pEVL: A Linear Plasmid for Generating mRNA IVT Templates With Extended Encoded Poly(A) Sequences

Engineered mRNA Delivery Systems for Biomedical Applications

Messenger RNA (mRNA)-based therapeutic strategies have shown remarkable promise in preventing and treating a staggering range of diseases. Optimizing the structure and delivery system of engineered mRNA has greatly improved its stability, immunogenicity, and protein expression levels, which has led to a wider range of uses for mRNA therapeutics. Herein, a thorough analysis of the optimization strategies used in the structure of mRNA is first provided and delivery systems are described in great detail. Furthermore, the latest advancements in biomedical engineering for mRNA technology, including its applications in combatting infectious diseases, treating cancer, providing protein replacement therapy, conducting gene editing, and more, are summarized. Lastly, a perspective on forthcoming challenges and prospects concerning the advancement of mRNA therapeutics is offered. Despite these challenges, mRNA-based therapeutics remain promising, with the potential to revolutionize disease treatment and contribute to significant advancements in the biomedical field.

Anion exchange HPLC monitoring of mRNA in vitro transcription reactions to support mRNA manufacturing process development

mRNA technology has recently demonstrated the ability to significantly change the timeline for developing and delivering a new vaccine from years to months. The potential of mRNA technology for rapid vaccine development has recently been highlighted by the successful development and approval of two mRNA vaccines for COVID-19. Importantly, this RNA-based approach holds promise for treatments beyond vaccines and infectious diseases, e.g., treatments for cancer, metabolic disorders, cardiovascular conditions, and autoimmune diseases. There is currently significant demand for the development of improved manufacturing processes for the production of mRNA therapeutics in an effort to increase their yield and quality. The development of suitable analytical methods for the analysis of mRNA therapeutics is critical to underpin manufacturing development and the characterisation of the drug product and drug substance. In this study we have developed a high-throughput, high-performance liquid chromatography (HPLC) workflow for the rapid analysis of mRNA generated using in vitro transcription (IVT). We have optimised anion exchange (AEX) HPLC for the analysis of mRNA directly from IVT. Chromatography was performed in under 6 min enabling separation of all of the key components in the IVT, including nucleoside triphosphates (NTPs), Cap analogue, plasmid DNA and mRNA product. Moreover, baseline separation of the NTPs was achieved, which facilitates accurate quantification of each NTP such that their consumption may be determined during IVT reactions. Furthermore, the HPLC method was used to rapidly assess the purification of the mRNA product, including removal of NTPs/Cap analogue and other contaminants after downstream purification, including solid phase extraction (SPE), oligo deoxythymidine (oligo-dT) affinity chromatography and tangential flow filtration (TFF). Using the developed method excellent precision was obtained with calibration curves for an external mRNA standard and NTPs giving correlation coefficients of 0.98 and 1.0 respectively. Intra- and inter-day studies on retention time stability of NTPs, showed a relative standard deviation ≤ 0.3% and ≤1.5% respectively. The mRNA retention time variability was ≤0.13%. This method was then utilised to monitor the progress of an IVT reaction for the production of Covid spike protein (C-Spike) mRNA to measure the increasing yield of mRNA alongside the consumption of NTPs during the reaction.

mRNA delivery systems for cancer immunotherapy: Lipid nanoparticles and beyond

mRNA-based vaccines are emerging as a promising alternative to standard cancer treatments and the conventional vaccines. Moreover, the FDA-approval of three nucleic acid based therapeutics (Onpattro, BNT162b2 and mRNA-1273) has further increased the interest and trust on this type of therapeutics. In order to achieve a significant therapeutic efficacy, the mRNA needs from a drug delivery system. In the last years, several delivery platforms have been explored, being the lipid nanoparticles (LNPs) the most well characterized and studied. A better understanding on how mRNA-based therapeutics operate (both the mRNA itself and the drug delivery system) will help to further improve their efficacy and safety. In this review, we will provide an overview of what mRNA cancer vaccines are and their mode of action and we will highlight the advantages and challenges of the different delivery platforms that are under investigation.

mRNA as a medicine in nephrology: the future is now

The successful employment of messenger RNA (mRNA) as vaccine therapy for the prevention of COVID-19 infection has spotlighted the attention of scientific community onto the potential clinical application of these molecules as innovative and alternative therapeutic approaches in different fields of medicine. As therapy, mRNAs may be advantageous due to their unique biological properties of targeting almost any genetic component within the cell, many of which may be unreachable using other pharmacological/therapeutic approaches, and encoding any proteins and peptides without the need for their transport into the nuclei of the target cells. Additionally, these molecules may be rapidly designed/produced and clinically tested. Once the chemistry of the RNA and its delivery system are optimized, the cost of developing novel variants of these medications for new selected clinical disorders is significantly reduced. However, although potentially useful as new therapeutic weapons against several kidney diseases, the complex architecture of kidney and the inability of nanoparticles that accommodate oligonucleotides to cross the integral glomerular filtration barrier have largely decreased their potential employment in nephrology. However, in the next few years, the technical improvements in mRNA that increase translational efficiency, modulate innate and adaptive immunogenicity, and increase their delivery at the site of action will overcome these limitations. Therefore, this review has the scope of summarizing the key strengths of these RNA-based therapies and illustrating potential future directions and challenges of this promising technology for widespread therapeutic use in nephrology.

A single-nucleotide resolution capillary gel electrophoresis workflow for poly(A) tail characterization in the development of mRNA therapeutics and vaccines

The 3' poly(A) tail is an important component of messenger RNA (mRNA). The length of the poly(A) tail has direct impact on the stability and translation efficiency of the mRNA molecule and is therefore considered to be a critical quality attribute (CQA) of mRNA-based therapeutics and vaccines. Various analytical methods have been developed to monitor this CQA. Methods like ion-pair reversed-phase liquid chromatography (IPRP-LC) can be used to quantify the percentage of mRNA with poly(A) tail but fail to provide further information on the actual length of poly(A). High-resolution methods such as liquid chromatography coupled with mass spectrometry (LC-MS) or next generation sequencing (NGS) can separate poly(A) tail length by one nucleotide (n/n + 1 resolution) but are complicated to implement for release testing of manufactured mRNA. In this study, a workflow utilizing capillary gel electrophoresis (CGE) for characterizing the poly(A) tail length of mRNA was developed. The CGE method demonstrated resolution comparable with the LC-MS method. With UV detection and the addition of poly(A) length markers, this method can provide poly(A) tail length information and can also provide quantitation of each poly(A) length, making it a suitable release method to monitor the CQA of poly(A) tail length.

Advances in Nonviral mRNA Delivery Materials and Their Application as Vaccines for Melanoma Therapy

Messenger RNA (mRNA) vaccines are promising platforms for cancer immunotherapy because of their potential to encode for a variety of tumor antigens, high tolerability, and capacity to induce strong antitumor immune responses. However, the clinical translation of mRNA cancer vaccines can be hindered by the inefficient delivery of mRNA in vivo. In this review, we provide an overview of mRNA cancer vaccines by discussing their utility in treating melanoma. Specifically, we begin our review by describing the barriers that can impede mRNA delivery to target cells. We then review native mRNA structure and discuss various modification methods shown to enhance mRNA stability and transfection. Next, we outline the advantages and challenges of three nonviral carrier platforms (lipid nanoparticles, polymeric nanoparticles, and lipopolyplexes) frequently used for mRNA delivery. Last, we summarize preclinical and clinical studies that have investigated nonviral mRNA vaccines for the treatment of melanoma. In writing this review, we aim to highlight innovative nonviral strategies designed to address mRNA delivery challenges while emphasizing the exciting potential of mRNA vaccines as next-generation therapies for the treatment of cancers.

mRNA Cancer Vaccines: Construction and Boosting Strategies

In late 2020, the U.S. Food and Drug Administration (FDA) approved a lipid-based mRNA vaccine for the prevention of COVID-19, which has pushed this field to be more closely studied and motivated researchers to delve deeper into mRNA therapeutics. To date, the research on mRNA cancer vaccines has been developed rapidly, and substantial hopeful therapeutic results have been achieved against various solid tumors in clinical trials. In this review, we first introduce three main components of mRNA cancer vaccines, including mRNA antigens, adjuvants, and delivery vectors. Engineering these components can optimize the therapeutic effects of mRNA cancer vaccines. For instance, appropriate modification of mRNA structure can alleviate the poor stability and innate immunogenicity of mRNA, and the use of mRNA delivery vectors can address the issues of low delivery efficiency in vivo. Second, we emphatically discuss some strategies to further improve the efficacy of mRNA cancer vaccines, namely modulating the immunosuppressive tumor environment, optimizing administration routes, achieving targeting delivery to intended tissues or organs, and employing combination therapy. These strategies can strengthen the tumor inhibitory ability of mRNA cancer vaccines and increase the possibility of tumor elimination. Finally, we point out some challenges in the clinical practice of mRNA cancer vaccines and offer our perspectives on future developments in this rapidly evolving field. It is anticipated that mRNA cancer vaccines will be rapidly developed for clinical cancer therapy in the near future.

In Vitro Transcribed RNA-Based Platform Vaccines: Past, Present, and Future

mRNA was discovered in 1961, but it was not used as a vaccine until after three decades. Recently, the development of mRNA vaccine technology gained great impetus from the pursuit of vaccines against COVID-19. To improve the properties of RNA vaccines, and primarily their circulation time, self-amplifying mRNA and trans-amplifying mRNA were developed. A separate branch of mRNA technology is circular RNA vaccines, which were developed with the discovery of the possibility of translation on their protein matrix. Circular RNA has several advantages over mRNA vaccines and is considered a fairly promising platform, as is trans-amplifying mRNA. This review presents an overview of the mRNA platform and a critical discussion of the more modern self-amplifying mRNA, trans-amplifying mRNA, and circular RNA platforms created on its basis. Finally, the main features, advantages, and disadvantages of each of the presented mRNA platforms are discussed. This discussion will facilitate the decision-making process in selecting the most appropriate platform for creating RNA vaccines against cancer or viral diseases.

mRNA Synthesis and Encapsulation in Ionizable Lipid Nanoparticles

mRNA vaccines have recently generated significant interest due to their success during the COVID-19 pandemic. Their success is due to advances in mRNA design and encapsulation into ionizable lipid nanoparticles (iLNPs). This has highlighted the potential for the use of mRNA-iLNPs in other settings such as cancer, gene therapy, or vaccines for different infectious diseases. Here, we describe the production of mRNA-iLNPs using commercially available reagents that are suitable for use as vaccines and therapeutics. This article contains detailed protocols for the synthesis of mRNA by in vitro transcription with enzymatic capping and tailing and the encapsulation of the mRNA into iLNPs using the ionizable lipid DLin-MC3-DMA. DLin-MC3-DMA is often used as a benchmark for new formulations and provides an efficient delivery vehicle for screening mRNA design. The protocol also describes how the formulation can be adapted to other lipids. Finally, a stepwise methodology is presented for the characterization and quality control of mRNA-iLNPs, including measuring mRNA concentration and encapsulation efficiency, particle size, and zeta potential. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Synthesis of mRNA by in vitro transcription and enzymatic capping and tailing Basic Protocol 2: Encapsulation of mRNA into ionizable lipid nanoparticles Alternate Protocol: Small-scale encapsulation of mRNA using preformed vesicles Basic Protocol 3: Characterization and quality control of mRNA ionizable lipid nanoparticles.

Recent Advances and Innovations in the Preparation and Purification of In Vitro-Transcribed-mRNA-Based Molecules

The coronavirus disease 2019 (COVID-19) pandemic poses a disruptive impact on public health and the global economy. Fortunately, the development of COVID-19 vaccines based on in vitro-transcribed messenger RNA (IVT mRNA) has been a breakthrough in medical history, benefiting billions of people with its high effectiveness, safety profile, and ease of large-scale production. This success is the result of decades of continuous RNA research, which has led to significant improvements in the stability and expression level of IVT mRNA through various approaches such as sequence optimization and improved preparation processes. IVT mRNA sequence optimization has been shown to have a positive effect on enhancing the mRNA expression level. The innovation of IVT mRNA purification technology is also indispensable, as the purity of IVT mRNA directly affects the success of downstream vaccine preparation processes and the potential for inducing unwanted side effects in therapeutic applications. Despite the progress made, challenges related to IVT mRNA sequence design and purification still require further attention to enhance the quality of IVT mRNA in the future. In this review, we discuss the latest innovative progress in IVT mRNA design and purification to further improve its clinical efficacy.

Modeling of MT. P495, an mRNA-based vaccine against the phosphate-binding protein PstS1 of Mycobacterium tuberculosis

Tuberculosis (TB) is a contagious disease that predominantly affects the lungs, but can also spread to other organs via the bloodstream. TB affects about one-fourth population of the world. With age, the effectiveness of Bacillus Calmette-Guérin (BCG), the only authorized TB vaccine, decreases. In the quest for a prophylactic and immunotherapeutic vaccine, in this study, a hypothetical mRNA vaccine is delineated, named MT. P495, implementing in silico and immunoinformatics approaches to evaluate key aspects and immunogenic epitopes across the PstS1, a highly conserved periplasmic protein of Mycobacterium tuberculosis (Mtb). PstS1 elicited the potential to generate 99.9% population coverage worldwide. The presence of T- and B-cell epitopes across the PstS1 protein were validated using several computational prediction tools. Molecular docking and dynamics simulation confirmed stable epitope-allele interaction. Immune cell response to the antigen clearance rate was verified by the in silico analysis of immune simulation. Codon optimization confirmed the efficient translation of the mRNA in the host cell. With Toll-like receptors, the vaccine exhibited stable and strong interactions. Findings suggest that the MT. P495 vaccine probably will elicit specific immune responses against Mtb. This mRNA vaccine model is a ready source for further wet-lab validation to confirm the efficacy of this proposed vaccine candidate.

Terminal hairpins improve protein expression in IRES-initiated mRNA in the absence of a cap and polyadenylated tail

Synthesizing mRNA in vitro is a standard and simple procedure. Adding the 5' cap and 3' polyadenylated (poly(A)) tail to make this mRNA functional for use as a vaccine or therapy increases the time and cost of production and usually decreases the yield, however. We designed mRNA that lacked a cap and poly(A) tail but included an internal ribosomal entry site (IRES) to initiate protein translation. To protect the 5' and 3' ends of mRNA from exonucleases, we added stable terminal hairpins. When compared against typical mRNA (i.e., mRNA that contained a cap and poly(A) tail but lacked hairpins), expression of the delivered reporter protein in HEK293 cells was similar. Using a triple instead of a single hairpin at each end increased protein expression even more. This method has the potential to simplify the production and reduce the cost of synthesizing exogenous mRNA for use as biologics or vaccines.

RNA Therapeutics: A Healthcare Paradigm Shift

COVID-19 brought about the mRNA vaccine and a paradigm shift to a new mode of treating and preventing diseases. Synthetic RNA products are a low-cost solution based on a novel method of using nucleosides to act as an innate medicine factory with unlimited therapeutic possibilities. In addition to the common perception of vaccines preventing infections, the newer applications of RNA therapies include preventing autoimmune disorders, such as diabetes, Parkinson's disease, Alzheimer's disease, and Down syndrome; now, we can deliver monoclonal antibodies, hormones, cytokines, and other complex proteins, reducing the manufacturing hurdles associated with these products. Newer PCR technology removes the need for the bacterial expression of DNA, making mRNA a truly synthetic product. AI-driven product design expands the applications of mRNA technology to repurpose therapeutic proteins and test their safety and efficacy quickly. As the industry focuses on mRNA, many novel opportunities will arise, as hundreds of products under development will bring new perspectives based on this significant paradigm shift-finding newer solutions to existing challenges in healthcare.

Revolutionizing viral disease vaccination: the promising clinical advancements of non-replicating mRNA vaccines

The mRNA vaccine technology was developed rapidly during the global pandemic of COVID-19. The crucial role of the COVID-19 mRNA vaccine in preventing viral infection also have been beneficial to the exploration and application of other viral mRNA vaccines, especially for non-replication structure mRNA vaccines of viral disease with outstanding research results. Therefore, this review pays attention to the existing mRNA vaccines, which are of great value for candidates for clinical applications in viral diseases. We provide an overview of the optimization of the mRNA vaccine development process as well as the good immune efficacy and safety shown in clinical studies. In addition, we also provide a brief description of the important role of mRNA immunomodulators in the treatment of viral diseases. After that, it will provide a good reference or strategy for research on mRNA vaccines used in clinical medicine with more stable structures, higher translation efficiency, better immune efficacy and safety, shorter production time, and lower production costs than conditional vaccines to be used as preventive or therapeutic strategy for the control of viral diseases in the future.

Research Advances on the Stability of mRNA Vaccines

Compared to other vaccines, the inherent properties of messenger RNA (mRNA) vaccines and their interaction with lipid nanoparticles make them considerably unstable throughout their life cycles, impacting their effectiveness and global accessibility. It is imperative to improve mRNA vaccine stability and investigate the factors influencing stability. Since mRNA structure, excipients, lipid nanoparticle (LNP) delivery systems, and manufacturing processes are the primary factors affecting mRNA vaccine stability, optimizing mRNA structure and screening excipients can effectively improve mRNA vaccine stability. Moreover, improving manufacturing processes could also prepare thermally stable mRNA vaccines with safety and efficacy. Here, we review the regulatory guidance associated with mRNA vaccine stability, summarize key factors affecting mRNA vaccine stability, and propose a possible research path to improve mRNA vaccine stability.

mRNA in the Context of Protein Replacement Therapy

Protein replacement therapy is an umbrella term used for medical treatments that aim to substitute or replenish specific protein deficiencies that result either from the protein being absent or non-functional due to mutations in affected patients. Traditionally, such an approach requires a well characterized but arduous and expensive protein production procedure that employs in vitro expression and translation of the pharmaceutical protein in host cells, followed by extensive purification steps. In the wake of the SARS-CoV-2 pandemic, mRNA-based pharmaceuticals were recruited to achieve rapid in vivo production of antigens, proving that the in vivo translation of exogenously administered mRNA is nowadays a viable therapeutic option. In addition, the urgency of the situation and worldwide demand for mRNA-based medicine has led to an evolution in relevant technologies, such as in vitro transcription and nanolipid carriers. In this review, we present preclinical and clinical applications of mRNA as a tool for protein replacement therapy, alongside with information pertaining to the manufacture of modified mRNA through in vitro transcription, carriers employed for its intracellular delivery and critical quality attributes pertaining to the finished product.

Liquid Chromatography-Mass Spectrometry-Based Qualitative Profiling of mRNA Therapeutic Reagents Using Stable Isotope-Labeled Standards Followed by the Automatic Quantitation Software Ariadne

mRNA-based medicines are a promising modality for preventing virus-caused illnesses, including COVID-19, and treating various types of cancer and genetic diseases. To develop such medicines, methods to characterize long mRNA molecules are needed for quality control and metabolic analysis. Here, we developed an analytical platform based on isotope-dilution liquid chromatography-mass spectrometry (LC-MS) that quantitatively characterizes long, modified mRNAs by comparing them to a stable isotope-labeled reference with an identical sequence to that of the target medicine. This platform also includes database searching using the mass spectra as a query, which allowed us to confirm the primary structures of 200 to 4300 nt mRNAs including chemical modifications, with sequence coverage at 100%, to detect/identify defects in the sequences, and to define the efficiencies of the 5'-capping and integrity of the polyadenylated tail. Our findings indicated that this platform should be valuable for quantitatively characterizing mRNA vaccines and other mRNA medicines.

Self-amplifying mRNA vaccines: Mode of action, design, development and optimization

The mRNA-based vaccines are quality-by-design (QbD) immunotherapies that provide safe, tunable, scalable, streamlined and potent treatment possibilities against different types of diseases. The self-amplifying mRNA (saRNA) vaccines, as a highly advantageous class of mRNA vaccines, are inspired by the intracellular self-multiplication nature of some positive-sense RNA viruses. Such vaccine platforms provide a relatively increased expression level of vaccine antigen(s) together with self-adjuvanticity properties. Lined with the QbD saRNA vaccines, essential optimizations improve the stability, safety, and immunogenicity of the vaccine constructs. Here, we elaborate on the concepts and mode-of-action of mRNA and saRNA vaccines, articulate the potential limitations or technical bottlenecks, and explain possible solutions or optimization methods in the process of their design and development.

Unlocking the promise of mRNA therapeutics

The extraordinary success of mRNA vaccines against coronavirus disease 2019 (COVID-19) has renewed interest in mRNA as a means of delivering therapeutic proteins. Early clinical trials of mRNA therapeutics include studies of paracrine vascular endothelial growth factor (VEGF) mRNA for heart failure and of CRISPR-Cas9 mRNA for a congenital liver-specific storage disease. However, a series of challenges remains to be addressed before mRNA can be established as a general therapeutic modality with broad relevance to both rare and common diseases. An array of new technologies is being developed to surmount these challenges, including approaches to optimize mRNA cargos, lipid carriers with inherent tissue tropism and in vivo percutaneous delivery systems. The judicious integration of these advances may unlock the promise of biologically targeted mRNA therapeutics, beyond vaccines and other immunostimulatory agents, for the treatment of diverse clinical indications.

mRNA delivery technologies: Toward clinical translation

Messenger RNA (mRNA)-therapies have recently taken a huge step toward clinic thanks to the first mRNA-based medicinal products marketed. mRNA features for clinical purposes are improved by chemical modifications, but the inclusion in a delivery system is a regular requirement. mRNA nanomedicines must be designed for the specific therapeutic purpose, protecting the nucleic acid and facilitating the overcoming of biological barriers. Polymers, polypeptides, and cationic lipids are the main used materials to design mRNA delivery systems. Among them, lipid nanoparticles (LNPs) are the most advanced ones, and currently they are at the forefront of preclinical and clinical evaluation in several fields, including immunotherapy (against infectious diseases and cancer), protein replacement, gene editing and regenerative medicine. This chapter includes an overview on mRNA delivery technologies, with special interest in LNPs, and the most recent advances in their clinical application. Liposomes are the mRNA delivery technology with the highest clinical translation among LNPs, whereas the first clinical trial of a therapeutic mRNA formulated in exosomes has been recently approved for protein replacement therapy. The first mRNA products approved by the regulatory agencies worldwide are LNP-based mRNA vaccines against viral infections, specifically against the 2019 coronavirus disease (COVID-19). The clinical translation of mRNA-therapies for cancer is mainly focused on three strategies: anti-cancer vaccination by means of delivering cancer antigens or acting as an adjuvant, mRNA-engineered chimeric antigen receptors (CARs) and T-cell receptors (TCRs), and expression of antibodies and immunomodulators. Cancer immunotherapy and, more recently, COVID-19 vaccines spearhead the advance of mRNA clinical use.

Novel Mobile Phase to Control Charge States and Metal Adducts in the LC/MS for mRNA Characterization Assays

Mass spectrometry is a widely used tool in the characterization of oligonucleotides. This analysis can be challenging due to the large number of possible charge states of oligonucleotides, which can limit the sensitivity of the assay, along with the propensity of oligonucleotides to readily form adducts with free alkali metals. To reduce the adduct formation, oligonucleotides are typically purified with desalting columns prior to analysis. We have developed a mobile phase that gives superior reduction in charge states and adduct formation compared to previously reported methods and, more importantly, obviates the requirement of desalting samples prior to mass spectrometric analysis, significantly decreasing the sample preparation time and amount of RNA required for analysis. We have applied this mobile phase to develop methods to quantify the 5'-capping efficiency and to characterize the polyadenosine (poly(A)) tail of mRNA synthesized in vitro: two critical quality attributes of mRNA therapeutics. Through this, we were able to demonstrate RNA that was co-transcriptionally capped to have capping efficiency equivalent (the percent total molecules that contain a cap) to other reports in the literature using materials that were generated using the same synthesis procedure. Furthermore, by using a mobile phase mixture comprised of hexafluoroisopropanol, triethylammonium acetate, triethylamine, and ethanol, we were able to determine the size distribution of the poly(A) tail in various mRNA samples from DNA templates that ranged from 50 to 150 nt poly(A) and verify that distribution with commercially available RNA standards, successfully demonstrating that this mobile phase composition could be used for characterization assays for both mRNA caps and tails.

mRNA-based therapeutics: powerful and versatile tools to combat diseases

The therapeutic use of messenger RNA (mRNA) has fueled great hope to combat a wide range of incurable diseases. Recent rapid advances in biotechnology and molecular medicine have enabled the production of almost any functional protein/peptide in the human body by introducing mRNA as a vaccine or therapeutic agent. This represents a rising precision medicine field with great promise for preventing and treating many intractable or genetic diseases. In addition, in vitro transcribed mRNA has achieved programmed production, which is more effective, faster in design and production, as well as more flexible and cost-effective than conventional approaches that may offer. Based on these extraordinary advantages, mRNA vaccines have the characteristics of the swiftest response to large-scale outbreaks of infectious diseases, such as the currently devastating pandemic COVID-19. It has always been the scientists’ desire to improve the stability, immunogenicity, translation efficiency, and delivery system to achieve efficient and safe delivery of mRNA. Excitingly, these scientific dreams have gradually been realized with the rapid, amazing achievements of molecular biology, RNA technology, vaccinology, and nanotechnology. In this review, we comprehensively describe mRNA-based therapeutics, including their principles, manufacture, application, effects, and shortcomings. We also highlight the importance of mRNA optimization and delivery systems in successful mRNA therapeutics and discuss the key challenges and opportunities in developing these tools into powerful and versatile tools to combat many genetic, infectious, cancer, and other refractory diseases.

mRNA vaccines: the most recent clinical applications of synthetic mRNA

Synthetic mRNA has been considered as an emerging biotherapeutic agent for the past decades. Recently, the SARS-CoV-2 pandemic has led to the first clinical use of synthetic mRNA. mRNA vaccines showed far surpassing influences on the public as compared to other vaccine platforms such as viral vector vaccines and recombinant protein vaccines. It allowed rapid development and production of vaccines that have never been achieved in history. Synthetic mRNA, called in vitro transcribed (IVT) mRNA, is the key component of mRNA vaccines. It has several advantages over conventional gene-expressing systems such as plasmid DNA and viral vectors. It can translate proteins in the cytoplasm by structurally resembling natural mRNA and exhibit various protein expression patterns depending on how it is engineered. Another advantage is that synthetic mRNA enables fast, scalable, and cost-effective production. Therefore, starting with the mRNA vaccine, synthetic mRNA is now in the spotlight as a promising new drug development agent. In this review, we will summarize the latest IVT mRNA technology such as new mRNA structures or large-scale production. In addition, the nature of the innate immunogenicity of IVT mRNA will be discussed along with its roles in the development of vaccines. Finally, the principles of the mRNA vaccine and the future direction of synthetic mRNA will be provided.

mRNA- and Adenovirus-Based Vaccines against SARS-CoV-2 in HIV-Positive People

About two years have passed since the identification of SARS-CoV-2 in China. The rapid spread of this virus all over the world and its high transmissibility and pathogenicity in humans have resulted in a global pandemic. The negative impact of COVID-19 on health, society and the economy at the global level has pushed researchers and pharmaceutical companies to develop effective vaccines to fight SARS-CoV-2. Thanks to this collaborative effort, the first COVID-19 vaccine was developed in less than a year. Since then, several COVID-19 vaccines have been validated for use by the World Health Organization. Among these, mRNA- (BNT162b2 and mRNA1273) and adenovirus-based (ChAdOx1) vaccines were developed through the use of novel technologies. While all three of these vaccines have shown effectiveness against the COVID-19 disease and their immunogenicity was characterized in clinical trials in the general population, data on their efficacy and immunogenicity in people living with HIV (PLWH) are limited. In this review, we provide a description of the characteristics of mRNA- and adenovirus-based vaccines and of the immune response elicited in the general population by vaccination. Then we describe the use of these vaccines and their efficacy and immunogenicity in people living with HIV and we conclude with a discussion regarding some open questions concerning the use of mRNA- and adenovirus-based COVID-19 vaccines in PLWH.

Structural Elements of DNA and RNA Eukaryotic Expression Vectors for In Vitro and In Vivo Genome Editor Delivery

Gene editing with programmable nucleases opens new perspectives in important practice areas, such as healthcare and agriculture. The most challenging problem for the safe and effective therapeutic use of gene editing technologies is the proper delivery and expression of gene editors in cells and tissues of different organisms. Virus-based and nonviral systems can be used for the successful delivery of gene editors. Here we have reviewed structural elements of nonviral DNA- and RNA-based expression vectors for gene editing and delivery methods in vitro and in vivo.

mRNA-Based Vaccines and Mode of Action

In the past 20 years, the mRNA vaccine technology has evolved from the first proof of concept to the first licensed vaccine against emerging pandemics such as SARS-CoV-2. Two mRNA vaccines targeting SARS-CoV-2 have received emergency use authorization by US FDA, conditional marketing authorization by EMA, as well as multiple additional national regulatory authorities. The simple composition of an mRNA encoding the antigen formulated in a lipid nanoparticle enables a fast adaptation to new emerging pathogens. This can speed up vaccine development in pandemics from antigen and sequence selection to clinical trial to only a few months. mRNA vaccines are well tolerated and efficacious in animal models for multiple pathogens and will further contribute to the development of vaccines for other unaddressed diseases. Here, we give an overview of the mRNA vaccine design and factors for further optimization of this new promising technology and discuss current knowledge on the mode of action of mRNA vaccines interacting with the innate and adaptive immune system.

mRNA Therapeutic Modalities Design, Formulation and Manufacturing under Pharma 4.0 Principles

In the quest for a formidable weapon against the SARS-CoV-2 pandemic, mRNA therapeutics have stolen the spotlight. mRNA vaccines are a prime example of the benefits of mRNA approaches towards a broad array of clinical entities and druggable targets. Amongst these benefits is the rapid cycle "from design to production" of an mRNA product compared to their peptide counterparts, the mutability of the production line should another target be chosen, the side-stepping of safety issues posed by DNA therapeutics being permanently integrated into the transfected cell's genome and the controlled precision over the translated peptides. Furthermore, mRNA applications are versatile: apart from vaccines it can be used as a replacement therapy, even to create chimeric antigen receptor T-cells or reprogram somatic cells. Still, the sudden global demand for mRNA has highlighted the shortcomings in its industrial production as well as its formulation, efficacy and applicability. Continuous, smart mRNA manufacturing 4.0 technologies have been recently proposed to address such challenges. In this work, we examine the lab and upscaled production of mRNA therapeutics, the mRNA modifications proposed that increase its efficacy and lower its immunogenicity, the vectors available for delivery and the stability considerations concerning long-term storage.

Therapeutic mRNA Engineering from Head to Tail

Synthetic messenger RNA (mRNA), once delivered into cells, can be readily translated into proteins by ribosomes, which do not distinguish exogenous mRNAs from endogenous transcripts. Until recently, the intrinsic instability and immunostimulatory property of exogenous RNAs largely hindered the therapeutic application of synthetic mRNAs. Thanks to major technological innovations, such as introduction of chemically modified nucleosides, synthetic mRNAs have become programmable therapeutic reagents. Compared to DNA or protein-based therapeutic reagents, synthetic mRNAs bear several advantages: flexible design, easy optimization, low-cost preparation, and scalable synthesis. Therapeutic mRNAs are commonly designed to encode specific antigens to elicit organismal immune response to pathogens like viruses, express functional proteins to replace defective ones inside cells, or introduce novel enzymes to achieve unique functions like genome editing. Recent years have witnessed stunning progress on the development of mRNA vaccines against SARS-Cov2. This success is built upon our fundamental understanding of mRNA metabolism and translational control, a knowledge accumulated during the past several decades. Given the astronomical number of sequence combinations of four nucleotides, sequence-dependent control of mRNA translation remains incompletely understood. Rational design of synthetic mRNAs with robust translation and optimal stability remains challenging. Massively paralleled reporter assay (MPRA) has been proven to be powerful in identifying sequence elements in controlling mRNA translatability and stability. Indeed, a completely randomized sequence in 5' untranslated region (5'UTR) drives a wide range of translational outputs. In this Account, we will discuss general principles of mRNA translation in eukaryotic cells and elucidate the role of coding and noncoding regions in the translational regulation. From the therapeutic perspective, we will highlight the unique features of 5' cap, 5'UTR, coding region (CDS), stop codon, 3'UTR, and poly(A) tail. By focusing on the design strategies in mRNA engineering, we hope this Account will contribute to the rational design of synthetic mRNAs with broad therapeutic potential.

Combining an optimized mRNA template with a double purification process allows strong expression of in vitro transcribed mRNA

mRNA is a blooming technology for vaccination and has gained global attention during the SARS-CoV-2 pandemic. However, the recent clinical trials have highlighted increased reactogenicity when using high mRNA doses. Intending to increase the potency of mRNA therapeutics and to decrease the therapeutic dose, we designed a mRNA backbone and optimized the mRNA purification process. We used the enhanced green fluorescent protein (eGFP) reporter gene flanked by one 5′ untranslated region (UTR) and two 3′ UTRs of the human β-globin as a reference mRNA and identified the most promising mRNA sequence using in vitro and in vivo models. First, we assessed the impact of different poly(A) sizes on translation and selected the most optimal sequence. Then, we selected the best 5′ UTR among synthetic sequences displaying a high ribosome loading. Finally, we evaluated the transfection efficiency of our standard mRNA template after two capping strategies and purification using either double-stranded RNA (dsRNA) depletion or dephosphorylation of 5′PPP RNA or both combined. Double purification was shown to give the best results. Altogether, the use of a newly defined 5′ UTR coupled to post-transcriptional treatments will be of great interest in the mRNA vaccine field, by limiting the amount of the antigen-coding transcript and subsequently the formulation components needed for an efficient vaccination.

mRNA - A game changer in regenerative medicine, cell-based therapy and reprogramming strategies

After thirty years of intensive research shaping and optimizing the technology, the approval of the first mRNA-based formulation by the EMA and FDA in order to stop the COVID-19 pandemic was a breakthrough in mRNA research. The astonishing success of these vaccines have brought the mRNA platform into the spotlight of the scientific community. The remarkable persistence of the groundwork is mainly attributed to the exceptional benefits of mRNA application, including the biological origin, immediate but transitory mechanism of action, non-integrative properties, safe and relatively simple manufacturing as well as the flexibility to produce any desired protein. Based on these advantages, a practical implementation of in vitro transcribed mRNA has been considered in most areas of medicine. In this review, we discuss the key preconditions for the rise of the mRNA in the medical field, including the unique structural and functional features of the mRNA molecule and its vehicles, which are crucial aspects for a production of potent mRNA-based therapeutics. Further, we focus on the utility of mRNA tools particularly in the scope of regenerative medicine, i.e. cell reprogramming approaches or manipulation strategies for targeted tissue restoration. Finally, we highlight the strong clinical potential but also the remaining hurdles to overcome for the mRNA-based regenerative therapy, which is only a few steps away from becoming a reality.

Modifications of mRNA vaccine structural elements for improving mRNA stability and translation efficiency

Background

mRNA vaccines hold great potential as therapeutic techniques against viral infections due to their efficacy, safety, and large-scale production. mRNA vaccines offer flexibility in development as any protein can be produced from mRNA without altering the production or application process.

Objective

This review highlights the iterative optimization of mRNA vaccine structural elements that impact the type, specificity, and intensity of immune responses leading to higher translational potency and intracellular stability.

Results

Modifying the mRNA structural elements particularly the 5′ cap, 5′-and 3′-untranslated regions (UTRs), the coding region, and polyadenylation tail help reduce the excessive mRNA immunogenicity and consistently improve its intracellular stability and translational efficiency.

Conclusion

Further studies regarding mRNA-structural elements and their optimization are needed to create new opportunities for engineering mRNA vaccines.

Strategies for controlling the innate immune activity of conventional and self-amplifying mRNA therapeutics: Getting the message across

The recent approval of messenger RNA (mRNA)-based vaccines to combat the SARS-CoV-2 pandemic highlights the potential of both conventional mRNA and self-amplifying mRNA (saRNA) as a flexible immunotherapy platform to treat infectious diseases. Besides the antigen it encodes, mRNA itself has an immune-stimulating activity that can contribute to vaccine efficacy. This self-adjuvant effect, however, will interfere with mRNA translation and may influence the desired therapeutic outcome. To further exploit its potential as a versatile therapeutic platform, it will be crucial to control mRNA's innate immune-stimulating properties. In this regard, we describe the mechanisms behind the innate immune recognition of mRNA and provide an extensive overview of strategies to control its innate immune-stimulating activity. These strategies range from modifications to the mRNA backbone itself, optimization of production and purification processes to the combination with innate immune inhibitors. Furthermore, we discuss the delicate balance of the self-adjuvant effect in mRNA vaccination strategies, which can be both beneficial and detrimental to the therapeutic outcome.

The infinite possibilities of RNA therapeutics

Although the study of ribonucleic acid (RNA) therapeutics started decades ago, for many years, this field of research was overshadowed by the growing interest in DNA-based therapies. Nowadays, the role of several types of RNA in cell regulation processes and the development of various diseases have been elucidated, and research in RNA therapeutics is back with force. This short literature review aims to present general aspects of many of the molecules currently used in RNA therapeutics, including in vitro transcribed mRNA (IVT mRNA), antisense oligonucleotides (ASOs), aptamers, small interfering RNAs (siRNAs), and microRNAs (miRNAs). In addition, we describe the state of the art of technologies applied for synthetic RNA manufacture and delivery. Likewise, we detail the RNA-based therapies approved by the FDA so far, as well as the ongoing clinical investigations. As a final point, we highlight the current and potential advantages of working on RNA-based therapeutics and how these could lead to a new era of accessible and personalized healthcare.

Engineering of the current nucleoside-modified mRNA-LNP vaccines against SARS-CoV-2

Currently, there are over 230 different COVID-19 vaccines under development around the world. At least three decades of scientific development in RNA biology, immunology, structural biology, genetic engineering, chemical modification, and nanoparticle technologies allowed the accelerated development of fully synthetic messenger RNA (mRNA)-based vaccines within less than a year since the first report of a SARS-CoV-2 infection. mRNA-based vaccines have been shown to elicit broadly protective immune responses, with the added advantage of being amenable to rapid and flexible manufacturing processes. This review recapitulates current advances in engineering the first two SARS-CoV-2-spike-encoding nucleoside-modified mRNA vaccines, highlighting the strategies followed to potentiate their effectiveness and safety, thus facilitating an agile response to the current COVID-19 pandemic.

The Ins and Outs of Messenger RNA Electroporation for Physical Gene Delivery in Immune Cell-Based Therapy

Messenger RNA (mRNA) electroporation is a powerful tool for transient genetic modification of cells. This non-viral method of genetic engineering has been widely used in immunotherapy. Electroporation allows fine-tuning of transfection protocols for each cell type as well as introduction of multiple protein-coding mRNAs at once. As a pioneering group in mRNA electroporation, in this review, we provide an expert overview of the ins and outs of mRNA electroporation, discussing the different parameters involved in mRNA electroporation as well as the production of research-grade and production and application of clinical-grade mRNA for gene transfer in the context of cell-based immunotherapies.

Self-assembled mRNA vaccines

mRNA vaccines have evolved from being a mere curiosity to emerging as COVID-19 vaccine front-runners. Recent advancements in the field of RNA technology, vaccinology, and nanotechnology have generated interest in delivering safe and effective mRNA therapeutics. In this review, we discuss design and self-assembly of mRNA vaccines. Self-assembly, a spontaneous organization of individual molecules, allows for design of nanoparticles with customizable properties. We highlight the materials commonly utilized to deliver mRNA, their physicochemical characteristics, and other relevant considerations, such as mRNA optimization, routes of administration, cellular fate, and immune activation, that are important for successful mRNA vaccination. We also examine the COVID-19 mRNA vaccines currently in clinical trials. mRNA vaccines are ready for the clinic, showing tremendous promise in the COVID-19 vaccine race, and have pushed the boundaries of gene therapy.

In vitro transcribed mRNA for expression of designer nucleases: Advantages as a novel therapeutic for the management of chronic HBV infection

Chronic infection with the hepatitis B virus (HBV) remains a significant worldwide medical problem. While diseases caused by HIV infection, tuberculosis and malaria are on the decline, new cases of chronic hepatitis B are on the rise. Because often fatal complications of cirrhosis and hepatocellular carcinoma are associated with chronic hepatitis B, the need for a cure is as urgent as ever. Currently licensed therapeutics fail to eradicate the virus and this is attributable to persistence of the viral replication intermediate comprising covalently closed circular DNA (cccDNA). Elimination or inactivation of the viral cccDNA is thus a goal of research aimed at hepatitis B cure. The ability to engineer nucleases that are capable of specific cleavage of a DNA sequence now provides the means to disable cccDNA permanently. The scientific literature is replete with many examples of using designer zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) and RNA-guided endonucleases (RGENs) to inactivate HBV. However, important concerns about safety, dose control and efficient delivery need to be addressed before the technology is employed in a clinical setting. Use of in vitro transcribed mRNA to express therapeutic gene editors goes some way to overcoming these concerns. The labile nature of RNA limits off-target effects and enables dose control. Compatibility with hepatotropic non-viral vectors is convenient for the large scale preparation that will be required for advancing gene editing as a mode of curing chronic hepatitis B.

mRNA Vaccine Era-Mechanisms, Drug Platform and Clinical Prospection

Messenger ribonucleic acid (mRNA)-based drugs, notably mRNA vaccines, have been widely proven as a promising treatment strategy in immune therapeutics. The extraordinary advantages associated with mRNA vaccines, including their high efficacy, a relatively low severity of side effects, and low attainment costs, have enabled them to become prevalent in pre-clinical and clinical trials against various infectious diseases and cancers. Recent technological advancements have alleviated some issues that hinder mRNA vaccine development, such as low efficiency that exist in both gene translation and in vivo deliveries. mRNA immunogenicity can also be greatly adjusted as a result of upgraded technologies. In this review, we have summarized details regarding the optimization of mRNA vaccines, and the underlying biological mechanisms of this form of vaccines. Applications of mRNA vaccines in some infectious diseases and cancers are introduced. It also includes our prospections for mRNA vaccine applications in diseases caused by bacterial pathogens, such as tuberculosis. At the same time, some suggestions for future mRNA vaccine development about storage methods, safety concerns, and personalized vaccine synthesis can be found in the context.

Nanomedicine-Based Approaches for mRNA Delivery

Messenger RNA (mRNA) has immense potential for developing a wide range of therapies, including immunotherapy and protein replacement. As mRNA presents no risk of integration into the host genome and does not require nuclear entry for transfection, which allows protein production even in nondividing cells, mRNA-based approaches can be envisioned as safe and practical therapeutic strategies. Nevertheless, mRNA presents unfavorable characteristics, such as large size, immunogenicity, limited cellular uptake, and sensitivity to enzymatic degradation, which hinder its use as a therapeutic agent. While mRNA stability and immunogenicity have been ameliorated by direct modifications on the mRNA structure, further improvements in mRNA delivery are still needed for promoting its activity in biological settings. In this regard, nanomedicine has shown the ability for spatiotemporally controlling the function of a myriad of bioactive agents in vivo. Direct engineering of nanomedicine structures for loading, protecting, and releasing mRNA and navigating in biological environments can then be applied for promoting mRNA translation toward the development of effective treatments. Here, we review recent approaches aimed at enhancing mRNA function and its delivery through nanomedicines, with particular emphasis on their applications and eventual clinical translation.

Co-delivery of NS1 and BMP2 mRNAs to murine pluripotent stem cells leads to enhanced BMP-2 expression and osteogenic differentiation

Application of messenger RNA (mRNA) for bone regeneration is a promising alternative to DNA, recombinant proteins and peptides. However, exogenous in vitro transcribed mRNA (IVT mRNA) triggers innate immune response resulting in mRNA degradation and translation inhibition. Inspired by the ability of viral immune evasion proteins to inhibit host cell responses against viral RNA, we applied non-structural protein-1 (NS1) from Influenza A virus (A/Texas/36/1991) as an IVT mRNA enhancer. We evidenced a dose-dependent blocking of RNA sensors by NS1 expression. The co-delivery of NS1 mRNA with mRNA of reporter genes significantly increased the translation efficiency. Interestingly, unlike the use of nucleosides modification, NS1-mediated mRNA translation enhancement does not dependent to cell type. Dual delivery of NS1 mRNA and BMP-2 mRNA to murine pluripotent stem cells (C3H10T1/2), promoted osteogenic differentiation evidenced by enhanced expression of osteoblastic markers (e.g. alkaline phosphatase, type I collagen, osteopontin, and osteocalcin), and extracellular mineralization. Overall, these results support the adjuvant potentiality of NS1 for mRNA-based regenerative therapies. STATEMENT OF SIGNIFICANCE: mRNA therapy has the potential to improve the efficiency of nucleic acid based regenerative medicine. Up to now, the incorporation of expensive modified nucleotides is a common way to avoid IVT mRNA-induced detrimental immunogenicity. We here introduce co-delivery of Influenza virus immune evasion protein-NS1 coding mRNA as a strategy to suppress RNA sensors for maximizing IVT mRNA expression. An increased osteogenic commitment of pluripotent stem cells was observed after BMP2 mRNA and NS1 mRNA delivery. This study revealed how applying non-modified mRNA with NS1 could be a promising alternative as a therapeutic in bone regeneration.

Tailoring mRNA Vaccine to Balance Innate/Adaptive Immune Response

mRNA vaccine platforms present numerous advantages, such as versatility, rapid production, and induction of cellular and humoral responses. Moreover, mRNAs have inherent adjuvant properties due to their complex interaction with pattern recognition receptors (PRRs). This recognition can be either beneficial in activating antigen-presenting cells (APCs) or detrimental by indirectly blocking mRNA translation. To decipher this Janus effect, we describe the different innate response mechanisms triggered by mRNA molecules and how each element from the 5' cap to the poly-A tail interferes with innate/adaptive immune responses. Then, we emphasize the importance of some critical steps such as production, purification, and formulation as key events to further improve the quality of immune responses and balance innate and adaptive immunity.

A convenient method to generate and maintain poly(A)-encoding DNA sequences required for in vitro transcription of mRNA

Generating mRNA in vitro to encode therapeutic or cell-modifying proteins is rapidly gaining favor. An important factor that determines efficiency of translation from in vitro transcribed mRNA is the length of the 3' poly(A) sequence. However, reproducibly generating and maintaining templates from circular plasmids to have consistent lengths of the homo poly(A) sequences is challenging. The procedure reported here entails repeated restriction digestion with type IIS enzymes, ligation and circular plasmid propagation. The homopolymeric sequence of approximately 100 bp that is generated using the method is approximately equal to the number of 3' A residues found in the mRNA of  mammalian cells. Evaluating expression in vivo of a reporter transcript produced using this method showed efficient expression in vivo.

Segmented poly(A) tails significantly reduce recombination of plasmid DNA without affecting mRNA translation efficiency or half-life

Extensive research in the past decade has brought mRNA closer to the clinical realization of its therapeutic potential. One common structural feature for all cellular messenger RNAs is a poly(A) tail, which can either be brought in cotranscriptionally via the DNA template (plasmid- or PCR-based) or added to the mRNA in a post-transcriptional enzymatic process. Plasmids containing poly(A) regions recombine in E. coli, resulting in extensive shortening of the poly(A) tail. Using a segmented poly(A) approach, we could significantly reduce recombination of plasmids in E. coli without any negative effect on mRNA half-life and protein expression. This effect was independent of the coding sequence. A segmented poly(A) tail is characterized in that it consists of at least two A-containing elements, each defined as a nucleotide sequence consisting of 40-60 adenosines, separated by a spacer element of different length. Furthermore, reducing the spacer length between the poly(A) segments resulted in higher translation efficiencies compared to homogeneous poly(A) tail and reduced recombination (depending upon the choice of spacer nucleotide). Our results demonstrate the superior potential of segmented poly(A) tails compared to the conventionally used homogeneous poly(A) tails with respect to recombination of the plasmids and the resulting mRNA performance (half-life and translational efficiency).

TALEN-Mediated Gene Editing of HBG in Human Hematopoietic Stem Cells Leads to Therapeutic Fetal Hemoglobin Induction

Elements within the γ-hemoglobin promoters (HBG1 and HBG2) function to bind transcription complexes that mediate repression of fetal hemoglobin expression. Sickle cell disease (SCD) subjects with a 13-bp deletion in the HBG1 promoter exhibit a clinically favorable hereditary persistence of fetal hemoglobin (HPFH) phenotype. We developed TALENs targeting the homologous HBG promoters to de-repress fetal hemoglobin. Transfection of human CD34⁺ cells with TALEN mRNA resulted in indel generation in HBG1 (43%) and HBG2 (74%) including the 13-bp HPFH deletion (∼6%). Erythroid differentiation of edited cells revealed a 4.6-fold increase in γ-hemoglobin expression as detected by HPLC. Assessment of TALEN-edited CD34⁺ cells in vivo in a humanized mouse model demonstrated sustained presence of indels in hematopoietic cells up to 24 weeks. Indel rates remained unchanged following secondary transplantation consistent with editing of long-term repopulating stem cells (LT-HSCs). Human γ-hemoglobin expressing F cells were detected by flow cytometry approximately 50% more frequently in edited animals compared to mock. Together, these findings demonstrate that TALEN-mediated indel generation in the γ-hemoglobin promoter leads to high levels of fetal hemoglobin expression in vitro and in vivo, suggesting that this approach can provide therapeutic benefit in patients with SCD or β-thalassemia.

Biomedical applications of mRNA nanomedicine

As an attractive alternative to plasmid DNA, messenger RNA (mRNA) has recently emerged as a promising class of nucleic acid therapeutics for biomedical applications. Advances in addressing the inherent shortcomings of mRNA and in the development of nanoparticle-based delivery systems have prompted the development and clinical translation of mRNA-based medicines. In this review, we discuss the chemical modification strategies of mRNA to improve its stability, minimize immune responses, and enhance translational efficacy. We also highlight recent progress in nanoparticle-based mRNA delivery. Considerable attention is given to the increasingly widespread applications of mRNA nanomedicine in the biomedical fields of vaccination, protein-replacement therapy, gene editing, and cellular reprogramming and engineering.

Poly A tail length analysis of in vitro transcribed mRNA by LC-MS

The 3'-polyadenosine (poly A) tail of in vitro transcribed (IVT) mRNA was studied using liquid chromatography coupled to mass spectrometry (LC-MS). Poly A tails were cleaved from the mRNA using ribonuclease T1 followed by isolation with dT magnetic beads. Extracted tails were then analyzed by LC-MS which provided tail length information at single-nucleotide resolution. A 2100-nt mRNA with plasmid-encoded poly A tail lengths of either 27, 64, 100, or 117 nucleotides was used for these studies as enzymatically added poly A tails showed significant length heterogeneity. The number of As observed in the tails closely matched Sanger sequencing results of the DNA template, and even minor plasmid populations with sequence variations were detected. When the plasmid sequence contained a discreet number of poly As in the tail, analysis revealed a distribution that included tails longer than the encoded tail lengths. These observations were consistent with transcriptional slippage of T7 RNAP taking place within a poly A sequence. The type of RNAP did not alter the observed tail distribution, and comparison of T3, T7, and SP6 showed all three RNAPs produced equivalent tail length distributions. The addition of a sequence at the 3' end of the poly A tail did, however, produce narrower tail length distributions which supports a previously described model of slippage where the 3' end can be locked in place by having a G or C after the poly nucleotide region. Graphical abstract Determination of mRNA poly A tail length using magnetic beads and LC-MS.

A Nonhuman Primate Transplantation Model to Evaluate Hematopoietic Stem Cell Gene Editing Strategies for β-Hemoglobinopathies

Reactivation of fetal hemoglobin (HbF) is a promising approach for the treatment of β-hemoglobinopathies and the targeting of genes involved in HbF regulation is under intensive investigation. Here, we established a nonhuman primate (NHP) transplantation model to evaluate hematopoietic stem cell (HSC)-based gene editing strategies aimed at reactivating HbF. We first characterized the transient HbF induction to autologous HSC transplantation in pigtailed macaques, which was comparable in duration and amplitude to that of human patients. After validating function of the HbF repressor BCL11A in NHPs, we transplanted a pigtailed macaque with CD34⁺ cells electroporated with TALE nuclease mRNA targeting the BCL11A coding sequence. In vivo gene editing levels were low, but some BCL11A deletions were detected as late as 200 days post-transplantation. HbF production, as determined by F-cell staining and γ-globin expression, was slightly increased in this animal as compared to transplant controls. We also provided proof-of-concept results for the selection of edited NHP CD34⁺ cells in culture following integration of the P140K/MGMT cassette at the BCL11A locus. In summary, the NHP model described here will allow the testing of novel therapeutic approaches for hemoglobinopathies and should facilitate clinical translation.

Homology-Directed Recombination for Enhanced Engineering of Chimeric Antigen Receptor T Cells

Gene editing by homology-directed recombination (HDR) can be used to couple delivery of a therapeutic gene cassette with targeted genomic modifications to generate engineered human T cells with clinically useful profiles. Here, we explore the functionality of therapeutic cassettes delivered by these means and test the flexibility of this approach to clinically relevant alleles. Because CCR5-negative T cells are resistant to HIV-1 infection, CCR5-negative anti-CD19 chimeric antigen receptor (CAR) T cells could be used to treat patients with HIV-associated B cell malignancies. We show that targeted delivery of an anti-CD19 CAR cassette to the CCR5 locus using a recombinant AAV homology template and an engineered megaTAL nuclease results in T cells that are functionally equivalent, in both in vitro and in vivo tumor models, to CAR T cells generated by random integration using lentiviral delivery. With the goal of developing off-the-shelf CAR T cell therapies, we next targeted CARs to the T cell receptor alpha constant (TRAC) locus by HDR, producing TCR-negative anti-CD19 CAR and anti-B cell maturation antigen (BCMA) CAR T cells. These novel cell products exhibited in vitro cytolytic activity against both tumor cell lines and primary cell targets. Our combined results indicate that high-efficiency HDR delivery of therapeutic genes may provide a flexible and robust method that can extend the clinical utility of cell therapeutics.