Leveraging mRNAs sequences to express SARS-CoV-2 antigens in vivo

Chunxi Zeng; Xucheng Hou; Jingyue Yan; Chengxiang Zhang; Wenqing Li; Weiyu Zhao; Shi Du; Yizhou Dong

Vaccine is the most effective strategy to prevent viral infections for a large population 4 . Different types of SARS-CoV-2 vaccines such as mRNA, DNA, and recombinant proteinbased antigens are currently in clinical trials 5 . Among these agents, mRNA-based vaccine candidates first entered the clinical trial, because of the fast process for developing and manufacturing mRNA 6 . To express an antigen effectively, an mRNA requires several essential components, including 5' cap, 5' untranslated region (5' UTR), antigen-encoding sequence, 3' untranslated region (3' UTR) , and polyadenylated tail 7 . Among these components, the 5' UTR and 3' UTR are unique regulators for protein translation 8 . The design and selection of 5' UTR and 3' UTR are critically important to ensure the sufficient production of antigens and efficacious vaccination of the host 9 . Therefore, systematic explorations of UTRs may provide broad applicability for mRNA vaccines in response to emerging pathogens such as SARS-CoV-2. Previous studies utilized many UTRs from endogenous genes for protein expression 8, 10, 11 . For example, the UTRs from human cytochrome B-245 alpha polypeptide (CYBA) outperformed several other UTRs for protein expression 12 . The 5' UTR from alpha globin mRNA enabled higher translation efficiency than that from beta globin mRNA in cells 13 . Alternatively, UTRs can be designed via a de novo method. A recent study reported a series of 5'UTRs consisting of 12-14 nucleotides (nt) 14 . Also, a deep learning method was applied to screen and analyze a large set of 5'UTRs 15 . Based on these significant advances, we hypothesize that the integration of endogenous UTRs with further de novo design may be a superior approach for UTRs engineering, facilitating the development of SARS-CoV-2 vaccines (Fig. 1) . Our results prove the concept of this approach and significantly increase protein production compared to the UTRs reported in the literatures 12, [16] [17] [18] . Lastly, a series of potential SARS-CoV-2 antigens are visualized via fluorescent imaging in both cell and animal models, which may serve as vaccine candidates for the clinical trials. Figure 1 . Schematic illustration of mRNA engineering. 5' UTR and 3' UTR of mRNA are comprehensively modulated based on the analysis of endogenous genes and further de novo design in order to enrich protein production and express SARS-CoV-2 antigens as potential vaccines.