Self-amplifying mRNA bicistronic influenza vaccines raise cross-reactive immune responses in mice and prevent infection in ferrets

Clade 2.3.4.4b highly pathogenic avian influenza H5N1 viruses: knowns, unknowns, and challenges

Since 2020, the clade 2.3.4.4b highly pathogenic avian influenza (HPAI) H5N1 viruses have caused unprecedented outbreaks in wild birds and domestic poultry globally, resulting in significant ecological damage and economic losses due to the disease and enforced stamp-out control. In addition to the avian hosts, the H5N1 viruses have expanded their host range to infect many mammalian species, potentially increasing the zoonotic risk. Here, we review the current knowns and unknowns of clade 2.3.4.4b HPAI H5N1 viruses, and we highlight common challenges in prevention. By integrating our knowledge of viral evolution and ecology, we aim to identify discrepancies and knowledge gaps for a more comprehensive understanding of the virus. Ultimately, this review will serve as a theoretical foundation for researchers involved in related avian influenza virus studies, aiding in improved control and prevention of H5N1 viruses.

The advent of clinical self-amplifying RNA vaccines

Self-amplifying RNA (saRNA) technology is an emerging platform for vaccine development, offering significant advantages over conventional mRNA vaccines. By enabling intracellular amplification of RNA, saRNA facilitates robust antigen expression at lower doses, thereby enhancing both immunogenicity and cost-effectiveness. This review examines the latest advancements in saRNA vaccine development, highlighting its applications in combating infectious diseases. This includes viral pathogens such as SARS-CoV-2, influenza, and emerging zoonotic threats. We discuss the design and optimization of saRNA vectors to maximize antigen expression while minimizing adverse immune responses. Recent studies demonstrating the safety, efficacy, and scalability of saRNA-based vaccines in clinical settings are also discussed. We address challenges related to delivery systems, stability, and manufacturing, along with novel strategies being developed to mitigate these challenges. As the global demand for rapid, flexible, and scalable vaccine platforms grows, saRNA presents a promising solution with enhanced potency and durability. This review emphasizes the transformative potential of saRNA vaccines to shape the future of immunization strategies, particularly in response to pandemics and other global health threats.

Clinical development of therapeutic mRNA applications

mRNA therapeutics are emerging as a transformative approach in modern medicine, providing innovative, highly adaptable solutions for a wide range of diseases, from viral infections to cancer. Since the approval of the first mRNA therapeutic-the coronavirus disease 2019 vaccines in 2021-we have identified more than 70 current clinical trials utilizing mRNA for various diseases. We propose classifying mRNA therapeutics into four main categories: vaccines, protein replacement therapies, antibodies, and mRNA-based cell and gene therapies. Each category can be further divided into subcategories. Vaccines include those targeting viral antigens, bacterial or parasitic antigens, general and individualized cancer antigens, and self-antigens. Protein replacement therapies include maintenance therapeutics designed to treat genetic disorders and interventional therapeutics, where delivering therapeutic proteins could improve patient outcomes, such as vascular endothelial growth factor A for ischemic heart disease or proinflammatory cytokines in cancer. Therapeutic antibodies are based on mRNA sequences encoding the heavy and light chains of clinically relevant antibodies, enabling patient cells to produce them directly, bypassing the costly and complex process of manufacturing protein-ready antibodies. Another category of mRNA-based therapeutics encompasses cell and gene therapies, including CRISPR with mRNA-mediated delivery of Cas9 and the in vivo generation of cells expressing CAR through mRNA. We discuss examples of mRNA therapeutics currently in clinical trials within each category, providing a comprehensive overview of the field's progress and highlighting key advancements as of the end of 2024.

Safety and immunogenicity of an optimized self-replicating RNA platform for low dose or single dose vaccine applications: a randomized, open label Phase I study in healthy volunteers

Self-replicating RNA (srRNA) technology, in comparison to mRNA vaccines, has shown dose-sparing by approximately 10-fold and more durable immune responses. However, no improvements are observed in the adverse events profile. Here, we develop an srRNA vaccine platform with optimized non-coding regions and demonstrate immunogenicity and safety in preclinical and clinical development. Optimized srRNA vaccines generate protective immunity (according to the WHO defined thresholds) at doses up to 1,000,000-fold lower than mRNA in female mouse models of influenza and rabies. Clinically, safety and immunogenicity of RBI-4000, an srRNA vector encoding the rabies glycoprotein, was evaluated in a Phase I study (NCT06048770). RBI-4000 was able to elicit de novo protective immunity in the majority of healthy participants when administered at a dose of 0.1, 1, or 10 microgram (71%, 94%, 100%, respectively) in a prime-boost schedule. Similarly, we observe immunity above the WHO benchmark of protection following a single administration in most participants at both 1 and 10 microgram doses. There are no serious adverse events reported across all cohorts. These data establish the high therapeutic index of optimized srRNA vectors, demonstrating feasibility of both low dose and single dose approaches for vaccine applications.

An influenza mRNA vaccine protects ferrets from lethal infection with highly pathogenic avian influenza A(H5N1) virus

The global spread of the highly pathogenic avian influenza (HPAI) A(H5N1) virus poses a serious pandemic threat, necessitating the swift development of effective vaccines. The success of messenger RNA (mRNA) vaccine technology in the COVID-19 pandemic, marked by its rapid development and scalability, demonstrates its potential for addressing other infectious threats, such as HPAI A(H5N1). We therefore evaluated mRNA vaccine candidates targeting panzootic influenza A(H5) clade 2.3.4.4b viruses, which have been shown to infect a range of mammalian species, including most recently being detected in dairy cattle. Ferrets were immunized with mRNA vaccines encoding either hemagglutinin alone or hemagglutinin and neuraminidase, derived from a 2.3.4.4b prototype vaccine virus recommended by the World Health Organization. Kinetics of the immune responses, as well as protection against a lethal challenge dose of A(H5N1) virus, were assessed. Two doses of mRNA vaccination elicited robust neutralizing antibody titers against a 2022 avian isolate and a 2024 human isolate. Further, mRNA vaccination conferred protection from lethal challenge, whereas all unvaccinated ferrets succumbed to infection. It also reduced viral titers in the upper and lower respiratory tracts of infected ferrets. These results underscore the effectiveness of mRNA vaccines against HPAI A(H5N1), showcasing their potential as a vaccine platform for future influenza pandemics.

Avian Influenza Virus A(H5Nx) and Prepandemic Candidate Vaccines: State of the Art

Avian influenza virus has been long considered the main threat for a future pandemic. Among the possible avian influenza virus subtypes, A(H5N1) clade 2.3.4.4b is becoming enzootic in mammals, representing an alarming step towards a pandemic. In particular, genotype B3.13 has recently caused an outbreak in US dairy cattle. Since pandemic preparedness is largely based on the availability of prepandemic candidate vaccine viruses, in this review we will summarize the current status of the enzootics, and challenges for H5 vaccine manufacturing and delivery.

Polymeric nanoparticle-based mRNA vaccine is protective against influenza virus infection in ferrets

New therapies and vaccines based on nucleic acids combined with an efficient nanoparticle delivery vehicle have a broad applicability for different disease indications. An alternative delivery technology for the successfully applied lipid nanoparticles in mRNA SARS-CoV-2 vaccines are nanoparticles composed of biodegradable poly(amido)amine-based polymers with mRNA payload. To show that these polymeric nanoparticles can efficiently deliver influenza hemagglutinin mRNA to target tissues and elicit protective immune responses, a relevant ferret influenza challenge model was used. In this model, our nanoparticle-based vaccine elicited strong humoral and cellular immune responses in the absence of local and systemic reactogenicity. Upon virus challenge, vaccinated animals exhibited reduced clinical signs and virus load relative to unvaccinated control animals. Based on these findings, further investigation of the polymeric nanoparticles in the context of prophylactic vaccination is warranted. Future studies will focus on optimizing the payload, the nanoparticle stability, the efficacy in the context of pre-existing immunity, and the applicability of the technology to prevent other infectious diseases.

An antibody-free evaluation of an mRNA COVID-19 vaccine

This manuscript describes the use of an analytical assay that combines transfection of mammalian cells and isotope dilution mass spectrometry (IDMS) for accurate quantification of antigen expression. Expired mRNA COVID-19 vaccine material was stored at 4 °C, room temperature (∼25 °C), and 56 °C over a period of 5 weeks. The same vaccine was also exposed to 5 freeze-thaw cycles. Every week, the spike protein antigenic expression in mammalian (BHK-21) cells was evaluated. Housekeeping proteins, β-actin and GAPDH, were simultaneously quantified to account for the variation in cell counts that occurs during maintenance and growth of cell cultures. Data show that vaccine stored at elevated temperatures results in reduced spike protein expression. Also, maintaining the vaccine in ultracold conditions or exposing the vaccine to freeze-thaw cycles had less effect on the vaccine's ability to produce the antigen in mammalian cells. We describe the use of IDMS as an antibody-free means to accurately quantify expressed protein from mammalian cells transfected with mRNA vaccine.

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.

Self-amplifying mRNA seasonal influenza vaccines elicit mouse neutralizing antibody and cell-mediated immunity and protect ferrets

Currently licensed influenza vaccines focus immune responses on viral hemagglutinin (HA), while the other major surface glycoprotein neuraminidase (NA) is not tightly controlled in inactivated vaccine formulations despite evidence that anti-NA antibodies reduce clinical disease. We utilized a bicistronic self-amplifying mRNA (sa-mRNA) platform encoding both HA and NA from four seasonal influenza strains, creating a quadrivalent influenza vaccine. sa-mRNA vaccines encoding an NA component induced the production of NA-inhibiting antibodies and CD4+ T-cell responses in both monovalent and quadrivalent formulations. Including NA in the vaccine enabled cross-neutralization against antigenically drifted strains and provided greater protection than HA alone upon A(H3N2) challenge in ferrets. These results demonstrate that next-generation bicistronic sa-mRNA vaccines expressing HA and NA induce potent antibodies against both viral coat proteins, as well as vaccine-specific cell-mediated immunity. When formulated as a quadrivalent seasonal influenza vaccine, the sa-mRNA platform provides an opportunity to increase the breadth of protection through cross-neutralizing anti-NA antibodies.

Self-Amplifying RNA Vaccine Candidates: Alternative Platforms for mRNA Vaccine Development

The present use of mRNA vaccines against COVID-19 has shown for the first time the potential of mRNA vaccines for infectious diseases. Here we will summarize the current knowledge about improved mRNA vaccines, i.e., the self-amplifying mRNA (saRNA) vaccines. This approach may enhance antigen expression by amplification of the antigen-encoding RNA. RNA design, RNA delivery, and the innate immune responses induced by RNA will be reviewed.