging that involve the development of new biomaterial-based formulations and surfaces endowed with broad-spectrum antiviral properties. Here, we review emerging biomaterials technologies for controlling viral infections. Relevant advances in biomaterials employed with nanotechnology to inactivate viruses or to inhibit virus replication and further their translation in safe and effective antiviral formulations in clinical trials are discussed. We have included antiviral approaches based on both organic and inorganic nanoparticles (NPs), which offer many advantages over molecular medicine. An insight into the development of immunomodulatory scaffolds in designing new platforms for personalized vaccines is also considered. Substantial research on natural products and herbal medicines and their potential in novel antiviral drugs are discussed. Furthermore, to control contagious viral infections, i.e., to reduce the viral load on surfaces, current strategies focusing on biomimetic anti-adhesive surfaces through nanostructured topography and hydrophobic surface modification techniques are introduced. Biomaterial surfaces functionalized with antimicrobial polymers and nanoparticles against viral infections are also discussed. We recognize the importance of research on antiviral biomaterials and present potential strategies for future directions in applying these biomaterial-based approaches to control viral infections and SARS-CoV-2.

Preparation, Functionalization, Modification, and Applications of Nanostructured Gold: A Critical Review

Gold nanoparticles (Au NPs) play a significant role in science and technology because of their unique size, shape, properties and broad range of potential applications. This review focuses on the various approaches employed for the synthesis, modification and functionalization of nanostructured Au. The potential catalytic applications and their enhancement upon modification of Au nanostructures have also been discussed in detail. The present analysis also offers brief summaries of the major Au nanomaterials synthetic procedures, such as hydrothermal, solvothermal, sol-gel, direct oxidation, chemical vapor deposition, sonochemical deposition, electrochemical deposition, microwave and laser pyrolysis. Among the various strategies used for improving the catalytic performance of nanostructured Au, the modification and functionalization of nanostructured Au produced better results. Therefore, various synthesis, modification and functionalization methods employed for better catalytic outcomes of nanostructured Au have been summarized in this review.

Transmission-Blocking Vaccines: Harnessing Herd Immunity for Malaria Elimination

INTRODUCTION

Transmission-blocking vaccines (TBV) prevent community spread of malaria by targeting mosquito sexual stage parasites, a life-cycle bottleneck, and will be used in elimination programs. TBV rely on herd immunity to reduce mosquito infections and thereby new infections in both vaccine recipients and non-recipients, but do not provide protection once an individual receives an infectious mosquito bite which complicates clinical development.

AREAS COVERED

Here, we describe the concept and biology behind TBV, and we provide an update on clinical development of the leading vaccine candidate antigens. Search terms 'malaria vaccine,' 'sexual stages,' 'transmission blocking vaccine,' 'VIMT' and 'SSM-VIMT' were used for PubMed queries to identify relevant literature.

EXPERT OPINION

Candidates targeting P. falciparum zygote surface antigen Pfs25, and its P. vivax orthologue Pvs25, induced functional activity in humans that reduced mosquito infection in surrogate assays, but require increased durability to be useful in the field. Candidates targeting gamete surface antigens Pfs230 and Pfs48/45, respectively, are in or nearing clinical trials. Nanoparticle platforms and adjuvants are being explored to enhance immunogenicity. Efficacy trials require special considerations, such as cluster-randomized designs to measure herd immunity that reduces human and mosquito infection rates, while addressing human and mosquito movements as confounding factors.

Experimental and Computational Observations of Immunogenic Cobalt Porphyrin Lipid Bilayers: Nanodomain-Enhanced Antigen Association

Cobalt porphyrin phospholipid (CoPoP) can incorporate within bilayers to enable non-covalent surface-display of antigens on liposomes by mixing with proteins bearing a polyhistidine tag (his-tag); however, the mechanisms for how this occurs are poorly understood. These were investigated using the his-tagged model antigen Pfs25, a protein antigen candidate for malaria transmission-blocking vaccines. Pfs25 was found to associate with the small molecule aquocobalamin, a form of vitamin B12 and a cobalt-containing corrin macrocycle, but without particle formation, enabling comparative assessment. Relative to CoPoP liposomes, binding and serum stability studies indicated a weaker association of Pfs25 to aquocobalamin or cobalt nitrilotriacetic acid (Co-NTA) liposomes, which have cobalt displayed in the aqueous phase on lipid headgroups. Antigen internalization by macrophages was enhanced with Pfs25 bound to CoPoP liposomes. Immunization in mice with Pfs25 bound to CoPoP liposomes elicited antibodies that recognized ookinetes and showed transmission-reducing activity. To explore the physical mechanisms involved, we employed molecular dynamics (MD) simulations of bilayers containing phospholipid, cholesterol, as well as either CoPoP or NTA-functionalized lipids. The results show that the CoPoP-containing bilayer creates nanodomains that allow access for a limited but sufficient amount of water molecules that could be replaced by his-tags due to their favorable free energy properties allowing for stabilization. The position of the metal center within the NTA liposomes was much more exposed to the aqueous environment, which could explain its limited capacity for stabilizing Pfs25. This study illustrates the impact of CoPoP-induced antigen particleization in enhancing vaccine efficacy, and provides molecular insights into the CoPoP bilayer properties that enable this.

Biomedical nanomaterials for immunological applications: ongoing research and clinical trials

Research efforts on nanomaterial-based therapies for the treatment of autoimmune diseases and cancer have spiked and have made rapid progress over the past years. Nanomedicine has been shown to contribute significantly to overcome current therapeutic limitations, exhibiting advantages compared to conventional therapeutics, such as sustained drug release, delayed drug degradation and site-specific drug delivery. Multiple nanodrugs have reached the clinic, but translation is often hampered by either low targeting efficiency or undesired side effects. Nanomaterials, and especially inorganic nanoparticles, have gained criticism due to their potential toxic effects, including immunological alterations. However, many strategies have been attempted to improve the therapeutic efficacy of nanoparticles and exploit their unique properties for the treatment of inflammation and associated diseases. In this review, we elaborate on the immunomodulatory effects of nanomaterials, with a strong focus on the underlying mechanisms that lead to these specific immune responses. Nanomaterials to be discussed include inorganic nanoparticles such as gold, silica and silver, as well as organic nanomaterials such as polymer-, dendrimer-, liposomal- and protein-based nanoparticles. Furthermore, various approaches for tuning nanomaterials in order to enhance their efficacy and attenuate their immune stimulation or suppression, with respect to the therapeutic application, are described. Additionally, we illustrate how the acquired insights have been used to design immunotherapeutic strategies for a variety of diseases. The potential of nanomedicine-based therapeutic strategies in immunotherapy is further illustrated by an up to date overview of current clinical trials. Finally, recent efforts into enhancing immunogenic cell death through the use of nanoparticles are discussed.

Pullulan-Coated Iron Oxide Nanoparticles for Blood-Stage Malaria Vaccine Delivery

Vaccines against blood-stage malaria often aim to induce antibodies to neutralize parasite entry into red blood cells, interferon gamma (IFNγ) produced by T helper 1 (Th1) CD4+ T cells or interleukin 4 (IL-4) produced by T helper 2 (Th2) cells to provide B cell help. One vaccine delivery method for suitable putative malaria protein antigens is the use of nanoparticles as vaccine carriers. It has been previously shown that antigen conjugated to inorganic nanoparticles in the viral-particle size range (~40–60 nm) can induce protective antibodies and T cells against malaria antigens in a rodent malaria challenge model. Herein, it is shown that biodegradable pullulan-coated iron oxide nanoparticles (pIONPs) can be synthesized in this same size range. The pIONPs are non-toxic and do not induce conventional pro-inflammatory cytokines in vitro and in vivo. We show that murine blood-stage antigen MSP4/5 from Plasmodium yoelii could be chemically conjugated to pIONPs and the use of these conjugates as immunogens led to the induction of both specific antibodies and IFNγ CD4+ T cells reactive to MSP4/5 in mice, comparable to responses to MSP4/5 mixed with classical adjuvants (e.g., CpG or Alum) that preferentially induce Th1 or Th2 cells individually. These results suggest that biodegradable pIONPs warrant further exploration as carriers for developing blood-stage malaria vaccines.

Lyophilized, antigen-bound liposomes with reduced MPLA and enhanced thermostability

Thermostability and decreased component costs are desirable features for adjuvanted, recombinant vaccines. We previously showed that a model malaria transmission-blocking vaccine candidate antigen, Pfs25, can be rendered more immunogenic when mixed with liposomes containing cobalt porphyrin-phospholipid (CoPoP) and a synthetic monophosphoryl lipid A (MPLA) variant. CoPoP can induce stable particle formation of recombinant antigens based on interaction with their polyhistidine tag. In the present work, different synthetic MPLA variants and concentrations were assessed in CoPoP liposomes. Long-term biophysical stability and immunogenicity were not adversely impacted by a 60% reduction in MPLA content. When admixed with Pfs25, the adjuvant formulations effectively induced functional antibodies in immunized mice and rabbits. Lyophilized, antigen-bound liposomes were formed using sucrose and trehalose cryoprotectants, which improved vaccine reconstitution for a variety of model antigens. Compared to liquid storage, the lyophilized Pfs25 and CoPoP liposomes exhibited thermostability with respect to size, biochemical integrity, binding capacity, protein folding and immunogenicity. Following 6 weeks of storage at 60 °C, the most extended storage period assessed, the lyophilized formulation induced functional antibodies in mice with immunization.

Comparison of carrier proteins to conjugate malaria transmission blocking vaccine antigens, Pfs25 and Pfs230

Malaria transmission blocking vaccines (TBV) target the sexual stage of the parasite and have been pursued as a stand-alone vaccine or for combination with pre-erythrocytic or blood stage vaccines. Our efforts to develop TBV focus primarily on two antigens, Pfs25 and Pfs230. Chemical conjugation of these poorly immunogenic antigens to carrier proteins enhances their immunogenicity, and conjugates of these antigens to Exoprotein A (EPA) are currently under evaluation in clinical trials. Nonetheless, more potent carriers may augment the immunogenicity of these antigens for a more efficacious vaccine; here, we evaluate a series of proteins to identify such a carrier. Pfs25 and Pfs230 were chemically conjugated to 4 different carriers [tetanus toxoid (TT), a recombinant fragment of tetanus toxin heavy chain (rTThc), recombinant CRM197 produced in Pseudomonas fluorescens (CRM197) or in E. coli (EcoCRM®)] and compared to EPA conjugates in mouse immunogenicity studies. Conjugates of each antigen formulated in Alhydrogel® elicited similar antibody titers but showed differences in functional activity. At a 0.5 µg dose, Pfs230 conjugated to TT, CRM197 and EcoCRM® showed significantly higher functional activity compared to EPA. When formulated with the more potent adjuvant GLA-LSQ, all 4 alternate conjugates induced higher antibody titers as well as increased functional activity compared to the EPA conjugate. IgG subclass analysis of Pfs230 conjugates showed no carrier-dependent differences in the IgG profile. While Alhydrogel® formulations induced a Th2 dominant immune response, GLA-LSQ formulations induced a mixed Th1/Th2 response.

Gold nanoparticles for preparation of antibodies and vaccines against infectious diseases

INTRODUCTION

Vaccination remains very effective in stimulating protective immune responses against infections. An important task in antibody and vaccine preparation is to choose an optimal carrier that will ensure a high immune response. Particularly promising in this regard are nanoscale particle carriers. An antigen that is adsorbed or encapsulated by nanoparticles can be used as an adjuvant to optimize the immune response during vaccination. a very popular antigen carrier used for immunization and vaccination is gold nanoparticles, with are being used to make new vaccines against viral, bacterial, and parasitic infections.

AREAS COVERED

This review summarizes what is currently known about the use of gold nanoparticles as an antigen carrier and adjuvant to prepare antibodies in vivo and design vaccines against viral, bacterial, and parasitic infections. The basic principles, recent advances, and current problems in the use of gold nanoparticles are discussed.

EXPERT OPINION

Gold nanoparticles can be used as adjuvants to increase the effectiveness of vaccines by stimulating antigen-presenting cells and ensuring controlled antigen release. Studying the characteristics of the immune response obtained from the use of gold nanoparticles as a carrier and an adjuvant will permit the particles' potential for vaccine design to be increased.

Advancements in prophylactic and therapeutic nanovaccines

Vaccines activate suitable immune responses to fight against diseases but can possess limitations such as compromised efficacy and immunogenic responses, poor stability, and requirement of adherence to multiple doses. ‘Nanovaccines’ have been explored to elicit a strong immune response with the advantages of nano-sized range, high antigen loading, enhanced immunogenicity, controlled antigen presentation, more retention in lymph nodes and promote patient compliance by a lower frequency of dosing. Various types of nanoparticles with diverse pathogenic or foreign antigens can help to overcome immunotolerance and alleviate the need of booster doses as required with conventional vaccines. Nanovaccines have the potential to induce both cell-mediated and antibody-mediated immunity and can render long-lasting immunogenic memory. With such properties, nanovaccines have shown high potential for the prevention of infectious diseases such as acquired immunodeficiency syndrome (AIDS), malaria, tuberculosis, influenza, and cancer. Their therapeutic potential has also been explored in the treatment of cancer. The various kinds of nanomaterials used for vaccine development and their effects on immune system activation have been discussed with special relevance to their implications in various pathological conditions.

Statement of Significance

Interaction of nanoparticles with the immune system has opened multiple avenues to combat a variety of infectious and non-infectious pathological conditions. Limitations of conventional vaccines have paved the path for nanomedicine associated benefits with a hope of producing effective nanovaccines. This review highlights the role of different types of nanovaccines and the role of nanoparticles in modulating the immune response of vaccines. The applications of nanovaccines in infectious and non-infectious diseases like malaria, tuberculosis, AIDS, influenza, and cancers have been discussed. It will help the readers develop an understanding of mechanisms of immune activation by nanovaccines and design appropriate strategies for novel nanovaccines.

Surface chemistry of gold nanoparticles for health-related applications

Functionalization of gold nanoparticles is crucial for the effective utilization of these materials in health-related applications. Health-related applications of gold nanoparticles rely on the physical and chemical reactions between molecules and gold nanoparticles. Surface chemistry can precisely control and tailor the surface properties of gold nanoparticles to meet the needs of applications. Gold nanoparticles have unique physical and chemical properties, and have been used in a broad range of applications from prophylaxis to diagnosis and treatment. The surface chemistry of gold nanoparticles plays a crucial role in all of these applications. This minireview summarizes these applications from the perspective of surface chemistry and explores how surface chemistry improves and imparts new properties to gold nanoparticles for these applications.

Malaria transmission-blocking vaccines: wheat germ cell-free technology can accelerate vaccine development

Introduction: Highly effective malaria vaccines are essential component toward malaria elimination. Although the leading malaria vaccine, RTS,S/AS01, with modest efficacy is being evaluated in a pilot feasibility trial, development of a malaria transmission-blocking vaccine (TBV) could make a major contribution toward malaria elimination. Only a few TBV antigens have reached pre-clinical or clinical development but with several challenges including difficulties in the expression of malaria recombinant proteins and low immunogenicity in humans. Therefore, novel approaches to accelerate TBV research to preclinical development are critical to generate an efficacious TBV.Areas covered: PubMed was searched to review the progress and future prospects of malaria TBV research and development. We also reviewed registered trials at ClinicalTrials.gov as well as post-genome TBV candidate discovery research including our efforts.Expert opinion: Wheat germ cell-free protein synthesis technology can accelerate TBV development by overcoming some current challenges of TBV research.

Display of malaria transmission-blocking antigens on chimeric duck hepatitis B virus-derived virus-like particles produced in Hansenula polymorpha

BACKGROUND

Malaria caused by Plasmodium falciparum is one of the major threats to human health globally. Despite huge efforts in malaria control and eradication, highly effective vaccines are urgently needed, including vaccines that can block malaria transmission. Chimeric virus-like particles (VLP) have emerged as a promising strategy to develop new malaria vaccine candidates.

METHODS

We developed yeast cell lines and processes for the expression of malaria transmission-blocking vaccine candidates Pfs25 and Pfs230 as VLP and VLP were analyzed for purity, size, protein incorporation rate and expression of malaria antigens.

RESULTS

In this study, a novel platform for the display of Plasmodium falciparum antigens on chimeric VLP is presented. Leading transmission-blocking vaccine candidates Pfs25 and Pfs230 were genetically fused to the small surface protein (dS) of the duck hepatitis B virus (DHBV). The resulting fusion proteins were co-expressed in recombinant Hansenula polymorpha (syn. Pichia angusta, Ogataea polymorpha) strains along with the wild-type dS as the VLP scaffold protein. Through this strategy, chimeric VLP containing Pfs25 or the Pfs230-derived fragments Pfs230c or Pfs230D1M were purified. Up to 100 mg chimeric VLP were isolated from 100 g dry cell weight with a maximum protein purity of 90% on the protein level. Expression of the Pfs230D1M construct was more efficient than Pfs230c and enabled VLP with higher purity. VLP showed reactivity with transmission-blocking antibodies and supported the surface display of the malaria antigens on the native VLP.

CONCLUSION

The incorporation of leading Plasmodium falciparum transmission-blocking antigens into the dS-based VLP scaffold is a promising novel strategy for their display on nano-scaled particles. Competitive processes for efficient production and purification were established in this study.

Outer membrane protein complex as a carrier for malaria transmission blocking antigen Pfs230

Malaria transmission blocking vaccines (TBV) target the mosquito stage of parasite development by passive immunization of mosquitoes feeding on a vaccinated human. Through uptake of vaccine-induced antibodies in a blood meal, mosquito infection is halted and hence transmission to another human host is blocked. Pfs230 is a gametocyte and gamete surface antigen currently under clinical evaluation as a TBV candidate. We have previously shown that chemical conjugation of poorly immunogenic TBV antigens to Exoprotein A (EPA) can enhance their immunogenicity. Here, we assessed Outer Membrane Protein Complex (OMPC), a membrane vesicle derived from Neisseria meningitidis, as a carrier for Pfs230. We prepared Pfs230-OMPC conjugates with varying levels of antigen load and examined immunogenicity in mice. Chemical conjugation of Pfs230 to OMPC enhanced immunogenicity and functional activity of the Pfs230 antigen, and OMPC conjugates achieved 2-fold to 20-fold higher antibody titers than Pfs230-EPA/AdjuPhos^® at different doses. OMPC conjugates were highly immunogenic even at low doses, indicating a dose-sparing effect. EPA conjugates induced an IgG subclass profile biased towards a Th2 response, whereas OMPC conjugates induced a strong Th1-biased immune response with high levels of IgG2, which can benefit Pfs230 antibody functional activity, which depends on complement activation. OMPC is a promising carrier for Pfs230 vaccines.

Malaria transmission blocking vaccines (TBV) target Plasmodium stages that transmit between human and mosquitos in order to interrupt the parasite’s life cycle and reduce spread. One TBV antigen currently under clinical development is Pf230, which is expressed on sexual Plasmodium stages. In this study, led by Patrick Duffy from the NIAID, researchers improve immunogenicity of Pf230. They chemically conjugate a part of Pf230 to membrane vesicles derived from bacteria, so-called outer membrane protein complexes (OMPC). Immunization of mice with Pf230-OMPC elicits a higher antibody response and a more balanced IgG subclass profile than control immunizations. Serum from Pf230-OMPC-vaccinated mice efficiently blocks infection of mosquitoes. These results with mice encourage further pre-clinical and clinical characterization of OMPC as a carrier for TBV antigens.

Nano-facilitated drug delivery strategies in the treatment of plasmodium infection

Malaria, one of the major infectious disease-causing sizeable morbidity, mortality and economic loss worldwide. The main drawback for the failure to eradicate malaria is the spread of multiple drug resistance to the majority of currently available chemotherapy. At present nanotechnology offers an advanced opportunity in the delivery of drugs and vaccines to the desired targeted site in the body following oral and systemic administration. It confers the major advantages like improving drug pharmacokinetic profiles, reduce dose frequency and reduction in drug toxicity. Hence, Nano-based drug delivery system can provide a promising prospect in the way of malaria treatment. This paper is a review of recent researches highlighting includes nanocarriers loaded antimalarial drugs for better therapeutic efficacy and future perspective in the treatment of malaria.

Characterization of Plasmodium berghei Homologues of T-cell Immunomodulatory Protein as a New Potential Candidate for Protecting against Experimental Cerebral Malaria

The pathogenesis of cerebral malaria is biologically complex and involves multi-factorial mechanisms such as microvascular congestion, immunopathology by the pro-inflammatory cytokine and endothelial dysfunction. Recent data have suggested that a pleiotropic T-cell immunomodulatory protein (TIP) could effectively mediate inflammatory cytokines of mammalian immune response against acute graft-versus-host disease in animal models. In this study, we identified a conserved homologue of TIP in Plasmodium berghei (PbTIP) as a membrane protein in Plasmodium asexual stage. Compared with PBS control group, the pathology of experimental cerebral malaria (ECM) in rPbTIP intravenous injection (i.v.) group was alleviated by the downregulation of pro-inflammatory responses, and rPbTIP i.v. group elicited an expansion of regulatory T-cell response. Therefore, rPbTIP i.v. group displayed less severe brain pathology and feverish mice in rPbTIP i.v. group died from ECM. This study suggested that PbTIP may be a novel promising target to alleviate the severity of ECM.

Malaria vaccines in the eradication era: current status and future perspectives

INTRODUCTION

The challenge to eradicate malaria is an enormous task that will not be achieved by current control measures, thus an efficacious and long-lasting malaria vaccine is required. The licensing of RTS, S/AS01 is a step forward in providing some protection, but a malaria vaccine that protects across multiple transmission seasons is still needed. To achieve this, inducing beneficial immune responses while minimising deleterious non-targeted effects will be essential.

AREAS COVERED

This article discusses the current challenges and advances in malaria vaccine development and reviews recent human clinical trials for each stage of infection. Pubmed and ScienceDirect were searched, focusing on cell mediated immunity and how T cell subsets might be targeted in future vaccines using novel adjuvants and emerging vaccine technologies.

EXPERT COMMENTARY

Despite decades of research there is no highly effective licensed malaria vaccine. However, there is cause for optimism as new adjuvants and vaccine systems emerge, and our understanding of correlates of protection increases, especially regarding cellular immunity. The new field of heterologous (non-specific) effects of vaccines also highlights the broader consequences of immunization. Importantly, the WHO led Malaria Vaccine Technology Roadmap illustrates that there is a political will among the global health community to make it happen.

A malaria vaccine adjuvant based on recombinant antigen binding to liposomes

Pfs25 is a malaria transmission-blocking vaccine antigen candidate, but its apparently limited immunogenicity in humans has hindered clinical development. Here, we show that recombinant, polyhistidine-tagged (his-tagged) Pfs25 can be mixed at the time of immunization with pre-formed liposomes containing cobalt porphyrin-phospholipid, resulting in spontaneous nanoliposome antigen particleization (SNAP). Antigens are stably presented in uniformly orientated display via his-tag insertion in the cobalt porphyrin-phospholipid bilayer, without covalent modification or disruption of antigen conformation. SNAP immunization of mice and rabbits is well tolerated with minimal local reactogenicity, and results in orders-of-magnitude higher functional antibody generation compared with other 'mix-and-inject' adjuvants. Serum-stable antigen binding during transit to draining lymph nodes leads to enhanced antigen uptake by phagocytic antigen-presenting cells, with subsequent generation of long-lived, antigen-specific plasma cells. Seamless multiplexing with four additional his-tagged Plasmodium falciparum polypeptides induces strong and balanced antibody production, illustrating the simplicity of developing multistage particulate vaccines with SNAP immunization.

Incorporation of a recombinant Eimeria maxima IMP1 antigen into nanoparticles confers protective immunity against E. Maxima challenge infection

The purpose of this study was to determine if conjugating a recombinant Eimeria maxima protein, namely EmaxIMP1, into 20 nm polystyrene nanoparticles (NP) could improve the level of protective immunity against E. maxima challenge infection. Recombinant EmaxIMP1 was expressed in Escherichia coli as a poly-His fusion protein, purified by NiNTA chromatography, and conjugated to 20 nm polystyrene NP (NP-EmaxIMP1). NP-EMaxIMP1 or control non-recombinant (NP-NR) protein were delivered per os to newly-hatched broiler chicks with subsequent booster immunizations at 3 and 21 days of age. In battery cage studies (n = 4), chickens immunized with NP-EMaxIMP1 displayed complete protection as measured by weight gain (WG) against E. maxima challenge compared to chickens immunized with NP-NR. WG in the NP-EMaxIMP1-immunized groups was identical to WG in chickens that were not infected with E. maxima infected chickens. In floor pen studies (n = 2), chickens immunized with NP-EMaxIMP1 displayed partial protection as measured by WG against E. maxima challenge compared to chickens immunized with NP-NR. In order to understand the basis for immune stimulation, newly-hatched chicks were inoculated per os with NP-EMaxIMP1 or NP-NR protein, and the small intestine, bursa, and spleen, were examined for NP localization at 1 h and 6 h post-inoculation. Within 1 h, both NP-EMaxIMP1 and NP-NR were observed in all 3 tissues. An increase was observed in the level of NP-EmaxIMP1 and NP-NR in all tissues at 6 h post-inoculation. These data indicate that 20 nm NP-EmaxIMP1 or NP-NR reached deeper tissues within hours of oral inoculation and elicited complete to partial immunity against E. maxima challenge infection.

Statistical Methods for Standard Membrane-Feeding Assays to Measure Transmission Blocking or Reducing Activity in Malaria

Transmission blocking vaccines for malaria are not designed to directly protect vaccinated people from malaria disease, but to reduce the probability of infecting other people by interfering with the growth of the malaria parasite in mosquitoes. Standard membrane-feeding assays compare the growth of parasites in mosquitoes from a test sample (using antibodies from a vaccinated person) compared to a control sample. There is debate about whether to estimate the transmission reducing activity (TRA) which compares the mean number of parasites between test and control samples, or transmission blocking activity (TBA) which compares the proportion of infected mosquitoes. TBA appears biologically more important since each mosquito with any parasites is potentially infective; however, TBA is less reproducible and may be an overly strict criterion for screening vaccine candidates. Through a statistical model, we show that the TBA estimand depends on μ _c , the mean number of parasites in the control mosquitoes, a parameter not easily experimentally controlled. We develop a standardized TBA estimator based on the model and a given target value for μ _c which has better mean squared error than alternative methods. We discuss types of statistical inference needed for using these assays for vaccine development.

Peptide and protein nanoparticle conjugates: versatile platforms for biomedical applications

Peptide- and protein-nanoparticle conjugates have emerged as powerful tools for biomedical applications, enabling the treatment, diagnosis, and prevention of disease. In this review, we focus on the key roles played by peptides and proteins in improving, controlling, and defining the performance of nanotechnologies. Within this framework, we provide a comprehensive overview of the key sequences and structures utilised to provide biological and physical stability to nano-constructs, direct particles to their target and influence their cellular and tissue distribution, induce and control biological responses, and form polypeptide self-assembled nanoparticles. In doing so, we highlight the great advances made by the field, as well as the challenges still faced in achieving the clinical translation of peptide- and protein-functionalised nano-drug delivery vehicles, imaging species, and active therapeutics.

Development of a bivalent conjugate vaccine candidate against malaria transmission and typhoid fever

Immune responses to poorly immunogenic antigens, such as polysaccharides, can be enhanced by conjugation to carriers. Our previous studies indicate that conjugation to Vi polysaccharide of Salmonella Typhi may also enhance immunogenicity of some protein carriers. We therefore explored the possibility of generating a bivalent vaccine against Plasmodium falciparum malaria and typhoid fever, which are co-endemic in many parts of the world, by conjugating Vi polysaccharide, an approved antigen in typhoid vaccine, to Pfs25, a malaria transmission blocking vaccine antigen in clinical trials. Vi-Pfs25 conjugates induced strong immune responses against both Vi and Pfs25 in mice, whereas the unconjugated antigens are poorly immunogenic. Functional assays of immune sera revealed potent transmission blocking activity mediated by anti-Pfs25 antibody and serum bactericidal activity due to anti-Vi antibody. Pfs25 conjugation to Vi modified the IgG isotype distribution of antisera, inducing a Th2 polarized immune response against Vi antigen. This conjugate may be further developed as a bivalent vaccine to concurrently target malaria and typhoid fever.

Gold nanoparticles - against parasites and insect vectors

Nanomaterials are currently considered for many biological, biomedical and environmental purposes, due to their outstanding physical and chemical properties. The synthesis of gold nanoparticles (Au NPs) is of high interest for research in parasitology and entomology, since these nanomaterials showed promising applications, ranging from detection techniques to drug development, against a rather wide range of parasites of public health relevance, as well as on insect vectors. Here, I reviewed current knowledge about the bioactivity of Au NPs on selected insect species of public health relevance, including major mosquito vectors, such as Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus. The toxicity of Au NPs against helminths was reviewed, covering Schistosoma mansoni trematodes as well as Raillietina cestodes. Furthermore, I summarized the information available on the antiparasitic role of Au NPs in the fight against malaria, leishmaniosis, toxoplasmosis, trypanosomiasis, cryptosporidiosis, and microsporidian parasites affecting human and animals health. Besides, I examined the employ of Au NPs as biomarkers, tools for diagnostics and adjuvants for the induction of transmission blocking immunity in malaria vaccine research. In the final section, major challenges and future outlooks for further research are discussed, with special reference to the pressing need of further knowledge about the effect of Au NPs on other arthropod vectors, such as ticks, tsetse flies, tabanids, sandflies and blackflies, and related ecotoxicology assays.

Immunization with Transgenic Rodent Malaria Parasites Expressing Pfs25 Induces Potent Transmission-Blocking Activity

An anti-malarial transmission blocking vaccine (TBV) would be an important tool for disease control or elimination, though current candidates have failed to induce high efficacy in clinical studies. The ookinete surface protein P25 is a primary target for TBV development, but heterologous expression of P25 with appropriate conformation is problematic and a pre-requisite for achieving functional titers. A potential alternative to recombinant/sub-unit vaccine is immunization with a non-pathogenic, whole-parasite vaccine. This study examines the ability of a purified transgenic rodent-malaria parasite (PbPfs25DR3), expressing Plasmodium falciparum P25 in native conformation on the P. berghei ookinete surface, to act as a TBV. Vaccination with purified PbPfs25DR3 ookinetes produces a potent anti-Pfs25 response and high transmission-blocking efficacy in the laboratory, findings that are then translated to experimentation on natural field isolates of P. falciparum from infected individuals in Burkina Faso. Efficacy is demonstrated in the lab and the field (up to 93.3%/97.1% reductions in transmission intensity respectively), with both a homologous strategy with one and two boosts, and as part of a prime-boost regime, providing support for the future development of a whole-parasite TBV.

Protein-protein conjugate nanoparticles for malaria antigen delivery and enhanced immunogenicity

Chemical conjugation of polysaccharide to carrier proteins has been a successful strategy to generate potent vaccines against bacterial pathogens. We developed a similar approach for poorly immunogenic malaria protein antigens. Our lead candidates in clinical trials are the malaria transmission blocking vaccine antigens, Pfs25 and Pfs230D1, individually conjugated to the carrier protein Exoprotein A (EPA) through thioether chemistry. These conjugates form nanoparticles that show enhanced immunogenicity compared to unconjugated antigens. In this study, we examined the broad applicability of this technology as a vaccine development platform, by comparing the immunogenicity of conjugates prepared by four different chemistries using different malaria antigens (PfCSP, Pfs25 and Pfs230D1), and carriers such as EPA, TT and CRM197. Several conjugates were synthesized using thioether, amide, ADH and glutaraldehyde chemistries, characterized for average molecular weight and molecular weight distribution, and evaluated in mice for humoral immunogenicity. Conjugates made with the different chemistries, or with different carriers, showed no significant difference in immunogenicity towards the conjugated antigens. Since particle size can influence immunogenicity, we tested conjugates with different average size in the range of 16–73 nm diameter, and observed greater immunogenicity of smaller particles, with significant differences between 16 and 73 nm particles. These results demonstrate the multiple options with respect to carriers and chemistries that are available for protein-protein conjugate vaccine development.

A growing world of small things: a brief review on the nanostructured vaccines

Vaccines are the most cost-effective intervention in the management of infectious disease. Much of what we perceive as quality of life is related to a good health status and disease absence, for which vaccines are substantially responsible. Nonetheless, there are many infectious diseases for which no vaccine solution is available. That could be due to limitations of the classic approaches to vaccine development, including inactivated, subunit and attenuated vaccines. Nanostructured immunogens belong to a class of nonclassic vaccines in which nanostructures are loaded with antigen-related molecules. Here, we briefly review important features of the nanostructured vaccines – mainly those based in carbon nanotubes and gold nanorods – and discuss their use to prevent infectious diseases, especially those caused by viruses.

Loading dendritic cells with gold nanoparticles (GNPs) bearing HIV-peptides and mannosides enhance HIV-specific T cell responses

Gold nanoparticles (GNPs) decorated with glycans ameliorate dendritic cells (DC) uptake, antigen-presentation and T-cells cross-talk, which are important aspects in vaccine design. GNPs allow for high antigen loading, DC targeting, lack of toxicity and are straightforward prepared and easy to handle. The present study aimed to assess the capacity of DC to process and present HIV-1-peptides loaded onto GNPs bearing high-mannoside-type oligosaccharides (P1@HM) to autologous T-cells from HIV-1 patients. The results showed that P1@HM increased HIV-specific CD4⁺ and CD8⁺ T-cell proliferation and induced highly functional cytokine secretion compared with HIV-peptides alone. P1@HM elicits a highly efficient secretion of pro-T_H1 cytokines and chemokines, a moderate production of pro-T_H2 and significant higher secretion of pro-inflammatory cytokines such as TNF-α and IL-1β. Thus, co-delivery of HIV-1 antigens and HM by GNPs is an excellent vaccine delivery system inducing HIV-specific cellular immune responses in HIV+ patients, being a promising approach to improve anti-HIV-1 vaccines.

Impact of the Charge Ratio on the In Vivo Immunogenicity of Lipoplexes

PURPOSE

The present study investigated the immunogenic potential of different cationic liposome formulations with a DNA plasmid encoding Pfs25, a malaria transmission-blocking vaccine candidate.

METHODS

Pfs25 plasmid DNA was complexed with cationic liposomes to produce lipoplexes at different charge ratios of the cationic lipid head group to the nucleotide phosphate (N:P). The formation of lipoplexes was visualized by Cryogenic-TEM. Confocal microscopy of lipoplexes formed with GFP encoding plasmid DNA, and flow cytometry was used to determine their in vitro transfection capability. Two different lipoplex formulations using plasmid DNA encoding Pfs25 were evaluated for in vivo immunogenicity after intramuscular administration in Balb/c mice. Immune sera were analyzed by ELISA.

RESULTS

The results demonstrated that the cationic liposome-mediated DNA immunization with an N:P charge ratio of 1:3 (anionic lipoplexes) is more effective than the use of naked plasmid DNA alone. No antibody response was observed when lipoplexes with a higher N:P charge ratio of 10:3 (cationic lipoplexes) were used. Trehalose was added to some lipoplex formulations as a cryoprotectant and adjuvant, but it did not yield any further improvement of immunogenicity in vivo.

CONCLUSIONS

The results suggest that Pfs25 plasmid DNA delivered as lipoplexes at a charge ratio of 1:3 elicited strong immunogenicity in mice and may be improved further to match the immune responses of DNA vaccines administered by in vivo electroporation.

Applications of Gold Nanoparticles in Nanomedicine: Recent Advances in Vaccines

Nowadays, gold is used in (nano-)medicine, usually in the form of nanoparticles, due to the solid proofs given of its therapeutic effects on several diseases. Gold also plays an important role in the vaccine field as an adjuvant and a carrier, reducing toxicity, enhancing immunogenic activity, and providing stability in storage. An even brighter golden future is expected for gold applications in this area.