Generation of Immunostimulating 130 nm Protamine-RNA nanoparticles

DNA-protamine condensates under low salt conditions: molecular dynamics simulation with a simple coarse-grained model focusing on electrostatic interactions

Protamine, a small, strongly positively-charged protein, plays a key role in achieving chromatin condensation inside sperm cells and is also involved in the formulation of nanoparticles for gene therapy and packaging of mRNA-based vaccines against viral infection and cancer. The detailed mechanisms of such condensations are still poorly understood especially under low salt conditions where electrostatic interaction predominates. Our previous study, with a refined coarse-grained model in full consideration of the long-range electrostatic interactions, has demonstrated the crucial role of electrostatic interaction in protamine-controlled reversible DNA condensation. Therefore, we herein pay our attention only to the electrostatic interaction and devise a coarser-grained bead-spring model representing the right linear charge density on protamine and DNA chains but treating other short-range interactions as simply as possible, which would be suitable for real-scale simulations. Effective pair potential calculations and large-scale molecular dynamics simulations using this extremely simple model reproduce the phase behaviour of DNA in a wide range of protamine concentrations under low salt conditions, again revealing the importance of the electrostatic interaction in this process and providing a detailed nanoscale picture of bundle formation mediated by a charge disproportionation mechanism. Our simulations also show that protamine length alters DNA overcharging and in turn redissolution thresholds of DNA condensates, revealing the important role played by entropies and correlated fluctuations of condensing agents and thus offering an additional opportunity to design tailored nanoparticles for gene therapy. The control mechanism of DNA-protamine condensates will also provide a better microscopic picture of biomolecular condensates, i.e., membraneless organelles arising from liquid-liquid phase separation, that are emerging as key principles of intracellular organization. Such condensates controlled by post-translational modification of protamine, in particular phosphorylation, or by variations in protamine length from species to species may also be responsible for the chromatin-nucleoplasm patterning observed during spermatogenesis in several vertebrate and invertebrate species.

Nonreplicating synthetic mRNA vaccines: A journey through the European (Journal of Immunology) history

The first worldwide article reporting that injections of synthetic nonreplicating mRNA could be used as a vaccine, which originated from a French team located in Paris, was published in the European Journal of Immunology (EJI) in 1993. It relied on work conducted by several research groups in a handful of countries since the 1960s, which put forward the precise description of eukaryotic mRNA and the method to reproduce this molecule in vitro as well as how to transfect it into mammalian cells. Thereafter, the first industrial development of this technology began in Germany in 2000, with the founding of CureVac, which stemmed from another description of a synthetic mRNA vaccine published in EJI in 2000. The first clinical studies investigating mRNA vaccines in humans were performed as collaboration between CureVac and the University of Tübingen in Germany as early as 2003. Finally, the first worldwide approved mRNA vaccine (an anti-COVID-19 vaccine) is based on the mRNA technologies developed by BioNTech since its 2008 foundation in Mainz, Germany, and earlier by the pioneering academic work of its founders. In addition to the past, present, and future of mRNA-based vaccines, the article aims to present the geographical distribution of the early work, how the development of the technology was implemented by several independent and internationally distributed research teams, as well as the controversies on the optimal way to design or formulate and administer mRNA vaccines.

Cationic Polymers as Transfection Reagents for Nucleic Acid Delivery

Nucleic acid therapy can achieve lasting and even curative effects through gene augmentation, gene suppression, and genome editing. However, it is difficult for naked nucleic acid molecules to enter cells. As a result, the key to nucleic acid therapy is the introduction of nucleic acid molecules into cells. Cationic polymers are non-viral nucleic acid delivery systems with positively charged groups on their molecules that concentrate nucleic acid molecules to form nanoparticles, which help nucleic acids cross barriers to express proteins in cells or inhibit target gene expression. Cationic polymers are easy to synthesize, modify, and structurally control, making them a promising class of nucleic acid delivery systems. In this manuscript, we describe several representative cationic polymers, especially biodegradable cationic polymers, and provide an outlook on cationic polymers as nucleic acid delivery vehicles.

mRNA vaccines in the prevention and treatment of diseases

Messenger ribonucleic acid (mRNA) vaccines made their successful public debut in the effort against the COVID-19 outbreak starting in late 2019, although the history of mRNA vaccines can be traced back decades. This review provides an overview to discuss the historical course and present situation of mRNA vaccine development in addition to some basic concepts that underly mRNA vaccines. We discuss the general preparation and manufacturing of mRNA vaccines and also discuss the scientific advances in the in vivo delivery system and evaluate popular approaches (i.e., lipid nanoparticle and protamine) in detail. Next, we highlight the clinical value of mRNA vaccines as potent candidates for therapeutic treatment and discuss clinical progress in the treatment of cancer and coronavirus disease 2019. Data suggest that mRNA vaccines, with several prominent advantages, have achieved encouraging results and increasing attention due to tremendous potential in disease management. Finally, we suggest some potential directions worthy of further investigation and optimization. In addition to basic research, studies that help to facilitate storage and transportation will be indispensable for practical applications.

Epitranscriptomics modifier pentostatin indirectly triggers Toll-like receptor 3 and can enhance immune infiltration in tumors

The adenosine deaminase inhibitor 2'-deoxycoformycin (pentostatin, Nipent) has been used since 1982 to treat leukemia and lymphoma, but its mode of action is still unknown. Pentostatin was reported to decrease methylation of cellular RNA. We discovered that RNA extracted from pentostatin-treated cells or mice has enhanced immunostimulating capacities. Accordingly, we demonstrated in mice that the anticancer activity of pentostatin required Toll-like receptor 3, the type I interferon receptor, and T cells. Upon systemic administration of pentostatin, type I interferon is produced locally in tumors, resulting in immune cell infiltration. We combined pentostatin with immune checkpoint inhibitors and observed synergistic anti-cancer activities. Our work identifies pentostatin as a new class of an anticancer immunostimulating drug that activates innate immunity within tumor tissues and synergizes with systemic T cell therapies.

Functional differences between protamine preparations for the transfection of mRNA

Protamine is a natural cationic peptide mixture used as a drug for the neutralization of heparin and in formulations of slow-release insulin. In addition, Protamine can be used for the stabilization and delivery of nucleic acids (antisense, small interfering RNA (siRNA), immunostimulatory nucleic acids, plasmid DNA, or messenger RNA) and is therefore included in several compositions that are in clinical development. Notably, when mixed with RNA, protamine spontaneously generates particles in the size range of 20-1000 nm depending on the formulation conditions (concentration of the reagents, ratio, and presence of salts). These particles are being used for vaccination and immuno-stimulation. Several grades of protamine are available, and we compared them in the context of complex formation with messenger RNA (mRNA). We found that the different available protamine preparations largely vary in their composition and capacity to transfect mRNA. Our data point to the source of protamine as an important parameter for the production of therapeutic protamine-based complexes.

Lipofection with Synthetic mRNA as a Simple Method for T-Cell Immunomonitoring

The quantification of T-cell immune responses is crucial for the monitoring of natural and treatment-induced immunity, as well as for the validation of new immunotherapeutic approaches. The present study presents a simple method based on lipofection of synthetic mRNA in mononuclear cells as a method to determine in vitro T-cell responses. We compared several commercially available transfection reagents for their potential to transfect mRNA into human peripheral blood mononuclear cells and murine splenocytes. We also investigated the impact of RNA modifications in improving this method. Our results demonstrate that antigen-specific T-cell immunomonitoring can be easily and quickly performed by simple lipofection of antigen-coding mRNA in complex immune cell populations. Thus, our work discloses a convenient solution for the in vitro monitoring of natural or therapy-induced T-cell immune responses.

Protamine-Based Strategies for RNA Transfection

Protamine is a natural cationic peptide mixture mostly known as a drug for the neutralization of heparin and as a compound in formulations of slow-release insulin. Protamine is also used for cellular delivery of nucleic acids due to opposite charge-driven coupling. This year marks 60 years since the first use of Protamine as a transfection enhancement agent. Since then, Protamine has been broadly used as a stabilization agent for RNA delivery. It has also been involved in several compositions for RNA-based vaccinations in clinical development. Protamine stabilization of RNA shows double functionality: it not only protects RNA from degradation within biological systems, but also enhances penetration into cells. A Protamine-based RNA delivery system is a flexible and versatile platform that can be adjusted according to therapeutic goals: fused with targeting antibodies for precise delivery, digested into a cell penetrating peptide for better transfection efficiency or not-covalently mixed with functional polymers. This manuscript gives an overview of the strategies employed in protamine-based RNA delivery, including the optimization of the nucleic acid's stability and translational efficiency, as well as the regulation of its immunostimulatory properties from early studies to recent developments.

Establishing Preferred Product Characterization for the Evaluation of RNA Vaccine Antigens

The preferred product characteristics (for chemistry, control, and manufacture), in addition to safety and efficacy, are quintessential requirements for any successful therapeutic. Messenger RNA vaccines constitute a relatively new alternative to traditional vaccine development platforms, and thus there is less clarity regarding the criteria needed to ensure regulatory compliance and acceptance. Generally, to identify the ideal product characteristics, a series of assays needs to be developed, qualified and ultimately validated to determine the integrity, purity, stability, and reproducibility of a vaccine target. Here, using the available literature, we provide a summary of the array of biophysical and biochemical assays currently used in the field to characterize mRNA vaccine antigen candidates. Moreover, we review various in vitro functional cell-based assays that have been employed to facilitate the early assessment of the biological activity of these molecules, including the predictive immune response triggered in the host cell. Messenger RNA vaccines can be produced rapidly and at large scale, and thus will particularly benefit from well-defined and well-characterized assays ultimately to be used for in-process, release and stability-indications, which will allow equally rapid screening of immunogenicity, efficacy, and safety without the need to conduct often lengthy and costly in vivo experiments.