Striking antibody evasion by emerging circulating SARS-CoV-2 variants drives the identification of broadly neutralizing antibodies (bNAbs). However, how a bNAb acquires increased neutralization breadth during antibody evolution is still elusive. Here, we identified a clonally-related antibody family from a convalescent individual. One of the members, XG005, exhibited potent and broad neutralizing activities against SARS-CoV-2 variants, while the other members showed significant reductions in neutralization breadth and potency, especially against the Omicron sublineages. Structural analysis visualizing the XG005-Omicron spike binding interface revealed how crucial somatic mutations endowed XG005 with greater neutralization potency and breadth. A single administration of XG005 with extended half-life, reduced antibody-dependent enhancement (ADE) effect, and increased antibody product quality, exhibited a high therapeutic efficacy in BA.2- and BA.5-challenged mice. Our results provided a natural example to show the importance of somatic hypermutation during antibody evolution for SARS-CoV-2 neutralization breadth and potency.

Striking antibody evasion by emerging circulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants drives the identification of broadly neutralizing antibodies (bNAbs). However, how a bNAb acquires increased neutralization breadth during antibody evolution is still elusive. Here, we identify a clonally related antibody family from a convalescent individual. One of the members, XG005, exhibits potent and broad neutralizing activities against SARS-CoV-2 variants, while the other members show significant reductions in neutralization breadth and potency, especially against the Omicron sublineages. Structural analysis visualizing the XG005-Omicron spike binding interface reveals how crucial somatic mutations endow XG005 with greater neutralization potency and breadth. A single administration of XG005 with extended half-life, reduced antibody-dependent enhancement (ADE) effect, and increased antibody product quality exhibits a high therapeutic efficacy in BA.2- and BA.5-challenged mice. Our results provide a natural example to show the importance of somatic hypermutation during antibody evolution for SARS-CoV-2 neutralization breadth and potency.

Background: Respiratory syncytial virus (RSV) poses a significant global health threat, particularly to children and the elderly. While progress has been made in RSV vaccine development, gaps remain, especially in protecting the elderly population. BARS13, a recombinant non-glycosylated G protein-based RSV vaccine, has shown promise in preclinical and Phase 1 studies. This phase II trial sought to determine whether escalating doses of BARS13 could enhance immune responses while maintaining safety and tolerability in healthy older adults aged 60–80 years. Methods: This study employed a rigorous randomized, double-blind, placebo-controlled design involving 125 participants across two Australian centers. Participants were randomized in a 3:1 (vaccine–placebo) ratio for Cohorts 1–2 (30 active, 10 placebo each) and a 2:1 ratio for Cohort 3 (30 active, 15 placebo). Cohort 1 (low dose) received 10 µg rRSV-G + 10 µg CsA in one arm + a placebo in the other (Days 1 and 29); Cohort 2 (high dose) received 10 µg rRSV-G + 10 µg CsA in both arms (20 µg total per dose, Days 1 and 29); Cohort 3 (multi-dose) received the same dose as that of Cohort 2 but with a third dose on Day 57. The placebo groups received IM injections in both arms at matching timepoints. The primary endpoints included safety and tolerability assessments, while the secondary endpoints evaluated the RSV G protein-specific IgG antibody concentrations using enzyme-linked immunosorbent assays (ELISAs). Statistical analysis was performed on both the safety and immunogenicity populations. Results: BARS13 was well-tolerated across all cohorts, with no serious adverse events (SAEs) related to the vaccine. The most common adverse events were mild local reactions (pain and tenderness) and systemic reactions (headache and fatigue), which resolved within 24–48 h. Immunogenicity analysis demonstrated a dose-dependent increase in the RSV G protein-specific IgG geometric mean concentrations (GMCs). Cohort 3, which received multiple high-repeat dose administrations, showed the highest immune response, with the IgG GMC rising from 1195.4 IU/mL on Day 1 to 1681.5 IU/mL on Day 113. Response rates were also the highest in Cohort 3, with 86.2% of participants showing an increase in antibody levels by Day 29. Conclusions: BARS13 demonstrated a favorable safety profile and strong immunogenicity in elderly participants, with a clear dose-dependent antibody response. These results support further development of BARS13 as a potential RSV vaccine candidate for the elderly. Further studies are needed to evaluate the long-term efficacy and optimal dosing schedule.