Development of a novel ELISA to detect total factor D in the presence of high levels of PEGylated anti-factor D Fab.

PEGylated anti-Factor D Fab (PEG-aFD) was developed as a potential therapeutic for geographic atrophy, targeting factor D, the rate-limiting enzyme in the alternative complement pathway. An assay was needed to measure total factor D as a pharmacodynamic biomarker in human aqueous humor in the presence of high PEG-aFD concentrations. Commercial kit met sensitivity requirement, but not drug tolerance requirement. In-house ELISA met both drug tolerance and sensitivity requirements. Addition of 100 ng/ml PEG-aFD to the sample diluent enabled accurate measurement of human factor D in the presence of 2.5 mg/ml of PEG-aFD in the in-house ELISA. Accurate measurement of total factor D in human aqueous humor containing high concentrations of PEG-aFD was achieved by adding PEG-aFD to sample diluent.