Enhanced Delivery and Potency of Self-Amplifying mRNA Vaccines by Electroporation in Situ

Oxaliplatin lipidated prodrug synergistically enhances the anti-colorectal cancer effect of IL12 mRNA

Colorectal cancer (CRC) is the fourth most common cancer in the world, with the second highest incidence rate after lung cancer. Oxaliplatin (OXA) is a broad-spectrum anti-tumor agent with significant therapeutic efficacy in colorectal cancer, and as a divalent platinum analog, it is not selective in its distribution in the body and has systemic toxicity with continued use. Interleukin-12 (IL12) is an immunostimulatory cytokine with cytokine monotherapy that has made advances in the fight against cancer, limiting the clinical use of cytokines due to severe toxicity. Here, we introduced a long alkyl chain and N-methyl-2,2-diaminodiethylamine to the ligand of OXA to obtain OXA-LIP, which effectively reduces its toxicity and improves the uptake of the drug by tumor cells. We successfully constructed IL12 mRNA and used LNPs to deliver IL12 mRNA, and in vivo pharmacodynamic studies demonstrated that OXA-LIP combined with IL12 mRNA had better tumor inhibition and higher biosafety. In addition, it was investigated by pharmacokinetic experiments that the OXA-LIP drug could accumulate in nude mice at the tumor site, which prolonged the half-life and enhanced the anti-tumor efficiency of OXA. It is hoped that these results will provide an important reference for the subsequent research and development of OXA-LIP with IL12 mRNA, as well as provide new therapeutic approaches for the treatment of colon cancer.

Advanced nanoscale delivery systems for mRNA-based vaccines

The effectiveness of messenger RNA (mRNA) vaccines, especially those designed for COVID-19, relies heavily on sophisticated delivery systems that ensure efficient delivery of mRNA to target cells. A variety of nanoscale vaccine delivery systems (VDSs) have been explored for this purpose, including lipid nanoparticles (LNPs), liposomes, and polymeric nanoparticles made from biocompatible polymers such as poly(lactic-co-glycolic acid), as well as viral vectors and lipid-polymer hybrid complexes. Among these, LNPs are particularly notable for their efficiency in encapsulating and protecting mRNA. These nanoscale VDSs can be engineered to enhance stability and facilitate uptake by cells. The choice of delivery system depends on factors like the specific mRNA vaccine, target cell types, stability requirements, and desired immune response. In this review, we shed light on recent advances in delivery mechanisms for self-amplifying RNA (saRNA) vaccines, emphasizing groundbreaking studies on nanoscale delivery systems aimed at improving the efficacy and safety of mRNA/saRNA vaccines.

Innovative Strategies to Enhance mRNA Vaccine Delivery and Effectiveness: Mechanisms and Future Outlook

The creation of mRNA vaccines has transformed the area of vaccination and allowed for the production of COVID-19 vaccines with previously unheard-of speed and effectiveness. The development of novel strategies to enhance the delivery and efficiency of mRNA vaccines has been motivated by the ongoing constraints of the present mRNA vaccine delivery systems. In this context, intriguing methods to get beyond these restrictions include lipid nanoparticles, self-amplifying RNA, electroporation, microneedles, and cell-targeted administration. These innovative methods could increase the effectiveness, safety, and use of mRNA vaccines, making them more efficient, effective, and broadly available. Additionally, mRNA technology may have numerous and far-reaching uses in the field of medicine, opening up fresh avenues for the diagnosis and treatment of disease. This paper gives an overview of the existing drawbacks of mRNA vaccine delivery techniques, the creative solutions created to address these drawbacks, and their prospective public health implications. The development of mRNA vaccines for illnesses other than infectious diseases and creating scalable and affordable manufacturing processes are some of the future directions for research in this area that are covered in this paper.

Tumor Vaccines: Unleashing the Power of the Immune System to Fight Cancer

This comprehensive review delves into the rapidly evolving arena of cancer vaccines. Initially, we examine the intricate constitution of the tumor microenvironment (TME), a dynamic factor that significantly influences tumor heterogeneity. Current research trends focusing on harnessing the TME for effective tumor vaccine treatments are also discussed. We then provide a detailed overview of the current state of research concerning tumor immunity and the mechanisms of tumor vaccines, describing the complex immunological processes involved. Furthermore, we conduct an exhaustive analysis of the contemporary research landscape of tumor vaccines, with a particular focus on peptide vaccines, DNA/RNA-based vaccines, viral-vector-based vaccines, dendritic-cell-based vaccines, and whole-cell-based vaccines. We analyze and summarize these categories of tumor vaccines, highlighting their individual advantages, limitations, and the factors influencing their effectiveness. In our survey of each category, we summarize commonly used tumor vaccines, aiming to provide readers with a more comprehensive understanding of the current state of tumor vaccine research. We then delve into an innovative strategy combining cancer vaccines with other therapies. By studying the effects of combining tumor vaccines with immune checkpoint inhibitors, radiotherapy, chemotherapy, targeted therapy, and oncolytic virotherapy, we establish that this approach can enhance overall treatment efficacy and offset the limitations of single-treatment approaches, offering patients more effective treatment options. Following this, we undertake a meticulous analysis of the entire process of personalized cancer vaccines, elucidating the intricate process from design, through research and production, to clinical application, thus helping readers gain a thorough understanding of its complexities. In conclusion, our exploration of tumor vaccines in this review aims to highlight their promising potential in cancer treatment. As research in this field continues to evolve, it undeniably holds immense promise for improving cancer patient outcomes.

Advances in saRNA Vaccine Research against Emerging/Re-Emerging Viruses

Although conventional vaccine approaches have proven to be successful in preventing infectious diseases in past decades, for vaccine development against emerging/re-emerging viruses, one of the main challenges is rapid response in terms of design and manufacture. mRNA vaccines can be designed and produced within days, representing a powerful approach for developing vaccines. Furthermore, mRNA vaccines can be scaled up and may not have the risk of integration. mRNA vaccines are roughly divided into non-replicating mRNA vaccines and self-amplifying RNA (saRNA) vaccines. In this review, we provide an overview of saRNA vaccines, and discuss future directions and challenges in advancing this promising vaccine platform to combat emerging/re-emerging viruses.

Checkpoint blockade meets gene therapy: Opportunities to improve response and reduce toxicity

Immune checkpoint inhibitors (ICIs) based on monoclonal antibodies represent a breakthrough for the treatment of cancer. However, their efficacy varies among tumor types and patients, and they can lead to adverse effects due to on-target/off-tumor activity, since they are administered systemically at high doses. An alternative and attractive approach for the delivery of ICIs is the use of gene therapy vectors able to express them in vivo. This review focuses on the most recent studies using viral vectors able to express ICIs locally or systemically in preclinical models of cancer. These vectors include non-replicating viruses, oncolytic viruses able to propagate specifically in tumor cells and destroy them, and self-amplifying RNA vectors, armed with different formats of antibodies against immune checkpoints. Non-replicating vectors usually lead to long-term ICI expression, potentially eliminating the need for repeated administration. Vectors with replication capacity, although they have a shorter window of expression, can induce inflammation which enhances the antitumor effect. Finally, these engineered vectors can be used in combination with other immunostimulatory molecules or with CAR-T cells, further boosting the antitumor immune responses.

Nucleic acid-based vaccine platforms against the coronavirus disease 19 (COVID-19)

The coronavirus disease 2019 (COVID-19) pandemic has infected 673,010,496 patients and caused the death of 6,854,959 cases globally until today. Enormous efforts have been made to develop fundamentally different COVID-19 vaccine platforms. Nucleic acid-based vaccines consisting of mRNA and DNA vaccines (third-generation vaccines) have been promising in terms of rapid and convenient production and efficient provocation of immune responses against the COVID-19. Several DNA-based (ZyCoV-D, INO-4800, AG0302-COVID19, and GX-19N) and mRNA-based (BNT162b2, mRNA-1273, and ARCoV) approved vaccine platforms have been utilized for the COVID-19 prevention. mRNA vaccines are at the forefront of all platforms for COVID-19 prevention. However, these vaccines have lower stability, while DNA vaccines are needed with higher doses to stimulate the immune responses. Intracellular delivery of nucleic acid-based vaccines and their adverse events needs further research. Considering re-emergence of the COVID-19 variants of concern, vaccine reassessment and the development of polyvalent vaccines, or pan-coronavirus strategies, is essential for effective infection prevention.

mRNA-Based Therapeutics in Cancer Treatment

Over the past two decades, significant technological innovations have led to messenger RNA (mRNA) becoming a promising option for developing prophylactic and therapeutic vaccines, protein replacement therapies, and genome engineering. The success of the two COVID-19 mRNA vaccines has sparked new enthusiasm for other medical applications, particularly in cancer treatment. In vitro-transcribed (IVT) mRNAs are structurally designed to resemble naturally occurring mature mRNA. Delivery of IVT mRNA via delivery platforms such as lipid nanoparticles allows host cells to produce many copies of encoded proteins, which can serve as antigens to stimulate immune responses or as additional beneficial proteins for supplements. mRNA-based cancer therapeutics include mRNA cancer vaccines, mRNA encoding cytokines, chimeric antigen receptors, tumor suppressors, and other combination therapies. To better understand the current development and research status of mRNA therapies for cancer treatment, this review focused on the molecular design, delivery systems, and clinical indications of mRNA therapies in cancer.

Self-Amplifying RNA Approach for Protein Replacement Therapy

Messenger RNA (mRNA) technology has already been successfully tested preclinically and there are ongoing clinical trials for protein replacement purposes; however, more effort has been put into the development of prevention strategies against infectious diseases. Apparently, mRNA vaccine approval against coronavirus disease 2019 (COVID-19) is a landmark for opening new opportunities for managing diverse health disorders based on this approach. Indeed, apart from infectious diseases, it has also been widely tested in numerous directions including cancer prevention and the treatment of inherited disorders. Interestingly, self-amplifying RNA (saRNA)-based technology is believed to display more developed RNA therapy compared with conventional mRNA technique in terms of its lower dosage requirements, relatively fewer side effects, and possessing long-lasting effects. Nevertheless, some challenges still exist that need to be overcome in order to achieve saRNA-based drug approval in clinics. Hence, the current review discusses the feasibility of saRNA utility for protein replacement therapy on various health disorders including rare hereditary diseases and also provides a detailed overview of saRNA advantages, its molecular structure, mechanism of action, and relevant delivery platforms.

Messenger RNA-Based Vaccines Against Infectious Diseases

In vitro-transcribed, messenger RNA-based infectious disease vaccines have the potential to successfully address many of the weaknesses of traditional vaccine platforms, such as the lack of potency and/or durability of vaccine protection, time-consuming, and expensive manufacturing, and, in some cases, safety issues. This optimism is fueled by a great deal of impressive recent data demonstrating that mRNA vaccines have many of the attributes that are necessary for a viable new vaccine class for human use. This review briefly describes mRNA vaccine types, discusses the most relevant and recent publications on infectious disease mRNA vaccines, and highlights the hurdles that need to be overcome to bring this promising novel vaccine modality to the clinic.

Self-amplifying mRNA-Based Vaccine Technology and Its Mode of Action

Self-amplifying mRNAs derived from the genomes of positive-strand RNA viruses have recently come into focus as a promising technology platform for vaccine development. Non-virally delivered self-amplifying mRNA vaccines have the potential to be highly versatile, potent, streamlined, scalable, and inexpensive. By amplifying their genome and the antigen encoding mRNA in the host cell, the self-amplifying mRNA mimics a viral infection, resulting in sustained levels of the target protein combined with self-adjuvanting innate immune responses, ultimately leading to potent and long-lasting antigen-specific humoral and cellular immune responses. Moreover, in principle, any eukaryotic sequence could be encoded by self-amplifying mRNA without the need to change the manufacturing process, thereby enabling a much faster and flexible research and development timeline than the current vaccines and hence a quicker response to emerging infectious diseases. This chapter highlights the rapid progress made in using non-virally delivered self-amplifying mRNA-based vaccines against infectious diseases in animal models. We provide an overview of the unique attributes of this vaccine approach, summarize the growing body of work defining its mechanism of action, discuss the current challenges and latest advances, and highlight perspectives about the future of this promising technology.

From bench side to clinic: Potential and challenges of RNA vaccines and therapeutics in infectious diseases

The functional and structural versatility of Ribonucleic acids (RNAs) makes them ideal candidates for overcoming the limitations imposed by small molecule-based drugs. Hence, RNA-based biopharmaceuticals such as messenger RNA (mRNA) vaccines, antisense oligonucleotides (ASOs), small interfering RNAs (siRNAs), microRNA mimics, anti-miRNA oligonucleotides (AMOs), aptamers, riboswitches, and CRISPR-Cas9 are emerging as vital tools for the treatment and prophylaxis of many infectious diseases. Some of the major challenges to overcome in the area of RNA-based therapeutics have been the instability of single-stranded RNAs, delivery to the diseased cell, and immunogenicity. However, recent advancements in the delivery systems of in vitro transcribed mRNA and chemical modifications for protection against nucleases and reducing the toxicity of RNA have facilitated the entry of several exogenous RNAs into clinical trials. In this review, we provide an overview of RNA-based vaccines and therapeutics, their production, delivery, current advancements, and future translational potential in treating infectious diseases.

HIV and Messenger RNA (mRNA) Vaccine

Human immunodeficiency virus (HIV) is a part of the lentivirus genus of the retroviridae family that incorporates its genome into the host DNA via a series of complex steps. HIV can be classified into two types, HIV-type 1 (HIV-1) and HIV-type 2 (HIV-2), with HIV-1 being the most common type worldwide. Seventy-six million people have been infected since the start of the pandemic, with a mortality rate of 33 million. Even after 40 years, no cure has been developed for this pandemic. The development of the mRNA vaccine has led to further research for the utilization of mRNA vaccine in HIV, in attempts to create a prophylactic and therapeutic treatment. Although messenger RNA (mRNA) vaccine has been around for many years, it has recently drawn attention due to its role and response in the unforeseen coronavirus pandemic. mRNA vaccine has faced its fair-share of challenges, but it also offers many advantages compared to conventional vaccines such as safety, efficacy, rapid preparation, and versatility. mRNA vaccine has shown promising results and has great potential. In this review, we discuss the types of mRNA vaccine, along with development, delivery, advantages, challenges, and how we are working to overcome these challenges.

Advances in gene-based vaccine platforms to address the COVID-19 pandemic

The novel betacoronavirus, SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), has spread across the globe at an unprecedented rate since its first emergence in Wuhan City, China in December 2019. Scientific communities around the world have been rigorously working to develop a potent vaccine to combat COVID-19 (coronavirus disease 2019), employing conventional and novel vaccine strategies. Gene-based vaccine platforms based on viral vectors, DNA, and RNA, have shown promising results encompassing both humoral and cell-mediated immune responses in previous studies, supporting their implementation for COVID-19 vaccine development. In fact, the U.S. Food and Drug Administration (FDA) recently authorized the emergency use of two RNA-based COVID-19 vaccines. We review current gene-based vaccine candidates proceeding through clinical trials, including their antigenic targets, delivery vehicles, and route of administration. Important features of previous gene-based vaccine developments against other infectious diseases are discussed in guiding the design and development of effective vaccines against COVID-19 and future derivatives.

HIV mRNA Vaccines-Progress and Future Paths

The SARS-CoV-2 pandemic introduced the world to a new type of vaccine based on mRNA encapsulated in lipid nanoparticles (LNPs). Instead of delivering antigenic proteins directly, an mRNA-based vaccine relies on the host's cells to manufacture protein immunogens which, in turn, are targets for antibody and cytotoxic T cell responses. mRNA-based vaccines have been the subject of research for over three decades as a platform to protect against or treat a variety of cancers, amyloidosis and infectious diseases. In this review, we discuss mRNA-based approaches for the generation of prophylactic and therapeutic vaccines to HIV. We examine the special immunological hurdles for a vaccine to elicit broadly neutralizing antibodies and effective T cell responses to HIV. Lastly, we outline an mRNA-based HIV vaccination strategy based on the immunobiology of broadly neutralizing antibody development.

Self-amplifying RNA vaccines for infectious diseases

Vaccinology is shifting toward synthetic RNA platforms which allow for rapid, scalable, and cell-free manufacturing of prophylactic and therapeutic vaccines. The simple development pipeline is based on in vitro transcription of antigen-encoding sequences or immunotherapies as synthetic RNA transcripts, which are then formulated for delivery. This approach may enable a quicker response to emerging disease outbreaks, as is evident from the swift pursuit of RNA vaccine candidates for the global SARS-CoV-2 pandemic. Both conventional and self-amplifying RNAs have shown protective immunization in preclinical studies against multiple infectious diseases including influenza, RSV, Rabies, Ebola, and HIV-1. Self-amplifying RNAs have shown enhanced antigen expression at lower doses compared to conventional mRNA, suggesting this technology may improve immunization. This review will explore how self-amplifying RNAs are emerging as important vaccine candidates for infectious diseases, the advantages of synthetic manufacturing approaches, and their potential for preventing and treating chronic infections.

A new generation of vaccines based on alphavirus self-amplifying RNA

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Alphavirus self-amplifiying RNA (saRNA) induces more potent immune responses than conventional mRNA.

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saRNA delivery can be enhanced by electroporation or conjugation with cationic lipid or polymers.

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saRNA vaccines induce protective responses against human pathogens in preclinical models.

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saRNA replication mediates innate immune signals that contribute to the strength of immune responses.

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saRNA vaccines could be generated in a quick way to face emergent pathogens like SARS-CoV-2.

DNA or mRNA vaccines have potential advantages over conventional vaccines since they are easier to manufacture and have higher safety profiles. In particular, self-amplifying RNA (saRNA) derived from alphavirus expression vectors has shown to be very efficient to induce humoral and cellular responses against many antigens in preclinical models, being superior to non-replicating mRNA and DNA. This is mainly due to the fact that saRNA can provide very high expression levels and simultaneously induces strong innate responses, potentiating immunity. saRNA can be administered as viral particles or DNA, but direct delivery as RNA represents a safer and more simple approach. Although saRNA can be delivered as naked RNA, in vivo transfection can be enhanced by electroporation or by complexing it with cationic lipids or polymers. Alphavirus saRNA could have broad application to vaccinate against human pathogens, including emerging ones like SARS-CoV-2, for which clinical trials have been recently initiated.

Opportunities and Challenges in the Delivery of mRNA-based Vaccines

In the past few years, there has been increasing focus on the use of messenger RNA (mRNA) as a new therapeutic modality. Current clinical efforts encompassing mRNA-based drugs are directed toward infectious disease vaccines, cancer immunotherapies, therapeutic protein replacement therapies, and treatment of genetic diseases. However, challenges that impede the successful translation of these molecules into drugs are that (i) mRNA is a very large molecule, (ii) it is intrinsically unstable and prone to degradation by nucleases, and (iii) it activates the immune system. Although some of these challenges have been partially solved by means of chemical modification of the mRNA, intracellular delivery of mRNA still represents a major hurdle. The clinical translation of mRNA-based therapeutics requires delivery technologies that can ensure stabilization of mRNA under physiological conditions. Here, we (i) review opportunities and challenges in the delivery of mRNA-based therapeutics with a focus on non-viral delivery systems, (ii) present the clinical status of mRNA vaccines, and (iii) highlight perspectives on the future of this promising new type of medicine.

Immunogenicity and Protection Efficacy of a Naked Self-Replicating mRNA-Based Zika Virus Vaccine

To combat emerging infectious diseases like Zika virus (ZIKV), synthetic messenger RNAs (mRNAs) encoding viral antigens are very attractive as they allow a rapid, generic, and flexible production of vaccines. In this work, we engineered a self-replicating mRNA (sr-mRNA) vaccine encoding the pre-membrane and envelope (prM-E) glycoproteins of ZIKV. Intradermal electroporation of as few as 1 µg of this mRNA-based ZIKV vaccine induced potent humoral and cellular immune responses in BALB/c and especially IFNAR1^-/- C57BL/6 mice, resulting in a complete protection of the latter mice against ZIKV infection. In wild-type C57BL/6 mice, the vaccine resulted in very low seroconversion rates and antibody titers. The potency of the vaccine was inversely related to the dose of mRNA used in wild-type BALB/c or C57BL/6 mice, as robust type I interferon (IFN) response was determined in a reporter mice model (IFN-β^+/Δβ-luc). We further investigated the inability of the sr-prM-E-mRNA ZIKV vaccine to raise antibodies in wild-type C57BL/6 mice and found indications that type I IFNs elicited by this naked sr-mRNA vaccine might directly impede the induction of a robust humoral response. Therefore, we assume that the efficacy of sr-mRNA vaccines after intradermal electroporation might be increased by strategies that temper their inherent innate immunogenicity.

Expression Kinetics and Innate Immune Response after Electroporation and LNP-Mediated Delivery of a Self-Amplifying mRNA in the Skin

In this work, we studied the expression kinetics and innate immune response of a self-amplifying mRNA (sa-RNA) after electroporation and lipid-nanoparticle (LNP)-mediated delivery in the skin of mice. Intradermal electroporation of the sa-RNA resulted in a plateau-shaped expression, with the plateau between day 3 and day 10. The overall protein expression of sa-RNA was significantly higher than that obtained after electroporation of plasmid DNA (pDNA) or non-replication mRNAs. Moreover, using IFN-β reporter mice, we elucidated that intradermal electroporation of sa-RNA induced a short-lived moderate innate immune response, which did not affect the expression of the sa-RNA. A completely different expression profile and innate immune response were observed when LNPs were used. The expression peaked 24 h after intradermal injection of sa-RNA-LNPs and subsequently showed a sharp drop. This drop might be explained by a translational blockage caused by the strong innate immune response that we observed in IFN-β reporter mice shortly (4 h) after intradermal injection of sa-RNA-LNPs. A final interesting observation was the capacity of sa-RNA-LNPs to transfect the draining lymph nodes after intradermal injection.

Improving the Repeatability and Efficacy of Intradermal Electroporated Self-Replicating mRNA

Local administration of naked self-replicating mRNA (sr-mRNA) in the skin or muscle using electroporation is effective but hampered by low repeatability. In this manuscript, we demonstrated that intradermal electroporation of sr-mRNA in combination with a protein-based RNase inhibitor increased the expression efficiency, success rate, and repeatability of the data. The RNase inhibitor should be added just before administration because storage of the inhibitor together with the sr-mRNA at −80°C resulted in a partial loss of the beneficial effect. Furthermore, the location of intradermal electroporation also had a major effect on the expression of the sr-mRNA, with the highest and longest expression observed at the tail base of the mice. In contrast with previous work, we did not observe a beneficial effect of calcium ions on the efficacy of naked sr-mRNA after intradermal injection. Finally, another important finding was that the traditional representation of in vivo bioluminescence data as means in logarithmic graphs can mask highly variable data. A more truthful representation can be obtained by showing the individual data points or by displaying median values in combination with interquartile ranges. In conclusion, intradermal sr-mRNA electroporation can be improved by adding an RNase inhibitor and injecting at the tail base.

Co-administration of GM-CSF expressing RNA is a powerful tool to enhance potency of SAM-based vaccines

Self-amplifying mRNAs (SAM)-based vaccines have been shown to induce a robust immune response in various animal species against both viral and bacterial pathogens. Due to their synthetic nature and to the versatility of the manufacturing process, SAM technology may represent an attractive solution for rapidly producing novel vaccines, which is particularly critical in case of pandemic infections or diseases mediated by newly emerging pathogens. Recent published data support the hypothesis that Antigen Presenting Cells (APCs) are responsible for CD8+ T-cell priming after SAM vaccination, suggesting cross-priming as the key mechanism for antigen presentation by SAM vaccines. In our study we investigated the possibility to enhance the immune response induced in mice by a single immunization with SAM by increasing the recruitment of APCs at the site of injection. To enhance SAM immunogenicity, we selected murine granulocyte-macrophage colony-stimulating factor (GM-CSF) as a model chemoattractant for APCs, and developed a SAM-GM-CSF vector. We evaluated whether the use of SAM-GM-CSF in combination with a SAM construct encoding the Influenza A virus nucleoprotein (NP) would lead to an increase of APC recruitment and NP-specific immune response. We indeed observed that the administration of SAM-GM-CSF enhances the recruitment of APCs at the injection site. Consistently with our hypothesis, co-administration of SAM-GM-CSF with SAM-NP significantly improved the magnitude of NP-specific CD8+ T-cell response both in terms of frequency of cytotoxic antigen-specific CD8+ T-cells and their functional activity in vivo. Furthermore, co-immunization with SAM-GM-CSF and SAM-NP provided an increase in protection against a lethal challenge with influenza virus. In conclusion, we demonstrated that increased recruitment of APCs at the site of injection is associated with an enhanced effectiveness of SAM vaccination and might be a powerful tool to potentiate the efficacy of RNA vaccination.

Prevention and Control Strategies to Counter Zika Virus, a Special Focus on Intervention Approaches against Vector Mosquitoes-Current Updates

Zika virus (ZIKV) is the most recent intruder that acquired the status of global threat creating panic and frightening situation to public owing to its rapid spread, attaining higher virulence and causing complex clinical manifestations including microcephaly in newborns and Guillain Barré Syndrome. Alike other flaviviruses, the principal mode of ZIKV transmission is by mosquitoes. Advances in research have provided reliable diagnostics for detecting ZIKV infection, while several drug/therapeutic targets and vaccine candidates have been identified recently. Despite these progresses, currently there is neither any effective drug nor any vaccine available against ZIKV. Under such circumstances and to tackle the problem at large, control measures of which mosquito population control need to be strengthened following appropriate mechanical, chemical, biological and genetic control measures. Apart from this, several other known modes of ZIKV transmission which have gained importance in recent past such as intrauterine, sexual intercourse, and blood-borne spread need to be checked and kept under control by adopting appropriate precautions and utmost care during sexual intercourse, blood transfusion and organ transplantation. The virus inactivation by pasteurization, detergents, chemicals, and filtration can effectively reduce viral load in plasma-derived medicinal products. Added to this, strengthening of the surveillance and monitoring of ZIKV as well as avoiding travel to Zika infected areas would aid in keeping viral infection under check. Here, we discuss the salient advances in the prevention and control strategies to combat ZIKV with a focus on highlighting various intervention approaches against the vector mosquitoes of this viral pathogen along with presenting an overview regarding human intervention measures to counter other modes of ZIKV transmission and spread. Additionally, owing to the success of vaccines for a number of infections globally, a separate section dealing with advances in ZIKV vaccines and transmission blocking vaccines has also been included.

Self-Amplifying RNA Vaccines Give Equivalent Protection against Influenza to mRNA Vaccines but at Much Lower Doses

New vaccine platforms are needed to address the time gap between pathogen emergence and vaccine licensure. RNA-based vaccines are an attractive candidate for this role: they are safe, are produced cell free, and can be rapidly generated in response to pathogen emergence. Two RNA vaccine platforms are available: synthetic mRNA molecules encoding only the antigen of interest and self-amplifying RNA (sa-RNA). sa-RNA is virally derived and encodes both the antigen of interest and proteins enabling RNA vaccine replication. Both platforms have been shown to induce an immune response, but it is not clear which approach is optimal. In the current studies, we compared synthetic mRNA and sa-RNA expressing influenza virus hemagglutinin. Both platforms were protective, but equivalent levels of protection were achieved using 1.25 μg sa-RNA compared to 80 μg mRNA (64-fold less material). Having determined that sa-RNA was more effective than mRNA, we tested hemagglutinin from three strains of influenza H1N1, H3N2 (X31), and B (Massachusetts) as sa-RNA vaccines, and all protected against challenge infection. When sa-RNA was combined in a trivalent formulation, it protected against sequential H1N1 and H3N2 challenges. From this we conclude that sa-RNA is a promising platform for vaccines against viral diseases.

Overcoming cellular barriers for RNA therapeutics

RNA-based therapeutics, such as small-interfering (siRNAs), microRNAs (miRNAs), antisense oligonucleotides (ASOs), aptamers, synthetic mRNAs and CRISPR-Cas9, have great potential to target a large part of the currently undruggable genes and gene products and to generate entirely new therapeutic paradigms in disease, ranging from cancer to pandemic influenza to Alzheimer's disease. However, for these RNA modalities to reach their full potential, they first need to overcome a billion years of evolutionary defenses that have kept RNAs on the outside of cells from invading the inside of cells. Overcoming the lipid bilayer to deliver RNA into cells has remained the major problem to solve for widespread development of RNA therapeutics, but recent chemistry advances have begun to penetrate this evolutionary armor.

Introduction to RNA Vaccines

RNA vaccines are attractive, because they exhibit characteristics of subunit vaccines and live-attenuated vectors, including flexible production and induction of both humoral and cellular immunity. While human proof-of-concept for RNA vaccines is still pending, the nascent field of RNA therapeutics has already attracted substantial industry and government funding as well as record investments of private venture capital. Most recently, the WHO acknowledged messenger RNA (mRNA) as a new therapeutic class. In this chapter, we briefly review key developments in RNA vaccines and outline the contents of this volume of Methods in Molecular Biology.

Enhanced Delivery of DNA or RNA Vaccines by Electroporation

Nucleic acid vaccines are a next-generation branch of vaccines which offer major benefits over their conventional protein, bacteria, or viral-based counterparts. However, to be effective in large mammals and humans, an enhancing delivery technology is required. Electroporation is a physical technique which results in improved delivery of large molecules through the cell membrane. In the case of plasmid DNA and mRNA, electroporation enhances both the uptake and expression of the delivered nucleic acids. The muscle is an attractive tissue for nucleic acid vaccination in a clinical setting due to the accessibility and abundance of the target tissue. Historical clinical studies of electroporation in the muscle have demonstrated the procedure to be generally well tolerated in patients. Previous studies have determined that optimized electroporation parameters (such as electrical field intensity, pulse length, pulse width and drug product formulation) majorly impact the efficiency of nucleic acid delivery. We provide an overview of DNA/RNA vaccination in the muscle of mice. Our results suggest that the technique is safe and effective and is highly applicable to a research setting as well as scalable to larger animals and humans.

Veterinary Replicon Vaccines

Vaccination is essential in livestock farming and in companion animal ownership. Nucleic acid vaccines based on DNA or RNA provide an elegant alternative to those classical veterinary vaccines that have performed suboptimally. Recent advances in terms of rational design, safety, and efficacy have strengthened the position of nucleic acid vaccines in veterinary vaccinology. The present review focuses on replicon vaccines designed for veterinary use. Replicon vaccines are self-amplifying viral RNA sequences that, in addition to the sequence encoding the antigen of interest, contain all elements necessary for RNA replication. Vaccination results in high levels of in situ antigen expression and induction of potent immune responses. Both positive- and negative-stranded viruses have been used to construct replicons, and they can be delivered as RNA, DNA, or viral replicon particles. An introduction to the biology and the construction of different viral replicon vectors is given, and examples of veterinary replicon vaccine applications are discussed.

A microarray MEMS device for biolistic delivery of vaccine and drug powders

We report a biolistic technology platform for physical delivery of particle formulations of drugs or vaccines using parallel arrays of microchannels, which generate highly collimated jets of particles with high spatial resolution. Our approach allows for effective delivery of therapeutics sequentially or concurrently (in mixture) at a specified target location or treatment area. We show this new platform enables the delivery of a broad range of particles with various densities and sizes into both in vitro and ex vivo skin models. Penetration depths of ∼1 mm have been achieved following a single ejection of 200 µg high-density gold particles, as well as 13.6 µg low-density polystyrene-based particles into gelatin-based skin simulants at 70 psi inlet gas pressure. Ejection of multiple shots at one treatment site enabled deeper penetration of ∼3 mm in vitro, and delivery of a higher dose of 1 mg gold particles at similar inlet gas pressure. We demonstrate that particle penetration depths can be optimized in vitro by adjusting the inlet pressure of the carrier gas, and dosing is controlled by drug reservoirs that hold precise quantities of the payload, which can be ejected continuously or in pulses. Future investigations include comparison between continuous versus pulsatile payload deliveries. We have successfully delivered plasmid DNA (pDNA)-coated gold particles (1.15 µm diameter) into ex vivo murine and porcine skin at low inlet pressures of ∼30 psi. Integrity analysis of these pDNA-coated gold particles confirmed the preservation of full-length pDNA after each particle preparation and jetting procedures. This technology platform provides distinct capabilities to effectively deliver a broad range of particle formulations into skin with specially designed high-speed microarray ejector nozzles.

A multi-head intradermal electroporation device allows for tailored and increased dose DNA vaccine delivery to the skin

The identification of an effective and tolerable delivery method is a necessity for the success of DNA vaccines in the clinic. This article describes the development and validation of a multi-headed intradermal electroporation device which would be applicable for delivering multiple DNA vaccine plasmids simultaneously but spatially separated. Reporter gene plasmids expressing green and red fluorescent proteins were used to demonstrate the impact of spatial separation on DNA delivery to increase the number of transfected cells and avoid interference through visible expression patterns. To investigate the impact of plasmid interference on immunogenicity, a disease target was investigated where issues with multi-valent vaccines had been previously described. DNA-based Hantaan and Puumala virus vaccines were delivered separately or as a combination and the effect of multi-valence was determined by appropriate assays. While a negative impact was observed for both antigenic vaccines when delivered together, these effects were mitigated when the vaccine was delivered using the multi-head device. We also demonstrate how the multi-head device facilitates higher dose delivery to the skin resulting in improved immune responses. This new multi-head platform device is an efficient, tolerable and non-invasive method to deliver multiple plasmid DNA constructs simultaneously allowing the tailoring of delivery sites for combination vaccines. Additionally, this device would allow the delivery of multi-plasmid vaccine formulations without risk of impacted immune responses through interference. Such a low-cost, easy to use device platform for the delivery of multi-agent DNA vaccines would have direct applications by the military and healthcare sectors for mass vaccination purposes.

A multi-head intradermal electroporation device allows for tailored and increased dose DNA vaccine delivery to the skin

The identification of an effective and tolerable delivery method is a necessity for the success of DNA vaccines in the clinic. This manuscript describes the development and validation of a multi-headed intradermal electroporation device which would be applicable for delivering multiple DNA vaccine plasmids simultaneously but spatially separated. Reporter gene plasmids expressing green and red fluorescent proteins were used to demonstrate the impact of spatial separation on DNA delivery to increase the number of transfected cells and avoid interference through visible expression patterns. To investigate the impact of plasmid interference on immunogenicity, a disease target was investigated where issues with multi-valent vaccines had been previously described. DNA-based Hantaan and Puumala virus vaccines were delivered separately or as a combination and the effect of multi-valence was determined by appropriate assays. While a negative impact was observed for both antigenic vaccines when delivered together, these effects were mitigated when the vaccine was delivered using the multi-head device. We also demonstrate how the multi-head device facilitates higher dose delivery to the skin resulting in improved immune responses. This new multi-head platform device is an efficient, tolerable and non-invasive method to deliver multiple plasmid DNA constructs simultaneously allowing the tailoring of delivery sites for combination vaccines. Additionally, this device would allow the delivery of multi-plasmid vaccine formulations without risk of impacted immune responses through interference. Such a low-cost, easy to use device platform for the delivery of multi-agent DNA vaccines would have direct applications by the military and healthcare sectors for mass vaccination purposes.

DNA Vaccines: Recent Developments and the Future

This special issue is focused on DNA vaccines, marking the two decades since the first demonstration of pre-clinical protection was published in Science (Ulmer et al.; Heterologous protection against influenza by injection of DNA encoding a viral protein. 1993). This introductory article provides an overview of the field and highlights the observations of the articles in this special issue while placing them in the context of other recent publications.

Self-replicating alphavirus RNA vaccines

Recombinant nucleic acids are considered as promising next-generation vaccines. These vaccines express the native antigen upon delivery into tissue, thus mimicking live attenuated vaccines without having the risk of reversion to pathogenicity. They also stimulate the innate immune system, thus potentiating responses. Nucleic acid vaccines are easy to produce at reasonable cost and are stable. During the past years, focus has been on the use of plasmid DNA for vaccination. Now mRNA and replicon vaccines have come into focus as promising technology platforms for vaccine development. This review discusses self-replicating RNA vaccines developed from alphavirus expression vectors. These replicon vaccines can be delivered as RNA, DNA or as recombinant virus particles. All three platforms have been pre-clinically evaluated as vaccines against a number of infectious diseases and cancer. Results have been very encouraging and propelled the first human clinical trials, the results of which have been promising.

Nucleic acid vaccines: prospects for non-viral delivery of mRNA vaccines

INTRODUCTION

Nucleic acid-based vaccines are being developed as a means to combine the positive attributes of both live-attenuated and subunit vaccines. Viral vectors and plasmid DNA vaccines have been extensively evaluated in human clinical trials and have been shown to be safe and immunogenic, although none have been licensed for human use. More recently, mRNA-based vaccine alternatives have emerged and might offer certain advantages over their DNA-based counterparts.

AREAS COVERED

This review describes the two main categories of mRNA vaccines: conventional non-amplifying and self-amplifying mRNA. It summarizes the initial clinical proof-of-concept studies and outlines the preclinical testing of the next wave of innovations for the technology. Finally, this review highlights the versatile functionality of the mRNA molecule and introduces opportunities for future improvements in vaccine design.

EXPERT OPINION

The prospects for mRNA vaccines are very promising. Like other types of nucleic acid vaccines, mRNA vaccines have the potential to combine the positive attributes of live attenuated vaccines while obviating many potential safety limitations. Although data from initial clinical trials appear encouraging, mRNA vaccines are far from a commercial product. These initial approaches have spurred innovations in vector design, non-viral delivery, large-scale production and purification of mRNA to quickly move the technology forward. Some improvements have already been tested in preclinical models for both prophylactic and therapeutic vaccine targets and have demonstrated their ability to elicit potent and broad immune responses, including functional antibodies, type 1 T helper cells-type T cell responses and cytotoxic T cells. Though the initial barriers for this nucleic acid vaccine approach seem to be overcome, in our opinion, the future and continued success of this approach lies in a more extensive evaluation of the many non-viral delivery systems described in the literature and gaining a better understanding of the mechanism of action to allow rational design of next generation technologies.