Optimization of clesrovimab cell-based assay with improved precision and throughput

Clesrovimab (Enflonsia™) is a long-acting prophylactic monoclonal antibody designed to protect infants from respiratory syncytial virus diseases. The potency of clesrovimab is measured by a cell-based assay using A549 cells and engineered RSV-NLP viruses. To further increase the throughput and improve the assay precision, the plate layout and data analysis models were optimized. In the updated plate layout, eleven concentrations of reference standard and five concentrations of one control sample and three test samples in duplicate were included in one 96-well plate. A Log-Log linear model using the same five concentrations of each test article was used to calculate the slope ratios for parallelism assessment. A restricted 4-parameter logistic model using logarithmic-transformed response variable was used to calculate the relative potency. The optimized cell-based assay allows more samples to be tested on one plate and has demonstrated improved precision compared to the previous version using regular 11-point 4-parameter logistic model. A comprehensive robustness study of the optimized clesrovimab cell-based assay has demonstrated fit-for-use assay performance by introducing small but deliberate variations of the selected assay parameters and reagents. The method was successfully validated and implemented for commercial release and stability testing of clesrovimab, and ultimately has been accepted by numerous global health authorities.