High titer of antibody against the SARS-CoV-2 spike protein among patients receiving neutralizing antibody cocktail therapy with REGN-COV

Purpose Casirivimab/imdevimab (REGN-COV), a cocktail of neutralizing antibodies against the receptor-binding domain of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein, was shown to be an effective treatment and post-exposure prophylaxis measure for coronavirus disease 2019 (COVID-19). We assessed the antibody titers among patients who received REGN-COV with the purpose of evaluating this therapeutic and prophylactic option from the serological point of view. Methods We collected serological data of patients with COVID-19 who were treated with REGN-COV 1200 mg (casirivimab 600 mg/imdevimab 600 mg). Antibody titers were assessed within 24 h before and within 48 h after the administration of REGN-COV using ARCHITECT SARS-CoV-2 immunoglobulin (Ig)G (IgG NC ), which is against nucleocapsid protein, and ARCHITECT SARS-CoV-2 IgG II Quant (IgG SP ), which is against spike protein. Results A total of nine patients were evaluated. IgG SP was elevated after REGN-COV administration with a median of 208,370 Arbitrary Units/mL while simultaneous IgG NC remained low. With the simple linear regression model, the IgG SP after the REGN-COV administration was correlated with the reciprocal of ideal body weight. Conclusion The high titer of IgG SP supports the clinical benefit of therapeutic and prophylactic use of REGN-COV from the serological point of view.