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Background Antibodies targeting envelope glycoproteins have been shown in some instances to enhance infection by subverting Fc receptor and complement function, or by directly inducing fusion with cellular membranes. The potential for antibody dependent enhancement (ADE) of infection raises concern that passive immunization with a therapeutic anti-viral antibody could increase risk of disease. As part of the nonclinical package characterizing the risk profile of the SARS-CoV-2 neutralizing monoclonal antibody bamlanivimab, studies were conducted to evaluate the potential for ADE of infection in vitro and in a non-human primate model of COVID-19. Methods In vitro assays were performed in primary human macrophage, Raji, or THP-1 cells exposed to SARS-CoV-2 in the presence of bamlanivimab ranging from approximately IC50 to more than 100-fold above or below the IC50. Samples were evaluated for demonstration of productive viral infection. Bamlanivimab binding to C1q and FcR were quantified, and activity was studied by cell-based assays. In vivo studies were performed in African green monkeys (AGM) infected with SARS-CoV-2 virus following sub-saturating or saturating doses of bamlanivimab or IgG control. Viral loads, clinical pathology, and histology endpoints were assessed to determine if bamlanivimab enhanced SARS-CoV-2 replication or clinical illness. Mixed model repeated measures were used to evaluate virology statistics. Results Bamlanivimab did not increase viral RNA production in FcγR-expressing cell lines, despite demonstration of effector function. No significant differences were found among the AGM groups in terms of weight, temperature, or food intake. Treatment with bamlanivimab reduced viral loads in nasal and oral swabs and BAL fluid relative to control groups. Viral antigen was not detected in lung tissue from animals treated with the highest dose of bamlanivimab. Microscopic findings along with decreases in viral loads in bamlanivimab-treated animals indicated that ADE of disease was not observed in this study. Conclusions Sub-saturating doses of bamlanivimab treatment do not induce ADE of SARSCoV2 infection in either in vitro or an AGM model of infection. Findings suggest that high affinity monoclonal antibodies pose a low risk of mediating ADE in patients and further supports their safety profile as a treatment of COVID-19 disease.

1. The effects of ipsapirone, nefazodone, tiaspirone, BMS-20661, buspirone and gepirone on the hypothalamic-pituitary-adrenal (HPA) axis were studied. These drugs were selected because they have serontonin 1A (5-HT1A) receptor-binding capability and have the potential for therapeutic activity in the treatment of major affective or anxiety disorders or both. 2. Plasma corticosterone level was used as the end point for determining the effect of each drug on the HPA axis. Each drug increased the plasma corticosterone levels in a dose-dependent manner. The ED50 values were 0.8 mg/kg for BMS-20661, 3.5 mg/kg for gepirone, 3.9 mg/kg for buspirone, 5.3 mg/ kg for tiaspirone, 10.5 mg/kg for ipsapirone and 73.5 mg/kg for nefazodone. Ipsapirone and buspirone were more efficacious than the other four drugs. 3. The effect of a 10-mg/kg (35 mg/kg for nefazodone) test dose of each drug reached a peak between 30 min and 1 hr, and plasma corticosterone levels generally returned to control levels after 2 hr. 4. When the drugs were given 30 min before decapitation, in conjunction with a rotatory stress, BMS-20661 significantly inhibited the stress-induced rise, whereas ipsapirone and gepirone caused a significant increase in plasma corticosterone levels. However, when the drugs were given 2 hr before decapitation, nefazodone caused a significant decrease, whereas ipsapirone, BMS-20661 and gepirone produced significant increases in HPA axis activity. An 0800 hr dose of 0.1 mg/kg of dexamethasone suppressed the 1500 hr HPA activity by 73.1%. The 0.1-mg/kg dose of dexamethasone significantly reduced the drug-activated HPA axis activity of all of the drugs from their saline-control levels. The rank order, from least to greatest inhibitory effect, produced by this dexamethasone treatment on the drug-control levels was gepirone (-42.6%), tiaspirone (-48.9%), buspirone (-56.1%), nefazodone (-68.5%), insapirone (-70.0%), and BMS-20661 (-74.3%).

The effects of tandospirone, enciprazine, gepirone, buspirone (5-HT1A agents) and carvotroline (5-HT2) on hypothalamic-pituitary-adrenocortical activity (HPA) activity were studied. These drugs increased the plasma corticosterone levels in a dose-dependent manner. Their ED50 values were 3.8, 31.8, 3.1, 3.4 and 7.0 mg/kg, respectively. Drug effects peaked between 30 min and 1 h, and plasma corticosterone levels returned to control levels after 2 h. When the drugs were given in conjunction with a rotatory stress, gepirone and enciprazine increased and carvotroline decreased plasma corticosterone levels. Dexamethasone (0.1 mg/kg) pretreatment reduced drug-activated HPA axis activity.