Antibody response to pegloticase. Screening ELISAs for Ab to pegloticase (A) and10 kDa mPEG (B). Horizontal axis: N = non, P = persistent, T = transient responder. Symbols: blue = pre-treatment; red = highest A405 during the trial; triangles = the non-responder. (C) Correlation between the anti-pegloticase and anti-10 kDa mPEG ELISAs. The highest A405 values during treatment from 2A and B are re-plotted. Symbols: blue = persistent (P), red = transient (T), green = non-responder (N). ( D) Correlation between ELISAs for Ab to pegloticase and PEGylated adenosine deaminase (PEG-ADA). Conditions for the ELISAs were the same except for the plate coating. Two samples, obtained on Day 0 (open symbols) and at the final visit (filled symbols) from six patients (distinguished by symbol shape) were studied. Competition ELISA (see Methods). (E). Pre-treatment. The non-responder (blue underline) and three previously treated patients (blue asterisks) are indicated on the horizontal axis. ( F ). Post-treatment. The last sample obtained from each Ab-positive patient was tested to minimize competition from circulating pegloticase (pUox was undetectable or <0.3 mU/mL). Data plotted are the mean and SEM for the 13 samples tested.