Construction and evaluation of a self-replicative RNA vaccine against SARS-CoV-2 using yellow fever virus replicon

Abstract

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is a global threat. To forestall the pandemic, developing safe and effective vaccines is necessary. Because of the rapid production and little effect on the host genome, mRNA vaccines are attractive, but they have a relatively low immune response after a single dose. Replicon RNA (repRNA) is a promising vaccine platform for safety and efficacy. RepRNA vaccine encodes not only antigen genes but also the genes necessary for RNA replication. Thus, repRNA is self-replicative and can play the role of an adjuvant by itself, which elicits robust immunity. This study constructed and evaluated a repRNA vaccine in which the gene encoding the spike (S) protein of SARS-CoV-2 was inserted into a replicon of yellow fever virus 17D strain. Upon electroporation of this repRNA into baby hamster kidney cells, the S protein and yellow fever virus protein were co-expressed. Additionally, the self-replication ability of repRNA vaccine was confirmed using qRT-PCR, demonstrating its potency as a vaccine. Immunization of C57BL/6 mice with 1 μg of the repRNA vaccine induced specific T-cell responses but not antibody responses. Notably, the T-cell response induced by the repRNA vaccine was significantly higher than that induced by the nonreplicative RNA vaccine in our experimental model. In the future, it is of the essence to optimize vaccine administration methods and improve S protein expression, like protection of repRNA by nanoparticles and evasion of innate immunity of the host to enhance the immune-inducing ability of the repRNA vaccine.

Detection of mRNA and Anibody in Mice Injected withPlasmid pCDNA3.1-SRM Carrying African SwineFever Virus Gen Able to Produce Self-Replicating RNA

“…The same result was found by Nakamura et al (2022), with mRNA that functions like saRNA having higher copy numbers than normal mRNA sampled from transfected BHK21 cells. Their saRNA's copy numbers decreased at 72 hours post-transfection.…”

“…Their results show that the highest mRNA concentration was found in injection location muscle and lymph nodes, while most mRNA concentration has reduced starting from eight days post-injection to 60 days post-injection except on lymph node. All of these results showed reduction in mRNA concentration starting from three days on this research (Table 1) and research by Nakamura et al (2022) and eight days post-injection found in Maruggi et al (2022) post-injection, but there might be mRNA left in the mice lymph node. For future research, further analysis in pCDNA3.1-SRM RNA polymerase function duration and capability are necessary.…”

RNA Combined with Nanoformulation to Advance Therapeutic Technologies

“…Compared to conventional mRNA, repRNA triggers prolonged gene expression lasting weeks to months after a single injection, making it a promising candidate for sustained antigen expression in vaccine design [8]. repRNA vaccines have emerged as promising candidates, showcasing exemplary safety and immunogenicity, and have already demonstrated encouraging results in various clinical trials [9,10].…”

YF17D‐based vaccines – standing on the shoulders of a giant

“…In a second part, we describe the design and performance of currently licensed recombinant vaccines and vaccine candidates that are based on YF17D as a live viral vector. The use of subgenomic YF17D replicons [19,20] as a basis for self-amplifying RNA vaccines [21] or of related Flaviviruses as live viral vectors [22][23][24][25][26] is not considered. Technical aspects of recombinant vaccine virus construction, vaccine safety and unique requirements of preclinical animal testing linked to the biology of YF17D are described in separate text boxes.…”