Serum AZD7442 (tixagevimab–cilgavimab) concentrations and in vitroIC₅₀ values predict SARS‐CoV‐2 neutralising antibody titres

Abstract

ObjectivesThe evolution of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) necessitates rapid methods for assessing monoclonal antibody (mAb) potency against emerging variants. Authentic virus neutralisation assays are considered the gold standard for measuring virus‐neutralising antibody (nAb) titres in serum. However, authentic virus‐based assays pose inherent practical challenges for measuring nAb titres against emerging SARS‐CoV‐2 variants (e.g. storing infectious viruses and testing at biosafety level‐3 facilities). Here, we demonstrate the utility of pseudovirus neutralisation assay data in conjunction with serum mAb concentrations to robustly predict nAb titres in serum.MethodsSARS‐CoV‐2 nAb titres were determined via authentic‐ and lentiviral pseudovirus‐based neutralisation assays using serological data from three AZD7442 (tixagevimab–cilgavimab) studies: PROVENT (NCT04625725), TACKLE (NCT04723394) and a phase 1 dose‐ranging study (NCT04507256). AZD7442 serum concentrations were assessed using immunocapture. Serum‐based half‐maximal inhibitory concentration (IC50) values were derived from pseudovirus nAb titres and serum mAb concentrations, and compared with in vitro IC50 measurements.ResultsnAb titres measured via authentic‐ and lentiviral pseudovirus‐based neutralisation assays were strongly correlated for the ancestral SARS‐CoV‐2 virus and SARS‐CoV‐2 Alpha. Serum AZD7442 concentrations and pseudovirus nAb titres were strongly correlated for multiple SARS‐CoV‐2 variants with all Spearman correlation coefficients ≥ 0.78. Serum‐based IC50 values were similar to in vitro IC50 values for AZD7442, for ancestral SARS‐CoV‐2 and Alpha, Delta, Omicron BA.2 and Omicron BA.4/5 variants.ConclusionsThese data highlight that serum mAb concentrations and pseudovirus in vitro IC50 values can be used to rapidly predict nAb titres in serum for emerging and historical SARS‐CoV‐2 variants.