Passive Infusion of an S2-Stem Broadly Neutralizing Antibody protects against SARS-CoV-2 infection and lower airway inflammation

The continued evolution of SARS-CoV-2 variants capable of subverting vaccine and infection-induced immunity suggests the advantage of a broadly protective vaccine against betacoronaviruses (β-CoVs). Recent studies have isolated monoclonal antibodies (mAbs) from SARS-CoV-2 recovered-vaccinated donors capable of neutralizing many variants of SARS-CoV-2 and other β-CoVs. Many of these mAbs target the conserved S2 stem region of the SARS-CoV-2 spike protein, rather the receptor binding domain contained within S1 primarily targeted by current SARS-CoV-2 vaccines. One of these S2-directed mAbs, CC40.8, has demonstrated protective efficacy in small animal models against SARS-CoV-2 challenge. As the next step in the pre-clinical testing of S2-directed antibodies as a strategy to protect from SARS-CoV-2 infection, we evaluated the in vivo efficacy of CC40.8 in a clinically relevant non-human primate model by conducting passive antibody transfer to rhesus macaques (RM) followed by SARS-CoV-2 challenge. CC40.8 mAb was intravenously infused at 10mg/kg, 1mg/kg, or 0.1 mg/kg into groups (n=6) of RM, alongside one group that received a control antibody (PGT121). Viral loads in the lower airway were significantly reduced in animals receiving higher doses of CC40.8. We observed a significant reduction in inflammatory cytokines and macrophages within the lower airway of animals infused with 10mg/kg and 1mg/kg doses of CC40.8. Viral genome sequencing demonstrated a lack of escape mutations in the CC40.8 epitope. Collectively, these data demonstrate the protective efficiency of broadly neutralizing S2-targeting antibodies against SARS-CoV-2 infection within the lower airway while providing critical preclinical work necessary for the development of pan–β-CoV vaccines. 24 RMs (6 females and 18 males; mean age of 5 years and 11 months old; range 5-6 years old) were infused intravenously 5 days pre infection with either a 0.1 mg/kg, 1mg/kg, or 10mg/kg concentration of experimental mAb CC40.8 or with control mAb PGT121, with each experimental group consisting of 6 animals (1 female and 5 males). Animals were screened for preexisting, SARS-CoV-2 spike specific antibodies prior to enrollment in this study. Preinfection baseline samples were collected 4 days prior to inoculation. At day 0, all RM were inoculated with 1mL intranasally and 1mL intratracheally with a combined total of 1.1 x 106 plaque forming units (PFU) of SARS-CoV-2 (2019-nCoV/USA-WA1/202). BAL and nasal swabs were collected from inoculated animals at 2dpi and at the time of necropsy (7 or 8dpi), with viral titers peaking in these tissues at 2dpi in the infected animals. PBMCs were isolated from the BAL of SARS-CoV-2 infected RM at 2 dpi and 7/8 dpi and captured for 10x scRNA-seq. Samples were multiplexed in groups of 3.