A potent neutralizing antibody provides protection against SARS-CoV-2 Omicron and Delta variants via nasal delivery

COVID-19, caused by SARS-CoV-2, continues to cause global morbidity and mortality. While drugs and vaccines have been deployed, rapid mutations in the spike (S) protein, particularly in the receptor-binding domain (RBD), have enabled variants of concern (VOCs) like Delta and Omicron to evade many neutralizing monoclonal antibodies (mAbs). Omicron harbors over 30 spike mutations, reducing the efficacy of most identified mAbs and becoming the dominant strain worldwide. There remains a need for broadly neutralizing antivirals that retain activity against current and future variants. This study aims to characterize a previously isolated human mAb, 586G, for breadth and potency against Delta and Omicron, and to evaluate intranasal delivery as a prophylactic and therapeutic strategy in a hamster model.

The paper outlines that multiple mAbs have been authorized for clinical use against COVID-19, yet many lose neutralizing activity against VOCs, especially Omicron due to extensive spike mutations. While some antibodies (e.g., S309/sotrovimab) retain activity against certain variants in pseudovirus assays, overall efficacy against Delta and particularly Omicron is often reduced or lost. This context motivates the search for broadly neutralizing antibodies targeting conserved RBD regions rather than the highly mutable receptor-binding motif (RBM).

- Ethics and biosafety: Female Syrian golden hamsters (5–6 weeks) were used under BSL-3 conditions with institutional animal care approval (WIVA20210214). - Cells/viruses: Vero E6 cells cultured in DMEM with FBS and antibiotics. Authentic WT SARS-CoV-2, Delta (B.1.617.2), and Omicron isolates were used. - ELISA: RBD proteins (WT, Delta, Omicron BA.1/BA.2) coated on 96-well plates; serial dilutions of 586G added; detection with HRP-conjugated anti-human IgG; absorbance at 450 nm; EC50 calculated. - Biolayer interferometry (BLI): Assessed affinities between 586G and spike proteins from WT, Delta, Omicron BA.1/BA.2 using an Octet system; kinetic analysis after association/dissociation with twofold serial dilutions of spike proteins. - Pseudovirus neutralization: Pseudotyped SARS-CoV-2 (WT, Delta, Omicron) incubated with serially diluted 586G; infection of 293T/ACE2 cells; luciferase readout at 72 h; IC50 via four-parameter logistic regression. - Live virus neutralization (plaque reduction): Vero E6 cells infected with authentic variants mixed with serial dilutions of 586G; after adsorption, overlay added; plaques fixed/stained; IC50 determined. - Animal studies (hamster model): Intranasal challenge with 10^4 PFU of Delta or Omicron. Prophylactic regimens included intranasal 586G dosing before and after challenge; therapeutic regimens dosed post-challenge. Sample collection at 3 days post-infection (dpi): nasal washes, throat swabs, trachea, and lung tissues. Body weight monitored up to 6–8 dpi. - Dose-finding: Tested intranasal prophylactic doses of 15, 10, 5, and 2 mg/kg against Omicron; an intraperitoneal 10 mg/kg group included for comparison. - Viral quantification: RT-qPCR for viral RNA in swabs/tissues; plaque assays in Vero E6 for infectious titers. - Histology: Lung tissues fixed and H&E stained; standardized scoring of alveolar wall thickening, inflammatory infiltrates, edema/fibrin, hemorrhage, and pneumocyte hyperplasia. - Statistics: Analyses performed with GraphPad Prism 9; unpaired t tests for two-group comparisons.

- Binding breadth: 586G bound RBDs from WT and variants. ELISA EC50 values: WT RBD 22.80 ng/ml; Delta RBD 22.17 ng/ml; Omicron BA.1 RBD 23.9 ng/ml; Omicron BA.2 RBD 953.7 ng/ml, indicating reduced binding to BA.2. - Neutralization potency: - Pseudoviruses (WT, Delta, Omicron): IC50 range 4.75–183.6 ng/ml (broad neutralization). - Authentic viruses: The abstract reports IC50 of 1.69 ng/ml (Delta) and 54.31 ng/ml (Omicron), indicating strong potency, especially against Delta. Most approved RBD-targeting mAbs reportedly lose activity against Omicron (IC50 > 10 µg/ml). - In vivo efficacy (Delta challenge, hamsters): Intranasal 586G used prophylactically and therapeutically reduced viral RNA in nasal washes and multiple tissues (lungs, heart, liver, kidneys) at 3 dpi, improved weight maintenance/recovery, and decreased infectious titers versus controls. Histopathology showed markedly reduced lung injury in prophylactic and treated groups compared with buffer controls. - In vivo efficacy (Omicron challenge, hamsters): Prophylactic intranasal 586G significantly reduced viral RNA in nasal washes, trachea, lungs, and throat swabs, with infectious titers at or below the limit of detection at 3 dpi; no weight loss observed. - Dose finding (Omicron): All tested intranasal prophylactic doses (15, 10, 5, 2 mg/kg) were effective in reducing viral RNA and infectious titers in respiratory tissues. Notably, 2 mg/kg achieved reductions comparable to higher doses, preventing lung replication and disease signs. A single intraperitoneal 10 mg/kg dose also showed efficacy.

586G targets conserved regions within the RBD, enabling broad neutralization despite extensive RBM mutations in VOCs. Its retained potency against Delta and substantial activity against Omicron address a critical gap where many authorized mAbs show reduced or lost efficacy. Intranasal delivery confers direct protection of the upper and lower respiratory tract, reduces viral loads, and mitigates lung pathology, offering a practical alternative to intravenous administration. The demonstrated efficacy at low intranasal doses suggests feasibility for prophylaxis and early treatment, potentially as a nebulized or intranasal therapy that is user-friendly and cost-effective. These findings support 586G as a promising countermeasure against current VOCs and possibly future variants with spike mutations.

The human monoclonal antibody 586G exhibits broad and potent neutralization of SARS-CoV-2 variants, including Delta and Omicron, and confers strong prophylactic and therapeutic protection in hamsters via intranasal delivery. Low-dose intranasal administration (as low as 2 mg/kg) effectively suppresses viral replication and prevents lung pathology. Given the diminished performance of many approved mAbs against Omicron, 586G represents a compelling candidate for development as an intranasal or nebulized prophylactic/therapeutic. Future work should include detailed head-to-head benchmarking against authorized mAbs, pharmacokinetic and safety profiling for intranasal delivery, and clinical evaluation in humans.

- Comparative benchmarking: The study notes that neutralization comparisons with approved mAbs were not conducted side-by-side, limiting direct efficacy comparisons. - Animal model: Efficacy was demonstrated in Syrian golden hamsters; translational relevance to humans requires clinical validation. - Sample sizes and groups: Some in vivo groups were small (e.g., n=3 per group in certain Omicron experiments), which may limit statistical power. - Variant coverage: While activity was shown against Delta and Omicron (including reduced binding to BA.2), comprehensive evaluation across emerging sublineages and escape profiling was limited in the presented text. - Delivery/PK data: Intranasal dosing regimens were effective, but pharmacokinetics, tissue distribution, and safety/tolerability data for intranasal or nebulized delivery were not provided.