Chemically modified tRNA enhances the translation capacity of mRNA rich in cognate codons [RNA-Seq]

Although messenger RNA (mRNA) vaccines have been employed to prevent the spread of COVID-19, they are critically limited by instability and low translation capacity. Alterations in tRNA abundance and modification, associated with codon optimality, impact mRNA stability and protein output in a codon-dependent manner, implying tRNA as a potential translation enhancer. Here, we report a strategy named tRNA-plus to augment translation based on artificially modulating the tRNA availability. We demonstrated that overexpression of specific tRNAs enhanced the stability and translation efficiency of SARS-CoV-2 Spike mRNA, resulting in substantial improvements in protein levels by up to 4.7-fold. In addition, chemically synthesized tRNAs bearing multiple site-specific modifications, particularly at the anticodon loop and TΨC-loop, exhibited an average of ~4-fold higher decoding efficacy than unmodified tRNA, along with increased stability and reduced immune toxicity. We further leveraged an optimized lipid nanoparticles (LNP) system for codelivery of Spike mRNA vaccine and tRNA, which elicited enhanced spike-specific humoral and cellular immune responses in vivo. The methods presented here may become a general approach for elevating mRNA translation potency, which can be applied to various translation-based fields.