Messenger RNA expressing PfCSP induces functional, protective immune responses against malaria in mice

mRNA vaccines for infectious diseases - advances, challenges and opportunities

The concept of mRNA-based vaccines emerged more than three decades ago. Groundbreaking discoveries and technological advancements over the past 20 years have resolved the major roadblocks that initially delayed application of this new vaccine modality. The rapid development of nucleoside-modified COVID-19 mRNA vaccines demonstrated that this immunization platform is easy to develop, has an acceptable safety profile and can be produced at a large scale. The flexibility and ease of antigen design have enabled mRNA vaccines to enter development for a wide range of viruses as well as for various bacteria and parasites. However, gaps in our knowledge limit the development of next-generation mRNA vaccines with increased potency and safety. A deeper understanding of the mechanisms of action of mRNA vaccines, application of novel technologies enabling rational antigen design, and innovative vaccine delivery strategies and vaccination regimens will likely yield potent novel vaccines against a wide range of pathogens.

Advances in Engineering Circular RNA Vaccines

Engineered circular RNAs (circRNAs) are a class of single-stranded RNAs with head-to-tail covalently linked structures that integrate open reading frames (ORFs) and internal ribosome entry sites (IRESs) with the function of coding and expressing proteins. Compared to mRNA vaccines, circRNA vaccines offer a more improved method that is safe, stable, and simple to manufacture. With the rapid revelation of the biological functions of circRNA and the success of Severe Acute Respiratory Coronavirus Type II (SARS-CoV-2) mRNA vaccines, biopharmaceutical companies and researchers around the globe are attempting to develop more stable circRNA vaccines for illness prevention and treatment. Nevertheless, research on circRNA vaccines is still in its infancy, and more work and assessment are needed for their synthesis, delivery, and use. In this review, based on the current understanding of the molecular biological properties and immunotherapeutic mechanisms of circRNA, we summarize the current preparation methods of circRNA vaccines, including design, synthesis, purification, and identification. We discuss their delivery strategies and summarize the challenges facing the clinical application of circRNAs to provide references for circRNA vaccine-related research.

Immature dendritic cell-targeting mRNA vaccine expressing PfCSP enhances protective immune responses against Plasmodium liver infection

Resurgence in malaria has been noted in 2022 with 249 million clinical cases resulting in 608,000 deaths, mostly in children under five. Two vaccines, RTS, S, and more recently R21, targeting the circumsporozoite protein (CSP) are recommended by the WHO but are not yet widely available. Strong humoral responses to neutralize sporozoites before they can infect the hepatocytes are important for vaccine-mediated protection. Suboptimal protection conferred by these first-generation vaccines highlight the need for approaches to improve vaccine-induced immune responses. With the recent success of mRNA-LNP vaccines against COVID-19, there is growing interest in leveraging this approach to enhance malaria vaccines. Here, we present the development of a novel chemokine fusion mRNA vaccine aimed at boosting immune responses to PfCSP by targeting the immunogen to immature dendritic cells (iDC). Vaccination of mice with mRNA encoding full-length CSP fused to macrophage inflammatory protein 3 alpha (MIP3α) encapsulated within lipid nanoparticles (LNP) elicited robust CD4+ T cell responses and enhanced antibody titers against NANP repeat epitopes compared to a conventional CSP mRNA-LNP vaccine. Importantly, the CSP-MIP3α fusion vaccine provided significantly greater protection against liver infection upon challenge with P. berghei PfCSP transgenic sporozoites. This enhanced protection was associated with multifunctional CD4+ T cells levels and anti-NANP repeat titers. This study highlights the potential to augment immune responses to PfCSP through iDC targeting and bolster protection against malaria liver infection.

Vaccines and monoclonal antibodies: new tools for malaria control

SUMMARYMalaria remains one of the biggest health problems in the world. While significant reductions in malaria morbidity and mortality had been achieved from 2000 to 2015, the favorable trend has stalled, rather significant increases in malaria cases are seen in multiple areas. In 2022, there were 249 million estimated cases, and 608,000 malaria-related deaths, mostly in infants and children aged under 5 years, globally. Therefore, in addition to the expansion of existing anti-malarial control measures, it is critical to develop new tools, such as vaccines and monoclonal antibodies (mAbs), to fight malaria. In the last 2 years, the first and second malaria vaccines, both targeting Plasmodium falciparum circumsporozoite proteins (PfCSP), have been recommended by the World Health Organization to prevent P. falciparum malaria in children living in moderate to high transmission areas. While the approval of the two malaria vaccines is a considerable milestone in vaccine development, they have much room for improvement in efficacy and durability. In addition to the two approved vaccines, recent clinical trials with mAbs against PfCSP, blood-stage vaccines against P. falciparum or P. vivax, and transmission-blocking vaccine or mAb against P. falciparum have shown promising results. This review summarizes the development of the anti-PfCSP vaccines and mAbs, and recent topics in the blood- and transmission-blocking-stage vaccine candidates and mAbs. We further discuss issues of the current vaccines and the directions for the development of next-generation vaccines.

Efficient in vitro and in vivo transfection of self-amplifying mRNA with linear poly(propylenimine) and poly(ethylenimine-propylenimine) random copolymers as non-viral carriers

Messenger RNA (mRNA) based vaccines have been introduced worldwide to combat the Covid-19 pandemic. These vaccines consist of non-amplifying mRNA formulated in lipid nanoparticles (LNPs). Consequently, LNPs are considered benchmark non-viral carriers for nucleic acid delivery. However, the formulation and manufacturing of these mRNA-LNP nanoparticles are expensive and time-consuming. Therefore, we used self-amplifying mRNA (saRNA) and synthesized novel polymers as alternative non-viral carrier platform to LNPs, which enable a simple, rapid, one-pot formulation of saRNA-polyplexes. Our novel polymer-based carrier platform consists of randomly concatenated ethylenimine and propylenimine comonomers, resulting in linear, poly(ethylenimine-ran-propylenimine) (L-PEIx-ran-PPIy) copolymers with controllable degrees of polymerization. Here we demonstrate in multiple cell lines, that our saRNA-polyplexes show comparable to higher in vitro saRNA transfection efficiencies and higher cell viabilities compared to formulations with Lipofectamine MessengerMAX™ (LFMM), a commercial, lipid-based carrier considered to be the in vitro gold standard carrier. This is especially true for our in vitro best performing saRNA-polyplexes with N/P 5, which are characterised with a size below 100 nm, a positive zeta potential, a near 100% encapsulation efficiency, a high retention capacity and the ability to protect the saRNA from degradation mediated by RNase A. Furthermore, an ex vivo hemolysis assay with pig red blood cells demonstrated that the saRNA-polyplexes exhibit negligible hemolytic activity. Finally, a bioluminescence-based in vivo study was performed over a 35-day period, and showed that the polymers result in a higher and prolonged bioluminescent signal compared to naked saRNA and L-PEI based polyplexes. Moreover, the polymers show different expression profiles compared to those of LNPs, with one of our new polymers (L-PPI250) demonstrating a higher sustained expression for at least 35 days after injection.

Transitional Insight into the RNA-Based Oligonucleotides in Cancer Treatment

Conventional cancer therapies with chemodrugs suffer from various disadvantages, such as irreversible side effects on the skin, heart, liver, and nerves with even fatal consequences. RNA-based therapeutic is a novel technology which offers great potential as non-toxic, non-infectious, and well-tolerable platform. Herein, we introduce different RNA-based platforms with a special focus on siRNA, miRNA, and mRNA applications in cancer treatment in order to better understand the details of their therapeutic effects. Of note, the co-delivery of RNAs with other distinct RNA or drugs has provided safe, efficient, and novel treatment modalities for cancer treatment.

Transmission-Blocking Vaccines against Schistosomiasis Japonica

Control of schistosomiasis japonica, endemic in Asia, including the Philippines, China, and Indonesia, is extremely challenging. Schistosoma japonicum is a highly pathogenic helminth parasite, with disease arising predominantly from an immune reaction to entrapped parasite eggs in tissues. Females of this species can generate 1000-2200 eggs per day, which is about 3- to 15-fold greater than the egg output of other schistosome species. Bovines (water buffalo and cattle) are the predominant definitive hosts and are estimated to generate up to 90% of parasite eggs released into the environment in rural endemic areas where these hosts and humans are present. Here, we highlight the necessity of developing veterinary transmission-blocking vaccines for bovines to better control the disease and review potential vaccine candidates. We also point out that the approach to producing efficacious transmission-blocking animal-based vaccines before moving on to human vaccines is crucial. This will result in effective and feasible public health outcomes in agreement with the One Health concept to achieve optimum health for people, animals, and the environment. Indeed, incorporating a veterinary-based transmission vaccine, coupled with interventions such as human mass drug administration, improved sanitation and hygiene, health education, and snail control, would be invaluable to eliminating zoonotic schistosomiasis.

Navigating the challenges of lipid nanoparticle formulation: the role of unpegylated lipid surfactants in enhancing drug loading and stability

Lipid nanoparticles have proved an attractive approach for drug delivery; however, the challenges of optimising formulation stability and increasing drug loading have limited progression. In this work, we investigate the role of unpegylated lipid surfactants (helper lipids) in nanoparticle formation and the effect of blending helper lipids with pegylated lipid surfactants on the formation and stability of lipid-based nanoparticles by nanoprecipitation. Furthermore, blends of unpegylated/pegylated lipid surfactants were examined for ability to accommodate higher drug loading formulations by means of a higher weight percentage (wt%) of drug relative to total mass of formulation components (i.e. drug, surfactants and lipids). Characterisation included evaluation of particle diameter, size distribution, drug loading and nanoformulation stability. Our findings demonstrate that the addition of unpegylated lipid surfactant (Lipoid S100) to pegylated lipid surfactant (Brij S20) enhances stability, particularly at higher weight percentages of the core material. This blending approach enables drug loading capacities exceeding 10% in the lipid nanoparticles. Notably, Lipoid S100 exhibited nucleating properties that aided in the formation and stabilisation of the nanoparticles. Furthermore, we examined the incorporation of a model drug into the lipid nanoparticle formulations. Blending the model drug with the core material disrupted the crystallinity of the core, offering additional potential benefits in terms of drug release and stability. This comprehensive investigation provides valuable insights into the interplay between surfactant properties, core material composition, and nanoparticle behaviour. The study enhances our understanding of lipid materials and offers guidance for the design and optimisation of lipid nanoparticle formulations.

Accelerated prime-and-trap vaccine regimen in mice using repRNA-based CSP malaria vaccine

Malaria, caused by Plasmodium parasites, remains one of the most devastating infectious diseases worldwide, despite control efforts to lower morbidity and mortality. Both advanced candidate vaccines, RTS,S and R21, are subunit (SU) vaccines that target a single Plasmodium falciparum (Pf) pre-erythrocytic (PE) sporozoite (spz) surface protein known as circumsporozoite (CS). These vaccines induce humoral immunity but fail to elicit CD8 + T-cell responses sufficient for long-term protection. In contrast, whole-organism (WO) vaccines, such as Radiation Attenuated Sporozoites (RAS), achieved sterile protection but require a series of intravenous doses administered in multiple clinic visits. Moreover, these WO vaccines must be produced in mosquitos, a burdensome process that severely limits their availability. To reduce reliance on WO while maintaining protection via both antibodies and Trm responses, we have developed an accelerated vaccination regimen that combines two distinct agents in a prime-and-trap strategy. The priming dose is a single dose of self-replicating RNA encoding the full-length P. yoelii CS protein, delivered via an advanced cationic nanocarrier (LIONTM). The trapping dose consists of one dose of WO RAS. Our vaccine induces a strong immune response when administered in an accelerated regimen, i.e., either 5-day or same-day immunization. Additionally, mice after same-day immunization showed a 2-day delay of blood patency with 90% sterile protection against a 3-week spz challenge. The same-day regimen also induced durable 70% sterile protection against a 2-month spz challenge. Our approach presents a clear path to late-stage preclinical and clinical testing of dose-sparing, same-day regimens that can confer sterilizing protection against malaria.

mRNA vaccines expressing malaria transmission-blocking antigens Pfs25 and Pfs230D1 induce a functional immune response

Malaria transmission-blocking vaccines (TBV) are designed to inhibit the sexual stage development of the parasite in the mosquito host and can play a significant role in achieving the goal of malaria elimination. Preclinical and clinical studies using protein-protein conjugates of leading TBV antigens Pfs25 and Pfs230 domain 1 (Pfs230D1) have demonstrated the feasibility of TBV. Nevertheless, other promising vaccine platforms for TBV remain underexplored. The recent success of mRNA vaccines revealed the potential of this technology for infectious diseases. We explored the mRNA platform for TBV development. mRNA constructs of Pfs25 and Pfs230D1 variously incorporating signal peptides (SP), GPI anchor, and Trans Membrane (TM) domain were assessed in vitro for antigen expression, and selected constructs were evaluated in mice. Only mRNA constructs with GPI anchor or TM domain that resulted in high cell surface expression of the antigens yielded strong immune responses in mice. These mRNA constructs generated higher transmission-reducing functional activity versus the corresponding alum-adjuvanted protein-protein conjugates used as comparators. Pfs25 mRNA with GPI anchor or TM maintained >99% transmission reducing activity through 126 days, the duration of the study, demonstrating the potential of mRNA platform for TBV.

A Pvs25 mRNA vaccine induces complete and durable transmission-blocking immunity to Plasmodium vivax

Plasmodium vivax (P. vivax) is the major malaria parasite outside of Africa and no vaccine is available against it. A vaccine that interrupts parasite transmission (transmission-blocking vaccine, TBV) is considered highly desirable to reduce the spread of P. vivax and to accelerate its elimination. However, the development of a TBV against this pathogen has been hampered by the inability to culture the parasite as well as the low immunogenicity of the vaccines developed to date. Pvs25 is the most advanced TBV antigen candidate for P. vivax. However, in previous phase I clinical trials, TBV vaccines based on Pvs25 yielded low antibody responses or had unacceptable safety profiles. As the nucleoside-modified mRNA-lipid nanoparticle (mRNA-LNP) vaccine platform proved to be safe and effective in humans, we generated and tested mRNA-LNP vaccines encoding several versions of Pvs25 in mice. We found that in a prime-boost vaccination schedule, all Pvs25 mRNA-LNP vaccines elicited robust antigen-specific antibody responses. Furthermore, when compared with a Pvs25 recombinant protein vaccine formulated with Montanide ISA-51 adjuvant, the full-length Pvs25 mRNA-LNP vaccine induced a stronger and longer-lasting functional immunity. Seven months after the second vaccination, vaccine-induced antibodies retained the ability to fully block P. vivax transmission in direct membrane feeding assays, whereas the blocking activity induced by the protein/ISA-51 vaccine dropped significantly. Taken together, we report on mRNA vaccines targeting P. vivax and demonstrate that Pvs25 mRNA-LNP outperformed an adjuvanted Pvs25 protein vaccine suggesting that it is a promising candidate for further testing in non-human primates.

Vaccines against tick-borne diseases: a big step forward?

Ticks and tick-borne diseases are on the rise due to socioecosystemic changes and climate modification and are affecting human and animal health. Few vaccines are available. Two recent articles from Matias et al. and Pine et al. used mRNA technology to explore tick and pathogen proteins as vaccine candidates.

Emulsion and liposome-based adjuvanted R21 vaccine formulations mediate protection against malaria through distinct immune mechanisms

Adjuvanted protein vaccines offer high efficacy, yet most potent adjuvants remain proprietary. Several adjuvant compounds are being developed by the Vaccine Formulation Institute in Switzerland for global open access clinical use. In the context of the R21 malaria vaccine, in a mouse challenge model, we characterize the efficacy and mechanism of action of four Vaccine Formulation Institute adjuvants: two liposomal (LQ and LMQ) and two squalene emulsion-based adjuvants (SQ and SMQ), containing QS-21 saponin (Q) and optionally a synthetic TLR4 agonist (M). Two R21 vaccine formulations, R21/LMQ and R21/SQ, offer the highest protection (81%-100%), yet they trigger different innate sensing mechanisms in macrophages with LMQ, but not SQ, activating the NLRP3 inflammasome. The resulting in vivo adaptive responses have a different TH1/TH2 balance and engage divergent innate pathways while retaining high protective efficacy. We describe how modular changes in vaccine formulation allow for the dissection of the underlying immune pathways, enabling future mechanistically informed vaccine design.

RNA vaccines in infectious diseases: A systematic review

Infectious diseases are a major health concern worldwide, especially as they are one of the main causes of mortality in underdeveloped and developing countries. Those that are considered emerging and re-emerging are characterized by unpredictability, high morbidity and mortality, exponential spread, and substantial social impact. These characteristics highlight the need to create an "on demand" control method, with rapid development, large-scale production, and wide distribution. In view of this, RNA vaccines have been investigated as an effective alternative for the treatment and prevention of infectious diseases since they can meet those needs and are considered safe, affordable, and totally synthetic. Therefore, this systematic review aimed to evaluate the use of RNA vaccines for infectious diseases from experimental, in vivo, and in vitro studies. PubMed, Web of Science, and Embase were searched for suitable studies. Additionally, further investigations, such as grey literature checks, were performed. A total of 723 articles were found, of which only 41 met the inclusion criteria. These studies demonstrated the potential of using RNA vaccines to control 19 different infectious diseases, of which COVID-19 was the most studied. Similarly, viruses comprised the largest number of reported vaccine targets, followed by protozoa and bacteria. The mRNA vaccines were the most widely used, and the intramuscular route of administration was the most reported. Regarding preclinical experimental models, mice were the most used to evaluate the impact and safety of the RNA vaccines developed. Thus, although further studies and evaluation of the subject are necessary, it is evident that RNA vaccines can be considered a promising alternative in the treatment and prophylaxis of infectious diseases.

Pseudovirus Nanoparticles Displaying Plasmodium Circumsporozoite Proteins Elicited High Titers of Sporozoite-Binding Antibody

BACKGROUND

malaria caused by Plasmodium parasites remains a public health threat. The circumsporozoite proteins (CSPs) of Plasmodium sporozoite play a key role in Plasmodium infection, serving as an excellent vaccine target.

METHODS

using a self-assembled S60 nanoparticle platform, we generated pseudovirus nanoparticles (PVNPs) displaying CSPs, named S-CSPs, for enhanced immunogenicity.

RESULTS

purified Hisx6-tagged or tag-free S-CSPs self-assembled into PVNPs that consist of a norovirus S60 inner shell and multiple surface-displayed CSPs. The majority of the PVNPs measured ~27 nm with some size variations, and their three-dimensional structure was modeled. The PVNP-displayed CSPs retained their glycan receptor-binding function. A mouse immunization study showed that PVNPs induced a high antibody response against CSP antigens and the PVNP-immunized mouse sera stained the CSPs of Plasmodium sporozoites at high titer.

CONCLUSIONS AND DISCUSSION

the PVNP-displayed CSPs retain their authentic antigenic feature and receptor-binding function. The CSP-specific antibody elicited by the S-CSP PVNPs binds original CSPs and potentially inhibits the attachment of Plasmodium sporozoites to their host cells, a key step for liver invasion by the sporozoites. Thus, S-CSP PVNPs may be an excellent vaccine candidate against malaria caused by Plasmodium parasites.

The advances of adjuvants in mRNA vaccines

The remarkable success of messenger RNA (mRNA) vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has propelled the rapid development of this vaccination technology in recent years. Over the last three decades, numerous studies have shown the considerable potential of mRNA vaccines that elicit protective immune responses against pathogens or cancers in preclinical studies or clinical trials. These effective mRNA vaccines usually contain specific adjuvants to obtain the desired immune effect. Vaccine adjuvants traditionally are immunopotentiators that bind to pattern recognition receptors (PRRs) of innate immune cells to increase the magnitude or achieve qualitative alteration of immune responses, finally enhancing the efficacy of vaccines. Generally, adjuvants are necessary parts of competent vaccines. According to the existing literature, adjuvants in mRNA vaccines can be broadly classified into three categories: 1) RNA with self-adjuvant characteristics, 2) components of the delivery system, and 3) exogenous immunostimulants. This review summarizes the three types of adjuvants used in mRNA vaccines and provides a comprehensive understanding of molecular mechanisms by which adjuvants exert their functions in mRNA vaccines.

An Ionizable Lipid Material with a Vitamin E Scaffold as an mRNA Vaccine Platform for Efficient Cytotoxic T Cell Responses

RNA vaccines based on lipid nanoparticles (LNPs) with in vitro transcribed mRNA (IVT-mRNA) encapsulated are now a currently successful but still evolving modality of vaccines. One of the advantages of RNA vaccines is their ability to induce CD8+ T-cell-mediated cellular immunity that is indispensable for excluding pathogen-infected cells or cancer cells from the body. In this study, we report on the development of LNPs with an enhanced capability for inducing cellular immunity by using an ionizable lipid with a vitamin E scaffold. An RNA vaccine that contained this ionizable lipid and an IVT-mRNA encoding a model antigen ovalbumin (OVA) induced OVA-specific cytotoxic T cell responses and showed an antitumor effect against an E.G7-OVA tumor model. Vaccination with the LNPs conferred protection against lethal infection by Toxoplasma gondii using its antigen TgPF. The vitamin E scaffold-dependent type I interferon response was important for effector CD8+ T cell differentiation induced by the mRNA-LNPs. Our findings also revealed that conventional dendritic cells (cDCs) were essential for achieving CD8+ T cell responses induced by the mRNA-LNPs, while the XCR1-positive subset of cDCs, cDC1 specialized for antigen cross-presentation, was not required. Consistently, the mRNA-LNPs were found to selectively transfect another subset of cDCs, cDC2 that had migrated from the skin to lymph nodes, where they could make vaccine-antigen-dependent contacts with CD8+ T cells. The findings indicate that the activation of innate immune signaling by the adjuvant activity of the vitamin E scaffold and the expression of antigens in cDC2 are important for subsequent antigen presentation and the establishment of antigen-specific immune responses.

Development of an mRNA-lipid nanoparticle vaccine against Lyme disease

Lyme disease is the most common vector-borne infectious disease in the United States, in part because a vaccine against it is not currently available for humans. We propose utilizing the lipid nanoparticle-encapsulated nucleoside-modified mRNA (mRNA-LNP) platform to generate a Lyme disease vaccine like the successful clinical vaccines against SARS-CoV-2. Of the antigens expressed by Borrelia burgdorferi, the causative agent of Lyme disease, outer surface protein A (OspA) is the most promising candidate for vaccine development. We have designed and synthesized an OspA-encoding mRNA-LNP vaccine and compared its immunogenicity and protective efficacy to an alum-adjuvanted OspA protein subunit vaccine. OspA mRNA-LNP induced superior humoral and cell-mediated immune responses in mice after a single immunization. These potent immune responses resulted in protection against bacterial infection. Our study demonstrates that highly efficient mRNA vaccines can be developed against bacterial targets.

Malaria Vaccines: From the Past towards the mRNA Vaccine Era

Plasmodium spp. is the etiological agent of malaria, a life-threatening parasitic disease transmitted by infected mosquitoes. Malaria remains a major global health challenge, particularly in endemic regions. Over the years, various vaccine candidates targeting different stages of Plasmodium parasite life-cycle have been explored, including subunit vaccines, vectored vaccines, and whole organism vaccines with Mosquirix, a vaccine based on a recombinant protein, as the only currently approved vaccine for Plasmodium falciparum malaria. Despite the aforementioned notable progress, challenges such as antigenic diversity, limited efficacy, resistant parasites escaping protective immunity and the need for multiple doses have hindered the development of a highly efficacious malaria vaccine. The recent success of mRNA-based vaccines against SARS-CoV-2 has sparked renewed interest in mRNA vaccine platforms. The unique mRNA vaccine features, including their potential for rapid development, scalability, and flexibility in antigen design, make them a promising avenue for malaria vaccine development. This review provides an overview of the malaria vaccines' evolution from the past towards the mRNA vaccine era and highlights their advantages in overcoming the limitations of previous malaria vaccine candidates.

mRNA vaccine against malaria tailored for liver-resident memory T cells

Malaria is caused by Plasmodium species transmitted by Anopheles mosquitoes. Following a mosquito bite, Plasmodium sporozoites migrate from skin to liver, where extensive replication occurs, emerging later as merozoites that can infect red blood cells and cause symptoms of disease. As liver tissue-resident memory T cells (Trm cells) have recently been shown to control liver-stage infections, we embarked on a messenger RNA (mRNA)-based vaccine strategy to induce liver Trm cells to prevent malaria. Although a standard mRNA vaccine was unable to generate liver Trm or protect against challenge with Plasmodium berghei sporozoites in mice, addition of an agonist that recruits T cell help from type I natural killer T cells under mRNA-vaccination conditions resulted in significant generation of liver Trm cells and effective protection. Moreover, whereas previous exposure of mice to blood-stage infection impaired traditional vaccines based on attenuated sporozoites, mRNA vaccination was unaffected, underlining the potential for such a rational mRNA-based strategy in malaria-endemic regions.

Induction of liver-resident memory T cells and protection at liver-stage malaria by mRNA-containing lipid nanoparticles

Recent studies have suggested that CD8+ liver-resident memory T (TRM) cells are crucial in the protection against liver-stage malaria. We used liver-directed mRNA-containing lipid nanoparticles (mRNA-LNPs) to induce liver TRM cells in a murine model. Single-dose intravenous injections of ovalbumin mRNA-LNPs effectively induced antigen-specific cytotoxic T lymphocytes in a dose-dependent manner in the liver on day 7. TRM cells (CD8+ CD44hi CD62Llo CD69+ KLRG1-) were induced 5 weeks after immunization. To examine the protective efficacy, mice were intramuscularly immunized with two doses of circumsporozoite protein mRNA-LNPs at 3-week intervals and challenged with sporozoites of Plasmodium berghei ANKA. Sterile immunity was observed in some of the mice, and the other mice showed a delay in blood-stage development when compared with the control mice. mRNA-LNPs therefore induce memory CD8+ T cells that can protect against sporozoites during liver-stage malaria and may provide a basis for vaccines against the disease.

Heterologous mRNA-protein vaccination with Tc24 induces a robust cellular immune response against Trypanosoma cruzi, characterized by an increased level of polyfunctional CD8+ T-cells

Tc24 is a Trypanosoma cruzi-derived flagellar protein that, when formulated with a TLR-4 agonist adjuvant, induces a balanced immune response in mice, elevating IgG2a antibody titers and IFN-γ levels. Furthermore, vaccination with the recombinant Tc24 protein can reduce parasite levels and improve survival during acute infection. Although some mRNA vaccines have been proven to elicit a stronger immune response than some protein vaccines, they have not been used against T. cruzi. This work evaluates the immunogenicity of a heterologous prime/boost vaccination regimen using protein and mRNA-based Tc24 vaccines. Mice (C57BL/6) were vaccinated twice subcutaneously, three weeks apart, with either the Tc24-C4 protein + glucopyranosyl A (GLA)-squalene emulsion, Tc24 mRNA Lipid Nanoparticles, or with heterologous protein/mRNA or mRNA/protein combinations, respectively. Two weeks after the last vaccination, mice were euthanized, spleens were collected to measure antigen-specific T-cell responses, and sera were collected to evaluate IgG titers and isotypes. Heterologous presentation of the Tc24 antigen generated antigen-specific polyfunctional CD8+ T cells, a balanced Th1/Th2/Th17 cytokine profile, and a balanced humoral response with increased serum IgG, IgG1 and IgG2c antibody responses. We conclude that heterologous vaccination using Tc24 mRNA to prime and Tc24-C4 protein to boost induces a broad and robust antigen-specific immune response that was equivalent or superior to two doses of a homologous protein vaccine, the homologous mRNA vaccine and the heterologous Tc24-C4 Protein/mRNA vaccine.

Accelerated prime-and-trap vaccine regimen in mice using repRNA-based CSP malaria vaccine

Malaria, caused by Plasmodium parasites, remains one of the most devastating infectious diseases worldwide, despite control efforts that have lowered morbidity and mortality. The only P. falciparum vaccine candidates to show field efficacy are those targeting the asymptomatic pre-erythrocytic (PE) stages of infection. The subunit (SU) RTS,S/AS01 vaccine, the only licensed malaria vaccine to date, is only modestly effective against clinical malaria. Both RTS,S/AS01 and the SU R21 vaccine candidate target the PE sporozoite (spz) circumsporozoite (CS) protein. These candidates elicit high-titer antibodies that provide short-term protection from disease, but do not induce the liver-resident memory CD8+ T cells (Trm) that confer strong PE immunity and long-term protection. In contrast, whole-organism (WO) vaccines, employing for example radiation-attenuated spz (RAS), elicit both high antibody titers and Trm, and have achieved high levels of sterilizing protection. However, they require multiple intravenous (IV) doses, which must be administered at intervals of several weeks, complicating mass administration in the field. Moreover, the quantities of spz required present production difficulties. To reduce reliance on WO while maintaining protection via both antibodies and Trm responses, we have developed an accelerated vaccination regimen that combines two distinct agents in a prime-and-trap strategy. While the priming dose is a self-replicating RNA encoding P. yoelii CS protein, delivered via an advanced cationic nanocarrier (LION™), the trapping dose consists of WO RAS. This accelerated regime confers sterile protection in the P. yoelii mouse model of malaria. Our approach presents a clear path to late-stage preclinical and clinical testing of dose-sparing, same-day regimens that can confer sterilizing protection against malaria.

Updates on Malaria Epidemiology and Prevention Strategies

Purpose of Review

The objective of this review was to provide an update on recent malaria epidemiology, both globally and in non-endemic areas, to identify the current distribution and repercussions of genetically diverse Plasmodium species and summarize recently implemented intervention and prevention tools.

Recent Findings

Notable changes in malaria epidemiology have occurred in recent years, with an increase in the number of total cases and deaths globally during 2020-2021, in part attributed to the COVID-19 pandemic. The emergence of artemisinin-resistant species in new areas and the expanding distribution of parasites harbouring deletions of the pfhrp2/3 genes have been concerning. New strategies to curb the burden of this infection, such as vaccination, have been implemented in certain endemic areas and their performance is currently being evaluated.

Summary

Inadequate control of malaria in endemic regions may have an effect on imported malaria and measures to prevent re-establishment of transmission in malaria-free areas are essential. Enhanced surveillance and investigation of Plasmodium spp. genetic variations will contribute to the successful diagnosis and treatment of malaria in future. Novel strategies for an integrated One Health approach to malaria control should also be strengthened.

A mosquito AgTRIO mRNA vaccine contributes to immunity against malaria

Malaria begins when an infected mosquito injects saliva containing Plasmodium sporozoites into the skin of a vertebrate host. To prevent malaria, vaccination is the most effective strategy and there is an urgent need for new strategies to enhance current pathogen-based vaccines. Active or passive immunization against a mosquito saliva protein, AgTRIO, contributes to protection against Plasmodium infection of mice. In this study, we generated an AgTRIO mRNA-lipid nanoparticle (LNP) and assessed its potential usefulness as a vaccine against malaria. Immunization of mice with an AgTRIO mRNA-LNP generated a robust humoral response, including AgTRIO IgG2a isotype antibodies that have been associated with protection. AgTRIO mRNA-LNP immunized mice exposed to Plasmodium berghei-infected mosquitoes had markedly reduced initial Plasmodium hepatic infection levels and increased survival compared to control mice. In addition, as the humoral response to AgTRIO waned over 6 months, additional mosquito bites boosted the AgTRIO IgG titers, including IgG1 and IgG2a isotypes, which offers a unique advantage compared to pathogen-based vaccines. These data will aid in the generation of future malaria vaccines that may include both pathogen and vector antigens.

Accelerated prime-and-trap vaccine regimen in mice using repRNA-based CSP malaria vaccine

Malaria, caused by Plasmodium parasites, remains one of the most devastating infectious diseases worldwide, despite control efforts that have lowered morbidity and mortality. The only P. falciparum vaccine candidates to show field efficacy are those targeting the asymptomatic pre-erythrocytic (PE) stages of infection. The subunit (SU) RTS,S/AS01 vaccine, the only licensed malaria vaccine to date, is only modestly effective against clinical malaria. Both RTS,S/AS01 and the SU R21 vaccine candidate target the PE sporozoite (spz) circumsporozoite (CS) protein. These candidates elicit high-titer antibodies that provide short-term protection from disease, but do not induce the liver-resident memory CD8+ T cells (Trm) that confer strong PE immunity and long-term protection. In contrast, whole-organism (WO) vaccines, employing for example radiation-attenuated spz (RAS), elicit both high antibody titers and Trm, and have achieved high levels of sterilizing protection. However, they require multiple intravenous (IV) doses, which must be administered at intervals of several weeks, complicating mass administration in the field. Moreover, the quantities of spz required present production difficulties. To reduce reliance on WO while maintaining protection via both antibodies and Trm responses, we have developed an accelerated vaccination regimen that combines two distinct agents in a prime-and-trap strategy. While the priming dose is a self-replicating RNA encoding P. yoelii CS protein, delivered via an advanced cationic nanocarrier (LION™), the trapping dose consists of WO RAS. This accelerated regime confers sterile protection in the P. yoelii mouse model of malaria. Our approach presents a clear path to late-stage preclinical and clinical testing of dose-sparing, same-day regimens that can confer sterilizing protection against malaria.

Clinical Delivery of Circular RNA: Lessons Learned from RNA Drug Development

Circular RNAs (circRNA) represent a distinct class of covalently closed-loop RNA molecules, which play diverse roles in regulating biological processes and disease states. The enhanced stability of synthetic circRNAs compared to their linear counterparts has recently garnered considerable research interest, paving the way for new therapeutic applications. While clinical circRNA technology is still in its early stages, significant advancements in mRNA technology offer valuable insights into its potential future applications. Two primary obstacles that must be addressed are the development of efficient production methods and the optimization of delivery systems. To expedite progress in this area, this review aims to provide an overview of the current state of knowledge on circRNA structure and function, outline recent techniques for synthesizing circRNAs, highlight key delivery strategies and applications, and discuss the current challenges and future prospects in the field of circRNA-based therapeutics.

The mRNA Vaccine Technology Era and the Future Control of Parasitic Infections

Despite intensive long-term efforts, with very few exceptions, the development of effective vaccines against parasitic infections has presented considerable challenges, given the complexity of parasite life cycles, the interplay between parasites and their hosts, and their capacity to escape the host immune system and to regulate host immune responses. For many parasitic diseases, conventional vaccine platforms have generally proven ill suited, considering the complex manufacturing processes involved and the costs they incur, the inability to posttranslationally modify cloned target antigens, and the absence of long-lasting protective immunity induced by these antigens. An effective antiparasite vaccine platform is required to assess the effectiveness of novel vaccine candidates at high throughput. By exploiting the approach that has recently been used successfully to produce highly protective COVID mRNA vaccines, we anticipate a new wave of research to advance the use of mRNA vaccines to prevent parasitic infections in the near future. This article considers the characteristics that are required to develop a potent antiparasite vaccine and provides a conceptual foundation to promote the development of parasite mRNA-based vaccines. We review the recent advances and challenges encountered in developing antiparasite vaccines and evaluate the potential of developing mRNA vaccines against parasites, including those causing diseases such as malaria and schistosomiasis, against which vaccines are currently suboptimal or not yet available.

Vaccine development for bacterial pathogens: Advances, challenges and prospects

The advent and use of antimicrobials have played a key role in treating potentially life-threatening infectious diseases, improving health, and saving the lives of millions of people worldwide. However, the emergence of multidrug resistant (MDR) pathogens has been a significant health challenge that has compromised the ability to prevent and treat a wide range of infectious diseases that were once treatable. Vaccines offer potential as a promising alternative to fight against antimicrobial resistance (AMR) infectious diseases. Vaccine technologies include reverse vaccinology, structural biology methods, nucleic acid (DNA and mRNA) vaccines, generalised modules for membrane antigens, bioconjugates/glycoconjugates, nanomaterials and several other emerging technological advances that are offering a potential breakthrough in the development of efficient vaccines against pathogens. This review covers the opportunities and advancements in vaccine discovery and development targeting bacterial pathogens. We reflect on the impact of the already-developed vaccines targeting bacterial pathogens and the potential of those currently under different stages of preclinical and clinical trials. More importantly, we critically and comprehensively analyse the challenges while highlighting the key indices for future vaccine prospects. Finally, the issues and concerns of AMR for low-income countries (sub-Saharan Africa) and the challenges with vaccine integration, discovery and development in this region are critically evaluated.

What We Lost in the Fire: Endemic Tropical Heart Diseases in the Time of COVID-19

The COVID-19 pandemic has profoundly influenced the effort to achieve global health equity. This has been particularly the case for HIV/AIDS, tuberculosis, and malaria control initiatives in low- and middle-income countries, with significant outcome setbacks seen for the first time in decades. Lost in the calls for compensatory funding increases for such programs, however, is the plight of endemic tropical heart diseases, a group of disorders that includes rheumatic heart disease, Chagas disease, and endomyocardial fibrosis. Such endemic illnesses affect millions of people around the globe and remain a source of substantial mortality, morbidity, and health disparity. Unfortunately, these conditions were already neglected before the pandemic, and thus those living with them have disproportionately suffered during the time of COVID-19. In this perspective, we briefly define endemic tropical heart diseases, summarizing their prepandemic epidemiology, funding, and control statuses. We then describe the ways in which people living with these disorders, along with the healthcare providers and researchers working to improve their outcomes, have been harmed by the ongoing COVID-19 pandemic. We conclude by proposing the path forward, including approaches we may use to leverage lessons learned from the pandemic to strengthen care systems for these neglected diseases.

mRNA vaccines: a new opportunity for malaria, tuberculosis and HIV

The success of the first licensed mRNA-based vaccines against COVID-19 has created a widespread interest on mRNA technology for vaccinology. As expected, the number of mRNA vaccines in preclinical and clinical development increased exponentially since 2020, including numerous improvements in mRNA formulation design, delivery methods and manufacturing processes. However, the technology faces challenges such as the cost of raw materials, the lack of standardization, and delivery optimization. MRNA technology may provide a solution to some of the emerging infectious diseases as well as the deadliest hard-to-treat infectious diseases malaria, tuberculosis, and human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), for which an effective vaccine, easily deployable to endemic areas is urgently needed. In this review, we discuss the functional structure, design, manufacturing processes and delivery methods of mRNA vaccines. We provide an up-to-date overview of the preclinical and clinical development of mRNA vaccines against infectious diseases, and discuss the immunogenicity, efficacy and correlates of protection of mRNA vaccines, with particular focus on research and development of mRNA vaccines against malaria, tuberculosis and HIV.

Immunization with a novel mRNA vaccine, TGGT1_216200 mRNA-LNP, prolongs survival time in BALB/c mice against acute toxoplasmosis

Toxoplasma gondii, a specialized intracellular parasite, causes a widespread zoonotic disease and is a severe threat to social and economic development. There is a lack of effective drugs and vaccines against T. gondii infection. Recently, mRNA vaccines have been rapidly developed, and their packaging materials and technologies are well established. In this study, TGGT1_216200 (TG_200), a novel molecule from T. gondii, was identified using bioinformatic screening analysis. TG_200 was purified and encapsulated with a lipid nanoparticle (LNP) to produce the TG_200 mRNA-LNP vaccine. The immune protection provided by the new vaccine and its mechanisms after immunizing BABL/C mice via intramuscular injection were investigated. There was a strong immune response when mice were vaccinated with TG_200 mRNA-LNP. Elevated levels of anti-T. gondii-specific immunoglobulin G (IgG), and a higher IgG2a-to-IgG1 ratio was observed. The levels of interleukin-12 (IL-12), interferon-γ (IFN-γ), IL-4, and IL-10 were also elevated. The result showed that the vaccine induced a mixture of Th1 and Th2 cells, and Th1-dominated humoral immune response. Significantly increased antigen-specific splenocyte proliferation was induced by TG_200 mRNA-LNP immunization. The vaccine could also induce T. gondii-specific cytotoxic T lymphocytes (CTLs). The expression levels of interferon regulatory factor 8 (IRF8), T-Box 21 (T-bet), and nuclear factor kappa B (NF-κB) were significantly elevated after TG_200 mRNA-LNP immunization. The levels of CD83, CD86, MHC-I, MHC-II, CD8, and CD4 molecules were also higher. The results indicated that TG_200 mRNA-LNP produced specific cellular and humoral immune responses. Most importantly, TG_200 mRNA-LNP immunized mice survived significantly longer (19.27 ± 3.438 days) than the control mice, which died within eight days after T. gondii challenge (P< 0.001). The protective effect of adoptive transfer was also assessed, and mice receiving serum and splenocytes from mice immunized with TG_200 mRNA-LNP showed improved survival rates of 9.70 ± 1.64 days and, 13.40 ± 2.32 days, respectively (P< 0.001). The results suggested that TG_200 mRNA-LNP is a safe and promising vaccine against T. gondii infection.

Advances in nanoparticle-based mRNA delivery for liver cancer and liver-associated infectious diseases

The liver is a vital organ that functions to detoxify the body. Liver cancer and infectious diseases such as influenza and malaria can fatally compromise liver function. mRNA delivery is a relatively new means of therapeutic treatment which enables expression of tumor or pathogenic antigens, and elicits immune responses for therapeutic or prophylactic effect. Novel nanoparticles with unique biological properties serving as mRNA carriers have allowed mRNA-based therapeutics to become more clinically viable and relevant. In this review, we highlight recent progress in development of nanoparticle-based mRNA delivery systems for treatment of various liver diseases. First, we present developments in nanoparticle systems used to deliver mRNAs, with specific focus on enhanced cellular uptake and endosomal escape achieved through the use of these nanoparticles. To provide context for diseases that target the liver, we provide an overview of the function and structure of the liver, as well as the role of the immune system in the liver. Then, mRNA-based therapeutic approaches for addressing HCC are highlighted. We also discuss nanoparticle-based mRNA vaccines for treating hepatotropic infectious diseases. Finally, we present current challenges in the clinical translation of nanoparticle-based mRNA delivery systems and provide outlooks for their utilization in treating liver-related diseases.

Exploring in vitro expression and immune potency in mice using mRNA encoding the Plasmodium falciparum malaria antigen, CelTOS

The secreted malarial protein, Cell-Traversal protein for Ookinetes and Sporozoites (CelTOS), is highly conserved among Plasmodium species, and plays a role in the invasion of mosquito midgut cells and hepatocytes in the vertebrate host. CelTOS was identified as a potential protective antigen based on a proteomic analysis, which showed that CelTOS stimulated significant effector T cells producing IFN-γ in peripheral blood mononuclear cells (PBMCs) from radiation attenuated sporozoite-immunized, malaria-naïve human subjects. In a rodent malaria model, recombinant full-length CelTOS protein/adjuvant combinations induced sterile protection, and in several studies, functional antibodies were produced that had hepatocyte invasion inhibition and transmission-blocking activities. Despite some encouraging results, vaccine approaches using CelTOS will require improvement before it can be considered as an effective vaccine candidate. Here, we report on the use of mRNA vaccine technology to induce humoral and cell-mediated immune responses using this antigen. Several pfceltos encoding mRNA transcripts were assessed for the impact on protein translation levels in vitro. Protein coding sequences included those to evaluate the effects of signal sequence, N-glycosylation on translation, and of nucleoside substitutions. Using in vitro transfection experiments as a pre-screen, we assessed the quality of the expressed CelTOS target relative to the homogeneity, cellular localization, and durability of expression levels. Optimized mRNA transcripts, which demonstrated highest protein expression levels in vitro were selected for encapsulation in lipid nanoparticles (LNP) and used to immunize mice to assess for both humoral and cellular cytokine responses. Our findings indicate that mRNA transcripts encoding pfceltos while potent for inducing antigen-specific cellular cytokine responses in mice, were less able to mount PfCelTOS-specific antibody responses using a two-dose regimen. An additional booster dose was needed to overcome low seroconversion rates in mice. With respect to antibody fine specificities, N-glycosylation site mutated immunogens yielded lower immune responses, particularly to the N-terminus of the molecule. While it remains unclear the impact on CelTOS antigen as immunogen, this study highlights the need to optimize antigen design for vaccine development.

Chemical Approaches to Synthetic Drug Delivery Systems for Systemic Applications

Poor water solubility and low bioavailability of active pharmaceutical ingredients (APIs) are major causes of friction in the pharmaceutical industry and represent a formidable hurdle for pharmaceutical drug development. Drug delivery remains the major challenge for the application of new small-molecule drugs as well as biopharmaceuticals. The three challenges for synthetic delivery systems are: (i) controlling drug distribution and clearance in the blood; (ii) solubilizing poorly water-soluble agents, and (iii) selectively targeting specific tissues. Although several polymer-based systems have addressed the first two demands and have been translated into clinical practice, no targeted synthetic drug delivery system has reached the market. This Review is designed to provide a background on the challenges and requirements for the design and translation of new polymer-based delivery systems. This report will focus on chemical approaches to drug delivery for systemic applications.

mRNA-LNP expressing PfCSP and Pfs25 vaccine candidates targeting infection and transmission of Plasmodium falciparum

Malaria is a deadly disease responsible for between 550,000 and 627,000 deaths annually. There is a pressing need to develop vaccines focused on malaria elimination. The complex lifecycle of Plasmodium falciparum provides opportunities not only to target the infectious sporozoite stage, introduced by anopheline mosquitoes, but also the sexual stages, which are ingested by mosquitoes during blood feeding, leading to parasite transmission. It is widely recognized that a vaccine targeting multiple stages would induce efficacious transmission reducing immunity. Technological advancements offer new vaccine platforms, such as mRNA-LNPs, which can be used to develop highly effective malarial vaccines. We evaluated the immunogenicity of two leading P. falciparum vaccine candidates, Pfs25 and PfCSP, delivered as mRNA-LNP vaccines. Both vaccines induced extremely potent immune responses when administered alone or in combination, which were superior to Pfs25 and PfCSP DNA vaccine formulations. Purified IgGs from Pfs25 mRNA-LNPs immunized mice were highly potent in reducing malaria transmission to mosquitoes. Additionally, mice after three and four immunizations with PfCSP mRNA-LNP provided evidence for varying degrees of protection against sporozoite challenge. The comparison of immune responses and stage-specific functional activity induced by each mRNA-LNP vaccine, administered alone or in combination, also supports the development of an effective combination vaccine without any risk of immune interference for targeting malaria parasites at various life cycle stages. A combination of vaccines targeting both the infective stage and sexual/midgut stages is expected to interrupt malaria transmission, which is critical for achieving elimination goals.

Advancing mRNA technologies for therapies and vaccines: An African context

Synthetic mRNA technologies represent a versatile platform that can be used to develop advanced drug products. The remarkable speed with which vaccine development programs designed and manufactured safe and effective COVID-19 vaccines has rekindled interest in mRNA technology, particularly for future pandemic preparedness. Although recent R&D has focused largely on advancing mRNA vaccines and large-scale manufacturing capabilities, the technology has been used to develop various immunotherapies, gene editing strategies, and protein replacement therapies. Within the mRNA technologies toolbox lie several platforms, design principles, and components that can be adapted to modulate immunogenicity, stability, in situ expression, and delivery. For example, incorporating modified nucleotides into conventional mRNA transcripts can reduce innate immune responses and improve in situ translation. Alternatively, self-amplifying RNA may enhance vaccine-mediated immunity by increasing antigen expression. This review will highlight recent advances in the field of synthetic mRNA therapies and vaccines, and discuss the ongoing global efforts aimed at reducing vaccine inequity by establishing mRNA manufacturing capacity within Africa and other low- and middle-income countries.

Malaria vaccine approaches leveraging technologies optimized in the COVID-19 era

Africa bears the greatest burden of malaria with more than 200 million clinical cases and more than 600,000 deaths in 2020 alone. While malaria-associated deaths dropped steadily until 2015, the decline started to falter after 2016, highlighting the need for novel potent tools in the fight against malaria. Currently available tools, such as antimalarial drugs and insecticides are threatened by development of resistance by the parasite and the mosquito. The WHO has recently approved RTS,S as the first malaria vaccine for public health use. However, because the RTS,S vaccine has an efficacy of only 36% in young children, there is need for more efficacious vaccines. Indeed, based on the global goal of licensing a malaria vaccine with at least 75% efficacy by 2030, RTS,S is unlikely to be sufficient alone. However, recent years have seen tremendous progress in vaccine development. Although the COVID-19 pandemic impacted malaria control, the rapid progress in research towards the development of COVID-19 vaccines indicate that harnessing funds and technological advances can remarkably expedite vaccine development. In this review, we highlight and discuss current and prospective trends in global efforts to discover and develop malaria vaccines through leveraging mRNA vaccine platforms and other systems optimized during COVID-19 vaccine studies.

Systems biology of malaria explored with nonhuman primates

"The Primate Malarias" book has been a uniquely important resource for multiple generations of scientists, since its debut in 1971, and remains pertinent to the present day. Indeed, nonhuman primates (NHPs) have been instrumental for major breakthroughs in basic and pre-clinical research on malaria for over 50 years. Research involving NHPs have provided critical insights and data that have been essential for malaria research on many parasite species, drugs, vaccines, pathogenesis, and transmission, leading to improved clinical care and advancing research goals for malaria control, elimination, and eradication. Whilst most malaria scientists over the decades have been studying Plasmodium falciparum, with NHP infections, in clinical studies with humans, or using in vitro culture or rodent model systems, others have been dedicated to advancing research on Plasmodium vivax, as well as on phylogenetically related simian species, including Plasmodium cynomolgi, Plasmodium coatneyi, and Plasmodium knowlesi. In-depth study of these four phylogenetically related species over the years has spawned the design of NHP longitudinal infection strategies for gathering information about ongoing infections, which can be related to human infections. These Plasmodium-NHP infection model systems are reviewed here, with emphasis on modern systems biological approaches to studying longitudinal infections, pathogenesis, immunity, and vaccines. Recent discoveries capitalizing on NHP longitudinal infections include an advanced understanding of chronic infections, relapses, anaemia, and immune memory. With quickly emerging new technological advances, more in-depth research and mechanistic discoveries can be anticipated on these and additional critical topics, including hypnozoite biology, antigenic variation, gametocyte transmission, bone marrow dysfunction, and loss of uninfected RBCs. New strategies and insights published by the Malaria Host-Pathogen Interaction Center (MaHPIC) are recapped here along with a vision that stresses the importance of educating future experts well trained in utilizing NHP infection model systems for the pursuit of innovative, effective interventions against malaria.

Current Developments and Challenges of mRNA Vaccines

mRNA vaccines have brought about a great revolution in the vaccine fields owing to their simplicity and adaptability in antigen design, potential to induce both humoral and cell-mediated immune responses and demonstrated high efficacy, and rapid and low-cost production by using the same manufacturing platform for different mRNA vaccines. Multiple mRNA vaccines have been investigated for both infectious diseases and cancers, showing significant superiority to other types of vaccines. Although great success of mRNA vaccines has been achieved in the control of the coronavirus disease 2019 pandemic, there are still multiple challenges for the future development of mRNA vaccines. In this review, the most recent developments of mRNA vaccines against both infectious diseases and cancers are summarized for an overview of this field. Moreover, the challenges are also discussed on the basis of these developments.

RTS,S today and tomorrow's science

The first malaria vaccine has been recently approved for children living in malaria-endemic areas. While this is long-awaited and welcome news, the modest efficacy of the vaccine highlights several areas that require further attention. Here, we describe the likely impact of the vaccine and where clinical and basic discovery research will still be required.

Mosquirix™ RTS, S/AS01 Vaccine Development, Immunogenicity, and Efficacy

Malaria is a parasitic infection caused by bites from Plasmodium falciparum (P. falciparum)-infected mosquitoes with a present scale of symptoms ranging from moderate fever to neurological disorders. P. falciparum is the most lethal of the five strains of malaria, and is a major case of morbidity and mortality in endemic regions. Recent advancements in malaria diagnostic tools and prevention strategies have improved conjugation antimalarial therapies using fumigation and long-lasting insecticidal sprays, thus lowering malarial infections. Declines in the total number of infected individuals have been correlated with antimalarial drugs. Despite this, malaria remains a major health threat, affecting more than 30 million men, women, and children around the globe, and 20 percent of all children around the globe have malaria parasites in their blood. To overcome this life-threatening condition, novel therapeutic strategies, including immunization, are urgently needed to tackle this infection around the world. In line with this, the development of the RTS, S vaccine was a significant step forward in the fight against malaria. RTS, S is a vaccine for P. falciparum in which R specifies central repeat units, T the T-cell epitopes, and S indicates surface antigen. The RTS, S/AS01 malarial vaccine was synthesized and screened in several clinical trials between 2009 and 2014, involving thousands of young children in seven African countries, showing that children who received the vaccine did not suffer from severe malaria. Mosquirix™ was approved by the World Health Organization in 2021, indicating it to be safe and advocating its integration into routine immunization programs and existing malaria control measures. This paper examines the various stages of the vaccine’s development, including the evaluation of its immunogenicity and efficacy on the basis of a total of 2.3 million administered doses through a routine immunization program. The protection and effectiveness provided by the vaccine are strong, and evidence shows that it can be effectively delivered through the routine child immunization platform. The economic cost of the vaccine remains to be considered.

Vaccines for Human Schistosomiasis: Recent Progress, New Developments and Future Prospects

Schistosomiasis, caused by human trematode blood flukes (schistosomes), remains one of the most prevalent and serious of the neglected tropical parasitic diseases. Currently, treatment of schistosomiasis relies solely on a single drug, the anthelmintic praziquantel, and with increased usage in mass drug administration control programs for the disease, the specter of drug resistance developing is a constant threat. Vaccination is recognized as one of the most sustainable options for the control of any pathogen, but despite the discovery and reporting of numerous potentially promising schistosome vaccine antigens, to date, no schistosomiasis vaccine for human or animal deployment is available. This is despite the fact that Science ranked such an intervention as one of the top 10 vaccines that need to be urgently developed to improve public health globally. This review summarizes current progress of schistosomiasis vaccines under clinical development and advocates the urgent need for the establishment of a revolutionary and effective anti-schistosome vaccine pipeline utilizing cutting-edge technologies (including developing mRNA vaccines and exploiting CRISPR-based technologies) to provide novel insight into future vaccine discovery, design, manufacture and deployment.

Lipid Nanoparticle Delivery Systems to Enable mRNA-Based Therapeutics

The world raced to develop vaccines to protect against the rapid spread of SARS-CoV-2 infection upon the recognition of COVID-19 as a global pandemic. A broad spectrum of candidates was evaluated, with mRNA-based vaccines emerging as leaders due to how quickly they were available for emergency use while providing a high level of efficacy. As a modular technology, the mRNA-based vaccines benefitted from decades of advancements in both mRNA and delivery technology prior to the current global pandemic. The fundamental lessons of the utility of mRNA as a therapeutic were pioneered by Dr. Katalin Kariko and her colleagues, perhaps most notably in collaboration with Drew Weissman at University of Pennsylvania, and this foundational work paved the way for the development of the first ever mRNA-based therapeutic authorized for human use, COMIRNATY^®. In this Special Issue of Pharmaceutics, we will be honoring Dr. Kariko for her great contributions to the mRNA technology to treat diseases with unmet needs. In this review article, we will focus on the delivery platform, the lipid nanoparticle (LNP) carrier, which allowed the potential of mRNA therapeutics to be realized. Similar to the mRNA technology, the development of LNP systems has been ongoing for decades before culminating in the success of the first clinically approved siRNA-LNP product, ONPATTRO^®, a treatment for an otherwise fatal genetic disease called transthyretin amyloidosis. Lessons learned from the siRNA-LNP experience enabled the translation into the mRNA platform with the eventual authorization and approval of the mRNA-LNP vaccines against COVID-19. This marks the beginning of mRNA-LNP as a pharmaceutical option to treat genetic diseases.

Increased Photostability of the Integral mRNA Vaccine Component N1 -Methylpseudouridine Compared to Uridine

N1 -Methylation of pseudouridine (m1 ψ) replaces uridine (Urd) in several therapeutics, including the Moderna and BioNTech-Pfizer COVID-19 vaccines. Importantly, however, it is currently unknown if exposure to electromagnetic radiation can affect the chemical integrity and intrinsic stability of m1 ψ. In this study, the photochemistry of m1 ψ is compared to that of uridine by using photoirradiation at 267 nm, steady-state spectroscopy, and quantum-chemical calculations. Furthermore, femtosecond transient absorption measurements are collected to delineate the electronic relaxation mechanisms for both nucleosides under physiologically relevant conditions. It is shown that m1 ψ exhibits a 12-fold longer 1 ππ* decay lifetime than uridine and a 5-fold higher fluorescence yield. Notably, however, the experimental results also demonstrate that most of the excited state population in both molecules decays back to the ground state in an ultrafast time scale and that m1 ψ is 6.7-fold more photostable than Urd following irradiation at 267 nm.

Norovirus Vaccines: Current Clinical Development and Challenges

Noroviruses are the major viral pathogens causing epidemic and endemic acute gastroenteritis with significant morbidity and mortality. While vaccines against norovirus diseases have been shown to be of high significance, the development of a broadly effective norovirus vaccine remains difficult, owing to the wide genetic and antigenic diversity of noroviruses with multiple co-circulated variants of various genotypes. In addition, the absence of a robust cell culture system, an efficient animal model, and reliable immune markers of norovirus protection for vaccine evaluation further hinders the developmental process. Among the vaccine candidates that are currently under clinical studies, recombinant VP1-based virus-like particles (VLPs) that mimic major antigenic features of noroviruses are the common ones, with proven safety, immunogenicity, and protective efficacy, supporting a high success likelihood of a useful norovirus vaccine. This short article reviews the recent progress in norovirus vaccine development, focusing on those from recent clinical studies, as well as summarizes the barriers that are being encountered in this developmental process and discusses issues of future perspective.

Plasmodium vivax transmission-blocking vaccines: Progress, challenges and innovation

Existing control measures have significantly reduced malaria morbidity and mortality in the last two decades, although these reductions are now stalling. Significant efforts have been undertaken to develop malaria vaccines. Recently, extensive progress in malaria vaccine development has been made for Plasmodium falciparum. To date, only the RTS,S/AS01 vaccine has been tested in Phase 3 clinical trials and is now under implementation, despite modest efficacy. Therefore, the development of a malaria transmission-blocking vaccine (TBV) will be essential for malaria elimination. Only a limited number of TBVs have reached pre-clinical or clinical development with several major challenges impeding their development, including low immunogenicity in humans. TBV development efforts against P. vivax, the second major cause of malaria morbidity, lag far behind those for P. falciparum. In this review we summarize the latest progress, challenges and innovations in P. vivax TBV research and discuss how to accelerate its development.