MRNA Delivery of a Class 1/4 SARS-CoV-2 Neutralizing Antibody Protects Against Diverse Sarbecoviruses in a Lethal Mouse Challenge Model

Why It Matters

Broadly neutralizing antibodies that work across sarbecovirus clades address the ongoing threat of SARS‑CoV‑2 variants and future spillovers, while mRNA delivery could streamline manufacturing and distribution compared with traditional protein therapeutics.

Key Takeaways

• Five bNAbs neutralize all 18 tested sarbecoviruses, including XBB.1.5
• mRNA‑encoded Ab401 protected mice from SARS‑CoV‑2 and bat virus
• Antibodies target conserved class 1/4 RBD epitopes with long CDR‑H3 loops
• mRNA antibody delivery offers a cost‑effective alternative to protein drugs

Pulse Analysis

The relentless evolution of SARS‑CoV‑2 and the looming risk of novel zoonotic sarbecoviruses have intensified the search for pan‑sarbecovirus therapeutics. Traditional monoclonal antibodies, while effective against early strains, lose potency as spike proteins mutate. Broadly neutralizing antibodies (bNAbs) that recognize conserved regions of the receptor‑binding domain (RBD) provide a promising solution, especially when derived from individuals with hybrid immunity—those who have both infection‑derived and vaccine‑induced responses. Such antibodies can inform next‑generation vaccine designs that aim to elicit similarly wide‑ranging protection.

In the new PNAS study, scientists screened a convalescent‑vaccinated donor and isolated 20 RBD‑directed bNAb lineages. Five of these, notably Ab401 and Ab568, displayed potent neutralization across a panel of 18 sarbecoviruses, covering all major clades and recent Omicron sub‑variants like XBB.1.5 and JN.1. Structural work revealed that these antibodies bind a cryptic class 1/4 epitope, using unusually long heavy‑chain CDR‑H3 loops (18‑26 amino acids) encoded by the IGHD3‑22 gene segment. This conserved binding mode underpins their breadth and makes them attractive templates for vaccine antigen engineering.

Beyond discovery, the research showcases a novel delivery platform: lipid‑nanoparticle‑encapsulated mRNA encoding both heavy and light chains of Ab401. In a lethal mouse model, a single prophylactic mRNA dose achieved protection comparable to that of the purified protein, shielding animals from both the ancestral SARS‑CoV‑2 strain and a bat‑derived sarbecovirus with zoonotic potential. mRNA‑based antibody delivery sidesteps the complex manufacturing and cold‑chain logistics of protein therapeutics, offering rapid scalability for outbreak response and a viable prophylactic option for immunocompromised patients who cannot mount robust vaccine responses. As the field moves toward universal coronavirus defenses, this approach could become a cornerstone of pandemic preparedness strategies.