Answering to social issues – Delivery of mRNA vaccines and therapeutics

Pandemic of coronavirus infectious diseaseCOVID-19 has exerted serious impacts on society and medical serves. Two messenger RNAmRNAvaccines were approved within one year after the outbreak of COVID-19, providing a hopeful solution to this issue. Meanwhile, Japan lags behind in vaccine development, which imposes economic burden and causes limited supply of vaccines. Along with vaccines for preventing infectious diseases, other medical fields are potential targets of mRNA therapeuticssuccessful outcomes have been reported in clinical trials of cancer vaccines and immunotherapy, genome editing, and protein replacement therapy, which will help to address medical issues associated with the declining birthrate and the aging population in the future. Japan has huge potentials to contribute to the field of mRNA vaccines and therapeutics, especially by utilizing its original technologies in drug delivery systemDDS. Notably, DDS, as well as chemical modification of mRNA, has played substantial roles in the development of mRNA COVID-19 vaccines. This review focuses on mRNA delivery systems, including synthetic nanoparticles from lipids and polymers and nature-derived systems, such as extracellular vesicles and naked mRNA.

Chemical modifications to mRNA nucleobases impact translation elongation and termination.

Messenger RNAs (mRNAs) serve as blueprints for protein synthesis by the molecular machine the ribosome. The ribosome relies on hydrogen bonding interactions between adaptor aminoacyl-transfer RNA molecules and mRNAs to ensure the rapid and faithful translation of the genetic code into protein. There is a growing body of evidence suggesting that chemical modifications to mRNA nucleosides impact the speed and accuracy of protein synthesis by the ribosome. Modulations in translation rates have downstream effects beyond protein production, influencing protein folding and mRNA stability. Given the prevalence of such modifications in mRNA coding regions, it is imperative to understand the consequences of individual modifications on translation. In this review we present the current state of our knowledge regarding how individual mRNA modifications influence ribosome function. Our comprehensive comparison of the impacts of 16 different mRNA modifications on translation reveals that most modifications can alter the elongation step in the protein synthesis pathway. Additionally, we discuss the context dependence of these effects, highlighting the necessity of further study to uncover the rules that govern how any given chemical modification in an mRNA codon is read by the ribosome.

Chemical modification of uridine modulates mRNA-mediated proinflammatory and antiviral response in primary human macrophages.

In vitro transcribed (IVT)-mRNA has been accepted as a promising therapeutic modality. Advances in facile and rapid production technologies make IVT-mRNA an appealing alternative to protein- or virus-based medicines. Robust expression levels, lack of genotoxicity, and their manageable immunogenicity benefit its clinical applicability. We postulated that innate immune responses of therapeutically relevant human cells can be tailored or abrogated by combinations of 5'-end and internal IVT-mRNA modifications. Using primary human macrophages as targets, our data show the particular importance of uridine modifications for IVT-mRNA performance. Among five nucleotide modification schemes tested, 5-methoxy-uridine outperformed other modifications up to 4-fold increased transgene expression, triggering moderate proinflammatory and non-detectable antiviral responses. Macrophage responses against IVT-mRNAs exhibiting high immunogenicity (e.g., pseudouridine) could be minimized upon HPLC purification. Conversely, 5'-end modifications had only modest effects on mRNA expression and immune responses. Our results revealed how the uptake of chemically modified IVT-mRNA impacts human macrophages, responding with distinct patterns of innate immune responses concomitant with increased transient transgene expression. We anticipate our findings are instrumental to predictively address specific cell responses required for a wide range of therapeutic applications from eliciting controlled immunogenicity in mRNA vaccines to, e.g., completely abrogating cell activation in protein replacement therapies.