Andes virus mRNA vaccines: comparison of unmodified and modified mRNA platforms

Abstract Andes virus (ANDV) is a rodent-borne zoonotic orthohantavirus endemic in South America that causes hantavirus pulmonary syndrome in humans, with up to a 40% case fatality rate. We developed ANDV mRNA vaccines based on the M segment of the viral genome that codes for glycoproteins Gn and Gc in a single open reading frame of glycoprotein precursor (GPC). We generated RNAs either with regular uridine (U-mRNA) or N1-methylpseudouridine (m1Ψ-mRNA). Mice immunized by either ANDV U-mRNA or m1Ψ-mRNA developed similar germinal center responses in lymph nodes. Single cell RNA and BCR sequencing of germinal center B cells from vaccinated mice demonstrated similar levels of activation, except an additional cluster of cells exhibiting strong interferon response that was present in animals vaccinated with U-mRNA but not m1Ψ-mRNA. Furthermore, similar immunoglobulin class-switching and somatic hypermutations were observed for the two vaccines. Golden Syrian hamsters were immunized intramuscularly with 2 doses of the vaccines on days 0 and 21. The titers of Gn/Gc-binding antibodies were moderately greater for U-mRNA construct than for m1Ψ-mRNA construct, however, the titers of ANDV-neutralizing antibodies were equivalent. Vaccinated animals were challenged with a lethal dose of ANDV at 21 days after the boost, along with the naïve control group. All control animals succumbed to infection whereas all vaccinated animals survived without any detectable disease or viral load. The data demonstrate the development of effective vaccines against ANDV and the lack of a significant effect of m1Ψ mRNA modification on immunogenicity and protection in the hamster model.