RSV mRNA-1345 Biosimilar Vaccine

mRNA-1345 (mRESVIA / crespimeran) is a RSV vaccine. mRNA-1345 encodes the RSV F glycoprotein (fusion glycoprotein) stabilized in the prefusion conformation — the target of the major class of RSV-neutralizing antibodies. The mRNA scaffold includes 5′-cap (m7G(5′)ppp(5′)G analog), V1-UTR (57 nt), ORF, alpha-globin HBA1-derived 3′ UTR (110 nt), and 3′-Poly(A) to mimic a fully processed mature mRNA. The ORF of mRNA-1345 encodes the RSV antigen (520 aa): Template: RSV A strain A2 F protein (P03420, 574 aa) 6 stabilising mutations: S155C + S290C (interprotomer disulfide DS1); S190F + V207L (cavity-filling) — from mRNA-1777; A149C + Y458C (interprotomer disulfide DS2) — from mRNA-1172 p27/furin-site replacement: aa 104–144 deleted, replaced by GS dipeptide (T103-GS-G145 in Moderna’s notation), creating a single-chain F2-F1 molecule that cannot undergo furin-triggered spring-loading ΔCT559: cytoplasmic tail (original aa 560–574) deleted; TM domain retained for membrane anchoring.